Local realism ruled out? (was: Photon entanglement and...) [Archive]

akhmeteli

Jan15-10, 07:05 AM

This is utterly confusing.

First, you argue that Bell, etc. theorem does NOT rule out local realism.
Dear ZapperZ,
I am afraid you may have misunderstood me. That means I was not clear enough. My reasoning was quite different. I concede that the Bell theorem (BT) per se rules out local realism (LR) (assuming that all predictions of standard QT are correct, and with the standard caveat on superdeterminism). I also concede that no LR theory can reproduce ALL results of standard quantum theory (QT). However, I argued that this does not mean LR is ruled out as 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP). Indeed, you cannot reasonably argue that the failure to absorb contradictions rules out LR. I argue that it’s good for LR that it cannot absorb them, and it’s bad for standard QT that it can. Further, as we cannot have both UE and PP as precise results, I expressed my opinion that PP cannot be precise, while it looks like UE is indeed precise.
Then you argue that even if they did, the absence of loophole-free experiments would not rule out local realism anyway!
Again, this is an unfortunate misunderstanding. Looks like I was not clear enough again. In fact, I concede that if BT ruled out LR, then loophole free experiments would indeed rule out LR (I won’t repeat the caveat on determinism in the future), because I concede that the Bell inequalities cannot be violated in any LR theory.

Let me summarize. I think you’ll agree that to rule out LR you necessarily need two things together: 1) mathematical proof that some results predicted by QT cannot be reproduced by any LR; 2) experimental proof that one of such predictions is indeed correct. I argue that, on the one hand, there is no such mathematical proof, as a proper mathematical proof cannot use two mutually contradictory assumptions, and there is no such experiment. Therefore, I argue, LR has not been ruled out so far. Furthermore (and here I speculate), I suspect that loophole free experiments would have ruled out UE, so I suspect our points of view are much closer than it looks, as it seems we both swear by unitary evolution.
I've already address the latter in a previous post when I complaint that people like you can't seem to accept that both the locality loophole and the detection loophole have been closed separately, and that the SHEER VOLUME OF EVIDENCE alone from each one of them make for a very compelling indication for ruling out local realism.
ZapperZ, I further concede that the loopholes have been closed separately. This is enough for you (although I gave my reasons to believe you’re not quite happy with that), but that is not quite enough for Shimony, Zeilinger and other experts, and it’s definitely not enough for me. Recently I offered you (okay, here I am cutting some corners) to indicate the difference between your reasoning and the following one: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sum of angles of a quadrangle and a triangle on a sphere are not equal to 180 degrees. I may have missed something, but I don’t think I’ve heard from you about that. It’s a theorem, for crying out loud! The same is true for BT: you have not even started to test it until you have made sure ALL its assumptions are fulfilled, and fulfilled simultaneously!
As for the former, each time an argument is presented on the logical deduction of Bell theorem as not being able to test local realism, it has been shot down. The most recent one, from a month ago, appeared in AJP. A paper by Guy Blaylock argued that both the EPR paradox and Bell's inequality fall short in testing the issue of locality[1]. This was summarily shot down in the SAME issue[2].
As I concede that the Bell inequalities cannot be violated in LR theories, the papers you quote do not seem relevant.
THIS is what I wanted you to do, i.e. publish your argument regarding your stand that all of these quantitative tests of local realism doesn't actually test local realism or rule them out. All of the EPR-type test papers have argued for that, and yet, you haven't written either a rebuttal or any papers to counter that. The fact that such an argument still may qualify as a paper, even if it is in AJP, implies that this is a new and not generally accepted argument, and thus, should NOT be done in PF until your proposition has been published.

Zz.

[1] G. Blaylock, Am. J. Phys. v.78, p.111 (2010).
[2] T. Maudlin, Am. J., Phys. v.78 p.121 (2010).

When you say such things, I feel somewhat confused. I had no intention to break the forum’s rules. Furthermore, to be on the safe side, I obtained a mentor’s permission to start this thread. If, however, you tell me, in your capacity of mentor, that my posts are inappropriate, I’ll certainly obey and stop discussing this topic. If, however, you, as a mentor, believe that my posts are appropriate, then the reference to the forum rules seems somewhat irrelevant.
On the other hand, I believe everything or almost everything I am saying was previously published by others in peer-reviewed journals, so I honestly don’t know what I could publish (even if I wanted to forget that I am mostly following nightlight’s reasoning).

ZapperZ

Jan15-10, 08:10 AM

Dear ZapperZ,
I am afraid you may have misunderstood me. That means I was not clear enough. My reasoning was quite different. I concede that the Bell theorem (BT) per se rules out local realism (LR) (assuming that all predictions of standard QT are correct, and with the standard caveat on superdeterminism). I also concede that no LR theory can reproduce ALL results of standard quantum theory (QT). However, I argued that this does not mean LR is ruled out as 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP). Indeed, you cannot reasonably argue that the failure to absorb contradictions rules out LR. I argue that it’s good for LR that it cannot absorb them, and it’s bad for standard QT that it can. Further, as we cannot have both UE and PP as precise results, I expressed my opinion that PP cannot be precise, while it looks like UE is indeed precise.

This only adds to the confusion. By saying " ... 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP)... , you are explicitly stating that there's a logical inconsistency with both theories! Isn't that what I've been saying all along of YOUR position? What am I missing here?

Secondly, can you cite explicit references where the same argument has been made with regards to both Bell theorem and QM. I mean, of all the intelligent people (some of which, you cited) who are looking into this, I can't believe that this issue has been missed by them. If they did, then this would be MY argument on why you are doing this here and not pointing this "important" aspect of both theories in a journal.

Zz.

DrChinese

Jan15-10, 10:13 AM

Let me summarize. I think you’ll agree that to rule out LR you necessarily need two things together: 1) mathematical proof that some results predicted by QT cannot be reproduced by any LR; 2) experimental proof that one of such predictions is indeed correct. I argue that, on the one hand, there is no such mathematical proof, as a proper mathematical proof cannot use two mutually contradictory assumptions, and there is no such experiment. Therefore, I argue, LR has not been ruled out so far. Furthermore (and here I speculate), I suspect that loophole free experiments would have ruled out UE, so I suspect our points of view are much closer than it looks, as it seems we both swear by unitary evolution.

Your position is fairly illogical and you should already know that from what has been said. There is no requirement that QM resolve anything for Bell to apply. And to make that even more clear, consider this:

1) Is there anything inconsistent or contradictory about Malus' Law? Obviously not. Then "presto" I have a new version of the Bell Theorem that says:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Malus' Law.

2) So now every Bell test still rules out local realism, just as before. QED.

You are quibbling in essence that QM cannot be considered a theory because it is internally inconsistent, a view which is not shared by the rest of the community. By the way, general relativity also yields inconsistent results during the very early universe. I guess by your reasoning, it should be abandoned in favor of Newtonian gravity.

Not that it matters to the application of Bell, but I would be interested in hearing a specific situation in which it is generally agreed that QM makes different predictions for the same setup. Please, make it an experiment that can be or has been performed. Then, we can ask others to judge it as to whether it makes inconsistent predictions.

ThomasT

Jan15-10, 01:41 PM

LOCAL REALISM ruled out?LHV theories of a particular form are ruled out. It's not clear yet whether Bell's LHV ansatz is general.
"which concept, locality or realism, is the problem?"Neither concept is a problem. The problem is the formalization of the concept of locality. Bell's ansatz is incompatible with that of standard QM (for the joint, entangled state), and with the design of entanglement producing experiments.

DrChinese

Jan15-10, 03:10 PM

LHV theories of a particular form are ruled out. It's not clear yet whether Bell's LHV ansatz is general.
Neither concept is a problem. The problem is the formalization of the concept of locality. Bell's ansatz is incompatible with that of standard QM (for the joint, entangled state), and with the design of entanglement producing experiments.

This gets tiring.

There is nothing wrong with the designs of the hundreds of different entanglement experiments which have been performed. These all demonstrate, using different setups and theoretical approaches, one thing: Bell Inequalities are violated wherever they are found.

There is currently NO local realistic theory in consideration - anywhere - which can reproduce all of the predictions of QM. There are a few people who are working on TRYING to create such a theory, and there is one in process I know of which is local realistic but contextual (thereby avoiding the Bell requirements). The reason there aren't any LHV candidates currently is simple: they keep getting knocked out by Bell tests. Once Bell showed us the way, scientists have been able to design new and improved ways to find and demonstrate entanglement - which BY DEFINITION does not exist in LHVs (since the correlations are thought to be spurious).

Here is one for you: model how an LHV produces entanglement for particles which have never interacted.

Non-local generation of entanglement of photons which do not meet each other (http://arxiv.org/abs/quant-ph/0609135)

MaxwellsDemon

Jan15-10, 05:06 PM

ZapperZ

Jan15-10, 05:21 PM

If I have to choose between a universe without locality or a universe without realism, I choose to get rid of locality. I was never too attached to it anyway. Good riddance. :) Would it really be such a terrible thing to abandon a local description of physical phenomena?

Well then, you may have a rough time. Tony Leggett has arrived at a rather elaborate argument that, even if you relax the locality requirement, one still cannot rescue realism unless one is willing to sacrifice, among other things, the arrow of time. See this:

http://www.physicsforums.com/showpost.php?p=1599072&postcount=62

and this:

http://www.physicsforums.com/showpost.php?p=1518312&postcount=57

and one more:

http://www.physicsforums.com/showpost.php?p=1307660&postcount=40

Zz.

Maaneli

Jan15-10, 06:24 PM

Well then, you may have a rough time. Tony Leggett has arrived at a rather elaborate argument that, even if you relax the locality requirement, one still cannot rescue realism unless one is willing to sacrifice, among other things, the arrow of time. See this:

http://www.physicsforums.com/showpost.php?p=1599072&postcount=62

and this:

http://www.physicsforums.com/showpost.php?p=1518312&postcount=57

and one more:

http://www.physicsforums.com/showpost.php?p=1307660&postcount=40

Zz.

That's not quite right. Leggett refers to "classical realism", which refers to the notions of realism in ontological (LCHV or NLCHV) theories that maintain NON-CONTEXTUALITY, and it is those such theories that are ruled out by the experiments he discusses (ignoring the detection loopholes, of course). Realism is perfectly safe however within a nonlocal, contextual, and causal HV theory (e.g. de Broglie-Bohm theories, stochastic mechanical theories, GRW and SCL theories, etc.). And yes, even Leggett acknowledges this distinction in his papers.

ZapperZ

Jan15-10, 06:48 PM

That's not quite right. Leggett refers to "classical realism", which refers to the notions of realism in ontological (LCHV or NLCHV) theories that maintain NON-CONTEXTUALITY, and it is those such theories that are ruled out by the experiments he discusses (ignoring the detection loopholes, of course). Realism is perfectly safe however within a nonlocal, contextual, and causal HV theory (e.g. de Broglie-Bohm theories, stochastic mechanical theories, GRW and SCL theories, etc.). And yes, even Leggett acknowledges this distinction in his papers.

"Quantum realism", if you want to call it that, was never in question, nor is there any falsifiable experiment to distinguish between all the different flavors. These experiments do not contradict anything about the superposition property.

I believe the "many worlds" and "Bohm-De Broglie" followers have their own thread to play with already in this forum. The issue so far has always been classical realism or macrorealism.

Zz.

Maaneli

Jan15-10, 07:47 PM

"Quantum realism", if you want to call it that, was never in question,

But in referring to Leggett's work, you didn't make a distinction between "classical" and "quantum" realism (which Leggett does), you just generically referred to "realism". So it was necessary for someone else to make the distinction.

nor is there any falsifiable experiment to distinguish between all the different flavors.

True, not yet, but there are proposals for such experiments in the near future.

These experiments do not contradict anything about the superposition property.

This isn't relevant to anything I said.

I believe the "many worlds" and "Bohm-De Broglie" followers have their own thread to play with already in this forum.

So? It's still relevant to mention the latter theory in the context of discussing Leggett's work, and in particular, when discussing what types of "nonlocal real" theories are and are not ruled out by current experiments.

ZapperZ

Jan15-10, 07:59 PM

But in referring to Leggett's work, you didn't make a distinction between "classical" and "quantum" realism (which Leggett does), you just generically referred to "realism". So it was necessary for someone else to make the distinction.

Not in the context of this thread. Furthermore, using the term "realism" as applied to this particular area of study to imply classical realism is done all the time without any confusion. See a related article covering the SAME set of reports:

http://physicsworld.com/cws/article/news/27640

So I'm not the only one doing this, and various other papers dealing with "realism" have expressed the same thing. How come you didn't write a rebuttal on those?

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

Zz.

MaxwellsDemon

Jan15-10, 09:05 PM

Hmm...interesting...especially the part regarding the arrow of time.... I'll have to check out those links tomorrow when I get some free time so I can let you know what I think. :)

Maaneli

Jan16-10, 03:58 AM

Not in the context of this thread. Furthermore, using the term "realism" as applied to this particular area of study to imply classical realism is done all the time without any confusion. See a related article covering the SAME set of reports:

http://physicsworld.com/cws/article/news/27640

So I'm not the only one doing this, and various other papers dealing with "realism" have expressed the same thing.

I disagree. You replied to someone's suggestion that locality is worth sacrificing for realism, with the claim that Leggett's work shows that even "realism" (no qualifications given about contextuality or non-contextuality) is not tenable without sacrificing another intuitively plausible assumption. But that characterization of Leggett's work is simply not accurate, which anyone can see by reading those abstracts you linked to. And I don't even think that's true that everyone in this field agrees that the word realism is used to imply classical realism, and that this is done without any confusion. I know several active researchers in this field who would dispute the validity of your use of terminology. Moreover, the link you gave to try and support your claim, doesn't actually do that. If you read your own link, you'll see that everything Aspelmeyer and Zeilinger conclude about realism from their experiment is qualified in the final paragraph:

However, Alain Aspect, a physicist who performed the first Bell-type experiment in the 1980s, thinks the team's philosophical conclusions are subjective. "There are other types of non-local models that are not addressed by either Leggett's inequalities or the experiment," he said.

So Aspect is clearly indicating that Aspelmeyer and Zeilinger's use of the word "realism" is intended in a broader sense than Leggett's use of the term "classical realism".

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

It's not nitpicking on semantics, it's getting the physics straight. If that's too difficult for you to do, then I'm sorry, but maybe you're just not cut out for this thread.

akhmeteli

Jan16-10, 10:15 AM

This only adds to the confusion. By saying " ... 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP)... , you are explicitly stating that there's a logical inconsistency with both theories! Isn't that what I've been saying all along of YOUR position? What am I missing here?

Your question seems to suggest that my phrases you quote contradict something else I wrote. What is this “something else” exactly? If it is my words that “I am not sure I have problems with the Bell theorem” (I said it long ago), then I explained that I don’t see any holes in the proof, but I believe its assumptions are mutually contradictory. The theorem is just a ”messenger” of standard quantum theory (and we should not kill a messenger:-) ), it does us a great service by pushing the assumptions of SQM to the extreme and thus baring its problems. I emphasize that I fully accept unitary evolution of quantum mechanics, the only thing I have problems with is the projection postulate, which, on the one hand, has limited experimental basis (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149), on the other hand, it explicitly introduces nonlocality, and last, but not least, contradicts UE.
Secondly, can you cite explicit references where the same argument has been made with regards to both Bell theorem and QM. I mean, of all the intelligent people (some of which, you cited) who are looking into this, I can't believe that this issue has been missed by them. If they did, then this would be MY argument on why you are doing this here and not pointing this "important" aspect of both theories in a journal.
I don’t have a reference “where the same argument has been made with regards to BOTH Bell theorem and QM”, though I cannot be sure it does not exist. The contradiction between UE and PP is well-known though. See e.g. http://plato.stanford.edu/entries/qt-measurement/ and references there. For example, the quote from Albert’s book there: “The dynamics and the postulate of collapse are flatly in contradiction with one another ... the postulate of collapse seems to be right about what happens when we make measurements, and the dynamics seems to be bizarrely wrong about what happens when we make measurements, and yet the dynamics seems to be right about what happens whenever we aren't making measurements. (Albert 1992, 79)”. The postulate of collapse, I believe, is pretty much the same as PP. Or, if you prefer a journal reference, see the following reference there: Bassi, A., Ghirardi, G.C., 2000, Physics Letters A, 275: 373-381 (and references there). (By the way, note that standard QT has lived happily with this contradiction for decades, and has the nerve to say that LR is untenable:-) ) So this issue "was not missed by intelligent people". The problem is, while this issue is recognized as such, people, all of a sudden, demand that LR theories faithfully reproduce this issue. This is rich!

As for what I am saying about the Bell theorem, I follow nightlight’s posts. Of course, they are no journal reference, but they were extremely useful for me, so I hope my posts can be useful for somebody else, as nightlight does not post here anymore. As for publishing, you see that I offered little if any original thinking.

Let me also quote the following work here: http://arxiv.org/PS_cache/quant-ph/pdf/0702/0702135v2.pdf (see references to their journal articles there): “The solution of our model shows that the so-called “measurement problem”, to wit, the fact that the final state … does not seem to be related unitarily to the initial state, has the same nature as the celebrated “paradox of irreversibility”, with additional quantum features. Here too, it is the large size of the apparatus which produces destructive interferences, thus generating inaccessible recurrence times; such times behave as exponentials of the level density, which itself is an exponential of the number of degrees of freedom.” This may explain how standard quantum mechanics can live with such contradiction and why PP is only an approximation. This may also explain that measurement process is relatively slow, as it requires a macroscopic system, so this may be a reason why it is both so difficult and so crucial to close all loopholes simultaneously in experiments.

DrChinese

Jan16-10, 11:32 AM

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

Zz.

I think I'm with you on that. Some people see the glass as 99.9% full. Others like to discuss the 0.1%.

akhmeteli simply ignores all experiment and theory that does not sit well, and somehow imagines that a Local Realistic theory (of which there are NONE to consider or discuss) can outperform an "inconsistent" QM. So we are arguing about the label "inconsistent" - i.e. semantics. Meanwhile, people come up with new and exciting work every day using that poor ol' inconsistent theory.

Maaneli agrees the any theory must be contextual. If someone wants to call their contextual theory "realistic" when particles clearly lack well-defined properties when not observed... I don't understand the meaning of the words the same way, which makes it an argument about semantics as well.

ThomasT

Jan16-10, 12:08 PM

This gets tiring.

There is nothing wrong with the designs of the hundreds of different entanglement experiments which have been performed.I didn't say there was. I said that Bell's generalized ansatz for LHV theories is incompatible with entanglement producing experimental designs. And that it's not clear yet whether his formulation is the definitively generalized form that any and all LHV theories must take.

These all demonstrate, using different setups and theoretical approaches, one thing: Bell Inequalities are violated wherever they are found.Ok. Again, my post doesn't contradict this.

There is currently NO local realistic theory in consideration - anywhere - which can reproduce all of the predictions of QM.Yes, this a difficult problem. And it might not have a solution. Which will mean that LHV theories of entangled states are impossible. But, establishing that definitively will require more than just Bell's Theorem, and that still wouldn't necessarily tell us anything about whether Nature is exclusively local or not.

Once Bell showed us the way, scientists have been able to design new and improved ways to find and demonstrate entanglement - which BY DEFINITION does not exist in LHVs (since the correlations are thought to be spurious).I don't know what the last part that sentence means.

Here is one for you: model how an LHV produces entanglement for particles which have never interacted.Same conceptual principle (and same modelling problem) as the archetypal setup -- subject the separated particles to a common torque or whatever. Spatially separated groups of many atoms have been entangled, haven't they?

And no, I can't do a viable LHV model for any of it.

Which doesn't have anything to do with what I wrote in reply to yoda jedi's question(s).

I don't see anything wrong with that reply, so I really don't know what you're on about with the this gets tiring comment. For you to reply that there's nothing wrong with the experimental designs indicates that you either misread what I wrote, or misunderstood it.

akhmeteli

Jan16-10, 12:37 PM

2. The answer is that it doesn't convince anyone. Which explains why the LR position is completely ignored professionally except by Santos and a few others.
So going against the opponent’s weakest argument is not good enough because it does not convince anyone? So am I supposed to go against the opponent’s strongest argument, even if I agree with this argument? Strange. For example, I readily agree that LR is not popular now. But we are discussing a different issue: has it been ruled out, say, by experiments or not?
3. True, they have elevated the detection loophole to a higher status. They even published a paper with Santos on the subject. For the reasons ZapperZ explained about loopholes above, I respectfully disagree with their assessment; but I understand their position as being for the sake of bringing a final and complete end to the "loopholes" discussion. I think Santos' statement you quote is ridiculous, I have seen it before and it always makes me mad. No one is a priori ignoring hidden variables. If they existed, context free, they should be noticable and yet they never are. There is absolutely NOTHING about the setups that can be said to select a subset which is biased in any way. If such bias occurs, it must be natural and subtle (like my standard candles example). The problem with that approach is that even then, there is NO known way to get the Bell results from a biased LR sample... as we see with Santos' repeated failures. And as detection efficiency improves: the Bell result simply gets stronger in complete violation of LR predictions. And finally, there is substantial independent corroboration from other experiments.
What Santos says is: if you assume fair sampling, you pretty much rule out LHV apriori. You, however, declare fair sampling all but a ”holy cow”. You pretty much forbid me to think that a possibility of such “natural and subtle bias” has not been ruled out. I cannot accept such demand, sorry.
4. You are completely wrong again, the violations are there every time. The thing you ignore is called the scientific method. There is no requirement in the method - EVER - that all loopholes be closed simultaneously to accept the results of an experiment. I would say in fact that this almost NEVER occurs in any scientific experiment. The normal technique is to vary one variable at a time and chart relationships. That is why science accepts the Bell test results. If everyone stuck their heads in the ground until "perfect" experiments were done (as you seem to suggest), we would have no science at all.
I asked ZapperZ, let me also ask you: what’s wrong with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees. Or do you think there is nothing wrong with it? In both cases we are talking about a theorem, remember? If you have not made sure that all assumptions of the theorem are fulfilled simultaneously, you cannot demand that the statement of the theorem hold true.

While I might agree that we accept many things without “perfect experiments”, I also have to note the following. I believe you’ll agree that elimination of LR is an extremely radical idea. You may also agree that the burden of proof is much higher for extremely radical ideas. We are not talking about a 40-dollar parking ticket. This idea turns philosophy upside down. So I have the right to state that LR has not been ruled out until we have proper experimental results. OK, you are quite happy that LR has been ruled out by experiments, Shimony and Zeilinger are not quite happy, I am not happy at all. So who’s right, you or I? I think the jury is still out. And I don’t hold my breath.
5. Now you are just trying to be contradictory. You say that correlations outside of Alice and Bob's light cones are within the scope of LR? As far as I know, there has not been any attempt by a local realist to address that one. Once again, your argument circles back to "I ignore all evidence in contradiction to my viewpoint" even though this one completely contradicts every possible LR perspective.
I argue that correlations predicted using PP have not been seen without loopholes. Are you telling me that the experiments you mentioned have achieved something that experiments on Bell violations have not been able to achieve for 45 years? Then I guess I need to find out more about the experiments in question, so could you give me a reference?
6. The local realistic school, of which Einstein was a member, is virtually non-existent now. So you are wrong again. QM has more interpretations now, but they are all either non-local or non-realistic.
As I tend to think Einstein was wrong about the uncertainty principle, I am not crying for that particular school. I am not wrong about Copenhagen interpretation though. And I guess the mere coexistence of many interpretations suggests that there is no one satisfactory interpretation.
7. Of course entanglement refutes LR. That is by definition! Or more precisely, LR flatly predicts that entanglement does not exist (correlations are spurious).
I don’t know what definition you use. I thought an entangled state is anything that is not a mixture of product states. To get nonlocality from that you need the very projection postulate I am trying to offend :-) And correlations may be for real if there is any loophole:-), for example, when there is no spatial separation.

8. As with Bell, the other no-gos compare the predictions of LR with the predictions of QM. They use different techniques, and they are generally not statistical. They are instead considered "all-or-nothing" and soundly support QM. I guess you will next tell us that is even more support for LR because QM is contradictory and should not be supported.
Exactly:-) If those other no-gos use both UE and PP (or something similar to PP), any problems LR can have with those theorems are no problems at all. I should emphasize though that I fully support the unitary evolution part of QM, so if you tell me there is a no-go theorem that uses UE only and rules out LR, I am all ears.
You see, your starting premise - that QM is contradictory - flies in the face of the science of the last 100 years.

No, it does not. The quantum measurement problem is recognized as such.
While you see problems, everyone else is using the theory to make new predictions and new advances. That is because QM is useful. Now, is it also true? That is not a scientific question, it is a philosophical one. QM is a model, and should not be confused with reality. See my tag line below.
You see, I like this one about two tradesmen: one of them offered the other one raspberry jam and second-hands for watches. The other one said he would buy the jam, but is not interested in second-hands at all. The first one said: "I cannot sell you the jam without the second-hands, as the second-hands are mixed with the jam."
QM is certainly very useful, but that does not mean we cannot try to separate jam from second-hands.

DrChinese

Jan16-10, 01:16 PM

I don't know what the last part that sentence means.

A local realist believes that the results at Alice are not dependent on the results at Bob. Therefore, any correlations between Alice and Bob must be SPURIOUS because they are both causally connected to some other (prior) event.

On the other hand, the SQM position is that the results are somehow causally connected, although there is no causality in the usual sense of the word (causes precede effects). This is simply another way of saying that there is entanglement, spooky action at a distance, etc.

Now, the reason why Bell is so important is that it gives me a way to attack ANY local realistic model. I will always know just where to look to find the Achilles Heel of any candidate theory. I simply look at how it explains entanglement. If you have read many papers on local realistic models, you know you will always find one thing: an explanation of how they (claim to) get around Bell's Theorem. And of course, they do that precisely because they know that is where they are vulnerable. Bell is the strongest argument against Local Realism.

DrChinese

Jan16-10, 01:28 PM

What Santos says is: if you assume fair sampling, you pretty much rule out LHV apriori.

That's funny! You should really re-read what you are writing first. :biggrin: Poor Santos, God picks unfair samples just to ruin him personally.

The humor here has gone far enough. You already know about the evidence - over and above Bell - which independently rules out LR (GHZ, Hardy, Leggett, etc.). That doesn't matter to you though. There are no candidate local realistic theories in existence at this time. You don't even care about that.

If God came down and told you LR is wrong, you would still be looking for another loophole. I am interested in science rather than listening to you nitpicking. My discussion with you on this point has ended.

yoda jedi

Jan16-10, 04:21 PM

Welcome to PhysicsForums, yoda jedi!

It is not clear whether it is realism, locality, or both which are ruled out. We simply know from Bell's Theorem and others, coupled with experimental verification, that at least one does not hold.

thanks !
answer on the right track, to alain aspect is locality.

but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

DrChinese

Jan16-10, 05:35 PM

thanks !
answer on the right track, to alain aspect is locality.

but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

That was the thinking of the EPR paper, and it is very reasonable. But it turns out that the cos^2(theta) rule throws a link into things. That is what we learned from Bell's Theorem. It is a little easier to discuss photon spin than electron spin (used by Bell) because that is how most experiments are formed today.

Specifically, the problem comes at various angle settings other than 0 and 90 degrees, although you also have some problems there. Try to imagine entangled photons measured at 45 degrees apart. You would expect them, according to the cos^2(theta) rule, to be completely randomly correlated - and they are (cos^2(45 degrees) is .5). However, if you look at correlations at 22.5 degrees - half way between 0 and 45 degrees, you get something like 85% correlation. That is way too high. There is no dataset of values that is random at 0 and 45 degrees and yet has 85% correlation at 22.5 degrees. The QM answer is that there is only reality for the angles actually measured, not for hypothetical (counterfactual) cases.

I realize my example is probably not clear. But the overall ooint is, you are looking at the most simple case only, so it is no surprise that the result works for your model. But almost any other case does not work when fully analyzed.

akhmeteli

Jan16-10, 07:18 PM

Sorry, it has taken me quite some time to reply.
There may be a measurement problem, but I doubt it is the problem you think it is. It is kind of like the problem of why there is more matter in the universe than anti-matter. Something it would be nice to understand, but not something that is actually in contradiction to theory.
Sorry, there is a contradiction between UE and collapse– see references in my post 31 in this thread. It’s something that has been known since von Neumann (I was not born then, so don’t blame me).
I would say that it is NOT generally accepted that QM is inconsistent.

I gave you the reasoning, I gave you the references, it’s not my independent research or something, you don’t seem to challenge my statement that there is indeed a contradiction (if you do, please advise), so does it really matter if it is generally accepted? I tend to believe it is generally accepted, you tend to believe it is not, but do we have to waste our time deciding if it is or isn’t, unless you personally dispute it?

And I would also say that it is not generally accepted that the validity (or lack thereof) of QM in any way affects the result of Bell Theorem.
I concede that it is not generally accepted.
Generally, Bell says:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

So this is a direct statement that the idea left by EPR - that a local realistic explanation could mimic QM - was untenable. If you advance a local realistic theory, it WILL make predictions different than QM.
I prefer your original wording: “the Bell Theorem states that no LHV theory can reproduce ALL of the predictions of quantum theory”. However, as I said, this is good for LR, not bad, that it cannot reproduce contradictory statements of QM.

akhmeteli

Jan16-10, 08:21 PM

You are misreading the quotes to your own position, there is NO SUCH CONSENSUS.
There is, sorry. I gave you the quotes by Shimony, Zeilinger, Genovese. You are just telling me that “there are hundreds of articles ruling out LR.” I am not sure you can offer a serious quote actually confirming that. The only thing that is controversial is how probable or improbable can be LR. This thread is about whether LR has or has not been ruled out. Probability is an important, but secondary issue.
Do you think there are any loophole free experiments for gravity? Or the speed of light in a vacuum? These are subjects that are in fact debated. However, the consensus is that a) we have a good theory for gravity; b) we know the speed of light in a vacuum; and c) Bell's Theorem is valid.
Again, ruling out LR is extremely radical, so the burden of proof is extremely high.
Read Genovese's statement again (which by the way is 5 years old), he uses 3 adjectives (conclusive, absolutely, uncontroversial) because there are some people - perhaps you are one - who cannot accept evidence that contradicts your world view. You are actually presenting NOTHING in support of your position.
He could have used seven adjectives, depending on his temperament, this does not change the essence of his statement: LR has not been ruled out (as for Genovese’s article being 5 year old, that could only matter if a loophole-free experiment had been performed since then). And I did present enough evidence to support my position. Indeed, you do not dispute that there have been no experiments without loopholes. You don’t seem to dispute that there is a contradiction between UE and PP (if you do, please give your reasoning). What else do I need to prove? Again, you can say LR is improbable, and I dispute that, but you cannot say it has been ruled out.
In probably 500+ papers in the past year alone, there are references to Bell's Theorem and EPR. These are accepted. The work on the so-called loopholes is more in analogy to finding the 5th decimal place to a number we already know to 4 decimal places. There are only a handful of working physicists still working on local realistic theories today, and that is precisely because of the convincing nature of the evidence.
I already offered this question: why experiments attempting to close loopholes are published in the best journals, if the evidence is overwhelming as it is? Again, your evidence is as good or as bad as my evidence that planar Euclidian geometry is wrong.
A better reference from you would show a specific case in which a quantum mechanical prediction for an entangled system was wrong, and the local realistic counterpart was right.

I can only offer a hint. As UE and PP contradict each other, there should be possible in principle to offer an experiment where they give different results. That would be the experiment where LR would give a different prediction from that of PP as well. I speculate that the predictions of LR and UE will coincide in such an experiment.

akhmeteli

Jan16-10, 10:24 PM

Your position is fairly illogical and you should already know that from what has been said. There is no requirement that QM resolve anything for Bell to apply.
How come??? In your wording, the Bell theorem states that no LR theory can mimic ALL predictions of QT. Until QT is free of contradictions, this cannot rule out LR: indeed, you just cannot demand with a straight face that a theory faithfully reproduce mutually contradictory predictions. So QT better sort out its own problems first, otherwise it’s a pot calling a kettle black.
And to make that even more clear, consider this:

1) Is there anything inconsistent or contradictory about Malus' Law? Obviously not.
Not so fast, please. Neither is PP per se inconsistent or contradictory. However, PP is inconsistent with UE, and PP and UE are mutually contradictory. Actually, as far as I understand, in the context of the Bell experiment, the Malus law and PP give the same result, therefore, strictly speaking, the Malus law is in contradiction with UE. Indeed, UE cannot turn a superposition into a mixture of states. Therefore, the rewording you offer does not change anything
You are quibbling in essence that QM cannot be considered a theory because it is internally inconsistent, a view which is not shared by the rest of the community.
I did not use quite that wording, I said that standard QT contains mutually contradictory assumptions. Maybe this is pretty much the same, but I still prefer this wording. As for incompatibility between UE and PP, I believe it is recognized. I gave you the references to work on quantum measurement problem. As I said, it is not a question of this being generally accepted or not. Do you personally agree with that or not? In essence, I guess you appreciate that a superposition cannot “unitarily evolve” into a mixture of states. Do you challenge that? Do you challenge my reversibility reasoning? Do you challenge the Bassi article? Please advise, and then we’ll either consider your objections, or agree on this issue.
By the way, general relativity also yields inconsistent results during the very early universe. I guess by your reasoning, it should be abandoned in favor of Newtonian gravity.
You see, I know next to nothing about gravity, but if general relativity is indeed inconsistent, it will eventually be replaced by a better theory. However, as far as Newtonian gravity is concerned, there is a difference between the situation you describe and the situation with LR and QT. Indeed, Newtonian gravity is a reasonably well-defined theory, and experiments demonstrate deviations from its predictions. However, it is really difficult to rule out the incredibly wide class of LR theories.
Not that it matters to the application of Bell, but I would be interested in hearing a specific situation in which it is generally agreed that QM makes different predictions for the same setup. Please, make it an experiment that can be or has been performed. Then, we can ask others to judge it as to whether it makes inconsistent predictions.
As I said, the contradiction between UE and PP suggests that it will be possible in principle to perform an experiment for which UE and PP give differing predictions. I cannot offer any specifics right now. I can even imagine that this can be as difficult as proving reversibility, which, however, is a direct consequence of UE. Do you really think that UE does not always hold? I guess the Schlosshauer article is relevant (I gave the reference in post 31 in this thread). His conclusions are:
(i) the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far;
(ii) all observed ‘‘restrictions’’ can be correctly and completely accounted for by taking into account environmental decoherence effects;
(iii) no positive experimental evidence exists for physical state-vector
collapse;
(iv) the perception of single ‘‘outcomes’’ is likely to be explainable through decoherence effects in the neuronal apparatus.

Another thing. I speculate that there will be no violations of the Bell inequalities in loophole-free experiments.

MaxwellsDemon

Jan17-10, 06:40 AM

So our conclusion here is either locality or realism or both must be abandoned or quantum mechanics is just plain wrong. (Its highly unlikely quantum physics is just plain wrong since it makes so many verified testable predictions) I wonder if entaglement would be a "problem" in general relativistic quantum mechanics. I mean our current theory must be wrong in some ways since it doesn't take general relativity into account. Still, if it is, I say we abandon locality. That might be a problem for reductionism though. If you can't describe basic physics in terms of local things, then it might be tough to describe the universe in terms of the sum of its parts interacting. Getting rid of locality might give us some deeper insight into the way our universe works though...specifically I'm thinking of something like Mach's principle where mass here is somehow dependent and defined by the existence of other objects out there.

PTM19

Jan17-10, 08:37 AM

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

So this is a direct statement that the idea left by EPR - that a local realistic explanation could mimic QM - was untenable. If you advance a local realistic theory, it WILL make predictions different than QM.

I just want to clarify that the above is true when locality is defined in terms of the speed of light. This may be the common usage but in general the concept of locality is independent of any particular speed limit it only requires that some limit does exist.

In the general sense local realistic hidden variable theories which reproduce QM are still possible. Experiments can never rule out this kind of locality, they can only place lower bounds on maximum signal propagation speed required to maintain locality.

DrChinese

Jan17-10, 09:45 AM

I just want to clarify that the above is true when locality is defined in terms of the speed of light. This may be the common usage but in general the concept of locality is independent of any particular speed limit it only requires that some limit does exist.

In the general sense local realistic hidden variable theories which reproduce QM are still possible. Experiments can never rule out this kind of locality, they can only place lower bounds on maximum signal propagation speed required to maintain locality.

Just to put this argument in perspective: the current experimental lower bound is somewhere between 10,000 and 10,000,000 times the speed of light. The difference has to do with assumptions about the movement of the earth through space. Either way, it far exceeds c.

Since c more or less defines relativistic constraints and defines what locality is, I would not call such a solution a local realistic one. It is a non-local one, such as Bohmian Mechanics. There are also true local solutions in which there is causal time symmetry (such as Relational BlockWorld, Cramer's, etc.). These are contextual so I would say they are not Bell realistic.

Dmitry67

Jan17-10, 10:00 AM

akhmeteli

Jan17-10, 12:13 PM

That's funny! You should really re-read what you are writing first. :biggrin: Poor Santos, God picks unfair samples just to ruin him personally.

Do you think I misrepresented Santos' position?

Again, for you the fair sampling assumption is a holy cow, but it isn't for me.

The humor here has gone far enough. You already know about the evidence - over and above Bell - which independently rules out LR (GHZ, Hardy, Leggett, etc.). That doesn't matter to you though.

Again, I admit that I don't know much about GHZ, Hardy, Legget. I know two things though. First, as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE. If you tell me, for example, that their proof does not use PP or something similar, that will matter to me, but you are not saying anything like this, so I’m not sure about “INDEPENDENTLY rules out”. Second, as far as I know, the number of experiments testing these newer statements is very limited so far compared to the number of experiments testing Bell.

There are no candidate local realistic theories in existence at this time. You don't even care about that.
I admit, this is an important consideration. However, some remarks may be appropriate here.
First, strictly speaking, in this thread I was not trying to convince anybody that QT will be eventually replaced by an LR theory. I was discussing a somewhat different question: has LR been ruled out by recent developments, both theoretical and experimental? You did not seem to challenge the factual basis of my reasoning (the mutually contradicting assumptions of Bell and no loophole-free experiments). Well, to be more precise, your objections to the statement on the mutually contradicting assumptions of Bell were half-hearted at best. If, however, you do want to challenge this statement head-on, please advise. Basically, you just argued that my point of view is not generally accepted, and LR is improbable. But “improbable” and “ruled out” are quite different expressions.
Second, let us imagine something improbable for a second: that we bought two sixpacks on a weekend and decided to find an LR replacement (LRR) to QT :-). The first question we’ll need to answer would be: is it possible in principle? Let us imagine something even more improbable: that you agreed with me that there are no no-go theorems or no-go experiments eliminating such a possibility. Then we’ll have to proceed with the next phase of our “brainstorming session”: what are the technical requirements to such LRR (specifications)? I think we’ll agree without any further fuss that our LRR does not need to mimic all predictions of QT, as they are mutually contradictory (so no LRR would be able to mimic them anyway). And I’d like to emphasize that this may be a crucial issue: finding LRR may be extremely difficult because it is not clear what requirements such LRR must meet.
Suppose, however, that we agree that if our LRR mimics “just” unitary evolution of QT, that would be enough for us. Is it possible to find such LRR? I don’t know. However, the following nightlight’s observation may be of great interest here: QTP-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post http://www.physicsforums.com/showpost.php?p=1825523&postcount=90 – it may be worth a glance).
If God came down and told you LR is wrong, you would still be looking for another loophole.
I don’t know, I guess I should wonder what you would do if god “came down and told you LR is” right? :-)
However, I guess yours is a good question (or is it a statement ? :-) ). Let me explain my position. I don’t think there is any credible evidence of god’s existence. However, I cannot be sure that there will be no such evidence tomorrow (indeed, I could imagine that human race can produce some tiny rational creatures in the future (using biological, chemical, or physical methods). For such creatures, we would be pretty much the same as gods).
I take a similar position with respect to LR. Right now I don’t think there is any credible evidence ruling out LR. But I cannot be sure that there will be no such evidence tomorrow. When there is such evidence, I will have to change my point of view.
I am interested in science rather than listening to you nitpicking.
Look, I gave you an example with planar Euclidian geometry. You don’t like it? You believe the sum of angles of a quadrangle is not quite relevant to the sum of angles of a triangle? C’mon, you’re nitpicking. You think the sum of angles of a triangle on a sphere is not quite relevant to the sum of angles of a planar triangle? C’mon, you’re nitpicking.
My discussion with you on this point has ended.
I do appreciate your time and input.

DrChinese

Jan17-10, 06:25 PM

I believe that Transactional Interpretation is an example of LR theory. But as it is explicitly retrocasual it does not help to recover a dream of local realists - to restore some newtonian-like theory, just with different formulas.

Am I right? How could one explain these desperate attempts to find a loophole, over and over again?

I don't think of retrocausal as being realistic, although I can see how some might. I think such interpretations are viable, certainly as viable as Bohmian types. I think there are particular theoretical reasons why you might be drawn to them: for example, relativity is respected as is T symmetry. I can also see where it might be too weird for some to accept. It certainly makes it easy to explain delayed choice quantum eraser experiments!

DrChinese

Jan17-10, 07:01 PM

...Again, I admit that I don't know much about GHZ, Hardy, Legget. I know two things though. First, as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE...

...the mutually contradicting assumptions of Bell and no loophole-free experiments). Well, to be more precise, your objections to the statement on the mutually contradicting assumptions of Bell were half-hearted at best....

This is why discussion with you is fruitless. I have said any number of times, in any number of ways, quite the opposite of what you portray here. There are NO contradictory elements of Bell. Period. And I HAVE said that these are fully independent of Bell. The only similarity to Bell is as follows:

The predictions of QM are set against the predictions of LR, and experiments support the predictions of QM.

You don't accept that QM can be considered as a valid theory, a position which is patently absurd. So you throw the baby out with the bathwater. I can't help in this matter, as it is strictly a matter of your personal opinion and has no element of science associated with it. Good luck with your next experiment, I want to see you do one without "contradictory" QM as your basis.

:rofl:

P.S. You REALLY ought to re-read what you are saying BEFORE you say it. I am sure you are impressing yourself with your brilliant logic, but it isn't working for others. Trying asking yourself: Why would someone who has spent a lot of time studying an area have a different opinion than I do? (Not talking about myself there.) There might be a strong reason that has nothing to do with their unreasonable, pigheaded stubbornness and blind following of orthodoxy. Maybe others use words differently than I do. Maybe addressing the substance of an argument is more important than semantics. Maybe others are actually open to useful ideas when they are accompanied by sound scientific reasoning. Maybe useful citations, rather than out-of-context quotes, go farther in making my points. Maybe there is a reason why my personal opinions are frowned upon on a physics board followed by lay readers.

akhmeteli

Jan17-10, 11:13 PM

This is why discussion with you is fruitless. I have said any number of times, in any number of ways, quite the opposite of what you portray here.
Evidently, I misrepresented your position, and I apologize. However, you’ll notice that I immediately asked you to clarify your position, and I am glad you did just that. When you reproached me, I tried to understand why your position did not seem clear to me. I found only three places in this and previous threads where you directly touched upon contradictions in Bell assumptions, here they are (in no particular order):
And I would also say that it is not generally accepted that the validity (or lack thereof) of QM in any way affects the result of Bell Theorem.

As to Bell using mutually contradictory assumptions: all Bell is saying is that LR predictions can never match QM. If you think QM itself is based on mutually contradictory assumptions (which some claim is the case), that is NOT equivalent to saying Bell itself is based on those assumptions. If QM is shown to be experimentally wrong tomorrow, then so be it. But the predictions of QM are still the predictions of QM, and I don't know anyone who sees any confusion (or contradiction) in the cos^2(theta) rule.

1. QM is not considered self contradictory, although a lot of folks don't like the collapse rules. But that is 100% irrelevant to Bell's Theorem, which merely points out that the predictions of QM and LR are different in specific areas. One has nothing to do with the other, and it is plain wrong to say "Bell is inconsistent because QM is inconsistent".
In the first quote you just do not express your personal opinion. In the second one you don’t state that there are no contradictions in Bell assumptions. The third one is indeed categorical, but it was said rather early in the game, and after that I explained that the mutually contradictory assumptions of QT are used in the proof of the Bell theorem. So I guess there were some reasons why I was not quite clear about your position. Anyway, I’m glad your position is clear now, so I may discuss it:
There are NO contradictory elements of Bell. Period.
Let me ask you for a favor. Could you please tell me which one (or more) of the following three statements you personally disagree with, so that we could pinpoint the source of our disagreement?

1. A typical Bell theorem proof assumes unitary evolution of QT (as it assumes, for example, that projections of spin of the two-particle system are conserved).

2. A typical Bell theorem proof assumes projection postulate of QT (or something similar) (when the QT correlations are calculated to prove that the inequalities can indeed be violated in QT).

3. Unitary evolution and projection postulate are, strictly speaking, mutually contradictory, as, for example, the latter introduces irreversibility, whereas UE, strictly speaking, is not compatible with irreversibility (for example, due to the quantum recurrence theorem).

And I HAVE said that these are fully independent of Bell.
But I did not state that you had not “said that these are fully independent of Bell”. I just expressed my doubts that they are independent, as, I suspect, they use pretty much the same assumptions as Bell. What I did state was that “as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE”. Do you disagree with that? If you do, then do you state that PP or something similar is not used to prove Leggett, GHZ, Hardy?

You don't accept that QM can be considered as a valid theory, a position which is patently absurd. So you throw the baby out with the bathwater. I can't help in this matter, as it is strictly a matter of your personal opinion and has no element of science associated with it. Good luck with your next experiment, I want to see you do one without "contradictory" QM as your basis.
No, I did not say that I “don't accept that QM can be considered as a valid theory”. I just did not say that. I have greatest respect for QT. I did say that standard QT contains mutually contradictory assumptions. This is quite different. And this is not just my personal opinion. The measurement problem in quantum mechanics had existed long before I was born. Don’t kill the messenger. Kill Albert, kill Bassi, even von Neumann.
P.S. You REALLY ought to re-read what you are saying BEFORE you say it. I am sure you are impressing yourself with your brilliant logic, but it isn't working for others. Trying asking yourself: Why would someone who has spent a lot of time studying an area have a different opinion than I do? There might be a strong reason that has nothing to do with their unreasonable, pigheaded stubbornness and blind following of orthodoxy.
DrChinese, If you believe I used personal attacks in my posts, please tell me where, and I’ll be happy to apologize. If I was not sensitive enough in my posts, I regret that and I can assure you that I meant no offence or disrespect. I do sincerely respect you as a knowledgeable and eloquent person, and I sincerely respect your opinion, even when I disagree. If my logic is faulty, it means I err in good faith, but I am not trying to sell you something I don’t believe myself using some court-room rhetoric. And I will certainly appreciate if you show where my logic is faulty.

Maybe others use words differently than I do. Maybe addressing the substance of an argument is more important than semantics. Maybe others are actually open to useful ideas when they are accompanied by sound scientific reasoning. Maybe useful citations, rather than out-of-context quotes, go farther in making my points. Maybe there is a reason why my personal opinions are frowned upon on a physics board followed by lay readers.
I believe I generally used sound scientific reasoning, but you may disagree, and I certainly appreciate your critique. As for “out-of-context quotes”, I don’t think I misrepresented Shimony, Zeilinger, and Genovese’s opinions. I was not trying to say that they believe in LR, they don’t. I said that they believe LR has not been ruled out by experiments so far. Therefore I strongly disagree that this is just my “personal opinion” (“LR has not been ruled out yet”), which may confuse “lay readers” of this forum. Again, don’t kill the messenger.

zonde

Jan18-10, 03:08 AM

model how an LHV produces entanglement for particles which have never interacted.

Non-local generation of entanglement of photons which do not meet each other (http://arxiv.org/abs/quant-ph/0609135)
Seems similar to double slit experiment in a sense that photon's context wave splits over two paths with exception that paths do not end at the same place.
At polarization independent beam splitter photon goes down one path but photon's context wave (pilot wave if you like) goes down by both paths. At PBS photon's context wave interacts with other photon's (empty) context wave and creates entanglement. Only requirement is that both photons come from common source and polarization of one of photons is rotated by 90deg (polarizer + HWP at 45deg relative to polarization axis of polarizer).

That seems to be common recipe for creating polarization entangled photons.

DrChinese

Jan18-10, 08:16 AM

Seems similar to double slit experiment in a sense that photon's context wave splits over two paths with exception that paths do not end at the same place.
At polarization independent beam splitter photon goes down one path but photon's context wave (pilot wave if you like) goes down by both paths. At PBS photon's context wave interacts with other photon's (empty) context wave and creates entanglement. Only requirement is that both photons come from common source and polarization of one of photons is rotated by 90deg (polarizer + HWP at 45deg relative to polarization axis of polarizer).

That seems to be common recipe for creating polarization entangled photons.

I don't think it is actually a requirement that they come from a common source (there does need to be phase matching). I think that it the easier way by far to create the pairs. They are no longer polarization entangled when they start their independent processes.

yoda jedi

Jan19-10, 12:22 PM

You don't accept that QM can be considered as a valid theory

and/or maybe a transitory one.

quantum mechanics is just plain wrong.

or inconsistent or incomplete.

many interpretations suggests that there is no one satisfactory interpretation.

and are "INTERPRETATIONS".................

That was the thinking of the EPR paper, and it is very reasonable.

thanks !
but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

a spin can be up and the other down, or both up ? or both down ?
but that it can be argued in any case, that results are predetermined (from the beginning).

-------------------------------------------

Proceedings Vol. 7421
Andrei Khrennikov

The main aim of this review is to show that the common conclusion that Bell's argument implies that any attempt to proceed beyond quantum mechanics induces a nonlocal model was not totally justified. Our analysis of Bell's argument demonstrates that violation of Bell's inequality implies neither "death of realism" nor nonlocality. This violation is just a sign of non-Kolmogorovness of statistical data - impossibility to put statistical data collected in a few different experiments (corresponding to incompatible settings of polarization beam splitters) in one probability space.

.

DrChinese

Jan19-10, 01:29 PM

1. and maybe a transitory one.

2. or just incomplete.

................

3. not 100 %, respect to ?
to non-contextuality ? contextuality ?
or independence ?

a spin can be up and the other down, or both up ? or both down ?
but that it can be argued in any case, that results are predetermined (from the beginning).

4. Proceedings Vol. 7421
Andrei Khrennikov

The main aim of this review is to show that the common conclusion that Bell's argument implies that any attempt to proceed beyond quantum mechanics induces a nonlocal model was not totally justified. Our analysis of Bell's argument demonstrates that violation of Bell's inequality implies neither "death of realism" nor nonlocality. This violation is just a sign of non-Kolmogorovness of statistical data - impossibility to put statistical data collected in a few different experiments (corresponding to incompatible settings of polarization beam splitters) in one probability space.

1. Sure, a better (more useful) theory could come along any day. In fact, I hope one does.

2. The incompleteness argument was made in EPR and is now soundly rejected.

3. The correlation is 85% when Alice measures at 0 degrees and Bob measures at 22.5 degrees. So not 100%.

4. A fair example of his thinking is from his paper: "Complete account of randomness in the
EPR-Bohm-Bell experiment" which is at: http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.0445v1.pdf

He derives the usually CHSH inequality but ends up with result CHSH<=8 when the accepted result is CHSH<=2. See his (2) on page 6. So he concludes that experiment does not rule out local reality, since a typical experimental result is aboout 2.4. The point is that makes no sense. If you know how CHSH is derived, that is like proving that 1=3. It really isn't worth time to dispute the logic here, as no one really accepts it as useful in the first place.

In the paper you reference, he attacks the Kolmogorov axioms - this has been raised previously as an objection and it basically defeats the local realistic agenda if accepted. So not much there.

Suffice it to say, publication is not equivalent to general acceptance per se, especially with pure theoretical work. Just ask anyone who publishes if they expect their work to end up in a textbook. In sum: Khrennikov's work is not generally accepted, and I don't see any merit to his argument as it stands.

He does have some interesting papers, though:

"A Conclusive Experimentation Evidences that Mental States Follow Quantum Mechanics." (I actually like this, strange as it seems.)

"Quantum-like Representation of Extensive Form Games: Wine Testing Game" (I am a fan of reds.)

He also has some interesting papers about random fields, including: "Demystification of quantum entanglement".

Dmitry67

Jan19-10, 01:38 PM

Can I ask my question again.
Why people are attacking that tiny partucular area?
There are no people who are trying to bring flogiston or either. Whats so special with LR?

DrChinese

Jan19-10, 03:23 PM

Can I ask my question again.
Why people are attacking that tiny partucular area?
There are no people who are trying to bring flogiston or either. Whats so special with LR?

If someone asserts something on this board that is not generally accepted as if it is traditional science (i.e. they label it as fact, not an opinion)... that is the invitation.

On the other hand, generally accepted science is not "proven" so much as "supported". It usually makes useful predictions which can be used to rule out that theory. When folks make predictions which are contradicted by experiment, then it is time to change their theories. QM does not make any predictions at this time which are inconsistent with entanglement experiments. LR does. QM is supported and LR is not.

That is a generally accepted statement within the physics community, like it or not.

yoda jedi

Jan19-10, 03:24 PM

2. The incompleteness argument was made in EPR and is now soundly rejected.

i refer to the "information loss problem" not to epr.

(and other details).

DrChinese

Jan19-10, 05:04 PM

i refer to the "information loss problem" not to epr.

(and other details).

Not sure I follow. Can you be more specific? Are you talking about with black holes? If so I don't see the issue as being relevant.

ThomasT

Jan20-10, 04:45 PM

A local realist believes that the results at Alice are not dependent on the results at Bob.If a local realist is one who believes that LHV theories of entangled states haven't been definitively ruled out, then I'm a local realist. If a local realist is one who believes that such a theory is likely to be forthcoming, then I'm not a local realist. :smile:

Either way, I believe that in order to produce entangled states experimentally, then it's necessary that the results at Alice and Bob be statistically interdependent (which is accomplished entirely via local interactions/transmissions during the pairing process), which will also ensure that any associated Bell-type inequality will be violated.

Therefore, any correlations between Alice and Bob must be SPURIOUS because they are both causally connected to some other (prior) event.Why would a common causal connection to some other (prior) event make them spurious? In fact we only see predictable correlations between results at Alice and Bob for two settings.

DrChinese

Jan20-10, 07:16 PM

Why would a common causal connection to some other (prior) event make them spurious? In fact we only see predictable correlations between results at Alice and Bob for two settings.

Because the results at Alice are not causally related to the results at Bob. They are instead both causally related to some other prior event.

On the other hand, entanglement acts "as if" there is a causal connection.

ThomasT

Jan21-10, 01:38 PM

Because the results at Alice are not causally related to the results at Bob. They are instead both causally related to some other prior event.

On the other hand, entanglement acts "as if" there is a causal connection.Thanks for the replies. My latest was hurried and I had to cut it short. I had a couple more comments/questions which it looks like will have to wait until later, or tomorrow.

yoda jedi

Jan23-10, 03:42 PM

why the glue ?

LOCAL REALISM ruled out?

"which concept, locality or realism, is the problem?"

i understand, is a type of realism (are jointly false).
a realism that is local.

cos the real, observed or not, exist.

-------------------
Bell inequalities are based on poincare relativity, have to be seen what happen in a sitter relativity.

Demystifier

Jan29-10, 07:57 AM

Generally, Bell says:
No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism. The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

Demystifier

Jan29-10, 09:03 AM

The superdeterminism loophole (http://arxiv.org/abs/0908.3408) won't be ruled out anytime soon.
Indeed. In fact, probably it will never be ruled out.

Demystifier

Jan29-10, 09:13 AM

DrChinese

Jan29-10, 11:11 AM

Indeed. In fact, probably it will never be ruled out.

And indeed, it is a loophole for all physical theories, not just quantum mechanics. Relativity, evolution, big bang... all can be equally well explained by superdeterminism. With a mere wave of the hand, at that!

ThomasT

Jan29-10, 02:25 PM

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.
I don't think this is the clearest (read: correct) way to talk about what Bell's theorem means.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism.Superdeterminism and free will have nothing to do with it. It just has to do with the formal expression of locality.

The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)Bell advanced a certain generic formulation for LHV models of quantum entangled states whose salient formal characteristic was assumed to be necessary for any LHV model of a quantum entangled state.

But that has by no means been proven to be the case.

The current state of affairs is that there's no formal expression of locality that is compatible with entanglement experimental designs and the salient feature of SQM formalization of entangled states (nonseparability or nonfactorability). Does 't Hooft's match all the precictions of SQM? Is it explicitly local?

A successful LHV model of entangled states can't be rendered in the straightforward factorable form proffered by Bell, because this alone contradicts a necessary condition of entanglement experiments which is the statistical interdependency of Alice's and Bob's results (outcome dependence) -- ie., Bell's locality condition is ambiguous.

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will). What's so realistic about the quantum potential and instantaneous action-at-a-distance?

Besides, there's no reason to give up locality.

So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists?Because of Bell?

Why nonlocality seems so difficult or weird to them?It has no empirical foundation. Just an easy explanation for entanglement corrolations.

MaxwellsDemon

Jan29-10, 04:50 PM

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

akhmeteli

Jan29-10, 05:15 PM

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I have been trying to avoid answering this question, but I guess your post was the last straw:-)

First, why was I reluctant to answer (of course, I cannot answer for other people)? Because, as long as there are no clear-cut theoretical or experimental reasons to reject locality (and I don't believe there are such reasons), this is a matter of personal preferences, maybe philosophical views, which a) take a long time to outline and b) are not very appropriate for this forum. So I'll try to stick to physical reasoning. I believe relativity strongly favors locality, and partial differential equations, which are all-pervading in physics, also favor locality. The absense of faster-than-light signaling also tends to suggest locality.

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

DrChinese

Jan29-10, 05:26 PM

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

You don't need to change your calculations as is, Demystifier has tried to show this on many occasions. So that doesn't seem a fair critique. And if you did need to change them, that would actually be a near-proof of non-locality.

As to reductionism, the alternative is to abandon realism (which I am personally OK with). So that is probably equally distasteful if it comes down to taste.

RUTA

Jan29-10, 05:43 PM

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

Causally local, constitutively non-local, i.e., non-separable.

MaxwellsDemon

Jan29-10, 07:05 PM

Demystifier

Jan30-10, 11:42 AM

and partial differential equations, which are all-pervading in physics, also favor locality.
Schrodinger equation for two particles is a partial differential equation, so it is local but in the (6+1)-dimensional CONFIGURATION space, not in the ordinary (3+1)-dimensional space. This is exactly why QM is nonlocal (or nonseparable to be more precise) in the ordinary space, even though it is described by a partial differential equation. You may say that the world is still local, but then you must also say that the world contains a huge number of dimensions (3 new space dimensions for each particle). Does such a multi-dimensional local world makes you more happy?

Demystifier

Jan30-10, 11:45 AM

And indeed, it is a loophole for all physical theories, not just quantum mechanics. Relativity, evolution, big bang... all can be equally well explained by superdeterminism. With a mere wave of the hand, at that!
Exactly.

akhmeteli

Jan30-10, 02:13 PM

Schrodinger equation for two particles is a partial differential equation, so it is local but in the (6+1)-dimensional CONFIGURATION space, not in the ordinary (3+1)-dimensional space. This is exactly why QM is nonlocal (or nonseparable to be more precise) in the ordinary space, even though it is described by a partial differential equation. You may say that the world is still local, but then you must also say that the world contains a huge number of dimensions (3 new space dimensions for each particle). Does such a multi-dimensional local world makes you more happy?

First, I said PDE favor locality, not dictate it.

Second, we don't know what the final theory will look like: according to your papers and our previous discussions, you don't even believe all predictions of quantum theory will be confirmed experimentally.

Third, for pretty much any system A of (nonlinear) PDE in 3+1 dimensions one can construct a system of linear differential equations in the Fock space, which is equivalent to A on the set of solutions of A (see the outline of this result by Kowalski/Steeb in my post http://www.physicsforums.com/showpost.php?p=1825523&postcount=90 - some time ago I read about this result in nightlight's posts). That means that if quantum unitary evolution is successfully described by a linear system of equations in the Fock space (which is broader than any configuration space), you cannot be sure that system cannot be successfully replaced by a system of nonlinear equations in 3+1 dimensions. Therefore, you cannot be sure the system in the Fock space describes nonlocal reality.

And I would very much appreciate your answer to my question: everything els being equal, would you prefer a local theory, or a nonlocal one?

yoda jedi

Jan30-10, 03:32 PM

Can you be more specific?

have not a unified dynamics for microscopic and macroscopic systems.
its physically incomplete.

RUTA

Jan31-10, 09:11 AM

Special Relativity is certainly local, but I would argue that General Relativity is not. In GR, the geometry is a global description, not a local one. Locally the geometry is flat, its only on a large scale that spacetime curvature comes into play. I would think that the principle of general covariance (where all “regular” derivatives in local laws are replaced with covariant derivatives when talking about large scale phenomena) is where this difference is most apparent. The covariant derivative still applies locally, but the extra term added in is dependent on the overall geometry. The curvature is something extra that requires a knowledge of the energy-momentum distribution in a region that goes beyond simply knowing the distribution in the here and now. The fact that we have to change our calculations in GR depending on the global geometric features of a region suggests to me that it is locality that needs to be abandoned. To me, abandoning realism is far more distasteful anyway. I prefer to think that concepts like position and momentum aren’t just ideas I have about nature, or biases from my human way of thinking, but that they have some objective foundation in reality. Even if they don’t exist exactly as I conceive of them, I’d like to think that a concrete objective phenomenon can be related to my ideas in some way. Color and temperature don’t exist as I perceive them, but there are still well defined objective things like wavelengths of light and atomic vibrations that can be related to my sensory experiences.

First, it looks like you’ve conflated causal and constitutive locality. Your argument for the “nonlocality” of the covariant derivative is of the constitutive variety. See Howard, D., “Spacetime and Separability: Problems of Identity and Individuation in Fundamental Physics” in Potentiality, Entanglement and Passion-at-a-Distance, edited by R.S. Cohen et al., Kluwer Academic, Great Britain, 1997, pp. 113-141. Then you argue to keep “realism,” but realism in this sense is associated with constitutive locality, i.e., that entanglement violates causal locality and/or realism per EPR --> causal and/or constitutive nonlocality per Healey and Howard, for example. See also Healey, R.: Holism and Nonseparability in Physics: In: Zalta, E.N. (ed.) The Stanford Encyclopedia of Philosophy (Spring 2009 Edition), http://plato.stanford.edu/archives/spr2009/entries/physics-holism. For the term “constitutive locality” see Healey, R.: Gauging What’s Real: The Conceptual Foundations of Gauge Theories. Oxford University Press, Oxford (2007).

Essentially, EPR said there are quantum “objects” which possess definite properties in and of themselves (realism) that are revealed by measurements independent of what’s being done to entangled partners at space-like separated events (causal locality). If you keep the causality requirement, you can explain the entangled outcomes by saying the quantum objects’ properties are not possessed in and of themselves, but they are “co-possessed” by entangled partners. That’s constitutive nonlocality/nonseparability.

Second, I don't agree that your argument establishes the constitutive nonlocality of the covariant derivative. As a differential geometry prof once emphasized, despite being definable via parallel transport, the covariant derivative is a local object independent of the choice of curve along which you parallel transport at a point on the manifold. You do need to input a vector in the tangent space of said point if by "covariant derivative" you mean the exterior derivative so restricted, but it's still local. See Misner, C.W., Thorne, K.S., Wheeler, J.A.: Gravitation. W.H. Freeman, San Francisco (1973).

So, while the measurement devices and outcomes are separated (constitutively local), the properties of the objects being measured are not per constitutive nonlocality. It’s hard to imagine (for most people, anyway) how nonseparability would be modeled, as the rest of your post indicates. If you’d like to see how we model constitutive nonlocality via discrete path integrals over graphs, see arXiv 0908.4348. It’s in the “revise and resubmit” mode at Foundations of Physics, but substantively it’s sound (at least the referees and editors had no complaints about its substance—if you find a mistake, please let us know).

Demystifier

Feb1-10, 04:09 AM

And I would very much appreciate your answer to my question: everything els being equal, would you prefer a local theory, or a nonlocal one?
I don't understand what do you mean by "everything else". :confused:

akhmeteli

Feb1-10, 07:23 AM

I don't understand what do you mean by "everything else". :confused:

That means just that - "everything else" :-), but since you insist:-), let me define it as follows. Let us imagine for a moment that in ten or twenty years from now, as a result of progress both in theory and experiment or just because some god told us the ultimate truth:-), we have a final quantum theory, which is fully self-consistent and perfectly agrees with all experiments. Would you prefer this theory to be local or nonlocal, provided that your own well-being and success of your own research does not depend on whether it is local or nonlocal?

You may wonder why I am persistently asking this question - because I would like to save some time:-) If you answer "yes", it'll be easier for me to answer or for you to understand why some people prefer locality, if you answer "no", maybe you'll be able to explain to me why you personally prefer nonlocality. So I am just trying to understand if your current preference for nonlocality can be explained by your personal preferences or you just believe that the current case for nonlocality is too strong to even think about a possibility of a local theory.

Demystifier

Feb1-10, 07:39 AM

jambaugh

Feb1-10, 09:18 AM

Akhmeteli, I would prefer nonlocality. The reasons are simple. First, because the Bell theorem strongly suggests (I will not say proves) that the quantum world is nonlocal, while experiments confirm the predictions of quantum mechanics.

(If I may hum yet another chorus of the CI song...)

It is hard to say an RAA argument "suggests" which of the prior assumptions should be considered false. It rather points that the assumptions as a whole are mutually inconsistent. However to my mind we can't have "reality" if we sacrifice local causality if one is to accept special relativity.

SR + violation of local causality implies future actions can affect past states of reality. What then is the meaning of "reality" if it is not objectively defined and immutable once in the past?

I think it no more strange to reject absolute reality in QM than to reject absolute time in SR. It just takes some getting used to. The alternative is not nihilism or illusory mind created phenomena. It is a relative actuality of observed phenomena without the underlying assumption of a clockwork objective mechanism. We don't assume, we don't deny we simply pay attention only to the scientifically meaningful observations and observables without painting our own prejudices about what must lie beneath.

Alternative "interpretations" always remind me of the epicycles invented to hold onto the Platonic perfection of circular motion in spite of the evidence to the contrary in observed planetary behavior. I think the "absolute objective reality" hypothesis is similar to the Platonism of old in this sense.

Demystifier

Feb1-10, 10:13 AM

SR + violation of local causality implies future actions can affect past states of reality. What then is the meaning of "reality" if it is not objectively defined and immutable once in the past?

There is a way out of this problem. Due to violation of local causality, some properties of the system in the past are determined by some properties of the system in the future. However, it does not mean that the past can be changed. Since there is only one future (the one that will actually happen), there is only one past as well (the one that has actually happened). Once the past is known, the future cannot be changed in a way that would contradict the known past.

See also the attachment in
http://www.physicsforums.com/showpost.php?p=2455753&postcount=109

jambaugh

Feb1-10, 10:28 AM

There is a way out of this problem. Due to violation of local causality, some properties of the system in the past are determined by some properties of the system in the future. However, it does not mean that the past can be changed. Since there is only one future (the one that will actually happen), there is only one past as well (the one that has actually happened). Once the past is known, the future cannot be changed in a way that would contradict the known past.

See also the attachment in
http://www.physicsforums.com/showpost.php?p=2455753&postcount=109

I understand that. But that just boils it all down to "known" past i.e. observables instead of states. As a philosophical foundation, the "reality" of the "unobserved past" is meaningless in this context so why continue to work with it? The reason for invoking the "reality hypothesis" is no less invalid given this "way out".

If you are going to work with "tentative reality" then call it what it is, classes of possible observations. My point is that one can still reject the absolute reality of what is not observed (past, present, and future) while retaining the desired local causality. The reverse just isn't possible, your comments not withstanding.

Either you have violation of local causality with its implied invalidation of (unobserved) reality or you have local causality with QM+Bell invalidation of unobserved reality.

So reality being lost, we can still retain local causality if it, by itself, is consistent with observation. We know it to be consistent with predicted observations in QM, via the "no Bell telephones" theorem.

Demystifier

Feb1-10, 10:38 AM

I understand that. But that just boils it all down to "known" past i.e. observables instead of states. As a philosophical foundation, the "reality" of the "unobserved past" is meaningless in this context so why continue to work with it? The reason for invoking the "reality hypothesis" is no less invalid given this "way out".

Well, this way out works even if you replace the word "known" by the word "real". I am not saying here that reality is necessary or needed or desirable (nor I'm saying that it is not), but I AM saying that reality may be compatible with SR and nonlocality. Maybe there is no reality, but SR+nonlocality are not a valid argument against reality.

yoda jedi

Feb1-10, 11:12 AM

Peter Morgan

Feb1-10, 11:15 AM

Well, this way out works even if you replace the word "known" by the word "real". I am not saying here that reality is necessary or needed or desirable (nor I'm saying that it is not), but I AM saying that reality may be compatible with SR and nonlocality. Maybe there is no reality, but SR+nonlocality are not a valid argument against reality.
All through this thread, I find no distinction made between dynamical nonlocality and nonlocality of initial conditions (not that the distinction is much made in the literature). Dynamical locality is essentially preferred by classical physics. Initial conditions of a classical dynamics, however, are essentially always nonlocal, whether the dynamics are Newtonian or Lorentz invariant, because at a given time we have to specify the position and momentum of all particles, everywhere on a space-like hyperplane. Furthermore, classically, if we observe some phenomenon that requires a weird set of initial conditions, then that just means that the initial conditions in the past were also weird. This is all that superdeterminism is --- if what we observe now is weird, the setup must have been weird too. It makes no difference whether we introduce local or nonlocal dynamics. All of which is to say, Demystifier, that I say with you that "reality may be compatible with SR and nonlocality".

The only superdeterminism that is required to model the Bell-EPR situation, however, is superdeterminism of the evolution of probability densities. That is, if the probability density now is weird, then the probability density in the past must also have been weird. Superdeterminism of the state of a classical deterministic dynamics is not necessary. Amongst other consequences, it's therefore not necessary to impinge much on free will, unless, I suppose, one wants to deny that probability can be applied to model people's microbehaviour.

Another distinction not introduced here, in my look through, is contextuality. It's well-established that noncontextuality alone is enough to derive Bell inequalities. The distinction can also be put in terms of whether we regard settings of an instrument as parameters of a model or as observables in the model. Noncontextuality is rather against the spirit of classical particle modeling, and arguably can be thought of as anti-realist relative to particle properties, but it is not against the spirit of classical field models. Indeed, for field systems at thermal equilibrium the global configuration of an experimental apparatus condition the thermal equilibrium state, just as the Copenhagen interpretation insists it should. Think heat equation in contact with various heat reservoirs. I include a sketch of an experiment that gives more detail (which is of course needed) in a recent preprint, Comment on "A glance beyond the quantum model" (http://arxiv.org/abs/1001.4993) (this says nothing against any of the sophisticated interpretations that are out there, each of which gives its own interesting way of thinking about QM, and each of which a person may reasonably find more-or-less in tune with their own intuitive preferences).

Happy hunting!

DrChinese

Feb1-10, 11:37 AM

All through this thread, I find no distinction made between dynamical nonlocality and nonlocality of initial conditions (not that the distinction is much made in the literature). Dynamical locality is essentially preferred by classical physics. Initial conditions of a classical dynamics, however, are essentially always nonlocal, whether the dynamics are Newtonian or Lorentz invariant, because at a given time we have to specify the position and momentum of all particles, everywhere on a space-like hyperplane. Furthermore, classically, if we observe some phenomenon that requires a weird set of initial conditions, then that just means that the initial conditions in the past were also weird. This is all that superdeterminism is --- if what we observe now is weird, the setup must have been weird too. It makes no difference whether we introduce local or nonlocal dynamics. All of which is to say, Demystifier, that I say with you that "reality may be compatible with SR and nonlocality".

The only superdeterminism that is required to model the Bell-EPR situation, however, is superdeterminism of the evolution of probability densities. That is, if the probability density now is weird, then the probability density in the past must also have been weird. Superdeterminism of the state of a classical deterministic dynamics is not necessary. Amongst other consequences, it's therefore not necessary to impinge much on free will, unless, I suppose, one wants to deny that probability can be applied to model people's microbehaviour.

Another distinction not introduced here, in my look through, is contextuality. It's well-established that noncontextuality alone is enough to derive Bell inequalities. The distinction can also be put in terms of whether we regard settings of an instrument as parameters of a model or as observables in the model. Noncontextuality is rather against the spirit of classical particle modeling, and arguably can be thought of as anti-realist relative to particle properties, but it is not against the spirit of classical field models. Indeed, for field systems at thermal equilibrium the global configuration of an experimental apparatus condition the thermal equilibrium state, just as the Copenhagen interpretation insists it should. Think heat equation in contact with various heat reservoirs. I include a sketch of an experiment that gives more detail (which is of course needed) in a recent preprint, Comment on "A glance beyond the quantum model" (http://arxiv.org/abs/1001.4993) (this says nothing against any of the sophisticated interpretations that are out there, each of which gives its own interesting way of thinking about QM, and each of which a person may reasonably find more-or-less in tune with their own intuitive preferences).

Happy hunting!

I saw that a few days ago on the arxiv and just starting reading it. For those interested, it comments on a paper by Navascues and Wunderlich regarding classic-quantum correspondence. It also has some good references.

nikman

Feb1-10, 11:42 AM

Peter Morgan

Feb1-10, 12:37 PM

I saw that a few days ago on the arxiv and just starting reading it. For those interested, it comments on a paper by Navascues and Wunderlich regarding classic-quantum correspondence. It also has some good references.
Thanks, DrC, and I'd be glad of your comments as always, here or by e-mail. There's an after-thought to this Comment, which is that a friend pointed out that the arXiv version of the paper it comments on does not includes the word "field" at all. To appreciate the details of the argument therefore requires the Proc.Roy.Soc.A paper. I'm somewhat curious whether the published version only introduces the classical field concept because a referee introduced the question (which might slightly improve the chances of the Comment being accepted, because the Proc.Roy.Soc.A editorial procedure for Comments includes the original paper's referee if the editors decided to send it to referees).

Fortunately, I believe the published version is freely available at http://rspa.royalsocietypublishing.org/content/466/2115/881 because of the Proc.Roy.Soc.A anniversary celebrations.

The chance of this Comment being accepted by Proc.Roy.Soc.A is small. The editorial board will presumably understand that discontent would be expressed in some quarters if they were to accept it, so I presume they will only accept it if it touches something of their own interests in the question.

yoda jedi

Feb1-10, 01:06 PM

"A glance beyond the quantum model"

Happy hunting!

http://arxiv.org/PS_cache/arxiv/pdf/0907/0907.0372v1.pdf

........Here we propose a fundamental axiom that we believe any reasonable post-quantum theory should satisfy, namely, that such a theory should recover classical physics in the macroscopic limit............

coincidence (a correlation, or better yet a metaphysical corelation), i am reading:

On the Classical Limit of Quantum Mechanics
http://www.springerlink.com/content/p57117239x631547/fulltext.pdf

..........In spite of many results of the standard approach, it is not yet clear how to explain within standard quantum mechanics the classical motion of macroscopic bodies..............

but suffers the same problems that standard quantum theory, is a patchwork proto-theory.

Peter Morgan

Feb1-10, 01:09 PM

FWIW in "Quantum nonlocality vs. Einstein locality" Dieter Zeh makes a distinction between "dynamic" and "kinematic" (quote):

Quantum theory is kinematically nonlocal, while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality"). How can these two elements of the theory (well based on experimental results) be simultaneously meaningful and compatible? How can dynamical locality even be defined in terms of kinematically nonlocal concepts?

http://www.rzuser.uni-heidelberg.de/~as3/nonlocality.html

Thanks for this. Definitely worthwhile. I'm not as familiar with Zeh's thinking on environmental decoherence as I should be.

As an aside, I went to Foundations of Physics for Zeh's most recently mentioned paper on his web-site, "Quantum discreteness is an illusion", which is not yet published but is available as an "online first" paper. The quality of the (69!) papers in the "online first" queue (that's probably 6 months ahead) shows signs of 't Hooft's tenure as editor starting to make a very big difference. The list of authors who have decided to publish at FoP is close to stellar.

ThomasT

Feb1-10, 01:23 PM

Akhmeteli, I would prefer nonlocality. The reasons are simple. First, because the Bell theorem strongly suggests (I will not say proves) that the quantum world is nonlocal ... Is Bell's theorem about the way the quantum world is, or is it about limitations on the formalization of entangled states?

nikman

Feb1-10, 02:47 PM

As an aside, I went to Foundations of Physics for Zeh's most recently mentioned paper on his web-site, "Quantum discreteness is an illusion", which is not yet published but is available as an "online first" paper. The quality of the (69!) papers in the "online first" queue (that's probably 6 months ahead) shows signs of 't Hooft's tenure as editor starting to make a very big difference. The list of authors who have decided to publish at FoP is close to stellar.

One was gratified that 't Hooft published Suarez's "Nonlocal 'Realistic' Leggett Models" paper. It's hard to imagine two scientists with more starkly contrasting world-views than that pair.

http://www.springerlink.com/content/v5652005u01628h2/

or, for you members of the vast unfunded public, grab it gratis:

http://www.quantumphil.org/SuarezFOOP201R2.pdf

yoda jedi

Feb1-10, 08:36 PM

akhmeteli

Feb1-10, 09:02 PM

Akhmeteli, I would prefer nonlocality. The reasons are simple. First, because the Bell theorem strongly suggests (I will not say proves) that the quantum world is nonlocal, while experiments confirm the predictions of quantum mechanics. Second, because the wave function is a single mathematical object describing all particles at once, and nobody knows a reformulation of quantum mechanics in which this fact can be avoided. See also
http://xxx.lanl.gov/abs/quant-ph/0703071

Thank you for your answer. So it looks like you prefer nonlocality not because you like it more than locality, but because you think theory and experiment favor it. However, as I argued starting this thread, there are no no-go theorems or no-go experiments ruling out locality, so I don't have your reasons to favor nonlocality, and I regard it as a radical notion, and the burden of proof is very high for such radical ideas. As for the absence of a local reformulation of quantum mechanics, let me give you an example. For a quarter of a century after formulation of modern quantum mechanics, the de Broglie - Bohm interpretation, while existed (in the form offered by de Broglie), was dead, for all intents and purposes. Nevertheless, it was resuscitated by Bohm. And even now, as far as I know, there is no generally recognized relativistic form of this interpretation (actually, you told me that some time ago, and I don't think much has changed since then). But I guess you believe there will be such relativistic form in the future, and even have your own suggestions. So we don't know what can happen in the future. And I mentioned one possibility how a nonlocal theory can be a local theory in disguise.

So it started with your question: what's so special about locality. I gave you my reasons. Again, if there were some iron-clad no-go arguments, I would have to accept nonlocality. So far I see no reasons for that.

Demystifier

Feb2-10, 01:25 AM

while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality").
You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

Demystifier

Feb2-10, 01:39 AM

theory and experiment favor it. However, as I argued starting this thread, there are no no-go theorems or no-go experiments ruling out locality, so I don't have your reasons to favor nonlocality, and I regard it as a radical notion, and the burden of proof is very high for such radical ideas.

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

And I mentioned one possibility how a nonlocal theory can be a local theory in disguise.

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea), then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

Maaneli

Feb2-10, 04:34 AM

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea), then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

I think Akhmeteli is referring to this claim in one of his prior posts:

... for pretty much any system A of (nonlinear) PDE in 3+1 dimensions one can construct a system of linear differential equations in the Fock space, which is equivalent to A on the set of solutions of A (see the outline of this result by Kowalski/Steeb in my post http://www.physicsforums.com/showpos...3&postcount=90 - some time ago I read about this result in nightlight's posts). That means that if quantum unitary evolution is successfully described by a linear system of equations in the Fock space (which is broader than any configuration space), you cannot be sure that system cannot be successfully replaced by a system of nonlinear equations in 3+1 dimensions. Therefore, you cannot be sure the system in the Fock space describes nonlocal reality.

jambaugh

Feb2-10, 11:30 AM

You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

Not as such, of course. (Special) Relativity however sets the stage for the argument of local causality. If SR is valid and the light-cone is not a causal horizon then we have the potential of (not certainty of) constructing causal paradoxes. So absent local causality how are such paradoxes prohibited? If we actually (in our conceptual model of how nature works) allow causal feedback, future to past, it seems to me then we must invoke a "meta-time" over which such phenomena would decay out or reinforce to a caustic threshold or stable oscillation, (the local "reality" oscillating w.r.t. this meta-time). This was an attractive idea to me once, as e.g. a model for superposition and interference phenomena. But eventually I rejected it as fanciful and meaningless.

The problem as I see it is this sort of speculation is not operationally meaningful. It's no different than supposing an invisible aether, or Everette many worlds. Sure you can speculate but you can't test within the bounds of science. Such phenomena are by their nature beyond observation. Again I see the "reality" of it as meaningless within the context of science. That isn't an argument, just the results of my many internal arguments over past years.

What in the end do we mean by "reality"? Generally it is the reality of a universe of objects with always defined (though not always observed) objective properties or states of being.
Classically that is either the particles or the field quantities at each point of space.

Quantum mechanically we work in a language of phenomena, observables and observations and interactions between systems. I think it incorrect to objectify the mathematical constructs (esp. wave function=hilbert space vector). For that matter I think we should abandon the use of the Hilbert spaces all together except in the mathematics of constructing the Lie algebras and groups where the observables and dynamics are represented.

As to causal locality, that is easily enough described within QM and QFT via the structure of the dynamics. And it is easily enough tested both conceptually via though experiments, and in the lab. The only evidence I can conceive of, for true non-local causation is a classical FTL signal, e.g. a "Bell telephone". If you can't send a classical signal then you aren't talking about observable non-locality and thus speculating beyond the scope of science.

Now having said all that, I do think that if we're ever going to succeed at merging GR and QM we'll need to start with a "pre-local" theory. That is to say a theory of interacting quantum systems out of which condenses the macroscopic classical world. In which case I envision the local causality definition to be rather reversed. Nearness is ultimately defined by causal interactions and the causal structure of interacting systems ultimately defines the light-cones, and space-time metric structure. Objects are spatially close because they look close. This means they strongly interact with our eyes and our flashlights, or our radar antennas, or our fingers or sticks in our hands.

So ultimately I think causality will by definition be local because locality is ultimately based on causal interactions. At the microscopic quantum level this may break down, but not in the causal aspect, but rather the loss of meaning to geometry (and possibly even topology) at the small scale.

nikman

Feb2-10, 11:36 AM

You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

You should really take that up with Herr Professor-Doktor Heinz-Dieter Zeh. I suspect he's making a deeper distinction relating to fundamental correlation and causality. Kinematics does of course rear its head in Relativity with the Lorentz contraction.

RUTA

Feb2-10, 12:25 PM

Objects are spatially close because they look close. This means they strongly interact with our eyes and our flashlights, or our radar antennas, or our fingers or sticks in our hands.

It's possible to have a distant object be brighter than a closer object, e.g., the Sun is much brighter than this computer screen. Likewise the angle subtended by an object doesn't discriminate relative spatial distance. How do you envision relating distance and interaction? And, how do you see your approach giving a Lorentz invariant result, since it can't give a definite spatial separation and be Lorentz invariant?

akhmeteli

Feb2-10, 12:34 PM

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

I will try to answer your question in the evening (Central time zone:-) )

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea)

Thank you very much, I highly value your opinion.

, then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

I agree, but Maaneli was right - I was not discussing my research, and I did have in mind my post #74 in this thread and the reference there.

jambaugh

Feb2-10, 04:57 PM

It's possible to have a distant object be brighter than a closer object, e.g., the Sun is much brighter than this computer screen. Likewise the angle subtended by an object doesn't discriminate relative spatial distance. How do you envision relating distance and interaction? And, how do you see your approach giving a Lorentz invariant result, since it can't give a definite spatial separation and be Lorentz invariant?

It is the light which we feel and the light which is then by definition "close". Chains of propagating effect are the meter sticks (and the clocks) of our universe.

Then again the sun IS close in the frame near that of the propagating light, that is to say the events of emission and absorption are distance near zero given the single photon carrier of the propagating effect.

The sun is also intimately close on the scale of the other stars in the universe. But we can also see that on our scale it is big by how it effects so many other systems near us, the light reflecting off the moon, and the planets, their very orbits, tell us that the sun is both big and (relatively) near. Then the (also relative) distance of the sun is to an extent the ratio of its affect on us and the scale of its effect on things near and far to us. This I think is quantifiable at least to the point of ordering which gives us topological structure.

What after all is a measuring rod but a rigid solid, e.g. a condensate of strongly coupled component atoms. The lengths are essentially measured by counting blocks of those atoms and thus the number of interactional links between the ends of the rods.

As we refine our description of interacting phenomena we however (lately) replace the rigid measuring rod with light signals and clocks.

What then is a clock but a series of "tick" events each causing the next and being caused by the previous.

The nullness of space-time distance between emission-absorption events points to that as the elementary unit of measurement, the --by definition-- invariant phenomenon by which all others are given relative scale.

In formulating any operationally meaningful definitions in the context of science we start with the primaries of observations vis a vis causally interacting with one's environment. It is sensible then that all other concepts, including metric distance and time are derivative of causal connection. The mystery to be solved is rather the extent to which mutually interacting systems either accidentally or necessarily resolve themselves into the space-time-field structure we are able to perceive and map with our theories. In doing that I think causality is necessarily local in that localization is necessarily defined causally.

I cannot help but think rejecting local causality in order to preserve a notion of objective reality is backwards.

[EDIT: Ruta, I'm not sure I fully addressed your question. I haven't tried to make the idea formal and quantifiable. More heuristic as I've expressed above. Let me consider it for a bit and see if it can be given a more formal, rigorous encoding... possibly the attempt will show the idea invalid. It should be a useful exercise.]

RUTA

Feb2-10, 06:49 PM

In formulating any operationally meaningful definitions in the context of science we start with the primaries of observations vis a vis causally interacting with one's environment. It is sensible then that all other concepts, including metric distance and time are derivative of causal connection. The mystery to be solved is rather the extent to which mutually interacting systems either accidentally or necessarily resolve themselves into the space-time-field structure we are able to perceive and map with our theories. In doing that I think causality is necessarily local in that localization is necessarily defined causally.

It seems difficult to define space and time using interacting systems because you need the concepts of space and time to make sense of what you mean by "systems" to begin the process. That is, what you mean by "a system" seems to require trans-temporal identification and to have "two systems" requires spatial separation -- what else would you use to discriminate between otherwise identical systems? That's why we chose a co-definition of space, time and sources (as understood in discrete QFT) as our fundamental operating principle. I look forward to your solution.

akhmeteli

Feb2-10, 08:02 PM

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

I know that it is generally recognized that "theory and experiment favor nonlocality". But no, I am afraid I don't agree with that for reasons outlined in my post #1 in this thread.

Demystifier

Feb3-10, 03:48 AM

I know that it is generally recognized that "theory and experiment favor nonlocality". But no, I am afraid I don't agree with that for reasons outlined in my post #1 in this thread.
Then my next question is: What WOULD you accept as a good argument for nonlocality? For example, if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?

Demystifier

Feb3-10, 03:54 AM

If we actually (in our conceptual model of how nature works) allow causal feedback, future to past, it seems to me then we must invoke a "meta-time" over which such phenomena would decay out or reinforce to a caustic threshold or stable oscillation, (the local "reality" oscillating w.r.t. this meta-time).

That's interesting, because my explicit Bohmian model of relativistic nonlocal reality does involve a "meta time".

The problem as I see it is this sort of speculation is not operationally meaningful. It's no different than supposing an invisible aether, or Everette many worlds. Sure you can speculate but you can't test within the bounds of science. Such phenomena are by their nature beyond observation. Again I see the "reality" of it as meaningless within the context of science. That isn't an argument, just the results of my many internal arguments over past years.

That objection can, of course, be also attributed to the nonrelativistic Bohmian interpretation that does not involve the "meta time".

akhmeteli

Feb3-10, 07:25 AM

Then my next question is: What WOULD you accept as a good argument for nonlocality? For example, if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?

Yes, that would certainly be a good evidence of nonlocality (I mean if violations of the genuine Bell inequalities, without loopholes, are demonstrated experimentally). In that case I would certainly have to reconsider my position. To be frank, I cannot promise I'll reject locality in that case and not free will, for example, but I will certainly have hard time trying to adapt to new reality. The problem is locality will not be the only thing I'll need to reconsider in that case. Such experimental demonstration would also undermine my firm belief in unitary evolution and relativity. And this is in fact the main reason I don't expect any violations of the genuine Bell inequalities.

To give a direct answer to your question "What WOULD I accept as a good argument for nonlocality?", I should also add that experimental demonstration of faster-than-light signaling would certainly be a much more direct and convincing evidence of nonlocality. But again, locality would not be the only casualty of such demonstration. Unitary evolution and relativity would also have hard time trying to survive.

Demystifier

Feb3-10, 08:09 AM

DrChinese

Feb3-10, 10:25 AM

The problem is locality will not be the only thing I'll need to reconsider in that case. Such experimental demonstration would also undermine my firm belief in unitary evolution and relativity. And this is in fact the main reason I don't expect any violations of the genuine Bell inequalities.

First, Bell tests ARE genuine. I think you mean "loophole" free. All experiments have "loopholes", some are simply more relevant than others - and you are free to your personal opinion. But it is manifestly unfair to characterize the hundreds/thousands of different Bell tests themselves as "not genuine".

Second: that is quite a bold prediction you are making, not sure what would make you think that quantum mechanics is actually incorrect (an absolute deduction from your statement).

And last: why do you need to abandon relativity in the case of a confirmed (for you) violation of a Bell Inequality? The speed of light will still remain a constant in all local reference frames. Mass and clocks will still follow the standard rules. So what changes? The only thing that changes are physical effects not described by relativity in the first place. I do not consider relativity to include the absolute prediction that nonlocal elements cannot exist. I think it is an implied result, and one that could well fit within a larger theory. In fact, that is a result that Demystifier has been expressing for some time.

jambaugh

Feb3-10, 11:16 AM

It seems difficult to define space and time using interacting systems because you need the concepts of space and time to make sense of what you mean by "systems" to begin the process. That is, what you mean by "a system" seems to require trans-temporal identification and to have "two systems" requires spatial separation -- what else would you use to discriminate between otherwise identical systems? That's why we chose a co-definition of space, time and sources (as understood in discrete QFT) as our fundamental operating principle. I look forward to your solution.

Well consider for example the entangled electron pair, totally anti-correlated . We typically factor the system into left-moving and right-moving particles (picking our orientation frame appropriately). And we then speak of entanglement of their spins. We could as easily speak of the up z-spin and the down z-spin particle. This is a distinct factorization of the composite system into "two particles". Another distinct factorization is into x-spin up vs down. Each is a different "reality" and the plurality of choices specifically shows our classical bias in thinking of the composite system as two objects. We should rather refer to "a factor" instead of "the component". (And I think equating different factorizations is the principle mistake in parsing the EPR experiment and other entangled systems.)

Now you may argue that spin is also a space-time concept but I could as easily used quark color instead of spin. More to the point, We may find it "difficult to define space and time using interacting systems because" We "need the concepts of space and time to make sense of what [We] mean by 'systems' to begin the process" due to our being space-time entities. That is to say it is a failing of our imagination and artifact of our nature not the universe itself.

Agreed initially we need a concept of time but it need not be metric, only topological and ordered to reflect causal sequence. I can then conceive of a large dimensional quantum system with a complicated random Hamiltonian. (reparametrizing time to make it t independent = pick a t-metric or class of metrics dictated by the dynamics.)

I can also conceive of factoring that system into N 2-dimensional components where 2^N is close to the dimension. Each 2-dim factor has its own U(2)~U(1)xSO(3) structure and I look at the global Hamiltonian and ask what form it takes in terms of internal plus interaction terms. I can then consider different choices of factorization which for the given Hamiltonian might simplify its form.

If I could find some way to formulate an iteration over cases and optimization principle (say minimum sum of component entropies, i.e. minimal entanglement, or otherwise some quantification of symmetry or near-symmetry of the Hamiltonian, or ...) then I might find a global su(2)xsu(2)~so(4) group [so(4) being the compact deformaton if iso(3) of the Euclidean group of spatial geometry. ] naturally emerges for random Hamiltonians under appropriate factorizations and as t increases sufficiently. In short a "natural" condensation into a 3-dimensional space as a spin network and with imperfections effecting e.g. gauge defects. Maybe with some arm-waving and invocation of anthropic principles I could reconstruct the universe in such a fashion.

The question is, for a random large quantum system, can we extrapolate how an entity within that system, able to develop science and formulate physics, would paint his universe. What is the range of possibilities?

I haven't yet of course and such a program may not be "the right way to go about it" (and indeed I can already see many problems) but it is an example of how one might go about constructing/determining spatial structure from scratch. It is not inconceivable to me.

RUTA

Feb3-10, 11:42 AM

Well consider for example the entangled electron pair, totally anti-correlated. We typically factor the system into left-moving and right-moving particles (picking our orientation frame appropriately). And we then speak of entanglement of their spins. We could as easily speak of the up z-spin and the down z-spin particle. This is a distinct factorization of the composite system into "two particles". Another distinct factorization is into x-spin up vs down. Each is a different "reality" and the plurality of choices specifically shows our classical bias in thinking of the composite system as two objects. We should rather refer to "a factor" instead of "the component". (And I think equating different factorizations is the principle mistake in parsing the EPR experiment and other entangled systems.)

You've snuck spatiality in the backdoor -- you need two experimental outcomes, so you need two detectors. You don't need to talk about spatiality in the context of a "quantum system," but you do need those detectors. And, of course, you need to define what you mean by "up" and "down" outcomes in the context of those detectors.

Now you may argue that spin is also a space-time concept but I could as easily used quark color instead of spin. More to the point, We may find it "difficult to define space and time using interacting systems because" [i]We "need the concepts of space and time to make sense of what [We] mean by 'systems' to begin the process" due to our being space-time entities. That is to say it is a failing of our imagination and artifact of our nature not the universe itself.

Moving to charge doesn't help -- you need "some thing" to "possess" the charge, even if you attribute it to the detectors. So, again, how do you distinquish two such otherwise identical "things" without space?

Agreed initially we need a concept of time but it need not be metric, only topological and ordered to reflect causal sequence. I can then conceive of a large dimensional quantum system with a complicated random Hamiltonian. (reparametrizing time to make it t independent = pick a t-metric or class of metrics dictated by the dynamics.)

Exactly what we concluded, "time" is inextricably linked to what we mean by "things" (discrete QFT sources for us). This is topological not geometric as you say. Now are you going to argue that time is "special" in this sense over "space?" That is, we "need" a notion of temporality at the topological level but not space?

I can also conceive of factoring that system into N 2-dimensional components where 2^N is close to the dimension. Each 2-dim factor has its own U(2)~U(1)xSO(3) structure and I look at the global Hamiltonian and ask what form it takes in terms of internal plus interaction terms. I can then consider different choices of factorization which for the given Hamiltonian might simplify its form.

Interaction between ... ? Again, more than one "thing" will require some form of differentiation. Are you saying you will have a theoretical counterpart to every particle in the universe? That is, you can't talk about electrons, quarks, muons, ... in general?

I haven't yet of course and such a program may not be "the right way to go about it" (and indeed I can already see many problems) but it is an example of how one might go about constructing/determining spatial structure from scratch. It is not inconceivable to me.

I don't see, as I argue above, that you've succeeded even conceptually. You need the notions of identification and differentiation to have "things."

akhmeteli

Feb3-10, 12:30 PM

Akhmeteli, that seems to be a reasonable answer. However, I think that nonlocality is compatible with relativity and unitary evolution. For more details see
http://www.physicsforums.com/showthread.php?t=354083
especially posts #1 and #109. I would like to see your opinion on that.

Dear Demystifier,

I did not say that "nonlocality is incompatible with relativity and unitary evolution". Indeed, tachyons are thinkable. However, it seems to me that relativity and unitary evolution in their current form leave little space for nonlocality. I remember studying quantum field theory many years ago. The lecturer was Professor Shirkov. Of course, we used his well-known book (N N Bogolyubov and D V Shirkov, `Introduction to the Theory of Quantized Fields'). One of the basic principles used in that book was microcausality. So I tend to believe nonlocality would lead to completely different forms of unitary evolution and relativity (for example, one of such new form may require tachyons). Explicit or implicit faster-than-light signaling does not follow from the current form of unitary evolution and relativity. To get such nonlocality in the Bell theorem you need something extra - such as the projection postulate. And this postulate generates nonlocality in a very direct way: indeed, according to this postulate, as soon as you measure a projection of spin of one particle of a singlet, the value of the projection of spin of the other particle immediately becomes determined, no matter how far from each other the particles are, and this is what the Bell theorem is about..

I looked at the references you gave. Again, I agree that unitary evolution and relativity, strictly speaking, do not eliminate nonlocality. However I wanted to ask you something. If I am not mistaken, you mentioned recently that Bohm's theory is superdeterministic.That seems reasonable. Furthermore, maybe unitary evolution is also, strictly speaking, superdeterministic. Indeed, it can include all observers and instruments, at least in principle. So my question is: What does this mean for nonlocality of Bohm's theory?

yoda jedi

Feb3-10, 01:27 PM

Akhmeteli, that seems to be a reasonable answer. However, I think that
nonlocality is compatible with relativity and unitary evolution.
For more details see
http://www.physicsforums.com/showthread.php?t=354083

i think the same.

http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.0177v1.pdf

specifically:

Tumulka:
http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf
and
http://arxiv.org/PS_cache/quant-ph/pdf/0602/0602208v2.pdf

Bedingham:
http://arxiv.org/PS_cache/arxiv/pdf/0907/0907.2327v1.pdf

ThomasT

Feb3-10, 02:10 PM

... if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?No, of course not.

I asked in a previous post:
Is Bell's theorem about the way the quantum world is, or is it about limitations on the formalization of entangled states?The formalism is in effect modelling, and must be compatible with, the experimental design(s) that it's associated with.

Quantum nonseparability, vis the SQM representation, has to do with the nonfactorability of entangled state representations, which reflects the necessary statistical dependency between A and B -- not some property of the underlying quantum world.

The predictions of Bell LHV models (characterized by their incorporation of the Bell locality condition, ie. factorability of the joint entangled state representation) don't fully agree with experimental results precisely because these models are incompatible with the salient feature of experiments designed to produce entanglement, namely statistical dependence between A and B.

And, the statistical dependence between A and B is produced solely vis the local transmissions and interactions involved in the pairing process.

So, the incompatibility of Bell LHV models with SQM and the experimental violation of Bell inequalities has nothing to do with nonlocality in Nature.

It might also be noted that calling SQM a local or nonlocal theory (whether due to Bell associated considerations or some interpretation of the formalism by itself) is more obfuscating than enlightening.

jambaugh

Feb3-10, 02:53 PM

RUTA,
As we seem to have moved into an independent conversation I thought it would be appropriate to move to a new thread. I took the liberty of creating one:

Non-spatial resolution of quanta (http://www.physicsforums.com/showthread.php?p=2562136#post2562136)

I posted there a reply to your last post.

jambaugh

Feb3-10, 03:31 PM

That's interesting, because my explicit Bohmian model of relativistic nonlocal reality does involve a "meta time".
...
That objection can, of course, be also attributed to the nonrelativistic Bohmian interpretation that does not involve the "meta time".

Yes I can see how the presence/absence of a meta-time would fit in and I don't object to its invocation per se. I see e.g. BI (and MW) not so much as an interpretation as it is a model given as I argue it is invoking non-operational components.

Thus if one were to simply drop the word "interpretation" from BI I'd be all for it.

Acknowledged as such, I think Bohmian QM could be a nice tool comparable to e.g. treating space-time as a dynamic manifold with its own meta-time and meta-dynamics to which it must relax to a stationary state yielding a solution of Einstein's equations. I don't have to assert the "reality" of extra dimensions or that meta-time in which space-time is embedded to use the model as a tool for calculation and enumeration of cases.

But I find "reality" is inherently a classical concept, and indeed the epitome of classical-ness. I see trying to hold onto the "reality" part of the negated local reality as regressive. (and should be replaced with non-objective "actuality".) That's a somewhat intuitive judgment of course but I believe based on good heuristic principles.

ThomasT

Feb3-10, 06:09 PM

Yes, that would certainly be a good evidence of nonlocality (I mean if violations of the genuine Bell inequalities, without loopholes, are demonstrated experimentally).Experimental loopholes have nothing to do with it. Bell's LHV ansatz is incompatible with QM, because QM, a statistical theory, correctly models the statistical dependency between A and B of the entangled state (vis nonfactorability of the joint state representation) while Bell's formulation doesn't.

To get such nonlocality in the Bell theorem you need something extra - such as the projection postulate. And this postulate generates nonlocality in a very direct way: indeed, according to this postulate, as soon as you measure a projection of spin of one particle of a singlet, the value of the projection of spin of the other particle immediately becomes determined, no matter how far from each other the particles are, and this is what the Bell theorem is about..The assumption underlying the projection postulate is that what is being jointly analyzed at A and B during the same coincidence interval is the same thing. Where's the nonlocality?

akhmeteli

Feb3-10, 08:26 PM

First, Bell tests ARE genuine. I think you mean "loophole" free. All experiments have "loopholes", some are simply more relevant than others - and you are free to your personal opinion. But it is manifestly unfair to characterize the hundreds/thousands of different Bell tests themselves as "not genuine".

Thank you for your comments.

I did not say the tests were not genuine. I just did not say that. However, the Bell inequalities violated in those tests were not genuine, i.e. those defined in the Bell theorem, because either they were doctored using the fair sampling assumption or the spatial separation was not sufficient. So I insist that genuine Bell inequalities were not violated in those experiments, and this is not just my opinion, this is mainstream (I admit that, strictly speaking, there is no consensus on that as you strongly disagree:-) )

Second: that is quite a bold prediction you are making, not sure what would make you think that quantum mechanics is actually incorrect (an absolute deduction from your statement).

What makes me think that is the fact that unitary evolution and the projection postulate contradict each other, so they cannot be both correct.

And last: why do you need to abandon relativity in the case of a confirmed (for you) violation of a Bell Inequality? The speed of light will still remain a constant in all local reference frames. Mass and clocks will still follow the standard rules. So what changes? The only thing that changes are physical effects not described by relativity in the first place. I do not consider relativity to include the absolute prediction that nonlocal elements cannot exist. I think it is an implied result, and one that could well fit within a larger theory. In fact, that is a result that Demystifier has been expressing for some time.

I answered this question replying to Demystifier. In brief, I admit that relativity and nonlocality, strictly speaking, are not incompatible, but I tend to believe that relativity and unitary evolution in their current form do not suggest nonlocality.

akhmeteli

Feb3-10, 08:31 PM

[QUOTE=yoda jedi;2561999]i think the same.

Please see my answers to Demystifier and DrChinese

akhmeteli

Feb3-10, 08:41 PM

Experimental loopholes have nothing to do with it. Bell's LHV ansatz is incompatible with QM, because QM, a statistical theory, correctly models the statistical dependency between A and B of the entangled state (vis nonfactorability of the joint state representation) while Bell's formulation doesn't.

The assumption underlying the projection postulate is that what is being jointly analyzed at A and B during the same coincidence interval is the same thing. Where's the nonlocality?

Dear ThomasT,

I am awfully sorry, I've read your post several times, but I just cannot understand a word.

Demystifier

Feb4-10, 02:43 AM

If I am not mistaken, you mentioned recently that Bohm's theory is superdeterministic.That seems reasonable. Furthermore, maybe unitary evolution is also, strictly speaking, superdeterministic. Indeed, it can include all observers and instruments, at least in principle. So my question is: What does this mean for nonlocality of Bohm's theory?
Bohmian mechanics is both superdeterministic and nonlocal. It should not be surprising, because Bohmian mechanics uses the wave function, and wave function is a nonlocal and deterministic object.

akhmeteli

Feb4-10, 05:49 AM

Bohmian mechanics is both superdeterministic and nonlocal. It should not be surprising, because Bohmian mechanics uses the wave function, and wave function is a nonlocal and deterministic object.

I have not given much thought to superdeterminism, so please forgive me if the following question will be downright stupid.

My understanding is that superdeterminism rejects free will. So it looks like, from the point of view of Bohmian mechanics, no possible results of Bell tests can eliminate local realism, because there is no free will anyway? I know that, Bohmian mechanics or not, the "superdeterminism hole" cannot be eliminated in Bell tests, but superdeterminism is typically considered a pretty extreme notion, and now it turns out it is alive and kicking in such a relatively established approach as Bohmian?

Dmitry67

Feb4-10, 06:03 AM

I as understand, just superdeterminism is not enough to create a loophole in Bells. In addition to superdeterminism, we also need an evil Nature, positioned BM particles in advance in a very special way, to trick the scientists and laugh at them.

In some sense that loophole is like 'Boltzmann brain' which also can not be ruled out. BTW, 'Boltzmann brain' agrument can be used even to deny QM at whole: world is just newtonian, but 'Boltzmann brain' has memories that QM was discovered and experimentally verified.

Peter Morgan

Feb4-10, 08:31 AM

Bohmian mechanics is both superdeterministic and nonlocal. It should not be surprising, because Bohmian mechanics uses the wave function, and wave function is a nonlocal and deterministic object.
That's a useful observation. It's obvious, as you say, if you think of it. Thanks.

Do you have a view of how this meshes with arguments about free will, or do you think the issue of free will is overblown?

Demystifier

Feb4-10, 09:57 AM

That's a useful observation. It's obvious, as you say, if you think of it. Thanks.

Do you have a view of how this meshes with arguments about free will, or do you think the issue of free will is overblown?
In my opinion, free will is only an illusion. See the attachment in
http://www.physicsforums.com/showpost.php?p=2455753&postcount=109

Demystifier

Feb4-10, 10:11 AM

My understanding is that superdeterminism rejects free will.

True.

So it looks like, from the point of view of Bohmian mechanics, no possible results of Bell tests can eliminate local realism, because there is no free will anyway?

Wrong. Bohmian mechanics is, by definition, a theory of nonlocal realism, so anything which assumes Bohmian mechanics eliminates local realism.

I know that, Bohmian mechanics or not, the "superdeterminism hole" cannot be eliminated in Bell tests, but superdeterminism is typically considered a pretty extreme notion, and now it turns out it is alive and kicking in such a relatively established approach as Bohmian?
Superdeterminism by itself is not extreme at all. After all, classical mechanics is also superdeterministic. What is extreme is the idea that superdeterminism may eliminate nonlocality in QM. Namely, superdeterminism alone is not sufficient to eliminate nonlocality. Instead, to eliminate nonlocality, superdeterminism must be combined with a VERY SPECIAL CHOICE OF INITIAL CONDITIONS (see also the post of Dmitry67 above). It is such special conspiratorial initial conditions that is considered extreme.

Peter Morgan

Feb4-10, 10:14 AM

In my opinion, free will is only an illusion. See the attachment in
http://www.physicsforums.com/showpost.php?p=2455753&postcount=109
Fair enough, given the just-hedged-enough nature of "you think that you have free will. But it may only be an illusion". For me, I'm not willing to make strong claims on something that appears not to be so easily looked at experimentally, but OK, if we have the hedge.

Demystifier

Feb4-10, 10:23 AM

Fair enough, given the just-hedged-enough nature of "you think that you have free will. But it may only be an illusion". For me, I'm not willing to make strong claims on something that appears not to be so easily looked at experimentally, but OK, if we have the hedge.
I'm glad to see that we (you and me) think similarly.

Peter Morgan

Feb4-10, 10:36 AM

After all, classical mechanics is also superdeterministic.
Right.
What is extreme is the idea that superdeterminism may eliminate nonlocality in QM. Namely, superdeterminism alone is not sufficient to eliminate nonlocality. Instead, to eliminate nonlocality, superdeterminism must be combined with a VERY SPECIAL CHOICE OF INITIAL CONDITIONS (see also the post of Dmitry67 above). It is such special conspiratorial initial conditions that is considered extreme.
The "very special"ness is only that, given that the state of the whole experimental apparatus at the times that simultaneous events were recorded, together with the instrument settings at the time, were what they were, the state of the whole experimental apparatus and its whole past light cone at some point in the past must have been consistent with the state that we observed. From a classical deterministic dynamics point of view, this is only to say that the initial conditions now determine the initial conditions at past times (and at future times).

A thermodynamic or statistical mechanical point of view of what the state is, however, places a less stringent requirement that the thermodynamic or statistical mechanical state in the past must have been consistent with the recorded measurements that we make now. An experiment that violates Bell-CHSH inequalities makes a record, typically, of a few million events that are identified as "pairs", which is not a very tight constraint on what the state of the universe was in the backward light-cone a year ago. A probabilistic dynamics, such as that of QM, only claims that the statistics that are observed now on various ensembles of data constrain what the statistics in the past would have been if we had measured them. This kind of move to probabilistic dynamics is as open to classical modeling in space-time as it is to QM, in which we make the superdeterminism apply only to probability distributions instead of to deterministic states. To some extent this move suggests giving up particle trajectories, but of course trajectories can be added that are consistent with the probabilistic dynamics of QM, in several ways, at least including deBB, Nelson, and SED (insofar as the trajectories that we choose to add are beyond being looked at by experiment, however, we should perhaps be metaphysically rather noncommittal).

nikman

Feb4-10, 10:44 AM

From an interview with Anton Zeilinger:

I'd like to come back to these freedoms. First, if you assumed there were no freedom
of the will – and there are said to be people who take this position – then you could
do away with all the craziness of quantum mechanics in one go.

True – but only if you assume a completely determined world where everything that
happened, absolutely everything, were fixed in a vast network of cause and effect.
Then sometime in the past there would be an event that determined both my choice of
the measuring instrument and the particle's behaviour. Then my choice would no
longer be a choice, the random accident would be no accident and the action at a
distance would not be action at a distance.

Could you get used to such an idea?

I can't rule out that the world is in fact like that. But for me the freedom to ask
questions to nature is one of the most essential achievements of natural science. It's a
discovery of the Renaissance. For the philosophers and theologians of the time, it
must have seemed incredibly presumptuousness that people suddenly started
carrying out experiments and asking questions of nature and deducing laws of nature,
which are in fact the business of God. For me every experiment stands or falls with
the fact that I'm free to ask the questions and carry out the measurements I want. If
that were all determined, then the laws of nature would only appear to be laws, and
the entire natural sciences would collapse.

http://print.signandsight.com/features/614.html

Peter Morgan

Feb4-10, 11:01 AM

Hi Nikman, but note that Zeilinger has limited the discussion to thinking it has to be "complete" determinism. As he says, he can't rule complete determinism out, but he doesn't like it, he'd rather do something else. Fair enough.

I'm curious what you think, Zeilinger being not here, in the face of a suggestion that we take the state to be either thermodynamic or statistical mechanical (i.e. a deterministic evolution of probabilities distributions, without necessarily introducing deterministic trajectories). Part of the suggestion here is to emulate, in a classical setting, the relative lack of metaphysical commitment of, say, the Copenhagen interpretation of QM to anything that we do not record as part of an experiment, which to me particularly includes trajectories.

DrChinese

Feb4-10, 11:10 AM

Superdeterminism by itself is not extreme at all. After all, classical mechanics is also superdeterministic. What is extreme is the idea that superdeterminism may eliminate nonlocality in QM. Namely, superdeterminism alone is not sufficient to eliminate nonlocality. Instead, to eliminate nonlocality, superdeterminism must be combined with a VERY SPECIAL CHOICE OF INITIAL CONDITIONS (see also the post of Dmitry67 above). It is such special conspiratorial initial conditions that is considered extreme.

I don't think that is a completely fair to say that classical mechanics is also superdeterministic, because I do not believe such is the case. If determinism was the same thing as superdeterminism, we would not need a special name for it. So I agree completely with your "extreme" initial conditions requirement at a minimum.

But I also question whether [classical mechanics] + [extreme initial conditions] can ever deliver superdeterminism. In a true superdeterministic theory, you would have an explicit description of the mechanism by which the *grand* conspiracy occurs (the conspiracy to violate Bell inequalities). For example: we could connect Alice's detector setting to a switch controlled by the timing of decays of a radioactive sample. So that is now part of the conspiracy too, and the instructions for when to click or not must be present in that sample (and therefore presumably everywhere). Were that true, why can't we see it before we run the experiment?

As I have said many times: if you allow the superdeterminism "loophole" as a hedge for Bell inequalities, you essentially allow it as a hedge for all physical laws. Which sorta takes the meaning away from it (as a hedge) in the first place.

[I probably shouldn't have even written this post, so my apologies in advance. I consider it akin to false histories (the Omphalos hypothesis (http://en.wikipedia.org/wiki/Omphalos_hypothesis)) - ad hoc and unfalsifiable.]

DrChinese

Feb4-10, 11:15 AM

From an interview with Anton Zeilinger:

... If that were all determined, then the laws of nature would only appear to be laws, and
the entire natural sciences would collapse.

http://print.signandsight.com/features/614.html

Thanks for the link! I think his quote says a lot.

Peter Morgan

Feb4-10, 12:38 PM

But I also question whether [classical mechanics] + [extreme initial conditions] can ever deliver superdeterminism. In a true superdeterministic theory, you would have an explicit description of the mechanism by which the *grand* conspiracy occurs (the conspiracy to violate Bell inequalities).
Part of the conspiracy, at least, comes from the experimenter. One of a specific symmetry class of experimental apparatuses has to be constructed, typically over months, insofar as it used not to be easy to violate Bell inequalities. The material physics that allows us to construct the requisite correlations between measurement results is arguably pretty weird.

Furthermore, the standard way of modeling Bell inequality violating experiments in QM is to introduce projection operators to polarization states of a single frequency mode of light, which are non-local operators. [A propos of which, DrC, do you know of a derivation that is truly careful about the field-theoretic locality?] The QM model, in other words, is essentially a description of steady state, time-independent statistics that has specific symmetry properties. Since I take violation of Bell inequalities to be more about contextuality than about nonlocality, which specifically is implemented by post-selection of a number of sub-ensembles according to what measurement settings were in fact chosen, this seems natural to me, but I wonder what you think?

Remember that with me you have to make a different argument than you might make with someone who thinks the measurement results are noncontextually determined by the state of each of two particles, since for me whether measurement events occur is determined jointly by the measurement devices and the field they are embedded in.
For example: we could connect Alice's detector setting to a switch controlled by the timing of decays of a radioactive sample. So that is now part of the conspiracy too, and the instructions for when to click or not must be present in that sample (and therefore presumably everywhere). Were that true, why can't we see it before we run the experiment?
I do wonder, but apparently that's how the statistics pile up. We have a choice of whether to just say, with Copenhagen, that we can say nothing at all about anything that is not macroscopic, or to consider what properties different types of models have to have in order to "explain" the results. A particle Physicist tells a causal story about what happens in experiments, using particles, anti-particles, and ghost and virtual particles, with various prevarications about what is really meant when one talks about such things (which is typically nonlocal if anything like Wigner's definition of a particle is mentioned, almost inevitably); so it seems reasonable to consider what prevarications there have to be in other kinds of models. It's good that we know moderately well what prevarications we have to introduce in the case of deBB, and that they involve a nonlocal trajectory dynamics in that case.
As I have said many times: if you allow the superdeterminism "loophole" as a hedge for Bell inequalities, you essentially allow it as a hedge for all physical laws. Which sorta takes the meaning away from it (as a hedge) in the first place.
This might be true, I guess, although proving that superdeterminism is a hedge for all possible physical laws looks like tough mathematics to me. Is the same perhaps true for backward causation? Do you think it's an acceptable response to ask what constraints have to be put on superdeterminism (or backward causation) to make it give less away?
[I probably shouldn't have even written this post, so my apologies in advance. I consider it akin to false histories (the Omphalos hypothesis (http://en.wikipedia.org/wiki/Omphalos_hypothesis)) - ad hoc and unfalsifiable.]
You're always welcome with me, DrC. I'm very pleased with your comments in this case. If you're ever in CT, look me up.
I like the Omphalos. Is it related to the heffalump?

Slightly after the above, I'm particularly struck by your emphasis on the degree of correlation required in the initial conditions to obtain the experimental results we see. Isn't the degree of correlation required in the past precisely the same as the degree of correlation that we note in the records of the experimental data? It's true that the correlations cannot be observed in the past without measurement of the initial state in outrageous detail across the whole of a time-slice of the past light-cone of a measurement event, insofar as there is any degree of dynamical chaos, but that doesn't take away from the fact that in a fine-grained enough description there is no change of entropy. [That last phrase is a bit cryptic, perhaps, but it takes my fancy a little. Measurements now are the same constraint on the state in the past as they are on the state now. Since they are actually observed constraints now, it presumably cannot be denied that they are constraints on the state now. If the actual experimental results look a little weird as constraints that one might invent now, then presumably they look exactly as weird as constraints on the state 10 years ago, no more and no less. As observed constraints, they are constraints on what models have to be like to be empirically adequate.] I'm worried that all this repetition is going to look somewhat blowhard, as it does a little to me now, so I'd be glad if you can tell me if you can see any content in it.

nikman

Feb4-10, 03:29 PM

Hi Nikman, but note that Zeilinger has limited the discussion to thinking it has to be "complete" determinism. As he says, he can't rule complete determinism out, but he doesn't like it, he'd rather do something else. Fair enough.

I made the mistake of claiming in a post some while back that the Zeilinger group's Leggett paper needs editing (for English clarity) because in its conclusion it seemed to suggest that the authors didn't foreclose even on superdeterminism (or something more or less equivalent). Well, I was wrong; they don't foreclose on it, as AZ makes clear here. He simply finds such a world unimaginable.

I'm curious what you think, Zeilinger being not here, in the face of a suggestion that we take the state to be either thermodynamic or statistical mechanical (i.e. a deterministic evolution of probabilities distributions, without necessarily introducing deterministic trajectories). Part of the suggestion here is to emulate, in a classical setting, the relative lack of metaphysical commitment of, say, the Copenhagen interpretation of QM to anything that we do not record as part of an experiment, which to me particularly includes trajectories.

I'm far more abashed than flattered at being considered an acceptable stand-in to speak for this astonishing, brilliant man. For gosh sakes I'm not even a physicist; I'm at best an 'umble physics groupie.

In this dilettante capacity I'm not aware that he's ever gone as far as (say) Mermin (in the Ithaca Interpretation) and suggested that everything's correlations, dear boy, correlations. What does Bruknerian coarse-grainedness as complementary to decoherence tell us? This is really in part about what macrorealism means, isn't it? Does the GHZ Emptiness of Paths Not Taken have any relevance here?

My understanding via Hans C. von Baeyer is that Brukner and Zeilinger have plotted state evolution in "information space" (in terms of classical mechanics, equivalent to trajectories of billiard balls perhaps) and then translated that into Hilbert space where the math reveals itself to be the Schrödinger equation. How truly deterministic is the SE? My mental clutch is starting to slip now.

yoda jedi

Feb4-10, 08:30 PM

I disagree. You replied to someone's suggestion that locality is worth sacrificing for realism, with the claim that Leggett's work shows that even "realism" (no qualifications given about contextuality or non-contextuality) is not tenable without sacrificing another intuitively plausible assumption. But that characterization of Leggett's work is simply not accurate, which anyone can see by reading those abstracts you linked to. And I don't even think that's true that everyone in this field agrees that the word realism is used to imply classical realism, and that this is done without any confusion. I know several active researchers in this field who would dispute the validity of your use of terminology. Moreover, the link you gave to try and support your claim, doesn't actually do that. If you read your own link, you'll see that everything Aspelmeyer and Zeilinger conclude about realism from their experiment is qualified in the final paragraph:

However, Alain Aspect, a physicist who performed the first Bell-type experiment in the 1980s, thinks the team's philosophical conclusions are subjective. "There are other types of non-local models that are not addressed by either Leggett's inequalities or the experiment," he said.

So Aspect is clearly indicating that Aspelmeyer and Zeilinger's use of the word "realism" is intended in a broader sense than Leggett's use of the term "classical realism".

It's not nitpicking on semantics, it's getting the physics straight. If that's too difficult for you to do, then I'm sorry, but maybe you're just not cut out for this thread.

i agree
reality is independence of observers.

DrChinese

Feb4-10, 09:09 PM

Part of the conspiracy, at least, comes from the experimenter. One of a specific symmetry class of experimental apparatuses has to be constructed, typically over months, insofar as it used not to be easy to violate Bell inequalities. The material physics that allows us to construct the requisite correlations between measurement results is arguably pretty weird.

Furthermore, the standard way of modeling Bell inequality violating experiments in QM is to introduce projection operators to polarization states of a single frequency mode of light, which are non-local operators. [A propos of which, DrC, do you know of a derivation that is truly careful about the field-theoretic locality?] The QM model, in other words, is essentially a description of steady state, time-independent statistics that has specific symmetry properties. Since I take violation of Bell inequalities to be more about contextuality than about nonlocality, which specifically is implemented by post-selection of a number of sub-ensembles according to what measurement settings were in fact chosen, this seems natural to me, but I wonder what you think?

Remember that with me you have to make a different argument than you might make with someone who thinks the measurement results are noncontextually determined by the state of each of two particles, since for me whether measurement events occur is determined jointly by the measurement devices and the field they are embedded in.

I do wonder, but apparently that's how the statistics pile up. We have a choice of whether to just say, with Copenhagen, that we can say nothing at all about anything that is not macroscopic, or to consider what properties different types of models have to have in order to "explain" the results. A particle Physicist tells a causal story about what happens in experiments, using particles, anti-particles, and ghost and virtual particles, with various prevarications about what is really meant when one talks about such things (which is typically nonlocal if anything like Wigner's definition of a particle is mentioned, almost inevitably); so it seems reasonable to consider what prevarications there have to be in other kinds of models. It's good that we know moderately well what prevarications we have to introduce in the case of deBB, and that they involve a nonlocal trajectory dynamics in that case.

This might be true, I guess, although proving that superdeterminism is a hedge for all possible physical laws looks like tough mathematics to me. Is the same perhaps true for backward causation? Do you think it's an acceptable response to ask what constraints have to be put on superdeterminism (or backward causation) to make it give less away?

You're always welcome with me, DrC. I'm very pleased with your comments in this case. If you're ever in CT, look me up.
I like the Omphalos. Is it related to the heffalump?

Slightly after the above, I'm particularly struck by your emphasis on the degree of correlation required in the initial conditions to obtain the experimental results we see. Isn't the degree of correlation required in the past precisely the same as the degree of correlation that we note in the records of the experimental data? It's true that the correlations cannot be observed in the past without measurement of the initial state in outrageous detail across the whole of a time-slice of the past light-cone of a measurement event, insofar as there is any degree of dynamical chaos, but that doesn't take away from the fact that in a fine-grained enough description there is no change of entropy. [That last phrase is a bit cryptic, perhaps, but it takes my fancy a little. Measurements now are the same constraint on the state in the past as they are on the state now. Since they are actually observed constraints now, it presumably cannot be denied that they are constraints on the state now. If the actual experimental results look a little weird as constraints that one might invent now, then presumably they look exactly as weird as constraints on the state 10 years ago, no more and no less. As observed constraints, they are constraints on what models have to be like to be empirically adequate.] I'm worried that all this repetition is going to look somewhat blowhard, as it does a little to me now, so I'd be glad if you can tell me if you can see any content in it.

We have a lot of jackalopes in Texas, but few heffalumps.

---------------------------------

The issue is this: Bell sets limits on local realistic theories. So there may be several potential "escape" mechanisms. One is non-locality, of which the Bohmian approach is one which attempts to explicitly describe the mechanism by which Bell violations can occur. Detail analysis appears to provide answers to how this could match observation. BM can be explicitly critiqued and answers can be provided to those critiques.

Another is the "superdeterminism" approach. Under this concept, the initial conditions are just such that all experiments which are done will always show Bell violations. However, like the "fair sampling" loophole, the idea is that from the full universe of possible observations - those which are counterfactual - the true rate of coincidence does NOT violate a Bell Inequality. So there is a bias function at work. That bias function distorts the true results because the experimenter's free will is compromised. The experimenter can only select to perform measurements which support QM due to the experimenter's (naive and ignorant) bias.

Now, without regard to the reasonableness of that argument, I point out the following cases, in which the results are identical.

a) The experimenter's detector settings are held constant for a week at a time.
b) The settings are changed at the discretion of the experimenter, at any interval.
c) The settings are changed at due to clicks from a radioactive sample, per an automated system, over which the experimenter has no direct control.
d) A new hypothesis, that the experiments actually show that a Bell Inequality is NOT violated, but the data recording device is modified coincidentally to show results indicating that the Bell Inequality was violated.

In other words, we know we won't see any difference in a), b) and c). And if d) occurred, it would be a different form of "superdeterminism". So the question I am asking: does superdeterminism need to obey any rules? Does it need to be consistent? Does it need to be falsifiable? Because clearly, the a) case above should be enough to rule out superdeterminism (at least in my mind - the experimenter is exercising no ongoing choice past an initial point). The c) case requires that superdeterminism flows from one force to another, when the standard model does not show any such mechanism (since there is no known connection between an experimental optical setting and the timing of radioactive decay). And the d) case shows that there is always one more avenue by which we can float an ad hoc hypothesis.

So you ask: is superdeterminism a hedge for all physical laws? If you allow the above, one might then turn around and say: does it not apply to other physical laws equally? Because my answer is that if so, perhaps relativity is not a true effect - it is simply a manifestation of superdeterminism. All of those GPS satellites... they suffer from the idea that the experimenter is not free to request GPS information freely. So while results appear to follow GR, they really do not. How is this less scientific than the superdeterminism "loophole" as applied to Bell?

In other words, there is no rigorous form of superdeterminism to critique at this point past an ad hoc hypothesis. And we can formulate ad hoc hypotheses about any physical law. None of which will ever have any predictive utility. So I say it is not science in the conventional sense.

-----------------------

You mention contextuality and the subsamples (events actually recorded). And you also mention the "degree of correlation required in the initial conditions to obtain the experimental results we see". The issue I return to time after time: the bias function - the delta between the "true" universe and the observed subsample correlation rates - must itself be a function of the context. But it is sometimes negative and sometimes positive. That seems unreasonable to me. Considering, of course, that the context is ONLY dependent on the relative angle difference and nothing else.

So we need a bias function that eliminates all other variables except the difference between measurement settings at a specific point in time. It must apply to entangled light, which will also show perfect correlations. But it must NOT apply to unentangled light (as you know, that is my criticism of the De Raedt model). And it must further return apparently random values in all cases. I believe these are all valid requirements of a superdeterministic model. As well as locality and realism, of course.

DrChinese

Feb4-10, 09:25 PM

Continued from above...

So what I am saying is: when you put together all of the requirements, I don't think you have anything that works remaining. You just get arguments that are no better than "last Thursdayism".

------------------------------

By the way, wouldn't GHZ falsify superdeterminism too? After all, there is no subsample.

Or would one make the argument that the experimenter had no free will as to the choice of what to measure? (That seems a stretch, since all observations yield results inconsistent with local realism - at least within experimental limits).

akhmeteli

Feb4-10, 09:49 PM

True.

Wrong. Bohmian mechanics is, by definition, a theory of nonlocal realism, so anything which assumes Bohmian mechanics eliminates local realism.

Superdeterminism by itself is not extreme at all. After all, classical mechanics is also superdeterministic. What is extreme is the idea that superdeterminism may eliminate nonlocality in QM. Namely, superdeterminism alone is not sufficient to eliminate nonlocality. Instead, to eliminate nonlocality, superdeterminism must be combined with a VERY SPECIAL CHOICE OF INITIAL CONDITIONS (see also the post of Dmitry67 above). It is such special conspiratorial initial conditions that is considered extreme.

Thank you very much for the explanations

Demystifier

Feb5-10, 03:52 AM

I don't think that is a completely fair to say that classical mechanics is also superdeterministic, because I do not believe such is the case. If determinism was the same thing as superdeterminism, we would not need a special name for it. So I agree completely with your "extreme" initial conditions requirement at a minimum.

I see what you mean, but note that I use a different DEFINITION of the term "superdeterminism". In my language, superdeterminism is nothing but determinism applied to everything. Thus, a classical deterministic model of the world is superdeterministic if one assumes that, according to this model, everything that exists is described by the classical laws of physics. In my language, superdeterminism does not imply the absence of specific laws, such as Newton law of gravitation.

Even with this definition of superdeterminism, it is not exactly the same as determinism. For example, if you believe that the classical laws of physics are valid everywhere except in the brain in which a genuine spiritual free will also acts on electric currents in the brain, then, according to my definition, such a view is deterministic but not superdeterministic.

ThomasT

Feb6-10, 12:10 PM

I am awfully sorry, I've read your post several times, but I just cannot understand a word.Ok, I'll try to present the gist of how I've learned to think about this in a less scattered way.

1. Bell locality can be parsed to include statistical independence between A and B.

2. Statistical dependence between A and B is sufficient to cause experimental violation of inequalities which are based on the (formal) assumption of statistical independence between A and B.

3. The statistical dependence is produced via local channels.

4. So, experimental violation of inequalities based on Bell locality doesn't imply nonlocality.

5. Formally, Bell locality entails that the joint probability of the entangled state be factorable into the product of the individual probabilities for A and B.

6. Bell locality is incompatible with the QM requirement that the entangled state representation be nonfactorable.

7. This nonfactorability or quantum nonseparability reflects the (locally produced) statistical dependencies required for the experimental production of entanglement.

8. Experimental loopholes notwithstanding, no Bell local theory can possibly reproduce the full range of QM predictions or experimental results wrt entangled states.

9. None of this implies the existence of nonlocality in Nature -- which is contrary to your idea that, in your words: Yes, that would certainly be a good evidence of nonlocality (I mean if violations of the genuine Bell inequalities, without loopholes, are demonstrated experimentally).

10. None of this implies that SQM (associated with Bell's theorem) is a nonlocal theory -- which is contrary to your idea that, in your words: To get such nonlocality in the Bell theorem you need something extra - such as the projection postulate. And this postulate generates nonlocality in a very direct way: indeed, according to this postulate, as soon as you measure a projection of spin of one particle of a singlet, the value of the projection of spin of the other particle immediately becomes determined, no matter how far from each other the particles are, and this is what the Bell theorem is about..

11. In fact, the standard QM methodology and account (including the projection postulate and any quantum level models associated with a particular experimental setup) is based on the (at least tacit, but explicit in the case of some models) assumption that there's a locally produced relationship between quantum disturbances analyzed at spacelike separations. (eg., in the case of Aspect et al experiments using atomic calcium cascades to produce entangled photons, the entangling relationship is assumed to be produced at emission -- and the experimental design must entail statistical dependence between A and B in order to pair photons emitted by the same atom).

akhmeteli

Feb6-10, 03:51 PM

Ok, I'll try to present the gist of how I've learned to think about this in a less scattered way.

Thank you very much for your patience with me. At least now I don't feel as if I were trying to decipher a text in double-Dutch:-)

3. The statistical dependence is produced via local channels.

What local channels, if there is enough spatial separation?

8. Experimental loopholes notwithstanding, no Bell local theory can possibly reproduce the full range of QM predictions or experimental results wrt entangled states.

Again, the fact that local theories cannot reproduce all QM predictions (which include contradictions) cannot be used as an argument against local theories - it's their strong point.

11. In fact, the standard QM methodology and account (including the projection postulate and any quantum level models associated with a particular experimental setup) is based on the (at least tacit, but explicit in the case of some models) assumption that there's a locally produced relationship between quantum disturbances analyzed at spacelike separations. (eg., in the case of Aspect et al experiments using atomic calcium cascades to produce entangled photons, the entangling relationship is assumed to be produced at emission -- and the experimental design must entail statistical dependence between A and B in order to pair photons emitted by the same atom).

"the entangling relationship assumed to be produced at emission" is one thing, but the choice of projection of spin or polarization measured at A seems to immediately change the situation at B. If it were indeed so, that would be a problem for locality. At least that's what I tend to think.

DrChinese

Feb6-10, 04:50 PM

9. None of this implies the existence of nonlocality in Nature ...

11. In fact, the standard QM methodology and account (including the projection postulate and any quantum level models associated with a particular experimental setup) is based on the (at least tacit, but explicit in the case of some models) assumption that there's a locally produced relationship between quantum disturbances analyzed at spacelike separations. (eg., in the case of Aspect et al experiments using atomic calcium cascades to produce entangled photons, the entangling relationship is assumed to be produced at emission -- and the experimental design must entail statistical dependence between A and B in order to pair photons emitted by the same atom).

A comment just to make sure everyone is up on some of the refinements to the original Bell test regimen.

We now have the ability to entangle photons that have never met - this is called "entanglement swapping" (ES). Early versions of this protocol did not effectively allow the photons to be created sufficiently far enough to eliminate local interaction, but the newer ones do. For example:

High-fidelity entanglement swapping with fully independent sources (http://arxiv.org/abs/0809.3991)
(2009) Rainer Kaltenbaek, Robert Prevedel, Markus Aspelmeyer, Anton Zeilinger

"Entanglement swapping allows to establish entanglement between independent particles that never interacted nor share any common past. This feature makes it an integral constituent of quantum repeaters. Here, we demonstrate entanglement swapping with time-synchronized independent sources with a fidelity high enough to violate a Clauser-Horne-Shimony-Holt inequality by more than four standard deviations. The fact that both entangled pairs are created by fully independent, only electronically connected sources ensures that this technique is suitable for future long-distance quantum communication experiments as well as for novel tests on the foundations of quantum physics."

Note that the experiment in this paper does not actually execute the variation where the photons are never in each other's light cones, but you can be sure that is coming (if not already published).

So basically, you have a pretty difficult time explaining the violation of a Bell Inequality by photon pairs that were never in a common light cone. Without having something being non-local, that is.
It is hard to imagine how you can have

ThomasT

Feb8-10, 03:44 PM

What local channels, if there is enough spatial separation?Statistical dependence refers to the fact that a detection at A changes the sample space at B, and vice versa.

This happens during the pairing process via the coincidence circuitry.

All very local, but sufficient to render Bell locality incompatible with QM and entanglement experiments.

Again, the fact that local theories cannot reproduce all QM predictions (which include contradictions) cannot be used as an argument against local theories - it's their strong point.But QM predictions agree with experimental results, and Bell local theories don't. More importantly, Bell local theories can't possibly agree with experimental results ... ever -- because Bell's formal expression of locality encodes statistical as well as causal independence.

Bell locality contradicts an integral part of entanglement experiments, statistical dependence between A and B. The upside, for LHV advocates, is that this doesn't rule out local realist theories -- just Bell local theories. The downside, for nonlocality advocates, is that this tells us nothing about nonlocality wrt either Nature or standard QM.

... the choice of projection of spin or polarization measured at A seems to immediately change the situation at B. If it were indeed so, that would be a problem for locality.Yes, that would be a problem for locality. But that's not what standard QM says, and that's not what happens experimentally.

akhmeteli

Feb8-10, 07:48 PM

Statistical dependence refers to the fact that a detection at A changes the sample space at B, and vice versa.

This happens during the pairing process via the coincidence circuitry.

All very local, but sufficient to render Bell locality incompatible with QM and entanglement experiments.

But QM predictions agree with experimental results, and Bell local theories don't. More importantly, Bell local theories can't possibly agree with experimental results ... ever -- because Bell's formal expression of locality encodes statistical as well as causal independence.

Bell locality contradicts an integral part of entanglement experiments, statistical dependence between A and B. The upside, for LHV advocates, is that this doesn't rule out local realist theories -- just Bell local theories. The downside, for nonlocality advocates, is that this tells us nothing about nonlocality wrt either Nature or QM.

Yes, that would be a problem for locality. But that's not what QM says, and that's not what happens experimentally.

Sorry, ThomasT, you've lost me again. This time I cannot say I don't understand a word, but 30% is too little for a meaningful discussion - this is a physics forum, not a crossword contest. With all due respect, if you believe you're saying something well-known that I don't know, give me a reference, if not, try to be clearer. And I mean much clearer.

yoda jedi

Feb9-10, 11:49 AM

"the entangling relationship assumed to be produced at emission" is one thing, but the choice of projection of spin or polarization measured at A seems to immediately change the situation at B. If it were indeed so, that would be a problem for locality. At least that's what I tend to think.

long time ago...

...........Quantum mechanics says that there should be a high correlation between results at the polarizers because the photons instantaneously "decide" together which polarization to assume at the moment of measurement, even though they are separated in space. Hidden variables, however, says that such instantaneous decisions are not necessary, because the same strong correlation could be achieved if the photons were somehow informed of the orientation of the polarizers beforehand.......................

..........Quantum mechanics predicts that “non-local” correlations can exist between the particles. This means that if one photon is polarized in, say, the vertical direction, the other will always be polarized in the horizontal direction, no matter how far away it is. However, some physicists argue that this cannot be true and that quantum particles must have local values – known as “hidden variables” – that we cannot measure....................

.

DrChinese

Feb9-10, 02:13 PM

But QM predictions agree with experimental results, and Bell local theories don't. More importantly, Bell local theories can't possibly agree with experimental results ... ever -- because Bell's formal expression of locality encodes statistical as well as causal independence.

...

Yes, that would be a problem for locality. But that's not what standard QM says, and that's not what happens experimentally.

These are not standard expressions of theory or experiment. Experimentally: when Alice acts, it appears "as if" the situation changes non-locally for Bob (and vice versa). Theoretically: A Bell local theory is one in which Alice action does not appear "as if" the situation changes at Bob to match UNLESS there is a sub-c channel for propagation (or possibly a common earlier cause within a mutual light cone).

ThomasT

Feb9-10, 05:04 PM

Sorry, ThomasT, you've lost me again. This time I cannot say I don't understand a word, but 30% is too little for a meaningful discussion - this is a physics forum, not a crossword contest. With all due respect, if you believe you're saying something well-known that I don't know, give me a reference, if not, try to be clearer. And I mean much clearer.I don't know if it's a well known approach or not.

The argument is that Bell's locality condition isn't, exclusively, a locality condition. If it isn't, then what might this entail wrt the interpretation of experimental violations of inequalities based on Bell locality?

In a nutshell:

Bell locality doesn't just represent causal independence between A and B, but also statistical independence between A and B.

Statistical dependence between A and B means that a detection at A changes the sample space at B, and vice versa. The pairing process entails statistical dependence between A and B, and this statistical dependence can be accounted for via the local transmissions and interactions of the coincidence circuitry.

Statistical dependence between A and B is sufficient to violate inequalities based on Bell locality.

So, experimental violations of inequalities based on Bell locality, while they do rule out Bell local theories, don't imply nonlocality or necessarily rule out local realism.

ThomasT

Feb9-10, 05:13 PM

These are not standard expressions of theory or experiment.If not, they should be.

Experimentally: when Alice acts, it appears "as if" the situation changes non-locally for Bob (and vice versa).This isn't the way that I've learned to think about it.

Theoretically: A Bell local theory is one in which Alice action does not appear "as if" the situation changes at Bob to match UNLESS there is a sub-c channel for propagation (or possibly a common earlier cause within a mutual light cone).I'm not sure what you're saying. Bell local theories of entangled states don't match QM or experiments, do they?

DrChinese

Feb9-10, 05:39 PM

I'm not sure what you're saying. Bell local theories of entangled states don't match QM or experiments, do they?

Bell local + Bell realistic = ruled out.

Eye_in_the_Sky

Feb9-10, 06:59 PM

Bell local + Bell realistic = ruled out.
Dr. Chinese, I am wondering, do you not also agree that the following stronger statement is true as well?

Bell local = ruled out

DrChinese

Feb10-10, 08:13 AM

Dr. Chinese, I am wondering, do you not also agree that the following stronger statement is true as well?

Bell local = ruled out

No, but I can certainly understand why you might feel that way.

The Bell argument - to me - centers around counterfactual reasoning (realism) more than locality (separability). Realism being the requirement that particles have definite values for observables regardless of their actually being measured. Without this critical requirement, the Bell Inequality cannot be derived, and therefore it cannot be violated.

But a reasonable person would also look at entanglement and say, gee, there must be *some* kind of non-local action occurring. I refer to that as "quantum non-locality" which to me simply encapsulates the idea that there are non-local correlations. But that does not strictly imply that Einsteinian (Bell) locality is violated.

ThomasT

Feb10-10, 03:37 PM

Sorry, ThomasT, you've lost me again. This time I cannot say I don't understand a word, but 30% is too little for a meaningful discussion - this is a physics forum, not a crossword contest. With all due respect, if you believe you're saying something well-known that I don't know, give me a reference, if not, try to be clearer. And I mean much clearer.I think I might have been presenting the argument the wrong way.

Bell locality applied to LHV representation of two photon entangled state entails this:

P(A,B) = P(A) P(B)

That is, it entails that the joint probability be factorable (separable) as the product of the individual probabilities.

From probability theory and statistics, if two (sets of) events, A and B, are independent, then their joint probability is the product of the individual probabilites, P(A) and P(B).

So, we start out by observing that Bell locality represents statistical independence.
(This is different from the previous approach of assuming that Bell's locality condition represents causal independence, and then parsing it to include statistical independence.)

Does statistical independence imply causal independence?

The answer is yes (causal dependence entails statistical dependence).

However, in order to ascertain whether or not Bell locality is viable (that is, whether or not its application allows us to deduce the presence of superluminal causality) we must ask:

Does statistical dependence imply causal dependence?

Ok so far?

DrChinese

Feb10-10, 06:37 PM

I think I might have been presenting the argument the wrong way.

Bell locality applied to LHV representation of two photon entangled state entails this:

P(A,B) = P(A) P(B)

That is, it entails that the joint probability be factorable (separable) as the product of the individual probabilities.

From probability theory and statistics, if two (sets of) events, A and B, are independent, then their joint probability is the product of the individual probabilites, P(A) and P(B).

So, we start out by observing that Bell locality represents statistical independence.
(This is different from the previous approach of assuming that Bell's locality condition represents causal independence, and then parsing it to include statistical independence.)

1. I agree that P(A,B) = P(A) P(B) is a test of a local realistic theory. Certainly I look for that in any model claiming to be local realistic. Actually I look for something in which P(A)=f(A, v1, v2, etc) as long as B is not a variable, even indirectly.

Because of the advent of Bell, though, the meaning of independence has been blurred. Because it is obvious now that somehow or another, P(A) and P(B) must be connected some way to make the relationships work out. In the De Raedt computer simulation, for example, random variables and specially shaped functions are introduced to achieve a pseudo dependence on theta=A-B.

2. Of course, P(A,B) = P(A) P(B) alone does not lead to a violation of a Bell Inequality. That requires P(A, B, C)>=0 which is actually not true for all A, B, C. So that too is something I test for. I want there to be values produced for an A, B and C simultaneously using the same f(...). Now according to your line of thinking, this is automatically true if there is a separable f(). So 2. must not be necessary.

3. Lastly, I want the results to match QM predictions. I know, on the other hand, that this will not happen because of requirement 2 above. In the De Raedt simulation, it is false. So their argument is that the full universe does not, in fact, match the QM predictions. So you might conclude that we have demonstrated that 2. is not necessary.

--------

So where is the problem? Because I can ALSO start with 2 as well, ignoring 1. All I need to do is ask you to provide me with a data set of values for an A, B and C I select (such as 0, 120, 240 degrees). You can make them up any way you want, and you can use A, B and C to determine those values... they do not need to be separable! You cannot do that AND have them match requirement 3, which is that they match QM predictions for those same angles.

So are these requirements simply alternative requirements? In some sense they are. Travis Norsen, for one, would agree with you that Bell locality (he defines it somewhat differently) is sufficient for Bell's Theorem. I.e. he believes that realism is NOT a requirement of Bell's Theorem, and therefore all Bell tests prove that nature is non-local.

On the other hand, I argue that realism IS a requirement of Bell's Theorem. It is the requirement of a simultaneous value for A, B and C that makes it work. I personally think the separability requirement is not as important, but again it too IS a requirement.

And that is the standard view. You can try to prove Bell's Theorem without either requirement (locality or realism), but you won't be able to. You need both the ideas of f(variables) and values for A, B and C to get the result.

Eye_in_the_Sky

Feb11-10, 04:27 AM

No, but I can certainly understand why you might feel that way.

The Bell argument - to me - centers around counterfactual reasoning (realism) more than locality (separability). Realism being the requirement that particles have definite values for observables regardless of their actually being measured. Without this critical requirement, the Bell Inequality cannot be derived, and therefore it cannot be violated.

But a reasonable person would also look at entanglement and say, gee, there must be *some* kind of non-local action occurring. I refer to that as "quantum non-locality" which to me simply encapsulates the idea that there are non-local correlations. But that does not strictly imply that Einsteinian (Bell) locality is violated.
In the above, you cite "realism" in connection with to different points:

CF ≡ counterfactuality

and

IS ≡ the existence of "instruction sets" .

How do you see the status of IS in Bell's derivation? Do you see it as a derived principle, or do you see it as an independent assumption? I see it as a derived principle in the following way:

BL Λ PC Λ CF → IS ,

where

BL ≡ Bell Locality

and

PC ≡ perfect (anti-)correlation for equal settings .

DrChinese

Feb11-10, 10:25 AM

In the above, you cite "realism" in connection with to different points:

CF ≡ counterfactuality

and

IS ≡ the existence of "instruction sets" .

How do you see the status of IS in Bell's derivation? Do you see it as a derived principle, or do you see it as an independent assumption? I see it as a derived principle in the following way:

BL Λ PC Λ CF → IS ,

where

BL ≡ Bell Locality

and

PC ≡ perfect (anti-)correlation for equal settings .

This is a good point. When you really break down Bell, you see what he has given us is a road map. Once we have that map, we have the key to breaking apart any local realistic theory. The map points out a lot of features of the territory. Some of these features probably should have been obvious even without the Inequality itself. And your point about perfect correlations (PC) is a great example.

PC needs to be a requirement of a LR theory, and Bell points this out early. It turns out this is NO MINOR POINT at all! Here we have inherent randomness that itself defies modeling (as the entangled outcomes are random at all settings) and yet they must match. Now, how can there be separability with this characteristic? Yes, we must add yet another constraint to account for this - one I didn't explicitly mention. I said: "... somehow or another, P(A) and P(B) must be connected some way to make the relationships work out." And that is both the PC you mention and more generally, Malus.

1. Instruction set may be a slight misnomer (although it is a good visual), because as Bell says: "...it follows that the result of any such measurement must actually be predetermined..." Now, of course you can say "don't forget the interaction with the polarizer" but that really makes no sense. Polarizer, beamsplitter, or whatever optical system, the results are PC. That is also true with electrons so obviously it has nothing whatsoever to do with underlying nature of the interaction with the measurement apparatus per se. There must be complete predetermination of all settings in an LR model if there is PC. You also have random results (RR). So to me, PC + RR -> IS. And so this simple case is not so simple at all.

2. If you have predetermination, then presumably you have the separability we are asking for AND we have the realism we are asking for. Now you just need one final point, that there are angle settings for which no predetermined IS will work. If Bell simply supplied these settings out of thin air, without a proof, it would still be enough to provide a contradiction. Assuming for a moment - as Bell does - that QM predictions would match experimental results: IS <> QM.

3. You then don't even need Bell's Theorem to be valid if you accept the reasoning so far. Because who cares if the theorem is even valid? Once you know - as Bell figured out - what those angles are, you have everything you need to finish the picture. Bell mentions the predetermination in the second paragraph of his paper (i.e. the first paragraph of his argument). If he stopped there and said: PC -> IS <> QM we would already have a big mess on our hands for those who advocate the HV position.

4. We are now left to struggle to determine what element(s) of IS precisely is wrong. And that is where everyone gets into a tizzy. Is it locality? Is it realism? Is it contextuality? Is it separability? Clearly, there are a lot of issues to consider, and a lot rides on your definitions for these terms. It is obvious to me that the IS cannot exist "there" and "then". I.e. at the spacetime point that the entangled particle pair comes into existence, the IS cannot be restricted to that location at that time. There MUST be information entering into the equation from somewhere else and/or at some other point in time.

5. QM considers the "context" of the setup as part of its successsful predictions. So I would simply state that the context spans points in space (i.e. is non-local), and the context somehow spans a points in time (non-temporal, non-causal, or whatever you want to call it). That context violates our notions of local realism.

yoda jedi

Feb11-10, 08:33 PM

zonde

Feb12-10, 03:05 AM

I don't know if it's a well known approach or not.

The argument is that Bell's locality condition isn't, exclusively, a locality condition. If it isn't, then what might this entail wrt the interpretation of experimental violations of inequalities based on Bell locality?

In a nutshell:

Bell locality doesn't just represent causal independence between A and B, but also statistical independence between A and B.

Statistical dependence between A and B means that a detection at A changes the sample space at B, and vice versa. The pairing process entails statistical dependence between A and B, and this statistical dependence can be accounted for via the local transmissions and interactions of the coincidence circuitry.

Statistical dependence between A and B is sufficient to violate inequalities based on Bell locality.

So, experimental violations of inequalities based on Bell locality, while they do rule out Bell local theories, don't imply nonlocality or necessarily rule out local realism.
I will try to describe the point of ThomasT a bit differently. I hope that I will be in line with what ThomasT is saying.

Lets take equation that describes correlations of photons from Type I PDC:
P_{VV}(\alpha,\beta) = sin^{2}\alpha\, sin^{2}\beta\, cos^{2}\theta_{l} + cos^{2}\alpha\, cos^{2}\beta\, sin^{2}\theta_{l} + \frac{1}{4}sin 2\alpha\, sin 2\beta\, sin 2\theta_{l}\, cos \phi
This is equation (9) from paper - Entangled photons, nonlocality and Bell inequalities in the undergraduate laboratory (http://arxiv.org/abs/quant-ph/0205171/)

This relation produces \frac{1}{2}cos^{2}(\alpha-\beta) law when \theta_{l} is Pi/4 and \phi is 0. But when for example \theta_{l} is 0 it produces sin^{2}\alpha\, sin^{2}\beta that is simply product of two probabilities from Malus law.

So lets rewrite this EPR state with \theta_{l}=\pi/4 and \phi=0:
P_{VV}(\alpha,\beta) = \frac{1}{2}sin^{2}\alpha\, sin^{2}\beta + \frac{1}{2}cos^{2}\alpha\, cos^{2}\beta + \frac{1}{4}sin 2\alpha\, sin 2\beta
First and second term have perfectly sensible physical interpretation - it's product of H (V) photon detection probabilities from Alice and Bob i.e. chance that we have a click at coincidence counter.
However if detection efficiency is not 100% then we have to make additional assumption that sample spaces of Alice and Bob for detected H(V) photons are completely uncorrelated (random).
But we have third - interference term that can be positive as well as negative. For me it seems that straight forward interpretation of this interference term is that sample spaces of detected photons can become correlated (as I understand this is the point of ThomasT). Say if sin 2\alpha becomes non zero Alice's side has uneven distribution of sample space but as long as sin 2\beta is zero (Bob has even distribution) Alice's uneven distribution has no effect. But if both sides have uneven distributions depending from correlation or anti-correlation of this unevenness this term becomes nonzero positive or negative.

Please note that this is just an interpretation of SQM and it confirms correctness of ensemble interpretation and denies correctness of other interpretations that unconditionally separate ensemble in individual photons.

Eye_in_the_Sky

Feb12-10, 04:46 AM

This is a good point. When you really break down Bell, you see what he has given us is a road map. Once we have that map, we have the key to breaking apart any local realistic theory. The map points out a lot of features of the territory. Some of these features probably should have been obvious even without the Inequality itself. And your point about perfect correlations (PC) is a great example.

PC needs to be a requirement of a LR theory, and Bell points this out early. It turns out this is NO MINOR POINT at all! Here we have inherent randomness that itself defies modeling (as the entangled outcomes are random at all settings) and yet they must match. Now, how can there be separability with this characteristic? Yes, we must add yet another constraint to account for this - one I didn't explicitly mention. I said: "... somehow or another, P(A) and P(B) must be connected some way to make the relationships work out." And that is both the PC you mention and more generally, Malus.

1. Instruction set may be a slight misnomer (although it is a good visual), because as Bell says: "...it follows that the result of any such measurement must actually be predetermined..." Now, of course you can say "don't forget the interaction with the polarizer" but that really makes no sense. Polarizer, beamsplitter, or whatever optical system, the results are PC. That is also true with electrons so obviously it has nothing whatsoever to do with underlying nature of the interaction with the measurement apparatus per se. There must be complete predetermination of all settings in an LR model if there is PC. You also have random results (RR). So to me, PC + RR -> IS. And so this simple case is not so simple at all.

2. If you have predetermination, then presumably you have the separability we are asking for AND we have the realism we are asking for. Now you just need one final point, that there are angle settings for which no predetermined IS will work. If Bell simply supplied these settings out of thin air, without a proof, it would still be enough to provide a contradiction. Assuming for a moment - as Bell does - that QM predictions would match experimental results: IS <> QM.

3. You then don't even need Bell's Theorem to be valid if you accept the reasoning so far. Because who cares if the theorem is even valid? Once you know - as Bell figured out - what those angles are, you have everything you need to finish the picture. Bell mentions the predetermination in the second paragraph of his paper (i.e. the first paragraph of his argument). If he stopped there and said: PC -> IS <> QM we would already have a big mess on our hands for those who advocate the HV position.

4. We are now left to struggle to determine what element(s) of IS precisely is wrong. And that is where everyone gets into a tizzy. Is it locality? Is it realism? Is it contextuality? Is it separability? Clearly, there are a lot of issues to consider, and a lot rides on your definitions for these terms. It is obvious to me that the IS cannot exist "there" and "then". I.e. at the spacetime point that the entangled particle pair comes into existence, the IS cannot be restricted to that location at that time. There MUST be information entering into the equation from somewhere else and/or at some other point in time.

5. QM considers the "context" of the setup as part of its successsful predictions. So I would simply state that the context spans points in space (i.e. is non-local), and the context somehow spans a points in time (non-temporal, non-causal, or whatever you want to call it). That context violates our notions of local realism.Dr. Chinese, thank you for your reply. However, I cannot see in it an answer to my question.

From your reply to ThomasT (sitting right above the post in which I asked my question), I think I can see what your answer would be.... he believes that realism is NOT a requirement of Bell's Theorem, and therefore all Bell tests prove that nature is non-local.

On the other hand, I argue that realism IS a requirement of Bell's Theorem. It is the requirement of a simultaneous value for A, B and C that makes it work.

And that is the standard view. You can try to prove Bell's Theorem without either requirement (locality or realism), but you won't be able to. You need both the ideas of f(variables) and values for A, B and C to get the result.It appears to me that your answer is:

I see the existence of instruction sets as an independent assumption and not as a derived principle in Bell's derivation.

... Am I correct?

DrChinese

Feb12-10, 01:16 PM

Dr. Chinese, thank you for your reply. However, I cannot see in it an answer to my question.

From your reply to ThomasT (sitting right above the post in which I asked my question), I think I can see what your answer would be.It appears to me that your answer is:

I see the existence of instruction sets as an independent assumption and not as a derived principle in Bell's derivation.

... Am I correct?

I think the Bell paper is a road map to a disproof of local realism. One of the paths is to to demonstrate that PC (perfect correlations) implies predetermination in a classical (local realistic) world. Bell makes several concurrent arguments, so I try not to specifically say X -> Y about too many things. To me, it is clear that the instruction set mentality cannot work, and there are several ways to arrive at that point - and it depends on which assumption you start with.

yoda jedi

Feb12-10, 02:37 PM

So, experimental violations of inequalities based on Bell locality, while they do rule out Bell local theories, don't imply nonlocality or necessarily rule out local realism.

imply nonlocality, but does not rule out realism.

http://arxiv.org/ftp/arxiv/papers/0811/0811.2862.pdf

...........the Bell theorem has demonstrably nothing to do with the 'realism' as defined
by these authors Leggett, Zeilinger, Gröblacher and that, as a consequence, their conclusions about the foundational significance of the Bell theorem are unjustified...........

............the role of Bell’s theorem is not to set constraints on how ‘realist’ we are allowed to be about quantum systems...............

http://arxiv.org/PS_cache/arxiv/pdf/0901/0901.4255v2.pdf

............In recent years the violation of Bell's inequality has often been interpreted as
either a failure of locality or of realism (or of both). The problem with such a
claim is that it is not clear what realism in this context should mean. Sometimes
realism is dened as the hypothesis that every physical quantity always has a
value and that measurements merely reveal these predetermined values. That
is, realism is identied with determinism. But if so, then, rst, why should
one use the word local realism instead of local determinism? And second, Bell's
inequality can be stated and proven without any assumption about determinism.
Consequently, determinism is not the issue......................

............In conclusion, the claim that the observation of a violation of a Bell inequality
leads to an alleged alternative between nonlocality and non-realism.............However, it is not specifc to Bell inequalities.......................Hence, all violations of Bell's inequality should be interpreted as a demonstration of nonlocality................

http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.4000v1.pdf

..........There is hardly a result that is more widely misunderstood in the scientific
community than Bell’s theorem............

...............To summarize, what can one conclude from the violation of Leggett’s
inequality ? .............That doesn’t tell us anything about determinism or any type of philosophical realism.

http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.0958v1.pdf

...........What really matters is the fact that the derivation of Bell’s inequality in no way whatsoever needs an assumption of realism................

.............This being the situation we must conclude that in no way whatsoever Bell’s
inequality has something to do with realism. It simply identifies in a straightforward
and lucid way that what quantum phenomena impose to us is to accept the
unescapable fact that natural processes involving entangled states of composite
and far-away systems turn out to be unavoidably non-local...............

.............or by those who derive from experimental results inspired by not strictly convincing theoretical models unjustified conclusions concerning such an important issue as the one of the reality of the world around us.............................

nikman

Feb13-10, 02:01 PM

DrChinese

Feb13-10, 03:19 PM

http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.0958v1.pdf

...........What really matters is the fact that the derivation of Bell’s inequality in no way whatsoever needs an assumption of realism................

.............This being the situation we must conclude that in no way whatsoever Bell’s
inequality has something to do with realism. It simply identifies in a straightforward
and lucid way that what quantum phenomena impose to us is to accept the
unescapable fact that natural processes involving entangled states of composite
and far-away systems turn out to be unavoidably non-local...............

.............or by those who derive from experimental results inspired by not strictly convincing theoretical models unjustified conclusions concerning such an important issue as the one of the reality of the world around us.............................

Yes I have seen some of these arguments and papers previously. There is, as I have mentioned, those such as Norsen that make the argument that realism is not assumed in Bell. Of course, it is but it is not marked as "Here is where the realism argument starts." So if you want to see it, look after Bell's (14). "It follows that c is another unit vector..." That is where the counterfactual argument begins, obviously with 2 photons there can only be 2 measurements (a and b).

So you can think whatever you want. On the other hand, there are plenty of other experiments - such as GHZ - in which the realistic position is demolished independently of Bell. So you might want to consider that as well.

As Gisin says, realism is often poorly defined. There is a reason for that, the fact is we don't know precisely how to define it. It could be considered akin to causality, non-contextuality, or something else. Experiments continue to probe the frontier.

DrChinese

Feb13-10, 03:47 PM

Paging DrC. Haven't really gotten my head around the Gisin paper. The Zeilinger group's Legget paper (arxiv 0704.2529) is titled "An experimental test of non-local realism" and starts out thus:

Most working scientists hold fast to the concept of 'realism' - a viewpoint according to which an external reality exists independent of observation. But quantum physics has shattered some of our cornerstone beliefs. According to Bell's theorem, any theory that is based on the joint assumption of realism and locality (meaning that local events cannot be aected by actions in spacelike separated regions) is at variance with certain quantum predictions. Experiments with entangled pairs of particles have amply conrmed these quantum predictions, thus rendering local realistic theories untenable. Maintaining realism as a fundamental concept would therefore necessitate the introduction of 'spooky' actions that defy locality. Here we show by both theory and experiment that a broad and rather reasonable class of such non-local realistic theories is incompatible with experimentally observable quantum correlations. In the experiment, we measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by Leggett for non-local realistic theories. Our result suggests that giving up the concept of locality is not sucient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned [1].

concluding in this wise:

We have experimentally excluded a class of important non-local hidden-variable theories. In an attempt to model quantum correlations of entangled states, the theories under consideration assume realism, a source emitting classical mixtures of polarized particles (for which Malus' law is valid) and arbitrary non-local dependencies via the measurement devices. Besides their natural assumptions, the main appealing feature of these theories is that they allow us both to model perfect correlations of entangled states and to explain all existing Bell-type experiments. We believe that the experimental exclusion of this particular class indicates that any non-local extension of quantum theory has to be highly counterintuitive. For example, the concept of ensembles of particles carrying denite polarization could fail. Furthermore, one could consider the breakdown of other assumptions that are implicit in our reasoning leading to the inequality. These include Aristotelian logic, counterfactual deniteness, absence of actions into the past or a world that is not completely deterministic [30]. We believe that our results lend strong support to the view that any future extension of quantum theory that is in agreement with experiments must abandon certain features of realistic descriptions.

In addition there are a couple of Charles Tresser papers (arxiv 0501030 and 0608008v2) proposing that the locality assumption isn't even necessary for Bell: Occamize it out and what you have left are actually tests that violate "classical realism".

I am with you on the Gisin paper, I don't really follow what point he is making. Clearly, he is in the middle of some of the most fascinating research on delayed choice experiments and quantum teleportation. To me, any delayed choice experiment is automatically an attack on realism. After all: if you can change the past with a future decision, how much realism can there be?

See also Hall's: Comment on 'Non-realism: deep thought or soft option?', by N. Gisin (http://arxiv.org/abs/0909.0015)

Tresser's are good papers, I have seen his previously and I happen to agree with him: I don't think you need locality to obtain the main Bell result. But I also believe that Bell's final conclusion does include a locality condition and I think that is a generally accepted result.

Zeilinger and others have come up with a number of experiments showing a similar result: realism suffers from severe problems which are fundamentally in conflict with QM. I think the HUP is such, for example. I think entanglement, delayed choice, quantum erasers, GHZ, all of these are counterexamples to realism. Also Adan Cabello is invloved in some good work, here is a paper he was involved with demonstrating contextuality in single photons (i.e. against realism).

http://arxiv.org/abs/0907.4494

"We present an experimental state-independent violation of an inequality for noncontextual theories on single particles. We show that 20 different single-photon states violate an inequality which involves correlations between results of sequential compatible measurements by at least 419 standard deviations. Our results show that, for any physical system, even for a single system, and independent of its state, there is a universal set of tests whose results do not admit a noncontextual interpretation. This sheds new light on the role of quantum mechanics in quantum information processing. "

akhmeteli

Feb14-10, 12:13 AM

akhmeteli

Feb14-10, 12:27 AM

DrChinese

Feb14-10, 01:23 PM

Haven't really gotten my head around the Gisin paper.

Just to make it a little weirder, what about this one from Gisin which superficially seems to be in direct opposition to the other one (by ruling out more classes of non-local theories):

On the Impossibility of Covariant Nonlocal "hidden" Variables in Quantum Physics (2010) (http://arxiv.org/abs/1002.1390)

"... Hence, any covariant nonlocal model is equivalent to a Bell-local model and, consequently, contradicts well tested quantum predictions, the violation of Bell's inequality. ..."

nikman

Feb14-10, 05:28 PM

Just to make it a little weirder, what about this one from Gisin which superficially seems to be in direct opposition to the other one (by ruling out more classes of non-local theories).... "... Hence, any covariant nonlocal model is equivalent to a Bell-local model and, consequently, contradicts well tested quantum predictions, the violation of Bell's inequality. ..."

Gisin (kind of like our own Peter Morgan?) seems to be zeroing in on the measurement problem as the nexus of all our confusions? The inputting must be considered real, he says, and both Alice and Bob must be assumed to have freedom of choice -- but the reality of the physical measurement itself isn't obvious and this fact surely points to something deeply important although without suggesting specific questions to ask.

In a paper from a year ago Gisin's occasional colleague Suarez, sounding a bit quantum mystical, advances this:

It is argued that the quantum correlations are not maximally nonlocal to make it possible to control local outcomes from outside spacetime, and quantum mechanics emerges from timeless nonlocality and biased local randomness. This rules out a world described by NL (nonlocal) boxes. A new type of experiments is suggested.

and continues a bit later:

The violation of Leggett inequalities was first interpreted as an experimental falsification of "nonlocal realism", where "realism" refers to the view that the single particles carry well defined properties when they leave the source. Such an interpretation is misleading: By testing models fulfilling Leggett inequalities one does not test "nonlocal realism", but rather models assuming both nonlocal randomness and outcomes that depend on biased random local variables. Nevertheless, it is the Colbeck-Renner theorem which clearly shows the relationship between nonlocality and biased local randomness in entanglement experiments.

Any relationship(s) here?

DrChinese

Feb14-10, 05:47 PM

Gisin (kind of like our own Peter Morgan?) seems to be zeroing in on the measurement problem as the nexus of all our confusions? The inputting must be considered real, he says, and both Alice and Bob must be assumed to have freedom of choice -- but the reality of the physical measurement itself isn't obvious and this fact surely points to something deeply important although without suggesting specific questions to ask.

In a paper from a year ago Gisin's occasional colleague Suarez, sounding a bit quantum mystical, advances this:

It is argued that the quantum correlations are not maximally nonlocal to make it possible to control local outcomes from outside spacetime, and quantum mechanics emerges from timeless nonlocality and biased local randomness. This rules out a world described by NL (nonlocal) boxes. A new type of experiments is suggested.

and continues a bit later:

The violation of Leggett inequalities was first interpreted as an experimental falsification of "nonlocal realism", where "realism" refers to the view that the single particles carry well defined properties when they leave the source. Such an interpretation is misleading: By testing models fulfilling Leggett inequalities one does not test "nonlocal realism", but rather models assuming both nonlocal randomness and outcomes that depend on biased random local variables. Nevertheless, it is the Colbeck-Renner theorem which clearly shows the relationship between nonlocality and biased local randomness in entanglement experiments.

Any relationship(s) here?

Not sure, I will need to look at the theorem you mention. I think it is interesting that NO model really seems to come close. You can start one place and rule out some things. Or start somewhere else and rule out what seems to be everything else. Maybe we should be considering non-local non-realistic solutions.

Eye_in_the_Sky

Feb15-10, 03:47 AM

I think the Bell paper is a road map to a disproof of local realism.Okay. I will look it up in the atlas.

In my atlas, the Bell map shows three roads converging into one main road called "local determinism" at which point there is a signpost reading "equation (1)". The three convergent roads are called:

"locality", "perfect anti-correlation for equal settings", and "counterfactuality".

The names of latter two roads are respectively abbreviated as "PC" and "CF". Now, in propositional terms, the convergence of these three roads into one means:

Proposition 1: locality Λ PC Λ CF → local determinism .

I invite anyone who wishes to verify the accuracy and validity of this proposition to do so. Here are Bell's own words:Consider a pair of spin one-half particles formed somehow in the singlet spin state and moving freely in opposite directions. Measurements can be made, say by Stem-Gerlach magnets, on selected components of the spins σ1 and σ2. If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa. Now we make the hypothesis [2], and it seems one at least worth considering, that if the two measurements are made at places remote from one another the orientation of one magnet does not influence the result obtained with the other. Since we can predict in advance the result of measuring any chosen component of σ2, by previously measuring the same component of σ1, it follows that the result of any such measurement must actually be predetermined.
-------------------------
[2] "But on one supposition we should, in my opinion, absolutely hold fast: the real factual situation of the system S2 is independent of what is done with the system S1, which is spatially separated from the former." A. EINSTEIN in Albert Einstein, Philosopher Scientist, (Edited by P. A. SCHILP) p. 85, Library of Living Philosophers, Evanston, Illinois (1949).Next:One of the paths is to to demonstrate that PC (perfect correlations) implies predetermination in a classical (local realistic) world.Dr. Chinese, by this statement do you mean?

"Proposition 1" above is both accurate and valid.

Next, returning once again to the Bell map, I see that the road called "local determinism" eventually merges with another road called "QM". They merge into an unnamed dirt path. This path leads directly into the mouth of an abyss. In propositional terms, this means:

Proposition 2: local determinism Λ QM → CONTRADICTION .
Bell makes several concurrent arguments, so I try not to specifically say X -> Y about too many things.Yes, and it is for this reason that you make a conceptual error in your reply to yoda jedi:There is ... those ... that make the argument that realism is not assumed in Bell. Of course, it is but it is not marked as "Here is where the realism argument starts." So if you want to see it, look after Bell's (14). "It follows that c is another unit vector..." That is where the counterfactual argument begins, obviously with 2 photons there can only be 2 measurements (a and b).No. That is not where the counterfactual argument begins. Counterfactuality has already been invoked in the first paragraph of the section II, "Formulation", of Bell's paper, the relevant part of which I have quoted above, whose argument therein I have summarized as "Proposition 1". But now we are in the section IV, "Contradiction", in the process of developing the validity of "Proposition 2". The premise of "local determinism" is now considered to be given, and therefore, at this stage, there is no difficulty with a counterfactual claim such as "It follows that c is another unit vector...". At this stage, there can be any number of simultaneous specifications of measurement outcomes.

That is to say, Dr. Chinese, any quarrel you may have with CF as it is used in Bell's original paper does not lie with an ad hoc simultaneous assignment of values to noncommuting observables, as you have been thinking it does; but, rather, any such quarrel you may have lies with the truth of CF as it is used as a premise in "Proposition 1" above.

Demystifier

Feb15-10, 04:28 AM

On the Impossibility of Covariant Nonlocal "hidden" Variables in Quantum Physics (2010) (http://arxiv.org/abs/1002.1390)

"... Hence, any covariant nonlocal model is equivalent to a Bell-local model and, consequently, contradicts well tested quantum predictions, the violation of Bell's inequality. ..."
Given the definition of the word "covariant" used in that paper, the conclusions of that paper are correct. However, his definition of the word "covariant" is, mildly speaking, quite unusual.

yoda jedi

Feb15-10, 04:00 PM

Yes I have seen some of these arguments and papers previously. There is, as I have mentioned, those such as Norsen that make the argument that realism is not assumed in Bell. Of course, it is but it is not marked as "Here is where the realism argument starts."

So if you want to see it,

look after Bell's (14). "It follows that c is another unit vector..." That is where the counterfactual argument begins, obviously with 2 photons there can only be 2 measurements (a and b).

So you can think whatever you want.

On the other hand, there are plenty of other experiments - such as GHZ - in which the realistic position is demolished independently of Bell.

So you might want to consider that as well.

the fact is we don't know precisely how to define it.

pathetical ludicrosity, then, how can be demolished ?

if it is not definite yet.............

...laughs....

in which the realistic position is demolished

wooowww DEMOLISHED !!!

ThomasT

Feb16-10, 12:33 PM

... your statement "The pairing process entails statistical dependence between A and B" is not obvious, so it needs proof ... It's not a matter of proof, it's just a matter of identifying the symbolic convention, statistical dependence, with the experimental setup. When a detection is registered at one end, then the sample space at the other end is altered. The matching of the separate data streams at A and B isn't done randomly. The matching process itself produces (via local interactions and transmissions) the statistical dependence between A and B -- and this is sufficient to violate Bell inequalities based on the assumption that the data set at A is statistically independent from the data set at B via Bell locality.

One would think that if experiments are performed infrequently, coincidence circuitry effect should not be important.The separate accumulations of data at A and B have to be matched somehow. The point is that the designs of entanglement experiments contradict Bell locality.

Does statistical dependence imply causal dependence?
In general, not necessarily. But if the Bell inequalities are violated, I guess yes.Statistical dependence between A and B doesn't imply a direct causal link between A and B whether Bell inequalities are violated or not.

Therefore, even though entanglement experimental designs and standard QM are incompatible with Bell locality, we can't conclude that violations of Bell inequalities require nonlocal propagations in Nature.

Eye_in_the_Sky

Feb17-10, 02:44 AM

This thread began with a post in which it was written:... the proof of the Bell theorem uses two mutually contradictory results/assumptions of quantum theory: unitary evolution and the projection postulate. Therefore, I argued, the Bell theorem is on a shaky ground ... on the theoretical ... level.Hello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

Bell's theorem, per se, is nothing more than a proposition of the form

P → D ,

where "P" is the conjunction of some set of premises, the 'truth' of which does not in any way require the 'truth' of any of the premises of Quantum Mechanics, and "D" is a certain condition (e.g. a Bell inequality).
________________

Now, it happens that Quantum Mechanics (let us denote its premises by "QM") is such that

QM → ~D .

Therefore, the conjunction "P Λ QM" is inconsistent.
________________

In the weak version of Bell's theorem

P = local determinism .

In the strong version of Bell's Theorem

P = locality Λ PC Λ CF ,

where

PC ≡ perfect anti-correlation for equal settings

and

CF ≡ counterfactuality .

In the strong version, of course, "PC" has been employed as premise; but this means only that we are considering any theory which admits "PC" as a feature.
________________

... Do you see what I am saying?

zonde

Feb17-10, 08:34 AM

Proposition 1: locality Λ PC Λ CF → local determinism .

I invite anyone who wishes to verify the accuracy and validity of this proposition to do so. Here are Bell's own words:
Can you tell where do you yourself see the problem?

As I understand the sentence you quoted from Bell ascribe counterfactuality to QM:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
This statement is taken as experimentally valid but on the other hand experiments with photons say that you can only detect 50% of photons maximum with one detector. So it is not conclusively true.
Then if we accept as empirical fact that only 50% of photons can be detected and we do not invoke counterfactuality then QM can not make prediction like that about photons.

ThomasT

Feb17-10, 05:04 PM

This thread began with a post in which it was written:Hello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

Bell's theorem, per se, is nothing more than a proposition of the form

P → D ,

where "P" is the conjunction of some set of premises, the 'truth' of which does not in any way require the 'truth' of any of the premises of Quantum Mechanics, and "D" is a certain condition (e.g. a Bell inequality).
________________

Now, it happens that Quantum Mechanics (let us denote its premises by "QM") is such that

QM → ~D .

Therefore, the conjunction "P Λ QM" is inconsistent.
________________

In the weak version of Bell's theorem

P = local determinism .

In the strong version of Bell's Theorem

P = locality Λ PC Λ CF ,

where

PC ≡ perfect anti-correlation for equal settings

and

CF ≡ counterfactuality .

In the strong version, of course, "PC" has been employed as premise; but this means only that we are considering any theory which admits "PC" as a feature.
________________

... Do you see what I am saying?In any version of Bell's theorem

P = statistical independence

and

P → D

where D is a Bell inequality .

We observe that

QM → ~D

and

Experiment → ~D .

Therefore, the conjunctions "P Λ QM" and "P Λ Experiment" are inconsistent.

This is all that can be said vis QM's incompatibility with Bell local formulations, and experimental violations of Bell inequalities.

Eye_in_the_Sky

Feb18-10, 02:59 AM

Can you tell where do you yourself see the problem?Do you mean:

Which premise in "locality Λ PC Λ CF" do I see as false?
As I understand the sentence you quoted from Bell ascribe counterfactuality to QM:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
This statement is taken as experimentally valid but on the other hand experiments with photons say that you can only detect 50% of photons maximum with one detector. So it is not conclusively true.
Then if we accept as empirical fact that only 50% of photons can be detected and we do not invoke counterfactuality then QM can not make prediction like that about photons.Zonde, I am sorry, but I cannot figure out what you mean here.

Eye_in_the_Sky

Feb18-10, 03:20 AM

In any version of Bell's theorem

P = statistical independence

and

P → D

where D is a Bell inequality .Of course, "statistical independence" alone is not enough to derive a Bell inequality. There must be other assumptions.

So maybe you mean this:

Regarding the proposition

BL Λ PC Λ CF → D ,

where

BL ≡ Bell Locality (mathematical formulation in terms of probabilities) ,

it will be found, upon scrutiny, that BL is not in fact an expression of local causality. Rather, it is merely an expression of statistical independence.

Is that what you mean?

zonde

Feb18-10, 04:04 AM

Do you mean:
Which premise in "locality Λ PC Λ CF" do I see as false?
Let's say do you see Proposition 1 (locality Λ PC Λ CF → local determinism) as not valid? Or is it valid but wrongly applied to physical situation? ... or neither.

Zonde, I am sorry, but I cannot figure out what you mean here.
Do you see any problems in this statement?
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."

SpectraCat

Feb18-10, 07:11 AM

Can you tell where do you yourself see the problem?

As I understand the sentence you quoted from Bell ascribe counterfactuality to QM:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
This statement is taken as experimentally valid but on the other hand experiments with photons say that you can only detect 50% of photons maximum with one detector. So it is not conclusively true.
Then if we accept as empirical fact that only 50% of photons can be detected and we do not invoke counterfactuality then QM can not make prediction like that about photons.

Hmmm ... while it is true that only 50% of entangled photons can be detected on a single detector in a polarization experiment, that is not the same as saying only 50% of photons can be detected. Couldn't one just use a polarizing beamsplitter with detectors for both the transmitted and reflected photons? Then the experiment would pick up 100% of the photons, and the measurements from Alice's two detectors could be compared with Bob's two detectors to reveal the perfect correlation between the two. Wouldn't this close the loophole you are talking about above?

zonde

Feb18-10, 08:40 AM

Hmmm ... while it is true that only 50% of entangled photons can be detected on a single detector in a polarization experiment, that is not the same as saying only 50% of photons can be detected. Couldn't one just use a polarizing beamsplitter with detectors for both the transmitted and reflected photons? Then the experiment would pick up 100% of the photons, and the measurements from Alice's two detectors could be compared with Bob's two detectors to reveal the perfect correlation between the two. Wouldn't this close the loophole you are talking about above?
I didn't mean that.
The question is whether increasing detection efficiency does not diminish result for perfect correlations settings. Because perfect correlations at theta=0 and pi/2 is a requirement for Bell inequalities.
I looked up about detection efficiencies of commercially available SPADs and it seems that 50% is not the limit however the question stays whether prefect correlations can be achieved with such levels of detection efficiency.

SpectraCat

Feb18-10, 09:39 AM

I didn't mean that.
The question is whether increasing detection efficiency does not diminish result for perfect correlations settings. Because perfect correlations at theta=0 and pi/2 is a requirement for Bell inequalities.
I looked up about detection efficiencies of commercially available SPADs and it seems that 50% is not the limit however the question stays whether prefect correlations can be achieved with such levels of detection efficiency.

Ok .. I see your point now. However, I don't think this is a real issue, because all it does is change the discussion from the realm of complete certainty (i.e. Bell inequalities are always violated) to the realm of probability (i.e. the result of a given set of measurements with some mean and standard deviation is outside the permissible range of the Bell inequality by 30 standard deviations).

My view on this is that it is easy to see that the second case approaches the first as the detector efficiency is improved, and so the gedanken conditions of "perfect detector efficiency" is a reasonable simplification to make. Thus the point you raised is really a non-issue in my view. Essentially, it puts you in the position of the sophists who say "well, the detectors aren't perfect, so you can't be sure". Granted .. but 30 standard deviations is close enough for me. :wink:

DrChinese

Feb18-10, 12:50 PM

... Essentially, it puts you in the position of the sophists who say "well, the detectors aren't perfect, so you can't be sure". Granted .. but 30 standard deviations is close enough for me. :wink:

30 and rising... some experiments are at 200+ SD.

zonde

Feb19-10, 07:05 AM

Ok .. I see your point now. However, I don't think this is a real issue, because all it does is change the discussion from the realm of complete certainty (i.e. Bell inequalities are always violated) to the realm of probability (i.e. the result of a given set of measurements with some mean and standard deviation is outside the permissible range of the Bell inequality by 30 standard deviations).
Not sure we are talking about the same thing.
You should actively tune experimental setup to reach as low as possible detection rate for perfect anti-correlation settings. How you can talk about standard deviation in this case? Of course no one is calculating standard deviation for minimum correlation settings because this is requirement not result.

SpectraCat

Feb19-10, 08:00 AM

Not sure we are talking about the same thing.
You should actively tune experimental setup to reach as low as possible detection rate for perfect anti-correlation settings. How you can talk about standard deviation in this case? Of course no one is calculating standard deviation for minimum correlation settings because this is requirement not result.

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?

akhmeteli

Feb19-10, 08:50 AM

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?

As far as I know, no violations of the Bell inequalities have been demonstrated - there was some "loophole" in each of the experiments claiming such violations. I suspect those "violations by over 30 standard deviations" were obtained using the fair sampling assumption, and if you use this assumption, you can get as many standard deviations as you want. The problem is it is not clear why anyone has to accept the fair sampling assumption.

zonde

Feb19-10, 09:06 AM

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?
Perfect anti-correlation settings are theta=0deg for Type II PDC. With that I do not mean "perfect detection" or rather noiseless non-detection.
The point is that you have to assume that coincidence count at minimum can be extrapolated linearly to reasonably low value at 100% efficiency in order to violate Bell inequalities.
If you can't do that then you don't have violation of Bell inequalities.

It has nothing to do with "Bell inequality violations by over 30 standard deviations".
Please look up in wikipedia Precision bias (http://en.wikipedia.org/wiki/Precision_bias) and Accuracy and precision (http://en.wikipedia.org/wiki/Accuracy_and_precision).

akhmeteli

Feb19-10, 09:24 AM

It's not a matter of proof, it's just a matter of identifying the symbolic convention, statistical dependence, with the experimental setup. When a detection is registered at one end, then the sample space at the other end is altered. The matching of the separate data streams at A and B isn't done randomly. The matching process itself produces (via local interactions and transmissions) the statistical dependence between A and B -- and this is sufficient to violate Bell inequalities based on the assumption that the data set at A is statistically independent from the data set at B via Bell locality.

The separate accumulations of data at A and B have to be matched somehow. The point is that the designs of entanglement experiments contradict Bell locality.

Statistical dependence between A and B doesn't imply a direct causal link between A and B whether Bell inequalities are violated or not.

Therefore, even though entanglement experimental designs and standard QM are incompatible with Bell locality, we can't conclude that violations of Bell inequalities require nonlocal propagations in Nature.

Sorry, has been busy again.

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do. I don't see solid reasoning behind your statements, so I cannot agree or disagree with them, as neither those statements nor their negations seem obvious. With all due respect, I cannot believe you on your word - you are not a priest (or maybe you are? :-)), and I am not religious. Until you give some reasoning, I just have no comments, sorry. For example, can you offer a local theory violating the Bell inequalities? Or, if you think this is a tall order, can you at least explain if your phrase "the designs of entanglement experiments contradict Bell locality" means the same as "there are loopholes in those experiments"?

zonde

Feb19-10, 10:30 AM

Sorry, has been busy again.

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do.
It seems that ThomasT is talking basically about the same thing - fair sampling.
Look, if sample space at one end exactly matches sample space at other end (say we have PBS and we detect photon always in one channel or the other) sample spaces stay the same after matching at coincidence counter (except of course that you have additional information about how different channels are matched). But if you don't have perfect efficiency then you reduce each sample space at coincidence counter.

Does not seem that this needs a proof.

However this part could be expanded as it is not obvious:
"this is sufficient to violate Bell inequalities based on the assumption that the data set at A is statistically independent from the data set at B via Bell locality."

DrChinese

Feb19-10, 10:48 AM

The problem is it is not clear why anyone has to accept the fair sampling assumption.

Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?

You keep saying the same thing without providing scientific basis. You don't have to accept the results, but you shouldn't state the "loophole" as being proof of anything. It isn't.

SpectraCat

Feb19-10, 10:50 AM

Perfect anti-correlation settings are theta=0deg for Type II PDC. With that I do not mean "perfect detection" or rather noiseless non-detection.
The point is that you have to assume that coincidence count at minimum can be extrapolated linearly to reasonably low value at 100% efficiency in order to violate Bell inequalities.
If you can't do that then you don't have violation of Bell inequalities.

Ok ... so you are saying that the "false coincidence" rate must be below some critical value in order to satisfy the Bell inequality, right? But false coincidences are included in the analysis, so that is accounted for in the experiment. If the false coincidence rate were too high, then the results would appear more "random" and so would no longer show a Bell inequality violation. That is, it is fundamentally IMPOSSIBLE to show a Bell inequality violation with an apparatus that has too high a rate of false coincidences. So your statement is correct, but again I don't see how this is an issue ... the fact that the experimental results do show a violation indicates that false coincidences are not an issue, right?

akhmeteli

Feb19-10, 09:48 PM

Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?

I have no reasons to accept the fair sampling assumption. You yourself mentioned a situation where it is not true (planets of the Solar system). Of course, my opinion means nothing, but Shimony, Zeilinger and many others believe "loopholes", such as fair sampling assumption, are essential, so I just side with the mainstream view. As for "other tests giving the same results" - I never heard from you on my example with Euclidian geometry.

You keep saying the same thing without providing scientific basis. You don't have to accept the results, but you shouldn't state the "loophole" as being proof of anything. It isn't.

I did provide scientific basis - the opinions of Shimony, Zeilinger, Genovese. You disagree with them, but why is this my problem? You don't seem to claim they are not experts. Again, don't kill the messenger. I keep saying local realism has not been ruled out. You keep saying it has been. Maybe you're right, maybe I am, but so far I don't see any reasons to accept your point of view. Looks like you don't see any reasons to agree with my point of view. So we disagree. So what?

DrChinese

Feb20-10, 12:14 AM

I did provide scientific basis - the opinions of Shimony, Zeilinger, Genovese. ... You don't seem to claim they are not experts. Again, don't kill the messenger. I keep saying local realism has not been ruled out. You keep saying it has been. Maybe you're right, maybe I am, but so far I don't see any reasons to accept your point of view. Looks like you don't see any reasons to agree with my point of view. So we disagree. So what?

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one. There are plenty (of his) proving LR is not. The difference in our opinions is that one is the mainstream and one is not. Local realism is not a mainstream view. The idea that "loopholes" support LR (or otherwise imply it is feasible) is not either. Don't advertise a false viewpoint. Yours is an extreme minority view in the scientific community.

As mentioned in another thread, for example, it is possible to entangle photons that have never even existed in each other's spacetime light cone. Oh, and that was courtesy Zeilinger. So I don't get where you think LR is considered a viable alternative. You are ignoring a substantial body of work that does not require the fair sampling assumption, such as this.

akhmeteli

Feb20-10, 01:50 AM

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one.

I gave you his quote confirming local realism has not been ruled out.
If you don't like the quote, it's not my problem.

There are plenty (of his) proving LR is not.

Give me one where he says local realism has been ruled out.

The difference in our opinions is that one is the mainstream and one is not.

I fully agree. And mine is mainstream, yours is not. I confirmed mine by quotes. Again, if you don't like the quotes, it's not my problem.

Local realism is not a mainstream view.

No, it isn't.

The idea that "loopholes" support LR (or otherwise imply it is feasible) is not either. Don't advertise a false viewpoint. Yours is an extreme minority view in the scientific community.

They do imply it is feasible, and this is mainstream. If you believe I advertise a false viewpoint, why don't you kick Shimony's behind, Zeilinger's behind, Genovese's behind? I am of no importance whatsoever. Nobody cares what I advertise. The problem is what I advertise is mainstream, sorry. And if you state that local realism has been ruled out, you're just trying to impose your personal opinion on the others.

As mentioned in another thread, for example, it is possible to entangle photons that have never even existed in each other's spacetime light cone. Oh, and that was courtesy Zeilinger. So I don't get where you think LR is considered a viable alternative. You are ignoring a substantial body of work that does not require the fair sampling assumption, such as this.

Does anybody (but you) claim that these experiments demonstrate loophole-free violations of the Bell inequalities?

Frame Dragger

Feb20-10, 02:25 AM

I gave you his quote confirming local realism has not been ruled out.
If you don't like the quote, it's not my problem.

Give me one where he says local realism has been ruled out.

I fully agree. And mine is mainstream, yours is not. I confirmed mine by quotes. Again, if you don't like the quotes, it's not my problem.

No, it isn't.

They do imply it is feasible, and this is mainstream. If you believe I advertise a false viewpoint, why don't you kick Shimony's behind, Zeilinger's behind, Genovese's behind? I am of no importance whatsoever. Nobody cares what I advertise. The problem is what I advertise is mainstream, sorry. And if you state that local realism has been ruled out, you're just trying to impose your personal opinion on the others.

Does anybody (but you) claim that these experiments demonstrate loophole-free violations of the Bell inequalities?

This isn't a rhetorical pissing match... the experimental evidence and lack of refutation is more important than your quotes. This is why results are PUBLISHED, and we don't just listen to the researcher's interpretation. As we see, results can be open to multiple interpretations. In short, answer his questions and cut the grade-school debate club horsh-****.

akhmeteli

Feb20-10, 04:01 AM

This isn't a rhetorical pissing match... the experimental evidence and lack of refutation is more important than your quotes. This is why results are PUBLISHED, and we don't just listen to the researcher's interpretation. As we see, results can be open to multiple interpretations. In short, answer his questions and cut the grade-school debate club horsh-****.

Sorry, I just cannot understand a word. Whose "his"? What questions? Do you mean "DrChinese'" and the following:
"Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?" ?

Then, as I said, I don't see any reason to accept the fair sampling assumption. If Dr Chinese (or you) wants to prove it, good luck, but I don't hold my breath, because he'll have to produce something Shimony and Zeilinger are not aware of. Furthermore, DrChinese himself gave an example where fair sampling does not work. If DrChinese (or you) believes that the assumption does not need any proof as it is obvious, I reject that. You would not understand if I said that local realism does not need any proof as it is obvious, so don't even try to sell me the fair sampling assumption without proof. And again, it does not really matter if you sell it to me or not, as I am of no consequence. Experts agree that the detection loophole is essential. If DrChinese (or you) disagrees, this is his (or your) personal opinion, nothing more.

Please try to understand this: I don't need to prove that fair sampling is wrong. If you like fair sampling, the burden of proof is all yours. Let me rephrase this. I could admit (cutting some corners, such as "free will") that experiments demonstrate that at least one of the following three is wrong: 1)locality; 2) realism; 3) fair sampling . For DrChinese, fair sampling is a "holy cow", for somebody else local realism is a "holy cow". What I am trying to say, there is not enough data so far to make a definite choice.

As for the last question: "why do other tests - not requiring the fair sampling assumption - give the same results?", as I said, I offered DrChinese to explain how my "proof" in post 34 in this thread (that the sum of angles of a planar triangle does not equal 180 degrees) is any worse than "closing loopholes separately". Not a word from him.

So what experimental evidence exactly? There has been no experimental demonstration of the genuine Bell inequalities - 45 years after Bell. And there has been all the refutation you want - if Shimony and Zeilinger admit that, strictly speaking, local realism has not been ruled out, I can assure you, this is not because they like local realism - nobody accused them of such love. So somebody raised the issue of the "detection loophole", somebody raised the issue of the "locality loophole". I am no expert in the Bell inequalities, and I don't even know who raised these issues first, but seems they did a pretty good job, if all the leading experts agree what was actually demonstrated experimentally, and what was not.

Frame Dragger

Feb20-10, 04:30 AM

Sorry, I just cannot understand a word. Whose "his"? What questions? Do you mean "DrChinese'"...

Let me get this straight... you have a firm grasp of QM, but contextual language eludes you? Yes, I mean Dr. Chinese, as you knew from the first. Care to answer those questions now that you've thrown your tantrum?

akhmeteli

Feb20-10, 06:33 AM

Let me get this straight... you have a firm grasp of QM, but contextual language eludes you? Yes, I mean Dr. Chinese, as you knew from the first. Care to answer those questions now that you've thrown your tantrum?

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one. There are plenty (of his) proving LR is not.

I did not say Zeilinger says local realism is plausible. He says it has not been ruled out, and I gave the quote. If DrChinese (or you) believes he changed his mind since then, why does not he give me a direct quote?

So I don't get where you think LR is considered a viable alternative.

Same answer. Zeilinger said LR has not been ruled out. I gave the quote confirming that. If later he said LR has been ruled out, give me the quote.

Why should you accept any scientific evidence?
As you (I mean Frame Dragger) said, this is not a rhetorical pissing match. I accept scientific evidence when I feel satisfied with it. Of course, there are a lot of areas where I just believe experts on their word, at least for the time being, as I cannot sort out everything myself. In this case, however, I don't see enough evidence to rule out local realism. Its elimination is a very radical idea, so the proof should be really good. However, both theoretical and experimental evidence against local realism is dubious in the best case.
And why do you suspect that the full universe would not match the results of a subsample?
For one, because the universe is not uniform in space or in time. And the application of fair sampling relevant to Bell is not about the universe. The question at hand is whether the set of detected photons has the same statistics as the set of undetected ones. Hidden variable theories suggest that there is a reason why one photon is detected and another is not. If you impose fair sampling, you reject such a possibility. Let me give you an example. Suppose you throw a lot of knives at a tree. Sometimes a knife gets stuck in the tree, sometimes it is bounced. The knives can have the same velocity and rotate in flight with the same angular velocity, but the results can vary depending on the phase (the knife can hit the tree point first or handle first). So if we try to build the statistics for the phase, the statistics will be different for knives stuck in the tree and for all knives. So, as Santos emphasized, fair sampling eliminates a great deal of local realistic theories immediately, so it would be indeed absurd to blindly accept fair sampling if you're trying to decide if local realistic theories are possible.
And why does increasing the sample percentage not lead to a different answer?
I don't know. In general, I don't know why physics laws are the laws we study at school, not some other laws. So what? But if you imply that the same results will hold for 100% efficiency, I don't buy it without proof. Indeed, you may try to break a steel bar by pulling it apart with a force of 1 N. No luck? Try one ton. Still no luck? Then let us conclude that the result remains the same as we increase the load. Of course, you'll just roll your eyes as you know that no material is infinitely strong. How the case of the Bell inequalities is any different? As long as you use some ersatz inequalities (using fair sampling), you can violate them with one hand tied behind your back. However, the entire humanity has not been able to violate the genuine inequalities for 45 years. You want to eliminate local realism? Break the true inequalities. Anything else is not enough. A theorem is a theorem. You cannot ensure its conclusion until its assumptions are fulfilled.
And why do other tests - not requiring the fair sampling assumption - give the same results?
Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

akhmeteli

Feb20-10, 06:56 AM

This thread began with a post in which it was written:Hello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

Bell's theorem, per se, is nothing more than a proposition of the form

P → D ,

where "P" is the conjunction of some set of premises, the 'truth' of which does not in any way require the 'truth' of any of the premises of Quantum Mechanics, and "D" is a certain condition (e.g. a Bell inequality).
________________
Sorry for the delay.

I am afraid I disagree that "Bell's theorem, per se, is nothing more than a proposition of the form

P → D"

Usually statement "QM → ~D" is also included in the Bell theorem.

Now, it happens that Quantum Mechanics (let us denote its premises by "QM") is such that

QM → ~D .

Therefore, the conjunction "P Λ QM" is inconsistent.
________________

In the weak version of Bell's theorem

P = local determinism .

In the strong version of Bell's Theorem

P = locality Λ PC Λ CF ,

where

PC ≡ perfect anti-correlation for equal settings

and

CF ≡ counterfactuality .

In the strong version, of course, "PC" has been employed as premise; but this means only that we are considering any theory which admits "PC" as a feature.
________________

... Do you see what I am saying?

Not really, sorry. It seems to me I understand what you wrote, but I don't quite see from your post where my misconception is. Could you please explain?

SpectraCat

Feb20-10, 09:05 AM

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.

I did not say Zeilinger says local realism is plausible. He says it has not been ruled out, and I gave the quote. If DrChinese (or you) believes he changed his mind since then, why does not he give me a direct quote?

Same answer. Zeilinger said LR has not been ruled out. I gave the quote confirming that. If later he said LR has been ruled out, give me the quote.

As you (I mean Frame Dragger) said, this is not a rhetorical pissing match. I accept scientific evidence when I feel satisfied with it. Of course, there are a lot of areas where I just believe experts on their word, at least for the time being, as I cannot sort out everything myself. In this case, however, I don't see enough evidence to rule out local realism. Its elimination is a very radical idea, so the proof should be really good. However, both theoretical and experimental evidence against local realism is dubious in the best case.

For one, because the universe is not uniform in space or in time. And the application of fair sampling relevant to Bell is not about the universe. The question at hand is whether the set of detected photons has the same statistics as the set of undetected ones. Hidden variable theories suggest that there is a reason why one photon is detected and another is not. If you impose fair sampling, you reject such a possibility. Let me give you an example. Suppose you throw a lot of knives at a tree. Sometimes a knife gets stuck in the tree, sometimes it is bounced. The knives can have the same velocity and rotate in flight with the same angular velocity, but the results can vary depending on the phase (the knife can hit the tree point first or handle first). So if we try to build the statistics for the phase, the statistics will be different for knives stuck in the tree and for all knives. So, as Santos emphasized, fair sampling eliminates a great deal of local realistic theories immediately, so it would be indeed absurd to blindly accept fair sampling if you're trying to decide if local realistic theories are possible.

I don't know. In general, I don't know why physics laws are the laws we study at school, not some other laws. So what? But if you imply that the same results will hold for 100% efficiency, I don't buy it without proof. Indeed, you may try to break a steel bar by pulling it apart with a force of 1 N. No luck? Try one ton. Still no luck? Then let us conclude that the result remains the same as we increase the load. Of course, you'll just roll your eyes as you know that no material is infinitely strong. How the case of the Bell inequalities is any different? As long as you use some ersatz inequalities (using fair sampling), you can violate them with one hand tied behind your back. However, the entire humanity has not been able to violate the genuine inequalities for 45 years. You want to eliminate local realism? Break the true inequalities. Anything else is not enough. A theorem is a theorem. You cannot ensure its conclusion until its assumptions are fulfilled.

Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

Ok .. so after reading this, I am confused. I realize that you are unconvinced by the experimental demonstrations of Bell inequality violations, because you are not willing to grant the fair sampling assumption. That seems fair to me ... I tend to be more willing to accept it, but perhaps that is because LHV theories have always seemed to me to fail the Occam's razor test.

However, on reading this post and others, it has become unclear to me whether you even accept Bell's theorem to begin with, or at least that you have some issues about how it is interpreted. So, just so I have it straight, do you accept that Bell's theorem proves that any theory that is consistent with QM experiments must violate either locality or counterfactual determinism?

EDIT: Sorry, you can ignore the above ... I should have gone back to the first pages again before posting. It had been a while since I read them, and I had forgotten your points about PP and UE with regards to Bell's theorem. No need to repeat yourself on my account.

ThomasT

Feb20-10, 01:06 PM

Of course, "statistical independence" alone is not enough to derive a Bell inequality. There must be other assumptions.

So maybe you mean this:

Regarding the proposition

BL Λ PC Λ CF → D ,

where

BL ≡ Bell Locality (mathematical formulation in terms of probabilities) ,

it will be found, upon scrutiny, that BL is not in fact an expression of local causality. Rather, it is merely an expression of statistical independence.

Is that what you mean?Yes.

DrChinese

Feb20-10, 01:14 PM

Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

In the case of photons created outside each others' light cones, how would that be? The Fair Sampling Assumption is not an issue, since NO local realistic explanation would hold anyway. According to the theoretical assumptions of LR, no such entanglement is possible under ANY scenario. Keep in mind that the photons don't even need to exist at the same time - and yet they are entangled.

Frame Dragger

Feb20-10, 01:30 PM

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.

Don't get snippy because you're being called on your statements by multiple individuals who are not distracted by your tone. It's good to see you've gotten back to substance in the meantime, but you still seem to completely miss the basic point of the thread again.

You believe somethiing which is outside the mainstream, and it's taken you a while to explain/admit that. Now the debate on SUBSTANCE can begin. Enjoy! :smile: By the way, scientific evidence doesn't become valid when YOU accept it, rather, it becomes increasingly well accepted as it is repeated, and stands up to scrutiny... unlike your rhetoric.

akhmeteli

Feb20-10, 02:08 PM

In the case of photons created outside each others' light cones, how would that be? The Fair Sampling Assumption is not an issue, since NO local realistic explanation would hold anyway. According to the theoretical assumptions of LR, no such entanglement is possible under ANY scenario. Keep in mind that the photons don't even need to exist at the same time - and yet they are entangled.

Dear DrChinese,

Thank you very much for your input, and let me explain my position. I am not an expert in the Bell theorem, and my posts in this thread are not based on my independent research. I just used published sources (and, of course, nightlight's posts strongly influenced my views). I work in quite a different field (I am also in Texas - Houston) and don't have much spare time, so I have to choose the battles I fight (I am sure you are very busy as well and I do value your time and input). So, if I can, I would not like to spend time right now and try to understand the new experiments that you are discussing. However, I may have to do that if I find that they are relevant to this discussion. So let me ask you the following questions.

Do you personally think these experiments demonstrated loophole-free violations of the Bell inequalities?

Do the authors of the articles claim they demonstrated (at long last) loophole-free violations of the Bell inequalities?

So far my understanding was there were no such claims. If I am right, these experiments do not change the existing situation, and I can wait until other people analyze these experiments and then use their conclusions.

Let me just re-emphasize one thing. Entanglement per se does not spell nonlocality (I usually use the following mental picture - it does not matter if it has anything to do with reality, what's important is this picture is a possibility: I visualize entangled particles of a spin singlet as constantly exchanging other particles; for example, for electrons it can be photons, and vice versa. This local visualisation is important, even if it is just an abstract possibility).

akhmeteli

Feb20-10, 02:40 PM

You believe somethiing which is outside the mainstream, and it's taken you a while to explain/admit that. Now the debate on SUBSTANCE can begin. Enjoy! :smile: By the way, scientific evidence doesn't become valid when YOU accept it, rather, it becomes increasingly well accepted as it is repeated, and stands up to scrutiny... unlike your rhetoric.

Frame Dragger,

I flatly refuse to discuss anything with you until you try to be much, much clearer.

What is it that I believe that is outside the mainstream?

What is it that I admit?

I could make a guess, but I have no reason to do any guessing, this is no twenty questions. QM is difficult enough as it is, thank you, so I am not going to waste any time deciphering your "contextual language".

ThomasT

Feb20-10, 02:42 PM

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do. I don't see solid reasoning behind your statements, so I cannot agree or disagree with them, as neither those statements nor their negations seem obvious. With all due respect, I cannot believe you on your word - you are not a priest (or maybe you are? :-)), and I am not religious. Until you give some reasoning, I just have no comments, sorry.I understand. My current line of thinking wrt the meaning of Bell's theorem is more a product of intuitive epiphany than rigorous development. :smile: So, please excuse the incompleteness of what I offer for your (or anyone's) criticism. (I'm sure that at least a few versions of what I'm saying are in the literature somewhere. I just don't remember exactly where.)

I do agree with you that some LHV formulation of entangled state hasn't been definitively ruled out yet. That is, some form of LHV theory is possible. But it definitely won't be a Bell local LHV theory, and it will probably involve some very arguable interpretations of the representation.

For example, ... can you at least explain if your phrase "the designs of entanglement experiments contradict Bell locality" means the same as "there are loopholes in those experiments"?They mean different things. The first phrase means that any Bell local formulation of the entangled state simply misrepresents, contradicts the statistical dependence (via experimental design) required to experimentally demonstrate the entangled state.

So, even if all the technical problems (experimental loopholes) were solved, any Bell local formulation would still be unable to reproduce all the experimental results.

But this doesn't imply nonlocality, because Bell locality just means statistical independence.

The second phrase (loopholes) means that there are technical problems.

akhmeteli

Feb20-10, 03:05 PM

They mean different things. The first phrase means that any Bell local formulation of the entangled state simply misrepresents, contradicts the statistical dependence (via experimental design) required to experimentally demonstrate the entangled state.

Again, I just see some statements, but reasoning or references are missing.

Frame Dragger

Feb20-10, 03:54 PM

Frame Dragger,

I flatly refuse to discuss anything with you until you try to be much, much clearer.

What is it that I believe that is outside the mainstream?

What is it that I admit?

I could make a guess, but I have no reason to do any guessing, this is no twenty questions. QM is difficult enough as it is, thank you, so I am not going to waste any time deciphering your "contextual language".

We're not having a discussion. What we're having was simply me saying, "answer [Dr. Chinese's] damned question already." What followed was simply trying to tamp down your rhetoric so that you, ThomasT, and Dr. Chinese could progress in your discussion of the science. You seem to have hit a bit of a roadblock for the last... couple of pages.

akhmeteli

Feb20-10, 04:39 PM

We're not having a discussion. What we're having was simply me saying, "answer [Dr. Chinese's] damned question already." What followed was simply trying to tamp down your rhetoric so that you, ThomasT, and Dr. Chinese could progress in your discussion of the science. You seem to have hit a bit of a roadblock for the last... couple of pages.

I believe I answered DrChinese's questions. You did not answer my questions in post 205. As for the roadblock, I cannot agree or disagree until you are much more clear and specific. So far your phrase about the roadblock is just a baseless statement. Or rhetoric, if you wish.

SpectraCat

Feb20-10, 05:50 PM

Let me just re-emphasize one thing. Entanglement per se does not spell nonlocality (I usually use the following mental picture - it does not matter if it has anything to do with reality, what's important is this picture is a possibility: I visualize entangled particles of a spin singlet as constantly exchanging other particles; for example, for electrons it can be photons, and vice versa. This local visualisation is important, even if it is just an abstract possibility).

Ok .. that clearly wrong to me. How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light? Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation.

Note that this does not require any sort of free-sampling assumption to be true, because the results predicted by any local realistic theory for such experiments would have to be random, and whatever else you might believe about the sampling of the data, you have to concede that the chance that the coincidence measurements from these experiments could arise randomly are astronomical.

So you are going to have to do better than that to justify a statement like, "entanglement per se does not spell non-locality", because contrary to your claim, such a model of particle transfer between an entangled pair is demonstrably NOT a possibility.

Frame Dragger

Feb20-10, 06:47 PM

I believe I answered DrChinese's questions. You did not answer my questions in post 205. As for the roadblock, I cannot agree or disagree until you are much more clear and specific. So far your phrase about the roadblock is just a baseless statement. Or rhetoric, if you wish.

See SpectraCat, and Dr. Chinese's posts for what my views are. As I said, we're not having a discussion; I just wanted you to stop talking in circles, cite evidence and not a lack of quotes, etc.

As for what you believe that is not mainstream, again, see SpectraCat's latest post. You're argument against non-locality is to rely on paradoxical mechanics.

akhmeteli

Feb20-10, 07:36 PM

Ok .. that clearly wrong to me. How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light?

They cannot. I assume they do not travel faster than light.

Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation.

Note that this does not require any sort of free-sampling assumption to be true, because the results predicted by any local realistic theory for such experiments would have to be random

I don't accept this without a proof. So far this is just your word. Remember, existing experiments have not ruled out local theories.

, and whatever else you might believe about the sampling of the data, you have to concede that the chance that the coincidence measurements from these experiments could arise randomly are astronomical.

This is not relevant, until you prove that "the results predicted by any local realistic theory for such experiments would have to be random"

So you are going to have to do better than that to justify a statement like, "entanglement per se does not spell non-locality", because contrary to your claim, such a model of particle transfer between an entangled pair is demonstrably NOT a possibility.

Maybe so, but you have not demonstrated its impossibility. You see, your "demonstration" seems to rule out any local theory, not just my mental picture, whereas people agree that such experiments do not rule out all local theories. I just cannot understand what part of my very vague "local theory" makes it less able to explain these experiments than other local theories. It looks like it's your "demonstration" that is clearly wrong, as it seems to prove much more than you wanted.

Frame Dragger

Feb20-10, 07:59 PM

They cannot. I assume they do not travel faster than light.

I don't accept this without a proof. So far this is just your word. Remember, existing experiments have not ruled out local theories.

This is not relevant, until you prove that "the results predicted by any local realistic theory for such experiments would have to be random"

Maybe so, but you have not demonstrated its impossibility. You see, your "demonstration" seems to rule out any local theory, not just my mental picture, whereas people agree that such experiments do not rule out all local theories. I just cannot understand what part of my very vague "local theory" makes it less able to explain these experiments than other local theories. It looks like it's your "demonstration" that is clearly wrong, as it seems to prove much more than you wanted.

Your argument is endlessly reductionist; demanding that a negative be proven in a context that is impossible. Your retort is, as you say, VAGUE. So vague that while you claim a local theory, in reality it's so vague as to need to rely on Hidden Variables. How else does entanglement work, if you reject non-locality, AND Hidden Variables in a Local theory?

akhmeteli

Feb20-10, 08:06 PM

See SpectraCat, and Dr. Chinese's posts for what my views are.

I did not ask you about your views, I asked you to answer my questions. If it is too much trouble for you to give clear and explicit answers, for a change, it is too much trouble for me to dig through the entire thread and try to guess what you meant. I owe no guesses to you.

As for what you believe that is not mainstream, again, see SpectraCat's latest post. You're argument against non-locality is to rely on paradoxical mechanics.

Again, instead of giving a clear and explicit answer, you suggest that I read something else (and it is not a reference, say, to an article with a clear indication to what exactly in the article you referred to). SpectraCat wrote something, and I replied to him. To reply to you I have to guess what you wrote. Your reference to my "argument against non-locality" is also extremely obscure. What argument, exactly? I did not say nonlocality has been ruled out, I said locality has not been ruled out, and this is indeed mainstream, whether you like it or not.

akhmeteli

Feb20-10, 08:50 PM

Your argument is endlessly reductionist; demanding that a negative be proven in a context that is impossible. Your retort is, as you say, VAGUE. So vague that while you claim a local theory, in reality it's so vague as to need to rely on Hidden Variables. How else does entanglement work, if you reject non-locality, AND Hidden Variables in a Local theory?

Frame Dragger,

I just give up. I cannot understand a word. Let me try to explain why reading your text is a struggle.

First you say that my "argument is endlessly reductionist", and I have to guess what argument, as I offered at least two arguments: first, that the randomness of results in a local theory needs a proof, and second, that SpectraCat's reasoning proves too much. Do I have to guess again what you had in mind?

Then you say "demanding that a negative be proven in a context that is impossible", and I have to guess what negative, what context, why it is impossible, and last but not least, if you declare that my demand to prove something is unreasonable, does it mean I have to believe SpectraCat on his (or her) word?

Then you say that my retort is "so vague as to need to rely on Hidden Variables." So did you want to say that my "model" requires hidden variables, or that it excludes hidden variables (as later you say that I "reject non-locality, AND Hidden Variables in a Local theory")? If, however, you believe my "model" requires hidden variables, does it mean this makes the "model" unacceptable?

So if you keep offering me such crosswords, I'll have to ignore them, sorry. It may well be that you have some interesting thoughts, but obscurity of your texts protects them too well.

Frame Dragger

Feb20-10, 08:51 PM

I did not ask you about your views, I asked you to answer my questions. If it is too much trouble for you to give clear and explicit answers, for a change, it is too much trouble for me to dig through the entire thread and try to guess what you meant. I owe no guesses to you.

Again, instead of giving a clear and explicit answer, you suggest that I read something else (and it is not a reference, say, to an article with a clear indication to what exactly in the article you referred to). SpectraCat wrote something, and I replied to him. To reply to you I have to guess what you wrote. Your reference to my "argument against non-locality" is also extremely obscure. What argument, exactly? I did not say nonlocality has been ruled out, I said locality has not been ruled out, and this is indeed mainstream, whether you like it or not.

Oh please... this is precisely the kind of rhetorical nonsense I'm trying to avoid. You didn't ask my views, and yet you have them. Such is life on the internet Mon Dauphine. :wink:

I'd start doing some real work on finding citations for you "vague theory"... you have 3 people asking you questions you aren't answering well, and you're wasting your time because you can't let go and accept that I was not trying to engage in debate, but rather refocus your attention to the matter at hand? Nothing has changed. Your desire for answers mean nothing to me; you're the one who quite literally has something to prove, or at least a position to defend. I'm not going to respond to your no-doubt brilliant next post. If you found any of this confusing... Sprechen sie Englisch? :smile:

Frame Dragger

Feb20-10, 08:53 PM

Frame Dragger,

I just give up. I cannot understand a word. Let me try to explain why reading your text is a struggle.

First you say that my "argument is endlessly reductionist", and I have to guess what argument, as I offered at least two arguments: first, that the randomness of results in a local theory needs a proof, and second, that SpectraCat's reasoning proves too much. Do I have to guess again what you had in mind?

Then you say "demanding that a negative be proven in a context that is impossible", and I have to guess what negative, what context, why it is impossible, and last but not least, if you declare that my demand to prove something is unreasonable, does it mean I have to believe SpectraCat on his (or her) word?

Then you say that my retort is "so vague as to need to rely on Hidden Variables." So did you want to say that my "model" requires hidden variables, or that it excludes hidden variables (as later you say that I "reject non-locality, AND Hidden Variables in a Local theory")? If, however, you believe my "model" requires hidden variables, does it mean this makes the "model" unacceptable?

So if you keep offering me such crosswords, I'll have to ignore them, sorry. It may well be that you have some interesting thoughts, but obscurity of your texts protects them too well.

What part is reductionistic?! Here's a hint... the part I put IN BOLD in the quote. It's really not my fault that forums, or language are not your forte.

DaTario

Feb20-10, 11:00 PM

Regarding the OP, I would say that technically I would follow Karl Popper, that has said:
No experimental evidence is really able to disprove a theoretical positioning.

This statement is part of his [B]demarcation criteria [\B].

Best Regards,

DaTario

zonde

Feb21-10, 10:32 AM

SpectraCat

Feb21-10, 12:30 PM

Ok .. that clearly wrong to me. How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light? Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation. They cannot. I assume they do not travel faster than light.

You did not answer my question .. how can particle exchange at sub-light speeds explain the observed statistical dependence of measurements on detectors with a space-like separation? It is not sufficient just to say "there could be a way, because you can't prove there isn't" .. that is not how physics works. You need to propose a physically-based explanation that explains the results from a local realistic perspective.

Note that this does not require any sort of free-sampling assumption to be true, because the results predicted by any local realistic theory for such experiments would have to be random, and whatever else you might believe about the sampling of the data, you have to concede that the chance that the coincidence measurements from these experiments could arise randomly are astronomical.
I don't accept this without a proof. So far this is just your word. Remember, existing experiments have not ruled out local theories.

Again, it is not incumbent on me to prove that they must be random, because that is what would be expected for uncorrelated photons based on Malus's law. In fact, uncorrelated basically *means* random in this context. Have you looked at the Mermin gedanken experiment? It is quite instructive in this regard.

Therefore since there is a good reason to expect for the local measurement results to be uncorrelated, AND there is no way for the particles to communicate when the detectors have a space-like separation, it is up to YOU to come up with a physically sensible reason for the observed statistical dependence of the coincidence measurements. Otherwise, all of your points reduce to pure sophistry ... which is basically Frame Dragger's point.

So you are going to have to do better than that to justify a statement like, "entanglement per se does not spell non-locality", because contrary to your claim, such a model of particle transfer between an entangled pair is demonstrably NOT a possibility.
Maybe so, but you have not demonstrated its impossibility. You see, your "demonstration" seems to rule out any local theory, not just my mental picture, whereas people agree that such experiments do not rule out all local theories. I just cannot understand what part of my very vague "local theory" makes it less able to explain these experiments than other local theories. It looks like it's your "demonstration" that is clearly wrong, as it seems to prove much more than you wanted.

See there you go with the sophistry again. You seem to be equating Zeilinger's statement that "LR has not been ruled out" with "LR is a reasonable and viable model". As has been pointed out to you time and again in this thread, this is misleading and wrong. Zeilinger is conceding that LR has not been ruled out BEYOND A SHADOW OF A DOUBT ... however what his experiments and others make clear is that there is a whole lot of work that needs to be done to come up with a LR theory that can explain the entire set of experimental results. Since no such theories are forthcoming, and it is very hard to see how they could possible be formulated, it is reasonable to take the position that LR is VERY PROBABLY not viable. We have a theory that is non-local and DOES explain all the results so far .. it is called Quantum Mechanics.

Finally, my "demonstration" did not rule out all possible local models, only those that require information transfer between the entangled particles at sub-light speeds.

Dmitry67

Feb21-10, 02:50 PM

Sorry, missed too many pages.
So what is consensus?
Is it ruled out or not?
Do you have a good definition of "realism"/"real"?

ThomasT

Feb21-10, 04:23 PM

Again, I just see some statements, but reasoning or references are missing.Ok, I'll run the latest by you again. Let me know any statements that aren't clear (and I'll elaborate and/or rephrase) or that you don't agree with. Any critical feedback is appreciated.

Phrase 1: The designs of entanglement experiments contradict Bell locality.

Bell locality entails that P(A,B) = P(A) P(B)

P(A,B) = P(A) P(B) means that events A and B are statistically independent.

Entanglement experiments are designed to produce statistically dependent events (via the emission and data matching processes).

So, the designs of entanglement experiments contradict Bell locality, and vice versa.

-----------------------

Phrase 2: There are loopholes in those (entanglement) experiments.

This just means that there are technical problems associated with Bell tests (eg., the production of entangled disturbances, detection efficiency, data matching/coincidence counting, etc.) -- and, of course, these technical problems might affect the results.

However, it follows from Phrase 1 that no Bell local formulation can ever be in total agreement with the results of any entanglement experiment, whether the experiment is loophole free or not.

-----------------------

To elaborate, Bell's formulation is supposed to represent local common cause via the hidden variable λ and its probability distribution ρ(λ).

Additionally, and most importantly, Bell's formulation is supposed to represent locality via the representation of independence (factorability of the joint probability) between A and B.

The problem is that A and B are not independent due to the data matching process (a trackable local process).

So, Bell's assumption that any LHV formulation of an entangled state must conform to his ansatz is incorrect. In fact, no LHV formulation of an entangled state can possibly conform to his ansatz.

Thus, Bell tests involving Bell inequalities based on Bell's ansatz are not a test of local realism or a demonstration of nonlocality.

Further, we can reasonably suppose that the correlations have underlying local causes due to the fact that the data matching process is based on the assumption that the relationship (the entanglement) between the separately analyzed disturbances is produced at emission (or via some other local common cause).

SpectraCat

Feb21-10, 05:13 PM

Ok, I'll run the latest by you again. Let me know any statements that aren't clear (and I'll elaborate and/or rephrase) or that you don't agree with. Any critical feedback is appreciated.

Phrase 1: The designs of entanglement experiments contradict Bell locality.

Bell locality entails that P(A,B) = P(A) P(B)

P(A,B) = P(A) P(B) means that events A and B are statistically independent.

Entanglement experiments are designed to produce statistically dependent events (via the emission and data matching processes).

So, the designs of entanglement experiments contradict Bell locality, and vice versa.

No, this is not correct in my opinion, because the experiments allow for the possibility that the results will be observed to be statistically independent. That is what the coincidence counting is all about. If the coincidence measurements showed that the results at detectors A and B were not correlated, then the Bell inequality would not be violated, in which case we would conclude that the results were statistically independent.

To state it another way, how could the experiments possibly test non-locality unless they allow for the possibility of non-locality? They already *inherently* allow for the possibility of locality, because that is what the experiment would show if there were no correlation of the supposedly entangled photons. If that had been observed, then QM would have been dealt a serious blow ... but the correlations were observed, which was taken to be evidence for non-locality. I definitely don't see the tautological reasoning that you are claiming/implying exists.

Phrase 2: There are loopholes in those (entanglement) experiments.

This just means that there are technical problems associated with Bell tests (eg., the production of entangled disturbances, detection efficiency, data matching/coincidence counting, etc.) -- and, of course, these technical problems might affect the results.

However, it follows from Phrase 1 that no Bell local formulation can ever be in total agreement with the results of any entanglement experiment, whether the experiment is loophole free or not.

Again, this seems wrong ... I think it amounts to the statement that "no entanglement experiment can ever show that a single set of results are simultaneously local and non-local", which is of course true, but irrelevant to anything.

To elaborate, Bell's formulation is supposed to represent local common cause via the hidden variable λ and its probability distribution ρ(λ).

Additionally, and most importantly, Bell's formulation is supposed to represent locality via the representation of independence (factorability of the joint probability) between A and B.

The problem is that A and B are not independent due to the data matching process (a trackable local process).

Ok, I don't get this last sentence at all. The data matching process (I assume you mean coincidence counting here) does not in any way imply statistical dependence between A and B as far as I can see. One could run the same experiments with separate, randomly-polarized sources, and there would be no observed correlation between the measurement sets at A and B, so the coincidence counting would conclude that the two sets are statistically independent, right? Am I missing something here?

So, Bell's assumption that any LHV formulation of an entangled state must conform to his ansatz is incorrect. In fact, no LHV formulation of an entangled state can possibly conform to his ansatz.

I am not sure how to parse this, and I definitely don't see how it follows from the previous arguments (even if I agreed those were correct). I think it would be useful if you could re-state it in the context of the Mermin gedanken experiment. I would also like a definition or at least an example of an "LHV formulation of an entangled state".

Further, we can reasonably suppose that the correlations have underlying local causes due to the fact that the data matching process is based on the assumption that the relationship (the entanglement) between the separately analyzed disturbances is produced at emission (or via some other local common cause).

Yes, it is assumed that the entanglement is typically created by a "local common cause", since parametric down conversion involves "splitting" of a single photon in a birefringent crystal. However, the rest of your statements don't follow from that, for the reasons I have outlined above. The only assumption made about the data sets at A & B involves the travel times of the photons, in that only a certain subset of detection events at A and B satisfy the criterion of coincidence. The experimenters are always quite careful about this when defining what "coincident detection" means in the context of their experiments. Essentially, what you seem to be saying is that the entangled photons could have received "instruction sets" controlling their measurement results, and this is *exactly* what the Bell theorem and the Mermin gedanken show is impossible.

akhmeteli

Feb21-10, 05:52 PM

You did not answer my question .. how can particle exchange at sub-light speeds explain the observed statistical dependence of measurements on detectors with a space-like separation?

I strongly disagree with this statement. The only question you asked in the previous post was "How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light?", and I answered that the particles do not carry information faster than the speed of light. And then I questioned your statement "Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation." as unsubstantiated, which it is. So I answered your question.

It is not sufficient just to say "there could be a way, because you can't prove there isn't" .. that is not how physics works. You need to propose a physically-based explanation that explains the results from a local realistic perspective.

OK, then, let me answer the question of your latest post "how can particle exchange at sub-light speeds explain the observed statistical dependence of measurements on detectors with a space-like separation?" and try to offer physical mechanisms.

Do you really think local theories cannot account for "statistical dependence of results measured at detectors with a spacelike separation"? What they cannot account for, is correlations violating the Bell inequalities. As for "physically based explanation", I can offer two things.

First is the mechanism offered by others (here I quote one of my earlier posts): "QTP-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post http://www.physicsforums.com/showpost.php?p=1825523&postcount=90."

Second, let me discuss a possible mechanism within my "model": Imagine that photons are only detected if their polarization is close to that measured by the detector (say, vertical), and the anticorrelation within pairs of such photons is caused by their common past. Later photons in such pairs, if undetected earlier, can change their polarisation through slow exchange of some particles (or interacting with couples of such particles having common past). If the detector measures a polarization different from vertical, photons from other pairs, having the relevant polarization, get detected. I explicitely use the detection loophole here to explain the statistical dependence by a local model (so I reject fair sampling here). Again, I am not saying that my "model" reflects reality, I am using it just as an instrument suggesting that entanglement per se does not spell nonlocality.

Again, it is not incumbent on me to prove that they must be random, because that is what would be expected for uncorrelated photons based on Malus's law. In fact, uncorrelated basically *means* random in this context. Have you looked at the Mermin gedanken experiment? It is quite instructive in this regard.

Yes, it is incumbent on you to prove that they must be random - I am under no obligation to believe you on your word. You did not mention Malus law in your previous post. However, as I wrote earlier, it is my understanding that Malus law is pretty much a consequence or an equivalent of the projection postulate for photons, and as such is in contradiction with unitary evolution, as I argued earlier. So Malus law may be a great approximation, but it is just an approximation. I fully accept unitary evolution and believe that Malus law can be derived as an approximation from unitary evolution, but not when it is pushed to the limits and pretty much equals nonlocality, same as the projection postulate. Of course, nobody cares what I believe or disbelieve, but it is pretty well known that projection postulate (or collapse) contradicts unitary evolution.

Therefore since there is a good reason to expect for the local measurement results to be uncorrelated, AND there is no way for the particles to communicate when the detectors have a space-like separation, it is up to YOU to come up with a physically sensible reason for the observed statistical dependence of the coincidence measurements. Otherwise, all of your points reduce to pure sophistry ... which is basically Frame Dragger's point.

I explained why I see no good reason to expect for the local measurement results to be uncorrelated, and in this post I explained (using reference to other people's work in http://www.physicsforums.com/showpost.php?p=1825523&postcount=90) how unitary evolution of quantum field theory (describing many particles) can be a disguise of local partial differential equations.

See there you go with the sophistry again. You seem to be equating Zeilinger's statement that "LR has not been ruled out" with "LR is a reasonable and viable model". As has been pointed out to you time and again in this thread, this is misleading and wrong. Zeilinger is conceding that LR has not been ruled out BEYOND A SHADOW OF A DOUBT ... however what his experiments and others make clear is that there is a whole lot of work that needs to be done to come up with a LR theory that can explain the entire set of experimental results. Since no such theories are forthcoming, and it is very hard to see how they could possible be formulated, it is reasonable to take the position that LR is VERY PROBABLY not viable. We have a theory that is non-local and DOES explain all the results so far .. it is called Quantum Mechanics.

I am not responsible for your perceptions. I may "seem to be equating" Zeilinger's statement with something else, but I am not "equating" them. The title of the thread speaks for itself. I'm saying (among other things) the following:

1) local realism has not been ruled out by experiments;
2) the previous statement is the mainstream.
3) the proof of the Bell theorem uses contradictory assumptions of unitary evolution and projection postulate, therefore, local realism has not been ruled theoretically either.

As for "probability" and "plausibility" of local realism, this issue is certainly very important, but secondary, because if local realism were ruled out, this issue would also be unambiguously solved.

I believe "plausibility" is a matter of opinion. Zeilinger seems to believe local realism is implausible, you agree with him, I may disagree, but again, who cares about my opinion? Let me just repeat that elimination of local realism is an extremely radical idea, so it requires a most solid proof. There is no such proof so far.

Finally, my "demonstration" did not rule out all possible local models, only those that require information transfer between the entangled particles at sub-light speeds.

Could you explain where you used "information transfer between the entangled particles at sub-light speeds" in your "demonstration"? I fail to find this place.

SpectraCat

Feb21-10, 07:55 PM

I strongly disagree with this statement. The only question you asked in the previous post was "How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light?", and I answered that the particles do not carry information faster than the speed of light. And then I questioned your statement "Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation." as unsubstantiated, which it is. So I answered your question.

It is not unsubstantiated, it is shown by Bell's theorem, and by Mermin's gedanken experiment. The latter case shows that it is not possible for "instruction sets" which explain how particles are supposed to register on detectors to be carried by those particles. Therefore, if the "information" that leads to the cannot carried with the particles themselves, and it cannot be exchanged by the entangled particles at the time of detection (since the detectors have a spacelike separation), then it cannot exist.

OK, then, let me answer the question of your latest post "how can particle exchange at sub-light speeds explain the observed statistical dependence of measurements on detectors with a space-like separation?" and try to offer physical mechanisms.

Do you really think local theories cannot account for "statistical dependence of results measured at detectors with a spacelike separation"? What they cannot account for, is correlations violating the Bell inequalities.

Of course that is what I meant, since that is the context of our current discussion. If you build the correlation into the source, it will be there at the detector, but that is precisely what CANNOT be happening with quantum entanglement, as demonstrated (again) by Bell's theorem and the Mermin gedanken.

As for "physically based explanation", I can offer two things.

First is the mechanism offered by others (here I quote one of my earlier posts): "QTP-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post http://www.physicsforums.com/showpost.php?p=1825523&postcount=90."

I looked at that post, and frankly I do not have the time to absorb and digest all the math .. I don't know what QTP means, and I am not intimately familiar with the mathematics of QFT, which apparently is necessary to understand what is referred to in that post.

Second, let me discuss a possible mechanism within my "model": Imagine that photons are only detected if their polarization is close to that measured by the detector (say, vertical), and the anticorrelation within pairs of such photons is caused by their common past.

I don't think it is physically reasonable to "imagine" that, because of Malus's law, but ok, I'll grant it for the purposes of this discussion.

Later photons in such pairs, if undetected earlier, can change their polarisation through slow exchange of some particles (or interacting with couples of such particles having common past).

I have no idea what the above statement refers to ... it makes no sense at all. What is "a later photon from such a pair", and what does the phrase "undetected earlier" mean? I am sorry but I need a lot more context and detail to begin to parse that.

If the detector measures a polarization different from vertical, photons from other pairs, having the relevant polarization, get detected. I explicitely use the detection loophole here to explain the statistical dependence by a local model (so I reject fair sampling here). Again, I am not saying that my "model" reflects reality, I am using it just as an instrument suggesting that entanglement per se does not spell nonlocality.

It's fine for you to use the detection loophole, but you have completely lost me at this point. What other pairs? Where is the space-like separation between the detectors and how is it overcome? You also seem to be indicating that there is some preferred direction of detection .. where is the basis for that?

Yes, it is incumbent on you to prove that they must be random - I am under no obligation to believe you on your word. You did not mention Malus law in your previous post. However, as I wrote earlier, it is my understanding that Malus law is pretty much a consequence or an equivalent of the projection postulate for photons, and as such is in contradiction with unitary evolution, as I argued earlier. So Malus law may be a great approximation, but it is just an approximation. I fully accept unitary evolution and believe that Malus law can be derived as an approximation from unitary evolution, but not when it is pushed to the limits and pretty much equals nonlocality, same as the projection postulate. Of course, nobody cares what I believe or disbelieve, but it is pretty well known that projection postulate (or collapse) contradicts unitary evolution.

I didn't ask you to believe me on my word, and I didn't mention Malus's law before because I didn't think I had to, since it has already come up in this thread. Malus's law has been extensively tested and never shown to be incorrect. So now you are not just questioning well accepted physical theorems, you are going after laws as well. Go for it!

I explained why I see no good reason to expect for the local measurement results to be uncorrelated, and in this post I explained (using reference to other people's work in http://www.physicsforums.com/showpost.php?p=1825523&postcount=90) how unitary evolution of quantum field theory (describing many particles) can be a disguise of local partial differential equations.

Unfortunately I can't understand the details of that post, as I already mentioned. However, even if I accepted its content, I am not sure why it is relevant to this discussion ... and earlier you said "nonlinear" PDE's, only here do you mention that they are local. Can you please break down the physical significance of this statement in the current context, or link to a post where you described it previously?

I am not responsible for your perceptions. I may "seem to be equating" Zeilinger's statement with something else, but I am not "equating" them. The title of the thread speaks for itself. I'm saying (among other things) the following:

1) local realism has not been ruled out by experiments;
2) the previous statement is the mainstream.
3) the proof of the Bell theorem uses contradictory assumptions of unitary evolution and projection postulate, therefore, local realism has not been ruled theoretically either.

Ok, so your point 3 above is really the only thing to take issue with. I confess I have not really spent much time trying to understand it's significance. I will try to do that and post when I have something more to say about it.

As for "probability" and "plausibility" of local realism, this issue is certainly very important, but secondary, because if local realism were ruled out, this issue would also be unambiguously solved.

I believe "plausibility" is a matter of opinion. Zeilinger seems to believe local realism is implausible, you agree with him, I may disagree, but again, who cares about my opinion? Let me just repeat that elimination of local realism is an extremely radical idea, so it requires a most solid proof. There is no such proof so far.

You say it is radical .. I don't agree, but I guess you are in good company .. Einstein couldn't accept it either. Q.M. predicts non-local correlations in a manner that is consistent with all available experimental evidence. Furthermore, Q.M. is also consistent with all classical results as well .. and classical systems are where local realism really makes sense, and as far as I know, there are no classical systems that are inconsistent with LR. So perhaps LR is a consequence of the Bohr correspondence principle somehow, and like CM is contained and explained within the context of Q.M. in the large mass/high quantum number limit.

Could you explain where you used "information transfer between the entangled particles at sub-light speeds" in your "demonstration"? I fail to find this place.

The post in question was entirely about why the experimental closing of the "locality loophole" showed that the entangled pairs could not be exchanging sub-light particles, as you had hypothesized. I didn't use or introduce that concept .. YOU did. I explained/argued why it cannot be used to explain the experimental results under discussion. You chose not to accept my explanation/argument, and I am still trying to understand why.

zonde

Feb22-10, 03:48 AM

The latter case [Mermin's gedanken experiment] shows that it is not possible for "instruction sets" which explain how particles are supposed to register on detectors to be carried by those particles. Therefore, if the "information" that leads to the cannot carried with the particles themselves, and it cannot be exchanged by the entangled particles at the time of detection (since the detectors have a spacelike separation), then it cannot exist.
Quick googling about Mermin's gedanken experiment led me to two links.
One is simple explanation of Mermin's experiment:
David Mermin’s EPR gedanken experiment (http://public.fh-wolfenbuettel.de/~ruediger/lehre/EPRapplet/EPRappletDescription.pdf)
Second shows how Mermin’s gedanken experiment fails if unfair sampling is used:
Quantum Mechanics and its Paradox: A Realistic Solution to Mermin's EPR Apparatus. (http://www.newtonphysics.on.ca/uncertainty/index.html)
In short this second link shows that required probabilities appear if one chooses instruction sets RRG;RGR;GRR and discards every second detection of R.
It can be easily made symmetrical in respect to R/G if we additionally take instruction sets GGR;GRG;RGG but for those instruction sets we discard every second detection of G.

So this Mermin’s gedanken experiment is no argument against local realism + hypothetical unfair sampling.

Frame Dragger

Feb22-10, 03:52 AM

Of course that is what I meant, since that is the context of our current discussion.

Watch out, Ahkmeteli has 'issues' with context... among other things. :smile:

Eye_in_the_Sky

Feb22-10, 04:45 AM

Can you tell where do you yourself see the problem?... Thank you zonde ... for helping to open me Eye.
____________________________________________
Let's say do you see Proposition 1 (locality Λ PC Λ CF → local determinism) as not valid? Or is it valid but wrongly applied to physical situation? ... or neither.I see the proposition as valid [... modulo other premises (e.g. free-choice of Alice and Bob)], and that it can be correctly applied to the "Bell argument" in terms of the joint-probability-function of the particle pair. (For anyone interested, the "Bell argument" is repeated at the end of this post.)

________________
Do you see any problems in this statement?
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."It is unclear to me what you are getting at here. Nonetheless, I would prefer to write the statement in this way (with no mention of QM):

[i]If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then measurement of σ2∙a must yield the value -1; and vice versa.

This statement can be said to be a theorem of Quantum Mechanics. Yet, it makes an infinity of assertions, only one of which, in any "real-world" instantiation, can ever be factual (the remaining ones then being counterfactual).

... Zonde, is this what you are getting at?
____________________________________________

The "Bell argument" is as follows (originally included as part of post #170 (http://www.physicsforums.com/showthread.php?p=2580757#post2580757) of this thread):

Consider a pair of spin one-half particles formed somehow in the singlet spin state and moving freely in opposite directions. Measurements can be made, say by Stem-Gerlach magnets, on selected components of the spins σ1 and σ2. If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa. Now we make the hypothesis [2], and it seems one at least worth considering, that if the two measurements are made at places remote from one another the orientation of one magnet does not influence the result obtained with the other. Since we can predict in advance the result of measuring any chosen component of σ2, by previously measuring the same component of σ1, it follows that the result of any such measurement must actually be predetermined.
----------
[2] "But on one supposition we should, in my opinion, absolutely hold fast: the real factual situation of the system S2 is independent of what is done with the system S1, which is spatially separated from the former." A. EINSTEIN in Albert Einstein, Philosopher Scientist, (Edited by P. A. SCHILP) p. 85, Library of Living Philosophers, Evanston, Illinois (1949).

Eye_in_the_Sky

Feb22-10, 04:58 AM

... It seems to me I understand what you wrote, but I don't quite see from your post where my misconception is. Could you please explain?

Let's try a different approach.

Please answer the two questions below.

1) Do you believe you understand the concept expressed by the following statement?

Alice and Bob's outcomes are governed by local determinism.

2) Do you consider the following statement to be true?

On the basis of the single assumption of "local determinism of Alice and Bob's outcomes", one can derive a Bell inequality.

Think about it carefully. Take your time.

Eye_in_the_Sky

Feb22-10, 05:02 AM

... So maybe you mean this:

Regarding the proposition

BL Λ PC Λ CF → D ,

where

BL ≡ Bell Locality (mathematical formulation in terms of probabilities) ,

it will be found, upon scrutiny, that BL is not in fact an expression of local causality. Rather, it is merely an expression of statistical independence.

Is that what you mean?Yes.

Okay. As soon as I am able, I will post something on Bell's "Local Causality Criterion", and put it up for evaluation in this thread. The two of us can discuss it, along with anyone else who is interested.
________________________
[EDIT: I just posted it a few posts down post#239 (http://www.physicsforums.com/showthread.php?p=2593824#post2593824)]

SpectraCat

Feb22-10, 06:51 AM

Quick googling about Mermin's gedanken experiment led me to two links.
One is simple explanation of Mermin's experiment:
David Mermin’s EPR gedanken experiment (http://public.fh-wolfenbuettel.de/~ruediger/lehre/EPRapplet/EPRappletDescription.pdf)
Second shows how Mermin’s gedanken experiment fails if unfair sampling is used:
Quantum Mechanics and its Paradox: A Realistic Solution to Mermin's EPR Apparatus. (http://www.newtonphysics.on.ca/uncertainty/index.html)
In short this second link shows that required probabilities appear if one chooses instruction sets RRG;RGR;GRR and discards every second detection of R.
It can be easily made symmetrical in respect to R/G if we additionally take instruction sets GGR;GRG;RGG but for those instruction sets we discard every second detection of G.

So this Mermin’s gedanken experiment is no argument against local realism + hypothetical unfair sampling.

I don't trust that Marmet link, because it seems he does not understand the Mermin experiment, as evidenced by this quote:

"However, one finds then that the relevant feature b is not satisfied now, because statistically, lights will flash the same color 5/9 (0.5555) of the time, instead of 0.50 that should be obtained. Bell's inequality theorem has been applied here. Since the denominator, (that is the possible number of settings in the calculation of probability), is an odd number (number 9) and the numerator is an integer, it is absolutely impossible to obtain this way, the exact fraction 0.5 required by the quantum mechanical calculation."

In the Mermin, when the polarizer settings are the same, the lights flash the same color all of the the time, which accounts for 3/9 of the cases. When the polarizer settings are different (the remaining 6/9 of cases), then the lights flash the same color 1/4 of the time. So, the total number of times the lights flash the same is:

1/3 + 1/4*2/3 = 2/6 + 1/6 = 3/6 = 1/2

So unless there is some hidden logic that Marmet doesn't explain .. I can't see how his quote can be correct.

zonde

Feb22-10, 07:00 AM

I see the proposition as valid [... modulo other premises (e.g. free-choice of Alice and Bob)], and that it can be correctly applied to the "Bell argument" in terms of the joint-probability-function of the particle pair.
Let's say I too see this proposition as valid but not exhaustive (I would feel more comfortable if I somehow could make sure that all the abstract terms in this proposition have unambiguous meaning).
I would say that PC is not a requirement for local determinism. So we can say: locality Λ CF → local determinism. That's because PC is certain arrangement of things that applies to one situation but doesn't apply to other.

It is unclear to me what you are getting at here. Nonetheless, I would prefer to write the statement in this way (with no mention of QM):

If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then measurement of σ2∙a must yield the value -1; and vice versa.

This statement can be said to be a theorem of Quantum Mechanics. Yet, it makes an infinity of assertions, only one of which, in any "real-world" instantiation, can ever be factual (the remaining ones then being counterfactual).

... Zonde, is this what you are getting at?
I am afraid what I am getting at is closer to the ground.
What I don't like about this theorem of QM is that it is placed as restriction on all possible LR theories even when this theorem is not experimentally verified.
Let's say we can formulate LR theory that says:
a) If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then measurement of σ2∙a must yield the value -1 or no value at all at least half the time.
b) If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then low efficiency measurement of σ2∙a must yield the value -1 with very high probability and value +1 with very low probability or no value at all. But as measurement efficiency increases relative probability of +1 value increases rapidly.

Obviously they are not covered by Bell's argument because they do not agree with this theorem of QM. And still they would not contradict experimental evidence we have today (well "a)" contradicts claims that single detector efficiency can exceed 50% but not "b)").

zonde

Feb22-10, 07:11 AM

I don't trust that Marmet link, because it seems he does not understand the Mermin experiment, as evidenced by this quote:

"However, one finds then that the relevant feature b is not satisfied now, because statistically, lights will flash the same color 5/9 (0.5555) of the time, instead of 0.50 that should be obtained. Bell's inequality theorem has been applied here. Since the denominator, (that is the possible number of settings in the calculation of probability), is an odd number (number 9) and the numerator is an integer, it is absolutely impossible to obtain this way, the exact fraction 0.5 required by the quantum mechanical calculation."

In the Mermin, when the polarizer settings are the same, the lights flash the same color all of the the time, which accounts for 3/9 of the cases. When the polarizer settings are different (the remaining 6/9 of cases), then the lights flash the same color 1/4 of the time. So, the total number of times the lights flash the same is:

1/3 + 1/4*2/3 = 2/6 + 1/6 = 3/6 = 1/2

So unless there is some hidden logic that Marmet doesn't explain .. I can't see how his quote can be correct.
This "the lights flash the same color 1/4 of the time" for different polarizer settings is prediction of QM but Mermin's realistic model (excluding two instruction sets - GGG;RRR) predicts 5/9 - 3/9 for the same settings and 2/9 for different settings. That can be seen in the first link I gave.

But you don't have to trust this Marmet link. I verified this claim that not detecting every second R gives required probabilities. I can present you my calculations. They are not too complicated.

yoda jedi

Feb22-10, 09:24 AM

local determinism .

Thats all.
Its determinism, no realism.
Just a "MISCONCEPTION"

Suarez
......refutation of nonlocal determinism.....

Groblacher
......a world that is not completely deterministic.....

Spekkens
......Bell’s argument is only necessary to rule out locality......

Gisin
......Hence, all violations of Bell's inequality should be interpreted as a demonstration of
nonlocality........

Hall
......the term ‘local realism’ be replaced by ‘local determinism’.....

and so on......

DrChinese

Feb22-10, 04:17 PM

1. This "the lights flash the same color 1/4 of the time" for different polarizer settings is prediction of QM but Mermin's realistic model (excluding two instruction sets - GGG;RRR) predicts 5/9 - 3/9 for the same settings and 2/9 for different settings. That can be seen in the first link I gave.

2. But you don't have to trust this Marmet link. I verified this claim that not detecting every second R gives required probabilities. I can present you my calculations. They are not too complicated.

1. The correct value for LR is >=2/6 for different settings, not 2/9.
The QM prediction is =.25.

2. The Marmet sample yields a value in excess of .33 and does not come close to .25. Of course, there are lots of other problems with the Marmet hypothesis.

ThomasT

Feb22-10, 06:15 PM

No, this is not correct in my opinion, because the experiments allow for the possibility that the results will be observed to be statistically independent.If an experiment is designed to produce entanglement, then that entails (via the execution of that design) a statistical dependency between the data sets, A and B.

That is what the coincidence counting is all about.Coincidence counting is about matching the separate data streams wrt some criterion or criteria, and then counting the coincidences.

If the coincidence measurements showed that the results at detectors A and B were not correlated, then the Bell inequality would not be violated, in which case we would conclude that the results were statistically independent.The correlation is between the angular difference |a-b| (or Theta, where a and b are the settings of the analyzers at A and B), and the rate of coincidental detection.

To get the QM-predicted, cos2Theta, angular dependency the experimental design has to involve and the execution has to produce a statistical dependency between the separately accumulated data sets.

To state it another way, how could the experiments possibly test non-locality unless they allow for the possibility of non-locality?That's the point of my line of thinking on this. Bell tests don't test nonlocality.

They already *inherently* allow for the possibility of locality, because that is what the experiment would show if there were no correlation of the supposedly entangled photons.There is no correlation between the supposedly entangled photons -- except for two settings, and at these settings, Theta = 0 and
Theta = pi/2, an LHV formulation can also show perfect correlation and anticorrelation, respectively. For all other values of Theta there's absolutely no correlation between A and B.

I'll continue with this reply when I get time.

akhmeteli

Feb22-10, 11:42 PM

1) Do you believe you understand the concept expressed by the following statement?

Alice and Bob's outcomes are governed by local determinism.

I think so

2) Do you consider the following statement to be true?

On the basis of the single assumption of "local determinism of Alice and Bob's outcomes", one can derive a Bell inequality.

I think so

Eye_in_the_Sky

Feb23-10, 02:58 AM

I think so

I think soOkay. My answers are the same.

How about this next statement, would you say that it is correct?

The assumption of "local determinism of Alice and Bob's outcomes" is independent of any assumptions concerning the truth or internal consistency of Quantum Mechanics.

Eye_in_the_Sky

Feb23-10, 03:14 AM

click here → diagram (http://www.physicsforums.com/attachment.php?attachmentid=23884&stc=1&d=1266916592) ← click here

"A theory will be said to be locally causal if the probabilities attached to values of local beables in a space-time region 1 are unaltered by specification of values of local beables in a space-like separated region 2, when what happens in the backward light cone of 1 is already sufficiently specified, for example by a full specification of local beables in a spacetime region 3."

"It is important that region 3 completely shields off from 1 the overlap of the backward light cones of 1 and 2. Otherwise the traces in region 2 of causes of events in 1 could well supplement whatever else was being used for calculating probabilities about 1. The hypothesis is that any such information about 2 becomes redundant when 3 is specified completely."

akhmeteli

Feb23-10, 03:32 AM

It is not unsubstantiated, it is shown by Bell's theorem, and by Mermin's gedanken experiment. The latter case shows that it is not possible for "instruction sets" which explain how particles are supposed to register on detectors to be carried by those particles. Therefore, if the "information" that leads to the cannot carried with the particles themselves, and it cannot be exchanged by the entangled particles at the time of detection (since the detectors have a spacelike separation), then it cannot exist.

Look, this is some substantiation "the morning after". Frame Grabber ridicules me for inability or reluctance to guess what he (or she) implied from the context. But when I don't see any explicit arguments, I cannot address them. Am I really supposed to criticize something "what I think" you or Frame Grabber mean? And if I cannot criticize it, am I supposed to agree with you just because I believe you on your word? So until you give some arguments, what you say is unsubstantiated.

OK, now you offered something that at least looks like some substantiation, and I can discuss it. Let us consider what you offered. Mermin's gedanken experiment seems to be just an illustration of the Bell theorem, so it seems irrelevant. In any case, it is a gedanken experiment, not a real one. So if it is any argument, it is only a theoretical one, not experimental. The same is true about the Bell theorem. I concede that local realism implies the Bell inequalities. On the other hand, you seem to be aware that no violations of the genuine Bell inequalities have been demonstrated. Therefore, the Bell's theorem's conclusion that the Bell inequalities can be violated in quantum theory has no experimental confirmation. Therefore, your statement that entanglement cannot be explained by exchange of "slow" particles has no experimental confirmation. Does it have theoretical confirmation? You offer the Bell theorem as the theoretical confirmation. However, I argue that *) the proof of the Bell theorem requires the use of two contradictory assumptions: unitary evolution (UE) and the projection postulate. I started this thread with this statement and supported it with the reversibility argument (another, more standard argument, is that unitary evolution cannot destroy a superposition, whereas the projection postulate does just that). I have yet to see a refutation of this statement *) - it's actually a rephrase of the relatively well-known measurement problem in quantum mechanics. It is difficult to rely on a consequence of two contradictory assumptions. Therefore, your statement has no experimental basis, and its theoretical confirmation is dubious.

Of course that is what I meant, since that is the context of our current discussion. If you build the correlation into the source, it will be there at the detector, but that is precisely what CANNOT be happening with quantum entanglement, as demonstrated (again) by Bell's theorem and the Mermin gedanken.

I can only repeat the above comment, both with respect to "reading from concept" and to "confirmation" by the Bell theorem.

I looked at that post, and frankly I do not have the time to absorb and digest all the math ..

I understand.

I don't know what QTP means,

My fault - I meant "QFT" - quantum field theory. Sorry.

and I am not intimately familiar with the mathematics of QFT, which apparently is necessary to understand what is referred to in that post.

I see. Maybe I'll try to write a longer comment on that mathematical result later.

I don't think it is physically reasonable to "imagine" that, because of Malus's law, but ok, I'll grant it for the purposes of this discussion.

I have no idea what the above statement refers to ... it makes no sense at all. What is "a later photon from such a pair", and what does the phrase "undetected earlier" mean? I am sorry but I need a lot more context and detail to begin to parse that.

It's fine for you to use the detection loophole, but you have completely lost me at this point. What other pairs? Where is the space-like separation between the detectors and how is it overcome? You also seem to be indicating that there is some preferred direction of detection .. where is the basis for that?

Never mind. As I said, that was just some illustration, and it fulfilled what it was designed for, namely, pinpointed the source of our disagreement. So it looks like you keep referring to the Malus law, and I argue that it is in contradiction with UE.

I didn't ask you to believe me on my word, and I didn't mention Malus's law before because I didn't think I had to, since it has already come up in this thread. Malus's law has been extensively tested and never shown to be incorrect. So now you are not just questioning well accepted physical theorems, you are going after laws as well. Go for it!

Again, guessing from context is not my favorite pastime. So Malus law is used to calculate the correlations of the Bell theorem in quantum mechanics for photons, and it is my understanding that it is an equivalent or consequence of the projection postulate and therefore introduces nonlocality directly: indeed, we are supposed to believe that as soon as the polarization of one photon of the entangled pair is measured, the polarization of the other photon becomes determined immediately, whatever the spatial separation. You actually need no Bell theorem after that - nonlocality is already there. You reproach me for going after laws. I don't want to go after any laws, actually, I am pretty conservative. But if two laws contradict each other, as UE and PP do, you have no choice but to go after one of them. Can you really accuse me for not being able to calmly swallow two mutually contradictory statements? As for Malus law being extensively tested, I am not sure it could be tested for undetected photons, so I suspect you need something like fair sampling to deduce the Bell inequality violations from Malus law.

Unfortunately I can't understand the details of that post, as I already mentioned. However, even if I accepted its content, I am not sure why it is relevant to this discussion ... and earlier you said "nonlinear" PDE's, only here do you mention that they are local. Can you please break down the physical significance of this statement in the current context, or link to a post where you described it previously?

I don't have time right now to explain how it's relevant or find references to nightlight's posts. I'll try to do that a day or two later. As for me adding the word "local", it does not change anything, as the relevant partial differential equations in 3+1 dimensions are inherently local, the same way as, say, the Maxwell equations are local. I added this word "local" just to emphasize how this is relevant.

Ok, so your point 3 above is really the only thing to take issue with. I confess I have not really spent much time trying to understand it's significance. I will try to do that and post when I have something more to say about it.

I am glad the area where we disagree has narrowed significantly.

You say it is radical .. I don't agree, but I guess you are in good company .. Einstein couldn't accept it either. Q.M. predicts non-local correlations in a manner that is consistent with all available experimental evidence. Furthermore, Q.M. is also consistent with all classical results as well .. and classical systems are where local realism really makes sense, and as far as I know, there are no classical systems that are inconsistent with LR. So perhaps LR is a consequence of the Bohr correspondence principle somehow, and like CM is contained and explained within the context of Q.M. in the large mass/high quantum number limit.

Again, the problem is such key parts of standard quantum theory as UE and PP are inconsistent

The post in question was entirely about why the experimental closing of the "locality loophole" showed that the entangled pairs could not be exchanging sub-light particles, as you had hypothesized. I didn't use or introduce that concept .. YOU did. I explained/argued why it cannot be used to explain the experimental results under discussion. You chose not to accept my explanation/argument, and I am still trying to understand why.

So it turned out you implicitly used the Malus law, which, I believe, contradicts unitary evolution. That's why I am less than impressed by your explanation. And until you explicitly mentioned the Malus law, I was not even able to see any coherent argument. Again, I don't think guessing games are appropriate here.

akhmeteli

Feb23-10, 03:43 AM

Okay. My answers are the same.

How about this next statement, would you say that it is correct?

The assumption of "local determinism of Alice and Bob's outcomes" is independent of any assumptions concerning the truth or internal consistency of Quantum Mechanics.

I think I disagree with this statement. Indeed, if QM is true and internally consistent, then the Bell inequalities can indeed be violated, so local determinism is eliminated. Therefore the assumption of local determinism does not seem to be independent of the assumptions of truth and consistency of quantum mechanics.

Demystifier

Feb23-10, 04:10 AM

I think I disagree with this statement. Indeed, if QM is true and internally consistent, then the Bell inequalities can indeed be violated, so local determinism is eliminated. Therefore the assumption of local determinism does not seem to be independent of the assumptions of truth and consistency of quantum mechanics.
So basically, you believe that QM is wrong. Am I right?

Frame Dragger

Feb23-10, 05:16 AM

So basically, you believe that QM is wrong. Am I right?

You're right, but he likes to preach. Maybe he was raised by Jesuits? (or wolves) :smile:

Never trust someone who isn't willing to state their beliefs before wasting several pages with rhetorical nonsense; as if this is a game to be won. :grumpy:

zonde

Feb23-10, 06:25 AM

1. The correct value for LR is >=2/6 for different settings, not 2/9.
The QM prediction is =.25.
In Mermin’s model 5/9 you get from 1 for the same setting and 2/6 for different settings. With respective probabilities for the same settings - 1/3 and for different settings - 2/3 you have:
1*1/3+2/6*2/3=5/9
This is Mermin’s model.

2. The Marmet sample yields a value in excess of .33 and does not come close to .25. Of course, there are lots of other problems with the Marmet hypothesis.
Mermin's model propose value that exceeds 0.33.
Marmet sample with discarding every second R is more complicated.
For the same settings: match - 1/2, blank - 1/2
For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value.
That way Marmet model does not reproduce all required probabilities but anyways Mermin's inequality is proved not to hold for realistic experimental conditions.

SpectraCat

Feb23-10, 07:17 AM

In Mermin’s model 5/9 you get from 1 for the same setting and 2/6 for different settings. With respective probabilities for the same settings - 1/3 and for different settings - 2/3 you have:
1*1/3+2/6*2/3=5/9
This is Mermin’s model.

Right, and my problem (well, one of them) with the Marmet paper is that the phase I quoted previously was being used to describe the Apsect experiments .. Marmet was claiming that coincidence measurements would be observed 5/9 of the time there (which is wrong), and only using "the denominator is an odd integer" to justify his reasoning.

[QUOTE]
Mermin's model propose value that exceeds 0.33.
Marmet sample with discarding every second R is more complicated.
For the same settings: match - 1/2, blank - 1/2
For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value.
That way Marmet model does not reproduce all required probabilities but anyways Mermin's inequality is proved not to hold for realistic experimental conditions.

I don't agree that discarding every second R (or G) is any more realistic than assuming 100% efficiency. It implies a very strict ordering of events that has no basis in reality as far as I can tell. If you want to say that the detector misses half of the time when it is supposed to blink red, I can live with that, but the ordering should be random in my view.

I also don't understand how you got matching only half the time under your setup when the detector settings are the same. You seem to be neglecting the times when both detectors blink green, which are not attenuated in your model, and so the matching rate should be greater than 0.5. A similar comment also pertains to your model when the settings are different.

Finally, if we can assume random ordering of the detector "failures", then we are free to throw out all of the times when one of the lights doesn't blink. But of course now you are going to tell me that is just the free sampling assumption .. and it is. My point is that without a realistic physical model to understand why there should be (or even could be) a bias for the "missed" detection events, it seems most reasonable to assume they are random. Another point is that the randomness of missed detections could be tested in principle, by deliberately blocking one of the beams in a random fashion. If there is a bias is the "missed" events due to detector design, then there should be a measurable difference between sets of results where the beam is never blocked, and those where it is blocked randomly.

SpectraCat

Feb23-10, 07:44 AM

If an experiment is designed to produce entanglement, then that entails (via the execution of that design) a statistical dependency between the data sets, A and B.

No, by making such a statement, you are assuming that the experiment will be successful, and you are assuming that the QM definition of entanglement is correct. That is precisely what these experiments were designed to measure. If they had failed to produce entanglement, or if the QM predictions had been incorrect, then that would have been reflected in the experimental results (i.e. no statistical dependence would have been observed between A and B).

Coincidence counting is about matching the separate data streams wrt some criterion or criteria, and then counting the coincidences.

Yes ... that is how the statistical dependence or independence of the A and B sets is determined .. aren't we saying the same thing here?

The correlation is between the angular difference |a-b| (or Theta, where a and b are the settings of the analyzers at A and B), and the rate of coincidental detection.

Ok, I agree with that too ...

To get observe the QM-predicted, cos2Theta, angular dependency the experimental design has to involve and the execution has to produce reveal a statistical dependency between the separately accumulated data sets.

If you allow the change I made above, then I agree .. to say "get" and "produce" in the context above implies that the data is somehow being "cooked", and I don't agree with that. The QM prediction is either right or wrong, the experiment tests it. The experiment can either succeed or fail .. if it fails (i.e no violation is observed), then EITHER it was a poor experiment OR it was a good experiment and QM is wrong. If the experiment succeeds .. then it either supports the QM prediction, at least up to the ability of the experiment to test it, or there is some flaw in the experiment which leaves the result ambiguous (i.e. these loopholes we have been discussing elsewhere in the thread).

My point here is that the possibility of failure is inherent in these experimental designs, so in my view they are in no way biasing the set of possible results by their construction, as you seem to be saying. I still don't understand why you are making that claim.

There is no correlation between the supposedly entangled photons -- except for two settings, and at these settings, Theta = 0 and
Theta = pi/2, an LHV formulation can also show perfect correlation and anticorrelation, respectively. For all other values of Theta there's absolutely no correlation between A and B.

Ok, this just seems flat wrong. What do you mean there is "absolutely no correlation between A and B"? Do you think the results of the experiments is wrong? Do you think the predictions of Q.M. are wrong? Because they definitely measure/predict correlations at all values for the relative angle between the two detectors, with the possible exception of 45 degrees, where the results should appear random.

In any case, if correlations were not possible at all measurement angles, then there would be no way to formulate the Bell inequalities for these systems. Perhaps we are using different definitions of the term "correlation"?

I'll continue with this reply when I get time.

I look forward to reading it ...

DrChinese

Feb23-10, 08:45 AM

In Mermin’s model 5/9 you get from 1 for the same setting and 2/6 for different settings. With respective probabilities for the same settings - 1/3 and for different settings - 2/3 you have:
1*1/3+2/6*2/3=5/9
This is Mermin’s model.

Mermin's model propose value that exceeds 0.33.
Marmet sample with discarding every second R is more complicated.
For the same settings: match - 1/2, blank - 1/2
For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value.
That way Marmet model does not reproduce all required probabilities but anyways Mermin's inequality is proved not to hold for realistic experimental conditions.

Let's just talk about the different settings, which means a correlation rate of .33 or higher for the full universe. Marmet's model actually produces a HIGHER - not lower - value for the biased sample. I believe he simply made a mistake and got confused. At any rate, his model is NOT symmetric (as you noted in an earlier post) and cannot be made so. It does not reproduce Malus AND it would be easily detectable via experiment.

zonde

Feb23-10, 09:15 AM

Right, and my problem (well, one of them) with the Marmet paper is that the phase I quoted previously was being used to describe the Apsect experiments .. Marmet was claiming that coincidence measurements would be observed 5/9 of the time there (which is wrong), and only using "the denominator is an odd integer" to justify his reasoning.
Strange, I understand this sentence differently:
"However, one finds then that the relevant feature b is not satisfied now, because statistically [using any of Mermin's instruction sets except RRR and GGG], lights will flash the same color 5/9 (0.5555) of the time, instead of 0.50 that should be obtained [as predicted by QM and observed in experiment]."
I can agree that his argument about "the denominator is an odd integer" is sloppy. But then this is much better explained in brief description of Mermin's article that I gave in my first link.

I don't agree that discarding every second R (or G) is any more realistic than assuming 100% efficiency. It implies a very strict ordering of events that has no basis in reality as far as I can tell. If you want to say that the detector misses half of the time when it is supposed to blink red, I can live with that, but the ordering should be random in my view.
Ordering can be random that is no problem. It can statistically miss half of R detections.

I also don't understand how you got matching only half the time under your setup when the detector settings are the same. You seem to be neglecting the times when both detectors blink green, which are not attenuated in your model, and so the matching rate should be greater than 0.5. A similar comment also pertains to your model when the settings are different.
Let me explain.
Proposed model is considering only instruction sets RRG;RGR;GRR.
So for the same settings before considering misses we have 2/3 RR, 1/3 GG.
Now as we consider misses we have 1/6 R-, 1/6 -R, 1/6 --, 1/6 RR and 1/3 GG
and so there are 1/6+1/3=1/2 successful detections and 3/6=1/2 misses.

Finally, if we can assume random ordering of the detector "failures", then we are free to throw out all of the times when one of the lights doesn't blink. But of course now you are going to tell me that is just the free sampling assumption .. and it is. My point is that without a realistic physical model to understand why there should be (or even could be) a bias for the "missed" detection events, it seems most reasonable to assume they are random.
This realistic model that says why there should be unfair sampling is Bell inequalities.
That's how I see this. :smile:

Another point is that the randomness of missed detections could be tested in principle, by deliberately blocking one of the beams in a random fashion. If there is a bias is the "missed" events due to detector design, then there should be a measurable difference between sets of results where the beam is never blocked, and those where it is blocked randomly.
That can be modeled mathematically to see if there should be any difference.
Another a bit harder part is that you should work out QM prediction for that modified setup.

DrChinese

Feb23-10, 09:28 AM

This realistic model that says why there should be unfair sampling is Bell inequalities.
That's how I see this. :smile:

If the model hypothesis is consistent, then it can be accepted. The problem is that NONE of the model hypotheses are ever consistent. The physical explanation CANNOT be true. That is what I discovered about the De Raedt simulation, and so now I know how to apply to any LR model hypothesis.

Even ignoring this issue, the model is wrong. If you look at a dataset that is not hand picked, you will see this.

zonde

Feb23-10, 09:29 AM

Let's just talk about the different settings, which means a correlation rate of .33 or higher for the full universe. Marmet's model actually produces a HIGHER - not lower - value for the biased sample. I believe he simply made a mistake and got confused. At any rate, his model is NOT symmetric (as you noted in an earlier post) and cannot be made so. It does not reproduce Malus AND it would be easily detectable via experiment.
Where is my mistake in this then :confused::
"For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value."

But yes this model is not very useful apart from revealing shortcomings of Mermin's argument.

DrChinese

Feb23-10, 11:10 AM

1. But yes this model is not very useful apart from revealing shortcomings of Mermin's argument.

2. Where is my mistake in this then :confused::
"For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value."

1. Mermin's argument is essentially identical to Bell's. There is definitely nothing wrong with it.

2. I doubt we are applying the rules the same. Here is my sample run:

a. Must use RRG, RGR or GRR instruction sets.
b. For any observer (Alice or Bob), strike every other R.
c. Any run with at least one struck R means it is ignored.

Here is my run (and I always have Alice looking at the first, Bob for the second, noone for the third - the third is there only to prove realism is in place):

01 RRG Match
02 GRR Bob strikes
03 RRG Alice strikes
04 RGR
05 RRG Alice and Bob strike
06 GRR
07 GRR Bob strikes
08 RRG Match
09 RGR Alice strikes
10 GRR Bob strikes
11 RGR
12 RGR Alice strikes

2 matches, 3 nonmatches, so 40% match rate is greater than 33%. You can also pick a sample that is as low as 20% but in general I don't think it can be 25%.

Of course, the issue is that R is suppressed while G is not, a condition which does not occur in real life so this whole exercise is moot.

akhmeteli

Feb23-10, 11:33 AM

So basically, you believe that QM is wrong. Am I right?

Demystifier,

Let me first repeat my rationale and then formulate my conclusion and a short answer to your question, because without this rationale the answer may be misleading.

Some time ago I asked you about the status of the projection postulate in the de Broglie - Bohm interpretation, namely, if it is a precise law or an approximation. You answered:

Yes, it is an approximation. However, due to decoherence, this is an extremely good approximation. Essentially, this approximation is as good as the second law of thermodynamics is a good approximation.

My reasoning is as follows.

1) Standard quantum mechanics (SQM) includes both unitary evolution (UE) and the projection postulate (PP).

2) UE and PP directly contradict each other, as UE cannot provide irreversibility or destroy superposition, while PP does just that.

3) Therefore, I cannot accept both UE and PP and believe that one of them (namely, PP) is, strictly speaking, wrong.

4) Therefore, I do believe that SQM is, strictly speaking wrong.

Just two concluding comments.

First, it looks like what I am saying is consistent with what you are saying.

Second, whatever Frame Dragger says, I have not tried to hide my views and stated the same things from the very beginning of this thread.

DrChinese

Feb23-10, 11:40 AM

Where is my mistake in this then :confused::
"For different settings: match - 1/12, mismatch - 4/12, blank - 7/12
So the probability is actually 0.2 ( 1/(1+4) ) i.e. below required value."

After reconsidering, I see where you get the 20% from and I think I agree with that particular item after all. Please note that it is impossible, in this model, to get a GG match (which would be noticable).

I guess your idea would be to make this symmetric somehow, curious as to whether that is possible. Note that the hypothesis only works if you suppress the detection of matches. I think you will see pretty quick that if G cases are considered for striking, the stats go back to normal as there is no preference for striking matches any longer.

Frame Dragger

Feb23-10, 12:20 PM

Demystifier,

Let me first repeat my rationale and then formulate my conclusion... [not a shock]...

[leading to the inevitable]...Therefore, I do believe that SQM is, strictly speaking wrong.

You need to reiterate your case AGAIN to simply say that, no, for this particular reason you believe that (S)QM doesn't lend itself to a reasonable physical interpretation, or that it's just wrong. Why am I not surprised.

Second, whatever Frame Dragger says, I have not tried to hide my views and stated the same things from the very beginning of this thread.

Whether you tried or not, the end result is that it is now many pages in that you've been asked this question point blank. That would imply your views were not clear earlier, unless you feel that your last sobriquet was really a brief restatement of your earlier posts. The fantastic thing about the internet, is that people can just read the text and draw their own conclusions.

ThomasT

Feb23-10, 04:19 PM

If an experiment is designed to produce entanglement, then that entails (via the execution of that design) a statistical dependency between the data sets, A and B.

No, by making such a statement, you are assuming that the experiment will be successful, and you are assuming that the QM definition of entanglement is correct.I'm assuming the experiment will be executed according to its design. If it is, then (from previous experiments) I'm assuming that the QM predictions will be accurate, and, in this sense, the QM definition of entanglement is correct. But it's not a deep, realistic definition.

That is precisely what these experiments were designed to measure. If they had failed to produce entanglement, or if the QM predictions had been incorrect, then that would have been reflected in the experimental results (i.e. no statistical dependence would have been observed between A and B).The statistical dependence between A and B is a result of the data matching process (wrt certain criteria, eg. time of detection) So, even if the QM-predicted correlation between Theta and coincidence rate isn't produced, there's still a statistical dependence between A and B.

Coincidence counting is about matching the separate data streams wrt some criterion or criteria, and then counting the coincidences.

Yes ... that is how the statistical dependence or independence of the A and B sets is determined .. aren't we saying the same thing here?I thought so.

The QM prediction is either right or wrong, the experiment tests it. The experiment can either succeed or fail .. if it fails (i.e no violation is observed), then EITHER it was a poor experiment OR it was a good experiment and QM is wrong. If the experiment succeeds .. then it either supports the QM prediction, at least up to the ability of the experiment to test it, or there is some flaw in the experiment which leaves the result ambiguous (i.e. these loopholes we have been discussing elsewhere in the thread).Not quite. If the experiment matches QM predictions, there might still be some in "flaw in the experiment which leaves the result ambiguous (i.e. these loopholes we have been discussing elsewhere in the thread)."

The point is that even if there are some remaining loopholes, this doesn't matter wrt the consideration of locality/nonlocality in Nature -- because that's not what Bell tests test.

SpectraCat

Feb23-10, 05:19 PM

I just wanted to point out a very interesting post from another, unrelated thread that provides an alternate mathematical explanation/justification for the observed features of entanglement, as well as a proof for the Bell theorem.

http://www.physicsforums.com/showpost.php?p=2594441&postcount=34

I reference this with the caveat that I don't really understand the underlying details yet (I'm not completely clear what a C*-algebra even is), but it certainly seems relevant, and perhaps others here would like to comment on it. I will try to read up on the required mathematical background in the meantime.

ThomasT

Feb23-10, 05:28 PM

To get (observe) the QM-predicted, cos2Theta, angular dependency the experimental design has to involve and the execution has to produce (reveal) a statistical dependency between the separately accumulated data sets.

If you allow the change I made above, then I agree .. to say "get" and "produce" in the context above implies that the data is somehow being "cooked", and I don't agree with that.The data is "cooked" via the data matching process.

The data sets at A and B can't be matched up just any way. The matching proceeds according to certain assumptions. For example, in the '82 Aspect et al. experiment, the design called for pairing detection attributes wrt detection time intervals. The idea being to pair detection attributes associated with optical disturbances emitted by the same atom. This requirement is based on the assumption that the underlying entanglement relationship (responsible for the observed angular dependency between Theta and coincidence rate) is produced via the emission process.

Bell, in his formulation, also assumes this. And, this assumption seems to be support by the experimental results.

However, Bell's formulation also assumes statistical independence between A and B, which is contradicted by the data matching requirement. And this can account for the violation of inequalities based on Bell's formulation.

My point here is that the possibility of failure is inherent in these experimental designs, so in my view they are in no way biasing the set of possible results by their construction, as you seem to be saying. I still don't understand why you are making that claim.If you match the data sets according to some criterion (or criteria) then this limits (biases) the set of possible results. If you do it "on the fly" via coincidence circuits that are gated open upon a detection at one end, then the sample space at the other end is thereby immediately altered.

There is no correlation between the supposedly entangled photons -- except for two settings, and at these settings, Theta = 0 and Theta = pi/2, an LHV formulation can also show perfect correlation and anticorrelation, respectively. For all other values of Theta there's absolutely no correlation between A and B.

Ok, this just seems flat wrong. What do you mean there is "absolutely no correlation between A and B"?For all settings other than Theta = 0 and Theta = pi/2, the individual detection attribute at one end, given the detection attribute at the other end, is random, ie. uncorrelated.

Do you think the results of the experiments is wrong? Do you think the predictions of Q.M. are wrong? Because they definitely measure/predict correlations at all values for the relative angle between the two detectors, with the possible exception of 45 degrees, where the results should appear random.That correlation is between Theta and coincidence rate. There's only a correlation between A and B for two values of Theta.

Demystifier

Feb24-10, 03:29 AM

4) Therefore, I do believe that SQM is, strictly speaking wrong.

The question is: Is there some CONCRETE non-standard variant of QM for which you believe that it might be correct? Namely, all non-standard variants of QM I know predict non-local correlations of the EPR type, and you seem to not believe in any of such variants.

Dmitry67

Feb24-10, 03:31 AM

My reasoning is as follows.

1) Standard quantum mechanics (SQM) includes both unitary evolution (UE) and the projection postulate (PP).

2) UE and PP directly contradict each other, as UE cannot provide irreversibility or destroy superposition, while PP does just that.

3) Therefore, I cannot accept both UE and PP and believe that one of them (namely, PP) is, strictly speaking, wrong.

4) Therefore, I do believe that SQM is, strictly speaking wrong.

Whats about non-collapse interpretations?

ThomasT

Feb24-10, 12:06 PM

2) UE and PP directly contradict each other, as UE cannot provide irreversibility or destroy superposition, while PP does just that.Why not think of them as tools that complement each other?

3) Therefore, I cannot accept both UE and PP and believe that one of them (namely, PP) is, strictly speaking, wrong.And yet using it in conjunction with UE gives accurate predictions.

4) Therefore, I do believe that SQM is, strictly speaking wrong.Wrong wrt what?

If the goal is a realistic theory, then SQM is incomplete.

DrChinese

Feb24-10, 12:16 PM

If the goal is a realistic theory, then SQM is incomplete.

That's exactly what EPR said! :smile:

ThomasT

Feb24-10, 06:54 PM

The problem is that A and B are not independent due to the data matching process (a trackable local process).

Ok, I don't get this last sentence at all. The data matching process (I assume you mean coincidence counting here) does not in any way imply statistical dependence between A and B as far as I can see.No, I don't mean the coincidence counting. The data matching process includes the criterion wrt which the data are matched (eg. time of detection via the assumption that detection attributes associated with the same time interval were, say, emitted by the same atom and thereby entangled at emission due to conservation of angular momentum).

One could run the same experiments with separate, randomly-polarized sources, and there would be no observed correlation between the measurement sets at A and B, so the coincidence counting would conclude that the two sets are statistically independent, right?Yes. In this case there's no design to relate the data sets (ie. the experiment is designed to produce two independent data sets) -- and, presumably, they could be matched according to any criterion and P(A,B) would never deviate from P(A) P(B).

No LHV formulation of an entangled state can possibly conform to Bell's ansatz.

I am not sure how to parse this, and I definitely don't see how it follows from the previous arguments (even if I agreed those were correct). I think it would be useful if you could re-state it in the context of the Mermin gedanken experiment. I would also like a definition or at least an example of an "LHV formulation of an entangled state".Bell's generic LHV form (for the expectation value of joint detection) is

P(a,b) = ∫dλρ(λ)A(a,λ)B(b,λ) .

Bell locality can be written

P(A,B) = P(A)P(B) .

Statistical independence is defined as

P(A,B) = P(A)P(B) .

Statistical dependence is designed into, and independence is structured out of, Bell tests -- presumably ... if they're executed correctly.

So, any Bell local hidden variable formulation is, prima facie, in direct contradiction to an essential design element of any Bell test.

The only assumption made about the data sets at A & B involves the travel times of the photons, in that only a certain subset of detection events at A and B satisfy the criterion of coincidence.That's based on the assumption that the relationship (the entanglement) between the separately analyzed(filtered) disturbances is produced at emission (or via some other local common cause), prior to filtration.

The experimenters are always quite careful about this when defining what "coincident detection" means in the context of their experiments.Yes, and, eg. wrt Aspect '82, the experiment was designed to pair detection attributes associated with optical disturbances emitted in opposite directions by the same atom during the same transition interval.

Essentially, what you seem to be saying is that the entangled photons could have received "instruction sets" controlling their measurement results, and this is *exactly* what the Bell theorem and the Mermin gedanken show is impossible.I don't know about instruction sets. I sense, intuitively :smile:, that that way of looking at Bell's theorem might tend to obfuscate rather than clarify its meaning.

The experiments themselves are about presumably related optical emissions, and crossed polarizers, and spacelike separated joint detection events, etc. -- the underlying physics of which is still a mystery -- not instruction sets.

An apparent disparity between Bell's LHV form and experimental design has been exposited, and imho Bell's theorem doesn't mean what it's commonly taken to mean for the rather simple reason that I've presented.

akhmeteli

Feb24-10, 07:59 PM

The question is: Is there some CONCRETE non-standard variant of QM for which you believe that it might be correct? Namely, all non-standard variants of QM I know predict non-local correlations of the EPR type, and you seem to not believe in any of such variants.

Certainly, your question is justified, but, I am afraid, a direct answer would be misleading again (I guess, Frame Dragger will have a field day:-) )

You see, I would like to emphasize first that I believe that UE of standard quantum mechanics is correct, and it describes pretty much everything you need. This is basically what nightlight said: use UE, add the Born rule (only as an operational principle), and you are fine.

Another note. You said "all non-standard variants of QM I know predict non-local correlations of the EPR type". "Non-local correlations" is one thing, but it seems a bit vague, so, to clarify this issue, let me ask you the following questions: Do they predict any experimental results incompatible with any LR models, as is the case for standard quantum mechanics? If you say they do (for example, I am not even sure if this is the case for dBB), then my second question is: Does the relevant proof (an analog of the proof of the Bell theorem in SQM) uses the projection postulate or something like that?

So let me try to summarize. Actually, I don't know the situation in non-standard variants of QM very well, so I am not sure about their being correct or wrong. (Neither do I know if they exclude any LR models.) For example, I strongly dislike MWI or GRW, I am not enthusiastic about the current forms of dBB, but I don't know if they are correct or wrong. As for SQM, it contains contradictory statements, that's why I know that, strictly speaking it is wrong.

So, to answer your question "Is there some CONCRETE non-standard variant of QM for which you believe that it might be correct?", yes, there is. For example, I believe SQM without the projection postulate might be correct (I guess I can call this a CONCRETE non-standard variant of QM:-) ).

If, however, you actually wanted to ask me if there is a concrete explicitly local variant of QM that I believe might be correct, please advise.

akhmeteli

Feb24-10, 08:03 PM

Whats about non-collapse interpretations?

Please see my reply to Demystifier, which can be summarized as follows: I don't know enough about non-collapse interpretations.

akhmeteli

Feb24-10, 08:46 PM

Why not think of them as tools that complement each other?

If you are comfortable with contradictions, why not?

And yet using it in conjunction with UE gives accurate predictions.

I tend to think that a contradiction suggests some limitations of applicability. Loophole-free Bell tests may be such area of limitation.

Wrong wrt what?.

With respect to itself. This is what a contradiction is about.

If the goal is a realistic theory, then SQM is incomplete.

To my taste, it is too complete:-), so something should be excluded, not added:-).

akhmeteli

Feb24-10, 08:52 PM

DrChinese

Feb24-10, 09:21 PM

Bell's generic LHV form (for the expectation value of joint detection) is

P(a,b) = ∫dλρ(λ)A(a,λ)B(b,λ) .

Bell locality can be written

P(A,B) = P(A)P(B) .

Statistical independence is defined as

P(A,B) = P(A)P(B) .

Statistical dependence is designed into, and independence is structured out of, Bell tests -- presumably ... if they're executed correctly.

So, any Bell local hidden variable formulation is, prima facie, in direct contradiction to an essential design element of any Bell test.

I really don't get what you are saying. The fact is, local realists deny that entanglement is a state. They say it is all coincidence, and there is a common cause. So it is true that Bell tests - which demonstrate entanglement as a state - will always violate LR.

But so what? All experiments are intended to show some aspect of our world. Bell tests show that entangled photons operate in a different spacetime view than the local realist would envision.

Demystifier

Feb25-10, 04:13 AM

You said "all non-standard variants of QM I know predict non-local correlations of the EPR type". "Non-local correlations" is one thing, but it seems a bit vague, so, to clarify this issue, let me ask you the following questions: Do they predict any experimental results incompatible with any LR models, as is the case for standard quantum mechanics?

Yes they do. For example, they all predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

If you say they do (for example, I am not even sure if this is the case for dBB), then my second question is: Does the relevant proof (an analog of the proof of the Bell theorem in SQM) uses the projection postulate or something like that?

Many-world and Bohmian interpretations do not use a projection postulate or anything like that.

So let me try to summarize. Actually, I don't know the situation in non-standard variants of QM very well, so I am not sure about their being correct or wrong. (Neither do I know if they exclude any LR models.)

That's fair to say. Anyway, if you did know more about them, it would probably much easier for you to accept quantum nonlocality, at least in the sense of violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

If, however, you actually wanted to ask me if there is a concrete explicitly local variant of QM that I believe might be correct, please advise.
Well, I would advise you to give up of searching for a variant of QM that does not predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

SpectraCat

Feb25-10, 09:59 AM

No, I don't mean the coincidence counting. The data matching process includes the criterion wrt which the data are matched (eg. time of detection via the assumption that detection attributes associated with the same time interval were, say, emitted by the same atom and thereby entangled at emission due to conservation of angular momentum).

Yes. In this case there's no design to relate the data sets (ie. the experiment is designed to produce two independent data sets) -- and, presumably, they could be matched according to any criterion and P(A,B) would never deviate from P(A) P(B).

Bell's generic LHV form (for the expectation value of joint detection) is

P(a,b) = ∫dλρ(λ)A(a,λ)B(b,λ) .

Bell locality can be written

P(A,B) = P(A)P(B) .

Statistical independence is defined as

P(A,B) = P(A)P(B) .

Statistical dependence is designed into, and independence is structured out of, Bell tests -- presumably ... if they're executed correctly.

So, any Bell local hidden variable formulation is, prima facie, in direct contradiction to an essential design element of any Bell test.

That's based on the assumption that the relationship (the entanglement) between the separately analyzed(filtered) disturbances is produced at emission (or via some other local common cause), prior to filtration.

Yes, and, eg. wrt Aspect '82, the experiment was designed to pair detection attributes associated with optical disturbances emitted in opposite directions by the same atom during the same transition interval.

I don't know about instruction sets. I sense, intuitively :smile:, that that way of looking at Bell's theorem might tend to obfuscate rather than clarify its meaning.

The experiments themselves are about presumably related optical emissions, and crossed polarizers, and spacelike separated joint detection events, etc. -- the underlying physics of which is still a mystery -- not instruction sets.

An apparent disparity between Bell's LHV form and experimental design has been exposited, and imho Bell's theorem doesn't mean what it's commonly taken to mean for the rather simple reason that I've presented.

I still completely fail to understand your point of view. You are simultaneously accepting and denying entanglement in separate points of your argument. You say that the experiment is designed to produce entanglement, and therefore the A and B sets are statistically dependent. Then you go on to say that there are no correlations between the A and B measurements except when the angle between the detector setting is 0 or pi, and that this can be explained by a purely local mechanism. Huh? That seems contradictory and non-sensical ... you can't have it both ways.

But there is a more basic issue with your arguments in my view. Consider the following:

The detectors and coincidence circuitry are controlled by Alice, who has no knowledge of the source conditions ... all she has is a definition of what a coincidence is in the context of the experiment. Bob has two experimental setups P and Q, both produce oppositely polarized pairs of counter-propagating photons, but in the case of P, they are entangled, and in Q they are not. From your previous statements, you appear to agree that for source P, the sets A and B will show a statistical dependence, and for source Q they will not. Therefore, simply from her observations, and without communicating with Bob, Alice can determine which source is being used, based on her measured coincidence statistics.

My point here is that it doesn't matter what the experimenters are *trying* to do with the source, because the detection scheme allows for the possibility that their design would fail, as I argued above.

Frame Dragger

Feb25-10, 10:43 AM

Certainly, your question is justified, but, I am afraid, a direct answer would be misleading again (I guess, Frame Dragger will have a field day:-) )

You see, I would like to emphasize first that I believe that UE of standard quantum mechanics is correct, and it describes pretty much everything you need. This is basically what nightlight said: use UE, add the Born rule (only as an operational principle), and you are fine.

Another note. You said "all non-standard variants of QM I know predict non-local correlations of the EPR type". "Non-local correlations" is one thing, but it seems a bit vague, so, to clarify this issue, let me ask you the following questions: Do they predict any experimental results incompatible with any LR models, as is the case for standard quantum mechanics? If you say they do (for example, I am not even sure if this is the case for dBB), then my second question is: Does the relevant proof (an analog of the proof of the Bell theorem in SQM) uses the projection postulate or something like that?

So let me try to summarize. Actually, I don't know the situation in non-standard variants of QM very well, so I am not sure about their being correct or wrong. (Neither do I know if they exclude any LR models.) For example, I strongly dislike MWI or GRW, I am not enthusiastic about the current forms of dBB, but I don't know if they are correct or wrong. As for SQM, it contains contradictory statements, that's why I know that, strictly speaking it is wrong.

So, to answer your question "Is there some CONCRETE non-standard variant of QM for which you believe that it might be correct?", yes, there is. For example, I believe SQM without the projection postulate might be correct (I guess I can call this a CONCRETE non-standard variant of QM:-) ).

If, however, you actually wanted to ask me if there is a concrete explicitly local variant of QM that I believe might be correct, please advise.

I'm not having a field day, however as others here have concluded you clearly believe in LHVs, but also accept the predictive capacity of SQM. I don't see how you can have it both ways, but that's your business. Anyway, I'm only one of several here who have questioned your basic assumptions, and the desire for a "concrete non-standard variant of QM".

Personally I respect and am constantly impressed by the ability of QM to predict, but I still can't bring myself to believe it's a theory which accurately depicts reality, or is complete. That said, I simply say that and go on with a combination of intellectual curiosity, and Instrumentalism in practice. Really, all I was trying to point out earlier is that when you're already looking for an alternative to the theory in which the question being discussed is couched, it's best to lead with that fact, and your assumptions.

Obviously I struck a nerve, or just plain annoyed you, but please do leave me out of future posts unless I'm actually involved, especially when I'm hardly alone in questioning you.

EDIT: I just have to say, when you say you want "concrete" out of the uncertainty and probabilities of QM I feel like screaming, "Get in line!" No offense, it's just a gut reaction and not angry.

ThomasT

Feb25-10, 08:34 PM

I still completely fail to understand your point of view. You are simultaneously accepting and denying entanglement in separate points of your argument. You say that the experiment is designed to produce entanglement, and therefore the A and B sets are statistically dependent.Yes, without statistical dependency between A and B you can't demonstrate entanglement. It's the successful matching of the separate data sets wrt certain criteria that makes the difference between seeing the QM-predicted correlations or not.

Then you go on to say that there are no correlations between the A and B measurements except when the angle between the detector setting is 0 or pi, and that this can be explained by a purely local mechanism. Huh? That seems contradictory and non-sensical ... you can't have it both ways.The correlation that the experiment is designed to produce, and that QM and proposed LHV models are making predictions about is the correlation between θ (the angular difference between the analyzer settings) and the rate of joint detection.

There's no correlation between individual detections at A and B except for θ=0 and θ=90 degrees. Wrt these two settings a simple LHV model (producing a linear correlation function between θ and rate of joint detection) predicts the same thing as QM for θ=0 and θ=90 degrees (as well as θ=45 degrees).

So, there is an LHV account of any correlation between A and B. What there's no complete LHV account of is the correlation between θ and rate of joint detection for values of θ between 0 and 90 degrees.

But there is a more basic issue with your arguments in my view. Consider the following:

The detectors and coincidence circuitry are controlled by Alice, who has no knowledge of the source conditions ... all she has is a definition of what a coincidence is in the context of the experiment. Bob has two experimental setups P and Q, both produce oppositely polarized pairs of counter-propagating photons, but in the case of P, they are entangled, and in Q they are not. From your previous statements, you appear to agree that for source P, the sets A and B will show a statistical dependence, and for source Q they will not. Therefore, simply from her observations, and without communicating with Bob, Alice can determine which source is being used, based on her measured coincidence statistics.

Statistical dependence between A and B means that a detection at A changes the sample space at B, and vice versa, in a nonrandom way. Setup P is designed to produce related counter-propagating photons via the emission process. Setup Q isn't.

The criterion for data matching has to do with the relationship between the counter-propagating photons.

So, yes Alice should observe that the P and Q results are different and that the P correlations closely resemble those predicted for certain entangled states.

My point here is that it doesn't matter what the experimenters are *trying* to do with the source, because the detection scheme allows for the possibility that their design would fail, as I argued above.I don't follow what you're saying here. The criterion for data matching has to do with the relationship between the counter-propagating photons. Setup P is designed to produce related counter-propagating photons via the emission process. Setup Q isn't.

yoda jedi

Feb25-10, 08:40 PM

4) Therefore, I do believe that SQM is, strictly speaking wrong.

not wrong, rather incomplete or aproximate.....

read:

Quantum Theory: Exact or Approximate?
http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.2211v1.pdf

.......There are two distinct approaches. One is to assume that quantum theory is exact, but that the interpretive postulates need modification, to eliminate apparent contradictions. Many worlds, decoherent histories, Bohmian mechanics, and quantum theory as information, all fall in this category. Although their underlying mathematical formulations differ, empirically they are indistinguishable, since they predict the same experimental results as does standard quantum theory.
The second approach is to assume that quantum mechanics is not exact, but instead is
a very accurate approximation to a deeper level theory, which reconciles the deterministic
and probabilistic aspects. This may seem radical, even heretical, but looking back in the
history of physics, there are precedents. Newtonian mechanics was considered to be exact
for several centuries, before being supplanted by relativity and quantum theory, to which
classical physics is an approximation. But apart from this history, there is another important
motivation for considering modifications of quantum theory. This is to give a quantitative
meaning to experiments testing quantum theory, by having an alternative theory, making
predictions that differ from those of standard quantum theory, to which these experiments
can be compared.......

http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.3964v1.pdf

.....quantum phenomena possibly emerge only at larger scales than LP (planck sclae) , the scale of spacetime discreteness............

http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.2845v2.pdf

.............The outcome of the second measurement will evidently be different from what quantum mechanics predicts for a pair of successive measurements............

Please see my reply to Demystifier, which can be summarized as follows: I don't know enough about non-collapse interpretations.

rather, objective collapse ?
Continuous Spontaneous Localization (Dynamical Reduction Models).

http://arxiv.org/PS_cache/quant-ph/pdf/0701/0701014v2.pdf

...........This idea, that the environment somehow naturally guarantees the emergence of definite properties when moving from the micro to the macro, by destroying coherence among different terms of a superposition, is very appealing. But wrong.....

......I note here that the division between a system and its environment is not
a division dictated by Nature. Such a division is arbitrarily set by the Physicist because he or
she is not able to solve the Schrodinger equation for the global system; he or she then decides to select some degrees of freedom as the relevant ones, and to trace over all other degrees. This is a very legitimate division, but not compelling at all. Such a division is more or less equivalent to the division between a quantum system and a measuring device: it’s artificial, just a matter of practical convenience. But if the physicist were able to analyze exactly the microscopic quantum system, the macroscopic apparatus and the surrounding environment together, i.e. if he or she used the Schr¨odinger equation to study the global system, he or she would get a very simple result: once more, because of linearity, all terms of the superposition would be present at the same time in the wave function, no one of them being singled out as that which really occurs when the measurement is performed in the laboratory.
The so called measurement problem of Quantum Mechanics is an open problem still waiting
for a solution. Dynamical reduction models, together with Bohmian Mechanics, up to now are,
in my opinion, the most serious candidates for a resolution of this problem.....

......He (S. Adler) assumes precisely that quantum mechanics is not a fundamental theory of nature but an emergent phenomenon arising from the statistical mechanics of matrix models with a global unitary invariance........

akhmeteli

Feb26-10, 03:12 AM

Yes they do. For example, they all predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

Many-world and Bohmian interpretations do not use a projection postulate or anything like that.

Thank you very much for this information. However, another question is in order in such case. Let me ask it using the example of the de Broglie - Bohm interpretation (dBB) (as, on the one hand, you are an expert in it, and on the other hand, because I know more about it than about other non-standard interpretations).

It is my understanding that dBB fully accepts unitary evolution (UE) of standard quantum mechanics (at least, in some of its versions).

If I am wrong, please advise. However, if I am indeed wrong (or for those versions that do not accept UE unconditionally), that means that dBB predicts deviations from UE and thus experimental results differing from those of SQM (at least in principle). How do we know that these predictions of dBB are indeed correct? I think you'll agree that we cannot know that until we have experimental confirmation. So anything that dBB has to say on nonlocality beyond what SQM says has no experimental basis.

If, however, I am right (or for those versions of dBB that fully accept UE), my question is as follows. Is UE enough to prove nonlocality in dBB? If it is enough, then the relevant proof can be translated into a proof for SQM, and that means that nonlocality in SQM can be proven without the projection postulate (PP) or something like that. That would mean that I was terribly wrong from the very beginning of this thread, and I would certainly want to know if this is indeed the case.

If, however, dBB adds something extra to UE to prove nonlocality, then this extra is either correct in SQM, or it's wrong there. If it's correct in SQM, then again we can translate the dBB proof of nonlocality into a proof for SQM, and it is possible to prove nonlocality in SQM without PP or something like that. Again, I would want to know if this is so.

If, however, this extra is wrong in SQM, that means that it has no experimental basis.

So the above reasoning has several branches generated by several ifs, and I would very much appreciate if you could tell me which branch is correct. Or maybe the entire reasoning is wrong for some other reason that I cannot see right now.

That's fair to say. Anyway, if you did know more about them, it would probably much easier for you to accept quantum nonlocality, at least in the sense of violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

That may be so. Right now, however, the above reasoning makes me doubt it.

Well, I would advise you to give up of searching for a variant of QM that does not predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

Thank you for your advice.

akhmeteli

Feb26-10, 03:46 AM

not wrong, rather incomplete or aproximate.....

I could agree with you for practical purposes (indeed, one can say that PP is not wrong, but it's approximate), but this thread is not about practical purposes. Indeed, SQM implies nonlocality. If I use your wording ("approximate" instead of "wrong"), then am I supposed to talk about "approximate nonlocality"? Then what, am I supposed to say that this "approximate nonlocality" rules out locality or does not rule out locality? Does not make much sense either way, if you ask me. So for the purpose of this thread I prefer the following wording: "strictly speaking, wrong".

As for work of Adler and others, their theories may be correct, but it is my understanding that they deny precise unitary evolution, and there is no experimental basis for that. Maybe there will be such experimental basis in the future, but I am not sure I can meaningfully discuss these theories now.

Actually, I have problems with the motivation of their work. They seem to believe that measurements have definite outcomes, and I doubt that. I quoted the articles by Allahverdyan a.o., where they rigorously study a model of measurement. In the process of measurement of a spin projection, the particle interacts with a paramagnetic system. This paramagnetic system evolves into some macroscopic state, and this seems to decide the outcome of the measurement. However, according to the quantum recurrence theorem, after an incredibly long period of time this macroscopic state will inevitably flip, if UE is correct, thus reversing the outcome of the measurement.

Demystifier

Feb26-10, 04:39 AM

If, however, I am right (or for those versions of dBB that fully accept UE), my question is as follows. Is UE enough to prove nonlocality in dBB? If it is enough, then the relevant proof can be translated into a proof for SQM, and that means that nonlocality in SQM can be proven without the projection postulate (PP) or something like that. That would mean that I was terribly wrong from the very beginning of this thread, and I would certainly want to know if this is indeed the case.

Yes, that seems to be the case. QM is nonlocal even without the PP. Essentially, QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated. For more elaborated argumentation that QM is nonlocal in ANY interpretation see
http://xxx.lanl.gov/abs/quant-ph/0703071

akhmeteli

Feb26-10, 05:56 AM

Yes, that seems to be the case. QM is nonlocal even without the PP. Essentially, QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated. For more elaborated argumentation that QM is nonlocal in ANY interpretation see
http://xxx.lanl.gov/abs/quant-ph/0703071

"Seems to be the case" is not the same as "is nonlocal". Neither is your article categorical ("strongly supports" is not the same as "proves"). You don't state that "nonlocality in SQM can be proven without the projection postulate (PP) or something like that", so while I certainly can be wrong saying it cannot, so far I stand by what I said. I certainly respect your opinion, but opinion is not a proof.

So I'd like to ask you again: is nonlocality proven in dBB using just UE?

As for "QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated." - I mentioned a mathematical mechanism suggesting that a QFT-like theory can be a disguise for a local theory. Or, reversing the argument, a local theory can have a seemingly nonlocal form.

akhmeteli

Feb26-10, 06:08 AM

Unfortunately I can't understand the details of that post, as I already mentioned. However, even if I accepted its content, I am not sure why it is relevant to this discussion ... and earlier you said "nonlinear" PDE's, only here do you mention that they are local. Can you please break down the physical significance of this statement in the current context, or link to a post where you described it previously?.

So let me try to explain. You see, in general, time evolution can be described by partial differential equations in 3+1 dimensions, such as the Maxwell equations, and they are typically local. There are also linear equations in the Fock space, such as in quantum electrodynamics (QED), and the Bell theorem seems to imply that, e.g., QED is nonlocal. So it seems that these two kinds of evolution are worlds apart. However, the formulae from Kowalski's book that I posted show that nonlinear equations in (3+1)D can be embedded in linear equations in the Fock space, and they look pretty much like unitary evolution in quantum field theory, and even the relevant Hamiltonian is expressed in terms of operators of creation and annihilation (I am hypothesizing now, but I think that similar results for fermions can be obtained using the fermionic coherent states (Cahill, Glauber, 1999)). So a local theory may be disguised as a nonlocal one.

Later I'll try to give a simple example of Carleman linearization to illustrate how a low-dimensional nonlinear differential equation can be embedded into a linear equation in infinitely many dimensions.

Demystifier

Feb26-10, 07:06 AM

So I'd like to ask you again: is nonlocality proven in dBB using just UE?

Yes, it is proven. Moreover, it is proven within any known formulation/interpretation of quantum theory.

As for "QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated." - I mentioned a mathematical mechanism suggesting that a QFT-like theory can be a disguise for a local theory. Or, reversing the argument, a local theory can have a seemingly nonlocal form.
As QFT is also a known formulation of quantum theory, my assertion above refers also to QFT. QFT also contains nonlocal objects - quantum states (represented by a sort of wave functions or something equivalent).

Demystifier

Feb26-10, 07:08 AM

"Seems to be the case" is not the same as "is nonlocal". Neither is your article categorical ("strongly supports" is not the same as "proves"). You don't state that "nonlocality in SQM can be proven without the projection postulate (PP) or something like that", so while I certainly can be wrong saying it cannot, so far I stand by what I said. I certainly respect your opinion, but opinion is not a proof.

Have you read my paper completely? I have an impression that you read the abstract only.

akhmeteli

Feb26-10, 07:28 AM

Yes, it is proven. Moreover, it is proven within any known formulation/interpretation of quantum theory.

This is strange. My understanding was nonlocality was not proven, e.g., in SQM, using just UE, and you have not stated the opposite before (your article is not at all categorical on this point, moreover, you are saying there that you don't have (yet) a proof of your conjecture). Maybe you misread my question? Or maybe you could give me a reference to such proof (using just UE) for SQM or dBB?

Demystifier

Feb26-10, 07:42 AM

This is strange. My understanding was nonlocality was not proven, e.g., in SQM, using just UE, and you have not stated the opposite before (your article is not at all categorical on this point, moreover, you are saying there that you don't have (yet) a proof of your conjecture). Maybe you misread my question? Or maybe you could give me a reference to such proof (using just UE) for SQM or dBB?
Or maybe you have not read my paper? Nonlocality (where the word "nonlocality" is defined in the algorithmic sense explained in the paper) is proven in any definite formulation/interpretation of QM. When I say that nonlocality is not proven, I mean that it is not proven that there does not exist another (yet unknown) formulation/interpretation which can avoid algorithmic nonlocality. All that is explained in the paper, for those who want to read it.

Furthermore, independent on my conjecture on "algorithmic" nonlocality that I haven't proven, Bell has already proven "realistic" nonlocality. My unproven "algorithmic" nonlocality is a generalization of the Bell's proven "realistic" nonlocality.

Frame Dragger

Feb26-10, 08:25 AM

@Akhmeteli: Did you even skim the paper? They address EXACTLY your concerns, and lay them to rest in all but a rhetorical sense. They begin in the last portion of page 3 and conclude with:

However, we emphasize that this is true
only if these hidden-variable formulations really are observationally
equivalent to the local formulation. In this
regard, we note that some variants of the Bohmian interpretation
may, under certain circumstances, observationally
differ from other formulations. The examples of
such circumstances are the early universe [26] and certain
relativistic conditions [27].

If you didn't read it, or can't grasp it then just say that. There's nothing wrong with that on an educational website, with a science advisor (Demystifier) who's bending over backwards trying to help you.
And yes... now I'm having a field day.

akhmeteli

Feb26-10, 10:59 PM

Or maybe you have not read my paper? Nonlocality (where the word "nonlocality" is defined in the algorithmic sense explained in the paper) is proven in any definite formulation/interpretation of QM. When I say that nonlocality is not proven, I mean that it is not proven that there does not exist another (yet unknown) formulation/interpretation which can avoid algorithmic nonlocality. All that is explained in the paper, for those who want to read it.

Furthermore, independent on my conjecture on "algorithmic" nonlocality that I haven't proven, Bell has already proven "realistic" nonlocality. My unproven "algorithmic" nonlocality is a generalization of the Bell's proven "realistic" nonlocality.

Demystifier,

To be frank, I am completely confused...

I asked you about nonlocality of non-standard interpretations of QM, such as dBB. You told me: yeah, sure, their nonlocality can be proven using UE only. Now you're telling me you had in mind YOUR VERY OWN definition of locality... And what definition it is!

My take on your article is as follows. Actually, you implicitly introduce at least two definitions.

One of them is as follows: "A theory is local if and only if there exists an FI [formulation/interpretation] of the theory in which all irreducible elements are local." Actually, I could live with such a definition. But you do not have a proof of nonlocality under such definition for QM, it's just your conjecture.

The other (implicit) definition is actually for FI, not theories, and it requires that all its irreducible elements are local. Under this definition you do prove that all known FI of quantum theory are not local (say, because they contain such elements as psi(x,y)). However, under this definition even the Hamilton-Jacobi formulation of classical mechanics is not local, as far as I can see. Some definition indeed...

As for Bell's proof, it requires something beyond UE, such as PP.

Demystifier

Feb27-10, 03:26 AM

DrChinese

Feb27-10, 01:37 PM

Frame Dragger

Feb27-10, 05:50 PM

As we keep telling you, it does NOT require such. You do NOT need to accept QM to rule out local realism. You only need to accept the cos^2(theta) experimental prediction. Which of course is incompatible with LR.

Please quit repeating what has already been pointed out as false. Whether you accept the experimental results of Bell tests or not, there is no sense in which Bell depends on one's acceptance of QM itself. And as such, your (also ridiculous) assessment of QM as "wrong" is completely meaningless.

P.S. All theories are "wrong" in some sense. A model is not reality. Please see my tag line.

Why do I think that akhmeteli would not be familiar with GS? Someone that enamoured with words in a physical discipline is obviously not concerned about GIGO in relation to their brain.

To follow that semantic thread... would it be better to say that all theories are incomplete representations of reality, and potentially misleading if taken as more? To me the terms "right and wrong" are polar opposites, not open to degrees. I'm open to correction on this point.

To Ahkmeteli: If you do reject the results of the Bell tests, I would be very interested to hear your defense of that unenviable position.

akhmeteli

Feb28-10, 12:13 AM

I don't understand what exactly you are confused about. That there are different inequivalent definitions of nonlocality? It's often the case in discussions on various stuff that the source of disagreement lies in the unrecognized fact that people have in mind different definitions of the same word. Thus, saying explicitly that there are different definitions is often the first and sometimes crucial step towards achieving agreement.

So, when you say that you believe in locality, what exactly your definition of that word is?

This thread is about the assumptions of the Bell theorem and experimental tests of the theorem, at least that’s how the thread started. Of course, the topic can change with time, but, on the one hand, I asked you the following questions about non-standard variants of QM:

"Do they predict any experimental results incompatible with any LR models, as is the case for standard quantum mechanics? If you say they do (for example, I am not even sure if this is the case for dBB), then my second question is: Does the relevant proof (an analog of the proof of the Bell theorem in SQM) uses the projection postulate or something like that?",

and you yourself mentioned that non-standard versions of QM "predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency", so I had all reasons to assume that you also had in mind the nonlocality as it is defined in the Bell theorem. Then you told me that nonlocality can be proven in, say, dBB using UE only. If you had in mind a new definition of nonlocality, would not it have been appropriate to warn me and other readers of your posts, the more so as you did not use some generally recognized definition, but your own one? That was one source of my confusion.

The other source of confusion was that the specific definition of nonlocality you used was downright unreasonable, as even the Hamilton-Jacobi formulation of classical mechanics satisfies it. You reproached me for not reading your article carefully enough, but I just could not imagine you took that definition seriously (let alone the fact that I was under no obligations to learn the article by heart).

As for your question on the definition of locality that I believe in, it would be more precise to talk about the definition of nonlocality that I don't believe in - existence of violation of the Bell inequalities.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.

akhmeteli

Feb28-10, 01:45 AM

As for Bell's proof, it requires something beyond UE, such as PP.

As we keep telling you, it does NOT require such. You do NOT need to accept QM to rule out local realism. You only need to accept the cos^2(theta) experimental prediction. Which of course is incompatible with LR.

You seem to be reproaching me for not listening to what you're saying, but it looks like you're not listening. Indeed, you mentioned the Malus law before in this thread, and I replied that "as far as I understand, in the context of the Bell experiment, the Malus law and PP give the same result, therefore, strictly speaking, the Malus law is in contradiction with UE. Indeed, UE cannot turn a superposition into a mixture of states." I have not seen any critique of this statement from you (and I repeated that statement replying to SpectraCat). Therefore I stand by what I said: "As for Bell's proof, it requires something beyond UE, such as PP."

You see, the Malus law may be a great approximation, but it's just an approximation. The Coulomb law is a great approximation, but it breaks exactly where it predicts nonlocality.

Please quit repeating what has already been pointed out as false.

If you pointed out that something is false, that does not necessarily mean it is indeed false. I believe I answered your critique, so I guess we just disagree on what is false and what is correct.

Whether you accept the experimental results of Bell tests or not, there is no sense in which Bell depends on one's acceptance of QM itself.

I emphasized that the proof of the Bell theorem uses as assumptions the mutually contradictory elements of standard quantum mechanics - UE and PP, so the problem of QM does indeed become a problem for the Bell theorem.

And as such, your (also ridiculous) assessment of QM as "wrong" is completely meaningless.

OK, so you think this assessment is ridiculous. The problem is I substantiated this assessment: UE and PP are mutually contradictory, because the former cannot destroy a superposition or introduce irreversibility, and PP does that. And this makes the assessment meaningful.

P.S. All theories are "wrong" in some sense. A model is not reality. Please see my tag line.

That does not mean theories cannot be improved.

Demystifier

Feb28-10, 04:23 AM

As for your question on the definition of locality that I believe in, it would be more precise to talk about the definition of nonlocality that I don't believe in - existence of violation of the Bell inequalities.

Good! Let's then talk only about this definition of locality and ignore other definitions.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.
Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

Frame Dragger

Feb28-10, 07:12 AM

Good! Let's then talk only about this definition of locality and ignore other definitions.

Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

Demystifier is a kind individual. It goes without SAYING that dBB satisfies the predictions of QM; this is why it's around when all of the LHV theories died; because dBB is NON-Local HV Theory. It's not a matter of reference, but a matter of the very definition of why dBB isn't dead, but rather no longer a shooting offense to teach.

Akhmeteli: You do realize you now have pages of your writing that boils down to, "I'M the sane one, it is all of THEM who are are mad *insane laughter"? No need to respond, I know you think you have your pride.

Edit @ Akhmeteli: I do believe you've annoyed DrChinese... which is a first I've seen. Why the insistance on rhetoric and not just a stand for what you believe? Do you even KNOW what it is you believe? I get the sense that maybe you're just blowing smoke here, and don't believe anything in particular, which you should also come out and say clearly.

DrChinese

Feb28-10, 10:09 AM

You seem to be reproaching me for not listening to what you're saying, but it looks like you're not listening. Indeed, you mentioned the Malus law before in this thread, and I replied that "as far as I understand, in the context of the Bell experiment, the Malus law and PP give the same result, therefore, strictly speaking, the Malus law is in contradiction with UE. Indeed, UE cannot turn a superposition into a mixture of states." I have not seen any critique of this statement from you (and I repeated that statement replying to SpectraCat). Therefore I stand by what I said: "As for Bell's proof, it requires something beyond UE, such as PP."

2. That does not mean theories cannot be improved.

1. Arrgh! Bell does NOT require you to believe ANYTHING other than the idea that QM predicts (rightly or wrongly) that there is a cos^2(theta) relationship. It does NOT matter how QM gets that prediction or whether it is observed in experiments (which it is). There is NO other prediction from QM other than the cos^2(theta) relationship (despite your absurd claims that QM is "wrong" whatever that means in this context). So WHAT ARE YOU TALKING ABOUT? Bell is not dependent on the correctness of QM in any way. That was Bell's point actually, that QM and LR are mutually incompatible.

There is no controversery to what I am saying. What you are saying not only makes NO SENSE, but is not accepted by anyone I have ever talked to or read. Forum rules require that you identify personal theories which are not generally accepted as such, and to back up your statements with references when challenged - and you are being challenged. Or better, acknowledge that it is a personal theory with no support other than your belief and stick to discussion points that are appropriate. In this forum, continuing to push points that have been discredited - as yours have - is poor etiquette. We have already covered this ground before in this thread!

2. I couldn't agree more - you can improve on theories. But theories should NOT be judged according to whether they are "right" or "wrong", but rather according to their utility. For example, Newtonian gravity is actually a better theory than General Relativity for many applications (it has fewer variables). You will see that the next time you calculate the velocity an apple drops from a tree.

akhmeteli

Feb28-10, 12:38 PM

Good! Let's then talk only about this definition of locality and ignore other definitions.

Very well, thank you.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.

Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

I am afraid we've run into one of the problems that I anticipated in my post 273 in this thread. If your following statement were precise: "ALL probabilistic predictions are the same as those of standard QM with a collapse", then dBB would have inherited the internal contradictions of standard quantum mechanics and would have been, strictly speaking, wrong. However, this statement is not a precise result in dBB. How do I know that? Just because you told me in another thread that the projection postulate is an approximation in dBB (http://www.physicsforums.com/showpost.php?p=2167542&postcount=19 ).

Therefore, I suspect that violations of the Bell inequalities cannot be proven in dBB using UE only, you need some additional assumptions (or approximations, if you like).

ThomasT

Feb28-10, 12:47 PM

SpectraCat, to revisit your last comments:
From your previous statements, you appear to agree that for source P, the sets A and B will show a statistical dependence, and for source Q they will not.The data sets A and B don't, by themselves, show anything. They're just random sequences of detection attributes.

Therefore, simply from her observations, and without communicating with Bob, Alice can determine which source is being used, based on her measured coincidence statistics.The matched data wrt Q won't show entanglement correlations no matter how you match it, while appropriately matched data wrt P will. P(A,B) can deviate from P(A)P(B) if there's some common cause connection between paired photons produced by Q. But only wrt setup P will rate of coincidental detection be cos2Θ .

My point here is that it doesn't matter what the experimenters are *trying* to do with the source, because the detection scheme allows for the possibility that their design would fail, as I argued above.How the counter-propagating optical disturbances are produced, how they're filtered, how they're detected and how the resulting data is processed all matters.

Am I missing your point?

ThomasT

Feb28-10, 01:55 PM

I really don't get what you are saying.Just that:

1. The factorability of the LHV form for Bell test joint probabilities is what makes this form incompatible with QM and entanglement experiments.
2. This factorability represents statistical dependence between A and B.
3. Statistical dependence between A and B doesn't require flt propagation between them.
4. Therefore, violation of Bell inequality doesn"t imply nonlocality.

The fact is, local realists deny that entanglement is a state.A state is just a mathematical representation of an experimental setup.

If you mean that they deny that the QM representation is the correct one, then, while this might be a fitting characterization in general, such a denial isn't required in order to be a local realist.

They say it is all coincidence, and there is a common cause.Of course. And because there's a common cause the rate of coincidental detection wrt angular difference is predictable.

So it is true that Bell tests - which demonstrate entanglement as a state - will always violate LR.I don't think this is why LHV formulations have so far been incompatible with Bell tests.

Bell tests show that entangled photons operate in a different spacetime view than the local realist would envision.Not necessarily, In fact the QM prediction, P(A,B) = cos2Θ , is what a local realist might expect for experiments in which counter-propagating optical disturbances emitted by the same atom are analyzed by crossed polarizers.

SpectraCat

Feb28-10, 02:06 PM

SpectraCat, to revisit your last comments:
The data sets A and B don't, by themselves, show anything. They're just random sequences of detection attributes.

The matched data wrt Q won't show entanglement correlations no matter how you match it, while appropriately matched data wrt P will. P(A,B) can deviate from P(A)P(B) if there's some common cause connection between paired photons produced by Q. But only wrt setup P will rate of coincidental detection be cos2Θ .

How the counter-propagating optical disturbances are produced, how they're filtered, how they're detected and how the resulting data is processed all matters.

Am I missing your point?

Yes, because without knowing about the source, and by applying a consistent treatment to the data, based only on a consistent definition of what construes a coincident detection event, Alice can use the data sets A and B to determine empirically if Bob is using the entangled source P, or the unentangled source Q. That is why the results of Bell tests are valid, because the measurement and data analysis *can distinguish* between entangled and unentangled pairs based on the coincidence counting. Note that the results will not necessarily be random if Bob uses an unentangled source, they will just fail to violate a Bell inequality, because the two measurement sets will not show a statistical dependence.

Finally, your assertion that the data sets are only correlated at the two relative measurement angles of 0 and pi/2 seems false to me. The fact is that more coincidences are observed when the angle is closer to pi/2 and fewer are observed when it is closer to 0. So yes, the correlation of any particular pair of measurements is fundamentally unknowable, but the probability of observing a coincindence will be given by Malus's law based on the *difference between the measurement angles at A and B* when an entangled source is used. If an unentangled source is used, then the results at detector B will be independent of the measurement angle choice at A, and vice versa. So the correlation between sets A and B for the entangled case is not "perfectly random" except for the two cases of theta=0 and theta=pi/2 as you are claiming, and certainly differs in a measurable way from the correlation in the unentangled case.

I know that the above is somewhat repetitive, but I don't know how else to explain it. I hope this makes it clearer

DrChinese

Feb28-10, 03:01 PM

If you mean that they deny that the QM representation is the correct one, then, while this might be a fitting characterization in general, such a denial isn't required in order to be a local realist.

Of course. And because there's a common cause the rate of coincidental detection wrt angular difference is predictable.

...

Not necessarily, In fact the QM prediction, P(A,B) = cos2Θ , is what a local realist might expect for experiments in which counter-propagating optical disturbances emitted by the same atom are analyzed by crossed polarizers.

Now, if you are a local realist, you say there is a common cause. And yet you cannot construct a dataset in which the cos^2 relationship holds. So what is all the deal about separability? Just show me the dataset for 0, 120 and 240 degrees and we will have something meaningful to discuss. I don't follow all your comments about Bell tests being biased from inception when you cannot do something this simple (because it is impossible).

And entanglement is not so easy to explain these days with some of the newer experiments. EPR is completely lost on these. Please explain, for example, how photons become entangled when they are not in each other's light cones - and never have been - and originate from different lasers. Meanwhile, QM can.

I just do not understand technical objections against Bell when it seems as if the entire point of Bell is lost. Bell is a road map to understanding that local realism is incompatible with the predictions of QM. No matter what the local realistic theory looks like, I can use the Bell thinking to disprove it when compared to experiment. Now, it matters not at all if my map has a small misprint or other minor issue as long as I can get where I need to go.

ThomasT

Feb28-10, 03:09 PM

Yes, because without knowing about the source, and by applying a consistent treatment to the data, based only on a consistent definition of what construes a coincident detection event, Alice can use the data sets A and B to determine empirically if Bob is using the entangled source P, or the unentangled source Q. That is why the results of Bell tests are valid, because the measurement and data analysis *can distinguish* between entangled and unentangled pairs based on the coincidence counting.Ok ...

Note that the results will not necessarily be random if Bob uses an unentangled source, ...Right, but P(A,B) won't be cos2Θ.

... they will just fail to violate a Bell inequality, because the two measurement sets will not show a statistical dependence.There will still be a statistical dependence between A and B if the (unentangled) counter-propagating disturbances have a common cause and the data are matched wrt this criterion. For example, where setup Q has (emitter - polarizer 1 - polarizer 2 - detector) on both sides, and polarizers 1 are aligned and the setting is changing rapidly and randomly so as to produce identical random polarization for each counter-propagating pair.

Finally, your assertion that the data sets are only correlated at the two relative measurement angles of 0 and pi/2 seems false to me.These are the only two settings wrt which you can predict B given A, and vice versa.

The fact is that more coincidences are observed when the angle is closer to pi/2 and fewer are observed when it is closer to 0.In the ideal, when Θ = 0 then P(A,B) = 1 (detection attributes for A and B are always identical), and when Θ = 90 degrees then P(A,B) = 0 (detection attributes for A and B are always opposite).

If an unentangled source is used, then the results at detector B will be independent of the measurement angle choice at A, and vice versa.This is true even wrt an entangling source.

So the correlation between sets A and B for the entangled case is not "perfectly random" except for the two cases of theta=0 and theta=pi/2 as you are claiming ... Actually, it is. To illustrate:

The polarizers at A and B are misaligned but not by 90 degrees. A has just registered a detection. Will B also register a detection wrt this pair or not?

ThomasT

Feb28-10, 03:50 PM

Now, if you are a local realist, you say there is a common cause. And yet you cannot construct a dataset in which the cos^2 relationship holds.Right, not if the LHV joint probability has to be expressed in factorable form.

So what is all the deal about separability?It entails that local realist models can be formulated as nonseparable states.

I don't follow all your comments about Bell tests being biased from inception when you cannot do something this simple (because it is impossible).I agree that it's impossible. That's the point of departure for the argument. The question, then, is why is it impossible. One answer is that it has to do with the factorability of the LHV representation of the joint probability.

Assuming that it has to do with this factorability, then the argument goes ... this factorability was meant to represent locality. Instead it merely represents statistical independence.

However, one might notice, Bell tests are designed to produce statistically dependent data sets, and this statistical dependence doesn't require nonlocal interactions/transmissions.

Hence, violation of Bell inequality doesn't mean that locality or realism has been contradicted, because the violation is simply due to a formal misapplication.

Please explain, for example, how photons become entangled when they are not in each other's light cones - and never have been - and originate from different lasers.Different lasers can produce the same light, indistinguishable photons.

akhmeteli

Feb28-10, 06:11 PM

1. Arrgh! Bell does NOT require you to believe ANYTHING other than the idea that QM predicts (rightly or wrongly) that there is a cos^2(theta) relationship.

I respectfully disagree. I think this is factually incorrect. Indeed, you need SOMETHING else to prove the Bell theorem, namely, conservation of angular momentum (otherwise how can you be sure that after you measured polarization of one photon of the entangled pair you definitively know polarization of the other one?) And conservation of angular momentum is a consequence of unitary evolution of QM. That is why I repeat that the proof of the Bell theorem requires both UE and PP, which contradict each other.

It does NOT matter how QM gets that prediction or whether it is observed in experiments (which it is). There is NO other prediction from QM other than the cos^2(theta) relationship (despite your absurd claims that QM is "wrong" whatever that means in this context). So WHAT ARE YOU TALKING ABOUT?

Again, I respectfully disagree. The cos^2(theta) relationship is not the only prediction from QM. Indeed, if the system was initially in a superposition, there is no way you can get destruction of this superposition or irreversibility, unless you reject unitary evolution for the entire system, including the instrument (and an observer, if you wish). So, if there is no irreversibility, that means that no measurement is ever final, in the first place. You want to know what this prediction is exactly? I cannot write the exact prediction, not within a reasonable time frame, but this is not just my opinion. Other people took the trouble to study the process of quantum measurement using a rigorously solved model and showed how the standard results we all are accustomed to arise as approximations, not as precise results, how the projection postulate evolves as a result of irreversibility, which irreversibility, strictly speaking, does not exist, e.g. due to the quantum recurrence theorem. I quoted this published work several times: arXiv:quant-ph/0702135 (Phys. Rev. A 64, 032108 (2001), Europhys. Lett. 61, 452 (2003), Physica E 29, 261 (2005)). Again, you don't need to believe me or Allahverdyan and coauthors. You are a knowledgeable person with profound understanding of quantum mechanics, you are fully aware of the measurement problem in quantum mechanics (and I gave you all the references), so I suspect you fully understand that UE and destruction of superposition are incompatible. Nevertheless, you keep saying something like "C'mon, you're nit-picking, nobody's perfect, so why pick at QM? Be a sport". Sorry, DrChinese, a spade is a spade.

Bell is not dependent on the correctness of QM in any way.

Yes, it is, as the Bell theorem proof requires both elements of QM as assumptions - UE and PP, which are mutually contradictory.

That was Bell's point actually, that QM and LR are mutually incompatible.

I agree. However, as I said, standard quantum mechanics is also incompatible with standard quantum mechanics, so if you believe your (or Bell's) statement rules out LR, it also means it rules out standard QM.

There is no controversery to what I am saying. What you are saying not only makes NO SENSE, but is not accepted by anyone I have ever talked to or read.

I am not sure this is technically correct:-), as I mostly follow nightlight's reasoning, and you criticized nightlight's opinions many times, so I guess you read them:-). Of course, that does not mean that nightlight's opinions or my opinions are correct, but that means that you have been exposed to such opinions.

Forum rules require that you identify personal theories which are not generally accepted as such, and to back up your statements with references when challenged - and you are being challenged. Or better, acknowledge that it is a personal theory with no support other than your belief and stick to discussion points that are appropriate. In this forum, continuing to push points that have been discredited - as yours have - is poor etiquette. We have already covered this ground before in this thread!

Again, what is it that I state? It's actually three statements:

1. There have been no loophole-less experimental demonstration of violations of the Bell inequalities.
2. The proof of the Bell theorem requires both unitary evolution (UE) and the projection postulate (PP) as assumptions.
3. UE and PP, strictly speaking, contradict each other.

and a conclusion:

The Bell theorem is on shaky grounds both experimentally and theoretically.

Statement 1 is the mainstream, and I gave all the references to Shimony, Zeilinger, Genovese.

For statement 2 I indicated where UE and PP are used in the proof of the Bell theorem (to use conservation of angular momentum and to calculate the QM correlations, respectively).

I gave the references to statement 3 (in the form of the problem of measurement in QM) - to von Neumann, Albert, Bassi.

So where is my personal theory? In the conclusion? I believe this conclusion immediately follows from Statements 1-3.

You state that my points were discredited. I reject your statement. I believe I gave adequate answers to the objections. You disagree. That does not mean you're correct and I am wrong or vice versa.

2. I couldn't agree more - you can improve on theories. But theories should NOT be judged according to whether they are "right" or "wrong", but rather according to their utility. For example, Newtonian gravity is actually a better theory than General Relativity for many applications (it has fewer variables). You will see that the next time you calculate the velocity an apple drops from a tree.

This is an excellent example. The problem is it proves my point, not yours. Indeed, Newtonian gravity is very useful. However, it is nonlocal (same as the Coulomb law), whereas general relativity is local, and wherever predictions of these theories differ, the predictions of the latter are correct. I highly respect Newtonian gravity, let alone quantum theory, which is a monumental achievement. But useful theories are not always sufficient to prove such notions as locality or nonlocality, which are important not just for physics, but also for philosophy.

Another example of this kind is thermodynamics. It's an extremely successful and useful theory, but more fundamental theories, such as mechanics or quantum mechanics, strictly speaking, do not allow any irreversibility, which is an integral part of thermodynamics.

Frame Dragger

Feb28-10, 06:18 PM

You state that my points were discredited. I reject your statement. I believe I gave adequate answers to the objections. You disagree. That does not mean you're correct and I am wrong or vice versa.

True, that's for staff to decide, but since "what naturally follows..." is that you reject Bell Theorem and that, believe me, is YOUR theory. Your view that UE and PP are contradictory have been addressed, and I suppose, "rejected" by you.

So, you've finally made yourself (mostly) clear. Now it's time for you to cite like crazy to support such an ATM view here.

SpectraCat

Feb28-10, 06:55 PM

Ok ...

Right, but P(A,B) won't be cos2Θ.

There will still be a statistical dependence between A and B if the (unentangled) counter-propagating disturbances have a common cause and the data are matched wrt this criterion. For example, where setup Q has (emitter - polarizer 1 - polarizer 2 - detector) on both sides, and polarizers 1 are aligned and the setting is changing rapidly and randomly so as to produce identical random polarization for each counter-propagating pair.

These are the only two settings wrt which you can predict B given A, and vice versa.

In the ideal, when Θ = 0 then P(A,B) = 1 (detection attributes for A and B are always identical), and when Θ = 90 degrees then P(A,B) = 0 (detection attributes for A and B are always opposite).

This is true even wrt an entangling source.

Actually, it is. To illustrate:

The polarizers at A and B are misaligned but not by 90 degrees. A has just registered a detection. Will B also register a detection wrt this pair or not?

None of what you are saying makes any sense .. in one breath you say that for entangled particles, the coincidence rate between A & B depends on cos2theta, and in the next breath you say that A & B are "completely random" for any choices of theta besides zero and pi/2. These statements are mutually contradictory. Of course I agree that except for those choices one cannot predict with certainty the outcome at B, given A. However, you can notice that the coincidence rate depends on theta, and that means that the results are not 'completely random". Look at it this way ... in my Alice & Bob example, if Bob used a type-II PDC for source P, and Alice measures compares measurements at theta=30º and theta=60º (theta here is the difference between the polarizer settings), then she will see coincidence rates of 25% and 75%, respectively. If he uses your randomly polarized example for source Q, Alice will see the same results for any value of theta.

Finally, it is a bit of a semantic point, but there is no way to get theta values of exactly zero and pi/2 experimentally .. there will always be at least a finite error. So by your argument, all of the A & B data sets in all the Bell test experiments ever carried out are "completely random" or "uncorrelated", or whatever you call it. Do you really believe that is true?

DrChinese

Feb28-10, 08:35 PM

1. I respectfully disagree. I think this is factually incorrect. Indeed, you need SOMETHING else to prove the Bell theorem, namely, conservation of angular momentum (otherwise how can you be sure that after you measured polarization of one photon of the entangled pair you definitively know polarization of the other one?) And conservation of angular momentum is a consequence of unitary evolution of QM. That is why I repeat that the proof of the Bell theorem requires both UE and PP, which contradict each other.

2. Again, I respectfully disagree. The cos^2(theta) relationship is not the only prediction from QM. Indeed, if the system was initially in a superposition, there is no way you can get destruction of this superposition or irreversibility, unless you reject unitary evolution for the entire system, including the instrument (and an observer, if you wish). So, if there is no irreversibility, that means that no measurement is ever final, in the first place. You want to know what this prediction is exactly? I cannot write the exact prediction, not within a reasonable time frame, but this is not just my opinion. Other people took the trouble to study the process of quantum measurement using a rigorously solved model and showed how the standard results we all are accustomed to arise as approximations, not as precise results, how the projection postulate evolves as a result of irreversibility, which irreversibility, strictly speaking, does not exist, e.g. due to the quantum recurrence theorem. I quoted this published work several times: arXiv:quant-ph/0702135 (Phys. Rev. A 64, 032108 (2001), Europhys. Lett. 61, 452 (2003), Physica E 29, 261 (2005)). Again, you don't need to believe me or Allahverdyan and coauthors. You are a knowledgeable person with profound understanding of quantum mechanics, you are fully aware of the measurement problem in quantum mechanics (and I gave you all the references), so I suspect you fully understand that UE and destruction of superposition are incompatible. Nevertheless, you keep saying something like "C'mon, you're nit-picking, nobody's perfect, so why pick at QM? Be a sport". Sorry, DrChinese, a spade is a spade.

3. Yes, it is, as the Bell theorem proof requires both elements of QM as assumptions - UE and PP, which are mutually contradictory.

4. I am not sure this is technically correct:-), as I mostly follow nightlight's reasoning, and you criticized nightlight's opinions many times, so I guess you read them:-). Of course, that does not mean that nightlight's opinions or my opinions are correct, but that means that you have been exposed to such opinions.

5. Again, what is it that I state? It's actually three statements:

1. There have been no loophole-less experimental demonstration of violations of the Bell inequalities.
2. The proof of the Bell theorem requires both unitary evolution (UE) and the projection postulate (PP) as assumptions.
3. UE and PP, strictly speaking, contradict each other.

and a conclusion:

The Bell theorem is on shaky grounds both experimentally and theoretically.

Statement 1 is the mainstream, and I gave all the references to Shimony, Zeilinger, Genovese.

For statement 2 I indicated where UE and PP are used in the proof of the Bell theorem (to use conservation of angular momentum and to calculate the QM correlations, respectively).

I gave the references to statement 3 (in the form of the problem of measurement in QM) - to von Neumann, Albert, Bassi.

So where is my personal theory? In the conclusion? I believe this conclusion immediately follows from Statements 1-3.

You state that my points were discredited. I reject your statement. I believe I gave adequate answers to the objections. You disagree. That does not mean you're correct and I am wrong or vice versa.

6. This is an excellent example. The problem is it proves my point, not yours. Indeed, Newtonian gravity is very useful. However, it is nonlocal (same as the Coulomb law), whereas general relativity is local, and wherever predictions of these theories differ, the predictions of the latter are correct. I highly respect Newtonian gravity, let alone quantum theory, which is a monumental achievement. But useful theories are not always sufficient to prove such notions as locality or nonlocality, which are important not just for physics, but also for philosophy.

Another example of this kind is thermodynamics. It's an extremely successful and useful theory, but more fundamental theories, such as mechanics or quantum mechanics, strictly speaking, do not allow any irreversibility, which is an integral part of thermodynamics.

What is wrong with you?

1. Bell points out about perfect correlations, which is also present in EPR. This does not require any further discussion, it is an experimental fact and accepted by all: entangled particles exhibit this, and no assumption is required. UE and PP are irrelevant to Bell, and I challenge you to produce a reference otherwise.

2. Do you not read anything I (or anyone else) says? I said that QM predicts the cos^2(theta) relationship for entangled particles. It does not predict otherwise. So who cares how that is arrived at if you think QM is wrong (an embarassing position by the way)? Bell says QM conflicts with LR, really, how hard is that for you to understand? It is absurd to repeat the same statements over and over in post after post. You don't have to agree with QM to know this is the prediction and there is no other (if so, what is it?). You don't have to be a genius to figure out that LR must respect Bell's Inequality once Bell's Theorem is considered. And that is different than QM.

3. Again, reference please.

4. nightlight? You must be kidding, right? He never said this that I recall. And I disagreed with almost everything he said. nightlight is a diehard local realist who ignores Bell test results and disagreed with Bell, as I recall. But never did I hear a comment that QM was "wrong" because of mutually contradictory elements. But perhaps you can correct me on that point, I would welcome that.

5. Laughable! You completely mischaracterize the nature of Zeilinger et al's position on loopholes by quoting out of context. It is true that Zeilinger would like to see a "loophole-free" demonstration of a Bell test, but that is for significantly different reasons than you describe. Zeilinger has already ruled out local realism in numerous OTHER experiments, need I re-reference these? GHZ is a good starter, and there are plenty of others. So it is not about LR being viable or not to him!

Further: the measurement problem - which I acknowledge freely - is hardly a flaw in QM. May as well say GR is wrong too at a singularity because of division by zero. You clearly like to turn back the clock hands with meaningless semantic diversions. How about a little useful science to go with your words? Noone - least of all me - claims QM answers all questions about all things. It is a model, and it is a very useful one. You have only to lay on the table a model that matches and exceeds it to get my attention. Short of that, you are nothing but HOT AIR.

Again, references for your claim that Bell assumes theoretical elements of QM. It ONLY requires knowledge of the predictions of QM, not how those predictions are arrived at.

6. Newtonian gravity IS a useful theory. The subject is theory utility, not theory correctness. Theories may be more or less useful, and they may be disproven as well. All you need to do is provide a more useful theory than QM and we can then discuss that. In the meantime, you again are saying nothing other that "I am right".

--------------------------

You manage to write a lot of words and make a lot of empty claims. I am certainly glad you agree with yourself, very impressive that. Meanwhile, quit making unsupported claims. Where is there a paper which says that Bell assumes UE or PP? HOW ABOUT A BONA FIDE DIRECT REFERENCE FROM A RESPECTED SOURCE?

Demystifier

Mar1-10, 04:28 AM

Therefore, I suspect that violations of the Bell inequalities cannot be proven in dBB using UE only, you need some additional assumptions (or approximations, if you like).
Oh, now I see. When you say "proof", you mean a rigorous mathematical-logical Proof (with capital "P"), not an approximative natural-science proof. Well, I must disappoint you. When applied to the real world without idealizations and approximations, physics cannot Prove anything. It can prove a lot, but it can Prove nothing. Nonlocality of QM is not an exception. You should either find a way to live with it, or leave physics entirely.

Demystifier

Mar1-10, 04:41 AM

... but rather no longer a shooting offense to teach.

English is your native language, right? Unfortunately, that's not the case with me. That's why I often have problems with understanding your beautiful phrases like the one above. :frown:
What do you mean by that?

jtbell

Mar1-10, 06:44 AM

Re: "shooting offense"

I think it's an expression from the cowboy days of the Wild West, where people walked around with guns strapped to their hips, and some were likely to shoot you if you did something that gave them serious offense. :smile:

[off-topic aside] I once watched a Western movie on TV in which the mountains looked strange, with bare rounded tops and rounded rock outcroppings. Yet they also looked familiar. It turned out that the movie had been filmed in Croatia, about which I had seen a travel program not long before!

Frame Dragger

Mar1-10, 06:59 AM

English is your native language, right? Unfortunately, that's not the case with me. That's why I often have problems with understanding your beautiful phrases like the one above. :frown:
What do you mean by that?

I apologize if I was confusing. "A shooting offense" is probably... mid-century (1900s) American Idiom. It's intentional exaggeration meaning that once people were dismissed or punished offhand for 'x' act. In modern parlance, it's often an intentional device used to point out how reactionary people were regarding a given subject at a period in history.

I believe, for the record, that back in the day (in the USA) when executions in the west were mostly hangings and shootings... well... you get the idea. Not a lot of "Due Process" in the old west.

In this context, I was (trying) to be dry, based on a conversation I once had with Zenith. In essence she made the point that not very long ago, it was not allowed to teach dBB in many respected universities. Now that dBB has survived and managed to hold its own, I was reflecting with some measure of sarcasm on a period in our history when the theory was treated like something criminal to be stamped out.

It's not an insult to the theory, but rather the system that is so judgemental of groups and not individuals.

EDIT:
@jtbell: Well, something lik that. I did a little checking when I saw you posted. It turns out it WASN'T the old west! They saved their bullets, and hanged you. :rofl: ouch. It was a much more "civilized" notion, describing the point at which a crime became a capitol offense.

EDIT: Croatia?! Wow... now I want to see that movie! I've seen a drinking show that made the place look wonderful, another travel show which did the same, and a friend (in Ireland) went to a party there for a week, and thought the people were amazing, the architecture stunning, the food damned good, and the weather fine.

I wouldn't mind sipping something cool while looking at ancient architecture. :smile:

Demystifier

Mar1-10, 07:34 AM

EDIT: Croatia?! Wow... now I want to see that movie! I've seen a drinking show that made the place look wonderful, another travel show which did the same, and a friend (in Ireland) went to a party there for a week, and thought the people were amazing, the architecture stunning, the food damned good, and the weather fine.

As someone who lives in Croatia for (almost) the whole life, I can only confirm that. :smile:
Well, except for the architecture. I wouldn't call it amazing, but perhaps that's because I'm used to it.

Frame Dragger

Mar1-10, 07:40 AM

As someone who lives in Croatia for (almost) the whole life, I can only confirm that. :smile:
Well, except for the architecture. I wouldn't call it amazing, but perhaps that's because I'm used to it.

Oh! Well, from the US, hello! I live on the east coast with very VERY British architecture. It's lovely, but after a while... eh. I love travel, as most countries have significantly longer and more diverse histories than the european history in the americas. For me, the architecture is great!

By the way... have you had Bermet? I've only ever heard of it, or seen it on television, but it sounds very interesting.

Demystifier

Mar1-10, 08:01 AM

By the way... have you had Bermet? I've only ever heard of it, or seen it on television, but it sounds very interesting.
It's an alcohol drink, right? Actually, I don't drink alcohol at all. (It's not a matter of principle, I simply don't like it. Well, except in some chocolate products.)

Frame Dragger

Mar1-10, 08:04 AM

It's an alcohol drink, right? Actually, I don't drink alcohol at all. (It's not a matter of principle, I simply don't like it. Well, except in some chocolate products.)

It is, and same here, although I can't claim to even enjoy the chocolate varieties. My friends still laugh at me (over decade later I should add) that my first words upon tasting my first beer were, "Thbbbppptt, what the ****?! Isn't this supposed to be sweet?!?! This is so bitter it's, ecchhhhh." And so forth. :shy:

Demystifier

Mar1-10, 08:10 AM

It is, and same here, although I can't claim to even enjoy the chocolate varieties. My friends still laugh at me (over decade later I should add) that my first words upon tasting my first beer were, "Thbbbppptt, what the ****?! Isn't this supposed to be sweet?!?! This is so bitter it's, ecchhhhh." And so forth. :shy:
I see we have a lot in common. :smile:

DrChinese

Mar1-10, 09:28 AM

Oh, now I see. When you say "proof", you mean a rigorous mathematical-logical Proof (with capital "P"), not an approximative natural-science proof. Well, I must disappoint you. When applied to the real world without idealizations and approximations, physics cannot Prove anything. It can prove a lot, but it can Prove nothing. Nonlocality of QM is not an exception. You should either find a way to live with it, or leave physics entirely.

akhmeteli: I guess your policy is to pick and choose what to accept or reject in QM. I have never seen you comment about any other aspect of QM as wrong. Yet I wonder why you bother with anything in quantum physics if it is all wrong.

So here are my challenges to you, please address any you are able: :biggrin:

1. Post a solid reference to paper that says Bell's Theorem is dependent on the theoretical constructs within QM (rather than the predictions, as most believe). You have so far failed to do this, instead posting references to the QM measurement problem which is hardly the same thing.

2. Provide a dataset for polarization values for 0, 120 and 240 degrees which match experimental statistics. You should be able to supply this if the Bell road map is invalid.

3. Provide an explanation of how particles can become entangled which have never met. Zeilinger and others have performed an entire series of experiments in the past 5+ years around this subject. I would think this would give pause to a local realist. Unless, of course, you simply disregard evidence going against your entrenched position.

Frame Dragger

Mar1-10, 09:55 AM

akhmeteli: I guess your policy is to pick and choose what to accept or reject in QM. I have never seen you comment about any other aspect of QM as wrong. Yet I wonder why you bother with anything in quantum physics if it is all wrong.

So here are my challenges to you, please address any you are able: :biggrin:

1. Post a solid reference to paper that says Bell's Theorem is dependent on the theoretical constructs within QM (rather than the predictions, as most believe). You have so far failed to do this, instead posting references to the QM measurement problem which is hardly the same thing.

2. Provide a dataset for polarization values for 0, 120 and 240 degrees which match experimental statistics. You should be able to supply this if the Bell road map is invalid.

3. Provide an explanation of how particles can become entangled which have never met. Zeilinger and others have performed an entire series of experiments in the past 5+ years around this subject. I would think this would give pause to a local realist. Unless, of course, you simply disregard evidence going against your entrenched position.

I would add this codicile: Do all of that in the minimum number of words required to do so.

DrChinese

Mar1-10, 12:12 PM

I would add this codicile: Do all of that in the minimum number of words required to do so.

Thank you! :biggrin:

akhmeteli

Mar2-10, 05:00 AM

Oh, now I see. When you say "proof", you mean a rigorous mathematical-logical Proof (with capital "P"), not an approximative natural-science proof. Well, I must disappoint you. When applied to the real world without idealizations and approximations, physics cannot Prove anything. It can prove a lot, but it can Prove nothing. Nonlocality of QM is not an exception. You should either find a way to live with it, or leave physics entirely.

Demystifier,

I am happy you understood me. Thank you.

So now the question is whether mathematical rigor is relevant to our discussion.

You see, I can live with nonlocality, no problem at all. I'm just curious: why should I?

You mentioned the real world. However, there is no signal nonlocality in the real world, no experimental demonstration of violations of the genuine Bell inequalities. So we are left with no-go theorems, such as the Bell theorem. But if it uses approximations as assumptions, that opens a hole for locality. Is this hole wide enough or too narrow? I don't know. Do you?

Quantum theory is mature and astonishingly precise, so we can and should judge it to the highest standards. Classical mechanics also was mature and astonishingly precise (and nonlocal, by the way, what with Newton gravity and things like that). But it had problems with birth control, so relativity and quantum theory were born. So is the Bell condom good enough to avoid the trouble of locality? I don't know. The only thing I know it has holes, both experimental and theoretical.

As for my leaving or not leaving physics... You see, physics is a very wide area, there is enough place there both for approximations and for rigorous results, for the Boltzmann equation and for Poincare recurrence theorem. You were very kind to call one of my ideas "interesting", and I am grateful to you, but that idea was based on a rigorous result. Actually, we all do what we can, not what we want.

Frame Dragger

Mar2-10, 05:20 AM

Demystifier,

I am happy you understood me. Thank you.

So now the question is whether mathematical rigor is relevant to our discussion.

You see, I can live with nonlocality, no problem at all. I'm just curious: why should I?

You mentioned the real world. However, there is no signal nonlocality in the real world, no experimental demonstration of violations of the genuine Bell inequalities. So we are left with no-go theorems, such as the Bell theorem. But if it uses approximations as assumptions, that opens a hole for locality. Is this hole wide enough or too narrow? I don't know. Do you?

Quantum theory is mature and astonishingly precise, so we can and should judge it to the highest standards. Classical mechanics also was mature and astonishingly precise (and nonlocal, by the way, what with Newton gravity and things like that). But it had problems with birth control, so relativity and quantum theory were born. So is the Bell condom good enough to avoid the trouble of locality? I don't know. The only thing I know it has holes, both experimental and theoretical.

As for my leaving or not leaving physics... You see, physics is a very wide area, there is enough place there both for approximations and for rigorous results, for the Boltzmann equation and for Poincare recurrence theorem. You were very kind to call one of my ideas "interesting", and I am grateful to you, but that idea was based on a rigorous result. Actually, we all do what we can, not what we want.

A question answered with a question devoid of any SEMBLANCE of new thinking or information? Oh wait, it was said in the MAXIMUM (ok, near max) number of words possible... what a shock.

Tell you what, since you're repeating yourself, go back and re-read the last few question Dr. Chinese has asked you, and answer them in order. As for leaving physics, I think it's a given you were never there based on your lack of responses, and the simple fact that if this is how you comported yourself, you would have been beaten to death by nerds. :smile:

akhmeteli

Mar2-10, 06:52 AM

You manage to write a lot of words and make a lot of empty claims. I am certainly glad you agree with yourself, very impressive that. Meanwhile, quit making unsupported claims. Where is there a paper which says that Bell assumes UE or PP? HOW ABOUT A BONA FIDE DIRECT REFERENCE FROM A RESPECTED SOURCE?

DrChinese, thank you for your time and your letters, I do appreciate them. Actually, they are quite helpful.

Unfortunately, I cannot answer all your questions immediately. I'll try to do it later, but let me start somewhere. So here's the reference:

E. Santos, "Bell’s theorem and the experiments: Increasing empirical support for local realism?", Studies in History and Philosophy of Modern Physics, 36 (2005) 544–565. It's mostly Section 7.

Some quotes:

"According to the traditional formulation, quantum mechanics consists of two quite different ingredients: the formalism (including the equations) and the theory of measurement, both of which are postulated independently. (Actually the two ingredients are to some extent contradictory, because the quantum evolution is continuous and deterministic except during the measurement, where the ‘‘collapse of the wavefuction’’ is discontinuous and stochastic. Thus the modern approach tends to remove any postulated theory of measurement...)."

"The point is that standard proofs of ‘‘Bell’s theorem’’ rest upon the theory of measurement (and preparation of states)."

Santos then mentions other elements of the measurement theory than PP, but you do need PP to calculate the correlations for quantum mechanics: say, you measure a spin projection of one particle of the entangled pair, say, you get value +1, then you use PP to state that after the measurement the system has a definite spin projection of the first particle, then you use UE to state that, due to conservation of angular momentum, the spin projection of the other particle on the same axis is -1, and only then you use the Born rule to find the probability of the other particle having a certain projection of spin on another axis. As the two measurements are spatially separated, it does not matter if you conduct one measurement earlier than the other, later, or simultaneously.

So you cannot take the Malus law from nowhere. It cannot appear in the proof of the Bell's theorem as an experimental law, it can appear there only as a derived result of quantum mechanics, otherwise you cannot say that quantum mechanics predicts nonlocality. And to derive the Malus law in quantum mechanics, you need the theory of measurement, e.g., PP (as I described above).

DrChinese

Mar2-10, 08:29 AM

SpectraCat

Mar2-10, 09:19 AM

DrChinese, thank you for your time and your letters, I do appreciate them. Actually, they are quite helpful.

Unfortunately, I cannot answer all your questions immediately. I'll try to do it later, but let me start somewhere. So here's the reference:

E. Santos, "Bell’s theorem and the experiments: Increasing empirical support for local realism?", Studies in History and Philosophy of Modern Physics, 36 (2005) 544–565. It's mostly Section 7.

Some quotes:

"According to the traditional formulation, quantum mechanics consists of two quite different ingredients: the formalism (including the equations) and the theory of measurement, both of which are postulated independently. (Actually the two ingredients are to some extent contradictory, because the quantum evolution is continuous and deterministic except during the measurement, where the ‘‘collapse of the wavefuction’’ is discontinuous and stochastic. Thus the modern approach tends to remove any postulated theory of measurement...)."

"The point is that standard proofs of ‘‘Bell’s theorem’’ rest upon the theory of measurement (and preparation of states)."

Santos then mentions other elements of the measurement theory than PP, but you do need PP to calculate the correlations for quantum mechanics: say, you measure a spin projection of one particle of the entangled pair, say, you get value +1, then you use PP to state that after the measurement the system has a definite spin projection of the first particle, then you use UE to state that, due to conservation of angular momentum, the spin projection of the other particle on the same axis is -1, and only then you use the Born rule to find the probability of the other particle having a certain projection of spin on another axis. As the two measurements are spatially separated, it does not matter if you conduct one measurement earlier than the other, later, or simultaneously.

So you cannot take the Malus law from nowhere. It cannot appear in the proof of the Bell's theorem as an experimental law, it can appear there only as a derived result of quantum mechanics, otherwise you cannot say that quantum mechanics predicts nonlocality. And to derive the Malus law in quantum mechanics, you need the theory of measurement, e.g., PP (as I described above).

Ok, so I think I finally understand why it has been to hard to understand your point of view here, at least in my case. You are actually challenging the foundations of the standard formulation of quantum mechanics, by attacking one of the core postulates. This is of course fine, but it would have been helpful if you constructed your arguments in that context from the beginning, rather than focusing on the Bell theorem, which is actually just collateral damage from your primary attack.

In truth, there is nothing wrong with Bell's theorem, because he simply takes for granted the postulates that are part and parcel of SQM ... that is what one is *supposed* to do with postulates, when working within a theoretical framework. On the other hand, you refuse to accept one of those postulates, as you have stated consistently from the beginning, and of course this is the really the only logical grounds on which to challenge an otherwise correct mathematical proof/derivation.

EDIT: As I said above, this is fine, but it is hardly mainstream in this case. While the "measurement problem" has been debated long and hard in quantum mechanics, I think most people would still concede that this has not so far proved to be a practical problem for either measurements, or for theoretical predictions derived from the accepted postulates.

Your challenges on the experimental side of things are also hard for me to accept, but as we have already realized, that is because I tend to accept the fair sampling assumption as valid, while you do not. We have each stated our case, and I guess neither has been convinced by the other ... we will simply have to wait for improved detection efficiencies to resolve this matter I guess.

So, while I tend to view your challenge to SQM as rather quixotic, who is to say that I am correct? All I can say is that the postulates of SQM have served us rather well to this point, and there are no clear-cut cases where they have been found to be false. Perhaps there is a point to be made that they are somehow self-contradictory, but so far that is not a widely held view. I have no problem "rationalizing away" the seeming contradiction that you raise, because the unitary evolution postulate pertains to the microscopic quantum system, whereas the measurement postulate pertains to the interaction of the quantum system with a macroscopic detector. Thus the apparent irreversibility that seems to be the focus of your concerns could in my view just be an "effective irreversibility" resulting from entropic effects as the quantum system interacts with the (effectively) continuous distribution of states represented in the macroscopic detector. I think that if this is correct (and I am not claiming that it is), it would be provide a nice symmetry with classical physics, where temporal irreversibility is also just an "effective" phenomenon resulting from the tendency of natural systems to seek states of high entropy.

DrChinese

Mar2-10, 09:38 AM

... This is of course fine, but it would have been helpful if you constructed your arguments in that context from the beginning, rather than focusing on the Bell theorem, which is actually just collateral damage from your primary attack.

In truth, there is nothing wrong with Bell's theorem, because he simply takes for granted the postulates that are part and parcel of SQM ... that is what one is *supposed* to do with postulates, when working within a theoretical framework. On the other hand, you refuse to accept one of those postulates, as you have stated consistently from the beginning, and of course this is the really the only logical grounds on which to challenge an otherwise correct mathematical proof/derivation.
...

I don't follow your assessment of the relationship of sQM and Bell. All Bell depends upon is the prediction of sQM - nothing else. It does not assume that prediction is correct. There is nothing about a Bell test, either, that assumes QM is correct. Maybe it isn't.

Either way, the point of Bell was to demonstrate that the Local Realistic view and the QM views are not compatible. After 1935, it was widely believed that they might be.

SpectraCat

Mar2-10, 09:51 AM

I don't follow your assessment of the relationship of sQM and Bell. All Bell depends upon is the prediction of sQM - nothing else. It does not assume that prediction is correct. There is nothing about a Bell test, either, that assumes QM is correct. Maybe it isn't.

Either way, the point of Bell was to demonstrate that the Local Realistic view and the QM views are not compatible. After 1935, it was widely believed that they might be.

Right, and the prediction of sQM follows from the postulates of sQM, that is all I am saying with the above. If one of those postulates were incorrect, as akhmeteli has hypothesized, then the prediction of sQM could be "wrong", which would then obviously impact the Bell theorem as well. Of course, as I have written, I find akhmeteli's characterization highly suspect ... I accept both the postulates of sQM and the Bell theorem as valid. However at least I now understand where he is coming from ...

MaxwellsDemon

Mar2-10, 10:22 AM

The postulates were chosen in accordance with experimental observations...basically because they work. Personally I think it would be nice if we could replace the highly abstract and mathematical postulates of QM with postulates that still make the same predictions but are more more physically intuitive aesthetically pleasing...more "human". When studying QM, I always get the feeling that I'm starting with Fermat's Last Theorem as an axiom and trying to prove that 2+2=4.

On a side note, I haven't been on this forum for a while...I'm amazed to see that this thread is still active! I thought the matter seemed settled on the first couple pages last I checked.

Oh, and I thought I'd mentioned that I really like beer. I think it tastes great. Nothing like beer and pizza...or beer and burgers...or beer and ____. :D

"Beer is proof that God loves us and wants us to prosper" - Ben Franklin

DrChinese

Mar2-10, 10:42 AM

Right, and the prediction of sQM follows from the postulates of sQM, that is all I am saying with the above. If one of those postulates were incorrect, as akhmeteli has hypothesized, then the prediction of sQM could be "wrong", which would then obviously impact the Bell theorem as well. Of course, as I have written, I find akhmeteli's characterization highly suspect ... I accept both the postulates of sQM and the Bell theorem as valid. However at least I now understand where he is coming from ...

So I think we are in sound agreement: Wrong postulates COULD possibly lead to bad predictions; bad predictions would lead to experimental falsification. But regardless, that has NO IMPACT at all on the incompatibility of QM and LR which Bell's Theorem addresses.

Ergo, bad postulates do not invalidate Bell's Theorem. Bell's Theorem in no way says "IF LR is wrong, then QM is true" or vice versa. They could both be false.

DrChinese

Mar2-10, 10:44 AM

Oh, and I thought I'd mentioned that I really like beer. I think it tastes great. Nothing like beer and pizza...or beer and burgers...or beer and ____. :D

"Beer is proof that God loves us and wants us to prosper" - Ben Franklin

SpectraCat still owes me a couple of beers and refuses to pay up. :biggrin:

Frame Dragger

Mar2-10, 10:48 AM

So, at what point do you accuse someone of being a crackpot who talks endlessly without producing meanginful citations, of being ATM in the thread; relentlessly and annoyingly? (ahkmeteli)

I realize this is a largely civil forum, but I feel that many pages have been wasted in an interesting discussion so that one indivudual could disagree with SQM without saying so. Can we just move on? DrChinese has stated what I believe all relevant members of this discusson agree on, and we can continue. We don't even need to agree with SQM, or Bells Theorem. Surely nothing could be simpler.

ThomasT

Mar2-10, 11:34 AM

None of what you are saying makes any sense .. in one breath you say that for entangled particles, the coincidence rate between A & B depends on cos2theta, and in the next breath you say that A & B are "completely random" for any choices of theta besides zero and pi/2. These statements are mutually contradictory.Let's try again.

At the outset of a run in an idealized, two-photon, optical Bell test the detection rate probabilities are:

for individual detection

P(A) = P(B) = 1/2

and for joint detection

P(A,B) = cos2Θ .

A and B are sets of time-ordered, random-valued, individual detection attributes -- unpredictable sequences of 1's and 0's.

The individual detection rates at A and B aren't correlated to each other, or to Θ, or to λ, or to a or b (the polarizer settings at A and B, respectively). They never vary from 1/2.

However, due to the assumption of common properties imparted to counter-propagating disturbances via emission, then if the value of Θ is known to be 0 or π/2, then if the attribute at A is known then the attribute at B for the pair can be deduced (and vice versa).

The set (A,B) is constructed by pairing the members of A with the members of B wrt detection times. The values of the members of (A,B) also occur randomly.

P(A,B), or the number of pairs containing identical detection attributes is correlated to Θ, and varies as cos2Θ.

Ok so far?

... all of the A & B data sets in all the Bell test experiments ever carried out are "completely random" or "uncorrelated", or whatever you call it. Do you really believe that is true?Yes. See above.

You still haven't (in fact nobody has) said what you think about the argument against the usual interpretation of the meaning of Bell's theorem and violations of Bell inequalities. I've restated it many times. It has simply to do with the contradiction between the factorability of a Bell LHV joint probability representation and Bell test experimental designs, as well as the contradiction between this factorability and QMs nonfactorable joint (entangled) state representation.

SpectraCat

Mar2-10, 12:39 PM

Let's try again.

At the outset of a run in an idealized, two-photon, optical Bell test the detection rate probabilities are:

for individual detection

P(A) = P(B) = 1/2

Just to be clear here, in a standard Bell test, *both* polarization components are measured at A and B. So, as long as you are not equating 0 with "no detection event", then I agree with your statement. What the value of 1/2 signifies to me is that, at detector A, a result of "H" is observed half the time, and "V" is observed for the other half of the events; they are never observed simultaneously. Here "H" and "V" refer to two orthogonal polarization directions.

and for joint detection

P(A,B) = cos2Θ .

Again, just to be clear, this is the case for an entangled source only ... the cos2Θ relationship will not hold for unentangled particles. If you use your earlier example of two independent, randomly polarized counter-propagating beams, then for *any* choice of measurement angles at A and B, you will observe P(A,B)=P(A)P(B)=1/4 (that is, paired detection events satisfying any particular choice of "H" and "V" at both A and B will be observed one quarter of the time).

Furthermore, you can make the polarization relationship between the two *independent* beams whatever you like, and while the overall analysis will become more complicated, Alice will still observe that the probability of observing a particular result at A remains independent of the choice of detection settings at B. That is how she can tell whether or not Bob is using an entangled source or not in the thought experiment I have described in my last few posts.

A and B are sets of time-ordered, randomly occuring individual detection attributes -- unpredictable sequences of 1's and 0's.

The individual detection rates at A and B aren't correlated to each other, or to Θ, or to λ, or to a or b (the polarizer settings at A and B, respectively). They never vary from 1/2.

Agreed ... and perhaps my phrasing was somehow unclear, but I never claimed anything different from this. What I have been saying is that for entangled particles, the likelihood of obtaining a coincidence between paired results at A and B depends in a predictable and non-random way on the relative choice of detection angles, which we have been calling Θ. (Note that it is only the relative value of theta that matters ... the absolute settings in the lab frame at A and B are irrelevant.) For unentangled particles, there is no general dependence of the coincidence rate on the choice of Θ, period.

However, due to the assumption of common properties imparted to counter-propagating disturbances via emission, then if the value of Θ is known to be 0 or π/2, then if the attribute at A is known then the attribute at B for the pair can be deduced (and vice versa).

I would phrase this differently. I would say that, in any setup, one can attempt to make a prediction of a measurement result at detector B, based on the observed result at A and the relative detection angle Θ. In the case of entangled particles, one will find upon comparing paired measurements that the chance that their prediction was correct is either cos2Θ, or 1 - cos2Θ, depending on particular type of entanglement. (As you say, these values become 0 and 1 for the choices of Θ you have been focusing on.) In the case of unentangled particles, one would find that the chance of their prediction being correct is independent of the choice of Θ.

But please consider what happens in both of our pictures when we change Θ by an infinitesimal amount from one of these values (0 or π/2). In my case, the chance of the prediction being correct changes by an infinitesimal amount .. in your case the results become "completely random", to use your words.

The set (A,B) is constructed by pairing the members of A with the members of B wrt detection times, and is also a random sequence.

I think the use of "random" is too vague here. I agree that the results of any particular pair cannot be predicted with certainty in the general case, however the likelihood of a coincidence is given by cos2Θ, so it is not purely random either. That is why I choose the term "correlated" ... I would use "perfectly correlated" or "perfectly anti-correlated" to describe the situation at Θ=0 and Θ=π/2.

P(A,B), or the number of pairs containing identical detection attributes is correlated to Θ, and varies as cos2Θ.

Again, I emphasize that P(A,B)=cos2Θ is only obtained for entangled particles. If you are restricting your statement to that case, then I agree.

SpectraCat

Mar2-10, 12:44 PM

You still haven't (in fact nobody has) said what you think about the argument against the usual interpretation of the meaning of Bell's theorem and violations of Bell inequalities. I've restated it many times. It has simply to do with the contradiction between the factorability of a Bell LHV joint probability representation and Bell test experimental designs, as well as the contradiction between this factorability and QMs nonfactorable joint (entangled) state representation.

Sure I have ... I have said that I thought that such arguments make no sense for the reasons that we have been discussing. The whole Alice and Bob thought experiment I have devised is intended to show that the "inherent contradiction" you mention regarding the experimental design of Bell tests does not exist. (DrChinese has also made similar points.) You have yet to understand the crux of my arguments, but that may be because I have not yet communicated my points clearly ... thus I keep trying.

DrChinese

Mar2-10, 01:30 PM

1. The individual detection rates at A and B aren't correlated to each other, or to Θ, or to λ, or to a or b (the polarizer settings at A and B, respectively). They never vary from 1/2.

2. However, due to the assumption of common properties imparted to counter-propagating disturbances via emission, then if the value of Θ is known to be 0 or π/2, then if the attribute at A is known then the attribute at B for the pair can be deduced (and vice versa).

1. Not exactly sure what you are saying here. I think you are saying that the values are random no matter where across 360 degrees you place the settings. There IS a correlation for Theta, although the values themselves are still random.

2. I think you are re-stating the QM rule used to get the prediction of cos^2(theta). I guess you could call it an assumption used to make the prediction, but that is really simply saying it is part of the theory (or theory application). It is not an assumption of Bell. It is more part of EPR.

SpectraCat

Mar2-10, 01:45 PM

SpectraCat still owes me a couple of beers and refuses to pay up. :biggrin:

Heh! I haven't conceded that I actually lost those beers yet :wink: ... but I can only carry on so many arguments at one time ... I hope to pick up ours again later.

Still, if ever I make it to Texas, I will look you up and buy you a couple brews, just to keep you quiet! :tongue:

DrChinese

Mar2-10, 02:02 PM

Still, if ever I make it to Texas, I will look you up and buy you a couple brews, just to keep you quiet! :tongue:

That works for me... :biggrin:

Frame Dragger

Mar2-10, 02:05 PM

Heh! I haven't conceded that I actually lost those beers yet :wink: ... but I can only carry on so many arguments at one time ... I hope to pick up ours again later.

Still, if ever I make it to Texas, I will look you up and buy you a couple brews, just to keep you quiet! :tongue:

Better yet: Oktoberfest in Germany as the location of 'The First National XXVIIth Industrial Summit For The Regulation of Swatches' could be a place to discuss physics in addition to the nature of swatches, and swatch regulation. Perhaps the argument as to wheh a swatch becomes a SAMPLE could be seen as the line between the macroscopic and microscropic in physics? Maybe I haven't slept in over 36 hours and my brain is playing tricks on me? *plays kazoo; runs away* :rofl:

ThomasT

Mar2-10, 08:34 PM

Just to be clear here, in a standard Bell test, *both* polarization components are measured at A and B. So, as long as you are not equating 0 with "no detection event", then I agree with your statement. What the value of 1/2 signifies to me is that, at detector A, a result of "H" is observed half the time, and "V" is observed for the other half of the events; they are never observed simultaneously. Here "H" and "V" refer to two orthogonal polarization directions.In the tests (eg. Aspect '82) I was thinking of, the counter-propagating optical disturbances incident on the polarizers are assumed to have identical polarizations. A detection attribute of "0" means no detection. The probability 1/2 means that the rate of detection at A and B with polarizers in place is 1/2 the rate of detection at A and B without polarizers. (And, since we're considering an idealization, the value 1/2 means that for N counter-propagating pairs emitted it's expected that N/2 detections will be registered at A and N/2 detections at B.)

... the cos2Θ relationship will not hold for unentangled particles.It might. For example, consider the standard (a la Aspect) Bell test setup, then add a polarizer between the emitter and the polarizer on each side. Let the transmission axes of these two additional polarizers be always aligned and changing randomly. Now the counter-propagating disturbances transmitted by the first set of polarizers are identically polarized, but not entangled. Then the resulting angular dependency will still be cos2Θ, but the probability or normalized rate of joint detection will be .125(1-(2cos2Θ).

What I have been saying is that for entangled particles, the likelihood of obtaining a coincidence between paired results at A and B depends in a predictable and non-random way on the relative choice of detection angles, which we have been calling Θ.I guess we're on the same page then.

... due to the assumption of common properties imparted to counter-propagating disturbances via emission, then if the value of Θ is known to be 0 or π/2, then if the attribute at A is known then the attribute at B for the pair can be deduced (and vice versa).

I would phrase this differently. I would say that, in any setup, one can attempt to make a prediction of a measurement result at detector B, based on the observed result at A and the relative detection angle Θ. In the case of entangled particles, one will find upon comparing paired measurements that the chance that their prediction was correct is either cos2Θ, or 1 - cos2Θ, depending on particular type of entanglement. (As you say, these values become 0 and 1 for the choices of Θ you have been focusing on.) In the case of unentangled particles, one would find that the chance of their prediction being correct is independent of the choice of Θ.

But please consider what happens in both of our pictures when we change Θ by an infinitesimal amount from one of these values (0 or π/2). In my case, the chance of the prediction being correct changes by an infinitesimal amount .. in your case the results become "completely random", to use your words.I think my phrasing is pretty clear (and yours is somewhat confusing). Keep in mind that we're considering idealization of Bell test. What can be deduced about B given knowledge of A and Θ?

I have said that I thought that such arguments make no sense for the reasons that we have been discussing. The whole Alice and Bob thought experiment I have devised is intended to show that the "inherent contradiction" you mention regarding the experimental design of Bell tests does not exist.Let's try again. I'll ask some questions beginning with:

Do you understand that P(A,B) = P(A)P(B), the definition of statistical independence, is also the definition of Bell locality?

akhmeteli

Mar2-10, 09:24 PM

A poor reference indeed. You may as well be quoting yourself.

Whether it's poor or not, it serves its purpose. Indeed, why did I need this reference in the first place? Not to convince you, but to prove that I complied with the forum rules and did not push any personal theory.

Now let us ask ourselves what is exactly controversial in the Santos' quotes I offered? The first quote about the contradiction between the equations of QM and the theory of measurement of QM? But we don't need to believe Santos, as I offered other references confirming this. Furthermore, you yourself "freely admit" the measurement problem in QM. So I just don't quite see what's controversial about the first quote.

Second quote? It says that "standard proofs of ‘‘Bell’s theorem’’ rest upon the theory of measurement". But can we really say with a straight face that we can get the expression for the correlations in QM without the theory of measurement of QM? I don't think so. If you do, then how exactly can you get this expression? You cannot get it from UE, because it is very difficult to compute UE for the particles plus the measuring instruments. Nobody does that to prove Bell. And there is nothing in QM but UE and the theory of measurement. And, as I said, you cannot just use the Malus law until you prove it based exclusively on the postulates of QM (otherwise the correlations will not be based on QM, so it will not be proven that the Bell inequalities can be violated in QM). Furthermore, you cannot use the theory of measurement to prove the Malus law, otherwise the second Santos' quote will still stand.

Santos is a sad figure (in my personal opinion), whose grand contribution is to convince a few good people that "all loopholes should be closed simultaneously" (a questionable conclusion).

Then let me ask you again (I don't remember which time it is - my understanding is I have not heard your opinion on this point), what's exactly wrong with my Euclidean geometry "proof", if it's "questionable" that ALL assumptions of a theorem must be fulfilled simultaneously to ensure its conclusion stands?

His referenced result is not generally accepted any more than Santos' stochastic mechanics hypotheses, all of which have been soundly critiqued. Gosh, they were published too! You'll have to do a lot better than this.

I have proven with this reference that I did not offer any personal theory. Could you please indicate which Santos' quote you personally disagree? The first? The second? Both? Again, I offered other references confirming the first quote and I offered some arguments (in this and the previous posts) confirming the second one.

Frame Dragger

Mar2-10, 09:36 PM

Whether it's poor or not, it serves its purpose. Indeed, why did I need this reference in the first place? Not to convince you, but to prove that I complied with the forum rules and did not push any personal theory.

You cite sources because:
1.) you claim to have them
2.) Why should anyone care about a baseless opinion in THIS forum (try general)
3.) The rules are the rules.

Your "source" serves no purpose; it only goes to the argument that you're just filling pages with your baseless sophistry, now girded by the baseless sophistry of one other person. You constantly attempt to pivot on the question and keep the rhetoric going, but this is not the point of a PHYSICS forum. Cite a meanginful source, answer the questions you've been asked, or take DrChinese's advice and leave the thread if not physics as a whole.

EDIT: Using Santos, who has no personal or professional crediblity or gravitas, is as close as you come in rhetoric to using a real straw man. A real man, if not really made of straw :smile: . As Santos is not respectable, and you have freely aditted the "utility" of your citation the issue returns to your personal beleifs.

SpectraCat

Mar2-10, 09:47 PM

In the tests (eg. Aspect '82) I was thinking of, the counter-propagating optical disturbances incident on the polarizers are assumed to have identical polarizations. A detection attribute of "0" means no detection. The probability 1/2 means that the rate of detection at A and B with polarizers in place is 1/2 the rate of detection at A and B without polarizers. (And, since we're considering an idealization, the value 1/2 means that for N counter-propagating pairs emitted it's expected that N/2 detections will be registered at A and N/2 detections at B.)

Aspect '82, while groundbreaking, is not up to date ... you no longer need to discard half the samples, as I pointed out in my post.

It might. For example, consider the standard (a la Aspect) Bell test setup, then add a polarizer between the emitter and the polarizer on each side. Let the transmission axes of these two additional polarizers be always aligned and changing randomly. Now the counter-propagating disturbances transmitted by the first set of polarizers are identically polarized, but not entangled. Then the resulting angular dependency will still be cos2Θ, but the probability or normalized rate of joint detection will be .125(1-(2cos2Θ).

I don't understand this yet ... I will think about it some more and respond. I am pretty sure that this case should be distinguishable from true entanglement, but I don't quite see how (yet).

I guess we're on the same page then.

Great!

I think my phrasing is pretty clear (and yours is somewhat confusing). Keep in mind that we're considering idealization of Bell test. What can be deduced about B given knowledge of A and Θ?

The probability of observing a coincident detection event within the experimental definition of such an event, as I have said.

Let's try again. I'll ask some questions beginning with:

Do you understand that P(A,B) = P(A)P(B), the definition of statistical independence, is also the definition of Bell locality?

I certainly agree that it is part of the definition ...

zonde

Mar3-10, 03:47 AM

Again, just to be clear, this is the case for an entangled source only ... the cos2Θ relationship will not hold for unentangled particles. If you use your earlier example of two independent, randomly polarized counter-propagating beams, then for *any* choice of measurement angles at A and B, you will observe P(A,B)=P(A)P(B)=1/4 (that is, paired detection events satisfying any particular choice of "H" and "V" at both A and B will be observed one quarter of the time).
It might be interesting to note that as it seems the same source that is used for generation of entangled pairs can be used to generate completely factorizable state i.e. P(A,B)=P(AH)P(BH)+P(AV)P(BV) that can be described using polarizator angles of Alice and Bob but can not be described using only relative angle.

Demystifier

Mar3-10, 04:04 AM

You see, I can live with nonlocality, no problem at all. I'm just curious: why should I?

Because there are many proofs that the world is nonlocal, even though none of these proofs is the Proof. (I hope you understand what I mean. If you don't, despite all the efforts of me and other contributors here, then I cannot find any new way to explain it to you.)

... no experimental demonstration of violations of the genuine Bell inequalities.

But we do have experimental demonstration of what-you-would-call non-genuine Bell inequalities. These experimental results are easily explained by nonlocal QM (combined with some approximations, of course), but are very difficult to explain with local laws of physics. Perhaps not impossible, but very difficult.

So we are left with no-go theorems, such as the Bell theorem. But if it uses approximations as assumptions, that opens a hole for locality. Is this hole wide enough or too narrow? I don't know. Do you?

I think it is the crucial question: Is this hole wide enough or too narrow? We do not have an exact measure of the wideness of this hole, but most physicists agree, even some of those you cited as a support of your views, that the hole seems rather narrow. So, if you ask me to estimate the likelyhoods that nature is nonlocal or local, my subjective estimate would be something like 99:1. What would be yours?

You were very kind to call one of my ideas "interesting", and I am grateful to you, but that idea was based on a rigorous result. Actually, we all do what we can, not what we want.
With that I agree. But that idea cannot be applied to the real world without some approximations that make it non-rigorous. Which, for me, does not make your idea less interesting.

Eye_in_the_Sky

Mar3-10, 05:33 AM

It looks like my opportunity to post at the forum is about to end. I feel hard-pressed, though, to (at least attempt to) close off as much as possible of what I have opened up.

Many posts ago, the first part of Bell's argument (in Bell's original paper) was summarized as follows:

Proposition 1: locality Λ PC Λ CF → local determinism ,

where

CF ≡ counterfactuality

and

PC ≡ perfect anti-correlation for equal settings .

The idea is that the above proposition can be joined to the second part of Bell's argument (in Bell's original paper) which can be summarized as:

Proposition 2: local determinism → D ,

where "D" is a certain condition (which turns out to be inconsistent with Quantum Mechanics).

So, there are two 'theorems', a weak one and a strong one:

Weak Theorem: local determinism → D ;

Strong Theorem: locality Λ PC Λ CF → D .
___________________
Let's say I too see this proposition as valid but not exhaustive ...Zonde, it has been quite a while. ... But I see you are still around.... (I would feel more comfortable if I somehow could make sure that all the abstract terms in this proposition have unambiguous meaning).I see two distinct 'levels' at which one can work in order to establish the validity of "Proposition 1".

One of these levels, I call the "object-level". At the object-level, one analyzes the scenario in terms of outcomes and potential outcomes as they may (or may not) occur in the given physical situation.

However, at this level, the argument suffers from ambiguity due to a lack of clarity in the definition of its essential terms. Just look at the definitions of "locality" and "CF" which one has to work with. These definitions are expressed in terms of words of informal, ordinary language.

For "locality", we have Einstein's words:

The real factual situation of the system S2 is independent of what is done with the system S1, which is spatially separated from the former.

And what about "CF"? At the object-level, "CF" becomes none other than "CFD", that is, "counterfactual definiteness", which as Stapp (the conceiver of the notion) explains is:

For each particle on which a measurement is performed, a definite value would have been found if a different spin component had been measured on it instead (although we cannot know what the specific value would have been) and, furthermore, the complete set of such values (measured and unmeasured together) can be meaningfully discussed.

But there is another level at which one can work to establish the validity of "Proposition 1". I call it the "meta-level". Here, one analyzes the scenario in terms of the joint-probability-function as it would be calculated at the level of a physical theory. At this level, "locality" can be defined in unambiguous, mathematical terms (i.e. in terms of "Bell Locality", which I took a step towards defining back in post #239 (http://www.physicsforums.com/showpost.php?p=2593824&postcount=239) (but I have not yet followed up on it)), while "CF" turns out to correspond to "the permissibility of exploring the causal structure of a physical theory".
___________________
I would say that PC is not a requirement for local determinism. So we can say: locality Λ CF → local determinism."Locality Λ CF" alone is not enough. As far as I can tell, "PC" is essential to the argument, in which case there is not even a substitute for it.That's because PC is certain arrangement of things that applies to one situation but doesn't apply to other.I can't tell what you're getting at here.
___________________
What I don't like about this theorem of QM is that it is placed as restriction on all possible LR theories even when this theorem is not experimentally verified.Zonde ... you are starting to lose me. I would think that "PC" ought to be a feature of any theory. Is "PC" not just the expression of conservation of angular momentum for a system whose angular momentum was initially zero?Let's say we can formulate LR theory that says:
a) If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then measurement of σ2∙a must yield the value -1 or no value at all at least half the time.
b) If measurement of the component σ1∙a, where a is some unit vector, yields the value +1, then low efficiency measurement of σ2∙a must yield the value -1 with very high probability and value +1 with very low probability or no value at all. But as measurement efficiency increases relative probability of +1 value increases rapidly.Okay. ... Now I'm lost.

Eye_in_the_Sky

Mar3-10, 05:41 AM

1) Do you believe you understand the concept expressed by the following statement?

Alice and Bob's outcomes are governed by local determinism.

2) Do you consider the following statement to be true?

On the basis of the single assumption of "local determinism of Alice and Bob's outcomes", one can derive a Bell inequality.I think so

I think soHow about this next statement, would you say that it is correct?

The assumption of "local determinism of Alice and Bob's outcomes" is independent of any assumptions concerning the truth or internal consistency of Quantum Mechanics.I think I disagree with this statement. Indeed, if QM is true and internally consistent, then the Bell inequalities can indeed be violated, so local determinism is eliminated. Therefore the assumption of local determinism does not seem to be independent of the assumptions of truth and consistency of quantum mechanics.Thank you, akhmeteli, for answering my questions. Originally, it appeared to me that there may have been some misconception in the way you were thinking about Bell's Theorem. But from the answers you have given, I do not detect any such misconception.

Indeed, we both agree:

local determinism → D

and

QM → ~D ,

where D is a certain condition.

So finally I am able to understand your position. Essentially, you are saying that the QM prediction of "~D" might be WRONG, and if so, then Bell's Theorem is of LITTLE significance.

But I think that even if this QM prediction did turn out to be wrong, Bell's Theorem would nonetheless be HIGHLY significant. It would still be telling us that two of THE MOST MAJOR world-views EVER to be found in the HISTORY of SCIENCE are FUNDAMENTALLY INCOMPATIBLE.

[The only remaining question (for me, at least) is whether or not one can derive the condition "D" from premises which are logically weaker than the premise of "local determinism" ... thereby strengthening Bell's Theorem.]

Dmitry67

Mar3-10, 05:59 AM

Frame Dragger

Mar3-10, 06:24 AM

Hm
Imagine that QM is not discovered yet (but SR is discovered)
However, there are many EPR Alice/Bob experiments and tons of data
I was thinking that in that case it would be possible to rule out local theories, even without QM, just based on the experiments. AM I wrong?

Maybe... but you'd be creating QM based on the predictions you'd expect a given non-local theory to match. People would probably laugh you out of the room in the absence of QM too. Logically I see your point, but practically, not so much.

zonde

Mar3-10, 08:36 AM

One of these levels, I call the "object-level". At the object-level, one analyzes the scenario in terms of outcomes and potential outcomes as they may (or may not) occur in the given physical situation.

However, at this level, the argument suffers from ambiguity due to a lack of clarity in the definition of its essential terms. Just look at the definitions of "locality" and "CF" which one has to work with. These definitions are expressed in terms of words of informal, ordinary language.

For "locality", we have Einstein's words:

The real factual situation of the system S2 is independent of what is done with the system S1, which is spatially separated from the former.
Ambiguity in this definition is that experiments are done with ensembles. SQM formalism refers to ensembles too. But in discussions single photons are used instead of ensembles.
So what leaves a doubt is if photons from ensemble at different times occupy the same place should this be treated as "locality" or not. But this is quite specific so I think it shouldn't cause problems in most cases.

And what about "CF"? At the object-level, "CF" becomes none other than "CFD", that is, "counterfactual definiteness", which as Stapp (the conceiver of the notion) explains is:

For each particle on which a measurement is performed, a definite value would have been found if a different spin component had been measured on it instead (although we cannot know what the specific value would have been) and, furthermore, the complete set of such values (measured and unmeasured together) can be meaningfully discussed.
That's clear. But does it mean that deterministic chaos is completely excluded by this definition?
It's hard to accept that deterministic chaos somehow contradicts local realism.

"Locality Λ CF" alone is not enough. As far as I can tell, "PC" is essential to the argument, in which case there is not even a substitute for it.I can't tell what you're getting at here.

Zonde ... you are starting to lose me. I would think that "PC" ought to be a feature of any theory. Is "PC" not just the expression of conservation of angular momentum for a system whose angular momentum was initially zero?
"PC" is essential for Bell's argument but is it essential for local realism?
And how you define "PC"?
Say if light is linearly polarized and then it goes through polarizer with the same orientation of polarization axis as for light. All light is passing through polarizer - perfect measurement.
Now polarizator is oriented at different angle and measurement becomes probabilistic.
Are you saying that local realism requires that probability for individual photon can depend only from properties of photon and in no way from context?

Now if we have chaotic context that determines probability and say we include some controllable factor that contributes to context. Now the the outcome will become predictable but only marginally. We can not eliminate chaotic context we can only override it with controllable factors to some extent.
Therefore I say "PC" are not realistic.

zonde

Mar3-10, 08:46 AM

But we do have experimental demonstration of what-you-would-call non-genuine Bell inequalities. These experimental results are easily explained by nonlocal QM (combined with some approximations, of course), but are very difficult to explain with local laws of physics. Perhaps not impossible, but very difficult.
This is no surprise that facts can be more easily explained using less restrictive rules than more restrictive rules.
Well if we talk about that I can explain anything using one rule - God wished it to be so. Are you satisfied with that explanation?

Frame Dragger

Mar3-10, 08:49 AM

This is no surprise that facts can be more easily explained using less restrictive rules than more restrictive rules.
Well if we talk about that I can explain anything using one rule - God wished it to be so. Are you satisfied with that explanation?

Why did you respond to a valid point with the ultimate in reductio ad absurdem?

DrChinese

Mar3-10, 09:28 AM

Whether it's poor or not, it serves its purpose. Indeed, why did I need this reference in the first place? Not to convince you, but to prove that I complied with the forum rules and did not push any personal theory.

Now let us ask ourselves what is exactly controversial in the Santos' quotes I offered? The first quote about the contradiction between the equations of QM and the theory of measurement of QM? But we don't need to believe Santos, as I offered other references confirming this. Furthermore, you yourself "freely admit" the measurement problem in QM. So I just don't quite see what's controversial about the first quote.

Second quote? It says that "standard proofs of ‘‘Bell’s theorem’’ rest upon the theory of measurement". But can we really say with a straight face that we can get the expression for the correlations in QM without the theory of measurement of QM? I don't think so.

All references are not equal, so please, you know better. Santos has been soundly plastered in his defence of LHV theories.

There is a measurement problem in QM, but it is not the kind of problem you imply. It is more of a theory scope issue. And it has nothing to do with Bell. As previously mentioned ad nauseum, if QM is wrong... so be it. But that does not change the fact that QM and LR are incompatible, which is the Bell result.

If you don't understand that QM IS CAPABLE of making predictions, then you haven't heard anything everyone has been telling you. I don't care what Santos said, he has a major ax to grind and wants to discredit any aspect of Bell, Bell tests, QM, etc. it takes in order to convince everyone he is "right" whatever that means. So far, he has been wrong about every single Bell experiment, has made zero correct predictions, and has added zero to our understanding of entanglement - a state he denies exists.

akhmeteli

Mar4-10, 04:59 AM

akhmeteli

Mar4-10, 05:07 AM

Thank you, akhmeteli, for answering my questions. Originally, it appeared to me that there may have been some misconception in the way you were thinking about Bell's Theorem. But from the answers you have given, I do not detect any such misconception.

Indeed, we both agree:

local determinism → D

and

QM → ~D ,

where D is a certain condition.

So finally I am able to understand your position. Essentially, you are saying that the QM prediction of "~D" might be WRONG, and if so, then Bell's Theorem is of LITTLE significance.

But I think that even if this QM prediction did turn out to be wrong, Bell's Theorem would nonetheless be HIGHLY significant. It would still be telling us that two of THE MOST MAJOR world-views EVER to be found in the HISTORY of SCIENCE are FUNDAMENTALLY INCOMPATIBLE.

[The only remaining question (for me, at least) is whether or not one can derive the condition "D" from premises which are logically weaker than the premise of "local determinism" ... thereby strengthening Bell's Theorem.]

Eye_in_the_Sky,

Thank you very much. I am happy that you understood my position.

And I fully agree that the Bell theorem is highly significant no matter what. It pushes standard quantum mechanics to the extreme (and I'd like to emphasize that what you wrote relates to standard quantum mechanics), and this is a great way to test a theory.

akhmeteli

Mar4-10, 05:58 AM

Because there are many proofs that the world is nonlocal, even though none of these proofs is the Proof. (I hope you understand what I mean. If you don't, despite all the efforts of me and other contributors here, then I cannot find any new way to explain it to you.)

I think I understand what you mean. But then I may say that there are many proofs (rather than Proof) that the world is local, such as: the absence of signal nonlocality; microcausality in quantum field theory; the absence of experimental violations of the genuine Bell inequalities; holes in no-go theorems, and so on.

But we do have experimental demonstration of what-you-would-call non-genuine Bell inequalities. These experimental results are easily explained by nonlocal QM (combined with some approximations, of course), but are very difficult to explain with local laws of physics. Perhaps not impossible, but very difficult.

Fair enough. However, I mentioned the astonishing mathematical trick (published by other people) that makes nonlinear differential equations in 3+1 dimensions look like linear unitary evolution equations of quantum field theory in the Fock space. This mechanism suggests that the explanation may be easier than it seems. I'll try to e-mail you about a specific implementation of this mechanism

I think it is the crucial question: Is this hole wide enough or too narrow? We do not have an exact measure of the wideness of this hole, but most physicists agree, even some of those you cited as a support of your views, that the hole seems rather narrow. So, if you ask me to estimate the likelyhoods that nature is nonlocal or local, my subjective estimate would be something like 99:1. What would be yours?

I cited those physicists just to support my view that LR has not been ruled out yet (I know that Shimony, Zeilinger, Genovese don't believe in LR at all, but that is why their honest assessment of the experimental situation is especially valuable), and, judging by your "subjective estimate", you agree that it has not, although you find LR highly unlikely.

As for my "subjective estimate", you see, on the one hand, I only have scientific basis to state that LR has not been ruled out, and I don't want to start a flame, but now that you ask, I admit that my "subjective estimate" is the inverse of yours. Again, I readily admit that I cannot support this estimate, so it's purely subjective. I fully agree that "We do not have an exact measure of the wideness of this hole". Furthermore, my estimate can change drastically in the future to reflect new experimental and theoretical developments.

With that I agree. But that idea cannot be applied to the real world without some approximations that make it non-rigorous. Which, for me, does not make your idea less interesting.

Thank you very much. But you can be sure that, emphasizing the value of rigorous results, I had no intention to "offend" approximate approaches - of course, physics is impossible without them.

Dmitry67

Mar4-10, 06:11 AM

It leads me to another question.

Say, we found a mapping of our physical spacetime P and any system in it into some other (abstract) space A. There is 1:1 relationship between P and A.

If theory is nonlocal in P but local in A, would you call such theory local or not?

Example: We map surface into line, R2 into R1
Theory, which is local in R2 is non local in R1.

Demystifier

Mar4-10, 06:45 AM

Akhmeteli, I have no objections to your last post. It's fair enough.

Demystifier

Mar4-10, 06:50 AM

akhmeteli

Mar4-10, 07:43 AM

Akhmeteli, I have no objections to your last post. It's fair enough.

Thank you very much!

DrChinese

Mar4-10, 08:26 AM

But then I may say that there are many proofs (rather than Proof) that the world is local, such as: the absence of signal nonlocality; microcausality in quantum field theory; the absence of experimental violations of the genuine Bell inequalities; holes in no-go theorems, and so on.

You might say the signal locality is evidence of locality, but the rest of what you say is wrong - again. If you want to reject evidence that goes against your personal opinion, please do not label it as science. Just call it for what it is: a quasi-religious view.

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities. There is no hole in the GHZ no-go. And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense. Please explain how photons that are not - and have never been - in each other's light cones can become entangled. According to local realism, that should not be possible. I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

ThomasT

Mar4-10, 08:28 AM

I am pretty sure that this case should be distinguishable from true entanglement, but I don't quite see how (yet).The first set of polarizers unentangles, but polarizes identically, the counter-propagating disturbances

I certainly agree that it is part of the definition ...Factorability of the joint probability expression defines Bell locality.

DrChinese

Mar4-10, 09:42 AM

But then I may say that there are many proofs (rather than Proof) that the world is local, such as: ... the absence of experimental violations of the genuine Bell inequalities...

Just to demonstrate a specific example that this makes no sense. The below reference was submitted this week by a highly respected research group. It demonstrates nonlocality, see the title. Now, according to your thinking, this is actually evidence of locality rather than non-locality as it states. Are you following any of this, or am I wasting my time? I don't expect you to change your position, rather to simply stop writing what has already been refuted here.

http://arxiv.org/abs/1003.0432

Testing nonlocality over 12.4 km of underground fiber with universal time-bin qubit analyzers

Felix Bussieres, Joshua A. Slater,Jeongwan Jin, Nicolas Godbout, and Wolfgang Tittel
(Dated: March 1, 2010)

"We experimentally demonstrate that the nonlocal nature of time-bin entangled photonic qubits persists when one or two qubits of the pair are converted to polarization qubits. This is possible by implementing a novel Universal Time-Bin Qubit Analyzer (UTBA), which, for the First time, allows analyzing time-bin qubits in any basis. We reveal the nonlocal nature of the emitted light by violating the Clauser-Horne-Shimony-Holt inequality with measurement bases exploring all the dimensions of the Bloch sphere. Moreover, we conducted experiments where one qubit is transmitted over a 12.4 km underground fiber link and demonstrate the suitability of our scheme for use in a real-world setting. The resulting entanglement can also be interpreted as hybrid entanglement between different types of degrees of freedom of two physical systems, which could prove useful in large scale, heterogeneous quantum networks. This work opens new possibilities for testing nonlocality and for implementing new quantum communication protocols with time-bin entanglement."

SpectraCat

Mar4-10, 09:50 AM

The first set of polarizers unentangles, but polarizes identically, the counter-propagating disturbances

I don't think that is an accurate description, not without some additional qualifying statements. In fact, I am not sure it is right ... how can you be so sure that the first set of polarizers breaks the entanglement? It certainly seems logical, but is there an experimental result confirming this? I originally thought as you did for this case, but I started looking for experimental verification, and it all seemed ambiguous. As far as I can tell, the only thing that can be said for sure is that detection of one member of an entangled pair breaks the entangled state, and I don't think it has been proven that interaction with a polarizer is the same as detection. (Actually, I would be happy if the polarizer interactions were proven to be equivalent to detection, because it would drastically strengthen my position in an argument with DrChinese that I have been having in another thread!)

Having said that, let's assume that you are correct, and the first set of polarizers does break the entanglement. In that case, the first set of polarizers will completely block all coincidence measurements if the source is the typical choice of a type-II PDC, which generates HV-VH type entanglement (Bell state). As you can see, if the entangled state is disrupted by the first set of polarizers, only one of the counter-propagating photons will be transmitted (although we don't know which one); the other will be blocked with 100% efficiency. For HH+VV type entanglement (which is not what is used in typical Aspect-style experiments), you would get 100% transmission in both directions ... I guess this is what you are talking about?

Now, the latter case means that both photons acquire a fixed polarization angle \phi relative to the lab frame. The detection probabilities are now dependent on the detection angles at A and B relative to the lab frame, call these \theta_{A} and \theta_{B}. So, for any single measurement, the individual probabilities of detection events at A and B are given by Malus's law as:

cos^{2}\left(\phi-\theta_{A}\right) and cos^{2}\left(\phi-\theta_{B}\right)

So the probability of a coincidence is given by:

cos^{2}\left(\phi-\theta_{A}\right)cos^{2}\left(\phi-\theta_{B}\right)=\frac{1}{4}\left\{2cos^{2}\left( \phi-\theta_{A}\right)+2cos^{2}\left(\phi-\theta_{B}\right)+cos^{2}\left(\theta_{A}-\theta_{B}\right)+cos^{2}\left(2\phi-\theta_{A}-\theta_{B}\right)-2\right\}

Now, I believe that your construction also had the angle \phi as random and variable throughout the experiment, so that means that for a large sample size, Alice's observations will amount to integration of the above expression over all possible values of \phi, which yields:

\frac{1}{4}\int^{2\pi}_{0}\frac{d\phi}{2\pi}\left\ {2cos^{2}\left(\phi-\theta_{A}\right)+2cos^{2}\left(\phi-\theta_{B}\right)+cos^{2}\left(\theta_{A}-\theta_{B}\right)+cos^{2}\left(2\phi-\theta_{A}-\theta_{B}\right)-2\right\}=\frac{\left[2cos^{2}\left(\theta_{A}-\theta_{B}\right)+1\right]}{8}

EDIT: I just noticed that you also give this same expression in an earlier post, so it looks like we are both approaching the problem the same way. Still, my conclusion seems different than yours ...

So, while this expression contains the cos2theta term (theta being the relative angle, or thetaA-thetaB), it is not equal to it. Most importantly, this expression never goes to zero for any choice of theta. So as I hypothesized, there will still be a measurable difference between the entangled and unentangled cases, even with your more elaborate unentangled source.

Factorability of the joint probability expression defines Bell locality.

Ok, I'll accept that if it moves things forward.

akhmeteli

Mar4-10, 11:52 PM

What is wrong with you?

1. Bell points out about perfect correlations, which is also present in EPR. This does not require any further discussion, it is an experimental fact and accepted by all: entangled particles exhibit this, and no assumption is required.

I am not quite sure what you're trying to say and don't want to guess. Care to explain?

UE and PP are irrelevant to Bell, and I challenge you to produce a reference otherwise.

I gave you the reference. I gave you the arguments indicating you need UE and PP or something like that to obtain the QM correlations in the Bell theorem. You don't like the author of the reference. You don't want to discuss his quotes or my arguments. I certainly can live with that.

2. Do you not read anything I (or anyone else) says? I said that QM predicts the cos^2(theta) relationship for entangled particles. It does not predict otherwise.

I reject this last statement ("it does not predict otherwise"). This is what the QM theory of measurement predicts. QM unitary evolution predicts something different: according to UE, there is no irreversibility, so no measurement is ever final. Thus, QM predicts at least two different things, not one, for the same phenomenon.

So who cares how that is arrived at if you think QM is wrong (an embarassing position by the way)?

People care. Not everybody is as flexible as you with logic to "freely admit" problems with QM theory of measurements and express indignation when somebody says that standard QM is, strictly speaking, wrong. I am not the only one who wants to know exactly what is right in QM and what is wrong. When people rigorously show that QM theory of measurement is just an approximate consequence of UE, it matters, because we then know that we cannot trust QM theory of measurement 100%, as you seem to do (while "freely admitting" problems with it :-( )

Bell says QM conflicts with LR, really, how hard is that for you to understand? It is absurd to repeat the same statements over and over in post after post.

I do understand that standard QM conflicts with LR. I repeat, I do understand that. What I am trying to explain is: standard QM conflicts with itself as well, so LR does not have more problems than standard QM itself.

You don't have to agree with QM to know this is the prediction and there is no other (if so, what is it?).

I agree this is a prediction of standard QM. And I disagree, there is other prediction based on UE only. I cannot rewrite the results of Allahverdyan's articles here or rederive them for any experimental setup you may wish to "challenge" me with to tell you "what is it"- the "other" prediction.

You don't have to be a genius to figure out that LR must respect Bell's Inequality once Bell's Theorem is considered.

Again, I agree, LR must respect the (genuine) Bell inequalities.

And that is different than QM.

And I question this. You can only prove that using both UE and QM theory of measurement, which contradict each other. Therefore, you can only state that LR cannot reproduce ALL predictions of QM - this is your phrase. But as long as S(tandard) QM contains mutually contradictory elements, this inability to reproduce all predictions of an internally inconsistent theory is not a problem of LR, but a problem of SQM

3. Again, reference please.

Again, I gave you a reference. I gave you the arguments. You don't like them and don't care to discuss? Fine with me.

4. nightlight? You must be kidding, right? He never said this that I recall.

He questioned that the Bell inequalities can be violated in QM, unless you use PP, which he rejected. He quoted Kowalski's results to suggest that linear equations of UE in Hilbert space can be a disguise for nonlinear differential equations in 3+1 dimensions. So, again, I mostly follow his reasoning.

And I disagreed with almost everything he said. nightlight is a diehard local realist who ignores Bell test results and disagreed with Bell, as I recall.

I did not say you praised his posts:-)

But never did I hear a comment that QM was "wrong" because of mutually contradictory elements. But perhaps you can correct me on that point, I would welcome that.

You did not hear that from nightlight or from anybody? I am not sure about nightlight. But I gave you other references to the contradiction between UE and QM theory of measurement, and you seem to agree there are problems in this area.

5. Laughable! You completely mischaracterize the nature of Zeilinger et al's position on loopholes by quoting out of context. It is true that Zeilinger would like to see a "loophole-free" demonstration of a Bell test, but that is for significantly different reasons than you describe. Zeilinger has already ruled out local realism in numerous OTHER experiments, need I re-reference these? GHZ is a good starter, and there are plenty of others. So it is not about LR being viable or not to him!

I fully agree that Zeilinger is no fan of LR. As for my "quoting out of context"... Look, with all due respect, I am not going to learn Zeilinger's articles by heart or look for a quote confirming YOUR point of view - that would be really rich. So I gave you a quote. You want to prove that Zeilinger believes LR has been ruled out by experiments - give me a direct quote with such claim, and we'll discuss it, don't give me a reference to a dozen articles where I am supposed to find confirmation of your point of view.

Further: the measurement problem - which I acknowledge freely - is hardly a flaw in QM. May as well say GR is wrong too at a singularity because of division by zero.

Look, I know next to nothing about GR, but it is my understanding the singularity is regarded as an indication that GR will be corrected in this point by a future theory. Wouldn't it be natural to think that same logic is in order for QM?

You clearly like to turn back the clock hands with meaningless semantic diversions. How about a little useful science to go with your words? Noone - least of all me - claims QM answers all questions about all things. I think the same conclusion is in order where there is a c It is a model, and it is a very useful one. You have only to lay on the table a model that matches and exceeds it to get my attention. Short of that, you are nothing but HOT AIR.

If I suggested that you do a little useful science and support YOUR hot air with a loophole-less experimental demonstration of violations of the Bell inequalities, I guess you would call my suggestion "empty rhetoric", although you seem to be sure we'll live long enough to see such a demonstration. Why should not I apply this term to your suggestion?

Dmitry67

Mar5-10, 01:12 AM

Is it possible to say that LR is ruled out experimentally and ignore all agruments about internal problems in QM?

Demystifier

Mar5-10, 04:36 AM

Is it possible to say that LR is ruled out experimentally and ignore all agruments about internal problems in QM?
It is possible, but not with absolute certainty. This is because the detectors have a very low efficiency, so the experimental statistics refers to a very small sample of actual particles. In principle, it is possible that this small sample is not a typical sample, but a sample with very special properties, making the illusion of violation of Bell inequalities. Nobody knows a good reason why this sample would not be a typical one, yet such a possibility in principle exists.

This is like president elections. Before the actual counting of all votes, usually there is a preliminary counting of a small sample of all votes. Usually it is a good representative of all the votes, yet the victory of one president candidate over the other cannot be proclaimed before the actual counting of all (or at least of the majority of all) votes.

Akhmetely is like a president candidate who believes that he will win the elections even though all statistics on small samples say the opposite. It's true, such a president candidate may still win, but statistically it is very unlikely.

ZapperZ

Mar5-10, 05:28 AM

It is possible, but not with absolute certainty. This is because the detectors have a very low efficiency, so the experimental statistics refers to a very small sample of actual particles. In principle, it is possible that this small sample is not a typical sample, but a sample with very special properties, making the illusion of violation of Bell inequalities. Nobody knows a good reason why this sample would not be a typical one, yet such a possibility in principle exists.

This is like president elections. Before the actual counting of all votes, usually there is a preliminary counting of a small sample of all votes. Usually it is a good representative of all the votes, yet the victory of one president candidate over the other cannot be proclaimed before the actual counting of all (or at least of the majority of all) votes.

Akhmetely is like a president candidate who believes that he will win the elections even though all statistics on small samples say the opposite. It's true, such a president candidate may still win, but statistically it is very unlikely.

Good analogy, but here's the second half of it.

Say that you DO ask all the citizens to vote, but not officially, i.e. not by casting it in a ballot on election day. For example, you got every single citizen to be at a voice caucus before the actual election. And they vote for the president. So you got the vote of every single citizen.

Yet, again, he refuses to accept the vote because this time, it is not an "official" vote because he said that between this caucus and the actual voting day, someone could change his/her mind.

This is what is going on with the EPR-type experiment using charge particles, where the detection efficiency is 100%. The only drawback here is that they still have not been able YET to close the locality loophole (and I fully expect that they will soon!). That's why I mentioned earlier that these loopholes are closed separately in different experiments. It is like you get the SAME result no matter if you only do a "sample election", or if you do a caucus of 100% of the citizen. What are the odds that if you do not win on any of those, that you will win if 100% of the citizen voted on election day? We live our lives with significantly lower odds than that!

Zz.

Dmitry67

Mar5-10, 05:49 AM

Thank you
What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?

Demystifier

Mar5-10, 06:48 AM

ZapperZ

Mar5-10, 07:15 AM

Zz, thanks for the second half. Can you give me a reference for the EPR-type experiment using charged particles with the 100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.

Demystifier

Mar5-10, 07:25 AM

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.
Thanks! The paper is available for free:
http://www.sciencemag.org/cgi/reprint/323/5913/486.pdf?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=olmschenk&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT

However, from the title and the abstract it is not obvious that this paper closes the fair sampling loophole of nonlocality. Do you know a paper which states it more explicitly?

EDIT: Now I've noticed that you added a PRL reference. It is more explicit. This is exactly what I needed. Thanks again.

zonde

Mar5-10, 07:39 AM

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities. There is no hole in the GHZ no-go.
There is exactly the same fair sampling hole in GHZ.
Basically Bell theorem says you can't get different correlations predicted by QM using the same pairs. That is exactly the same with GHZ. Only in GHZ this is purer as you have group of four correlations where one of them falls out if you assume the same detected pairs for all correlations.

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.
That's right. Failure of disproof is a failure. It can't be proof of something else.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled. According to local realism, that should not be possible. I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.
Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

DrChinese

Mar5-10, 08:24 AM

1. There is exactly the same fair sampling hole in GHZ.

2. Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

zonde

Mar5-10, 08:39 AM

D.N. Matsukevich et al., PRL v.100, p.150404 (2008).
http://arxiv.org/abs/0801.2184
"We observe violation of a Bell inequality between the quantum states of two remote Yb+ ions separated by a distance of about one meter with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography."
As I understand it states that emitted photons of two ions interact and as a result two ions become entangled (entanglement teleportation) and as a result the same photons that where used to entangle ions instantaneously show signs of ion entanglement (result of entanglement is telported back to photons). And then these photons are detected. Right?

Interesting but it is quite unclear what it has to do with local realism.

Demystifier

Mar5-10, 08:41 AM

SpectraCat

Mar5-10, 08:44 AM

zonde

Mar5-10, 08:58 AM

zonde

Mar5-10, 09:27 AM

What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?
Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

Dmitry67

Mar5-10, 09:45 AM

Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

well, yes, but:
* there is no alternative suggested by local realists. there are no neo-LR interpretations to compare with. Even MOND curvefitting, no matter how naive is it, is better: at least, it is something.
* Why intuition insists on locality? Mine does not.

Demystifier

Mar5-10, 09:53 AM

* Why intuition insists on locality? Mine does not.
Mine too. For example, the Newton law of gravity is quite intuitive to me. Also, when I was a little child, I thought that light and sound come to me from their source instantaneously.

DrChinese

Mar5-10, 10:10 AM

Zonde's criticism is actually a reasonable one, and is not really addressed in the paper. The fact is that the pump photons for this experiment come from the same source, and an interferometer is actually part of the experimental scheme upstream of the two independent PDC's. Therefore, I think any claim that the two initial entangled pairs in this experiment are "independent" needs to be very carefully examined. I have been thinking about this since zonde first mentioned this criticism a few weeks ago, and I have not been able to disprove or rectify it. I definitely don't think it can be dismissed out of hand.

I would like to see a version of this experiment that uses two independent pump lasers ... but that is quite technically challenging from a synchronization point of view. There are also non-trivial issues concerning how "identical" the pump pulses are in such a case, because distinguishability of the B & C photons could (would?) disrupt the entanglement swapping. That last point in particular is why I think zonde's criticism is deserving of very careful analysis.

It is true that the same pump is being used in the referenced experiment. But subseqently, Zeilinger has put together a method of synchronizing separate lasers. Nothing changes when the proper setup is used and the photons are indistinguishable - as would be expected from QM. I think it is only a matter of time before all of the separate elements can be assembled into a single experiment. I would agree that it is always desirable to run the experiment with all the refinements together, where possible and practical.

http://arxiv.org/abs/0809.3991

In the above, there is entanglement swapping but there is no attempt (as I recall) to also perform delayed choice.

DrChinese

Mar5-10, 10:18 AM

Theoretically LR was ruled out by Bell theorem.
And no you can't do that with sample size of 1. You need 4 experiments (with sample size of 1):
- one channel H/V, other L/R, third L/R
- one channel L/R, other H/V, third L/R
- one channel L/R, other L/R, third H/V
- one channel H/V, other H/V, third H/V
or if we can't do H/V and L/R simultaneously then even 8 experiments.

No, not Zeilinger. See post #219 where I gave the quote (and link to paper):
http://www.physicsforums.com/showthread.php?p=2590786#post2590786
That is the same paper you discussed in other thread.

OK, Tittel & Gisin et al. I guess I am missing what you are saying, because you cannot be questioning these folks' conclusions.

akhmeteli

Mar6-10, 01:55 AM

You might say the signal locality is evidence of locality, but the rest of what you say is wrong - again. If you want to reject evidence that goes against your personal opinion, please do not label it as science. Just call it for what it is: a quasi-religious view.

With all due respect, if you declare something wrong, it does not necessarily mean it is indeed wrong. I discuss your specific arguments below.

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities.

There are none. Nil. Gimme a break, or a reference to experimental violations without loopholes.

There is no hole in the GHZ no-go.

Does not it use the QM theory of measurement?

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.

If you think that a no-go theorem with a hole is a proof of nonlocality, then a hole in that theorem is certainly a proof of locality. I could agree that a hole is not a proof of locality, but not before you agree that a theorem with a hole is not a proof of nonlocality. This is a zero-sum game, and I believe the rules should be the same for proponents of both views.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled.

First of all, I said several times that entanglement per se does not spell nonlocality (if you disagree, and you seem to disagree, the burden of proof is on you - I reject your "by definition" argument - indeed, if, for example the entangled particles are not spatially separated, they are no problem for locality, so don't tell me about definitions), so I don't need to explain anything. You can only declare nonlocality if the Bell inequalities are violated, and there is no evidence of violations of the genuine Bell inequalities. If you deny that, this is just your personal theory.

Ok, so, as I said, I am under no obligation to explain entanglement. However, I can repeat the following: "QFT-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post http://www.physicsforums.com/showpost.php?p=1825523&postcount=90." So we have nonlinear differential equations in 3+1 dimensions, which are local, as input, use the referenced mathematical trick, and get something looking very much like quantum field theory, but equivalent to the input local equations on the set of solutions of those local equations. But now you have linear evolution equations in the Fock space, so there could be at least an appearance of entanglement. Again, I did not explore this much further as a local explanation of entanglement, but this does look like a possibility.

According to local realism, that should not be possible.

Sez who? See above.

I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

Look, in this post I had to pretty much repeat myself, that means I did not "avoid these difficult questions" previously.

akhmeteli

Mar6-10, 03:22 AM

Ok, so I think I finally understand why it has been to hard to understand your point of view here, at least in my case. You are actually challenging the foundations of the standard formulation of quantum mechanics, by attacking one of the core postulates. This is of course fine, but it would have been helpful if you constructed your arguments in that context from the beginning, rather than focusing on the Bell theorem, which is actually just collateral damage from your primary attack.

I regret that I was not able to make my posts easier to understand.

In truth, there is nothing wrong with Bell's theorem, because he simply takes for granted the postulates that are part and parcel of SQM ... that is what one is *supposed* to do with postulates, when working within a theoretical framework. On the other hand, you refuse to accept one of those postulates, as you have stated consistently from the beginning, and of course this is the really the only logical grounds on which to challenge an otherwise correct mathematical proof/derivation.

I agree on these points.

EDIT: As I said above, this is fine, but it is hardly mainstream in this case. While the "measurement problem" has been debated long and hard in quantum mechanics, I think most people would still concede that this has not so far proved to be a practical problem for either measurements, or for theoretical predictions derived from the accepted postulates.

I'd say it is not the mainstream in the sense that few people care about it. On the other hand, not many people deny there is a problem. For example, DrChinese does not deny this. So in this sense you may perhaps say it is the mainstream. You may also wish to look at the Schlosshauer quote at the end of my post 41 in this thread.

So, while I tend to view your challenge to SQM as rather quixotic, who is to say that I am correct?

Quixotic? I don't know. Well, sometimes even I think that there should be less painful ways to make friends:-) On the other hand, I think my arguments are pretty straightforward, so many people do understand them, like you understood them. You did not become a local realist, you still think Nature is nonlocal, we still disagree, but you just understood my arguments, and I think this is good for both of us. You see, I am not even sure I can call myself a local realist: indeed, if tomorrow experiments prove me wrong, so be it, I'll have to change my views.

Actually, I guess you would say nightlight is quixotic as well, but I am grateful to him, as he made clear some things that looked totally mysterious.

All I can say is that the postulates of SQM have served us rather well to this point, and there are no clear-cut cases where they have been found to be false. Perhaps there is a point to be made that they are somehow self-contradictory, but so far that is not a widely held view. I have no problem "rationalizing away" the seeming contradiction that you raise, because the unitary evolution postulate pertains to the microscopic quantum system, whereas the measurement postulate pertains to the interaction of the quantum system with a macroscopic detector. Thus the apparent irreversibility that seems to be the focus of your concerns could in my view just be an "effective irreversibility" resulting from entropic effects as the quantum system interacts with the (effectively) continuous distribution of states represented in the macroscopic detector. I think that if this is correct (and I am not claiming that it is), it would be provide a nice symmetry with classical physics, where temporal irreversibility is also just an "effective" phenomenon resulting from the tendency of natural systems to seek states of high entropy.

Neither would I have problems "rationalizing away" the contradiction, but it introduces nonlocality, and that is a really radical notion. I do need iron-clad arguments to accept it.

Count Iblis

Mar6-10, 07:58 AM

How does this all square with the fact that I'm unquestionably real and local? :confused:

Frame Dragger

Mar6-10, 08:39 AM

How does this all square with the fact that I'm unquestionably real and local? :confused:

Are you?

ThomasT

Mar6-10, 08:40 AM

... how can you be so sure that the first set of polarizers breaks the entanglement? As far as I can tell, the only thing that can be said for sure is that detection of one member of an entangled pair breaks the entangled state, and I don't think it has been proven that interaction with a polarizer is the same as detection. (Actually, I would be happy if the polarizer interactions were proven to be equivalent to detection, because it would drastically strengthen my position in an argument with DrChinese that I have been having in another thread!) In the entangled state polarization is undetermined and QM just specifies the relationship between the counter-propagating disturbances incident on the polarizers.

Afaik, when polarization is determined, then entanglement is broken. The polarization is determined by the polarizer via transmission along its axial setting.

ThomasT

Mar6-10, 09:12 AM

Why intuition insists on locality? Mine does not.Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

Frame Dragger

Mar6-10, 09:27 AM

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

IMHO Most people, myself included, believe that your viewpoint only exists through those means in bold; I might add a forcefully willful ignorance that borders on the religious.

Dmitry67

Mar6-10, 10:21 AM

For me no-FTL and locality is something which emerges only macroscopically. So locality, while it is observed in most cases and is only "weakly" violated in EPR is not "natural"

akhmeteli

Mar6-10, 12:25 PM

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

DrChinese,

I admit that I don't know much about GHZ. However, in the article by Zeilinger e.a., Nature 403, 515-519 (3 February 2000),
Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement, I found the following quote:
"However, we realise that, as for all existing two-particle tests of local
realism, our experiment has rather low detection efficiencies.
Therefore we had to invoke the fair sampling hypothesis21,22,
where it is assumed that the registered events are a faithful
representative of the whole."
So, at least on the face of it, fair sampling is used in GHZ experiments. Of course, the article is relatively old. However, in the following article (GHZ and Shimony, Bell's theorem without inequalities, Am. J. Phys., 58 (12), 1990) I found the following: (the authors discuss a possible GHZ experiment):
"The second step is to show how the test could be done even with low-efficiency detectors, provided that we make a plausible auxiliary assumption, which we call fair sampling. Finally, we show that the auxiliary assumption is dispensable if detector efficiencies exceed 90.8%." So it looks like you need 90% efficient detectors to do without fair sampling in GHZ. To the best of my knowledge, there are no such optical detectors. Please advise if I am wrong.

As for your latest reference (12.4 km experiment), the authors seem to be remarkably reticent on the issue of absence/presence of loopholes.

Another thing. At http://www.quantum.at/fileadmin/Presse/2008-07-01-MG-PW_A_Quantum__Renaissance.pdf Aspelmeyer and Zeilinger (Physics World July 2008, p. 22) write the following:

"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism." Then they discuss GHZ and do not claim that a loophole-free experiment had been performed. This article is recent, unlike the 1998 article in arxiv that I quoted before, so it looks like I did not misrepresent Zeilinger's opinion.

SpectraCat

Mar6-10, 01:19 PM

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

ok ..

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.
[/QUOTE]

Please explain this somewhat cryptic statement in more detail. Do you mean that the interpretation assumes that the photon has to interact locally with the polarizer in order for the measurement at a given detector to occur? Or do you mean something else?

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

Please elaborate on the "local common cause explanation" in this case, not in terms of the Aspect '82 experiment you have mentioned before, but rather in terms of a modern experiment where both polarization components are detected at each detector, so that in the ideal case (100% detector efficiency) there would be no missed detection events.

The coincidental detection angular dependency can be reproduced via LHV formulation.

No, it cannot. If you are refering to the discussion we have been having recently, as I stated in my last post, your "broken entanglement" source produces results that are fundamentally different from the predictions of QM, in that they never go to zero for *any* choice of theta. You have certainly agreed previously that for entangled particles, there will be a relative detector setting (0 or pi, depending on the entangled state), which produces a coincidence rate of zero.

What's the intuitive support for nonlocality?

Who needs it? Where's the intuitive support for the speed of light being a fundamental physical "speed limit"?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

:smile: Yikes ... IMO, that O is not very H :wink: More to the point, I guess you don't dispute that SQM predicts some non-local phenomena? Are those predictions "manipulations of terms" or "misinterpretations" in your view, and why?

yoda jedi

Mar6-10, 01:33 PM

In the entangled state polarization is undetermined and QM just specifies the relationship between the counter-propagating disturbances incident on the polarizers.

Afaik, when polarization is determined, then entanglement is broken. The polarization is determined by the polarizer via transmission along its axial setting.

on pre-determined (polarization values) polarizers ?

but what about ten particles (previous pre-entangled) up and the other ten, down, then make the ten particles up to spin down, and see how spin the other ten particles.............
if change the spin, well that`s no-locality, but i wish to see that......

yoda jedi

Mar6-10, 01:47 PM

Who needs it? Where's the intuitive support for the speed of light being a fundamental physical "speed limit"?

maybe not INTUITIVE.
the "need" is for no-paradoxical reality or a self contradictory posibility.

need-> necessary = of an inevitable nature, logically unavoidable.

Dmitry67

Mar6-10, 02:32 PM

Locality does not save you from the closed timelike curves inside kerr black holes anyway. In curved spacetime, "local" locality does not save you from the global non-local effects :)

yoda jedi

Mar6-10, 04:49 PM

Locality does not save you from the closed timelike curves inside kerr black holes anyway. In curved spacetime, "local" locality does not save you from the global non-local effects :)

yes i know, a possible time travel,
maybe the REALITY is poly-ordered or omni-ordered, can coexist (in principle or possibily) past, present and the future.

irrespective of locality, have to be seen if the CPC negates CTCs.

GeorgCantor

Mar7-10, 02:27 AM

Does the violation of Bell's inequalities and Alain Aspect's experiment lend support to the idea that there is no mind-independent world?

akhmeteli

Mar7-10, 04:51 AM

Just to demonstrate a specific example that this makes no sense. The below reference was submitted this week by a highly respected research group. It demonstrates nonlocality, see the title. Now, according to your thinking, this is actually evidence of locality rather than non-locality as it states. Are you following any of this, or am I wasting my time? I don't expect you to change your position, rather to simply stop writing what has already been refuted here.

Is this the first-ever article with "nonlocality" in the title? As I said, they say absolutely nothing about absence/presence of loopholes. I think they would certainly claim a first-ever loophole-free demonstration of nonlocality, if they could.

And I do believe that the failure to demonstrate nonlocality for 45 years suggests locality.

So, with all due respect, if you say that you refuted something, that does not necessarily mean you refuted it.

ThomasT

Mar7-10, 03:11 PM

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.
IMHO Most people, myself included, believe that your viewpoint only exists through those means in bold; I might add a forcefully willful ignorance that borders on the religious.That's a curious belief. :smile:

Certainly there's more to reality than meets the eye. However, the assumption of nonlocality wrt an underlying reality is based on our ignorance, not our knowledge, of that underlying reality.

People can read what they want into QM formalism and technique, and Bell's theorem, and attribute EPR-Bell correlations to nonlocal whatevers. People can see the Virgin Mary in a splatter of spilled gazpacho and attribute that to a personal God giving a sign, or they can attribute the composition and appearance of natural objects to the will of an intelligent designer who they can pray to for free hockey tickets.

For me no-FTL and locality is something which emerges only macroscopically.Does this macroscopic emergence require the prior assumption that there's an underlying physical medium which propagates disturbances ftl?

So locality, while it is observed in most cases and is only "weakly" violated in EPR is not "natural"Locality is what we experience ... exclusively. So it's certainly natural. And, since Bell's locality condition isn't a locality condition, then locality isn't contradicted by Bell tests.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.
Please explain this somewhat cryptic statement in more detail. Do you mean that the interpretation assumes that the photon has to interact locally with the polarizer in order for the measurement at a given detector to occur? Or do you mean something else?The assumption is that the optical disturbances incident on the polarizers have an emission-produced, common property which is being jointly analyzed by the crossed polarizers. Interaction of each disturbance with its associated polarizer is local.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.
Please elaborate on the "local common cause explanation" in this case, not in terms of the Aspect '82 experiment you have mentioned before, but rather in terms of a modern experiment where both polarization components are detected at each detector, so that in the ideal case (100% detector efficiency) there would be no missed detection events.The type of experiment doesn't matter. A<->B type correlations have a local common cause explanation. The problem for the local realist isn't explaining correlation (anticorrelation) between A and B, it's reproducing the full range of QM predicted and observed experimental results.

... as I stated in my last post, your "broken entanglement" source produces results that are fundamentally different from the predictions of QM ... The result that you (and I) posted is the QM prediction for that setup.

... I guess you don't dispute that SQM predicts some non-local phenomena? Are those predictions "manipulations of terms" or "misinterpretations" in your view, and why?Whether or not SQM predicts non-local phenomena depends on how SQM is interpreted. There are no, per se, nonlocal phenomena.

Frame Dragger

Mar7-10, 04:58 PM

DrChinese

Mar7-10, 06:55 PM

DrChinese,

I admit that I don't know much about GHZ. However, in the article by Zeilinger e.a., Nature 403, 515-519 (3 February 2000),
Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement, I found the following quote:
"However, we realise that, as for all existing two-particle tests of local
realism, our experiment has rather low detection efficiencies.
Therefore we had to invoke the fair sampling hypothesis21,22,
where it is assumed that the registered events are a faithful
representative of the whole."
So, at least on the face of it, fair sampling is used in GHZ experiments. Of course, the article is relatively old. However, in the following article (GHZ and Shimony, Bell's theorem without inequalities, Am. J. Phys., 58 (12), 1990) I found the following: (the authors discuss a possible GHZ experiment):
"The second step is to show how the test could be done even with low-efficiency detectors, provided that we make a plausible auxiliary assumption, which we call fair sampling. Finally, we show that the auxiliary assumption is dispensable if detector efficiencies exceed 90.8%." So it looks like you need 90% efficient detectors to do without fair sampling in GHZ. To the best of my knowledge, there are no such optical detectors. Please advise if I am wrong.

As for your latest reference (12.4 km experiment), the authors seem to be remarkably reticent on the issue of absence/presence of loopholes.

Another thing. At http://www.quantum.at/fileadmin/Presse/2008-07-01-MG-PW_A_Quantum__Renaissance.pdf Aspelmeyer and Zeilinger (Physics World July 2008, p. 22) write the following:

"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism." Then they discuss GHZ and do not claim that a loophole-free experiment had been performed. This article is recent, unlike the 1998 article in arxiv that I quoted before, so it looks like I did not misrepresent Zeilinger's opinion.

I would say again that you have substantially misrepresented Zeilinger's position by pulling out a early quote from a historical narrative prior to his reaching the end. He goes on to say (regarding 3 particle GHZ and then summarizing the results of both GHZ and Bell tests):

"...three entangled particles can produce an immediate
conflict in a single measurement result because
measurements on two of the particles allow us to predict
with certainty the property of the third particle.
The first experiments on three entangled photons
were performed in late 1999 by AZ and co-workers, and
they revealed a striking accordance with quantum theory
(Nature 403 515). So far, all tests of both Bell’s inequalities
and on three entangled particles (known as
GHZ experiments) (see figure 1) confirm the predictions
of quantum theory, and hence are in conflict with
the joint assumption of locality and realism as underlying
working hypotheses for any physical theory that
wants to explain the features of entangled particles."

and later:

"One such question concerns once again the notions
of locality and realism. The whole body of Bell and
GHZ experiments performed over the years suggests
that at least one of these two assumptions is inadequate
to describe the physical world (at least as long
as entangled states are involved). But Bell’s theorem
does not allow us to say which one of the two should
be abandoned."

Next time, try sticking to the gist of the article. Zeilinger goes on to mention Leggett (as I have as well) and the fact that this rules out even many forms of non-local realism. In the meantime, I noticed you have also failed to produce any of the following:

a) Decent reference for Bell being dependent on QM theory or the measurement problem.
b) A dataset that matches the QM predictions that is realistic.

And referring to your post stating the absurdly illogical "And I do believe that the failure to demonstrate nonlocality for 45 years suggests locality." At least you finally mention it is your opinion in the statement, a position to which you are entitled and I would not bother to try to change your mind about. (Perhaps I should state the highly insightful: "And I do believe that the failure to demonstrate non-existence of leprechauns for 45 years suggests the leprechaun exists.")

Honestly, I think our dialogue has reached an end. I simply ask that from here on out, you label your opinions as such. And please, do not misrepresent the opinions (or general scientific acceptance thereof) of other authors. You are entitled to your opinion, but you are not entitled to misled others who may not know as much about the area.

DrChinese

Mar7-10, 06:58 PM

Does the violation of Bell's inequalities and Alain Aspect's experiment lend support to the idea that there is no mind-independent world?

As far as I know, the answer is NO. But there are others who disagree. There is no meaningful evidence on this question.

akhmeteli

Mar7-10, 08:16 PM

I would say again that you have substantially misrepresented Zeilinger's position by pulling out a early quote from a historical narrative prior to his reaching the end. He goes on to say (regarding 3 particle GHZ and then summarizing the results of both GHZ and Bell tests):

"...three entangled particles can produce an immediate
conflict in a single measurement result because
measurements on two of the particles allow us to predict
with certainty the property of the third particle.
The first experiments on three entangled photons
were performed in late 1999 by AZ and co-workers, and
they revealed a striking accordance with quantum theory
(Nature 403 515). So far, all tests of both Bell’s inequalities
and on three entangled particles (known as
GHZ experiments) (see figure 1) confirm the predictions
of quantum theory, and hence are in conflict with
the joint assumption of locality and realism as underlying
working hypotheses for any physical theory that
wants to explain the features of entangled particles."

and later:

"One such question concerns once again the notions
of locality and realism. The whole body of Bell and
GHZ experiments performed over the years suggests
that at least one of these two assumptions is inadequate
to describe the physical world (at least as long
as entangled states are involved). But Bell’s theorem
does not allow us to say which one of the two should
be abandoned."

Look, people ask you if GHZ produced loophole-free evidence against LR. You choose to keep silence on this point. I gave you a 2008 quote by Zeilinger that there had been no loophole-free experiments ruling out LR by that time. (Nobody claimed such experiments since then, as far as I know, and there are no such claims in work referenced by you). So who misrepresents him?

Next time, try sticking to the gist of the article. Zeilinger goes on to mention Leggett (as I have as well) and the fact that this rules out even many forms of non-local realism.

See above

In the meantime, I noticed you have also failed to produce any of the following:

a) Decent reference for Bell being dependent on QM theory or the measurement problem.
b) A dataset that matches the QM predictions that is realistic.

First you demand a reference, now you demand what you call a "decent reference", next you'll require a "perfect reference"? I reject your demand. The rules demand that I present a published reference, I did just that. You refuse to criticize the quotes from the reference I offered or my arguments supporting them, you prefer to criticize the author of the reference - it's your decision.

Neither am I under any obligation to produce any "dataset". I state that LR has not been ruled out so far. To this end, I proved by references that no violations of the genuine Bell inequalities had been demonstrated experimentally and that the Bell theorem itself uses mutually contradictory assumptions from standard QM (or, if you wish, consequences of these assumptions), thus it cannot be considered a no-go theorem for LR. If you have other proofs that LR has been ruled out, then YOU are supposed to present them. I indicated a general approach demonstrating at least appearance of entanglement in local theories. I don't have to accept any "challenges" you may wish to offer. Again, you would not understand if I demanded that you conduct a loophole-free experiment. So either put up a proof that LR has been ruled out, or...

By the way, how about Euclidian geometry?

Honestly, I think our dialogue has reached an end.

As you wish.

I simply ask that from here on out, you label your opinions as such. And please, do not misrepresent the opinions (or general scientific acceptance thereof) of other authors. You are entitled to your opinion, but you are not entitled to misled others who may not know as much about the area.

I reject your allegations that I misrepresented "the opinions (or general scientific acceptance thereof) of other authors".

zonde

Mar8-10, 03:33 AM

and later:
"One such question concerns once again the notions
of locality and realism. The whole body of Bell and
GHZ experiments performed over the years suggests
that at least one of these two assumptions is inadequate
to describe the physical world (at least as long
as entangled states are involved). But Bell’s theorem
does not allow us to say which one of the two should
be abandoned."
Suggests but does not prove. So nothing new here.

a) Decent reference for Bell being dependent on QM theory or the measurement problem.
Why separate reference when Bell's paper can be used instead:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
And anyone wishing to confirm that this statement has crucial role for Bell argument can examining his paper. http://www.drchinese.com/David/Bell_Compact.pdf

Demystifier

Mar8-10, 04:15 AM

Do the authors of the paper reporting the actual GHZ experiment explicitly claim that this disproof of LR does not contain any experimental loopholes?
I asked it Dr Chinese, but now Akhmeteli answered it in #385. Not only that they do not claim that, but they explicitly claim the opposite. Of course, it does not change my opinion that nature is nonlocal, but it's fair to say honestly how much the existing evidence for it is certain. The evidence is indeed strong, but there is no need to exaggerate that it is even stronger than it really is.

Hans de Vries

Mar8-10, 05:31 AM

And entanglement is not so easy to explain these days with some of the newer experiments. EPR is completely lost on these. Please explain, for example, how photons become entangled when they are not in each other's light cones - and never have been - and originate from different lasers. Meanwhile, QM can..

It would be a totally sensational result if there was any correlation outside the
lightcone but I can't draw this conclusion from these experiments.

If there is correlation between pair A1,B1 and independently there is correlation
between pair A2,B2. Then the (random) relation between A1 and A2 is also
expected between B1 and B2 even if B1 and B2 have never met.

Regards, Hans

SpectraCat

Mar8-10, 07:15 AM

Why separate reference when Bell's paper can be used instead:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
And anyone wishing to confirm that this statement has crucial role for Bell argument can examining his paper. http://www.drchinese.com/David/Bell_Compact.pdf

I don't really see how this is crucial for his *argument*. In section II, he sets up the test cases for his proof in terms of the predictions of QM, which have been adequately supported by experimental measurements (EDIT: although not at the time, and this is my opinion of the modern experimental results). However everything concerning the proof in section IV is completely independent of how those test cases were determined. So, the only way that Bell's paper "depends on QM", is for the generation of the test case. Since this is outside the scope of the rest of the derivation, the idea of a "Bell test" certainly seems valid outside the scope of the initial test case it was devised to explain.

DrChinese

Mar8-10, 07:17 AM

Suggests but does not prove. So nothing new here.

Why separate reference when Bell's paper can be used instead:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
And anyone wishing to confirm that this statement has crucial role for Bell argument can examining his paper. http://www.drchinese.com/David/Bell_Compact.pdf

That is a prediction of QM. Maybe it was wrong. It doesn't matter HOW the prediction was arrived at for Bell. The important thing is the QM and LR are incompatible as to their predictions.

SpectraCat

Mar8-10, 07:19 AM

It would be a totally sensational result if there was any correlation outside the
lightcone but I can't draw this conclusion from these experiments.

If there is correlation between pair A1,B1 and independently there is correlation
between pair A2,B2. Then the (random) relation between A1 and A2 is also
expected between B1 and B2 even if B1 and B2 have never met.

Regards, Hans

Yes, but the correlations between the non-interacting photons (B1 and B2 in your example) violate a Bell inequality, which means that they cannot be explained in terms of simple random coincidences. Whether or not these results are proof of quantum non-locality is still open for discussion .. it depends on if you accept the assumptions of the experiment (i.e. independence of initial entangled pairs, fair sampling assumption), which some are not prepared to do yet. (that is the whole reason for this thread)

DrChinese

Mar8-10, 07:19 AM

I asked it Dr Chinese, but now Akhmeteli answered it in #385. Not only that they do not claim that, but they explicitly claim the opposite. Of course, it does not change my opinion that nature is nonlocal, but it's fair to say honestly how much the existing evidence for it is certain. The evidence is indeed strong, but there is no need to exaggerate that it is even stronger than it really is.

You should re-read my response or look at the original. Akhmeteli takes the comment out of context. As per usual. It is clear by the end of the article that they do not consider LR viable per experiment.

From my #395:

"...three entangled particles can produce an immediate
conflict in a single measurement result because
measurements on two of the particles allow us to predict
with certainty the property of the third particle.
The first experiments on three entangled photons
were performed in late 1999 by AZ and co-workers, and
they revealed a striking accordance with quantum theory
(Nature 403 515). So far, all tests of both Bell’s inequalities
and on three entangled particles (known as
GHZ experiments) (see figure 1) confirm the predictions
of quantum theory, and hence are in conflict with
the joint assumption of locality and realism as underlying
working hypotheses for any physical theory that
wants to explain the features of entangled particles."

I don't think that this in any way deviates from what I have been saying, of course Zeilinger says it much more clearly.

DrChinese

Mar8-10, 07:22 AM

Frame Dragger

Mar8-10, 08:15 AM

It is not random as you suggest. They are entangled, and exhibit statistics to match. Correlated but unentangled photons do not show those statistics.

I read this paper and I don't see how there can be this apparant level of confusion regarding these entangled photons. We can parse the language to fit our agendas (ahkmeteli) or be genuinely confused (ThomasT), or truly believe (DrChinese) or not (Demystifier).

Some relevant questions about the laser source for supposedly "never met each other" photons seem germaine. This endless meandering about ERB and Bell has become so cyclical and predictable that I set my clock by them now. Can we please jettison disruptive elements (akhmeteli and any like), and get back to the real questions about the LR or not?

The next person who says "loophole" is going to be on the wrong end of a slap to the face, or maybe a botnet. I'm tired, so it'll be a coinflip. :rofl: I'm kidding, or am I? Ahhh....

DrChinese

Mar8-10, 08:38 AM

I read this paper and I don't see how there can be this apparant level of confusion regarding these entangled photons. We can parse the language to fit our agendas (ahkmeteli) or be genuinely confused (ThomasT), or truly believe (DrChinese) or not (Demystifier).

Some relevant questions about the laser source for supposedly "never met each other" photons seem germaine. This endless meandering about ERB and Bell has become so cyclical and predictable that I set my clock by them now. Can we please jettison disruptive elements (akhmeteli and any like), and get back to the real questions about the LR or not?

The next person who says "loophole" is going to be on the wrong end of a slap to the face, or maybe a botnet. I'm tired, so it'll be a coinflip. :rofl: I'm kidding, or am I? Ahhh....

Ha!

A note about the "photons that never met each other". This is something of a misnomer (of course perpetrated by the article's author), and I will direct my comments to the other thread we have on the subject so that we can reserve this one for discussion of LR.

zonde

Mar8-10, 08:48 AM

I don't really see how this is crucial for his *argument*. In section II, he sets up the test cases for his proof in terms of the predictions of QM, which have been adequately supported by experimental measurements (EDIT: although not at the time, and this is my opinion of the modern experimental results). However everything concerning the proof in section IV is completely independent of how those test cases were determined. So, the only way that Bell's paper "depends on QM", is for the generation of the test case. Since this is outside the scope of the rest of the derivation, the idea of a "Bell test" certainly seems valid outside the scope of the initial test case it was devised to explain.
For Bell's argument it is crucial that all single measurements are predictable.
Say if there are measurements that are more predictable and others are less predictable it will spoil the whole picture.

DrChinese

Mar8-10, 09:07 AM

SpectraCat

Mar8-10, 09:15 AM

For Bell's argument it is crucial that all single measurements are predictable.
Say if there are measurements that are more predictable and others are less predictable it will spoil the whole picture.

I have no idea what you mean here ... how does anything that is written in that paper even imply that, "all single measurements are predictable"??? The whole point of QM is that, in the general case, the results of single measurements are NOT PREDICTABLE. The only thing that *is* predictable for the case in Bell's paper is the coincidence rate, which is a statistical relationship that is built up from the observation of MANY measurements.

Anyway, as I said, even if you were correct, it wouldn't affect the logic of Bell's deduction at all ... it would only affect whether or not QM predicted violations of the Bell inequality. Those "more and less predictable measurements" you are talking about are completely covered by Bell's LHV formulation AFAICS, so they are handled generally in the proof without any reference to or assumption of the correctness of QM.

Demystifier

Mar8-10, 09:35 AM

Frame Dragger

Mar8-10, 10:11 AM

Just for the record, I also truly believe in nonlocality. However, I allow for a possibility (with a very very small probability) that my belief may be incorrect. :tongue2:

I stand corrected; I share your view with the same modest belief in it possibly being wrong. :smile:

yoda jedi

Mar8-10, 10:45 AM

a new experiment

on pre-determined (polarization values) polarizers ?

but what about ten particles (previous pre-entangled) up and the other ten, down, then make the ten particles up to spin down, and see how spin the other ten particles.............
if change the spin, well that`s no-locality, but i wish to see that......

I read this paper and I don't see how there can be this apparant level of confusion regarding these entangled photons.

We can parse the language to fit our agendas (ahkmeteli) or be genuinely confused (ThomasT), or truly believe (DrChinese) or not (Demystifier).

Some relevant questions about the laser source for supposedly "never met each other" photons seem germaine. This endless meandering about ERB and Bell has become so cyclical and predictable that I set my clock by them now. Can we please jettison disruptive elements (akhmeteli and any like), and get back to the real questions about the LR or not?

The next person who says "loophole" is going to be on the wrong end of a slap to the face, or maybe a botnet. I'm tired, so it'll be a coinflip. :rofl: I'm kidding, or am I? Ahhh....

...laughs......

Very Concise !
and for me, the answer have to be developed (for locality).

as for REALITY

........existing a long time before us......

Hans de Vries

Mar8-10, 01:59 PM

It is not random as you suggest. They are entangled, and exhibit statistics to match. Correlated but unentangled photons do not show those statistics.

Maybe I didn't express myself clear enough. If A1 and A2 meet then they have a
random relation ship because they are not entanglement. Upon determining the
relation between A1 and A2 you know that B1 and B2 will have a similar relation.

Regards, Hans

Frame Dragger

Mar8-10, 02:03 PM

a new experiment

...laughs......

Very Concise !
and for me, the answer is beyond (for locality).

as for REALITY existing a long time before us......

Thank you ;) ... I become downright expressive when I'm cranky. While it seems that LR is out, like you once that ruling is on the table as a strong possiblity, I feel out of sorts as a seemingly local and real meat-puppet. :wink:

SpectraCat

Mar8-10, 02:42 PM

Maybe I didn't express myself clear enough.

perhaps ...

If A1 and A2 meet then they have a random relation ship because they are not entanglement. Upon determining the relation between A1 and A2 you know that B1 and B2 will have a similar relation.

Unfortunately, that doesn't make your point a whole lot clearer (at least not to me). In the "normal" interpretation of the experiment we are discussing (i.e. the one put forward by the authors of the paper), photons A1 and A2 (in your notation) become entangled when they interfere at the fiber beam splitter. This entanglement is then teleported to the "non-interacting" pair B1 and B2, as confirmed by violation of a Bell inequality.

Are you proposing an alternative explanation of the experiment, whereby A1 and A2 do not become entangled at the beamsplitter, or are you saying that their entanglement is not required for observation of a Bell violation for B1 and B2? Or are you saying something else entirely?

DrChinese

Mar8-10, 02:50 PM

Maybe I didn't express myself clear enough. If A1 and A2 meet then they have a
random relation ship because they are not entanglement. Upon determining the
relation between A1 and A2 you know that B1 and B2 will have a similar relation.

Regards, Hans

You might think so, but that doesn't work unless the photons are actually entangled. Remember that you need the so-called "perfect" correlations when you have the same settings for Alice and Bob. That doesn't happen in the case you describe. You only have to try a few data points to see what I am talking about. The best you can get out of the scenario you describe is Product state statistics, not Entangled State statistics.

ThomasT

Mar8-10, 05:44 PM

@ThomasT: You are the undisputed master of copy-pasta... moreso even than Akhmeteli. Sadly, you're lacking in even his meager content. Your response is not meaningful given the context of the quote you're using.

This is what comes of endless discussions of "Interpretations"... and it's not science. :smile: Your commentary is amusing, but please feel free to contribute an idea or to comment on some specific aspect of the thread discussion other than the styles, etc. of the other contributors.

Frame Dragger

Mar8-10, 06:22 PM

:smile: Your commentary is amusing

Thanks

...but please feel free to contribute an idea or to comment on some specific aspect of the thread discussion other than the styles, etc. of the other contributors.

Awww, I just knew there was a catch. I've made my views clear in this thread, and then when it started to run I commented. Other than your response and this counter-point, I'd say the thread has improved since.

zonde

Mar9-10, 02:44 AM

I have no idea what you mean here ... how does anything that is written in that paper even imply that, "all single measurements are predictable"??? The whole point of QM is that, in the general case, the results of single measurements are NOT PREDICTABLE. The only thing that *is* predictable for the case in Bell's paper is the coincidence rate, which is a statistical relationship that is built up from the observation of MANY measurements.

Anyway, as I said, even if you were correct, it wouldn't affect the logic of Bell's deduction at all ... it would only affect whether or not QM predicted violations of the Bell inequality. Those "more and less predictable measurements" you are talking about are completely covered by Bell's LHV formulation AFAICS, so they are handled generally in the proof without any reference to or assumption of the correctness of QM.
I will try a bit differently. I understand that analogy is not the best argument but let me use one this time.

Let's consider an experiment.
You and I each take ten pebbles. We arrange them so that we can later identify pairs from our pebbles (say we number them from 1 to 10 and my n-th pebble makes pair with your's n-th pebble).
Now each of us picks one pebble and we compare them and identify if they are from the same pair. If they do not make pair we discard them. If they make a pair then we record whether your pebble is bigger than mine or not.
After that we repeat from start - you and I each take ten pebbles ...
When we have collected some amount of data we find out that your pebble is bigger in almost all cases (or more precisely there is on average one exclusion for every 200 000 successful runs).
Now there are two observers that analyze this data.
Observer A says that this result indicates that your pebbles are bigger than mine.
Observer B says that this result does not indicate anything particular about our pebbles but it shows that I am picking smallest pebble out of my ten but you are picking biggest pebble out of yours.
However observer A insists that he is correct because as he speculates if we modify the experiment so that we take only one pebble instead of ten then we will observe the same result.

Now do you agree with observer A?

SpectraCat

Mar9-10, 06:29 AM

I will try a bit differently. I understand that analogy is not the best argument but let me use one this time.

Let's consider an experiment.
You and I each take ten pebbles. We arrange them so that we can later identify pairs from our pebbles (say we number them from 1 to 10 and my n-th pebble makes pair with your's n-th pebble).
Now each of us picks one pebble and we compare them and identify if they are from the same pair. If they do not make pair we discard them. If they make a pair then we record whether your pebble is bigger than mine or not.
After that we repeat from start - you and I each take ten pebbles ...
When we have collected some amount of data we find out that your pebble is bigger in almost all cases (or more precisely there is on average one exclusion for every 200 000 successful runs).
Now there are two observers that analyze this data.
Observer A says that this result indicates that your pebbles are bigger than mine.
Observer B says that this result does not indicate anything particular about our pebbles but it shows that I am picking smallest pebble out of my ten but you are picking biggest pebble out of yours.
However observer A insists that he is correct because as he speculates if we modify the experiment so that we take only one pebble instead of ten then we will observe the same result.

Now do you agree with observer A?

What does this prove, other than that one can construct a random example where the free sampling assumption is not valid (in this case because choices of conscious beings are involved, which is hardly apropos of anything in the physical example we are discussing)?

Most significantly, what does it have to do with the Bell theorem? Analogies are only useful to the extent that they draw *clear* parallels between the elements of the physical systems they are created to explain/clarify.

Frame Dragger

Mar9-10, 06:34 AM

What does this prove, other than that one can construct a random example where the free sampling assumption is not valid (in this case because choices of conscious beings are involved, which is hardly apropos of anything in the physical example we are discussing)?

Most significantly, what does it have to do with the Bell theorem? Analogies are only useful to the extent that they draw *clear* parallels between the elements of the physical systems they are created to explain/clarify.

Thank god you said that. I thought I was just being dense and missing some deep point. I agree with DrChinese (you're out beers Cat, sorry), but this metaphor seems... odd.

I think the issue here is that there is a cos^2Theta statistical relationship between photons that never "met" each other (I'm convinced of this via another thread). I can see the holes in it, I just think it's a "preponderance of the evidence" in favour of LR being out. I remain to be convinced "beyond a reasonable doubt".

I'd like to get back to the nuts and bolts of whether or not two entangled photons (really one photon), can be generated from seperate sources. The implications are really disturbing if you accept them on their face.

zonde

Mar9-10, 06:39 AM

Unfortunately, that doesn't make your point a whole lot clearer (at least not to me). In the "normal" interpretation of the experiment we are discussing (i.e. the one put forward by the authors of the paper), photons A1 and A2 (in your notation) become entangled when they interfere at the fiber beam splitter. This entanglement is then teleported to the "non-interacting" pair B1 and B2, as confirmed by violation of a Bell inequality.

Are you proposing an alternative explanation of the experiment, whereby A1 and A2 do not become entangled at the beamsplitter, or are you saying that their entanglement is not required for observation of a Bell violation for B1 and B2? Or are you saying something else entirely?
A1 and A2 photon interfere at beam splitter provides information about B1 and B2.
You have to determine this information by detections after beam splitter. If this wouldn't be so you wouldn't need any detections after BS.

zonde

Mar9-10, 07:43 AM

What does this prove, other than that one can construct a random example where the free sampling assumption is not valid (in this case because choices of conscious beings are involved, which is hardly apropos of anything in the physical example we are discussing)?

Most significantly, what does it have to do with the Bell theorem? Analogies are only useful to the extent that they draw *clear* parallels between the elements of the physical systems they are created to explain/clarify.
Yes I agree that parallels should be clear between analogy and topic in question.
So the parallel is that if QM observable comes from this type of measurement described in this analogy then it might turn out that the thing you measure is actually workings of your measurement equipment and in no way your supposed measurement object.
In this case observable becomes more and more uncertain with increase of detection efficiency while becomes completely uncertain at 100% efficiency. And this is not tested experimentally so you can't exclude this (quite classical) possibility.

About fair or unfair sampling assumption - yes this is unfair sampling demonstration. But then what did you expected? About the choices of conscious beings I would say that they are quite mechanical so nothing unphysical here.

And what does it have to do with Bell is that fair sampling comes into the argument right at the start motivated by questionable interpretation of QM.

DrChinese

Mar9-10, 08:48 AM

I will try a bit differently. I understand that analogy is not the best argument but let me use one this time.

Let's consider an experiment.
You and I each take ten pebbles. We arrange them so that we can later identify pairs from our pebbles (say we number them from 1 to 10 and my n-th pebble makes pair with your's n-th pebble).
Now each of us picks one pebble and we compare them and identify if they are from the same pair. If they do not make pair we discard them. If they make a pair then we record whether your pebble is bigger than mine or not.
After that we repeat from start - you and I each take ten pebbles ...
When we have collected some amount of data we find out that your pebble is bigger in almost all cases (or more precisely there is on average one exclusion for every 200 000 successful runs).
Now there are two observers that analyze this data.
Observer A says that this result indicates that your pebbles are bigger than mine.
Observer B says that this result does not indicate anything particular about our pebbles but it shows that I am picking smallest pebble out of my ten but you are picking biggest pebble out of yours.
However observer A insists that he is correct because as he speculates if we modify the experiment so that we take only one pebble instead of ten then we will observe the same result.

Now do you agree with observer A?

The problem with this argument is that it actually does not work! Designing an analogy that meets this criteria is not so simple as you imply, and the reason is as follows:

You must choose the larger pebble in some cases and the smaller one in others! How do you know which to do? You must communicate classically!!

The De Raedt group attempted the same with their computer simulation. At first it appears that such a simulation can be constructed. However, the requirements of matching the QM predictions are so difficult that this turns out to be impossible.

It is NOT enough to say you can do it - without actually doing it!!

DrChinese

Mar9-10, 08:50 AM

In this case observable becomes more and more uncertain with increase of detection efficiency while becomes completely uncertain at 100% efficiency. And this is not tested experimentally so you can't exclude this (quite classical) possibility.

Except that when the full sample is counted, the results still match the QM prediction. That experiment has already been performed.

SpectraCat

Mar9-10, 10:01 AM

Yes I agree that parallels should be clear between analogy and topic in question.
So the parallel is that if QM observable comes from this type of measurement described in this analogy then it might turn out that the thing you measure is actually workings of your measurement equipment and in no way your supposed measurement object.
In this case observable becomes more and more uncertain with increase of detection efficiency while becomes completely uncertain at 100% efficiency. And this is not tested experimentally so you can't exclude this (quite classical) possibility.

About fair or unfair sampling assumption - yes this is unfair sampling demonstration. But then what did you expected? About the choices of conscious beings I would say that they are quite mechanical so nothing unphysical here.

And what does it have to do with Bell is that fair sampling comes into the argument right at the start motivated by questionable interpretation of QM.

No, you seem to be missing the point. The Bell theorem has nothing to do with QM per se, only the test case for which it was initially devised has to do with QM. So any flaw in predictions or interpretation of QM is not transferred to the Bell theorem, all it does it cast some doubt on the proper interpretation of an experiment where an apparent Bell inequality violation is observed.

Second, I had not thought of this before, but it seems unfair sampling is covered within the context of the Bell theorem, as far as I can see. Bell uses \rho\left(\lambda\right) to represent the probability distribution of the hidden variable parameter lambda, and the only assumption he makes about it is that it is normalized to 1. So, in the case of unfair sampling, the assumption is that the actual experiment only samples a subset, call it \rho'\left(\lambda\right) of the "real" probability distribution, correct? If so, this should make *no difference* on the predictions of the Bell theorem, because it is valid for any probability distribution. All that is required is a "renormalization" of the \rho' distribution to 1, which certainly seems valid, since that distribution now represents all of the possible measurement results for A and B.

Am I missing something with the above analysis? If not, what is the big deal about "unfair sampling"?

DrChinese

Mar9-10, 02:05 PM

Second, I had not thought of this before, but it seems unfair sampling is covered within the context of the Bell theorem, as far as I can see. Bell uses \rho\left(\lambda\right) to represent the probability distribution of the hidden variable parameter lambda, and the only assumption he makes about it is that it is normalized to 1. So, in the case of unfair sampling, the assumption is that the actual experiment only samples a subset, call it \rho'\left(\lambda\right) of the "real" probability distribution, correct? If so, this should make *no difference* on the predictions of the Bell theorem, because it is valid for any probability distribution. All that is required is a "renormalization" of the \rho' distribution to 1, which certainly seems valid, since that distribution now represents all of the possible measurement results for A and B.

Am I missing something with the above analysis? If not, what is the big deal about "unfair sampling"?

Preaching to the choir here... :)

The issue of unfair sampling seems to revolve around an idea which changes every time you ask anyone to be specific. Sometimes it relates to the coincidence time window. Sometimes it is that actual entire pairs go undetected (which would be bizarre given detector efficiencies).

I simply challenge anyone who asserts the fair sampling assumption is a valid loophole to provide a dataset in which the full universe differs suitably from the sample. Then tell me by what rule data items are included or excluded. Then we can see if that hypothesis can be physically viable. So far, there have been no takers. But there have been a lot of hand wavers - because the constraints are quite severe when you actually run the exercise.

So yes, I think the Bell Inequality applies, and this becomes clear during the exercise when you try to think up a universe in which the QM predictions are wrong.

ThomasT

Mar9-10, 08:39 PM

Awww, I just knew there was a catch. I'd say the thread has improvedThere's always a catch. :smile: I'm betting that there's one regarding the standard interpretation of Bell's theorem.

... I've made my views clear in this thread ...You haven't commented on any specific aspect of the formal incompatibility between Bell's ansatz and Bell tests. I gather that you think that nonlocality can be inferred from Bell test results. This requires that something in Bell's generalized LHV formulation represents locality. What exactly do you think that is?

... I'd say the thread has improved ...At least they're not talking about superdeterminism and free will any more.

I've learned some things from the thread, and, as always, these discussions get me thinking about this stuff again -- and, yes, I'm still confused. :smile:

The OP's (akhmeteli) main points are not supported.

Bell test results do not imply nonlocality.

Bell's general LR formulation doesn't represent locality.

LR is not definitively ruled out (but it doesn't look promising for the LRists).

Ruling out LR doesn't entail that Nature is nonlocal.

A more reasonable viewpoint is that our lack of a detailed qualitative understanding of quantum level reality (and other technical problems which prohibit the accurate prediction of individual results) is what prohibits a viable LR description.

Is it possible to say that LR is ruled out experimentally and ignore all arguments about internal problems in QM?Yes. The ruling out, or not, of LR has nothing to do with QM. It has to do with the problem of formalizing locality. Bell expresses locality as the factorability of the joint probability. Do you see a problem with that? If not, you should. :smile:

Hm
Imagine that QM is not discovered yet (but SR is discovered)
However, there are many EPR Alice/Bob experiments and tons of data
I was thinking that in that case it would be possible to rule out local theories, even without QM, just based on the experiments. AM I wrong?No. Let's go further and say that you've got tons of data from biphoton Bell-type experiments, and there's no Bell's theorem, no QM, and no consideration of nonlocality.

You're producing pairs of counter-propagating optical disturbances via atomic cascades, with each pair randomly polarized (and members of each pair identically polarized via emission by the same atom), and you're analyzing each pair with 2 crossed polarizers.

From classical optics, which is all you've got to refer to, What sort of correlation would you expect to see between rate of joint detection, P(A,B), and the angular difference (|a-b|, or θ) between the polarizer's transmission axes?

You would expect to see P(A,B) = cos2θ . Why? Because when you put two polarizers between a source of randomly polarized light and a detector, then the measured intensity (the rate of coincidental detection) varies as cos2θ.

Intuitively, from the above, this seems like a local common cause scenario, right? Now formalize it.

If you can't construct a viable and explicitly local model for joint detection, then does that mean that joint detection is determined nonlocally? No.

But suppose that you are able to construct a viable and explicitly nonlocal model, then does that mean that joint detection is determined nonlocally? No.

SpectraCat

Mar9-10, 09:31 PM

Bell expresses locality as the factorability of the joint probability. Do you see a problem with that? If not, you should. :smile:

You keep saying that, but I went back to the original Bell paper again recently to check something else, and I really don't think your statement is correct.

The passage from Bell's paper addressing locality is from section II:

"The result A of measuring \vec{\sigma_{1}}\cdot\vec{a} is then determined by \vec{a} and \lambda, and the result B of measuring \vec{\sigma_{2}}\cdot\vec{b} in the same instance is determined by \vec{b} and \lambda, and
A\left(\vec{a},\lambda\right)=\pm1, B(\vec{b},\lambda)=\pm1.
The vital assumption [here he references Einstein's definition of locality from an earlier text] is that the result B for particle 2 does not depend on the setting \vec{a}, of the magnet for particle 1, nor A on \vec{b}."

Just to be clear, the definitions of the terms are: \sigma refers to the spin of one member of an entangled pair, a and b are the settings of the detectors (Stern-Gerlach magnets in his example), and \lambda is the parameter introduced to account for any and all hidden variables.

So, at this point, he is just using the definition of locality put forth by Einstein, summarized in the last sentence of the quote above. That seems a good definition of locality to me, do you find fault with it?

He then goes on to say,

"If \rho\left(\lambda\right) is the probability distribution of \lambda then the expectation value of the product of the two components \vec{\sigma_{1}}\cdot\vec{a} and \vec{\sigma_{2}}\cdot\vec{b} is
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\lambda)B(\vec{b},\ lambda)

So, what is the problem with that? Where is the contradictory assumption that you keep asserting exists? I have reproduced it all here in Bell's words so that you can point it out, because I cannot find it.

I also don't think this is simply the "factorability of the joint probability" ... the integration is significant there, and as far as I can see prevents any factorization as you suggest.

In past posts, you have written that Bell locality is *defined as* P(A,B)=P(A)P(B) ... that certainly looks different to me from what is actually written in his paper.

Dmitry67

Mar10-10, 01:18 AM

Yes. The ruling out, or not, of LR has nothing to do with QM. It has to do with the problem of formalizing locality. Bell expresses locality as the factorability of the joint probability. Do you see a problem with that? If not, you should. :smile:

Got it.

But lets approach it from another side: if we take QM and assume any Interpretation where wavefunction is "real/objective" (whatever it means :) ) we automatically assume that Nature is nonlocal?

So Local Realists have a shorter list of Interpretations to be used?

zonde

Mar10-10, 04:11 AM

No, you seem to be missing the point. The Bell theorem has nothing to do with QM per se, only the test case for which it was initially devised has to do with QM. So any flaw in predictions or interpretation of QM is not transferred to the Bell theorem, all it does it cast some doubt on the proper interpretation of an experiment where an apparent Bell inequality violation is observed.
The goal of Bell's theorem is to compare QM prediction with something else. You can not compare apples with oranges so you have to make similar formulation to QM formulation. If QM formulation is misleading you would replicate the same flaw in alternate formulation.
Look you can see this here:
"If \rho\left(\lambda\right) is the probability distribution of \lambda then the expectation value of the product of the two components \vec{\sigma_{1}}\cdot\vec{a} and \vec{\sigma_{2}}\cdot\vec{b} is
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\lambda)B(\vec{b},\ lambda)
This should equal the quantum mechanical expectation value, which for the singlet state is
<\vec{\sigma_{1}}\cdot\vec{a}\,\vec{\sigma_{2}}\cdo t\vec{b}>=-\vec{a}\cdot\vec{b}"

It all comes from interpretation of QM that QM probability should look something like that:
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\vec{b},\lambda)B(\ vec{b},\vec{a},\lambda)

Second, I had not thought of this before, but it seems unfair sampling is covered within the context of the Bell theorem, as far as I can see. Bell uses \rho(\lambda) to represent the probability distribution of the hidden variable parameter lambda, and the only assumption he makes about it is that it is normalized to 1. So, in the case of unfair sampling, the assumption is that the actual experiment only samples a subset, call it \rho'(\lambda) of the "real" probability distribution, correct? If so, this should make *no difference* on the predictions of the Bell theorem, because it is valid for any probability distribution. All that is required is a "renormalization" of the \rho' distribution to 1, which certainly seems valid, since that distribution now represents all of the possible measurement results for A and B.

Am I missing something with the above analysis? If not, what is the big deal about "unfair sampling"?
Yes you are missing that you have \rho'_{a}(\lambda) and \rho'_{b}(\lambda) and you can't both of them normalize to 1 at the same time.
So you will have something like that:
P(\vec{a},\vec{b})=\int d\lambda\rho'_{a}(\lambda)\rho'_{b}(\lambda)A(\vec {a},\lambda)B(\vec{b},\lambda)

Or alternatively you can look at counter example that I have posted here in attachment:
http://www.physicsforums.com/showthread.php?p=2538611#post2538611

Eye_in_the_Sky

Mar10-10, 05:26 AM

And how you define "PC"?For a photon ("twin-state") pair emitted in opposite directions, we can define the "PC" feature as follows:

Whenever Alice and Bob set their polarizers to the same angle, they get the same result.
"PC" is essential for Bell's argument but is it essential for local realism?I think "PC" would be an essential ingredient of any theory which incorporates in it the notion of "angular momentum" as construed in conventional terms. Up here in_the_Sky all theories are formulated with respect to ideal detectors.
Say if light is linearly polarized and then it goes through polarizer with the same orientation of polarization axis as for light. All light is passing through polarizer - perfect measurement.
Now polarizator is oriented at different angle and measurement becomes probabilistic. Are you saying that local realism requires that probability for individual photon can depend only from properties of photon and in no way from context?Of course it depends on the context – the polarizer orientation, for example. But you mean something else. (Does it have something to do with non-ideal detection?)
________________

Let's go back to Stapp's definition of "CFD":

For each particle on which a measurement is performed, a definite value would have been found if a different spin component had been measured on it instead (although we cannot know what the specific value would have been) and, furthermore, the complete set of such values (measured and unmeasured together) can be meaningfully discussed.
That's clear.Is it?
But does it mean that deterministic chaos is completely excluded by this definition?Not at all. This definition has no conflict with deterministic theories, be they of the "controllable" or "chaotic" genre. "CFD" is only in (apparent) conflict with irreducibly stochastic theories of the "fuzzy ontology" genre.
It's hard to accept that [local] deterministic chaos somehow contradicts local realism.There is no contradiction.
________________

Now if we have chaotic context that determines probability and say we include some controllable factor that contributes to context. Now the the outcome will become predictable but only marginally. We can not eliminate chaotic context we can only override it with controllable factors to some extent.Okay.
Therefore I say "PC" are not realistic.
Zonde_on_the_Ground, you have done it again. ... I have no idea what you mean.

Eye_in_the_Sky

Mar10-10, 05:37 AM

... I had not thought of this before, but it seems unfair sampling is covered within the context of the Bell theorem, as far as I can see. Bell uses \rho\left(\lambda\right) to represent the probability distribution of the hidden variable parameter lambda, and the only assumption he makes about it is that it is normalized to 1. So, in the case of unfair sampling, the assumption is that the actual experiment only samples a subset, call it \rho'\left(\lambda\right) of the "real" probability distribution, correct? If so, this should make *no difference* on the predictions of the Bell theorem, because it is valid for any probability distribution. All that is required is a "renormalization" of the \rho' distribution to 1, which certainly seems valid, since that distribution now represents all of the possible measurement results for A and B.

Am I missing something with the above analysis? If not, what is the big deal about "unfair sampling"?My reply is essentially the same as zonde's.

Let p(a,λ) denote:

the probability that a particle incident on the detector will be registered as a detection event when the measuring device is set to a and the incident particle is in the state λ.

Sampling is unfair iff p(a,λ)≠const.

In the case of (nontrivial) functional dependence on a, Bell's equation (2) needs to be replaced with

P(a,b) = [1/N(a,b)] ∫dλ ρ(λ) p(a,λ) p(b,λ) A(a,λ) B(b,λ) ,

where

N(a,b) = ∫dλ ρ(λ) p(a,λ) p(b,λ) .

Frame Dragger

Mar10-10, 05:39 AM

For a photon ("twin-state") pair emitted in opposite directions, we can define the "PC" feature as follows:

Whenever Alice and Bob set their polarizers to the same angle, they get the same result.
I think "PC" would be an essential ingredient of any theory which incorporates in it the notion of "angular momentum" as construed in conventional terms. Up here in_the_Sky all theories are formulated with respect to ideal detectors.
Of course it depends on the context – the polarizer orientation, for example. But you mean something else. (Does it have something to do with non-ideal detection?)
________________

Let's go back to Stapp's definition of "CFD":

For each particle on which a measurement is performed, a definite value would have been found if a different spin component had been measured on it instead (although we cannot know what the specific value would have been) and, furthermore, the complete set of such values (measured and unmeasured together) can be meaningfully discussed.
Is it?
Not at all. This definition has no conflict with deterministic theories, be they of the "controllable" or "chaotic" genre. "CFD" is only in (apparent) conflict with irreducibly stochastic theories of the "fuzzy ontology" genre.
There is no contradiction.
________________

Okay.

Zonde_on_the_Ground, you have done it again. ... I have no idea what you mean.

Wow... talk about reaching back in the discussion. I had to go back to page 22 (post 343, thanks for that information) to pick up the thread of just what the hell you were saying.

Oh, and what the hell is this "in the sky" and "on the ground" nonsense? Either it's a joke about your nickname that falls flat, or it's arrogant as hell and laughably unwarrented. Either way, if you're going to ignore the last 5 pages and take things up as though they hadn't happened, how about a little "head up, this is from post #..." ok?

EDIT: You've posted again I see. Are you proposing a revision of Bell's Theorem, or just that there is the famous "loophole" *grits teeth* ? How do you arrive at your "corrections", without piggybacking Zonde's argument which you "basically" have in common?

Eye_in_the_Sky

Mar10-10, 06:14 AM

Wow... talk about reaching back in the discussion. I had to go back to page 22 (post 343, thanks for that information) to pick up the thread of just what the hell you were saying.All you needed to do was click on the little blue arrow-thing where it says "Originally Posted by zonde".
Oh, and what the hell is this "in the sky" and "on the ground" nonsense? Either it's a joke about your nickname that falls flat, or it's arrogant as hell and laughably unwarrented.It's me joking.
Either way, if you're going to ignore the last 5 pages and take things up as though they hadn't happened, how about a little "head up, this is from post #..." ok?Again, click on the little blue arrow-thing.
EDIT: You've posted again I see. Are you proposing a revision of Bell's Theorem, or just that there is the famous "loophole" *grits teeth* ?Neither. I was just responding to SpectraCat's query in terms which I thought were absolutely clear.
How do you arrive at your "corrections", without piggybacking Zonde's argument which you "basically" have in common?I don't know what you mean by this.

SpectraCat

Mar10-10, 06:33 AM

The goal of Bell's theorem is to compare QM prediction with something else. You can not compare apples with oranges so you have to make similar formulation to QM formulation. If QM formulation is misleading you would replicate the same flaw in alternate formulation.

Again, look at what is written carefully, and you will see that equation 2 in his text is completely unrelated to any postulates of quantum mechanics. It is phenomenologically based, with each term carefully defined, and makes no unstated assumptions, except perhaps that the properties of the entangled particles can somehow be measured in the lab. His "formulation" is not in any way quantum mechanical that I can see.

Bell's theorem is a completely general theorem concerning the joint probability of obtaining particular values from two independent events, that may or may not share a connection through hidden variables.

Look you can see this here:
"If \rho\left(\lambda\right) is the probability distribution of \lambda then the expectation value of the product of the two components \vec{\sigma_{1}}\cdot\vec{a} and \vec{\sigma_{2}}\cdot\vec{b} is
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\lambda)B(\vec{b},\ lambda)
This should equal the quantum mechanical expectation value, which for the singlet state is
<\vec{\sigma_{1}}\cdot\vec{a}\,\vec{\sigma_{2}}\cdo t\vec{b}>=-\vec{a}\cdot\vec{b}"

It all comes from interpretation of QM that QM probability should look something like that:
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\vec{b},\lambda)B(\ vec{b},\vec{a},\lambda)

I do not think it says what you imply, I think you are reading it backward, and inserting a sense that is not there. Bell is just stating what QM predicts for P(a,b), assuming QM is correct. He is establishing his "test case", against which the hidden variable probability expression in equation 2 will be compared, as I have said before. Also, you will have to show me where he makes the statement that:
QM probability should look something like that:
P(\vec{a},\vec{b})=\int d\lambda\rho(\lambda)A(\vec{a},\vec{b},\lambda)B(\ vec{b},\vec{a},\lambda)

as you claim. What he says is (paraphrasing section III), *if* the results at A and B are allowed to depend on the settings at *both* detectors, then a hidden variables description can be formed that is consistent with the predictions of QM, but you are inherently sacrificing locality to do this.

Yes you are missing that you have \rho'_{a}(\lambda) and \rho'_{b}(\lambda) and you can't both of them normalize to 1 at the same time.
So you will have something like that:
P(\vec{a},\vec{b})=\int d\lambda\rho'_{a}(\lambda)\rho'_{b}(\lambda)A(\vec {a},\lambda)B(\vec{b},\lambda)

You have not defined what you mean by \rho'_{a}(\lambda) and \rho'_b{b}(\lambda), and it is not clear what they are supposed to be from context. Bell's \rho(\lambda) and my \rho'(\lambda) are probability distributions for lambda. Presumably your expressions are intended to reflect that the behavior at a given detector, or for a given setting may depend on lambda in a way that is different from other detectors or settings? But that is already accounted for in Bell's definition of the measurements A and B .. in fact, I cannot see any possible definition for your "probability sub-distributions" that is not already accounted for in the definitions of A(\vec{a},\lambda) and B(\vec{a},\lambda) in Bell's paper.

Or alternatively you can look at counter example that I have posted here in attachment:
http://www.physicsforums.com/showthread.php?p=2538611#post2538611

The link in the last post is broken ... I will read through the thread when I have more time .. it seems like there is a lot there to absorb.

SpectraCat

Mar10-10, 06:59 AM

My reply is essentially the same as zonde's.

Let p(a,λ) denote:

the probability that a particle incident on the detector will be registered as a detection event when the measuring device is set to a and the incident particle is in the state λ.

Sampling is unfair iff p(a,λ)≠const.

In the case of (nontrivial) functional dependence on a, Bell's equation (2) needs to be replaced with

P(a,b) = [1/N(a,b)] ∫dλ ρ(λ) p(a,λ) p(b,λ) A(a,λ) B(b,λ) ,

where

N(a,b) = ∫dλ ρ(λ) p(a,λ) p(b,λ) .

Ok, if that is what zonde was trying to say, then I missed it, but I see your point, and it is basically that unfair sampling is inherently only a problem when the detection efficiency is less than 100%. Since Bell did not account for that, it seems that his formulation does not account for all forms of unfair sampling, as I had thought. I'm not sure I agree with your "iff" above though, because it seems that there could be other ways of introducing a bias through the hidden variables. But in any case, I think those *are* taken care of in Bell's theorem, based on my earlier analysis.

So, would you then agree that a Bell test with 100% detector efficiencies and a spacelike separation between the detectors would be loophole free?

zonde

Mar10-10, 09:15 AM

I do not think it says what you imply, I think you are reading it backward, and inserting a sense that is not there. Bell is just stating what QM predicts for P(a,b), assuming QM is correct.
And what I imply?
Yes, Bell is just stating what QM predicts for P(a,b), assuming QM is correct.
What I imply is that Bell have to make comparable prediction for local realism. That is what he does in (2) prior to (3).

He is establishing his "test case", against which the hidden variable probability expression in equation 2 will be compared, as I have said before.
Yes and you are saying that this test case can be viewed independently from QM predictions and I kind of disagree with that.

Also, you will have to show me where he makes the statement that:
...
as you claim.
I am not claiming that. Read carefully. I am saying that this is implied QM context for the test case.

You have not defined what you mean by \rho'_{a}(\lambda) and \rho'_b{b}(\lambda), and it is not clear what they are supposed to be from context. Bell's \rho(\lambda) and my \rho'(\lambda) are probability distributions for lambda. Presumably your expressions are intended to reflect that the behavior at a given detector, or for a given setting may depend on lambda in a way that is different from other detectors or settings? But that is already accounted for in Bell's definition of the measurements A and B .. in fact, I cannot see any possible definition for your "probability sub-distributions" that is not already accounted for in the definitions of A(\vec{a},\lambda) and B(\vec{a},\lambda) in Bell's paper.
Sorry for that.
\rho'_{a}(\lambda) and \rho'_b{b}(\lambda) are probability distributions for measurements of Alice and Bob respectively.
And what I say is that your proposed \rho'(\lambda) describes subsample of pairs and therefore it incorporates fair sampling too. In general case you make two subsamples for measurement of Alice and Bob. Then you join them but in case of unfair sampling you get something like that for joined distribution \rho'(\lambda,\vec{a},\vec{b}).

The link in the last post is broken ... I will read through the thread when I have more time .. it seems like there is a lot there to absorb.
Ok, I attached it here. In this file you have to fill rows up to 10001 except in first sheet. That's so to keep file small.

DrChinese

Mar10-10, 09:32 AM

So, would you then agree that a Bell test with 100% detector efficiencies and a spacelike separation between the detectors would be loophole free?

Just to be clear about the state of things:

a) Bell tests with 100% detection support QM and rule out LR.
b) Bell tests with spacelike separation support QM and rule out LR.

So far, there is NO LR candidate that can account for Fair Sampling loophole. As I have previously demonstrated, for example, the De Raedt model does not qualify. So I am really curious as to HOW any loopholes are supposed to yield a) and b) separately (supporting QM) but together work to give results consistent with LR. Because I don't think that is possible.

yoda jedi

Mar10-10, 11:32 AM

However, his definition of the word "covariant" is, mildly speaking, quite unusual.

....Quantum measurements applied to systems composed of several distant subsystems, as those used in Bell inequality tests, are at odds with special relativity. Indeed, quantum measurements "collapse" the wavefunction of the system in a non-covariant way. This is true even if one doesn't strictly apply the projection postulate, as long as one admits that (at least some) measurements have defnite classical results secured in a fnite time. Consequently, the usual wavefunction (or equivalently the state vector) is not a covariant object. This led many authors to conclude that only the probabilities that appear in quantum physics can be described in a covariant way, not the state........Should one conclude that the real stuf in quantum physics is not the state, but the probabilities? Or in more dramatic words, that the real stuf are the probabilities, not the probability amplitudes? In this little note I would like to plunge into quantum ontology and ask what is the real stuf in quantum physics and what are these covariant quantum probabilities....

(and beyond that, ontic vs epistemic vs complete (STATE))

.........lies in very different understanding of what a “covariant quantum process” is......................Covariant dynamics refers to events that are related to each other through only covariant or Lorentz invariant links. If these events are locally deterministic one has a covariant deterministic model, and if they are locally random a covariant stochastic one.....................

maybe the REALITY is poly-ordered or omni-ordered, can coexist (in principle or possibily) past, present and the future.

irrespective of locality, have to be seen if the CPC negates CTCs.

better yet, establishes order without time (no determinism or a convoluted determinism, non chronological determinism).

(nonlocal determinism requires nonlocal influences in time ordered manner).

Ruling out LR doesn't entail that Nature is nonlocal.

A more reasonable viewpoint is that our lack of a detailed qualitative understanding of quantum level reality (and other technical problems which prohibit the accurate prediction of individual results) is what prohibits a viable LR description.

maybe order come outside space-time.

REALITY is more.

Eye_in_the_Sky

Mar10-10, 09:14 PM

I'm not sure I agree with your "iff" above though, ...
As far as I know "unfair sampling" is synonymous with "variable detection probability". If that is correct, then it seems to me that the double "f" of my "iff" is appropriate:
Sampling is unfair iff p(a,λ)≠const.
And then you say:... it seems that there could be other ways of introducing a bias through the hidden variables. But in any case, I think those *are* taken care of in Bell's theorem, based on my earlier analysis.It sounds like you are talking about the case where p(a,λ) has no functional dependence on a, so it depends on λ alone. If that is what you mean, then yes I agree: redefine "ρ(λ)" as "ρ(λ)p(λ)2 normalized".So, would you then agree that a Bell test with 100% detector efficiencies and a spacelike separation between the detectors would be loophole free?I do not know much about the experimental side of things, and I have not been following this issue of "loopholes" closely at all. Albeit, I have known about the "light-cone" loophole for quite some time, it was only after reading your remarks concerning ρ(λ) and ρ'(λ) that I decided to start reading a little bit about just what the "fair-sampling" assumption is supposed be. Since then, I have gone on to read a little more about some of the various "loophole" concerns which are being raised.

With regard to practical loopholes, the only ones that seem readily understandable to me are the "fair-sampling" and "light-cone" loopholes. These two, it seems, are considered to be the most serious. Of course, "100% detector efficiencies" and "spacelike separation" would rule them both out. But with regard to any of the other (alleged) practical loopholes, I just do not know enough about them to formulate an opinion.

... But there will always be the "superdeterminism" loophole. (My only reason for ever entertaining it, however, is for it to entertain me. :biggrin:)

Eye_in_the_Sky

Mar10-10, 09:56 PM

The Bell theorem has nothing to do with QM per se, only the test case for which it was initially devised has to do with QM. So any flaw in predictions or interpretation of QM is not transferred to the Bell theorem, all it does it cast some doubt on the proper interpretation of an experiment where an apparent Bell inequality violation is observed.The goal of Bell's theorem is to compare QM prediction with something else. You can not compare apples with oranges so you have to make similar formulation to QM formulation. If QM formulation is misleading you would replicate the same flaw in alternate formulation. ...Again, look at what is written carefully, and you will see that equation 2 in his text is completely unrelated to any postulates of quantum mechanics. It is phenomenologically based, with each term carefully defined, and makes no unstated assumptions, except perhaps that the properties of the entangled particles can somehow be measured in the lab. His "formulation" is not in any way quantum mechanical that I can see.
In section IV, "Contradiction", of Bell's paper, the argument presented there can be formally written as:

local determinism Λ QM → CONTRADICTION .

What we need to do is CORRECTLY split this proposition up into two parts. In my discussions with akhmeteli, unfortunately, I did not do it right! (Sorry, akhmeteli!) There I wrote:local determinism → D

and

QM → ~D ,

where D is a certain condition

The correct way to do the split is:

local determinism Λ [P(a,a) = <σ1∙a σ2∙a> , for any a] → D

and

QM → ~D .

You can see this from Bell's words centered around equation (13). There he argues that the minimum value of P(a,b) [where P(a,b) is the LHV expectation value as defined in equation (2)] is -1. This follows from relations (1), (2), and (12). So far nothing from QM has been invoked. And then he writes:

It can reach -1 at a = b only if

A(a,λ) = - B(a,λ)

except at a set of points λ of zero probability. Assuming this ...

What is the "this" in the "Assuming this"? It is the condition:

P(a,b) = -1 , for a = b .

And why is he assuming this? ... Because he is assuming:

P(a,a) = <σ1∙a σ2∙a> , for any a .
_____________________

SpectraCat, me thinks this is what zonde is getting at.

(... once again, zonde, thanks for helping to open me-Eye)

Demystifier

Mar11-10, 02:51 AM

....Quantum measurements applied to systems composed of several distant subsystems, as those used in Bell inequality tests, are at odds with special relativity. Indeed, quantum measurements "collapse" the wavefunction of the system in a non-covariant way. This is true even if one doesn't strictly apply the projection postulate, as long as one admits that (at least some) measurements have defnite classical results secured in a fnite time. Consequently, the usual wavefunction (or equivalently the state vector) is not a covariant object.
What do YOU mean by the word "covariant"?
Anyway, with the usual definition of that word, there is a way to make the wave function covariant:
http://xxx.lanl.gov/abs/1002.3226

zonde

Mar11-10, 06:52 AM

For a photon ("twin-state") pair emitted in opposite directions, we can define the "PC" feature as follows:
Whenever Alice and Bob set their polarizers to the same angle, they get the same result.
I would use "entangled state" instead of "twin-state" because that way you imply certain things that might not be very appropriate.
But otherwise I think we are on the same line here with addition that instead of the same result (maximally similar) there might be maximally opposite result as well depending from setup.

I think "PC" would be an essential ingredient of any theory which incorporates in it the notion of "angular momentum" as construed in conventional terms. Up here in_the_Sky all theories are formulated with respect to ideal detectors.
I would say that I do not quite understand how do you incorporate "angular momentum" in this context. If you associate "angular momentum" with polarization of individual photon then allowing the idea that individual photon is quantized interaction of individual photon with polarizer does not conserve "angular momentum".
If you however take the whole ensemble then yes it seems like you conserve "angular momentum". But then if we will correlate entangled ensembles as a whole we would find out that independent from angle half of both ensembles is passing polarizer. So nothing useful here.
But entanglement is measured by correlating individual photons from entangled ensembles and here it is not obvious that your point about "angular momentum" holds.

And let me even say that it does not hold. Let's take equation that describes entangled state:
P_{VV}(\alpha,\beta) = sin^{2}\alpha\, sin^{2}\beta\, cos^{2}\theta_{l} + cos^{2}\alpha\, cos^{2}\beta\, sin^{2}\theta_{l} + \frac{1}{4}sin 2\alpha\, sin 2\beta\, sin 2\theta_{l}\, cos \phi
Allow for a moment the possibility that interference (third) term in this equation describes unfair sampling effect. Then by manipulating \phi (phase between polarization components) we can reduce interference term to 0.
Resulting equation is completely factorizable and easily explained classically. However if I understand your point correctly it is excluded by your hypothetical classical theory.

zonde

Mar11-10, 08:09 AM

Just to be clear about the state of things:

a) Bell tests with 100% detection support QM and rule out LR.
b) Bell tests with spacelike separation support QM and rule out LR.
Just to be clear. Your position is that QM without involving Bell inequalities can not stand on it's own complete or incomplete, right?

Btw would you care to scrutinize any particular Bell test with 100% detection?

DrChinese

Mar11-10, 01:24 PM

1. Just to be clear. Your position is that QM without involving Bell inequalities can not stand on it's own complete or incomplete, right?

2. Btw would you care to scrutinize any particular Bell test with 100% detection?

1. I do not follow this statement. My stand is that the predictions of QM are well supported by experiment. Also that QM does not need to be accurate for Bell's Theorem to be meaningful, as Bell points out that QM and LR are incompatible.

2. Sure:

"Experimental violation of a Bell's inequality with efficient detection" (2001) Rowe et al.

http://www.nature.com/nature/journal/v409/n6822/full/409791a0.html

Not actually 100% detection but high enough. This uses Be ions rather than photons.

"Our measured value of the appropriate Bell's 'signal' is 2.25+/- 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called 'detection' loophole."

DrChinese

Mar11-10, 02:09 PM

..And why is he assuming this? ... Because he is assuming:

P(a,a) = <σ1∙a σ2∙a> , for any a .

This comment is intended for zonde as much as anyone:

Please, don't forget the historical background. EPR considered that perfect correlations could be explained by a Local Realistic theory. So this must always be considered as well for any candidate theory. Of course, it could be a bad assumption but the evidence says it is not.

ytuab

Mar11-10, 08:27 PM

1. I do not follow this statement. My stand is that the predictions of QM are well supported by experiment. Also that QM does not need to be accurate for Bell's Theorem to be meaningful, as Bell points out that QM and LR are incompatible.

2. Sure:

"Experimental violation of a Bell's inequality with efficient detection" (2001) Rowe et al.

http://www.nature.com/nature/journal/v409/n6822/full/409791a0.html

Not actually 100% detection but high enough. This uses Be ions rather than photons.

"Our measured value of the appropriate Bell's 'signal' is 2.25+/- 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called 'detection' loophole."

Actually, Be ion is a "more real" thing than a photon, so the detection efficiency becomes high.

This experiment uses the Paul trap (like the Penning trap?).
This trap probably uses the "external magnetic field and electronic field" to trap the ion correctly.
In page 792(of this paper), " After making the state \psi_{2}, we again Raman beams for a pulse of short duraion(~400ns) so that the state of each ion j is transformed in the interaction picture as,......

This means the "manipulation" is a laser wave in this experiment?
I have a question about this.
Is it possible that the paul trap influence on the ions is so "strong" that this manipulation of a laser is meaningless?

SpectraCat

Mar11-10, 11:38 PM

Actually, Be ion is a "more real" thing than a photon, so the detection efficiency becomes high.

This experiment uses the Paul trap (like the Penning trap?).
This trap probably uses the "external magnetic field and electronic field" to trap the ion correctly.
In page 792(of this paper), " After making the state \psi_{2}, we again Raman beams for a pulse of short duraion(~400ns) so that the state of each ion j is transformed in the interaction picture as,......

This means the "manipulation" is a laser wave in this experiment?
I have a question about this.
Is it possible that the paul trap influence on the ions is so "strong" that this manipulation of a laser is meaningless?

No ... if that were that case, the states giving rise to the spectroscopic transitions would be perturbed by the Stark effect, shifting the transition out of resonance with the laser. The lasers are not being used to "manipulate" the ions in the sense of changing their positions ... they are being used to prepare quantum states in those atoms. The electric fields used in these experiments to confine the ions in the Paul trap are not nearly strong enough to measurably affect the energies of these states.

Eye_in_the_Sky

Mar11-10, 11:58 PM

Previously, I began a discussion with akhmeteli saying:
Hello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

At the conclusion of our discussion, I said:
Thank you, akhmeteli, for answering my questions. Originally, it appeared to me that there may have been some misconception in the way you were thinking about Bell's Theorem. But from the answers you have given, I do not detect any such misconception.

Indeed ...

local determinism → D

and

QM → ~D ,

where D is a certain condition.

Now I see it has been I who harbours a misconception. The first proposition in the above is INCORRECT. The correct statement is:

local determinism Λ PC → D ;

this is the weak version of deriving a Bell inequality.

The strong version reads like this:

locality Λ CF Λ PC → D .

The first is only a corollary of the second, because

local determinism → locality Λ CF ,

but not conversely.
____________________

In case anyone is wondering:

PC ≡ perfect (anti-) correlation ,

CF ≡ counterfactuality ,

D ≡ a Bell inequality .
------------------------------------------------------
------------------------------------------------------
Oh Mom … there it is again!

... So, there are two 'theorems', a weak one and a strong one:

Weak Theorem: local determinism → D ;

Strong Theorem: locality Λ PC Λ CF → D .
... whoops!!! :blushing:

Eye_in_the_Sky

Mar12-10, 12:34 AM

Bell expresses locality as the factorability of the joint probability.You keep saying that, but I went back to the original Bell paper again recently to check something else, and I really don't think your statement is correct.

The passage from Bell's paper addressing locality is from section II ...
SpectraCat, ThomasT's claim does not apply to the part of Bell's paper that you quoted. The part you quoted is the beginning of "stage 2" in Bell's two-stage argument. At that spot, at the beginning of "stage 2", all outcomes are assumed to be predetermined (yet unknown). ThomasT's claim applies to "stage 1", not "stage 2".

So where then in Bell's paper is "stage 1" to be found? It is to be found in the first paragraph of section II as follows:
Consider a pair of spin one-half particles formed somehow in the singlet spin state and moving freely in opposite directions. Measurements can be made, say by Stern-Gerlach magnets, on selected components of the spins σ1 and σ2. If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa. Now we make the hypothesis [2], and it seems one at least worth considering, that if the two measurements are made at places remote from one another the orientation of one magnet does not influence the result obtained with the other. Since we can predict in advance the result of measuring any chosen component of σ2, by previously measuring the same component of σ1, it follows that the result of any such measurement must actually be predetermined.
-------------------------------------------------------------------------
[2] "But on one supposition we should, in my opinion, absolutely hold fast: the real factual situation of the system S2 is independent of what is done with the system S1, which is spatially separated from the former."

Note, however, that ThomasT's claim can only be applied to the above argument after that argument has been reformulated in terms of the joint-probability-function of the particle pair as calculated at the level of a physical theory. At this level, Einstein's locality statement [2] is transferred over to a mathematical condition which the joint-probability-function must then satisfy. That mathematical condition has come to be called "Bell Locality".

ThomasT's claim, then, boils down to the following:

"Bell Locality" is not a faithful representation of a principle of "Local Causality".
___________________________

Way back in post #239 (http://www.physicsforums.com/showthread.php?p=2593824#post2593824), I posted a diagram and two quotes on Bell's "Local Causality Criterion", thinking it might stimulate some discussion. When I saw that it did not do so, I decided I had better follow up on it with some more information on the matter. Thereafter, I decided I ought to attempt to present a 'clean presentation' of the entire matter. So far, this has proved to be exceedingly difficult for me.

Unfortunately, my time is running out, and by next week I will definitely have to stop posting here in the forum for quite some time.

So maybe I will have to compromise in some way.

Eye_in_the_Sky

Mar12-10, 12:48 AM

I would use "entangled state" instead of "twin-state" because that way you imply certain things that might not be very appropriate.
But otherwise I think we are on the same line here with addition that instead of the same result (maximally similar) there might be maximally opposite result as well depending from setup.
Yes we are 'on the same line' here. "Twin-state" is idiomatic for

(|x>|x> + |y>|y>) / √2 .
I would say that I do not quite understand how do you incorporate "angular momentum" in this context. If you associate "angular momentum" with polarization of individual photon then ...
For the moment, let us restrict our considerations to the singlet spin-½ pair with Stern-Gerlach magnets. In this context, would you say that the following statement is true?

"PC" is an essential ingredient of any theory which incorporates in it the notion of "angular momentum" as construed in conventional terms.

If the statement is true in the spin-½ context, then it might be possible (... at this stage I do not quite see how) to construct an argument for its truth in the optical context. On the other hand, if even in the spin-½ context the statement is false, then surely it is also false in the optical context.

zonde

Mar12-10, 04:06 AM

"Experimental violation of a Bell's inequality with efficient detection" (2001) Rowe et al.

http://www.nature.com/nature/journal/v409/n6822/full/409791a0.html

Not actually 100% detection but high enough. This uses Be ions rather than photons.

"Our measured value of the appropriate Bell's 'signal' is 2.25+/- 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called 'detection' loophole."
This experiment makes joined detection for photons scattered from both ions. It can be picked out here:
"The state of an ion, |down> or |up>, is determined by probing the ion with circularly polarized light from a 'detection' laser beam. During this detection pulse, ions in the |down> or bright state scatter many photons, and on average about 64 of these are detected with a photomultiplier tube, while ions in the |up> or dark state scatter very few photons. For two ions, three cases can occur: zero ions bright, one ion bright, or two ions bright. In the one-ion-bright case it is not necessary to know which ion is bright because the Bell's measurement requires only knowledge of whether or not the ions' states are different. Figure 2 shows histograms, each with 20,000 detection measurements. The three cases are distinguished from each other with simple discriminator levels in the number of photons collected with the phototube."

So the photon interference happens and result of measurement is not discrete sum of two photon ensembles but result of interference of two photon ensembles.
For easier visualization I can suggest to compare this experiment with double slit experiment where two ions play the role of slits. Difference is that each ion separately produces sharp bands but presence of other ion shifts the bands to one side.

So my point is that you don't even need any specific LR theory to account for results of this experiment in local realistic fashion.

Frame Dragger

Mar12-10, 04:28 AM

So my point is that you don't even need any specific LR theory to account for results of this experiment in local realistic fashion.

As long as you realize that you're in a terribly small minority. Frankly, I'd make your point from the outset and seek to justify it, not the other way around.

Bell is a test for LR matching QM's predictions, and there is a REASON why dBB is the only HV theory to be left after Bell (that is meaningful in any way, which is debatable)

You're seeming to advocate the notion of ensembles of particles creating apparant interference patterns, but that it is not a property of a single photon (or particle). If you're formulating this through LHVs, just say it so we can all go on our way.

SpectraCat

Mar12-10, 07:19 AM

SpectraCat, ThomasT's claim does not apply to the part of Bell's paper that you quoted. The part you quoted is the beginning of "stage 2" in Bell's two-stage argument. At that spot, at the beginning of "stage 2", all outcomes are assumed to be predetermined (yet unknown). ThomasT's claim applies to "stage 1", not "stage 2".

So where then in Bell's paper is "stage 1" to be found? It is to be found in the first paragraph of section II as follows:

Note, however, that ThomasT's claim can only be applied to the above argument after that argument has been reformulated in terms of the joint-probability-function of the particle pair as calculated at the level of a physical theory. At this level, Einstein's locality statement [2] is transferred over to a mathematical condition which the joint-probability-function must then satisfy. That mathematical condition has come to be called "Bell Locality".
You have lost me here ... what is equation 2 if not a reformulation "in terms of the joint-probability-function of the particle pair as calculated at the level of a physical theory", which also allows for the possibility of hidden variables?

I agree that, if there are no hidden variables, then that expression reduces to P(A,B)=P(A)P(B), as ThomasT says .. is that what you mean? If so, what is wrong with that as a definition of locality? I have checked back through his posts (although not exhaustively), and it seems ThomasT says cryptic things like "if you don't see something wrong with this, then you should", instead of explaining what he actually means. Perhaps I am just dense, but I don't see this ...

Eye_in_the_Sky

Mar12-10, 02:04 PM

(|x>|x> + |y>|y>) / √2
Something is bothering me here.

Should the sign be "+" as I have written it? Or should the sign be "-"?

Eye_in_the_Sky

Mar13-10, 11:30 PM

(|x>|x> + |y>|y>) / √2
Okay, I see it now.

When the polarization basis vectors of both particles are referenced to the same set of axes, the "+" sign applies.

Alternatively, one may prefer to write the joint state with respect to two different sets of axes such that each particle propagates in the "+z" direction of its own set. Say, for example, the two sets are related by a half turn about the x-axis. In that case, the "-" sign applies. But then, one is required to put tags (e.g. subscripts) on the basis vectors because the two pairs of linear polarization basis vectors are no longer the same; i.e.

|x>1 corresponds to |x>2 ,

but

|y>1 corresponds to -|y>2 ,

and the state is written

(|x>1|x>2 - |y>1|y>2) / √2 .

ThomasT

Mar14-10, 02:28 PM

I agree that, if there are no hidden variables, then that expression reduces to P(A,B)=P(A)P(B) ... what is wrong with that as a definition of locality?Maybe it's an ok definition of locality. Maybe the locality condition has nothing to do with why Bell inequalities are violated. Maybe common cause hidden variable assumption has nothing to do with why Bell inequalities are violated. Maybe there's another assumption underlying the construction of inequalities that is the real reason for their violation.

Bell's theorem seems to be based on the notion that the correlation between P(A,B) and Θ must be a linear one, as, for example, the archetypal Bell inequality, (1-P(Θ)) + (1-P(Θ)) <= 1-P(2Θ), where P(Θ) is the normalized rate of detection wrt some angular difference, Θ, of the polarizers.

I'm not sure where this notion (the assumption of linear correlation between P(A,B) and Θ) comes from, but it would account for violation of inequalities based on it.

Does it come from the notion that LR formalization of entanglement entails assignment of definite value(s) to λ? If so, that is a problem since λ can't be tracked (ie., it has no definite value at any given time).

Well, maybe LR formalization requires this, and maybe not. However, I think that a LR understanding of entanglement doesn't require it.

Consider a source producing pairs of counter-propagating photons entangled in polarization. The polarization, λ, is varying randomly from pair to pair with photonA and photonB of each pair polarized identically due to, presumably, emission by the same atom.

The normalized rates of detection are:

1. With no polarizers,

P(A) = P(B) = P(A,B) = 1

2. With 1 polarizer, b, at B,

P(A) = 1
P(B) = cos2(|b - λ|avg) = cos2(450) = .5
P(A,B) = .5

3. With 2 polarizers, b1 and b2, at B,

P(A) = 1
P(B) = cos2|b1-b2|
P(A,B) = cos2|b1-b2|

4. With 1 polarizer, a, at A, and 1 polarizer, b, at B,

P(A) = cos2(|a - λ|avg) = cos2(450) = .5
P(B) = cos2(|b - λ|avg) = cos2(450) = .5
P(A,B) = cos2|a-b|

The applicability of Malus Law above seems quite (LRly) understandable to me. If it's applicable in 3, then why not in 4?

If the foregoing makes any sense then consider also that the QM calculation wrt 4 incorporates Malus Law for the same reason that Malus Law applies to 3 -- crossed polarizers analyzing randomly polarized light. Nothing nonlocal about 3, is there? So, should QM be deemed a local theory? :smile:

Anyway, requiring a definite value for λ isn't a realistic requirement :smile:

So what is Bell's theorem supposed to be telling us that we couldn't have surmised without it?

Frame Dragger

Mar14-10, 03:04 PM

Maybe it's an ok definition of locality. Maybe the locality condition has nothing to do with why Bell inequalities are violated. Maybe common cause hidden variable assumption has nothing to do with why Bell inequalities are violated. Maybe there's another assumption underlying the construction of inequalities that is the real reason for their violation.

Bell's theorem seems to be based on the notion that the correlation between P(A,B) and Θ must be a linear one, as, for example, the archetypal Bell inequality, (1-P(Θ)) + (1-P(Θ)) <= 1-P(2Θ), where P(Θ) is the normalized rate of detection wrt some angular difference, Θ, of the polarizers.

I'm not sure where this notion (the assumption of linear correlation between P(A,B) and Θ) comes from, but it would account for violation of inequalities based on it.

Does it come from the notion that LR formalization of entanglement entails assignment of definite value(s) to λ? If so, that is a problem since λ can't be tracked (ie., it has no definite value at any given time).

Well, maybe LR formalization requires this, and maybe not. However, I think that a LR understanding of entanglement doesn't require it.

Consider a source producing pairs of counter-propagating photons entangled in polarization. The polarization, λ, is varying randomly from pair to pair with photonA and photonB of each pair polarized identically due to, presumably, emission by the same atom.

The normalized rates of detection are:

1. With no polarizers,

P(A) = P(B) = P(A,B) = 1

2. With 1 polarizer, b, at B,

P(A) = 1
P(B) = cos2(|b - λ|avg) = cos2(450) = .5
P(A,B) = .5

3. With 2 polarizers, b1 and b2, at B,

P(A) = 1
P(B) = cos2|b1-b2|
P(A,B) = cos2|b1-b2|

4. With 1 polarizer, a, at A, and 1 polarizer, b, at B,

P(A) = cos2(|a - λ|avg) = cos2(450) = .5
P(B) = cos2(|b - λ|avg) = cos2(450) = .5
P(A,B) = cos2|a-b|

The applicability of Malus Law above seems quite (LRly) understandable to me. If it's applicable in 3, then why not in 4?

If the foregoing makes any sense then consider also that the QM calculation wrt 4 incorporates Malus Law for the same reason that Malus Law applies to 3 -- crossed polarizers analyzing randomly polarized light. Nothing nonlocal about 3, is there? So, should QM be deemed a local theory? :smile:

Anyway, requiring a definite value for λ isn't a realistic requirement :smile:

So what is Bell's theorem supposed to be telling us that we couldn't have surmised without it?

Science doesn't look kindly on surmise when a test and a theorem can be constructed instead...

I think you should just accept that you believe there is an underlying flaw, or ensemble of local hidden variables, and that Bell is hogwash. You'd be in the minority, but you're entitled to your opinion after all.

ThomasT

Mar14-10, 03:41 PM

Science doesn't look kindly on surmise when a test and a theorem can be constructed instead...

I think you should just accept that you believe there is an underlying flaw, or ensemble of local hidden variables, and that Bell is hogwash. You'd be in the minority, but you're entitled to your opinion after all.There's disagreement wrt the meaning of Bell's theorem and violation of Bell inequalities. Is it locality, or hidden variables, or some other assumption that we should be focusing on?

Since a local (if not quite realistic) understanding of Bell test results (via appropriate application of Malus Law) seems possible, I proposed that maybe the problem is the assumption that correlation between P(A,B) and Θ must be linear when, on its face, this assumption contradicts classical and quantum optical application of Malus Law.

This assumption follows from the requirement that LR model specify definite value of λ. But, since λ has no definite value at any given time, then this is an unwarranted requirement. Only the assumption of locally caused relationship or common property wrt entangled disturbances is necessary for local understanding of Bell test results and correct application of Malus Law to Bell test setups.

So, I propose that the reason why Bell inequalities are violated, and why this doesn't tell us anything about Nature, is due to their being based on the unwarranted assumption that, wrt a LR understanding, P(A,B) and Θ must be linearly correlated.

Frame Dragger

Mar14-10, 04:37 PM

There's disagreement wrt the meaning of Bell's theorem and violation of Bell inequalities. Is it locality, or hidden variables, or some other assumption that we should be focusing on?

Since a local (if not quite realistic) understanding of Bell test results (via appropriate application of Malus Law) seems possible, I proposed that maybe the problem is the assumption that correlation between P(A,B) and Θ must be linear when, on its face, this assumption contradicts classical and quantum optical application of Malus Law.

This assumption follows from the requirement that LR model specify definite value of λ. But, since λ has no definite value at any given time, then this is an unwarranted requirement. Only the assumption of locally caused relationship or common property wrt entangled disturbances is necessary for local understanding of Bell test results and correct application of Malus Law to Bell test setups.

So, I propose that the reason why Bell inequalities are violated, and why this doesn't tell us anything about Nature, is due to their being based on the unwarranted assumption that, wrt a LR understanding, P(A,B) and Θ must be linearly correlated.

There is a disagreement on this forum; out in the world, there is very little as to what Bell means. Whether you accept or reject it is another matter, but it's hardly controversial. Most people, myself included, believe that BI's DO tell us something about nature, but most importantly they tell us what theories can match QM and in what fashion. The fact that it's all counterintuitive and weird doesn't change matters, at least, not for most. Some theoreticians do need to worry about alternatives, but to be blunt, it's looking bleak for them right now.

DrChinese

Mar15-10, 09:11 AM

So, I propose that the reason why Bell inequalities are violated, and why this doesn't tell us anything about Nature, is due to their being based on the unwarranted assumption that, wrt a LR understanding, P(A,B) and Θ must be linearly correlated.

I still don't know what this means. Bell does not assume anything about LR other than LR itself and general equivalence to the predictions of QM (which of course leads to contradictions). So you still have not made much of a case for your perspective. And as Frame Dragger says, this is looking pretty bleak.

ThomasT

Mar15-10, 10:07 AM

There is a disagreement on this forum; out in the world, there is very little as to what Bell means.That might be true. Things like this are explored on PF in order to get a better understanding of them. Wasn't von Neumann's no HV theorem noncontroversial, sort of taken for granted, until knowledge of its flawed assumption became mainstream?

Whether you accept or reject it is another matter, but it's hardly controversial. Most people, myself included, believe that BI's DO tell us something about nature ... Now is your chance to put in your own words what you think violations of BI's tell us about Nature, and why you think they tell us that.

... but most importantly they tell us what theories can match QM and in what fashion.Isn't discovering the existence of underlying FTL propagations at least as important? :smile:

The fact that it's all counterintuitive and weird doesn't change matters, at least, not for most.The application of Malus Law to Bell test preparations isn't counterintuitive, and no weirder than the results with a standard polariscope setup.

What is weird and counterintuitive is the assumption that the correlation between |a-b| and P(A,B) should be a linear one if the crossed polarizers, a and b, are jointly analyzing identically polarized members of randomly polarized pairs.

DrChinese

Mar15-10, 10:58 AM

What is weird and counterintuitive is the assumption that the correlation between |a-b| and P(A,B) should be a linear one if the crossed polarizers, a and b, are jointly analyzing identically polarized members of randomly polarized pairs.

The only linear relationship I can think of in this context is a common Local Realistic boundary condition. I.e. what values a local realistic theory could predict and NOT run afoul of a Bell Inequality. Is that what you are referring to?

If so, I have some comments on that surrounding experiment. If not, can you explain what linear correlation you are referring to?

Eye_in_the_Sky

Mar15-10, 11:54 PM

You have lost me here ...
... Hopefully the following approach will make what I am trying to say clearer.
___________________

If I were asked to write down a theorem associated with stage 2 of Bell's argument, I would write down something like this:

Theorem 2: Suppose T is a fundamentally deterministic theory which has the PC-feature. Then, Bell's inequality holds in T, if T is local.

[NOTE: I have merely exchanged the term "realistic" (in the expression "local realistic") with the words "fundamentally deterministic".]
___________________

If I were asked to write down a theorem associated with stage 1 of Bell's argument in the case where that argument is formulated along the lines of the original language of EPR, I would write down something like this:

Theorem 1 (old version): If Quantum Mechanics is local, and counterfactual definiteness is a valid principle, then Quantum Mechanics is incomplete.

On the other hand, if I were asked to write down a theorem associated with stage 1 of Bell's argument in the case where that argument is formulated in terms of the joint-probability-function of the particle pair as calculated at the level of a physical theory, I would write down something like this:

Theorem 1: Suppose T is a complete stochastic theory which has the PC-feature. Then, if T satisfies the "Bell Locality" condition, T is fundamentally deterministic. In that case T is local in the sense of Theorem 2.
___________________

As I tried to point out in post #452 (http://www.physicsforums.com/showthread.php?p=2620117#post2620117), the "Bell Locality" condition pertains to "stage 1", not "stage 2". That is to say, "Bell Locality" was designed specifically for "stage 1". It was designed to elevate "Theorem 1 (old version)" to the rank of Theorem 1, the new version. What does this accomplish? It allows us to link Theorem 1 to Theorem 2, thereby yielding:

Theorem 3: Suppose T is a complete stochastic theory which has the PC-feature. Then, Bell's inequality holds in T, if T satisfies the "Bell Locality" condition.

Compare this to:

Theorem 2: Suppose T is a fundamentally deterministic theory which has the PC-feature. Then, Bell's inequality holds in T, if T is local.

As you can see, Theorem 3 is a generalization of Theorem 2. This is because the category of "complete stochastic" includes the category of "fundamentally deterministic" as a particular case – i.e. it is the case of a stochastic theory for which all of the irreducible probabilities are always either 0 or 1. In that case, "Bell Locality" becomes "locality" in the sense of Theorem 2.

But Theorem 3 can still be refined. This is because "locality" (in the sense of special relativity) implies "Bell Locality". Or equivalently, a violation of "Bell Locality" implies "nonlocality".

So, I would rewrite Theorem 3 as:

Bell's Inequality Theorem: Suppose T is a complete stochastic theory which has the PC-feature. Then, if Bell's inequality is violated in T, T is nonlocal.

[NOTE: In such a theory T, there is no assumption of "hidden variables" of any kind.]
___________________

Of course, I have not stated definitions of "complete stochastic" and "Bell Locality". Nor have I established the truth of Theorem 1. Nor have I shown that "locality" (in the sense of special relativity) implies "Bell Locality".

My purpose in the above was just to identify the conceptual context in which the "Bell Locality" condition applies and to specify its point of application within that context. That point is in "stage 1, Theorem 1".

SpectraCat

Mar16-10, 12:56 AM

... Hopefully the following approach will make what I am trying to say clearer.
___________________

If I were asked to write down a theorem associated with stage 2 of Bell's argument, I would write down something like this:

Theorem 2: Suppose T is a fundamentally deterministic theory which has the PC-feature. Then, Bell's inequality holds in T, if T is local.

[NOTE: I have merely exchanged the term "realistic" (in the expression "local realistic") with the words "fundamentally deterministic".]
___________________

If I were asked to write down a theorem associated with stage 1 of Bell's argument in the case where that argument is formulated along the lines of the original language of EPR, I would write down something like this:

Theorem 1 (old version): If Quantum Mechanics is local, and counterfactual definiteness is a valid principle, then Quantum Mechanics is incomplete.

On the other hand, if I were asked to write down a theorem associated with stage 1 of Bell's argument in the case where that argument is formulated in terms of the joint-probability-function of the particle pair as calculated at the level of a physical theory, I would write down something like this:

Theorem 1: Suppose T is a complete stochastic theory which has the PC-feature. Then, if T satisfies the "Bell Locality" condition, T is fundamentally deterministic. In that case T is local in the sense of Theorem 2.
___________________

As I tried to point out in post #452 (http://www.physicsforums.com/showthread.php?p=2620117#post2620117), the "Bell Locality" condition pertains to "stage 1", not "stage 2". That is to say, "Bell Locality" was designed specifically for "stage 1". It was designed to elevate "Theorem 1 (old version)" to the rank of Theorem 1, the new version. What does this accomplish? It allows us to link Theorem 1 to Theorem 2, thereby yielding:

Theorem 3: Suppose T is a complete stochastic theory which has the PC-feature. Then, Bell's inequality holds in T, if T satisfies the "Bell Locality" condition.

Compare this to:

Theorem 2: Suppose T is a fundamentally deterministic theory which has the PC-feature. Then, Bell's inequality holds in T, if T is local.

As you can see, Theorem 3 is a generalization of Theorem 2. This is because the category of "complete stochastic" includes the category of "fundamentally deterministic" as a particular case – i.e. it is the case of a stochastic theory for which all of the irreducible probabilities are always either 0 or 1. In that case, "Bell Locality" becomes "locality" in the sense of Theorem 2.

But Theorem 3 can still be refined. This is because "locality" (in the sense of special relativity) implies "Bell Locality". Or equivalently, a violation of "Bell Locality" implies "nonlocality".

So, I would rewrite Theorem 3 as:

Bell's Inequality Theorem: Suppose T is a complete stochastic theory which has the PC-feature. Then, if Bell's inequality is violated in T, T is nonlocal.

[NOTE: In such a theory T, there is no assumption of "hidden variables" of any kind.]
___________________

Of course, I have not stated definitions of "complete stochastic" and "Bell Locality". Nor have I established the truth of Theorem 1. Nor have I shown that "locality" (in the sense of special relativity) implies "Bell Locality".

My purpose in the above was just to identify the conceptual context in which the "Bell Locality" condition applies and to specify its point of application within that context. That point is in "stage 1, Theorem 1".

Wait ... you thought that would make it clearer??:eek:

In all seriousness, that may be clearer in the sense that you have laid it all out, but it's gonna take a while for me to wade through it all. Some definitions would help .. I can probably look them up in past posts, but it would be easier if you could reiterate the following:

What is the PC-feature?

What do you mean by a complete stochastic theory in the context of Theorems 1 and 3 (new version)?

Eye_in_the_Sky

Mar16-10, 03:08 AM

Wait ... you thought that would make it clearer??:eek:

In all seriousness, that may be clearer in the sense that you have laid it all out ...
Sorry about that. ... Yes, "clearer" ONLY in the sense that it has all been laid out.
Some definitions would help ..
I had hoped to avoid the labour of having to define the terms, thinking that it would suffice to present things in a way that it could all be followed at the linguistic level of merely matching words.

As I said:

"My purpose ... was just to identify the conceptual context in which the 'Bell Locality' condition applies and to specify its point of application within that context."
I can probably look them up in past posts, but it would be easier if you could reiterate the following:

What is the PC-feature?
Okay, the "PC-feature" is easy enough. In words it goes like this:

When Alice and Bob's settings are the same, their outcomes are opposite with probability equal to 1.

Thus, "PC" is short for "perfect anti-correlation at equal settings".
___________________________________
What do you mean by a complete stochastic theory in the context of Theorems 1 and 3 (new version)?
As for "complete stochastic", that is something rather more involved. As yet the term has not been defined in this thread.

But since you are asking, I will put down the words.

To say that a stochastic theory is complete means:

1) With respect to a given spacelike hypersurface S, the theory correctly identifies all possible "states" of the system, each of which constitutes "a complete description" in terms of local beables along S. Let ΛS denote the set of all such states.

2) For any given state λЄΛS, the value which the theory assigns to P(X|Y,λ) – i.e. "the probability of X, given Y when the state is λ" – takes into account all of the relevant information contained the condition Y and the complete state λ.

I have selected the term "complete stochastic" and assembled its definition on the basis of what is written in the following reference:

Travis Norsen, "Bell Locality and the Nonlocal Character of Nature" (http://arxiv.org/PS_cache/quant-ph/pdf/0601/0601205v2.pdf)

(In fact, in that reference you will find a proof of what I have referred to as Theorem 1.)

Next ... it is essential to recognize the following consequence of the above definition:

From the definition above, it follows that in a complete stochastic theory all probabilities of the form P(X|Y,λ) assigned by the theory are irreducible. That is to say, these elements of randomness ascribed by the theory belong to the "real physical situation" as an intrinsic property. These probabilities do not in any way arise on account of a lack of information concerning the relevant facts upon which physical predictions are to be made.

And for further emphasis, here is how Maudlin puts it:

"... any theory which takes stochastic laws seriously at the ontological level must take ascriptions of probability equally seriously. If we believe that a photon approaching a polarizer has a 50 percent chance of passing and a 50 percent chance of being absorbed, and that these probabilities are reflections not of our ignorance but of a basic indeterminism in nature, then we must take an event’s having a particular probability as a basic physical fact. In this case a change from 50 percent probability of passage to 99 percent probability is a physical change."

The above quote, I have taken from this reference:

Travis Norsen, "J.S. Bell’s Concept of Local Causality" ( http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.0401v1.pdf)

DrChinese

Mar16-10, 08:36 AM

I have selected the term "complete stochastic" and assembled its definition on the basis of what is written in the following reference:

Travis Norsen, "Bell Locality and the Nonlocal Character of Nature" (http://arxiv.org/PS_cache/quant-ph/pdf/0601/0601205v2.pdf)

(In fact, in that reference you will find a proof of what I have referred to as Theorem 1.)

Travis is brilliant, and I reference some of his work from my own web page. But I would not consider his as a good reference for definitions like this. If you start from the perspective that locality/separability is the fundamental premise of Bell, all you end up seeing is a proof of non-locality - which he does.

If you start from a premise of realism/counterfactual definiteness (CD) - as I tend to - then you see a proof of contextuality (non-realistic interpretations). I believe it is correct to see the conjunction of assumptions in Bell: locality + realism. Look to other theorems for more than this.

ThomasT

Mar16-10, 09:43 AM

The only linear relationship I can think of in this context is a common Local Realistic boundary condition. I.e. what values a local realistic theory could predict and NOT run afoul of a Bell Inequality. Is that what you are referring to?Yes, that's it. It's the specific reason why BI's are violated, right? OK, so the discussion regarding the meaning of Bell's theorem and violation of BI's has to do with what, exactly, this boundary condition comes from.
If so, I have some comments on that surrounding experiment. OK.

DrChinese

Mar16-10, 12:04 PM

Yes, that's it. It's the specific reason why BI's are violated, right? OK, so the discussion regarding the meaning of Bell's theorem and violation of BI's has to do with what, exactly, this boundary condition comes from.

Well... Let's look at this as a boundary. Bell assumed that the LRT would need to match the predictions of QM. So if you follow that approach, there is no boundary. LR is simply ruled out, and that is the end of it. Of course, you must prove that the predictions of QM are supported to get this result.

Next, there is the boundary you describe. This comes from a relaxed assumption. The relaxed assumption is that the perfect correlations of EPR are in effect, but the Local Realistic Theory does not match QM. This yields the Bell Inequality, which is essentially the "closest" any LR can come to the predictions of QM. Of course it still wouldn't match the predictions of QM. But it would not violate Bell's Theorem/Inequality.

So the boundary condition is a result of Bell pointing out that QM and LR are incompatible as to their predictions. It really has nothing to say about assumptions within those theories OTHER than the LR being realistic/separable. Amd there is certainly no requirement that the LR have the linear relationship you mention. The function could be anything, since it doesn't match QM (or experiment).

yoda jedi

Mar16-10, 04:00 PM

What do YOU mean by the word "covariant"?
Anyway, with the usual definition of that word, there is a way to make the wave function covariant:
http://xxx.lanl.gov/abs/1002.3226

context independent.

Eye_in_the_Sky

Mar17-10, 04:21 AM

Back in post #468 (http://www.physicsforums.com/showthread.php?p=2626557#post2626557), I wrote down a definition of the term "complete" in connection with the notion of a complete stochastic theory.

... There is a 'bug' in that definition. I will show you where:

1) With respect to a given spacelike hypersurface S, the theory correctly identifies all possible "states" of the system, each of which constitutes "a complete description" in terms of local beables along S. Let ΛS denote the set of all such states.

The words in bold face do not belong in the definition. Those words should be deleted. The definition should read as follows.

To say that a stochastic theory is complete means:

1) With respect to a given spacelike hypersurface S, the theory correctly identifies all possible "states" of the system, each of which constitutes "a complete description" along S. Let ΛS denote the set of all such states.

2) For any given state λЄΛS, the value which the theory assigns to P(X|Y,λ) – i.e. "the probability of X, given Y when the state is λ" – takes into account all of the relevant information contained the condition Y and the complete state λ.

... Soon, I will go back over everything and try to determine whether or not those words which 'snuck' into the definition were entirely superfluous. If they were not, I will try to determine their proper place.

Eye_in_the_Sky

Mar17-10, 04:26 AM

... :eek:

... but it's gonna take a while for me to wade through it all.... Please, ONLY do so if it pleases you to do so. :smile:

As I said:

"As I said:

'My purpose ... was just to identify the conceptual context in which the "Bell Locality" condition applies and to specify its point of application within that context.' "

Eye_in_the_Sky

Mar17-10, 04:36 AM

If you start from a premise of realism/counterfactual definiteness (CD) - as I tend to - then you see a proof of contextuality (non-realistic interpretations).
Dr. Chinese, I do not understand what you mean by this. Can you explain it?
_______________________
I believe it is correct to see the conjunction of assumptions in Bell: locality + realism.
In connection with "stage 2" of Bell's argument, I agree with you. But in connection with "stage 1" I do not see it.

Now that I have fixed-up the definition of a "complete" stochastic theory, Quantum Mechanics can be admitted as a candidate. The λ's all have the form

λ = [ψ1(x,to) + ψ2(x,to)] ⊗ |singlet> ,

where the spacelike hypersurface S is given by t=to in the mutual rest frame of Alice and Bob.

Over the next month or so, I will put some time into trying to make a determination of whether or not Theorem 1 (as I have written it) is in fact valid. I will also check to see that I have properly understood the true meaning of "Bell Locality".

DrChinese

Mar17-10, 09:59 AM

Dr. Chinese, I do not understand what you mean by this. Can you explain it?

I had said: If you start from a premise of realism/counterfactual definiteness (CD) - as I tend to - then you see a proof of contextuality (non-realistic interpretations).

Understand that my argument is not rigorous. I am simply saying that when you start from one side, that is what you tend to see and ignore much other material. That is certainly what Travis does, as he denies that realism is a part of the Bell argument despite my pointing out to him the exact spot it is introduced many times.

So a good example of my argument is Mermin's example of the "instruction sets". That is the CD assumption. Don't need to assume separability for that, just the usual realistic requirement. In my mind, this argument applies without regard to locality. As I say that is just a perspective, and should not be taken too literally. However, there are a number of authors - certainly as respected as Norsen - who make this argument more strongly. I'll see if I can dig up a reference. But keep in mind that neither of the "Bell only requires locality assumption" or "Bell only requires realism assumption" schools is considered generally accepted. The general conclusion is that both assuptions are present in Bell.

Eye_in_the_Sky

Mar18-10, 04:45 AM

I had said: If you start from a premise of realism/counterfactual definiteness (CD) - as I tend to - then you see a proof of contextuality (non-realistic interpretations).

Understand that my argument is not rigorous.
A non-rigorous argument can have merit.
I am simply saying that when you start from one side, that is what you tend to see and ignore much other material.
If you "start from one side" and derive Bell's inequality from it (and the derivation is correct), then you have found sufficient conditions for Bell's inequality to hold. Relative to those conditions, all other conditions are not necessary.
I am simply saying that when you start from one side, that is what you tend to see and ignore much other material. That is certainly what Travis does, as he denies that realism is a part of the Bell argument despite my pointing out to him the exact spot it is introduced many times.
That would be because you are pointing out the spot in "stage 2" of Bell's argument. But (according to Travis) already at the very beginning of that stage, 'realism' has been established as a consequence of three other premises: 'completeness', 'PC', and 'Bell Locality'. Travis's proof is "stage 1" of Bell's argument as Bell ultimately intended it to be: 'realism' follows as a consequence of the "stage 1" argument.

A "consequence" ... do you understand that? ... a "consequence".

So in order to debunk Travis's claim, one needs to directly address the argument of "stage 1" and show that 'realism' cannot be derived from the conjunction of 'completeness', 'PC', and 'Bell Locality' (as Travis claims it can) – i.e. either there is some flaw in the argument, or 'realism' has been smuggled into it.
So a good example of my argument is Mermin's example of the "instruction sets". That is the CD assumption.
"Counterfactual definiteness" is a weaker premise than "instruction sets".

"Counterfactual definiteness" is the assumption that there would have been definite outcomes in the counterfactual cases (without necessarily assigning specific values to those outcomes).

"Instruction sets" is the assumption in which the definite outcomes in (at least some of) the counterfactual cases are assigned specific values.

I am not familiar with Mermin's example. Is this it?

David Mermin’s EPR gedanken experiment (http://public.fh-wolfenbuettel.de/~ruediger/lehre/EPRapplet/EPRappletDescription.pdf)

Yes, I think it must be.
Don't need to assume separability for that, just the usual realistic requirement. In my mind, this argument applies without regard to locality.
What you are saying is wrong.

"Instruction sets" always require "separability". This is because each particle is assigned its own separate set of instructions. The joint state is separable.

Moreover, Mermin's example is "local". This because each particle is assigned its instructions at the source and there is no communication between wings.

So, Mermin's example is a particular instance of the general principle that "local classical instruction sets" cannot account for all of the quantum correlation predictions.
As I say that is just a perspective, and should not be taken too literally. However, there are a number of authors - certainly as respected as Norsen - who make this argument more strongly. I'll see if I can dig up a reference.
Do you mean an argument in support of the following claim?

Some form of 'realism' must necessarily be assumed in order to arrive at Bell's inequality.

If so, then by all means find some references.
But keep in mind that neither of the "Bell only requires locality assumption" or "Bell only requires realism assumption" schools is considered generally accepted.
There is no such thing as a "Bell only requires realism assumption" school. Belief in the existence of such a school is DELUSIONAL.

DrChinese

Mar18-10, 10:12 AM

1. A non-rigorous argument can have merit.

2. A "consequence" ... do you understand that? ... a "consequence".

So in order to debunk Travis's claim, one needs to directly address the argument of "stage 1" and show that 'realism' cannot be derived from the conjunction of 'completeness', 'PC', and 'Bell Locality' (as Travis claims it can) – i.e. either there is some flaw in the argument, or 'realism' has been smuggled into it.

3. "Counterfactual definiteness" is a weaker premise than "instruction sets".

"Counterfactual definiteness" is the assumption that there would have been definite outcomes in the counterfactual cases (without necessarily assigning specific values to those outcomes).

"Instruction sets" is the assumption in which the definite outcomes in (at least some of) the counterfactual cases are assigned specific values.

4. I am not familiar with Mermin's example. Is this it?

David Mermin’s EPR gedanken experiment (http://public.fh-wolfenbuettel.de/~ruediger/lehre/EPRapplet/EPRappletDescription.pdf)

Yes, I think it must be.

5. "Instruction sets" always require "separability". This is because each particle is assigned its own separate set of instructions. The joint state is separable.

Moreover, Mermin's example is "local". This because each particle is assigned its instructions at the source and there is no communication between wings.

So, Mermin's example is a particular instance of the general principle that "local classical instruction sets" cannot account for all of the quantum correlation predictions.

6. Do you mean an argument in support of the following claim?

Some form of 'realism' must necessarily be assumed in order to arrive at Bell's inequality.

If so, then by all means find some references.

7. There is no such thing as a "Bell only requires realism assumption" school. Belief in the existence of such a school is DELUSIONAL.

1. Sure, and I make them all the time.

2. Well actually I don't have to do anything to debunk Norsen. He has some followers and I respect that. There are plenty of others who disagree, and some have in fact already debunked his general line of thinking.

The point is that IF you assume completeness - which Bell doesn't - then perhaps you can get X conclusion. EPR did exactly that.

3. Sorry, to me CD = realism and yes I know that it doesn't to some people. If you can give me a specific example of a relevant difference, that would be wonderful. Meanwhile, most attempts to explain the difference end up being a semantic exercise that puts me to sleep. If it has a value but it is unknown (and perhaps unknowable), that is one thing. If it has no definite value, that is another.

I guess there are shades of gray in between, but they actually don't matter. Because Bell assumes realism, that there is a specific outcome possible for an observation that is not performed. Which is the definition of Bell realism. Same essential definition as for EPR's element of reality, by the way.

QM itself is not CD (or realistic) in the formalism (HUP's non-commuting operators).

4. Yes, or my own version:

http://drchinese.com/David/Bell_Theorem_Easy_Math.htm

Naturally, it is more eloquent. :tongue:

5. Whoa, I wouldn't agree that the instruction set implies separability! That's sorta the point, actually. I am saying - non-rigorously - that where you start colors what you conclude. You see separability, while I see realism.

Maybe the system is non-local realistic (and not necessarily separable because they share a single instruction set) ! But if it were, you couldn't replicate the QM predictions. Now I know you are going to object about BM, but that is not what I am talking about; as BM is not only non-local realistic but it is ALSO contextual. So clearly, somehow, there is a group of people who see the need to support contextuality along with realism. (I non-rigorously accept contextuality and reject realism. But of course, maybe I am wrong.) But either way, Bell stands.

6. Sure, how about this member of your "non-existent" school:

A Bell Theorem with no locality assumption (2006), C. Tresser.
http://arxiv.org/abs/quant-ph/0608008

A pint of beer says you debate the merit of the paper BEFORE you acknowledge the existence of the school... and that you are flat out incorrect on this point.

7. Well, I think we found your hot spot. :biggrin: See 6.

yoda jedi

Mar18-10, 05:14 PM

There is no such thing as a "Bell only requires realism assumption" school. Belief in the existence of such a school is DELUSIONAL.

..........If one uses a broader and more common definition of locality........... (C. Tresser)

that`s the problem, people confusing ontology with semantics, distorting, stretching or whatever....

imagine:
"or using a shorter and less common definition of realism" or
"realism according groblacher" or " a very bizzarre notion of locality"

accommodative opinions.

Some form of 'realism' must necessarily be assumed.

indeed, with "NOTHING" nothing can be conceived.

Frame Dragger

Mar18-10, 07:25 PM

indeed, with "NOTHING" nothing can be conceived.

Well, you could be into that whole "let there be light" bit, but really I like your explanation much better. :wink:

Eye_in_the_Sky

Mar19-10, 03:53 AM

6. Sure, how about this member of your "non-existent" school:

A Bell Theorem with no locality assumption (2006), C. Tresser.
http://arxiv.org/abs/quant-ph/0608008

A pint of beer says you debate the merit of the paper BEFORE you acknowledge the existence of the school... and that you are flat out incorrect on this point.

7. Well, I think we found your hot spot. :biggrin: See 6.
Sorry about that. I thought you meant a school which claims that 'realism' alone is a sufficient condition for a derivation of Bell's inequality. ... :surprised

But now I see it seems you mean something else. From what is said in the abstract of that paper, it looks like you are referring to a school which claims that 'realism' alone is the reason for the violation of Bell's inequality.
... Okay, this can make sense.
____________________________________

My opportunity for posting in the forum is about to expire. In a month or so I will be able to come back, but then, only infrequently.

Dr. Chinese, I have printed out a copy of your post, and I will take it with me when I go. I will also print out copies of the references you have cited. When I return, I will post back in this thread any responses I may have.

There is, however, one more thing you might be able to help me with.
Well actually I don't have to do anything to debunk Norsen. ... some have in fact already debunked his general line of thinking.
If you can post some links to references which do the debunking, then please do so. I may still have a chance to print more things out before I go.
____________________________________

BE WELL, ALL.
... "let there be light" ...

... one-we-all SHINE! :smile:

DrChinese

Mar19-10, 07:20 AM

Sorry about that. I thought you meant a school which claims that 'realism' alone is a sufficient condition for a derivation of Bell's inequality. ... :surprised

But now I see it seems you mean something else. From what is said in the abstract of that paper, it looks like you are referring to a school which claims that 'realism' alone is the reason for the violation of Bell's inequality.
... Okay, this can make sense.
____________________________________

My opportunity for posting in the forum is about to expire. In a month or so I will be able to come back, but then, only infrequently.

Dr. Chinese, I have printed out a copy of your post, and I will take it with me when I go. I will also print out copies of the references you have cited. When I return, I will post back in this thread any responses I may have.

There is, however, one more thing you might be able to help me with.

If you can post some links to references which do the debunking, then please do so. I may still have a chance to print more things out before I go.
____________________________________

BE WELL, ALL.

... one-we-all SHINE! :smile:

Well, I am going to award you the pint of beer... although I think you are splitting a few hairs in your acknowledgement.

I am scared now that you will say this reference is not a "debunking" of Travis... as perhaps it is more of taking issue with a specific item. However, coming as it is from Shimony (and you don't see a lot of "named" critiques), I think you have to take it that it is Norsen's essential program that is coming under fire. Everyone who knows Norsen has a great respect for him, as I do, but that does not color the fact that I disagree with 2 key elements of his analyses. Specifically, I object to Norsen's historical characterization of the EPR argument; and his assertion that Bell tests prove non-locality. The below does not touch too much on either of these, so I simply provide it for your interest. Please do not respond to the merits of the actual argument as I am not trying to debate those, nor is this paper related to this thread in and of itself.

http://www.brown.edu/Departments/EEB/roberts/sawicki/sawickietal_AJP_adaircomment_reply_2005.pdf

We look forward to your return, as always...

-DrC

Frame Dragger

Mar19-10, 07:47 AM

@Eye: Hurry back, this is all very interesting to read as it's developed! :smile: I learn so much from the struggle when people try to communicate (and then succeed) on these complex and/or weighty topics, especially on the net.

@DrChinese: I've just had a friend corner me about superdeterminism, and while my instinct was to scoff, I wanted to come here first. My understanding is that it is vanishingly unlikely, or an excuse to say "god". Does anyone really explore that as a viable loophole? It seems impossible, but I often miss the long-shot and go with the more balanced->depressive view. :wink:

From my understand, Bell's Inequalities really were about starting with many of EPR's "assumptions", and trying to work with them towards some kind of test of LR. The notion of superdeterminism just seems to be a pointless exercise IF it existed, and pointless if it doesn't. Am I really off-base here or flat out wrong?

DrChinese

Mar19-10, 08:36 AM

Frame Dragger

Mar19-10, 10:08 AM

t' Hooft has written about superdeterminism, and I will send a reference. Others too. I say it is just another way of saying god. I will explain in a follow up post.

Bell definitely was responding to EPR specifically. He wanted to address Einstein's idea that a form of local realism - more complete and to be discovered in the future - could be compatible with the predictions of QM.

Thank you very much DrChinese! I look forward to the reference, but to be fair I believe as you do, that it's the "Creationism" of LR et al.

EDIT: Not to mention the whole idea is so terribly... bleak. It says something about the lengths people will go to when resolving cognitive dissonance.

ThomasT

Mar19-10, 10:45 AM

Well... Let's look at this as a boundary. Bell assumed that the LRT would need to match the predictions of QM. So if you follow that approach, there is no boundary. LR is simply ruled out, and that is the end of it. Of course, you must prove that the predictions of QM are supported to get this result.

Next, there is the boundary you describe. This comes from a relaxed assumption. The relaxed assumption is that the perfect correlations of EPR are in effect, but the Local Realistic Theory does not match QM. This yields the Bell Inequality, which is essentially the "closest" any LR can come to the predictions of QM. Of course it still wouldn't match the predictions of QM. But it would not violate Bell's Theorem/Inequality.

So the boundary condition is a result of Bell pointing out that QM and LR are incompatible as to their predictions. It really has nothing to say about assumptions within those theories OTHER than the LR being realistic/separable. And there is certainly no requirement that the LR have the linear relationship you mention. The function could be anything, since it doesn't match QM (or experiment).What I'm asking is:

How is, eg., (1-P(|a-b|)) + (1-P(|a-b|)) => 1-P(2|a-b|) , the simplest and archetypal Bell inequality, derived?

The assumption of a local common cause wrt the relationship between entangled photons isn't enough to warrant the assumption that the above inequality literally represents. So, I'm guessing that the derivation of this inequality depends on the assumption of realism wherein the term realism means attributing definite values to the relevant property (or properties) of polarizer-incident optical disturbances in optical Bell tests.

As I see it, the assumption of local common cause, without realism, justifies the application of Malus Law in Bell tests. Would you agree with this?

Considering this, and from Tresser's and others' formulations of inequalities without an explicit locality condition, it appears that not only can nonlocality in Nature not be inferred but also that the applicability of Malus Law supports the continued assumption that Nature is exclusively locally causal in line with the requirements of SR.

So, it seems to me at this time (and of course I'm still somewhat confused by it all :smile:) that LR models ARE ruled out -- but due to the realism part (not the localism part).

P(A,B) = cos2|a-b| can therefore be considered as a local nonrealistic understanding of optical Bell test correlations.
-------------------------------------
Wrt superdeterminism, hasn't it already been agreed that this term just means determinism applied to everything in our universe -- and doesn't determinism already mean that?

I do hope that if this thread continues it doesn't digress to include discussions of superdeterminism and free will, again.

Frame Dragger

Mar19-10, 10:47 AM

@ThomasT: As DrChinese and I were just discussing, and as he's been saying OVER and OVER... Realism as defined by EPR!!!

ThomasT

Mar19-10, 10:52 AM

@ThomasT: As DrChinese and I were just discussing, and as he's been saying OVER and OVER... Realism as defined by EPR!!!What's your point?

yoda jedi

Mar19-10, 12:08 PM

Well, you could be into that whole "let there be light" bit, but really I like your explanation much better. :wink:

of course, clarity as of water.

real or realistic is the term to distinguish, simply, what exists from what does not exist.
come from the latin realis.
and ontology is the philosophical study of the existence or reality in general.

"the science of being qua being", 'Qua' means 'in the capacity of'.

Frame Dragger

Mar19-10, 12:25 PM

yoda jedi

Mar19-10, 01:59 PM

Again, the WORD "Realism" does not matter. The term Realism in this context is the realism as defined by EPR. Call it butternut squash if that helps... the name doesn't matter, the understanding of the principle does.

oh sorry, then EPR is the owner of reality :eek:
consecuently,

http://physicsworld.com/cws/article/news/27640
"Quantum physics says goodbye to reality"

................giving the uneasy consequence that reality does not exist when we are not observing it...........

then nothing exist, of course ! who care about names, words, concepts ! if nothing exist !

or if i or you wish name CAT to BUILDINGS or BUILDINGS to CATS who cares ?
and cats does not exist, is just semantics, all depend of the context, you live in some context (wait, you not exist if nobody measure you) and myself live in other context (if somebody measure observe me ! or EPR save me)

REALITY goes beyond contextuality or non-contextuality, counterfactual definiteness or indefiniteness, determinism or indeterminism, with unitary evolution or not.

the misundertanding goes back to:

http://arxiv.org/ftp/quant-ph/papers/0402/0402001.pdf

........Quantum Mechanics is not complete. And this is why such additional properties are referred to as « supplementary parameters », or « hiddenvariables.-----Einstein actually did not speak of « hidden variables » or « supplementary parameters », but rather of
« elements of the physical reality ». Accordingly, many authors refer to « realistic theories » rather than to « hidden variable theories », or to « supplementary variable theories »........

Frame Dragger

Mar19-10, 02:28 PM

DrChinese

Mar19-10, 04:07 PM

1. What I'm asking is:

How is, eg., (1-P(|a-b|)) + (1-P(|a-b|)) => 1-P(2|a-b|) , the simplest and archetypal Bell inequality, derived?

2. The assumption of a local common cause wrt the relationship between entangled photons isn't enough to warrant the assumption that the above inequality literally represents. So, I'm guessing that the derivation of this inequality depends on the assumption of realism wherein the term realism means attributing definite values to the relevant property (or properties) of polarizer-incident optical disturbances in optical Bell tests.

As I see it, the assumption of local common cause, without realism, justifies the application of Malus Law in Bell tests. Would you agree with this?

3. Considering this, and from Tresser's and others' formulations of inequalities without an explicit locality condition, it appears that not only can nonlocality in Nature not be inferred but also that the applicability of Malus Law supports the continued assumption that Nature is exclusively locally causal in line with the requirements of SR.

So, it seems to me at this time (and of course I'm still somewhat confused by it all :smile:) that LR models ARE ruled out -- but due to the realism part (not the localism part).

1. This is essentially a restatement of the realism requirement for ANY 2 pairs of "somethings" that take binary values. It could be sock colors, coin sides, or pretty much anything. This is not the "proper" form but I follow what you mean. This requirement has nothing at all to do with quantum mechanics. It follows some the probability ideas of Kolgomorov.

2. What you call a common cause is expressed a little differently usually. This comes from EPR originally, and I would say it is the idea that there are elements of reality. Those elements of reality would be what you would get from this idea:

A experiments measuring any observable attribute of Alice would allow you to predict the same attribute on Bob.

Keep in mind: these particles do NOT need to be entangled to demonstrate this effect. So it is not an assumption. It will be a demonstrated fact.

3. I happen to agree with this, although as I say it is not from a rigorous perspective. If you take a single photon - not part of an entangled pair but just one lone photon - you will eventually realize that Malus does not provide a self-consistent description of its spin either. So whatever the issue is, it does not seem to me to relate to separability/locality.

And I completely agree that if we are going to discuss/debate suprerdeterminism, we should start a new thread. Frame Dragger? Although it would probably make sense to skip it for a while if you want to follow some references first.

DrChinese

Mar19-10, 04:20 PM

No, but to have a discussion about something we have to first agree on what it is we're talking about. It happens to be that in the case of BELL the standard for reality that was "agreed" on WAS EPR, so yes... EPR owns reality as far as Bell's Theorems are concerned. That's the whole damned point. If you don't get that, you're missing everything that follows.

You are SOOOOOO right about this. It makes it hard to discuss local realism when you change definitions away from the EPR/Bell concepts. Bell knew that his idea of realism would be immediately obvious to those who knew the EPR paper (his audience). He didn't really bother with explanations and definitions, thinking that the result he had would speak for itself.

Bell/Einstein realism = EPR elements of reality, including counterfactuals, since Einstein insisted on this.

Bell/Einstein locality = No spooky action at a distance, for similar reasons.

At the time of Bell's paper, there was a standoff: it was generally believed that QM was correct in all particulars, but might be a subset of a greater theory yet to be discovered. Much like Special Relativity was a subset of General Relativity. So the importance of Bell was to show that Einstein's realism was incompatible with Einstein's locality.

Now, the question many ask is: Does Bell locality = Einstein locality? In other words, is Bell's separability the same thing as Einsteinian locality? I am not really into debating that, because I think you just go around in circles.

As to realism, I think there is no doubt that Bell intended a definition as close to EPR as possible. He specifically talks at length about the idea that the perfect correlations are consistent between some local realistic theories and QM. Which was where the standoff was at that time. Again, the standoff being between those who followed Einstein's tenets versus those that saw QM as complete already. ANd by complete, I mean in the sense of EPR.

Frame Dragger

Mar19-10, 04:20 PM

@DrChinese: I found some good references and am reading through them, I won't derail the subject! Pinky swear. :wink:

Edit: I see your second post... hmmm... First thank you. Second... I really don't know. Circles, as you say. It makes me wonder if we're really capable of formulating this "theory of everything" in terms that will make sense to us as humans. It may provide guidance as to the future of technology, but so many of these issues still come down to the fact that we're brains in a box so to speak.

I agree that Bell and EPR Realism are the same; as you say it was CLEARLY Bell's intent.

I hope we all live long enough to see something like answers to these questions... they're so captivating.

yoda jedi

Mar19-10, 04:54 PM

Frame Dragger

Mar19-10, 05:32 PM

agreement on ? on misunderstandings ? (from whoever)

and agreement ? where ?
here, there are only claims, opinions, if you (or whoever) wish name cat to reality or reality to cats that is your (their) misinterpretation (oh sorry, you do not exist, you are not real :surprised).

*sigh* Just because your nickname is Yoda, doesn't mean you have to start rambling like him.... :rolleyes:

ThomasT

Mar21-10, 02:33 PM

1. This is essentially a restatement of the realism requirement for ANY 2 pairs of "somethings" that take binary values. It could be sock colors, coin sides, or pretty much anything. This is not the "proper" form but I follow what you mean. This requirement has nothing at all to do with quantum mechanics. It follows some the probability ideas of Kolgomorov.

2. What you call a common cause is expressed a little differently usually. This comes from EPR originally, and I would say it is the idea that there are elements of reality. Those elements of reality would be what you would get from this idea:

A experiments measuring any observable attribute of Alice would allow you to predict the same attribute on Bob.

Keep in mind: these particles do NOT need to be entangled to demonstrate this effect. So it is not an assumption. It will be a demonstrated fact.

3. I happen to agree with this, although as I say it is not from a rigorous perspective. If you take a single photon - not part of an entangled pair but just one lone photon - you will eventually realize that Malus does not provide a self-consistent description of its spin either. So whatever the issue is, it does not seem to me to relate to separability/locality.

4. And I completely agree that if we are going to discuss/debate suprerdeterminism, we should start a new thread. Frame Dragger? Although it would probably make sense to skip it for a while if you want to follow some references first.
1. Ok, and its connection to Nature is via the faulty assumption that we can attribute definite values to the property or properties being jointly analyzed in Bell tests.

2. Ok, what I meant by common cause doesn't imply that we can attribute definite values (vis EPR elements of reality) to the locally imparted common property or properties. The only assumption necessary to justify the application of Malus Law in optical Bell tests is that whatever property or properties are being jointly analyzed, and whatever values they might have wrt some specific value of the global measurement parameter, they are the same for each of the counter-propagating disturbances incident on a and b during any given emission-coincidence interval.

It also follows from this assumption that if the angular difference of the joint polarizer settings |a-b| = 0, then the results at A and B for this setting should be identical -- and we can deduce A given B, and vice versa.

3. I think that many useful explanatory schemes don't start out very rigorously. The application of Malus Law in Bell tests follows from its application in previous (to Bell tests) similar setups (or setups with similar features). The considerations and assumptions leading to its application are all grounded in the assumption that Nature is exclusively locally causal in line with SR.

The assumption of nonlocality wrt entangled photons is just a bit too convenient, imho -- and, it creates other problems while still not really explaining entanglement.

4. As far as I'm concerned there's nothing to discuss/debate wrt superdeterminism. I agree with you that it's a completely superfluous consideration.

yoda jedi

Mar23-10, 10:19 AM

..............differed with Einstein about the (allegedly) fundamental nature of the Born probabilities and hence on the issue of -> determinism. Indeed, whereas Born and the others just listed after him believed the outcome of any individual quantum measurement to be unpredictable in principle, Einstein felt this unpredictability was just caused by the incompleteness of quantum mechanics (as he saw it)......................

---------------------------

......Bell himself has stressed this aspect and has remarked that it is extremely difficult to eradicate this prejudice:

"My own first paper (Physics 1, 195 (1965.) on this subject starts with a summary of the EPR argument from locality to deterministic hidden variables. But the commentators have almost universally reported that it begins with deterministic hidden variables." .....

.....It has to be remarked that deterministic hidden variable theories assume that the complete specification of the state of the system implies that all physical properties are actually possessed by the systems prior to any measurement process. This is equivalent to the request of realism discussed by the above mentioned authors.........

DrChinese

Mar23-10, 11:28 AM

......Bell himself has stressed this aspect and has remarked that it is extremely difficult to eradicate this prejudice......

"My own first paper (Physics 1, 195 (1965.) on this subject starts with a summary of the EPR argument from locality to deterministic hidden variables. But the commentators have almost universally reported that it begins with deterministic hidden variables."

.....It has to be remarked that deterministic hidden variable theories assume that the complete specification of the state of the system implies that all physical properties are actually possessed by the systems prior to any measurement process. This is equivalent to the request of realism discussed by the above mentioned authors.........

Yes, this is a bit of a tricky area. First, Bell did write about his paper after the fact... and in some cases those words can be different than the original paper. So which is the proper reference? What do you make of an author's subsequent comments to an important paper like this?

Second, what difference does it make whether he goes from locality to realism (or determinism or hidden variables or whatever) or vice versa? I think you end up at the same point either way.

Lastly, I think Bell should be looked at like a road map. Once you can see where Bell journeyed, the path becomes so much clearer for those who follow. Once you see the internal inconsistency of a local realistic approach, you realize that something has to give.

yoda jedi

Mar24-10, 11:32 AM

Second, what difference does it make whether he goes from locality to realism (or determinism or hidden variables or whatever) or vice versa? I think you end up at the same point either way.

absolute irrelevant, directionality it doesnt matter, the emphasis is on DETERMINISM look the word FROM not bold, but persist the word TO (my mistake).

i have to post in this way:

..............differed with Einstein about the (allegedly) fundamental nature of the Born probabilities and hence on the issue of -> determinism. Indeed, whereas Born and the others just listed after him believed the outcome of any individual quantum measurement to be unpredictable in principle, Einstein felt this unpredictability was just caused by the incompleteness of quantum mechanics (as he saw it)......................

---------------------------

......Bell himself has stressed this aspect and has remarked that it is extremely difficult to eradicate this prejudice:

"My own first paper (Physics 1, 195 (1965.) on this subject starts with a summary of the EPR argument from locality to deterministic hidden variables. But the commentators have almost universally reported that it begins with deterministic hidden variables." .....

.....It has to be remarked that deterministic hidden variable theories assume that the complete specification of the state of the system implies that all physical properties are actually possessed by the systems prior to any measurement process. This is equivalent to the request of realism discussed by the above mentioned authors.........

Realism is not Determinism (and Determinism is not Realism)
Reality can be deterministic or not, be real is exist, determined or undertermined (defined or undefined, counterfactual definiteness or indefiniteness) contextual or non contextual, predictable or unpredictable.
be real is : "being qua being", just being.

Eye_in_the_Sky

Apr27-10, 04:40 AM

Back in post #477 (http://www.physicsforums.com/showthread.php?p=2629841#post2629841), I wrote the following:

"Counterfactual definiteness" is a weaker premise than "instruction sets".

"Counterfactual definiteness" is the assumption that there would have been definite outcomes in the counterfactual cases (without necessarily assigning specific values to those outcomes).

"Instruction sets" is the assumption in which the definite outcomes in (at least some of) the counterfactual cases are assigned specific values.
3. Sorry, to me CD = realism and yes I know that it doesn't to some people. If you can give me a specific example of a relevant difference, that would be wonderful.
Below, I give an example in which counterfactual reasoning is used to reach a certain conclusion. If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

The validity of the argument itself requires the acceptability of a certain type of 'counterfactual reasoning'. What I have in mind is a principle which asserts merely that

there would have been definite outcomes in the counterfactual cases.

Taken on its own, the principle would not permit an a priori assignment of specific values to any of the outcomes in the counterfactual cases. [... And, as far as I can tell, nowhere in the argument is such an assignment required to be made.]

Perhaps such a principle is not the same as "CFD", i.e. "counterfactual definiteness", and so I am incorrect in my post #477 (http://www.physicsforums.com/showthread.php?p=2629841#post2629841) characterization of "CFD" (repeated at the top of this post) [... at later time, I would like to look into this question of 'definition' in more detail]. Therefore, I will return to my earlier nomenclature of using the expression "CF" ("counterfactuality") to denote the notion of 'counterfactual reasoning' in general.

Finally, the question I wish to raise (at least, preliminarily) is the following:

What, if anything, is wrong with the type of CF employed in the argument of the example below?
_______________________________________

Example

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t1 Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t2 the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t3 after t2, with subsequent registration occurring at a time t4.

So, we have

t1 [Alice chooses] < t2 [Alice gets result] < t3 [Bob chooses] < t4 [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t1 and t2, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t3 and t4, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Let us fix our attention to a time t, where t2 < t < t3. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa'.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of Sa would apply, whereas in case (2) an eigenstate of Sa' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Therefore, Quantum Mechanics is "incomplete".

DrChinese

Apr27-10, 09:03 AM

...it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of Sa would apply, whereas in case (2) an eigenstate of Sa' would apply....Therefore, Quantum Mechanics is "incomplete".

This was the EPR argument. Local causality + HUP -> (QM is incomplete) or (Reality is observer dependent - in this case Alice).

The above statement is a shortcut way of saying this argument is no longer accepted. It was not universally accepted even when first presented in 1935. But certainly it went out of fashion after that.

Note your assumption: local causality. Hmmm. Is that valid? No, that is suspect. Also, the usual deduction is that Bob's reality is dependent on a choice made by Alice if QM is complete. I would say this is a generally accepted conclusion: that either locality does not hold, or reality is dependent on observeration.

RUTA

Apr27-10, 01:07 PM

Below, I give an example in which counterfactual reasoning is used to reach a certain conclusion. If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

Finally, the question I wish to raise (at least, preliminarily) is the following:

What, if anything, is wrong with the type of CF employed in the argument of the example below?
_______________________________________

Example

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t1 Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t2 the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t3 after t2, with subsequent registration occurring at a time t4.

So, we have

t1 [Alice chooses] < t2 [Alice gets result] < t3 [Bob chooses] < t4 [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t1 and t2, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t3 and t4, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Let us fix our attention to a time t, where t2 < t < t3. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa'.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of Sa would apply, whereas in case (2) an eigenstate of Sa' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Therefore, Quantum Mechanics is "incomplete".

Your use of the term "locality" encompasses both causal locality and separability, but otherwise it looks like the EPR argument with the same conclusion. To finish the story you've only to add QM's predicted violation of the Bell inequality with its subsequent experimental confirmation whence people believe QM is complete. Get rid of superdeterminism (keep free will) and that leaves you having to discard causal locality and/or separability, which is where the debate is centered.

yoda jedi

Apr27-10, 02:56 PM

Back in post #477 (http://www.physicsforums.com/showthread.php?p=2629841#post2629841),

(iii) QM is "complete" ,

Therefore, Quantum Mechanics is "incomplete".

the quantum state is not just incomplete, but epistemic, i.e. a representation of an
observer’s knowledge of reality rather than reality itself.

Frame Dragger

Apr27-10, 03:01 PM

............the quantum state is not just incomplete, but epistemic..............

...And yet his was still not a particularly good way of demonstrating that.

yoda jedi

Apr27-10, 03:07 PM

being incomplete can not propose or derive any ontological premise.

Frame Dragger

Apr27-10, 03:26 PM

being incomplete can not propose or derive any ontological premise.

I truly look forward to RUTA's reply to this, as I suspect s/he will have something interesting on the subject.

Demystifier

Apr28-10, 04:13 AM

If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

I think that we can safely say that (i) is not compatible with (iii).
Namely, if QM (where by QM I mean QM in its standard form) is complete then everything about nature can be derived from QM. However, from QM one cannot derive that some macroscopic objects (e.g., humans) have ability to make a free choice. Therefore, if QM is complete, then free choice does not exist.
Similarly, if free choice exists, then it is something that is not explained by QM. Therefore, if free choice exists, then QM is not complete.

It follows that QM cannot be consistently interpreted such that only (ii) or only (iv) or even only (ii) and (iv) are relinquished. Instead, one must relinquish (i) or (iii) or both. (Which does not exclude the possibility that something else should be relinquished as well.)

SpectraCat

Apr28-10, 06:27 AM

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t1 Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t2 the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t3 after t2, with subsequent registration occurring at a time t4.

So, we have

t1 [Alice chooses] < t2 [Alice gets result] < t3 [Bob chooses] < t4 [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t1 and t2, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t3 and t4, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Everything up to here looks fine

Let us fix our attention to a time t, where t2 < t < t3. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of Sa'.

Here is where you run into problems IMO ... Alice in fact cannot say anything about the "information" relevant to region B at any point. She cannot know for sure if her measurement was the one that destroyed the entanglement, and thus established the eigenstates of which operator (Sa or S[sub]a') should be measured in region B, until she hears from Bob on a normal channel. Until then, she must allow for the possibility that Bob previously made a measurement that destroyed the entanglement, and she is measuring the projection of a well-defined eigenstate at her end.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of S[sub]a would apply, whereas in case (2) an eigenstate of Sa' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Hopefully my comment above helps to illustrate why (I think) the above analysis is flawed. The space-like separation between Alice and Bob means that they cannot know anything about measurements performed in the each other's regions until those results are communicated somehow. Alice is of course free to *assume* whatever she likes about what is going on in region B, but she can't *know* for sure until she hears from Bob. The apparent contradiction you have raised therefore does not seem to hold for Alice, or for Bob ... it would only hold for a hypothetical omniscient observer who could "see" what was going on in both space-time regions simultaneously. Since we know from SR that such an observer cannot exist, I don't see any contradiction here. Am I missing something?

Gordon Watson

Apr28-10, 07:15 PM

What am I missing?

If I prepare photon-pairs correlated via identical linear polarization (say, some pairs V-correlated and some pairs H-correlated) then Bell-tests show Bell's inequality to be satisfied ... with no suggestion of nonlocal influences. Right? [Let's call these photon-pairs classically correlated.]

BUT if I prepare more highly correlated photon-pairs (say, correlated via identical angular momentum) then Bell-tests show Bell's inequality to be false. [Let's call these photon-pairs quantum-mechanically correlated.]

Why should more highly correlated results (from more highly correlated photon-pairs) be attributed to nonlocal influences?

DrChinese

Apr29-10, 09:28 AM

What am I missing?

1. If I prepare photon-pairs correlated via identical linear polarization (say, some pairs V-correlated and some pairs H-correlated) then Bell-tests show Bell's inequality to be satisfied ... with no suggestion of nonlocal influences. Right? [Let's call these photon-pairs classically correlated.]

2. BUT if I prepare more highly correlated photon-pairs (say, correlated via identical angular momentum) then Bell-tests show Bell's inequality to be false. [Let's call these photon-pairs quantum-mechanically correlated.]

3. Why should more highly correlated results (from more highly correlated photon-pairs) be attributed to nonlocal influences?

1. These are not polarization entangled. The Bell Inequality does not really apply.

2. These are polarization entangled. The Bell Inequality should apply if you assert local realism, but experiments show the inequality is violated.

3. Because the inequality is violated, you must reject local realism. Essentially, the correlation level crosses a boundary. You shouldn't be able to have this level of correlation if locality and realism apply. So many people reject locality, and assert non-locality.

Gordon Watson

May4-10, 07:03 AM

1. These are not polarization entangled. The Bell Inequality does not really apply.

2. These are polarization entangled. The Bell Inequality should apply if you assert local realism, but experiments show the inequality is violated.

3. Because the inequality is violated, you must reject local realism. Essentially, the correlation level crosses a boundary. You shouldn't be able to have this level of correlation if locality and realism apply. So many people reject locality, and assert non-locality.

Thank you DrC.

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

DrChinese

May4-10, 09:09 AM

Thank you DrC.

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

1, 2: Sorry, not sure I follow what you are saying. If Bell's Inequality is respected, the photons are not polarization entangled. Entangled photons can be entangled on one or more pairs of observables.

3. Yes and no. There is no quantum of action to figure in for the realistic argument.

4. Some in fact do abandon realism. I personally lean in that direction a bit. But I am also slippery and sometimes change my mind.

5. Double slit is not a factor either way.

6. There are reasons, although they are subjective: a) It is easier to picture a non-local influence than the non-realistic alternative. I.e. thinking of a physical mechanism. b) Bohm worked out a non-local model to a sufficient level as to show it is conceptually viable.

RUTA

May4-10, 10:13 AM

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

I took the non-separable approach (aka non-EPR-realism) in my interpretation (“Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090 & “Why Quantum Mechanics Favors Adynamical and Acausal Interpretations such as Relational Blockworld over Backwardly Causal and Time-Symmetric Rivals,” Michael Silberstein, Michael Cifone & W.M. Stuckey, Studies in History & Philosophy of Modern Physics 39, No. 4, 736 – 751 (2008). http://dx.doi.org/10.1016/j.shpsb.2008.07.005).

I've given many presentations to experts in the foundations community and even though the formalism is textbook (irreps of spacetime symmetry group (FoP supra) or path integrals over graphs (arXiv 0908.4348)), people have a very difficult time with our brand of nonseparability, i.e., ontic structural realism. It runs contrary to the fundamental manner by which our brains construct perceptions -- things moving in space as a function of time, i.e., dynamism. In all honesty, my colleagues and I sometimes find ourselves asking questions in the wrong (dynamical) fashion and we've been working with RBW for 5 yrs.

So, I suspect we hear more about non-local solutions to EPR than non-separable ones because at least people can imagine a non-local dynamism.

Gordon Watson

May5-10, 05:52 PM

I took the non-separable approach (aka non-EPR-realism) in my interpretation (“Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090 & “Why Quantum Mechanics Favors Adynamical and Acausal Interpretations such as Relational Blockworld over Backwardly Causal and Time-Symmetric Rivals,” Michael Silberstein, Michael Cifone & W.M. Stuckey, Studies in History & Philosophy of Modern Physics 39, No. 4, 736 – 751 (2008). http://dx.doi.org/10.1016/j.shpsb.2008.07.005).

I've given many presentations to experts in the foundations community and even though the formalism is textbook (irreps of spacetime symmetry group (FoP supra) or path integrals over graphs (arXiv 0908.4348)), people have a very difficult time with our brand of nonseparability, i.e., ontic structural realism. It runs contrary to the fundamental manner by which our brains construct perceptions -- things moving in space as a function of time, i.e., dynamism. In all honesty, my colleagues and I sometimes find ourselves asking questions in the wrong (dynamical) fashion and we've been working with RBW for 5 yrs.

So, I suspect we hear more about non-local solutions to EPR than non-separable ones because at least people can imagine a non-local dynamism.

Dear RUTA: Your alternative approach sounds interesting, and worthy of extra study, and in line with my own thoughts, so I'd encourage you to put ALL your papers on arViv (with hot-links on PF, if that is permitted). Or open a PF IR page with hot links?

"Studies in History & Philosophy of Modern Physics" is not available at my library.

I would introduce RBW as an explicit non-EPR-realism [nEPRr] approach <full stop> on the grounds that you see clearly that EPR "elements of physical reality" are false and that (as a consequence), locality does not need to be abandoned until we have explored more realistic [i.e., nEPRr] approaches. [EPR-realism being totally unrealistic, IMO.]

In this way you can introduce strangers such as me to your "non-separable" approach without the suspicion that "non-separable" is sneaky shorthand for "non-locality". As to the difficulty of imagining your approach? Can it be more difficult than imagining that the speed of light is constant?

I'm off to study your RBW.

Is RBW the correct and universal designation of your approach?

Gordon Watson

May5-10, 06:11 PM

1, 2: Sorry, not sure I follow what you are saying. If Bell's Inequality is respected, the photons are not polarization entangled. Entangled photons can be entangled on one or more pairs of observables.

3. Yes and no. There is no quantum of action to figure in for the realistic argument.

4. Some in fact do abandon realism. I personally lean in that direction a bit. But I am also slippery and sometimes change my mind.

5. Double slit is not a factor either way.

6. There are reasons, although they are subjective: a) It is easier to picture a non-local influence than the non-realistic alternative. I.e. thinking of a physical mechanism. b) Bohm worked out a non-local model to a sufficient level as to show it is conceptually viable.

Dear DrC, what I was saying in my 1 and 2 is not that important. It was not (in your words)

"If Bell's Inequality is respected, the photons are not polarization entangled"

but rather:

"Classically-correlated photons satisfy BI, quantum-correlated photons do not."

This view leads me to reject EPR-realism (which I view as so amateurish as to be not worthy of a second thought). IMO, EPR-realism neglects the measurement interaction (for I understand EPR-realism to mean that measurement outcomes reflect "one-to-one" input properties) and yet we see that (in a Bell-test) even classically-correlated photons are modified by measurement.

So my 1 and 2 were to explain why I reject EPR-realism ... and seek a new REALISM ... before I reject locality.

That is why I am interested in (and don't understand) those who take the opposite approach. And why I'm interested especially in what leads you to occasionally flip-flop?

Also, how do you view RUTA's RBW approach?

RUTA

May6-10, 11:45 AM

Dear RUTA: Your alternative approach sounds interesting, and worthy of extra study, and in line with my own thoughts, so I'd encourage you to put ALL your papers on arViv (with hot-links on PF, if that is permitted). Or open a PF IR page with hot links?

"Studies in History & Philosophy of Modern Physics" is not available at my library.

You can get the RBW papers from my homepage: http://users.etown.edu/s/stuckeym/
I would introduce RBW as an explicit non-EPR-realism [nEPRr] approach <full stop> on the grounds that you see clearly that EPR "elements of physical reality" are false and that (as a consequence), locality does not need to be abandoned until we have explored more realistic [i.e., nEPRr] approaches. [EPR-realism being totally unrealistic, IMO.]

In this way you can introduce strangers such as me to your "non-separable" approach without the suspicion that "non-separable" is sneaky shorthand for "non-locality". As to the difficulty of imagining your approach? Can it be more difficult than imagining that the speed of light is constant?

I'm off to study your RBW.

Is RBW the correct and universal designation of your approach?

Thanks for the hints as to how to explain RBW :-) Yes, Relational Blockworld or RBW is the "universal designation."

DrChinese

May6-10, 01:44 PM

Dear DrC, what I was saying in my 1 and 2 is not that important. It was not (in your words)

"If Bell's Inequality is respected, the photons are not polarization entangled"

but rather:

"Classically-correlated photons satisfy BI, quantum-correlated photons do not."

This view leads me to reject EPR-realism (which I view as so amateurish as to be not worthy of a second thought). IMO, EPR-realism neglects the measurement interaction (for I understand EPR-realism to mean that measurement outcomes reflect "one-to-one" input properties) and yet we see that (in a Bell-test) even classically-correlated photons are modified by measurement.

So my 1 and 2 were to explain why I reject EPR-realism ... and seek a new REALISM ... before I reject locality.

That is why I am interested in (and don't understand) those who take the opposite approach. And why I'm interested especially in what leads you to occasionally flip-flop?

Also, how do you view RUTA's RBW approach?

Flip flop! Me? :smile:

I flip flop a bit on interpretations, mainly because I am always trying to determine if any interpretation might make a subtle assumption which could lead to a test.

I really like the RBW approach. It considers future context as relevant to fundamental quantum interactions, which seems to make sense (to me).

On the other hand: I would not be so quick to reject the EPR definition of realism. It is a powerful definition, a good line in the sand.

IcedEcliptic

May6-10, 01:53 PM

how do we talk about local realism without invoking EPR? "real" has too many definitions otherwise, we need somewhere to begin, yes?

yoda jedi

May6-10, 09:21 PM

how do we talk about local realism without invoking EPR? "real" has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

IcedEcliptic

May6-10, 09:32 PM

be real is independent of any conceptual consideration.

We need to discuss something yoda jedi, and reality is a standard we believe we experience. Contrasting with that seems sensible.

RUTA

May7-10, 11:33 AM

I had just posted this reference in another thread, but maybe you should read it to if you're not aware of it.

M.D. Reid et al. Rev. Mod. Phys. v.81, p.1727 (2009).

If you think that none of the violation of EPR/Bell, GHZ, CHSH, Leggett, etc. inequalities constitutes a violation of local realism, then you ARE proposing something that is not already established. This means that you need to back this up with a published work to support that you are not proposing your own personal theory.

Zz.

Do you have a title for that reference? The title is required for my interlibrary loan request.

yoda jedi

May7-10, 11:46 AM

We need to discuss something yoda jedi, and reality is a standard we believe we experience. Contrasting with that seems sensible.

Reality does not need you, to exist.

IcedEcliptic

May7-10, 12:49 PM

Reality does not need you, to exist.

Cute, but metaphysics and philosophy, and not helpful when discussing non-locality.

yoda jedi

May8-10, 12:28 PM

Cute, but metaphysics and philosophy, and not helpful when discussing non-locality.

i am not discussing NON LOCALITY.

"real" has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

We need to discuss something yoda jedi, and reality is a standard we believe we experience.

Reality does not need you.

Frame Dragger

May8-10, 01:25 PM

Ahh, it's good to be back. I see this thread has not changed much.

@Yoda Jedi: what kind of reality are you talking about in a local realism thread? I'm not getting what you're driving at, and I've been reading this thread for a while. The title is photon entanglment, so, I'm genuinely not getting your drift here.

IcedEcliptic

May8-10, 01:38 PM

i am not discussing NON LOCALITY.

You are not discussing the topic of the thread? I'm completely confused, perhaps if you spoke in more than single sentences I could learn more from you.

yoda jedi

May8-10, 02:36 PM

You are not discussing the topic of the thread? I'm completely confused, perhaps if you spoke in more than single sentences I could learn more from you.

Discussing:

"real"has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

reality is a standard we believe we experience.

Reality does not need you.

DrChinese

May8-10, 03:37 PM

Ahh, it's good to be back. I see this thread has not changed much.

:smile:

Eye_in_the_Sky

May26-10, 03:12 AM

I think it is true to say that Quantum Mechanics implies 'nonlocality'.

This 'nonlocality' is either in a sense of 'causation' or in a sense of 'existence' or (say maybe) 'identity'.

Eye_in_the_Sky

May26-10, 03:16 AM

Your use of the term "locality" encompasses both causal locality and separability, but otherwise it looks like the EPR argument with the same conclusion. To finish the story you've only to add QM's predicted violation of the Bell inequality with its subsequent experimental confirmation whence people believe QM is complete. Get rid of superdeterminism (keep free will) and that leaves you having to discard causal locality and/or separability, which is where the debate is centered. ______________

As a matter orientation with regard to perspective, here are three (takes on) takes on "separability" I have come across:

State Separability: The "state" 'assigned' to a "compound physical system" at any time is supervenient on the "states" then 'assigned' to its "component subsystems".

... that which we conceive as 'existing' ('real') should somehow be localized in time and space. That is, the 'real' in one part of space, A, should (in theory) somehow 'exist' independently of that which is thought of as 'real' in another part of space, B. If a physical system stretches over the parts of space A and B, then what is 'present' in B should somehow have an 'existence' independent of what is 'present' in A.

SEPARABILITY: mutually independent 'existence' of spatially distant 'things'.
______________

In connection with the scenario of Alice and Bob, I am trying to imagine a 'reality' in which the "microsystem" 'exists' in a 'manner' which is not "existentially separable", whereas, on the other hand, the "macro-instruments" (of Alice and Bob) do 'exist' in a 'manner' which is "existentially separable".
______

So, for example – as applied to the "macro-instruments" (of Alice and Bob) – by "existentially separable" I mean (something like):

The 'real' "state of Alice's instrument" and the 'real' "state of Bob's instrument" 'exist' independently of one another.

That is ... in any theory in which a notion of "state" is 'assigned' to the "instruments" of Alice and Bob, the following two conditions will hold:

1) The "state of Alice's instrument" and the "state of Bob's instrument" can be 'specified' independently of one another;

and

2) A 'specification' of the "joint state of Alice's instrument and Bob's instrument" is equivalent to a joint 'specification' of the "state of Alice's instrument" and the "state of Bob's instrument".
______

So, to repeat:

I am trying to imagine a 'reality' in which:

the "microsystem" (i.e. "singlet state") 'exists' in a 'manner' which is not "existentially separable",

whereas, on the other hand,

the "macro-instruments" (of Alice and Bob) do 'exist' in a 'manner' which is "existentially separable" [... except(,) perhaps(?) possibly(??) where/when their mutual "instruments" happen to be 'linked' via a common, "existentially nonseparable" 'onething' (such as, a "singlet state")].

... I seem to be getting stuck at this spot.

Eye_in_the_Sky

May26-10, 03:24 AM

This was the EPR argument. Local causality + HUP -> (QM is incomplete) or (Reality is observer dependent - in this case Alice).
Yes. The only essential difference between the argument I have given and that of original EPR lies in the "completeness" condition.

I agree. Even if the argument I have posed can go through, its 'lesson' can be no different from that of original EPR.

So ... I see then ... as far as original EPR is concerned, you have no objection to the type of CF used. Okay. That helps clarify for me your position on CF. Good.

So, we are left with the question of which notion(s) ought to be relinquished:
... one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

You suggest:
... Bob's reality is dependent on a choice made by Alice if QM is complete. I would say this is a generally accepted conclusion: that either locality does not hold, or reality is dependent on observeration.
Okay. Let us write this as:

(QM is complete) Λ (local causality) → Bob's 'reality' depends on Alice's choice ,

where the 'reality'-dependence is "non-causal".
_________

For clarity, let us consider an example.

Suppose Alice measures Sx and gets the result "+". Then Bob's 'reality' is such that

if Bob measures Sx then he cannot obtain the result "+".

On the other hand, if Alice had measured Sy (instead of Sx), then Bob's 'reality' would have been such that

if Bob measures Sx then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

Only now is it beginning to become clearer to me (although, not yet quite 'altogether') what is going on here.

First, let me explain the two motivations I had for my having posed the argument in the manner I did:

motivation 1: Somehow, vaguely, I felt that by stripping the microsystem of all 'reality', then (as a consequence) the "nonseparability" issue would – simply – disappear; [... Now, however, I see it seems that the issue has not just disappeared, but rather, it has been transferred over to the macroscopic experimental arrangement;]

and

motivation 2: Since Bell's "local causality" criterion is about 'probability' 'assignments' made on the basis of "complete" 'information', I suspected that by couching the quantum state in terms of 'information', then somehow, a previously hidden insight would emerge. [... And indeed (... I think)... I see it now.]

Bell's "local causality" criterion goes like this ["types" of emphasis added] (diagram (http://www.physicsforums.com/attachment.php?attachmentid=23884&stc=1&d=1266916592)):

A ["complete" stochastic] theory will be said to be "locally causal" if:

The 'probabilities' 'attached' to 'values' of "local beables" in a spacetime region 1 are unaltered by 'specification' of 'values' of "local beables" in a spacelike separated region 2, when what happens in the backward light cone of 1 is already sufficiently 'specified', for example by a full 'specification' of ['values' of] "local beables" in a spacetime region 3.

Now here comes the 'catch':

... what sort of 'existence' do these "local" 'beables' have?

These "local beables" belong to a 'realm' regarding which the principle of "separability" applies.
________

For example, the following four quantities are all construed (by Bell) as being "local beables":

a ≡ Alice's setting ,
b ≡ Bob's setting ,
A ≡ Alice's outcome ,
B ≡ Bob's outcome .
________

So ... "separability" as applied to (these) "local beables" (in this context of Alice and Bob) would (seem to) mean (among other things (something like this)):

The 'real' "state of Alice's instrument" and the 'real' "state of Bob's instrument" 'exist' independently of one another.

This then is (supposed) to imply that in any theory in which a notion of "state" is 'assigned' to the "instruments" of Alice and Bob, the following two conditions will hold:

1) The "state of Alice's instrument" and the "state of Bob's instrument" can be 'specified' independently of one another;

and

2) A 'specification' of the "joint state of Alice's instrument and Bob's instrument" is equivalent to a joint 'specification' of the "state of Alice's instrument" and the "state of Bob's instrument".
_____________________
I believe it is correct to see the conjunction of assumptions in Bell: locality + realism.
In connection with "stage 2" of Bell's argument, I agree with you. But in connection with "stage 1" I do not see it.

Okay, now I see it. That is, what I am now seeing regarding "stage 1" (in terms of a conjunction of assumptions) in Bell is very much along the lines of what you had put as:

locality + realism .

(After quite some thought ... I think) I would (like to) put it like this:

Bell's "local causality" criterion ↔

"causally local" 'reality' Λ "existentially separable" 'macro-apparatus-world' .

... Does this make sense to you?

DrChinese

May26-10, 07:11 AM

Y

For clarity, let us consider an example.

Suppose Alice measures Sx and gets the result "+". Then Bob's 'reality' is such that

if Bob measures Sx then he cannot obtain the result "+".

On the other hand, if Alice had measured Sy (instead of Sx), then Bob's 'reality' would have been such that

if Bob measures Sx then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

Yes, that pretty well sums it up. By the EPR reasoning, Bob's reality is determined by a choice of measurement by Alice. This is required by the HUP.

RUTA

May26-10, 09:29 AM

I think it is true to say that Quantum Mechanics implies 'nonlocality'.

This 'nonlocality' is either in a sense of 'causation' or in a sense of 'existence' or (say maybe) 'identity'.

Or both.

RUTA

May26-10, 09:40 AM

motivation 1: Somehow, vaguely, I felt that by stripping the microsystem of all 'reality', then (as a consequence) the "nonseparability" issue would – simply – disappear; [... Now, however, I see it seems that the issue has not just disappeared, but rather, it has been transferred over to the macroscopic experimental arrangement;]

Correct. This is the basis for the Relational Blockworld interpretation, i.e., no microsystem plus nonseparable experimental equipment.

DevilsAvocado

May27-10, 06:53 PM

Suppose Alice measures Sx and gets the result "+". Then Bob's 'reality' is such that

if Bob measures Sx then he cannot obtain the result "+".

And if we add Relativity of Simultaneity (http://en.wikipedia.org/wiki/Relativity_of_simultaneity) to that – I say Bob can do whatever he likes = free-choice.

jambaugh

May28-10, 10:34 AM

For clarity, let us consider an example.

Suppose Alice measures Sx and gets the result "+". Then Bob's 'reality' is such that

if Bob measures Sx then he cannot obtain the result "+".

On the other hand, if Alice had measured Sy (instead of Sx), then Bob's 'reality' would have been such that

if Bob measures Sx then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

There is a critical distinction I would make here. When you speak of what might happen from Bob's end you are not describing an Objective Reality (what is) but rather as you've presented it the actuality of what may happen.

If you further interpret the "Why" of this actualization then you may invoke an objective reality, i.e. the state of Bob's system is in the subset of states which exclude those where property S_x has value "+". In so doing you will run into the Bell type inequalities which are violated by QM because the presumption that the system and its environment is in a set of states implies the probabilities of outcomes defines a probability measure over that set.

It is this transition from "what happens" actuality to a "what is" reality that we non-realists object to. But note that you can avoid this, still speak of what happens in an objective way (which is why in CI you need the measuring devices to be classical level, you need objective reality of your measurement record) and avoid the need to invoke non-local causation.

That's I believe the heart of classic Copenhagen interpretation.

You needn't invoke CI if you prefer another interpretation (though I think you'd be incorrect) but you should be careful to distinguish when you are describing a reality=objective state of existence vs. actuality=behavior.

It is hard to recognize this distinction at first since we grow up thinking classically where all that happens can be equivalently described in terms of what is.

Count Iblis

May28-10, 10:55 AM

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

jambaugh

May28-10, 11:08 AM

And if we add Relativity of Simultaneity (http://en.wikipedia.org/wiki/Relativity_of_simultaneity) to that – I say Bob can do whatever he likes = free-choice.

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time. Space/time was a Fiber Bundle (http://en.wikipedia.org/wiki/Fiber_bundle) with time as the base and each slice of space (and the state of all within it) is a fiber indexed by this time base. Very much the continuum analogue of a movie with each frame a reality snapshot.

Relativity of simultaneity already begins to sand away at our old concept of objective reality. To preserve it in classical SR we invoke the frozen history of all past and future in a composite space-time. This of course doesn't allow choice or change except by selecting a whole new space-time universe.

In order to still speak of possibilities and probabilities and choices in a deterministic setting we invoke typically a classical field theory, again a fiber-bundle (space-time base with fibers the possible configurations of local reality and typically also some gauge degrees of freedom).

Now any time we see fiber-bundles we can be sure there is a relativity principle which may unify base with fiber and with is a group deformation of actions where the one-way dependence of fiber action on base coordinate becomes a two-way interaction. In this case matter affects the space-time just as space-time affects the matter and we get GR.

Well I'm getting off track... the point is that we already have good reason to soften up our traditional "objective reality" mindset and begin thinking in terms closer to the epistemological basis of science, the actuality of what we observe instead of the imagined state of reality with which we modeled it in past.

jambaugh

May28-10, 11:25 AM

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

This is exactly the process of transitioning to the classical scale. We look at the necessary conditions for a system of events to behave classically, e.g. commutativity of observables on the scale to which we make distinctions. When the pointer on a particle counter is set to large units so that the momentum of that pointer can be similarly refined, we don't care about the hbar's worth or error. The device has amplified the microscopic observable (of say a particle's spin) to one which is classical in scale (say the loud clicks of one of two particle detectors). (and this amplification is an irreversible thermodynamic process b.t.w.)

The critical question is "does a classical reality-model work adequately for the system?" if so then we have no problem treating the system classically. But we can also embed this classical system inside a large quantum one (the classical variables are a commuting subset of the larger class of quantum observables.) This is what we must do in order to see that classical measuring devices in a quantum universe is perfectly consistent and not dualistic.

Think of it in terms of the actuality of people living in the US and the construct of "Government" and "Law" which has a more objective behavior (ideally) than the actual people but which none-the-less is a function of and embedded within the world of people doing what people do. Note we also see in this analogy that when pushed to cases the idealized law breaks down (corruption,miscarriages of justice, civil disobedience, et al) because at the fundamental level the people are not just clockwork objects and thus their implementation of law is not perfect according to how the law itself defines "what ought to be". And yet to function as a society we must work with an objective system of government and laws, recognizing them as not the fundamental nature of us but a useful and necessary construct.

EDIT: So too I say is "reality" a useful and necessary construct but not fundamental.

RUTA

May29-10, 10:30 AM

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time. Space/time was a Fiber Bundle (http://en.wikipedia.org/wiki/Fiber_bundle) with time as the base and each slice of space (and the state of all within it) is a fiber indexed by this time base. Very much the continuum analogue of a movie with each frame a reality snapshot.

Relativity of simultaneity already begins to sand away at our old concept of objective reality. To preserve it in classical SR we invoke the frozen history of all past and future in a composite space-time. This of course doesn't allow choice or change except by selecting a whole new space-time universe.

In order to still speak of possibilities and probabilities and choices in a deterministic setting we invoke typically a classical field theory, again a fiber-bundle (space-time base with fibers the possible configurations of local reality and typically also some gauge degrees of freedom).

Now any time we see fiber-bundles we can be sure there is a relativity principle which may unify base with fiber and with is a group deformation of actions where the one-way dependence of fiber action on base coordinate becomes a two-way interaction. In this case matter affects the space-time just as space-time affects the matter and we get GR.

Well I'm getting off track... the point is that we already have good reason to soften up our traditional "objective reality" mindset and begin thinking in terms closer to the epistemological basis of science, the actuality of what we observe instead of the imagined state of reality with which we modeled it in past.

I don't see how you can distinguish base from fibers in the case of GR as you can with Newtonian space/time, since the local configurations are given by the stress-energy tensor (SET), the components of which require the notions of space and time (can define SET via variation of matter-energy Lagrangian with respect to the spacetime metric). The so-called "interaction" between base and fiber here is not a relation between distinguishable concepts. Therefore, I would say GR is rather a self-consistency criterion for the co-construction of the two.

GeorgCantor

May29-10, 02:17 PM

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

Yes that seems to be true, at least in the perspective of quantum entities in time and space. There can be no 1 electron, if there was a universe with exactly one electron, then that electron has NO objective reality, i.e. it doesn't exist. It doesn't matter if you believe in decoherence, measurement-causes-collapse, MWI, BM or some other stuff. All these interpretations require a CONTEXT, i.e. they require relationships with other quantum entities. No interpretation that i know of can restore the objective reality of objects in time and space existing in and of themselves, without a context. In this view, local realism is not ruled out but dead as a complete picture of reality.

DevilsAvocado

May29-10, 07:25 PM

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time.

All I wanted to say is that there is no way to tell if Alice or Bob does the measurement first – therefore they both have absolute non-deterministic "QM-probability-freedom" to do any measurement they like.

zonde

May31-10, 08:18 AM

Relativity of simultaneity already begins to sand away at our old concept of objective reality.
It's not so much about concept of objective reality as about concept of rigidity of our measurements.
So we have good reason to soften up our traditional "rigid measurements" mindset. :wink:

Geigerclick

May31-10, 09:20 AM

It's not so much about concept of objective reality as about concept of rigidity of our measurements.
So we have good reason to soften up our traditional "rigid measurements" mindset. :wink:

What do you mean?

zonde

Jun1-10, 03:45 AM

What do you mean?
I mean that relativity of simultaneity applies to both measured object and measurement equipment. So we can't have non-contextual (rigid) measurement.
And I think that the same applies to QM measurements i.e. they are contextual.

Objective reality however means that we can fit it all together when we take into account contextuality of measurements. That is easily demonstrated is SR - all measurements fit together when using Lorentz transformations.

filegraphy

Jun3-10, 03:14 PM

"There may be a measurement problem, but I doubt it is the problem you think it is. It is kind of like the problem of why there is more matter in the universe than anti-matter. Something it would be nice to understand, but not something that is actually in contradiction to theory." Dr. Chinese

In the book Antimatter by Frank Close, there is a process when matter and antimatter form that allows more matter to remain than antimatter.

jambaugh

Jun4-10, 08:00 AM

I don't see how you can distinguish base from fibers in the case of GR as you can with Newtonian space/time, since the local configurations are given by the stress-energy tensor (SET), the components of which require the notions of space and time (can define SET via variation of matter-energy Lagrangian with respect to the spacetime metric). The so-called "interaction" between base and fiber here is not a relation between distinguishable concepts. Therefore, I would say GR is rather a self-consistency criterion for the co-construction of the two.

The point I inferred was that GR is less separated into fiber/base than field theory in SR. But still the definition of locality makes a distinction. One localizes with regard to the base space-time manifold and not with regard to to the fiber matter fields. (But note asymptotic freedom seems to localize in the momentum domain as well) We also --of course-- have the the fiber bundle structure of the tangent bundle on the manifold, but we may view this as our linearization of the description. Kaluza-Klein type theories show how the field/space-time may be unified into a space-time-gauge manifold. We then better see the tangent bundle structure as one of convention and not essence.

I presume then that brane theories attempt to quantize from this point. I'm inclined to think the objectification of space-time is a "wrong tract" and that a more Eulerian than Lagrangian description is "the way to go". But I haven't much in the way of example theories to suggest in that direction.

We can also view the classical probability description as a fiber-bundle with base, the state manifold and fibers of probability density. This is the heart of the Bell inequality derivation which is equivalent to the assumption that probabilities form a measure over a manifold of objective states of reality. No locality issues need apply. (And "rigidity" or its lack in measurement is not the issue.)

jambaugh

Jun4-10, 09:38 AM

I mean that relativity of simultaneity applies to both measured object and measurement equipment. So we can't have non-contextual (rigid) measurement.
And I think that the same applies to QM measurements i.e. they are contextual.
This is true I believe but the QM case goes beyond that. With the classical SR case you get mappings from each observer's measurements, which we then see as perspectives on an objective whole. i.e. the length of an object is, in the whole, seen as one observer's cross-section of the object's world-volume (the locus of all space-time events associated directly to that object.) One still has an objective reality-history.

The contextual nature of quantum systems is in the objective reality (or reality-history) itself. We may have the objective reality of any one set of commuting measurements. But one does not map given measurements to given measurements in the unitary transformations (in the sense of outcomes=values of observables). One rather maps certainty of measurements to probabilities of measurements, or in the more general case, map amplitudes to amplitudes some of which may take on the value of certainty. One has thereby abstracted from the objective (though relative) description of the system itself to the statistical description of our knowledge about how the system might behave.

Yes the math parallels but the "thing" upon which the relativity group acts is no longer the system state. It is the "state vector" or "mode of preparation" vector identifying a class of actual systems. One cannot narrow this class to the point of all systems acting identically under any possible measurement and thus one cannot speak of a instantiation of the class as being in an objective state of reality in that this state determines the outcome of all measurements exactly. Contextuality is an important feature of understanding the quantum description but there is more than that going on here.

RUTA

Jun5-10, 10:42 AM

We can also view the classical probability description as a fiber-bundle with base, the state manifold and fibers of probability density. This is the heart of the Bell inequality derivation which is equivalent to the assumption that probabilities form a measure over a manifold of objective states of reality. No locality issues need apply. (And "rigidity" or its lack in measurement is not the issue.)

The forms of locality involved with violations of Bell's inequality are associated with the spacetime manifold -- causal and constitutive. The manifold of objective states of reality necessarily contain violations of one or both when the states are those of QM, but to "see" that locality is in jeopardy, one needs to go to spacetime. That's why so many physicists don't "get it," i.e., they work in Hilbert space where it all makes sense. I teach QM using both Heisenberg and Schrodinger formalisms, QM makes perfect sense. You have to move beyond playing with the formalism to appreciate the ontological implications (those highlighted in the popular literature). However, if you're only concerned with formal consequences, you have them -- if QM is right, GR can't be right because GR is both causally and constitutively local. Where do you fall on that issue?

zonde

Jun8-10, 07:56 AM

Yes the math parallels but the "thing" upon which the relativity group acts is no longer the system state. It is the "state vector" or "mode of preparation" vector identifying a class of actual systems. One cannot narrow this class to the point of all systems acting identically under any possible measurement and thus one cannot speak of a instantiation of the class as being in an objective state of reality in that this state determines the outcome of all measurements exactly. Contextuality is an important feature of understanding the quantum description but there is more than that going on here.
Why would you require that all representations act identically under any possible measurement. Maybe you mean in exact manner?

Well in relativity contextuality means that it is quite useless to talk about preferred reference frame.
In QM contextuality makes it quite hard to talk about preferred measurement base.
But here is equivalence between representations of ensemble in different measurement bases. That's the idea of "state vector", isn't it?

But otherwise absence of preferred measurement base is of course only a small part of QM.

jambaugh

Jun8-10, 01:54 PM

Why would you require that all representations act identically under any possible measurement. Maybe you mean in exact manner?

If many representations are representing the same physical entity then the many representations must transform isomorphically under the relativity group. But that is not what I'm talking about...rather the reverse. Two distinct categories of entities may transform isomorphically but this isomorphism does not imply they are the same type of entity.

In the case to which I refer, there is the objective reality of a classical object, the traditional observables of which are as you say "contextual" and as I would say relative. To each classical objective measurable quantity acting as coordinate the object's reality there is the act of measurement, the classes of experimental procedures which yield identical information about the state of that classical entity. These classes (of observations) necessarily transform isomorphically (or dually depending on the representation) to the objective reality they measure. They are none the less a distinct category of entities in the physics from the category of physical objective states.

Now hop into QM and you have the same (and typically a larger relativity group of) transformations acting on the classes of measurement actions/devices. You however lose the whole of the dual objective reality that in the classical case they were presumed to measure for a single physical entity. Instead you have each observation individually corresponding to an instance of actuality but only commuting subsets able to correspond to a single physical instance of the quantum entity.

Indeed in QM the term "system" refers more to the system of empirical actions on the physical entity, rather than to the entity directly. Contextuality is a prerequisite to this quantum non-objective actuality but (especially since contextuality can be invoked classically), by no means is it the sole defining characteristic.

Well in relativity contextuality means that it is quite useless to talk about preferred reference frame.
In QM contextuality makes it quite hard to talk about preferred measurement base.
But here is equivalence between representations of ensemble in different measurement bases. That's the idea of "state vector", isn't it?

(A side note, and repetition of one of my usual speeches)

The essence of a state vector is a maximal measurement of the physical system. Since this measurement is not classically total, it should no longer be referred to as a "state vector" but more properly (as you'll find in some literature) as a mode vector as in describing the mode of measurement or equivalently mode of preparation of the actual physical entity.

With that in mind, when we speak of the relativity group it again has passive and active context, i.e. we can rotate the physical entity or reverse rotate our measuring devices and achieve the same change of outcomes but in both cases we work within the same representation framework (of "state" vector i.e. measured values i.e. measurement processes) because we cease to have the "metaphysical" duality of measurement process+ objective state.

This is proper, and indeed imperative in the discipline of science since science is an epistemological discipline. Within the doctrine of modern science the observation is most fundamental component of a theory and not the objective state.

But otherwise absence of preferred measurement base is of course only a small part of QM.
Yes, that was principally my point.

Another note, in this non-object understanding of QM one can still be reductive in the sense of say reducing the behavior of the moon to the behaviors of its component elementary particles, however the contextuality gets "squared" in the treatment of composite systems. Not only do we have the sum of relativity transformations for the components, we have the product which implies there is not only a contextual aspect to how you measure the components to derive a quantity corresponding to the composite but also that there is a contextual aspect to how you actually subdivide the composite into components.

For a concrete example consider a ground state helium-4 atom. In subdividing into nucleus and 2 electrons we may speak of the spin z +1/2 electron and spin z -1/2 electron, or alternatively into spin x +1/2 and spin x -1/2 (since we know the electron pair is in a singlet state mode ).

In the two cases we are subdividing the electron pair into two electrons in very distinct ways. This is something we must be conscious of when we parse e.g. EPR type experiments especially with our common language which has evolved to describe classical rather than quantum entities. This is where the conterfactuality landmine can trip us up.

jambaugh

Jun8-10, 03:10 PM

The forms of locality involved with violations of Bell's inequality are associated with the spacetime manifold -- causal and constitutive.
To this I disagree strongly. Bell (and Einstein, Podolsky, & Rosen) invokes space-time locality only in so far as it enables him (them) to exemplify the more basic concept of independent acts of measurement. One can also derive, and then observe the violation of Bell's inequality by considering say two independent observables of a single localized particle. Assuming probabilities derive from a measure on a state manifold for the outcomes and assuming causal independence in the process of the two classes of measurements one may derive Bell's inequality. By entangling and then measuring one can demonstrate (or predict via QM) violation of the inequality.

For example one could take a spin-3/2 system (4 dimensional Hilbert space) and consider the cross commuting pair of observables constructable via complex superpositions from z-spin > 0 vs z-spin < 0, and separately |z-spin component| = 3/2 vs |z-spin component| = 1/2. The observables sets (block) commute which means they are causally isolated.

Of course as a practical matter it is terribly terribly difficult to isolate the two measurement processes. But for cross commuting sets one can in principle construct the devices to carry out actual experiments. Distance is the easiest means but not the only means.

The manifold of objective states of reality necessarily contain violations of one or both when the states are those of QM, but to "see" that locality is in jeopardy, one needs to go to spacetime.
It is a question of what assumptions one wants to make. ( I don't see locality as ever having been in jeopardy). Just as we empirically verify spatial locality to assure ourselves it is a valid assumption we can similarly verify that say gross position and spin measurements are similarly independent (commuting). And in both cases we may hypothesize that our assumption is wrong when we see Bell inequality violation and that there is some mechanism of interaction beyond the theoretical prediction that they are causally independent.

But QM predicts any pair of commuting observables may be none-the-less entangled and thus that you can both derive a Bell inequality from "reality assumptions" and that said inequality gets violated. It isn't about the locality! It's about the reality!

However, if you're only concerned with formal consequences, you have them -- if QM is right, GR can't be right because GR is both causally and constitutively local. Where do you fall on that issue?

I don't agree with that statement. GR and QM are perfectly compatible beyond GR being as yet still a classical theory. With regard to causal vs constitutive locality I fully believe in causal locality but am not sure how you mean constitutive locality. Especially I'm not sure "constitutive anything" is proper in QM if by that you are invoking an objective reality of the physical system or its constituents.

I think in the end, as long as by "constitutively local" one is referring to the ability to expand measurement processes into constituent local measurements (invoking superposition) and thus so that this becomes a further qualification on the causal locality of the measurements then your fine.

Said better one may postulate "a complete set of causally local observables."

If you mean otherwise then you may be reifing the wave-function further than I think is proper.

zonde

Jun9-10, 06:49 AM

Indeed in QM the term "system" refers more to the system of empirical actions on the physical entity, rather than to the entity directly.
That is no different in relativity. In relativity physical entity is not described directly with length and time but rather with measurements of length (rulers) and measurements of time (clocks) and of course along with synchronization procedure for clocks instead of universal simultaneity.

But I agree that there is significant diference between limits of objective reality under relativity and QM.
Let's formulate it this way and see if you will agree that this is the key difference.
Relativity allow reductionism and that is one of the key parts of objective reality. You can split description of reality however you like and all parts will still obey the same isomorphism of different measurements.

Actually you say yourself something like that here:
Another note, in this non-object understanding of QM one can still be reductive in the sense of say reducing the behavior of the moon to the behaviors of its component elementary particles, however the contextuality gets "squared" in the treatment of composite systems. Not only do we have the sum of relativity transformations for the components, we have the product which implies there is not only a contextual aspect to how you measure the components to derive a quantity corresponding to the composite but also that there is a contextual aspect to how you actually subdivide the composite into components.

With that in mind, when we speak of the relativity group it again has passive and active context, i.e. we can rotate the physical entity or reverse rotate our measuring devices and achieve the same change of outcomes but in both cases we work within the same representation framework (of "state" vector i.e. measured values i.e. measurement processes) because we cease to have the "metaphysical" duality of measurement process+ objective state.
Actually I didn't mean that when I said that there is no preferred measurement base.
What I mean is that when we talk about non-commuting measurements ensemble is represented using two orthogonal vectors and you do not necessarily have preferred basis for representation of those two vectors. Actually you have preferred basis in case when in that basis one of the vectors becomes zero.
But then if we want to relate this back to relativity then you have preferred representation there in special case when you have reference frame where every object under consideration is at rest. In that reference frame all effects of relativity will disappear.

And there is another thing where have different viewpoints that prevents me from accepting your arguments about probabilistic measurements.
You talk about uncertainty of measurement and with that you imply that single entity of ensemble is fair representative of whole ensemble and you acquire some certainty of measurement only as statistical build-up of individual independent probabilistic measurements.
I say that there is more than statistics in QM and ensemble is not statistical ensemble (at least not always) but physical ensemble i.e. measurement of ensemble can acquire such certainties that are not possible for simple statistical ensemble. So I talk about certainty of measurement of ensemble (rate of clicks versus individual click).
That's a bit similar as we talk about length measurement of a stick instead of count of atoms along the length of a stick.

RUTA

Jun9-10, 10:07 AM

Jambaugh, clearly you’re not familiar with the terminology of the foundations community. Let me provide the background via excerpts from “Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090 and arXiv 0908.4348 (accepted for presentation at PSA 2010, revised version under re-review at FoP).

Fm second paper:

In Healey’s language, strong nonseparability might be dubbed a kind of non-locality, not “causal non-locality” but rather “constitutive non-locality” (Healey, R.: Gauging What’s Real: The Conceptual Foundations of Gauge Theories. Oxford University Press, Oxford (2007), p 127). As he says, strong nonseparability strongly suggests physical property holism, i.e., “There is some set of physical objects from a domain D subject only to type P processes, not all of whose qualitative intrinsic physical properties and relations supervene on qualitative intrinsic physical properties and relations in the supervenience basis of their basic physical parts (relative to D and P) (Healey, 2007, p 125).”

From first paper:

In particular, the implied metric isn’t an “extreme embodiment of the separability principle” (D. Howard, in Potentiality, Entanglement and Passion-at-a-Distance, edited by R.S. Cohen et al. (Kluwer Academic, Great Britain, 1997), p 122).

As Howard notes in the following passage, one of the central debates between the founding fathers of quantum mechanics was over the conflict between the spacetime picture and the quantum picture of reality and how they may be reconciled (Howard, 1997, pp 114-115):

"The second striking feature of Pauli’s last-quoted paragraph is that it points backward to what was by 1935 an old debate over the nonseparable manner in which quantum mechanics describes interacting systems. The fact that this was the central issue in the pre-1935 debate over the adequacy of the quantum theory disappeared from the collective memory of the physics community after EPR….Einstein had been trying in every which way to convince his colleagues that this was sufficient reason to abandon the quantum path…But it was not just Einstein who worried about quantum nonseparability in the years before 1935. It was at the forefront of the thinking of Bohr and Schrödinger."

In today’s terminology we would say that the spacetime picture of relativity adheres to the following principles (Howard, 1997, pp 124-125):

Separability principle: any two systems A and B, regardless of the history of their interactions, separated by a non-null spatiotemporal interval have their own independent real states such that the joint state is completely determined by the independent states.

Locality principle: any two space-like separated systems A and B are such that the separate real state of A let us say, cannot be influenced by events in the neighborhood of B.

It is now generally believed that Einstein-Podolsky-Rosen (EPR) correlations, i.e., correlated space-like separated experimental outcomes which violate Bell’s inequality, force us to abandon either the separability or locality principle.

As Howard notes, Einstein thought that both these principles, but especially the latter, were transcendental grounds for the very possibility of science. Einstein’s spatiotemporal realism is summarized in his own words (A. Einstein, Deutsche Literaturzeitung 45, 1685-1692 (1924)):

"Is there not an experiential reality that one encounters directly and that is also, indirectly, the source of that which science designates as real? Moreover, are the realists and, with them, all natural scientists not right if they allow themselves to be led by the startling possibility of ordering all experience in a (spatio-temporal-causal) conceptual system to postulate something real that exists independently of their own thought and being?"

Minkowski spacetime (M4) is a perfect realization of Einstein’s vision but as Howard says (D. Howard, “Einstein and the Development of Twentieth-Century Philosophy of Science” to appear in Cambridge Companion to Einstein, from his website):

"Schrödinger’s introduction of entangled n-particle wave functions written not in 3-space but in 3n-dimensional configuration space offends against space-time description because it denies the mutual independence of spatially separated systems that is a fundamental feature of a space-time description."

In this sense, we agree with Howard (Howard, 1997, pp 124-129) that NRQM is best understood as violating “separability” (i.e., independence) rather than “locality” (i.e., no action at a distance, no super-luminal signaling), and we take to heart Pauli’s admonition that “in providing a systematic foundation for quantum mechanics, one should start more from the composition and separation of systems than has until now (with Dirac, e.g.) been the case” (W. Pauli, Scientific Correspondence with Bohr, Einstein, Heisenberg a.o., Vol 2, 1930-1939, edited by Karl von Meyenn (Springer-Verlag, Berlin, 1985), pp 402-404).
************************************************** *

Given your postings to date, Jambaugh, I’m guessing you’ll fall into our camp, i.e., causal locality is maintained, QM is “right” and GR is “wrong” in that the separability of GR is only an approximation. So, what say you?

jambaugh

Jun10-10, 12:46 AM

Jambaugh, clearly you’re not familiar with the terminology of the foundations community. Let me provide [...]

In Healey’s language, strong nonseparability might be dubbed a kind of non-locality, not “causal non-locality” but rather “constitutive non-locality”

Thanks for the translation. Yes I'm not familiar with "constitutive (non)locality" as a phrase. To my mind "nonseparability" is more encompassing since it reflects not just spatial issues. inseparability is clear enough in the subadditivity of entropy for quantum systems.

Separability principle: any two systems A and B, regardless of the history of their interactions, separated by a non-null spatiotemporal interval have their own independent real states such that the joint state is completely determined by the independent states.
But I am of the camp that feels even a single system A has no "independent real state" as such so this definition of separability fails from the start. (I think the issue being considered in defining separability vs nonseparability is one of trying to reconcile QM with a ontology... a futile quest IMNSHO).

"Locality principle: any two space-like separated systems A and B are such that the separate real state of A let us say, cannot be influenced by events in the neighborhood of B."
Here again I see a bias toward "statism";-) if you pardon the misuse of the term. Rather try:

Observational locality principle: An action carried out in region A spatially separated from region B can have no effect on measurements made in region B.

Probably I could word that better given time but you see the point. Avoid reference to operationally meaningless unobserved states of reality and stick to the operationally meaningful actions such as measurements.

Given your postings to date, Jambaugh, I’m guessing you’ll fall into our camp, i.e., causal locality is maintained, QM is “right” and GR is “wrong” in that the separability of GR is only an approximation. So, what say you?

Fairly accurate except I see nothing wrong with GR at its foundation, only in the categorization of the geometric model of GR as an ontological theory as opposed to being a model. The elimination of the gravitational force qua dynamic force is to my mind a "gauge condition" and the full power of the equivalence principle has yet to be invoked in attempts to quantize GR.

I bring this up because I think the separability of GR is a function of its typical geometric formulation (model) and not the theory itself when "properly" (i.e. operationally) interpreted.

RUTA

Jun10-10, 03:40 PM

But I am of the camp that feels even a single system A has no "independent real state" as such so this definition of separability fails from the start. (I think the issue being considered in defining separability vs nonseparability is one of trying to reconcile QM with a ontology... a futile quest IMNSHO).

You have to have some ontology to do physics; the formalism is meaningless in and of itself. I teach QM using actual experiments, so all the formalism translates immediately to actual experimental configurations and measurement devices. Anyway, no ontology, no physics.

Probably I could word that better given time but you see the point. Avoid reference to operationally meaningless unobserved states of reality and stick to the operationally meaningful actions such as measurements.

And when I teach QM according to experiments, like I said before, QM is perfectly clear. It's not until you ask, "How can that be?" that you run into confusion.

Fairly accurate except I see nothing wrong with GR at its foundation, only in the categorization of the geometric model of GR as an ontological theory as opposed to being a model. The elimination of the gravitational force qua dynamic force is to my mind a "gauge condition" and the full power of the equivalence principle has yet to be invoked in attempts to quantize GR.

I bring this up because I think the separability of GR is a function of its typical geometric formulation (model) and not the theory itself when "properly" (i.e. operationally) interpreted.

And this is where we in the foundations community see a benefit to asking, "How can that be?" By understanding that QM is nonlocal and/or nonseparable while GR is local and separable, you see immediately that one or both have to be corrected in one or both respects. Our formalism has GR as a statistical limit to quantum physics when the approximation of separability holds. We developed our approach to QG via our interpretation of QM. So, while foundational issues may be irrelevant to you, they were sine qua non for us.

jambaugh

Jun11-10, 01:16 PM

You have to have some ontology to do physics; the formalism is meaningless in and of itself. I teach QM using actual experiments, so all the formalism translates immediately to actual experimental configurations and measurement devices. Anyway, no ontology, no physics.

Not to my mind. The formalism can be meaningfully interpreted without invoking ontology of the system; e.g. "an electron" is the phenomenon of an electron detector going "click". Of course one must invoke an ontological description of the measuring devices and the records of measurements.

And when I teach QM according to experiments, like I said before, QM is perfectly clear. It's not until you ask, "How can that be?" that you run into confusion.

Right, and in teaching QM according to experiments you should be demonstrating that the formalism is operationally applied to the configuration of experimental devices. I assert that the confusion arises when one tries to push beyond that operational interpretation.

And this is where we in the foundations community see a benefit to asking, "How can that be?" By understanding that QM is nonlocal and/or nonseparable while GR is local and separable, you see immediately that one or both have to be corrected in one or both respects. Our formalism has GR as a statistical limit to quantum physics when the approximation of separability holds. We developed our approach to QG via our interpretation of QM. So, while foundational issues may be irrelevant to you, they were sine qua non for us.
I rather see QM as non-separable, causally local, while CM is separable, causally local. Classical GR is separable, causally local and a QGR should be non-separable, causally local.

RUTA

Jun11-10, 01:57 PM

Not to my mind. The formalism can be meaningfully interpreted without invoking ontology of the system; e.g. "an electron" is the phenomenon of an electron detector going "click". Of course one must invoke an ontological description of the measuring devices and the records of measurements.

Exactly my point. In fact, in RBW the ontology is "there is no system" (other than the experimental equipment).

Right, and in teaching QM according to experiments you should be demonstrating that the formalism is operationally applied to the configuration of experimental devices. I assert that the confusion arises when one tries to push beyond that operational interpretation.

I start my QM course with the Mermin device, interaction-free measurement, delayed choice (Zeilinger and Aharonov have done some cool experiments that I show them), and the quantum liar experiment. Then we use the QM formalism to describe all these experiments. I have them read many articles, but the texts are Shankar and Albert. For example, we work through "Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory," D. Dehlinger & M.W. Mitchell, Am. J. Phys. 58, Sep 2002, 903-910, in detail. We also reproduce all the results in Mermin's three AJP papers. So, the students see how QM works and why most physicists don't see anything "weird" about it. But, they also see that QM violates separability and/or locality, which strikes them as "weird," so they can appreciate all the "fuss" made over this fact.

I rather see QM as non-separable, causally local, while CM is separable, causally local. Classical GR is separable, causally local and a QGR should be non-separable, causally local.

Exactly what we believe. Our approach to QG can be described as non-separable Regge calculus. The manner by which this unifies physics is explained in 0908.4348. What is your approach to QG?

DrChinese

Jun11-10, 02:09 PM

For example, we work through "Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory," D. Dehlinger & M.W. Mitchell, Am. J. Phys. 58, Sep 2002, 903-910, in detail.

RUTA, do you ever run that experiment in your lab?

RUTA

Jun11-10, 02:59 PM

RUTA, do you ever run that experiment in your lab?

I'm a theorist. I was told as an undergrad to avoid the lab -- I destroyed too much equipment :-)

DevilsAvocado

Jun12-10, 10:05 AM

RUTA

Jun12-10, 10:12 AM

RUTA, it would be great if you could explain one thing to me, regarding photon entanglement (superposition polarization):

Are the entangled superposition (of two photons) described by one single wavefunction?

Yes, |psi> ~ |HH> + |VV> is what Dehlinger created (well, close thereto, see eqns 1 and 6). |psi> ~ |HV> - |VH>, called the "singlet state," also gives results consistent with the Mermin device.

DevilsAvocado

Jun12-10, 10:25 AM

Yes, |psi> ~ |HH> + |VV> is what Dehlinger created (well, close thereto, see eqns 1 and 6). |psi> ~ |HV> - |VH>, called the "singlet state," also gives results consistent with the Mermin device.

WOW! Just great! Many thanks RUTA!!

I’m working on a "personal surprise" that’s going to cause "some trouble" in the "EPR-FTL-Department". :wink:

Will post it in Is action at a distance possible as envisaged by the EPR Paradox (http://www.physicsforums.com/showthread.php?t=395509) in a couple of days...

Just a small follow-up: A measurement on any of these two photons will collapse/decohere the wavefunction/"singlet state", right?

EDIT: I think I found the answer in Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory (http://www.optics.rochester.edu/workgroups/lukishova/QuantumOpticsLab/homepage/mitchel1.pdf):
Despite the randomness, the choice of a clearly has an effect on the state of the idler photon: it gives it a definite polarization in the |Va>i ,|Ha>i basis, which it did not have before the measurement.

RUTA

Jun12-10, 10:43 AM

Just a small follow-up: A measurement on any of these two photons will collapse/decohere the wavefunction/"singlet state", right?

It will collapse the wavefunction, but neither party knows whether the other has made a measurement -- they both get what looks to them like totally random results (50-50 V H outcomes, regardless of setting) whether or not the other guy is doing anything at his end. You only see "weirdness" in the correlations, which are exchanged at sub-light or light speed b/w observers.

DevilsAvocado

Jun12-10, 10:53 AM

It will collapse the wavefunction, ...

This is just marvelous! Thanks again!!

This is going to be very interesting and fun, as soon as I have everything ready for posting. Watch out! :smile:

DrChinese

Jun12-10, 11:34 AM

This is just marvelous! Thanks again!!

This is going to be very interesting and fun, as soon as I have everything ready for posting. Watch out! :smile:

Looking forward to it... :smile:

DevilsAvocado

Jun12-10, 11:46 AM

Looking forward to it... :smile:

Me too. (why am I suddenly getting 'nervous'... ?:bugeye:?)

:wink:

RUTA

Jun12-10, 12:02 PM

Me too. (why am I suddenly getting 'nervous'... ?:bugeye:?)

:wink:

Because you're about to learn something via one of DrC's painful lessons. No pain, no gain :-)

DrChinese

Jun12-10, 12:14 PM

Because you're about to learn something via one of DrC's painful lessons. No pain, no gain :-)

Aw, I promise to be gentle.

Actually RUTA, I am quite in the same boat right now. I just completed a draft of a paper which is available for comments - and yours would be welcome. It has nothing to do with this thread, but check it out if anyone wants to skewer me:

DrC's New Paper and opportunity to bash me with your comments (http://www.drchinese.com/David/EntangledFrankensteinPhotonsA.pdf)

Here's your chance! Email me (I'm not ready for a new thread quite yet as I submitted to PF Independent Research for review).

DevilsAvocado

Jun12-10, 02:20 PM

DrC's painful lessons. No pain, no gain :-)
I promise to be gentle.

There seems to be some "entangled discrepancy" here... flip side of the coin...? :biggrin:

I better keep my big mouth shut until there’s something more substantial for the "wolf" to tear apart. :eek:

Demystifier

Jun15-10, 07:44 AM

That's interesting, because my explicit Bohmian model of relativistic nonlocal reality does involve a "meta time".

Now I have a better understanding of the physical meaning of this "meta time". It can be viewed as a generalization of the notion of proper time. It is also formally analogous to the Newton absolute time (even though it is fully relativistic covariant). More details can be found in
http://xxx.lanl.gov/abs/1006.1986

akhmeteli

Jul25-10, 08:28 AM

I have not posted here for quite some time as I did not feel I could add anything new. I am posting now because, on the one hand, the thread has apparently drawn a lot of interest, on the other hand, my paper has just been accepted for publication in the International Journal of Quantum Information (there is a preprint at http://www.akhmeteli.org/akh-prepr-ws-ijqi2.pdf ), so I guess it would be appropriate to summarize its results here, as they are quite relevant to this discussion.

So the article starts with the equations of (non-second-quantized) scalar electrodynamics. They describe a Klein-Gordon particle (a scalar particle described by the Klein-Gordon equation) interacting with electromagnetic field (described by the Maxwell equations). It is shown that this model is equivalent (at least locally) to a local realistic model – modified electrodynamics without particles, as the matter (particle) field can be naturally eliminated from the equations of scalar electrodynamics, and the resulting equations describe independent evolution of the electromagnetic field (electromagnetic 4-potential). Furthermore, this evolution is shown to be equivalent to unitary evolution of a certain (second-quantized) quantum field theory.

This is clearly relevant to the topic of this thread: indeed, it turns out that unitary evolution of a quantum field theory can be reproduced in a local realistic (LR) model, so it is impossible to rule out the LR model without using some additional postulates, such as the projection postulate of the quantum theory of measurement. On the other hand, as I argued repeatedly, this postulate directly contradicts the unitary evolution.

JesseM

Jul25-10, 09:22 AM

This is clearly relevant to the topic of this thread: indeed, it turns out that unitary evolution of a quantum field theory can be reproduced in a local realistic (LR) model, so it is impossible to rule out the LR model without using some additional postulates, such as the projection postulate of the quantum theory of measurement.
Can this quantum field theory be used to describe entangled particles and predict the results of Aspect-type experiments? Are you claiming that the LR model can violate any Bell inequalities?

akhmeteli

Jul25-10, 10:45 AM

Can this quantum field theory be used to describe entangled particles

Yes, this quantum field theory (QFT) can definitely be used to describe entangled particles.

However, this answer, while correct, can be misleading, because another question is relevant here: "Can this local realistic model (LRM) be used to describe entangled particles?" These two questions are not equivalent, as QFT and LRM are not equivalent, they just have the same evolution. One can say that LRM is a subset of QFT.

So what is the answer to the second question? The short answer is "yes". However, it depends on how you would answer the following question: "Can a 3-dimensional body be used to describe its 2-dimensional projections?" If you believe it can, then this LRM can definitely be used to describe entangled particles. If you believe it cannot, then the answer to this question is negative.

Let me explain. The states of the LRM are so called generalized coherent states, which are a superposition of several (infinite number of) states having definite number of particles, including a state with, say, 2 particles, so an entangled state of two particles is a projection of a state of the LRM.

and predict the results of Aspect-type experiments?

I think so. As I argued here, quoting the leading experts in the field, the genuine Bell inequalities have never been violated in Aspect-type experiments so far.

However, a caveat is required here as well. I don't claim that the QFT or the LRM correctly describe the entire Nature, as, for example, being based on the scalar electrodynamics, they do not describe electronic spin. However, the scalar electrodynamics is a decent theory, successfully describing a very wide area of phenomena.

Are you claiming that the LR model can violate any Bell inequalities?

No, I definitely do not claim that (though there is an unfortunate typo in the article, which I will correct in the proofs). This LRM does not violate the Bell inequalities. But I don't think this is a weak point of the model for the reasons I explained in this thread:

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

So I don't think one can demand that the LRM faithfully reproduce the relevant mutually contradicting predictions of quantum theory. On the other hand, this LRM has exactly the same evolution as the QFT.

By the way, this also suggests that one needs more than unitary evolution to prove the violations in quantum theory.

JesseM

Jul25-10, 11:24 AM

I think so. As I argued here, quoting the leading experts in the field, the genuine Bell inequalities have never been violated in Aspect-type experiments so far.
I haven't read the whole thread, are you just talking about experimental loopholes like the ones discussed here (http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments)? There have been experiments that closed the detector efficiency loophole and experiments that closed the locality loophole, but no experiment that closed both loopholes simultaneously--still I think most experts would agree you'd need a very contrived local realist model to get correct predictions (agreeing with those of QM) for the experiments that have already been performed, but which would fail to violate Bell inequalities (in contradiction with QM) in an ideal experiment.
No, I definitely do not claim that (though there is an unfortunate typo in the article, which I will correct in the proofs). This LRM does not violate the Bell inequalities. But I don't think this is a weak point of the model for the reasons I explained in this thread:

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.
What do you mean by "mutally contradicting postulates"? Remember, in its basic form QM is nothing more than a recipe for making predictions about experimental results, it doesn't come with any built-in interpretation of the "meaning" of this recipe...the fact that the recipe involves calculating the evolution of the wavefunction between measurements and then using the projection postulate to get the probabilities of different measurement results doesn't imply that either the wavefunction or the "collapse of the wavefunction" have any independent reality outside the fact that when we use this recipe we do get correct statistical predictions. Indeed, the example of Bohmian mechanics (http://plato.stanford.edu/entries/qm-bohm/) proves that we are free to believe there is some underlying model that explains the origin of the probabilities given in the recipe without the need to assume anything special really happens during the measurement process. And the only assumption about ordinary QM used in Bell's proof that QM is incompatible with local realism is the assumption that the recipe does indeed give correct statistical predictions about experimental results, regardless of the underlying explanation for the predicted statistics.

Quantum field theory is also just a recipe for making predictions, and although I haven't studied QFT I'm pretty sure that known quantum field theories like quantum electrodynamics do mirror nonrelativistic QM in predicting violations of Bell inequalities. Does the simplified quantum field theory you are considering differ from known quantum field theories in this respect?

RUTA

Jul25-10, 01:51 PM

No, I definitely do not claim that (though there is an unfortunate typo in the article, which I will correct in the proofs). This LRM does not violate the Bell inequalities. But I don't think this is a weak point of the model for the reasons I explained in this thread:

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

So I don't think one can demand that the LRM faithfully reproduce the relevant mutually contradicting predictions of quantum theory. On the other hand, this LRM has exactly the same evolution as the QFT.

By the way, this also suggests that one needs more than unitary evolution to prove the violations in quantum theory.

So, are you claiming that QM's prediction of the violation of Bell inequalities is wrong?

akhmeteli

Jul25-10, 02:11 PM

I haven't read the whole thread, are you just talking about experimental loopholes like the ones discussed here (http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments)?

Yes, that's what I am talking about.

There have been experiments that closed the detector efficiency loophole and experiments that closed the locality loophole, but no experiment that closed both loopholes simultaneously

I agree. Some people think that closing separate loopholes in separate experiments is good enough though. In post 34 of this thread I asked one of them:

"what’s wrong [then] with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees."

I have never heard an answer from anybody.

--still I think most experts would agree you'd need a very contrived local realist model to get correct predictions (agreeing with those of QM) for the experiments that have already been performed, but which would fail to violate Bell inequalities (in contradiction with QM) in an ideal experiment.

I agree, "most experts would agree" on that. But what conclusions am I supposed to draw from that? That the model I offer is "very contrived"? I cannot agree with that, as it's essentially old good scalar electrodynamics (non-second-quantized). That the model does not "get correct predictions (agreeing with those of QM) for the experiments that have already been performed"? But it has the same evolution as the relevant QFT. I agree that the QFT is not the same as the standard quantum electrodynamics (QED), but it is pretty close, so I guess the predictions will be close to those of QED in many cases, although, as I admitted, the QFT fails to describe the electronic spin, for example. So while I cannot state that the LRM gives correct predictions for all experiments performed so far, I would say it suggests that a local realistic theory giving correct predictions for the past experiments and failing in an ideal experiment must not necessarily be "very contrived".

What do you mean by "mutally contradicting postulates"? Remember, in its basic form QM is nothing more than a recipe for making predictions about experimental results, it doesn't come with any built-in interpretation of the "meaning" of this recipe...the fact that the recipe involves calculating the evolution of the wavefunction between measurements and then using the projection postulate to get the probabilities of different measurement results doesn't imply that either the wavefunction or the "collapse of the wavefunction" have any independent reality outside the fact that when we use this recipe we do get correct statistical predictions.

I think the postulates are indeed "mutually contradicting", as the projection postulate predicts transformation of a pure wavefunction into a mixture and it predicts irreversibility. Neither is true for unitary evolution. Of course, you can indeed avoid a contradiction, saying (following von Neumann) that unitary evolution is correct between measurements, and the projection postulate is correct during measurements. But I think it is rather difficult to cling to that position now, 80 years after von Neumann. Are you ready to say that if you call something "an instrument", it evolves in one way, and if you don't call it that, it evolves differently? Do you think that unitary evolution is wrong for instruments? Or for observers? I quoted Schlosshauer in post 41 in this thread, he reviewed modern experiments and concluded, among other things (please see the exact wording in post 41), that unitary dynamics has been confirmed everywhere it was tested and that there is no positive evidence of collapse.

Indeed, the example of Bohmian mechanics (http://plato.stanford.edu/entries/qm-bohm/) proves that we are free to believe there is some underlying model that explains the origin of the probabilities given in the recipe without the need to assume anything special really happens during the measurement process.

No, this is not quite so. If I understand Demystifier (http://www.physicsforums.com/showpost.php?p=2167542&postcount=19) correctly (and he has written maybe dozens of articles on Bohmian mechanics), although the projection postulate can be derived in Bohmian mechanics, it can only be derived as an approximation, maybe a very good approximation, but an approximation.

And the only assumption about ordinary QM used in Bell's proof that QM is incompatible with local realism is the assumption that the recipe does indeed give correct statistical predictions about experimental results, regardless of the underlying explanation for the predicted statistics.

The problem is this recipe includes mutually contradictory components, so it cannot be always correct.

Quantum field theory is also just a recipe for making predictions, and although I haven't studied QFT I'm pretty sure that known quantum field theories like quantum electrodynamics do mirror nonrelativistic QM in predicting violations of Bell inequalities.

I think this is correct, but they still have the same mutually contradictory components as the standard quantum theory (SQM), so what I said about SQM is true about quantum field theories, such as QED.

Does the simplified quantum field theory you are considering differ from known quantum field theories in this respect?

I don't think it differs in this respect, if you include the standard measurement theory in it. But I did not say the LRM reproduces both unitary evolution and the measurement theory of this QFT, it just reproduces its unitary evolution. As unitary evolution and measurement theory are mutually contradictory, I don't think the failure to reproduce the measurement theory is a weak point of the LRM.

akhmeteli

Jul25-10, 02:38 PM

So, are you claiming that QM's prediction of the violation of Bell inequalities is wrong?

Not exactly. I suspect that this prediction may be wrong, but I cannot claim that it is wrong. Indeed, I do understand that the violations can be found in a loophole-free experiment, say, tomorrow. Following other people, I am just saying (right now, not tomorrow) that 1) there has been no evidence of violations of the genuine Bell inequalities so far, and that 2) mutually contradictory assumptions are required to derive the QM's prediction of the violation of Bell inequalities. Therefore, local realism has not been ruled out so far.

JesseM

Jul25-10, 03:30 PM

I agree. Some people think that closing separate loopholes in separate experiments is good enough though. In post 34 of this thread I asked one of them:

"what’s wrong [then] with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees."

I have never heard an answer from anybody.
This is kind of a strawman, no one is asking you to adopt a general principle along the lines of "if X is true when condition Y but not condition Z holds, and X is also true when condition Z but not condition Y holds, then we can assume X is true when both conditions Y and Z hold simultaneously". Rather, the reason physicists think we can be pretty confident that Bell inequalities would be violated in an experiment where both loopholes were closed simultaneously has to do with specific considerations about the physical situation we're looking at, like the idea I already mentioned that it would require a very contrived local theory that would exploit both loopholes in just the right way that it would perfectly agree with QM in all experiments done to date.
still I think most experts would agree you'd need a very contrived local realist model to get correct predictions (agreeing with those of QM) for the experiments that have already been performed, but which would fail to violate Bell inequalities (in contradiction with QM) in an ideal experiment.
I agree, "most experts would agree" on that. But what conclusions am I supposed to draw from that? That the model I offer is "very contrived"?
Are you claiming that your model gives correct statistical predictions about the empirical results of all the Aspect-type experiments that have been done to date?
That the model does not "get correct predictions (agreeing with those of QM) for the experiments that have already been performed"? But it has the same evolution as the relevant QFT.
That seems like a slightly evasive answer, since you later say that you distinguish the unitary evolution aspect of QM/QFT from the projection postulate, and only claim that your model reproduces the unitary evolution, but isn't the projection postulate the only way to get actual predictions about empirical experiments from QM/QFT? Do you claim that your model can correctly predict actual empirical experimental results in the types of experiments that have been done to date, yes or no?
I think the postulates are indeed "mutually contradicting", as the projection postulate predicts transformation of a pure wavefunction into a mixture and it predicts irreversibility.
Why is this a "contradiction", if we don't assume that either the wavefunction or its collapse on measurement are in any sense "real", but just treat them as parts of a pragmatic recipe for making quantitative predictions about experimental results? Do you claim there are any situations where the two postulates don't lead to a unique prediction about the statistics we should expect to see in some empirical experiment? If so, what situation would that be?
Neither is true for unitary evolution. Of course, you can indeed avoid a contradiction, saying (following von Neumann) that unitary evolution is correct between measurements, and the projection postulate is correct during measurements.
Yes, this is just what the pragmatic recipe says we should do.
But I think it is rather difficult to cling to that position now, 80 years after von Neumann. Are you ready to say that if you call something "an instrument", it evolves in one way, and if you don't call it that, it evolves differently?
Personally I believe there are some true set of laws that describe what's "really" going on (I'd favor some type of many-worlds type view) and which work exactly the same for interactions between quantum systems and "instruments" as they do for interactions between individual particles. But again, if QM is treated just as a pragmatic recipe for making predictions which says nothing about the underlying "reality" one way or another, then in practice I don't think there is much ambiguity about what constitutes a "measurement", my understanding is that it's basically synonymous with interactions that involve environmental decoherence (http://arxiv.org/abs/quant-ph/9908008). And the types of experiments that physicists do are typically carefully controlled to prevent environmental decoherence from any other system besides the assigned "measuring device" (for example, a double-slit experiment with an electron will be done in a vacuum to prevent decoherence from interactions between the electrons and air molecules).
Do you think that unitary evolution is wrong for instruments? Or for observers?
I don't think it's likely to be wrong in reality since I favor some sort of variant of the many-worlds interpretation, but I do think it's hard to get concrete predictions about empirical results using unitary evolution alone
I quoted Schlosshauer in post 41 in this thread, he reviewed modern experiments and concluded, among other things (please see the exact wording in post 41), that unitary dynamics has been confirmed everywhere it was tested and that there is no positive evidence of collapse.
You didn't actually give a link to the paper, but you seem to be talking about this one (http://arxiv.org/abs/quant-ph/0506199). Anyway, Schlosshauer seems to be just arguing for the many-worlds interpretation (see the discussion beginning with 'The basic idea was introduced in Everett’s proposal of a relative-state view of quantum mechanics' on p. 1) and against any sort of objective collapse theory (http://en.wikipedia.org/wiki/Objective_collapse_theory) (see p. 13 where he talks about 'physical collapse models'--note that such models would actually be empirically distinguishable from ordinary QM in certain situations, like if information could be recorded and then 'erased' in a sufficiently large system completely isolated from environmental decoherence), but this is not the same as arguing that on a pragmatic level there's anything wrong with using the projection postulate to get quantitative predictions about experimental results. And it typically requires a lot of sophisticated argument to show how any many-worlds type interpretation can give concrete predictions in the form of probabilities (see the preferred basis problem (http://plato.stanford.edu/entries/qm-manyworlds/#6.2)), with no complete agreement among many-worlds advocates on how to do this (Schlosshauer discusses the problem on p. 14 of the paper, in the section 'Emergence of probabilities in a relative-state framework'); I think they all agree that the probabilities should be the same as the ones given by the pragmatic recipe involving the projection postulate, though. Indeed, Schlosshauer says at the beginning of that section that "The question of the origin and meaning of probabilities in a relative state–type interpretation that is based solely on a deterministically evolving global quantum state, and the problem of how to consistently derive Born’s rule in such a framework, has been the subject of much discussion and criticism aimed at this type of interpretation." And a bit later he says "The solution to the problem of understanding the meaning of probabilities and of deriving Born’s rule in a relative-state framework must therefore be sought on a much more fundamental level of quantum mechanics."
Indeed, the example of Bohmian mechanics proves that we are free to believe there is some underlying model that explains the origin of the probabilities given in the recipe without the need to assume anything special really happens during the measurement process.
No, this is not quite so. If I understand Demystifier (http://www.physicsforums.com/showpost.php?p=2167542&postcount=19) correctly (and he has written maybe dozens of articles on Bohmian mechanics), although the projection postulate can be derived in Bohmian mechanics, it can only be derived as an approximation, maybe a very good approximation, but an approximation.
I don't think Demystifier was actually saying that there'd be situations where Bohmian mechanics would give different predictions about empirical results than the normal QM recipe involving the Born rule; I think he was just saying that in Bohmian mechanics the collapse is not "real" (i.e. the laws governing measurement interactions are exactly the same as the laws governing other interactions) but just a pragmatic way of getting the same predictions a full Bohmian treatment would yield. In section 4 (http://plato.stanford.edu/entries/qm-bohm/#eqs) of the Stanford article on Bohmian mechanics, they say:
However, the form given above has two advantages: First, it makes sense for particles with spin — and all the apparently paradoxical quantum phenomena associated with spin are, in fact, thereby accounted for by Bohmian mechanics without further ado. Secondly, and this is crucial to the fact that Bohmian mechanics is empirically equivalent to orthodox quantum theory, the right hand side of the guiding equation is J/ρ, the ratio of the quantum probability current to the quantum probability density. This shows first of all that it should require no imagination whatsoever to guess the guiding equation from Schrödinger's equation, provided one is looking for one, since the classical formula for current is density times velocity.

...

This demonstrates that all claims to the effect that the predictions of quantum theory are incompatible with the existence of hidden variables, with an underlying deterministic model in which quantum randomness arises from averaging over ignorance, are wrong. For Bohmian mechanics provides us with just such a model: For any quantum experiment we merely take as the relevant Bohmian system the combined system that includes the system upon which the experiment is performed as well as all the measuring instruments and other devices used in performing the experiment (together with all other systems with which these have significant interaction over the course of the experiment). The "hidden variables" model is then obtained by regarding the initial configuration of this big system as random in the usual quantum mechanical way, with distribution given by |ψ|2. The initial configuration is then transformed, via the guiding equation for the big system, into the final configuration at the conclusion of the experiment. It then follows that this final configuration of the big system, including in particular the orientation of instrument pointers, will also be distributed in the quantum mechanical way, so that this deterministic Bohmian model yields the usual quantum predictions for the results of the experiment.
I don't think it differs in this respect, if you include the standard measurement theory in it. But I did not say the LRM reproduces both unitary evolution and the measurement theory of this QFT, it just reproduces its unitary evolution. As unitary evolution and measurement theory are mutually contradictory, I don't think the failure to reproduce the measurement theory is a weak point of the LRM.
But if it only reproduces unitary evolution, can it reproduce any of the empirical predictions about probabilities made by the standard pragmatic recipe which includes the Born rule? Or can it only predict complex amplitudes, which can't directly be compared to empirical probabilities without making use of the Born rule or some subtle many-worlds type argument?

One last thing: note that Bell's proof strictly speaking showed that QM was incompatible with local realism if we assume that part of the definition of "realism" is that each measurement has a unique outcome, rather than each experiment splitting the experimenter into multiple copies who observe different outcomes. See the simple toy model I provided in post #11 of this thread (http://www.physicsforums.com/showthread.php?t=206291) showing how, if two experimenters Alice and Bob split into multiple copies on measurement and the universe doesn't have to decide which copy of Alice is matched to which copy of Bob until there's been time for a signal to pass between them, then we can get a situation where a randomly selected Alice-Bob pair will see statistics that violate Bell inequalities in a purely local model. Likewise, see my post #8 on this thread (http://www.physicsforums.com/showthread.php?t=221870) for links to various many-worlds advocates arguing that the interpretation is a purely local model.

akhmeteli

Jul25-10, 11:26 PM

This is kind of a strawman, no one is asking you to adopt a general principle along the lines of "if X is true when condition Y but not condition Z holds, and X is also true when condition Z but not condition Y holds, then we can assume X is true when both conditions Y and Z hold simultaneously".
I am happy that you don’t use this argument. But it does not look like a strawman to me. See, e.g., post 7 in this thread. Furthermore, Aspelmeyer and Zeilinger wrote as follows (see the reference in post 385 in this thread):
"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism."
While they are careful enough to avoid saying anything that is factually incorrect, they do use this argument. So this argument is indeed widely used.
Rather, the reason physicists think we can be pretty confident that Bell inequalities would be violated in an experiment where both loopholes were closed simultaneously has to do with specific considerations about the physical situation we're looking at, like the idea I already mentioned that it would require a very contrived local theory that would exploit both loopholes in just the right way that it would perfectly agree with QM in all experiments done to date.
I believe I addressed this statement in my previous post and I am not sure I have anything to add.

Are you claiming that your model gives correct statistical predictions about the empirical results of all the Aspect-type experiments that have been done to date?

That seems like a slightly evasive answer, since you later say that you distinguish the unitary evolution aspect of QM/QFT from the projection postulate, and only claim that your model reproduces the unitary evolution, but isn't the projection postulate the only way to get actual predictions about empirical experiments from QM/QFT? Do you claim that your model can correctly predict actual empirical experimental results in the types of experiments that have been done to date, yes or no?
I appreciate that my answer may look evasive, but I was not trying to sweep anything under the carpet, so maybe the question is not quite appropriate? Let me give you an example. Suppose I’d ask you if the Schroedinger equation correctly describes all experiments performed so far? Yes or no? Strictly speaking, the correct answer is “no”, because the equation is not relativistic and does not describe the electronic spin. But perhaps you’ll agree that this “correct” answer is somewhat misleading because this is a damn good equation :-) So if you want a yes or no answer, then no, the model I offer cannot describe all experiments performed so far, e.g., because it does not describe the electronic spin, and I said so in my previous post. However, this is a quite decent model, as it includes the entire scalar electrodynamics, a well-established theory.
Why is this a "contradiction", if we don't assume that either the wavefunction or its collapse on measurement are in any sense "real", but just treat them as parts of a pragmatic recipe for making quantitative predictions about experimental results? Do you claim there are any situations where the two postulates don't lead to a unique prediction about the statistics we should expect to see in some empirical experiment? If so, what situation would that be?
According to the projection postulate, after a measurement, the system is in an eigenstate, so another measurement will produce the same result (say, if the relevant operator commutes with the Hamiltonian). According to unitary evolution, though, a measurement cannot turn a superposition of states into a mixture, so there is a probability that the next measurement will return a different result. If this is not a contradiction, what is? Another situation where the two postulates don’t lead to a unique prediction is, I believe, a loophole-free Bell experiment. You cannot get a violation using just unitary evolution.

Yes, this is just what the pragmatic recipe says we should do.

Personally I believe there are some true set of laws that describe what's "really" going on (I'd favor some type of many-worlds type view) and which work exactly the same for interactions between quantum systems and "instruments" as they do for interactions between individual particles.
This is just great, so we pretty much agree with each other. Then what seems to be the problem?:-)
But again, if QM is treated just as a pragmatic recipe for making predictions which says nothing about the underlying "reality" one way or another, then in practice I don't think there is much ambiguity about what constitutes a "measurement", my understanding is that it's basically synonymous with interactions that involve environmental decoherence (http://arxiv.org/abs/quant-ph/9908008). And the types of experiments that physicists do are typically carefully controlled to prevent environmental decoherence from any other system besides the assigned "measuring device" (for example, a double-slit experiment with an electron will be done in a vacuum to prevent decoherence from interactions between the electrons and air molecules).
JesseM, again, it looks like we pretty much agree. I could agree, say, that the difference between unitary evolution and the projection postulate can be explained by environmental decoherence, but let us agree first what we are talking about. This thread is not about quantum theory being good or bad, everybody agrees that it is extremely good. The question of this thread is whether local realism has been ruled out or not. You see, you are talking about something “pragmatic”, but the question of this thread is not exactly pragmatic. As I said earlier in this thread, Nature cannot be “approximately local” or “approximately nonlocal”, it is either precisely local or precisely nonlocal. Or, if you disagree, then please explain what “approximate locality” can possibly be, because I don’t have a slightest idea:-) So yes, quantum theory is extremely good, but this is not relevant to the issue at hand.

I don't think it's likely to be wrong in reality since I favor some sort of variant of the many-worlds interpretation, but I do think it's hard to get concrete predictions about empirical results using unitary evolution alone
Again, I agree, but, as I noted in our previous discussion (http://www.physicsforums.com/showpost.php?p=1706652&postcount=78), you may just complement unitary evolution with the Born rule as an operational principle.
You didn't actually give a link to the paper, but you seem to be talking about this one (http://arxiv.org/abs/quant-ph/0506199).
That’s correct. Though I did not give a direct link, post 41 referenced post 31, where there is a reference to the article:-) Sorry for the inconvenience:-)
Anyway, Schlosshauer seems to be just arguing for the many-worlds interpretation (see the discussion beginning with 'The basic idea was introduced in Everett’s proposal of a relative-state view of quantum mechanics' on p. 1) and against any sort of objective collapse theory (http://en.wikipedia.org/wiki/Objective_collapse_theory) (see p. 13 where he talks about 'physical collapse models'--note that such models would actually be empirically distinguishable from ordinary QM in certain situations, like if information could be recorded and then 'erased' in a sufficiently large system completely isolated from environmental decoherence), but this is not the same as arguing that on a pragmatic level there's anything wrong with using the projection postulate to get quantitative predictions about experimental results. And it typically requires a lot of sophisticated argument to show how any many-worlds type interpretation can give concrete predictions in the form of probabilities (see the preferred basis problem (http://plato.stanford.edu/entries/qm-manyworlds/#6.2)), with no complete agreement among many-worlds advocates on how to do this (Schlosshauer discusses the problem on p. 14 of the paper, in the section 'Emergence of probabilities in a relative-state framework'); I think they all agree that the probabilities should be the same as the ones given by the pragmatic recipe involving the projection postulate, though. Indeed, Schlosshauer says at the beginning of that section that "The question of the origin and meaning of probabilities in a relative state–type interpretation that is based solely on a deterministically evolving global quantum state, and the problem of how to consistently derive Born’s rule in such a framework, has been the subject of much discussion and criticism aimed at this type of interpretation." And a bit later he says "The solution to the problem of understanding the meaning of probabilities and of deriving Born’s rule in a relative-state framework must therefore be sought on a much more fundamental level of quantum mechanics."
Again, I agree that quantum theory is a great practical value, but we are not discussing practicality. Again, it seems we both seem to agree that unitary evolution is always correct. However, it is worth mentioning that you are both telling me that you favor many worlds interpretation(s) and that there is no “complete agreement” on how “any many-worlds type interpretation can give concrete predictions in the form of probabilities”. This means that “many-worlds” people can actually live without the projection postulate. They may “all agree that the probabilities should be the same as the ones given by the pragmatic recipe involving the projection postulate”, but, strictly speaking, they are just unable to derive these probabilities. And it is good for them that they cannot derive those probabilities, because if they derived them from unitary evolution, that would mean that they made a mistake somewhere, as you cannot derive from unitary evolution something that directly contradicts it – the projection postulate. Let me emphasize that for all practical purposes you don’t need the Born rule or the projection postulate as precise principles – if they are approximately correct, they may be good enough for practice, but not when you’re trying to understand if Nature is local or not

I don't think Demystifier was actually saying that there'd be situations where Bohmian mechanics would give different predictions about empirical results than the normal QM recipe involving the Born rule; I think he was just saying that in Bohmian mechanics the collapse is not "real" (i.e. the laws governing measurement interactions are exactly the same as the laws governing other interactions) but just a pragmatic way of getting the same predictions a full Bohmian treatment would yield.
There is no need to guess what he said, as I gave you the reference to what he actually said. He said that the projection postulate is an approximation in Bohmian mechanics. Of course, you are free to disagree with him, with me or anybody else, but if you do, just say so. Do you believe that the projection postulate can be derived in Bohmian mechanics as a precise principle? With all due respect, I strongly doubt that it can (for reasons I explained), so could you give me a reference to such a result? The Born rule is one thing, the projection postulate is something different.

In section 4 (http://plato.stanford.edu/entries/qm-bohm/#eqs) of the Stanford article on Bohmian mechanics, they say:
Again, the Born rule is one thing, the projection postulate is something different. In the quote from Stanford encyclopedia (SE), I’d say, the Born rule is an operational principle. Furthermore, everything they say can be applied to the model I offer. Moreover, one can say that this model is a variant of Bohmian mechanics, which just happens to be local.

But if it only reproduces unitary evolution, can it reproduce any of the empirical predictions about probabilities made by the standard pragmatic recipe which includes the Born rule? Or can it only predict complex amplitudes, which can't directly be compared to empirical probabilities without making use of the Born rule or some subtle many-worlds type argument?
As I said, your SE quote above applies to this model. If you believe the Bohmian mechanics can reproduce “any of the empirical predictions about probabilities”, then why should you have a problem with this model? If you don’t believe that, well, at least this model is in good company:-)

One last thing: note that Bell's proof strictly speaking showed that QM was incompatible with local realism if we assume that part of the definition of "realism" is that each measurement has a unique outcome, rather than each experiment splitting the experimenter into multiple copies who observe different outcomes. See the simple toy model I provided in post #11 of this thread (http://www.physicsforums.com/showthread.php?t=206291) showing how, if two experimenters Alice and Bob split into multiple copies on measurement and the universe doesn't have to decide which copy of Alice is matched to which copy of Bob until there's been time for a signal to pass between them, then we can get a situation where a randomly selected Alice-Bob pair will see statistics that violate Bell inequalities in a purely local model. Likewise, see my post #8 on this thread (http://www.physicsforums.com/showthread.php?t=221870) for links to various many-worlds advocates arguing that the interpretation is a purely local model.
I see. I am just not sure such radical ideas as many worlds are really necessary. Furthermore, as I said in our previous discussion, I believe unitary evolution implies that no measurement is ever final, so, strictly speaking, there are never any definite outcomes, but they may seem definite, as transitions between different states of a macroscopic instrument can take an eternity.

In general, I would say our positions have a lot in common.

DevilsAvocado

Jul26-10, 07:00 AM

With all due respect akhmeteli, to a layman like me, this looks like a "beat around the bushes"...?

The title of your paper is: "IS NO DRAMA QUANTUM THEORY POSSIBLE?"

I could be wrong, but I interpret "NO DRAMA QUANTUM THEORY" as no "spooky action at a distance", i.e. local realism. But then you say:
Is it possible to offer a "no drama" quantum theory? Something as simple (in principle) as classical electrodynamics - a local realistic theory described by a system of partial differential equations in 3+1 dimensions, but reproducing unitary evolution of quantum theory in the configuration space?

Of course, the Bell inequalities cannot be violated in such a theory. This author has little, if anything, new to say about the Bell theorem, and this article is not about the Bell theorem. However, this issue cannot be "swept under the carpet" and will be discussed in Section 5 using other people's arguments.(My emphasis)

In Section 5, you state:
In Section 3, it was shown that a theory similar to quantum field theory (QFT) can be built that is basically equivalent to non-second-quantized scalar electrodynamics on the set of solutions of the latter. However, the local realistic theory violates the Bell inequalities, so this issue is discussed below using other people's arguments.I take for granted that this is the (calamitous) typo??While the Bell inequalities cannot be violated in local realistic theories, there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory. Indeed, there seems to be a consensus among experts that "a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing".(My emphasis)

To me this looks like a not very fair 'mixture' of; personal speculations + bogus statements + others statements concerning the current status of EPR-Bell experiments, resulting in the stupendous conclusion that Bell "inequalities cannot be violated either in experiments or in quantum theory" ...!:bugeye:?

And how on earth is this 'compatible' with your initial statement:
This author has little, if anything, new to say about the Bell theorem, and this article is not about the Bell theorem.?:confused:?

I trust in RUTA (Mark Stuckey). He’s a working PhD Professor of Physics:
When I first entered the foundations community (1994), there were still a few conference presentations arguing that the statistical and/or experimental analyses of EPR-Bell experiments were flawed. Such talks have gone the way of the dinosaurs. Virtually everyone agrees that the EPR-Bell experiments and QM are legit, so we need a significant change in our worldview. There is a proper subset who believe this change will be related to the unification of QM and GR :-)(My emphasis)

I looked at your homepage (http://www.akhmeteli.org/) and there are no references at all...?

To me, this looks like "personal speculations", and not mainstream physics:
... This LRM does not violate the Bell inequalities. But I don't think this is a weak point of the model for the reasons I explained in this thread:

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

And to be frank, your reasoning also looks dim. You are claiming a Local Realistic Model (LRM) that is not capable of violating Bell's Inequality, but that doesn’t matter, because – "these inequalities cannot be violated either in experiments or in quantum theory".

Exactly how do you derive "cannot" from your previous statements ...?:eek:?

RUTA

Jul26-10, 07:47 AM

Not exactly. I suspect that this prediction may be wrong, but I cannot claim that it is wrong. Indeed, I do understand that the violations can be found in a loophole-free experiment, say, tomorrow.

If the prediction is wrong, then QM is wrong. That's the bold assertion I'm fishing for :-)

Following other people, I am just saying (right now, not tomorrow) that 1) there has been no evidence of violations of the genuine Bell inequalities so far,

Given the preponderance of experimental evidence and the highly contrived nature by which loop holes must exist to explain away violations of Bell inequalities, the foundations community has long ago abandoned any attempt to save local realism. But, you're right, there are no truly "loop hole free" experiments, so die hard local realists can cling to hope.

and that 2) mutually contradictory assumptions are required to derive the QM's prediction of the violation of Bell inequalities. Therefore, local realism has not been ruled out so far.

Are you talking about the measurement problem? That applies to all QM predictions, not just those that violate Bell inequalities.

zonde

Jul26-10, 08:09 AM

There have been experiments that closed the detector efficiency loophole and experiments that closed the locality loophole, but no experiment that closed both loopholes simultaneously--still I think most experts would agree you'd need a very contrived local realist model to get correct predictions (agreeing with those of QM) for the experiments that have already been performed, but which would fail to violate Bell inequalities (in contradiction with QM) in an ideal experiment.
It does not require contrived model to spot the likely source of systematic error in NIST experiment (if that's the one you have on mind as efficient detection experiment).
In this experiment only one measurement is performed for both particles and that way detection photons are subject to interference.
As authors of that paper say: "Also, the detection solid angle is large enough that Young's interference fringes, if present are averaged out."
First, this interference effect of photons scattered from two ions is experimentally verified so there should be no reason to say that there are no interference fringes (negligible might be a better word).
Second, assumption that interference effect of detection photons is averaged out even when they are conditioned on different ion configurations is the same fair sampling assumption as used in different photon experiments.

zonde

Jul26-10, 08:25 AM

If the prediction is wrong, then QM is wrong. That's the bold assertion I'm fishing for :-)
If prediction of some green alternate theory is found out to be wrong then theory is wrong.
If prediction of well established theory with proven usefulness is found out to be wrong then domain of it's applicability is established instead. :wink:

DevilsAvocado

Jul26-10, 09:04 AM

P.S. akhmeteli
... these inequalities cannot be violated either in experiments or in quantum theory ...

It would be interesting to hear your view on this:
Stanford Encyclopedia of Philosophy – Bell's Theorem (http://plato.stanford.edu/entries/bell-theorem/)
...
The incompatibility of Local Realistic Theories with Quantum Mechanics permits adjudication by experiments, some of which are described here. Most of the dozens of experiments performed so far have favored Quantum Mechanics, but not decisively because of the “detection loophole” or the “communication loophole.” The latter has been nearly decisively blocked by a recent experiment and there is a good prospect for blocking the former. The refutation of the family of Local Realistic Theories would imply that certain peculiarities of Quantum Mechanics will remain part of our physical worldview: notably, the objective indefiniteness of properties, the indeterminacy of measurement results, and the tension between quantum nonlocality and the locality of Relativity Theory.

And while you’re at it: Could you please explain why not one (1) EPR-Bell experiment so far has clearly favored Local Realistic Theories? Not one (1).

And, if you have some extra spare time: Could you also explain how nature is providing the "detection loophole", which is regarded as the most 'severe'. I mean, if you look at this slide from Alain Aspect, it’s clear that this "magic LRM function" must be wobbling between "too much" and "too little" to provide the measured data. And last but not least, this "magic LRM function" must KNOW which photons are entangled or not!?!? (Looks like a very "spooky function" to me... :bugeye:)

http://i39.tinypic.com/2wr1cgm.jpg

RUTA

Jul26-10, 09:09 AM

If prediction of some green alternate theory is found out to be wrong then theory is wrong.
If prediction of well established theory with proven usefulness is found out to be wrong then domain of it's applicability is established instead. :wink:

So, QM is alright as long as you don't have entangled states? Restrictions on applicability are acceptable when a theory is superceded, e.g., Newtonian dynamics is ok when v << c and was superceded by SR to account for v ~ c, but no one has a theory superceding QM that gets rid of its entangled states. And, unlike v ~ c prior to SR, we have the means to create and explore entangled states and all such experiments vindicate QM.

No, zonde, this is not a mere restriction on the applicability of QM.

JesseM

Jul26-10, 09:34 AM

I am happy that you don’t use this argument. But it does not look like a strawman to me. See, e.g., post 7 in this thread. Furthermore, Aspelmeyer and Zeilinger wrote as follows (see the reference in post 385 in this thread):
"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism."
While they are careful enough to avoid saying anything that is factually incorrect, they do use this argument. So this argument is indeed widely used.
Nowhere in that quote do they imply it is true in general that "if X is true when condition Y but not condition Z holds, and X is also true when condition Z but not condition Y holds, then we can assume X is true when both conditions Y and Z hold simultaneously". Rather they refer to the specific conditions of the experiment when they say "It is very unlikely that such an experiment will disagree with the prediction of quantum mechanics, since this would imply that nature makes use of both the detection loophole in the Innsbruck experiment and of the locality loophole in the NIST experiment." It's quite possible (and I think likely) that the reason they consider it "unlikely" is because a theory making use of both loopholes would be very contrived-looking.
Rather, the reason physicists think we can be pretty confident that Bell inequalities would be violated in an experiment where both loopholes were closed simultaneously has to do with specific considerations about the physical situation we're looking at, like the idea I already mentioned that it would require a very contrived local theory that would exploit both loopholes in just the right way that it would perfectly agree with QM in all experiments done to date.
I believe I addressed this statement in my previous post and I am not sure I have anything to add.
You addressed it by suggested your own model was non-contrived, but didn't give a clear answer to my question about whether it can actually give statistical predictions about experiments so far like the Innsbruck experiment and the NIST experiment (or any experiments whatsoever, see below)--if it can't, then it obviously doesn't disprove the claim that any local realist theory consistent with experiments so far would have to be very contrived!
Are you claiming that your model gives correct statistical predictions about the empirical results of all the Aspect-type experiments that have been done to date?

That seems like a slightly evasive answer, since you later say that you distinguish the unitary evolution aspect of QM/QFT from the projection postulate, and only claim that your model reproduces the unitary evolution, but isn't the projection postulate the only way to get actual predictions about empirical experiments from QM/QFT? Do you claim that your model can correctly predict actual empirical experimental results in the types of experiments that have been done to date, yes or no?
I appreciate that my answer may look evasive, but I was not trying to sweep anything under the carpet, so maybe the question is not quite appropriate? Let me give you an example. Suppose I’d ask you if the Schroedinger equation correctly describes all experiments performed so far? Yes or no? Strictly speaking, the correct answer is “no”, because the equation is not relativistic and does not describe the electronic spin. But perhaps you’ll agree that this “correct” answer is somewhat misleading because this is a damn good equation :-) So if you want a yes or no answer, then no, the model I offer cannot describe all experiments performed so far, e.g., because it does not describe the electronic spin, and I said so in my previous post. However, this is a quite decent model, as it includes the entire scalar electrodynamics, a well-established theory.
OK, but can your model actually give "correct predictions about statistical results" for any actual experiments, or does it only reproduce the unitary evolution? If it can't predict actual real-valued statistics that are measured empirically, as opposed to complex amplitudes, then it isn't a local realist model that can explain any existing experiments (you may be able to derive probabilities from amplitudes using many-worlds type arguments, but as I said part of the meaning of 'local realism' is that each measurement yields a unique outcome)
According to the projection postulate, after a measurement, the system is in an eigenstate, so another measurement will produce the same result (say, if the relevant operator commutes with the Hamiltonian). According to unitary evolution, though, a measurement cannot turn a superposition of states into a mixture, so there is a probability that the next measurement will return a different result.
Suppose we do a Wigner's friend (http://en.wikipedia.org/wiki/Wigner%27s_friend) type thought-experiment where we imagine a small quantum system that's first measured by an experimenter in an isolated box, and from our point of view this just causes the experimenter to become entangled with the system rather than any collapse occurring. Then we open the box and measure both the system and the record of the previous measurement taken by the experimenter who was inside, and we model this second measurement as collapsing the wavefunction. If the two measurements on the small system were of a type that according to the projection postulate should yield a time-independent eigenstate, are you claiming that in this situation where we model the first measurement as just creating entanglement rather than collapsing the wavefunction, there is some nonzero possibility that the second measurement will find that the record of the first measurement will be of a different state than the one we find on the second measurement? I'm not sure but I don't think that would be the case--even if we assume unitary evolution, as long as there is some record of previous measurements then the statistics seen when comparing the records to the current measurement should be the same as the statistics you'd have if you assumed the earlier measurements (the ones which resulted in the records) collapsed the wavefunction of the system being measured according to the projection postulate.

In any case, the projection postulate does not actually specify that each "measurement" must collapse the wavefunction onto an eigenstate in cases where you're performing a sequence of different measurements. The "pragmatic recipe" is entirely compatible with the notion that in a problem like this, the projection postulate should only be used once at the very end of the complete experiment, when you make a measurement of all the records that resulted from earlier measurements.
JesseM, again, it looks like we pretty much agree. I could agree, say, that the difference between unitary evolution and the projection postulate can be explained by environmental decoherence, but let us agree first what we are talking about. This thread is not about quantum theory being good or bad, everybody agrees that it is extremely good. The question of this thread is whether local realism has been ruled out or not.
But there are two aspects of this question--the first is whether local realism can be ruled out given experiments done so far, the second is whether local realism is consistent with the statistics predicted theoretically by QM. Even if you don't use the projection postulate to generate predictions about statistics, you need some real-valued probabilities for different outcomes, you can't use complex amplitudes alone since those are never directly measured empirically. And if we understand local realism to include the condition that each measurement has a unique outcome, then it is impossible to get these real-valued statistics from a local realist model.
You see, you are talking about something “pragmatic”, but the question of this thread is not exactly pragmatic. As I said earlier in this thread, Nature cannot be “approximately local” or “approximately nonlocal”, it is either precisely local or precisely nonlocal.
No idea where you got the idea that I would be talking about "approximate" locality from anything in my posts. I was just talking about QM being a "pragmatic" recipe for generating statistical predictions, I didn't say that Bell's theorem and the definition of local realism were approximate or pragmatic. Remember, Bell's theorem is about any black-box experiment where two experimenters at a spacelike separation each have a random choice of detector setting, and each measurement must yield one of two binary results--nothing about the proof specifically assumes they are measuring anything "quantum", they might be choosing to ask one of three questions with yes-or-no answers to a messenger sent to them or something. Bell's theorem proves that according to local realism, any experiment of this type must obey some Bell inequalities. So then if you want to show that QM is incompatible with local realism, the only aspect of QM you should be interested in is its statistical predictions about some experiment of this type, all other theoretical aspects of QM are completely irrelevant to you. Unless you claim that the "pragmatic recipe" I described would actually make different statistical predictions about this type of experiment than some other interpretation of QM like Bohmian mechanics or the many-worlds-interpretation, then it's pointless to quibble with the pragmatic recipe in this context.
Again, I agree, but, as I noted in our previous discussion (http://www.physicsforums.com/showpost.php?p=1706652&postcount=78), you may just complement unitary evolution with the Born rule as an operational principle.
But that won't produce a local realist theory where each measurement has a unique outcome. Suppose you have two separate computers, one modeling the amplitudes for various measurements which could be performed in the local region of one simulated experimenter "Alice", another modeling the amplitudes for various measurements which could be performed in the local region of another simulated experimenter "Bob", with the understanding that these amplitudes concerned measurements on a pair of entangled particles that were sent to Alice and Bob (who make their measurements at a spacelike separation). If you want to simulate Alice and Bob making actual measurements, and you must assume that each measurement yields a unique outcome (i.e. Alice and Bob don't each split into multiple copies as in the toy model I linked to at the end of my last post), then if the computers running the simulation are cut off from communicating with one another and neither computer knows in advance what measurement will be performed by the simulated experimenter on the other computer, then there is no way that such a simulation can yield the same Bell-inequality-violating statistics predicted by QM, even if you program the Born rule into each computer to convert amplitudes into probabilities which are used to generate the simulated outcome of each measurement. Do you disagree that there is no way to get the correct statistics predicted by any interpretation of QM in a setup like this where the computers simulating each experimenter are cut off from communicating? (which corresponds to the locality condition that events in regions with a spacelike separation can have no causal effect on one another)
Again, I agree that quantum theory is a great practical value, but we are not discussing practicality. Again, it seems we both seem to agree that unitary evolution is always correct. However, it is worth mentioning that you are both telling me that you favor many worlds interpretation(s) and that there is no “complete agreement” on how “any many-worlds type interpretation can give concrete predictions in the form of probabilities”. This means that “many-worlds” people can actually live without the projection postulate. They may “all agree that the probabilities should be the same as the ones given by the pragmatic recipe involving the projection postulate”, but, strictly speaking, they are just unable to derive these probabilities.
The problem is that there is no agreement on how the many-worlds interpretation can be used to derive any probabilities. If we're not convinced it can do so then we might not view it as being a full "interpretation" of QM yet, rather it'd be more like an incomplete idea for how one might go about constructing an interpretation of QM in which measurement just caused the measuring-system to become entangled with the system being measured.
And it is good for them that they cannot derive those probabilities, because if they derived them from unitary evolution, that would mean that they made a mistake somewhere, as you cannot derive from unitary evolution something that directly contradicts it – the projection postulate.
See my comments above about the Wigner's friend type thought experiment. I am not convinced that you can actually find a situation where a series of measurements are made that each yield records of the result, such that using the projection postulate for each measurement gives different statistical predictions then if we just treat this as a giant entangled system which evolves in a unitary way, and then at the very end use the Born rule to find statistical expectations for the state of all the records of prior measurements. And as I said there as well, the projection postulate does not actually specify whether in a situation like this you should treat each successive measurement as collapsing the wavefunction onto an eigenstate or whether you should save the "projection" for the very last measurement.
I don't think Demystifier was actually saying that there'd be situations where Bohmian mechanics would give different predictions about empirical results than the normal QM recipe involving the Born rule; I think he was just saying that in Bohmian mechanics the collapse is not "real" (i.e. the laws governing measurement interactions are exactly the same as the laws governing other interactions) but just a pragmatic way of getting the same predictions a full Bohmian treatment would yield.
There is no need to guess what he said, as I gave you the reference to what he actually said.
I wasn't guessing what he said, I was guessing what he meant by what he said. What he said was only the very short statement "Yes, it is an approximation. However, due to decoherence, this is an extremely good approximation. Essentially, this approximation is as good as the second law of thermodynamics is a good approximation." I think this statement is compatible with my interpretation of what he may have meant, namely "in Bohmian mechanics the collapse is not 'real' (i.e. the laws governing measurement interactions are exactly the same as the laws governing other interactions) but just a pragmatic way of getting the same predictions a full Bohmian treatment would yield." Nowhere did he say that using the projection postulate will yield different statistical predictions about observed results than those predicted by Bohmian mechanics.
The Born rule is one thing, the projection postulate is something different.
I think they are different only if you assume multiple successive measurements, and understanding "the projection postulate" to imply that each measurement collapses the wavefunction onto an eigenstate, and assuming that for some of the measurements the records of the results are "erased" so that it cannot be known later what the earlier result was. If you are dealing with a situation where none of the measurement records are erased, I'm pretty sure that the statistics for the measurement results you get using the projection postulate will be exactly the same as the statistics you get if you model the whole thing as a giant entangled system and then use the Born rule at the very end to find the probabilities of different combinations of recorded measurement results. And once again, the "projections postulate" does not precisely define when projection should occur anyway, you are free to interpret the projection postulate to mean that only the final measurement of the records at the end of the entire experiment actually collapses the wavefunction.

JesseM

Jul26-10, 09:34 AM

(continued from previous post)

But if it only reproduces unitary evolution, can it reproduce any of the empirical predictions about probabilities made by the standard pragmatic recipe which includes the Born rule? Or can it only predict complex amplitudes, which can't directly be compared to empirical probabilities without making use of the Born rule or some subtle many-worlds type argument?
As I said, your SE quote above applies to this model. If you believe the Bohmian mechanics can reproduce “any of the empirical predictions about probabilities”, then why should you have a problem with this model?
I think you misunderstood what I meant by "any" above, I wasn't asking if your model could reproduce any arbitrary prediction made by the "standard pragmatic recipe" (i.e. whether it would agree with the standard pragmatic recipe in every possible case, as I think Bohmian mechanics does). Rather, I was using "any" in the same sense as it's used in the question priests used to ask at weddings, "If any person can show just cause why they may not be joined together, let them speak now or forever hold their peace"--in other words, I was asking if there was even a single instance of a case where your model reproduces the probabilistic predictions of standard QM, or whether your model only deals with complex amplitudes that result from unitary evolution. The reason I asked this is that the statement of yours I was responding to was rather ambiguous on this point:
I don't think it differs in this respect, if you include the standard measurement theory in it. But I did not say the LRM reproduces both unitary evolution and the measurement theory of this QFT, it just reproduces its unitary evolution. As unitary evolution and measurement theory are mutually contradictory, I don't think the failure to reproduce the measurement theory is a weak point of the LRM.
If your model does predict actual measurement results, then if the model was applied to an experiment intended to test some Bell inequality, would it in fact predict an apparent violation of the inequalites in both experiments where the locality loophole was closed but not the detector efficiency loophole, and in experiments where the efficiency loophole was closed but not the locality loophole? I think you said your model would not predict violations of Bell inequalities in experiments with all loopholes closed--would you agree that if we model such experiments using unitary evolution plus the Born rule (perhaps applied to the records at the very end of the full experiment, after many trials had been performed, so we don't have to worry about whether applying the Born rule means we have to invoke the projection postulate), then we will predict violations of Bell inequalities even in loophole-free experiments? Likewise, would you agree that Bohmian mechanics also predicts violations in loophole-free experiments, and many-worlds advocates would expect the same prediction even if there is disagreement on how to derive it?

DrChinese

Jul26-10, 10:31 AM

If prediction of some green alternate theory is found out to be wrong then theory is wrong.

If prediction of well established theory with proven usefulness is found out to be wrong then domain of it's applicability is established instead. :wink:

I agree with this. Technically, theories should not be seen as "Proven" or "Wrong" or whatever; rather as "More Useful" or "Useless". And the scope/domain of a theory may need to be modified from time to time as new information arises. So a theory could remain useful in a narrowed domain if new information is acquired. Newtonian gravity after GR is an example. Still quite useful. I would definitely not call Newtonian gravity a wrong theory.

DevilsAvocado

Jul26-10, 10:44 AM

... OK, but can your model actually give "correct predictions about statistical results" for any actual experiments, or does it only reproduce the unitary evolution?
... No, I definitely do not claim that (though there is an unfortunate typo in the article, which I will correct in the proofs). This LRM does not violate the Bell inequalities. But I don't think this is a weak point of the model for the reasons I explained in this thread:

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

This is how I get it, and I apologize in advance if it’s wrong:

According to akhmeteli, the LRM does not violate the Bell inequalities, but that doesn’t matter much, because according to akhmeteli, there are no experimental evidence of violations of Bell's Inequalities so far, and Bell's Theorem is faulty in using two mutually contradicting postulates of QM.

If I’m right, it doesn’t impress me... all he’s saying is that EPR-Bell experiments & Bell's Theorem are wrong, without delivering any proofs for that claim.

RUTA

Jul26-10, 10:53 AM

I agree with this. Technically, theories should not be seen as "Proven" or "Wrong" or whatever; rather as "More Useful" or "Useless". And the scope/domain of a theory may need to be modified from time to time as new information arises. So a theory could remain useful in a narrowed domain if new information is acquired. Newtonian gravity after GR is an example. Still quite useful. I would definitely not call Newtonian gravity a wrong theory.

Whether you choose to call Newtonian gravity "wrong," given it has been superceded by GR, is semantics. The claim that QM should be restricted to use with non-entangled states is not at all consistent with this type of "wrong" b/c there is no theory superceding QM that clearly shows why QM's treatment of entangled states is wrong -- no semantics here, GR says clearly that Newtonian gravity fails in certain regimes and tests of this claim vindicate GR. We don't have any such theory, claims and vindication against QM's predictions for entangled states. Quite the contrary, we've many experiments consistent with QM's predictions with entangled states. Thus, there is a huge burden of proof for anyone claiming QM's prediction of Bell inequality violations is wrong and, in my opinion, this burden is nowhere near being fulfilled by the proponents of local realism.

DevilsAvocado

Jul26-10, 11:24 AM

DrChinese

Jul26-10, 11:44 AM

Whether you choose to call Newtonian gravity "wrong," given it has been superceded by GR, is semantics. The claim that QM should be restricted to use with non-entangled states is not at all consistent with this type of "wrong" b/c there is no theory superceding QM that clearly shows why QM's treatment of entangled states is wrong -- no semantics here, GR says clearly that Newtonian gravity fails in certain regimes and tests of this claim vindicate GR. We don't have any such theory, claims and vindication against QM's predictions for entangled states. Quite the contrary, we've many experiments consistent with QM's predictions with entangled states. Thus, there is a huge burden of proof for anyone claiming QM's prediction of Bell inequality violations is wrong and, in my opinion, this burden is nowhere near being fulfilled by the proponents of local realism.

I agree with what you are saying, and note that I missed a big new chunk of the thread regarding akhmeteli's claims. So my bad for chiming in irelevantly as I do sometimes. akhmeteli's "suspicion" that QM makes a wrong prediction is strange given every experiment performed to date is clearly within the predicted range of QM (but not any prior LR).

akhmeteli: My big question for your model is a familiar one. If it is local realistic, can you tell me what the correct (if QM is wrong in this regard) statistical predictions are for coincidences at a, b, c = 0, 120, 240 degrees? Can you supply a dataset which is in indicative of the rules of your model?

Alice:
a b c
+ - +
- + +
- - +
+ - -

... or whatever you imagine a batch of Alices to be, independent of Bob. A local realistic model should be able to provide this. If not, it does not fulfill the claim of being realistic. And please, do not point me to your paper as proof. The proof is in the pudding, and I am looking to taste some.

RUTA

Jul26-10, 11:53 AM

RUTA & DrC, this is interesting. If we assume that one day all EPR-Bell loopholes are closed simultaneously, and we all (maybe even ThomasT :wink:) agree that nonlocality and/or nonseparability is a fact; would that mean that Quantum Mechanics has proven Relativity Theory wrong (or slightly "useless")?

GR is both causally local and separable, so if QM is "right," GR is "wrong." I would use DrC's semantic choice here and refuse to say GR is wrong :-) However, I have to admit an enormous bias -- grade school records show my hero was Einstein, I did my undergrad major in physics when I read about SR, and did my PhD in GR. So, for my own sanity, I must believe that GR is the local, separable approximation to the "correct" theory of gravity.

As an aside, we're working on just such a theory now -- nonseparable Regge calculus. Since our Relational Blockworld interpretation of QM and QFT assumes a nonseparable theory X underlying quantum physics*, we developed a "direct action," path integral approach over graphs for theory X. Regge calculus is a path integral approach over graphs for GR so, of course, that's where we expect to link theory X to classical physics. The only difference between Regge calculus and our approach is that our path integrals are "direct action," i.e., link only sources. Since there are no source-free solutions in our theory X (this is the mathematics behind "nonseparability" in our approach), the vacuum solns of GR are only approximations (as well as its use of continuum mathematics). Anyway, it looks like nonseparable Regge calculus will survive the weak field tests of GR, but predict deviations from GR at large distances (galactic scales and larger). I'll keep you apprised :-)

*Here we follow the possibility articulated by Wallace (p 45) that, “QFTs as a whole are to be regarded only as approximate descriptions of some as-yet-unknown deeper theory,” which he calls “theory X.” Wallace, D.: In defence of naiveté: The conceptual status of Lagrangian quantum field theory. Synthese 151, 33-80 (2006).

JesseM

Jul26-10, 02:23 PM

RUTA & DrC, this is interesting. If we assume that one day all EPR-Bell loopholes are closed simultaneously, and we all (maybe even ThomasT :wink:) agree that nonlocality and/or nonseparability is a fact; would that mean that Quantum Mechanics has proven Relativity Theory wrong (or slightly "useless")?
As I mentioned at the end of post #581, there is a theoretical loophole in Bell's proof due to the implicit assumption that each measurement yields a unique outcome, so with a many-worlds-type interpretation you could have a local model consistent with observed violations of Bell inequalities in experiments with all the experimental loopholes closed:
One last thing: note that Bell's proof strictly speaking showed that QM was incompatible with local realism if we assume that part of the definition of "realism" is that each measurement has a unique outcome, rather than each experiment splitting the experimenter into multiple copies who observe different outcomes. See the simple toy model I provided in post #11 of this thread (http://www.physicsforums.com/showthread.php?t=206291) showing how, if two experimenters Alice and Bob split into multiple copies on measurement and the universe doesn't have to decide which copy of Alice is matched to which copy of Bob until there's been time for a signal to pass between them, then we can get a situation where a randomly selected Alice-Bob pair will see statistics that violate Bell inequalities in a purely local model. Likewise, see my post #8 on this thread (http://www.physicsforums.com/showthread.php?t=221870) for links to various many-worlds advocates arguing that the interpretation is a purely local model.

RUTA

Jul26-10, 02:54 PM

As I mentioned at the end of post #581, there is a theoretical loophole in Bell's proof due to the implicit assumption that each measurement yields a unique outcome, so with a many-worlds-type interpretation you could have a local model consistent with observed violations of Bell inequalities in experiments with all the experimental loopholes closed:

I'm familiar with the no-collapse account whereby the universe has many copies, each instantiating a possible experimental outcome, but I haven't heard of a no-collapse account whereby the universe itself is being split. Is that what you're saying? If so, in what "time" does the "reconstruction" take place? Sounds like you need a metatime and a cosmic conductor orchestrating the proper mix of outcomes, but I'll let you explain before commenting further :-)

JesseM

Jul26-10, 03:11 PM

I'm familiar with the no-collapse account whereby the universe has many copies, each instantiating a possible experimental outcome, but I haven't heard of a no-collapse account whereby the universe itself is being split. Is that what you're saying?
No, only individual systems are being split in a local manner. And "split" doesn't need to be taken too literally, we could imagine an ensemble of preexisting copies of each experimenter that are identical up to the point of measurement, and then at the moment of measurement some copies see one result while others see a different result (so this would be more like 'differentiating' rather than 'splitting'). The key point is just that if you have a bunch of copies of Alice over here and Bob over there, until there's been time for a signal to travel from Bob to Alice (moving at the speed of light or slower), there doesn't need to be any objective truth about whether a given copy of Alice is part of the same "world" as a copy of Bob who saw the result spin-up or a copy of Bob who saw the result spin-down (and once a signal has had time to reach Alice's position, this just causes the copies of Alice to split/differentiate further, so some copies of Alice that saw result spin-up would get a message saying Bob had gotten result spin-down, while others would get a message saying Bob had gotten result spin-up). If this is unclear, please take a look at the toy model I offered in post #11 here (http://www.physicsforums.com/showthread.php?t=206291).
If so, in what "time" does the "reconstruction" take place? Sounds like you need a metatime and a cosmic conductor orchestrating the proper mix of outcomes, but I'll let you explain before commenting further :-)
What do you mean by "reconstruction", and why do you think the splitting/differentiating would need to occur in "metatime" rather than ordinary time? Again, just look at the toy model, it's the sort of thing that could be simulated on a pair of classical computers (with an actual spacelike separation between the two simulated measurements on each computer) in realtime.

RUTA

Jul26-10, 03:33 PM

No, only individual systems are being split in a local manner. And "split" doesn't need to be taken too literally, we could imagine an ensemble of preexisting copies of each experimenter that are identical up to the point of measurement, and then at the moment of measurement some copies see one result while others see a different result (so this would be more like 'differentiating' rather than 'splitting'). The key point is just that if you have a bunch of copies of Alice over here and Bob over there, until there's been time for a signal to travel from Bob to Alice (moving at the speed of light or slower), there doesn't need to be any objective truth about whether a given copy of Alice is part of the same "world" as a copy of Bob who saw the result spin-up or a copy of Bob who saw the result spin-down (and once a signal has had time to reach Alice's position, this just causes the copies of Alice to split/differentiate further, so some copies of Alice that saw result spin-up would get a message saying Bob had gotten result spin-down, while others would get a message saying Bob had gotten result spin-up). If this is unclear, please take a look at the toy model I offered in post #11 here (http://www.physicsforums.com/showthread.php?t=206291).

What do you mean by "reconstruction", and why do you think the splitting/differentiating would need to occur in "metatime" rather than ordinary time? Again, just look at the toy model, it's the sort of thing that could be simulated on a pair of classical computers (with an actual spacelike separation between the two simulated measurements on each computer) in realtime.

Ah, I read through the many exchanges you had with "colorspace" and I will only end up echoing his many complaints. We don't need to repeat that :-)

JesseM

Jul26-10, 03:58 PM

Ah, I read through the many exchanges you had with "colorspace" and I will only end up echoing his many complaints. We don't need to repeat that :-)
Many of colorspace's complaints seemed to suggest little working understanding of how real theories of physics work, like his argument in post #12 that if it would take time for a computer to compute which copies of signals from Bob should be matched to which copies of Alice, then it must take time in reality too (when of course we have plenty of examples of theories which say the state of each point in space is being continuously updated in response to its surroundings according to differential equations, in a way that would be impossible to simulate perfectly accurately with finite computing power...likewise the fact that an infinite number of Feynman diagrams must be summed to get completely accurate predictions about probabilities in quantum field theory doesn't imply that nature takes an infinite time to 'compute' the outgoing particles in a collision). That's why I eventually abandoned the discussion, since I can't really explain the mathematically abstract nature of modern physics to someone who's insistent on acting incredulous towards any theory that doesn't make sense in concrete "common sense" terms. Since you seem more well-versed in modern physics than colorspace, a discussion of what you find implausible about this type of model might be more fruitful, if you have the time and are so inclined (if not, no problem).

DrChinese

Jul26-10, 04:03 PM

I would use DrC's semantic choice here and refuse to say GR is wrong :-)

Sorry bout giving things an accidental semantic twist. When it comes to theories, I have a decidedly utilitarian bent. But some theories *are* useless enough to be called wrong.

But of course, GR is not one of those. :smile: I will defend Einstein as I do Newton.

RUTA, your research sounds very exciting! Always enjoy your posts.

DevilsAvocado

Jul26-10, 04:18 PM

my hero was Einstein
Einstein is my hero! :smile:

As an aside, we're working on just such a theory now -- nonseparable Regge calculus.
Cool! :cool: (And you know me and English... first I’d read "Reggae calculus"... :uhh: (:biggrin:))

Since our Relational Blockworld interpretation of QM and QFT assumes a nonseparable theory X underlying quantum physics*, we developed a "direct action," path integral approach over graphs for theory X. Regge calculus is a path integral approach over graphs for GR so, of course, that's where we expect to link theory X to classical physics.
Very cool and interesting! My personal "layman-gut-feeling" tell me that this kind of approach must be the only logical path forward, looking for the underlying "theory X". I cannot understand how some people seems to be willing to do almost anything to "disarm" the EPR-Bell issue, including getting hazardous close to deceitfulness, in order to get back to status quo and business as usual.

I think EPR & Bell's Theorem is gift from above! How utterly boring it would be, if everything was already worked out... no scientific news... no interesting discussions on internet... what should one do? Retire and play golf!? :zzz:

To me, the current situation looks like 1887 and Michelson–Morley experiment (http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment), when the experimental data was crying out for a 'logical' solution!

As I understand, this new underlying "theory X" must be fairly compatible with both QM & SR/GR, as this has been the case in history of science. Crackpots, starting from square one by dismissing both QM & SR/GR, are most probably doomed to lose...

But how to marry QM + GR is way beyond my understanding. But it is nevertheless very thrilling!!

(Let me know when "it’s" solved! :wink:)

DevilsAvocado

Jul26-10, 05:47 PM

As I mentioned at the end of post #581, there is a theoretical loophole in Bell's proof due to the implicit assumption that each measurement yields a unique outcome, so with a many-worlds-type interpretation you could have a local model consistent with observed violations of Bell inequalities in experiments with all the experimental loopholes closed:

Thanks for the info JesseM. I am aware that MWI is a possible solution to get out of the EPR(B) paradox. I’ll check out your toy model, and The Everett FAQ. I think I have a question about EPR & MWI...

Meanwhile, what’s your view on EPR/MWI and splitting worlds, in respect of Occam's razor...?

JesseM

Jul26-10, 06:14 PM

Meanwhile, what’s your view on EPR/MWI and splitting worlds, in respect of Occam's razor...?
Personally I lean strongly towards MWI type interpretations, I think Occam's razor just says our theoretical assumptions should be fairly simple but it doesn't say that the actual number of entities predicted by the theory should be small (for example, it's no strike against current cosmological theories that they postulate a huge number of stars in the observable universe, and likely many more--perhaps an infinite number--beyond the limits of what we can observe).

RUTA

Jul26-10, 10:13 PM

Many of colorspace's complaints seemed to suggest little working understanding of how real theories of physics work, like his argument in post #12 that if it would take time for a computer to compute which copies of signals from Bob should be matched to which copies of Alice, then it must take time in reality too (when of course we have plenty of examples of theories which say the state of each point in space is being continuously updated in response to its surroundings according to differential equations, in a way that would be impossible to simulate perfectly accurately with finite computing power...likewise the fact that an infinite number of Feynman diagrams must be summed to get completely accurate predictions about probabilities in quantum field theory doesn't imply that nature takes an infinite time to 'compute' the outgoing particles in a collision). That's why I eventually abandoned the discussion, since I can't really explain the mathematically abstract nature of modern physics to someone who's insistent on acting incredulous towards any theory that doesn't make sense in concrete "common sense" terms. Since you seem more well-versed in modern physics than colorspace, a discussion of what you find implausible about this type of model might be more fruitful, if you have the time and are so inclined (if not, no problem).

I'm willing to spend time trying to figure out what you're saying unless it involves Many Worlds. The reason I dismiss Many Worlds is that if it's true, there's no way to do science. That is, if all possible outcomes are always realized, there are universes in which the participants don't get the right statistics, i.e., those that are dictating the split rates. And, there's no way any participant in any of the splits can know whether his results are the "correct" results or not. Therefore, you can't do science.

But, anyway, if you're not going to use Many Worlds, go ahead and try to explain your model.

akhmeteli

Jul26-10, 10:16 PM

With all due respect akhmeteli, to a layman like me, this looks like a "beat around the bushes"...?

The title of your paper is: "IS NO DRAMA QUANTUM THEORY POSSIBLE?"

I could be wrong, but I interpret "NO DRAMA QUANTUM THEORY" as no "spooky action at a distance", i.e. local realism.
Not just that. The goal is described in the first paragraph you quote: “Something as simple (in principle) as classical electrodynamics - a local realistic theory described by a system of partial differential equations in 3+1 dimensions, but reproducing unitary evolution of quantum theory in the configuration space”. Simplicity of the model was extremely important.
But then you say:
(My emphasis)

In Section 5, you state:
I take for granted that this is the (calamitous) typo??(My emphasis)
Yes, it is. Sorry about that.
To me this looks like a not very fair 'mixture' of; personal speculations + bogus statements + others statements concerning the current status of EPR-Bell experiments, resulting in the stupendous conclusion that Bell "inequalities cannot be violated either in experiments or in quantum theory" ...!:bugeye:?
“not very fair 'mixture'…, bogus statements” –I cannot meaningfully discuss your personal opinions until you give some reasons for them. If you mean the following phrase is “unfair” or “bogus”: “there seems to be a consensus among experts that "a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing".”, then I quoted Genovese , Shimony, Aspelmeyer and Zeilinger to support that. I guess these people are indeed “experts”. On the other hand, I just don’t know any responsible and knowledgeable people who would state that there have been any Bell experiments without loopholes. If you know such people, quote them. Maybe you know somebody who knows something that Genovese, Shimony and Zeilinger don’t know about Bell experiments.

As for the “stupendous conclusion”, strictly speaking, there is no such “conclusion” as “Bell "inequalities cannot be violated either in experiments or in quantum theory"”, there is actually the following statement, which you quote earlier: “there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory.” This is a very different statement, and I support it with the relevant arguments.

And how on earth is this 'compatible' with your initial statement:
?:confused:?
And how on earth is it “incompatible”? I insist that I said “little, if anything, new … about the Bell theorem”, as I mostly outlined other people’s arguments, and I insist that the “article is not about the Bell theorem”, it is about a specific model. I just could not offer a local realistic model and avoid a discussion of the Bell theorem.
I trust in RUTA (Mark Stuckey). He’s a working PhD Professor of Physics:
This is no place for a pissing contest, but if you wish to know more about my background, let me know, and I’ll send you a PM.
(My emphasis)
Again, with all due respect, Ruta is not the only one to go to conferences on foundations of quantum theory, and my impression is somewhat different. Maybe we go to different conferences?:-)
Anyway, these issues are not decided by popular vote. For example, as far as I understand, there was a consensus in 1952 that hidden variable theories are not possible, but Bohm’s work proved otherwise. I like this saying: “It is difficult to make forecasts, especially for the future”:-)
I looked at your homepage (http://www.akhmeteli.org/) and there are no references at all...?
References to what? If for peer reviewed articles, let me know, and I’ll PM you.
To me, this looks like "personal speculations", and not mainstream physics:
I gave references and arguments in this thread to support these statements. Anyway, which one (or two) of them are you challenging? Let’s talk specifics, not perceptions.

And to be frank, your reasoning also looks dim. You are claiming a Local Realistic Model (LRM) that is not capable of violating Bell's Inequality, but that doesn’t matter, because – "these inequalities cannot be violated either in experiments or in quantum theory".
Again, I’m not saying “they cannot”, I am saying “there are reasons to believe they cannot”, these are very different statements.

Exactly how do you derive "cannot" from your previous statements ...?:eek:?
Again, I don’t derive “cannot”, I derive “there are reasons to believe they cannot”. Exactly how? Just offering the reasons for that. You challenge my reasons? Again, how about some specifics, rather than perceptions?

akhmeteli

Jul26-10, 11:14 PM

If the prediction is wrong, then QM is wrong. That's the bold assertion I'm fishing for :-)

I am not sure this is a bold assertion for the reasons given in my post 252 in this thread.

Given the preponderance of experimental evidence

Well, you see "preponderance of experimental evidence". My take is: no violations of the genuine Bell inequalities have been demonstrated. 46 years and counting after Bell. I already offered this quote from Heller's "Catch-22" some time ago:

"I've got just the twelve-year-old virgin you're looking for," he announced jubilantly. "This twelve-year-old virgin is really only thirty-four, but she was brought up on a low-protein diet by very strict parents and didn't start sleeping with men until"

So I am sure all those experiments were "brought up on a low-protein diet by very strict parents".

and the highly contrived nature by which loop holes must exist to explain away violations of Bell inequalities, the foundations community has long ago abandoned any attempt to save local realism.

I respect the foundations community. But when I see that the simple local realistic model of my article (nothing contrived about it) has the same unitary evolution as a quantum field theory, I do become suspicious about quantum magic...

But, you're right, there are no truly "loop hole free" experiments,

Thank you:-) Some otherwise knowledgeable people in this thread vehemently deny that...:-)

Are you talking about the measurement problem?

Yes, I do.

That applies to all QM predictions, not just those that violate Bell inequalities.

Yes, but Bell takes the postulates of standard quantum theory to the extreme. So do I get it right that you agree with both of the following points? :-)

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

akhmeteli

Jul27-10, 12:24 AM

P.S. akhmeteli

It would be interesting to hear your view on this:

I don't quite get it - I give this very Shimony's quote in my article. So my opinion is the same: this quote confirms that there have been no loophole-free demonstrations of violations.

And while you’re at it: Could you please explain why not one (1) EPR-Bell experiment so far has clearly favored Local Realistic Theories? Not one (1).

What would you need to say that an experiment clearly favors local realistic theories? A discrepancy with quantum theory? But quantum theory is a damn good theory, furthermore, I believe unitary evolution of quantum theory is precisely correct, and we will not see any discrepancy with it for the next 200 years:-) As for the projection postulate... I don't quite know, maybe it is a good approximation, maybe decoherence masks discrepancy with the postulate, but I don't really care, because the projection postulate clearly contradicts unitary evolution, so one of these principles will be found deficient eventually.

I would also add that the entire body of Bell experiments does provide some support to local realistic theories as no genuine violations have been found yet, many years after Bell.

And, if you have some extra spare time: Could you also explain how nature is providing the "detection loophole", which is regarded as the most 'severe'. I mean, if you look at this slide from Alain Aspect, it’s clear that this "magic LRM function" must be wobbling between "too much" and "too little" to provide the measured data. And last but not least, this "magic LRM function" must KNOW which photons are entangled or not!?!? (Looks like a very "spooky function" to me... :bugeye:)

I don't know. I cannot offer any specifics here. But when I see that a simple local realistic model has the same unitary evolution as a quantum field theory, I conclude that LR models can emulate much more than we can imagine.

zonde

Jul27-10, 02:49 AM

So, QM is alright as long as you don't have entangled states? Restrictions on applicability are acceptable when a theory is superceded, e.g., Newtonian dynamics is ok when v << c and was superceded by SR to account for v ~ c, but no one has a theory superceding QM that gets rid of its entangled states. And, unlike v ~ c prior to SR, we have the means to create and explore entangled states and all such experiments vindicate QM.

No, zonde, this is not a mere restriction on the applicability of QM.
Absence of absolute preferred frame for electric and magnetic fields was recognized before SR. And there were experiments that explored duality of electric and magnetic fields.
SR does not appeared in empty place without any evidence about shortcomings of existing models. The same for GR.

As to QM existing experiments of entangled photon states take prediction about perfect correlations for matching measurement settings as given while there is no good evidence about it. So there is no viable alternative to QM with that assumption taken as true. But test this assumption and if (when) it fails there might appear new models very quickly.

Dmitry67

Jul27-10, 03:52 AM

Why if multi-history argument can be used to 'save' LR, it is not used by the die-hard local realists?

DevilsAvocado

Jul27-10, 03:59 AM

As for the “stupendous conclusion”, strictly speaking, there is no such “conclusion” as “Bell "inequalities cannot be violated either in experiments or in quantum theory"”, there is actually the following statement, which you quote earlier: “there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory.” This is a very different statement, and I support it with the relevant arguments.
Maybe it’s because English is not my native language, but I interpret this quote as: there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory, EVER.

To do statements like this, that is indistinct, is not fair. Also to connect Anton Zeilinger with this ambiguous statement is in fact bogus – because Zeilinger would never say that Bell's Inequalities can NEVER be violated in Bell experiments. Why? How can I be sure?? Well, the man is working every day, as the leading expert, on violating Bell's Inequalities in various Bell experiments. Only a madman would do that, if he already knew that it would NEVER be possible.

Mixing statement as the first, with this one, is just confusing:

there seems to be a consensus among experts that "a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing".”, then I quoted Genovese , Shimony, Aspelmeyer and Zeilinger to support that.

Why not include this quote, to give a 'slightly' more unbiased picture?
Stanford Encyclopedia of Philosophy – Bell's Theorem
...
In the face of the spectacular experimental achievement of Weihs et al. and the anticipated result of the experiment of Fry and Walther there is little that a determined advocate of local realistic theories can say except that, despite the spacelike separation of the analysis-detection events involving particles 1 and 2, the backward light-cones of these two events overlap, and it is conceivable that some controlling factor in the overlap region is responsible for a conspiracy affecting their outcomes. There is so little physical detail in this supposition that a discussion of it is best delayed until a methodological discussion in Section 7.

In the light of above, statements like this one can only regarded as wild "personal speculations":
I would also add that the entire body of Bell experiments does provide some support to local realistic theories as no genuine violations have been found yet, many years after Bell.

Personally, I don’t get it. You are claiming that both EPR-Bell experiments and Bell's Theorem are wrong, but you cannot give any specific proofs for that statement:
I don't know. I cannot offer any specifics here. But when I see that a simple local realistic model has the same unitary evolution as a quantum field theory, I conclude that LR models can emulate much more than we can imagine.

How about imagine two polarizers rotating independently random at very high speed between 0º and 360º, separated by 20 km which takes light 66 microseconds, and the final relative angle between the two polarizers are set the last 100 nanoseconds.

Also imagine the relative angle was measured at 22.5º which gives cos^2(22.5) = 85% correlation between Alice & Bob.

Now please tell me exactly how your "LR model" can 'emulate' this experimental fact?

If you can’t deliver an answer – then please stop saying that you have a working "LR model", because you don’t.

DevilsAvocado

Jul27-10, 04:00 AM

Why if multi-history argument can be used to 'save' LR, it is not used by the die-hard local realists?

Very good question Dmitry67!

DevilsAvocado

Jul27-10, 05:10 AM

Personally I lean strongly towards MWI type interpretations, I think Occam's razor just says our theoretical assumptions should be fairly simple but it doesn't say that the actual number of entities predicted by the theory should be small (for example, it's no strike against current cosmological theories that they postulate a huge number of stars in the observable universe, and likely many more--perhaps an infinite number--beyond the limits of what we can observe).

Okay, that sounds reasonably fair, but I was thinking more like: Could we really regard MWI as simpler solution than nonlocality?

And I also have some 'difficulty' (in line of RUTA's last post) about all possible outcomes...

As I understand – if there is a slightest possibility for an outcome, it will happen in one of MWI worlds. Therefore, in one of the MWI worlds: I must be a most appreciated Nobel Laureate, happily married to Kim Basinger and Michelle Pfeiffer, and I’m winning on the lottery every day, millions.

Why doesn’t this happen in "our world"?? My "personal luck" is not important – but in all random possibilities that happen all the time, every day, we should see something somewhere that doesn’t fit our "classical assumptions". But we don’t see that...?

Why!?

zonde

Jul27-10, 06:14 AM

Dmitry67

Jul27-10, 06:17 AM

Why doesn’t this happen in "our world"?? My "personal luck" is not important – but in all random possibilities that happen all the time, every day, we should see something somewhere that doesn’t fit our "classical assumptions". But we don’t see that...?

MWI has a problem with Born rule.
It is not clear why, while ALL weird world exist, the ones with low 'intensity' are somehow less important.
My personal opinion is that the Born rule is an artifact created my our consciousness (like the very special moment of time called NOW - so important for us, and having 0 value in block world and 0 explanation in physics). It is also might be a result of entropy of consciousness (or consciousness is not 1 MWI branch, but a set of branches, distinguished microscopically, but changing nothing to state of consciousness)

In any case, it would be very nice to have:
1. An analysis of Bell from MWI point of view
2. Entropy from MWI point of view (any links?)

RUTA

Jul27-10, 08:07 AM

Unitary evolution and projection postulate are not contradicting.

They are insidiously contradicting. See the chapter on the measurement problem in Quantum Mechanics and Experience, David Z. Albert, Harvard Univ Press, 1992, ISBN 0-674-74113-7.

RUTA

Jul27-10, 08:22 AM

Yes, but Bell takes the postulates of standard quantum theory to the extreme. So do I get it right that you agree with both of the following points? :-)

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

1) Yes, but the loop holes that exist, if realized in Nature, would mean Nature is extremely contrived -- a giant conspiracy to "trick" us. No one that I know in the foundations community believes this is the case.

2) Yes, but the measurement problem is a problem for QM as a whole and does not allow for the selective dismissal of any particular QM result without impugning all of QM. And, QM works very well even though it's not a rigorously self-consistent formal system (same can be said of QFT).

zonde

Jul27-10, 08:36 AM

They are insidiously contradicting. See the chapter on the measurement problem in Quantum Mechanics and Experience, David Z. Albert, Harvard Univ Press, 1992, ISBN 0-674-74113-7.
Unfortunately I don't have access to this book but as I understand the contradiction is usually considered to be related to unclear definition of what constitutes measurement.
But I just gave clear distinction between measurement and unitary evolution.
So if you there other considerations or if you don't agree with my definition then maybe you can give more specific comments.

zonde

Jul27-10, 08:45 AM

1) Yes, but the loop holes that exist, if realized in Nature, would mean Nature is extremely contrived -- a giant conspiracy to "trick" us.
No it it is not contrived. You just take away interference term in equation describing entangled state and you have restored it to product state - not contrived at all, rather very elegant.
Interesting thing is that you can do it physically in experiment by manipulation temporal walkoff.

DrChinese

Jul27-10, 09:19 AM

So do I get it right that you agree with both of the following points? :-)

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

Disagree, as we have already been through this many times. There is nothing BUT evidence of violation of Bell Inequalities. To use a variation on your 34 year old virgin example:

Prosecutor: "We found the suspect over the victim, holding the murder weapon. The victim's last words identified the suspect as the perp. The murder weapon was recently purchased by the suspect, and there are witnesses who testified that the suspect planned to use it to kill the victim." Ah, says the defense attorney, but where is the photographic evidence of the crime itself? This failure is proof of the suspect's innocence!

You can always demand one more nail in the coffin. In fact, it is good science to seek it. But the extra nail does not change it from "no experimental evidence" (as you claim) to "experimental evidence". It changes it from "overwhelming experimental evidence" (my claim) to "even more overwhelming experimental evidence".

As to the second of your assertions: how QM arrives at its predictions may be "inconsistent" in your book. But it does not cause a local realistic theory to be any more valid. If QM is wrong, so be it. That does not change the fact that all local realistic theories are excluded experimentally.

RUTA

Jul27-10, 10:48 AM

No it it is not contrived. You just take away interference term in equation describing entangled state and you have restored it to product state - not contrived at all, rather very elegant.
Interesting thing is that you can do it physically in experiment by manipulation temporal walkoff.

You can prevent or destroy entangled states very easily -- making and keeping them entangled is the difficult part. There is no getting around violations of Bell inequalities by entangled states in certain situations unless you destroy the situations, which is, again, easy to do.

RUTA

Jul27-10, 10:54 AM

Unfortunately I don't have access to this book but as I understand the contradiction is usually considered to be related to unclear definition of what constitutes measurement.
But I just gave clear distinction between measurement and unitary evolution.
So if you there other considerations or if you don't agree with my definition then maybe you can give more specific comments.

You used the phrase "in the case of measurement." That is the problem, we don't have a definition for what constitutes a "measurement." We know it when we see it, so we know how to use QM, that's not the problem.

I'm not going to type 100 pages of Albert's text explaining exactly how it's a problem. Get the book and read it; maybe someone here can suggest an alternative reading if you can't find Albert.

akhmeteli

Jul27-10, 10:59 AM

Nowhere in that quote do they imply it is true in general that "if X is true when condition Y but not condition Z holds, and X is also true when condition Z but not condition Y holds, then we can assume X is true when both conditions Y and Z hold simultaneously". Rather they refer to the specific conditions of the experiment when they say "It is very unlikely that such an experiment will disagree with the prediction of quantum mechanics, since this would imply that nature makes use of both the detection loophole in the Innsbruck experiment and of the locality loophole in the NIST experiment." It's quite possible (and I think likely) that the reason they consider it "unlikely" is because a theory making use of both loopholes would be very contrived-looking.
Then maybe you are drawing a distinction that is too fine for me:-). Indeed, your rephrasing of their phrase can be successfully applied to my statement about Euclidian geometry:-) Until you have an actual geometry in your possession, you can also argue that a theory “making use of both loopholes would be very contrived-looking”.

You addressed it by suggested your own model was non-contrived, but didn't give a clear answer to my question about whether it can actually give statistical predictions about experiments so far like the Innsbruck experiment and the NIST experiment
I did not give you a clear answer because I don’t have it and don’t know how to obtain it within a reasonable time frame. You want me to emulate the above experiments in “my” model. Generally speaking, this is a reasonable request. However, so far I can see only one way to address it: approximate the initial state(s) of those experiments by some fields and run the equations of the nonlinear electrodynamics over a relatively long time period and in a relatively large spatial volume (to ensure reasonable separation). Conducting such a numerical experiment in a clean way (and no other way is good enough) does not seem easy. There may also be some other complications with emulating switching detectors “in flight”. This seems like a lot of work, and I certainly have other priorities.
Therefore, so far my reasoning is different. Let me ask you this: if I offered a model that would have the same unitary evolution as quantum electrodynamics, not just “a” quantum field theory, would that suggest that the actual results of past experiments may be successfully emulated in this model? I’ll proceed (or not, depending on your answer) when I have your answer.
(or any experiments whatsoever, see below)
As I said, the model gives predictions for probabilities the same way Bohmian mechanics does that – you yourself described the relevant procedure. So let me ask you another question: do you think that Bohmian mechanics offers expressions for probabilities? If yes, then how “my” model is different from Bohmian mechanics that it cannot give expressions for probabilities? (its locality should not be a problem in this respect). More specifically, charge density can be calculated in my model, and it can be regarded as probability density (up to a certain factor).
--if it can't, then it obviously doesn't disprove the claim that any local realist theory consistent with experiments so far would have to be very contrived!
I contend that, strictly speaking, it does not disprove that claim, but has that claim been ever proven, in the first place? I have not heard about any “proof” of that claim, only some (pretty vague) arguments. Have you? Similarly, “my” model is, if not a “disproof”, an argument against this claim.
OK, but can your model actually give "correct predictions about statistical results" for any actual experiments, or does it only reproduce the unitary evolution? If it can't predict actual real-valued statistics that are measured empirically, as opposed to complex amplitudes, then it isn't a local realist model that can explain any existing experiments
See above, starting with words “As I said, the model gives predictions”.
(you may be able to derive probabilities from amplitudes using many-worlds type arguments, but as I said part of the meaning of 'local realism' is that each measurement yields a unique outcome)
Again, as I said, “local realism” does not necessarily require that “each measurement yields a unique outcome” (see also below), and I don’t need any “many-worlds type arguments”.
Suppose we do a Wigner's friend (http://en.wikipedia.org/wiki/Wigner%27s_friend) type thought-experiment where we imagine a small quantum system that's first measured by an experimenter in an isolated box, and from our point of view this just causes the experimenter to become entangled with the system rather than any collapse occurring. Then we open the box and measure both the system and the record of the previous measurement taken by the experimenter who was inside, and we model this second measurement as collapsing the wavefunction. If the two measurements on the small system were of a type that according to the projection postulate should yield a time-independent eigenstate, are you claiming that in this situation where we model the first measurement as just creating entanglement rather than collapsing the wavefunction, there is some nonzero possibility that the second measurement will find that the record of the first measurement will be of a different state than the one we find on the second measurement? I'm not sure but I don't think that would be the case--even if we assume unitary evolution, as long as there is some record of previous measurements then the statistics seen when comparing the records to the current measurement should be the same as the statistics you'd have if you assumed the earlier measurements (the ones which resulted in the records) collapsed the wavefunction of the system being measured according to the projection postulate.
Sorry, JesseM, I cannot accept this argument. The reason is as follows. If you take unitary evolution seriously (and I suspect you do), then you may agree that unitary evolution does not allow irreversibility, so, strictly speaking, no “record” can be permanent, so a magnetic domain on a hard disk can flip, furthermore, ink in a lab log can disappear, however crazy that may sound. If you challenge that, you challenge unitary evolution, if you challenge unitary evolution, there’s little left of quantum theory. Furthermore, in our previous discussion, I argued that even death (we were talking abot Schroedinger’s cat), strictly speaking, cannot be permanent because of unitary evolution and the quantum recurrence theorem. A superposition just cannot be destroyed.
In any case, the projection postulate does not actually specify that each "measurement" must collapse the wavefunction onto an eigenstate in cases where you're performing a sequence of different measurements. The "pragmatic recipe" is entirely compatible with the notion that in a problem like this, the projection postulate should only be used once at the very end of the complete experiment, when you make a measurement of all the records that resulted from earlier measurements.
It is not so important for this thread how the “pragmatic recipe” is used in general, it is important how the projection postulate is used in the proof of the Bell theorem: it is supposed that as soon as you measure the spin projection of one particle, the spin projection of the other particle becomes definite immediately, according to the projection postulate. So the projection postulate is not "only" used here “at the very end of the complete experiment”, so you have highlighted an important point.

I hope I’ll be able to address your other points later.

akhmeteli

Jul27-10, 11:37 AM

This is how I get it, and I apologize in advance if it’s wrong:

According to akhmeteli, the LRM does not violate the Bell inequalities, but that doesn’t matter much, because according to akhmeteli, there are no experimental evidence of violations of Bell's Inequalities so far, and Bell's Theorem is faulty in using two mutually contradicting postulates of QM.

If I’m right, it doesn’t impress me... all he’s saying is that EPR-Bell experiments & Bell's Theorem are wrong, without delivering any proofs for that claim.

I would prefer different wordings.

I am not saying that EPR-Bell experiments are wrong, I hope most of them were performed with proper care and professionalism. I am saying (and support this with quotes) that in each and every such experiment there was at least one loophole, therefore, there was no evidence of violations of the genuine Bell inequalities.

I am not quite saying the Bell theorem is wrong. My take is it uses postulates of standard quantum theory to derive some implications. I don't see any holes in the derivation. However, the input postulates are mutually contradictory (I support this statement with arguments and references), so they cannot be true simultaneously.

So, while I agree that no local realistic theory can emulate ALL predictions of standard quantum theory, I argue that this cannot be an argument against local realistic theories as, on the one hand, those predictions are mutually contradictory, on the other hand, in the part that eliminates local realistic theories (i.e. where Bell ineqs are violated) those predictions have no experimental confirmation.

Note that Ruta basically agreed with my points 1) and 2) in his post 618. True, he immediately "butted" his agreement, but I'd say his "buts" are supported by opinions, not by facts.

GeorgCantor

Jul27-10, 11:46 AM

I am saying (and support this with quotes) that in each and every such experiment there was at least one loophole, therefore, there was no evidence of violations of the genuine Bell inequalities.

Do you know of a totally 100% loophole-free experiement from anywhere in the universe?

akhmeteli

Jul27-10, 11:51 AM

akhmeteli: My big question for your model is a familiar one. If it is local realistic, can you tell me what the correct (if QM is wrong in this regard) statistical predictions are for coincidences at a, b, c = 0, 120, 240 degrees? Can you supply a dataset which is in indicative of the rules of your model?

Alice:
a b c
+ - +
- + +
- - +
+ - -

... or whatever you imagine a batch of Alices to be, independent of Bob. A local realistic model should be able to provide this. If not, it does not fulfill the claim of being realistic. And please, do not point me to your paper as proof. The proof is in the pudding, and I am looking to taste some.

Please see my reply to JesseM in post 624 in this thread (starting with words "I did not give you a clear answer").

To summarize: yours is a reasonable request, but I cannot address it within a reasonable time frame - seems like a lot of work for this model, and I have other priorities.

DrChinese

Jul27-10, 12:22 PM

Do you know of a totally 100% loophole-free experiement from anywhere in the universe?

Great point. So there is no evidence for GR either. :biggrin:

There is another issue with akhmeteli's line of reasoning IF CORRECT: there is a currently unknown local force which connects Alice and Bob. This kicks in on Bell tests like Rowe et al which closes the detection loophole. But not otherwise as far as we know.

There is also a strong bias - also previously unknown and otherwise undetected - which causes an unrepresentative sample of entangled pairs to be detected. This kicks in on Bell tests such as Weihs et al, which closes the locality loophole. Interestingly, this special bias does NOT appear when all pairs are considered such as in Rowe, however, the effect of the unknown local force is exactly identical. What a happy coincidence!

And so on for every loophole when closed individually. All the loopholes have exactly the same effect at every angle setting! And if you leave 2 open instead of 1, you also get the same effect! (I.e. if you leave the locality and detection loopholes open simultaneously, the effect is the same as either one individually.)

Stangely, the entanglement effect (remember that this is just a coincidence per Local Realism) completely disappears if you learn the values of Alice and Bob. Just as QM predicts, but surprisingly, quite contrary to the ideals of Local Realism. After all, EPR thought that you could beat the HUP with entangled particle pairs, and yet you can't!

So to summarize: akhmeteli is essentially asserting that a) 2 previously unknown and otherwise undetected effects exist (accounting for the loopholes); b) these effects are not only exactly equal to each other but are also equal to their combined impact; and c) an expected ability to beat the HUP (per EPR's local realism) has not materialized.

akhmeteli

Jul27-10, 01:15 PM

Maybe it’s because English is not my native language, but I interpret this quote as: there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory, EVER.
Yes, that is exactly what I mean:-)
To do statements like this, that is indistinct, is not fair.
Why so? I give my reasons, don’t I?
Also to connect Anton Zeilinger with this ambiguous statement is in fact bogus
I did not connect Zeilinger “with this ambiguous statement”, I connected him with his unambiguous quote.
– because Zeilinger would never say that Bell's Inequalities can NEVER be violated in Bell experiments. Why? How can I be sure?? Well, the man is working every day, as the leading expert, on violating Bell's Inequalities in various Bell experiments. Only a madman would do that, if he already knew that it would NEVER be possible.
I did not say he does not expect experimental demonstrations of genuine violations. I did not accuse him of being a fan of local realism:-) – nobody of them (Shimony, Zeilinger, Genovese) is. That makes their quotes even more valuable – they all reluctantly admit that there have been no loophole-free demonstrations of violations.
Mixing statement as the first, with this one, is just confusing:
How can this be confusing? Those experts are telling us, mere mortals, that there have been no loophole-free Bell experiments. You are certainly free to disagree with them, but then why don’t you just pinpoint that loophole-free experiment? And it would be most helpful if you could explain how it so happened that Shimony, Zeilinger and Genovese have no knowledge whatsoever about this experiment.
Again, Ruta is no fan of local realism either, but he also admits that there are no such experiments.
So, to summarize, it seems obvious that there have been no such experiments so far (DrChinese will strongly disagree, but let me ask you, DevilsAvocado, what is your personal opinion?) I call this a reason to believe there will be no demonstrations of violations of genuine Bell inequalities ever. I concede that this is no proof, but I honestly cannot understand why this is not a “reason to believe”? As far as my article is concerned, it is my right to indicate that there have been no experiments ruling out local realism, so “my” model has the right to exist right now.

Why not include this quote, to give a 'slightly' more unbiased picture?
I could include it, no problem with that. But is there any mention of an already performed loophole-free experiment in this quote? Again, what is your personal opinion, after all, has there been such an experiment, or not?

In the light of above, statements like this one can only regarded as wild "personal speculations":
I believe numerous failed attempts to build a perpetuum mobile (PM) did give support to the idea that PM is impossible. How is experimental elimination of local realism different? (By the way, I just follow Santos’ reasoning here – of course, you are free to disagree with him, with me or anybody you want).

Personally, I don’t get it. You are claiming that both EPR-Bell experiments and Bell's Theorem are wrong, but you cannot give any specific proofs for that statement:
See my post 625

How about imagine two polarizers rotating independently random at very high speed between 0º and 360º, separated by 20 km which takes light 66 microseconds, and the final relative angle between the two polarizers are set the last 100 nanoseconds.

Also imagine the relative angle was measured at 22.5º which gives cos^2(22.5) = 85% correlation between Alice & Bob.

Now please tell me exactly how your "LR model" can 'emulate' this experimental fact?
Please see my reply to JesseM in post 624 in this thread (starting with words "I did not give you a clear answer").
If you can’t deliver an answer – then please stop saying that you have a working "LR model", because you don’t.
If I could give you an answer, you could ask me another 100 questions, but this is irrelevant to existence of the model. I insist that I offered an LR model having the same unitary evolution as a quantum field theory (QFT). It is certainly important how well or badly this model describes experimental results, but I think the model is important anyway, because it shows how a seemingly nonlocal QFT may be just a disguise for an LR model, so even if “my” LR is not very good at describing experimental results, some of its modifications may fare much better.

akhmeteli

Jul27-10, 01:24 PM

Unitary evolution and projection postulate are not contradicting.
Physical situations that correspond to two different evolutions are different.
In case of unitary evolution all particles from ensemble are preserved.
In case of measurement original ensemble is reduced to subensemble (or split in two or more subensembles).
This is clear difference between unitary evolution and measurement.

Measurement when you measure system that is in eigenstate in respect to operator does not reduce ensemble and that is the only case when measurement can be regarded as unitary evolution.

If "Unitary evolution and projection postulate are not contradicting", then the results for the subensemble should not contradict the results for the ensemble, however, they do contradict, as, unlike unitary evolution, the projection postulate destroys superposition and introduces irreversibility.

akhmeteli

Jul27-10, 02:02 PM

Ruta,

first off, thank you very much for agreeing with these points in principle, it's quite a relief after I have been trying hard (and in vain) to explain those points to otherwise knowledgeable people.

1) Yes, but the loop holes that exist, if realized in Nature, would mean Nature is extremely contrived -- a giant conspiracy to "trick" us. No one that I know in the foundations community believes this is the case.

I am sure you can separate facts from opinions. In this case you are talking about opinions. As I said, this matter cannot be resolved by popular vote.

2) Yes, but the measurement problem is a problem for QM as a whole and does not allow for the selective dismissal of any particular QM result without impugning all of QM. And, QM works very well even though it's not a rigorously self-consistent formal system (same can be said of QFT).

You just cannot reasonably demand that I embrace mutually contradicting postulates.

DrChinese

Jul27-10, 02:43 PM

I am sure you can separate facts from opinions.

You apparently cannot, as you put forth your opinions as fact. Further, you apparently cannot tell the difference between ad hoc speculation and evidence based opinions. To reasonable people, there is a difference.

There is a huge difference in your speculation on loopholes (notice how you cannot model the behavior of these despite your unsupported claims) and RUTA's opinions (which he can model nicely using both standard and original science).

DrChinese

Jul27-10, 03:05 PM

I insist that I offered an LR model having the same unitary evolution as a quantum field theory (QFT). It is certainly important how well or badly this model describes experimental results, but I think the model is important anyway, because it shows how a seemingly nonlocal QFT may be just a disguise for an LR model, so even if “my” LR is not very good at describing experimental results, some of its modifications may fare much better.

So basically, this version is useless as is (since it cannot predict anything new and cannot explain existing well); but you want us to accept that a future version might be valuable. That may be reasonable, I can see the concept and that is certainly a starting point for some good ideas. But it is a far cry to go from here to saying your point is really made. Santos, Hess and many others have gone down similar paths with similar arguments for years. Where did they end up?

It is clear to a lot of people that it is possible to construct models that emulate *some* of the predictions of QM in a local realistic manner. Cleaning up one tiny item (which I guess is your perceived inconsistency in QM) but breaking 2 more major ones (such as HUP, entanglement) is not a profitable start, in my opinion.

Please keep in mind that you should not expect to post speculative ideas in this forum with impunity. This forum is for generally accepted science.

JesseM

Jul27-10, 03:28 PM

Then maybe you are drawing a distinction that is too fine for me:-). Indeed, your rephrasing of their phrase can be successfully applied to my statement about Euclidian geometry:-) Until you have an actual geometry in your possession, you can also argue that a theory “making use of both loopholes would be very contrived-looking”.
Well, here I suppose I must appeal to mathematical and physical intuitions--I don't in fact think it's plausible that a smart mathematician living in the days before Euclidean and non-Euclidean geometry would believe the fact that a quadrangle on a plane and a triangle on a sphere have angles adding up to other than 180 should imply that only a "contrived" theory of geometry would agree with the conjecture that triangles in a plane have angles that sum to 180. In contrast, I think lots of very smart physicists would agree with the intuition that a local realist theory consistent with all past experiments but which predicted no Bell inequality violation in ideal loophole-free experiments would have to be rather "contrived". Perhaps one reason for this is that we know what is required to exploit each loophole individually--exploiting the detector efficiency loophole requires that in some pairs of particles, one of the pair has a hidden variable that makes it impossible to detect (see billschnieder's example in posts #113 and #115 on this thread (http://www.physicsforums.com/showthread.php?t=409161&page=8)), whereas exploiting the locality loophole requires that whichever member of the pair is detected first will send out some sort of signal containing information about what detector setting was used, a signal which causes the other particle to change its own hidden variables in just the right way as to give statistics that agree with QM predictions. Does your model contain both such features?
You addressed it by suggested your own model was non-contrived, but didn't give a clear answer to my question about whether it can actually give statistical predictions about experiments so far like the Innsbruck experiment and the NIST experiment
I did not give you a clear answer because I don’t have it and don’t know how to obtain it within a reasonable time frame.
OK, but then when I said "still I think most experts would agree you'd need a very contrived local realist model to get correct predictions (agreeing with those of QM) for the experiments that have already been performed, but which would fail to violate Bell inequalities (in contradiction with QM) in an ideal experiment", why did you respond by saying (in post #579) "I agree, "most experts would agree" on that. But what conclusions am I supposed to draw from that? That the model I offer is "very contrived"? After all, the question of whether your model is "contrived" is only relevant to my own statement if in fact your model can "get correct predictions ... for those experiments that have already been performed". If you don't yet know whether your model does this, then you can't offer it as a counterexample to the claim that any model that did do it would have to be very contrived.
You want me to emulate the above experiments in “my” model.
Yes, that would be needed to show that you have a model that's a counterexample to the "contrived" claim. And even if you can't yet apply your model to existing experiments in all their precise details, you could at least start by seeing what it predicts about some simplified Aspect-type experiment that closes the locality loophole but not the detector efficiency loophole, and another simplified experiment that closes the efficiency loophole but not the locality loophole, and see if it predicts Bell inequality violations here. As an even more basic step, you could just explain whether it has the two features I noted above: 1) hidden variables which ensure that some particles aren't detected, no matter how good the detectors, and 2) some sort of signal from the first measured particle that contains information about the detector setting, and a way for the other particle to alter its own hidden variables in response to this signal.
Therefore, so far my reasoning is different. Let me ask you this: if I offered a model that would have the same unitary evolution as quantum electrodynamics, not just “a” quantum field theory, would that suggest that the actual results of past experiments may be successfully emulated in this model? I’ll proceed (or not, depending on your answer) when I have your answer.
Unitary evolution only predicts complex amplitudes, not real-valued probabilities. If you have some model that predicts actual statistics in a local way, and whose predictions agree with those of unitary evolution + the Born rule, then say so--but of course unitary evolution + the Born rule predicts violations of Bell inequalities even in loophole-free experiments, and you said earlier that you weren't claiming your model could give BI violations even in loophole-free experiments. So your claims about your model are rather confusing to say the least.
As I said, the model gives predictions for probabilities the same way Bohmian mechanics does that
When did you say that?
– you yourself described the relevant procedure.
I don't remember describing a procedure for getting probabilities in Bohmian mechanics, what post are you talking about? Bohmian mechanics treats the position variable as special, its equations saying that particles have a well-defined position at all times, and measurement results all depend on position in a fairly straightforward way (for example, spin measurements can be understood in terms of whether a particle is deflected to a higher position or a lower position by a Stern-Gerlach apparatus). The equations for particle behavior are deterministic, but for every initial quantum state Bohmian mechanics posits an ensemble of possible hidden-variable states compatible with that measured quantum state, so probabilities are derived by assuming each hidden state in the ensemble is equally probable (this is analogous to classical statistical mechanics, where we consider the set of possible 'microstates' (http://en.wikipedia.org/wiki/Microstate_(statistical_mechanics)) compatible with a given observed 'macrostate' and treat each microstate as equally probable). Does all of this also describe how predictions about probabilities are derived in your model? If not, where does the procedure in your model differ?
So let me ask you another question: do you think that Bohmian mechanics offers expressions for probabilities? If yes, then how “my” model is different from Bohmian mechanics that it cannot give expressions for probabilities?
I'll answer that question based on your answer to my questions above.
(you may be able to derive probabilities from amplitudes using many-worlds type arguments, but as I said part of the meaning of 'local realism' is that each measurement yields a unique outcome)
Again, as I said, “local realism” does not necessarily require that “each measurement yields a unique outcome” (see also below), and I don’t need any “many-worlds type arguments”.
I think you may be misunderstanding what I mean by "unique outcome". Suppose the experimenter has decided that if he sees the result "spin-up" on a certain measurement he will kill himself, but if he sees the result "spin-down" he will not. Are you saying that at some specific time shortly after the the experiment, there may not be a unique truth about whether the experimenter is alive or dead at that time? If you do think there should be a unique truth, then that implies you do think that "each measurement yields a unique outcome" in the sense I meant. If you don't think there is a unique truth, then isn't this by definition a "many-world type argument" since you are positing multiple "versions" of the same experimenter?
Suppose we do a Wigner's friend type thought-experiment where we imagine a small quantum system that's first measured by an experimenter in an isolated box, and from our point of view this just causes the experimenter to become entangled with the system rather than any collapse occurring. Then we open the box and measure both the system and the record of the previous measurement taken by the experimenter who was inside, and we model this second measurement as collapsing the wavefunction. If the two measurements on the small system were of a type that according to the projection postulate should yield a time-independent eigenstate, are you claiming that in this situation where we model the first measurement as just creating entanglement rather than collapsing the wavefunction, there is some nonzero possibility that the second measurement will find that the record of the first measurement will be of a different state than the one we find on the second measurement? I'm not sure but I don't think that would be the case--even if we assume unitary evolution, as long as there is some record of previous measurements then the statistics seen when comparing the records to the current measurement should be the same as the statistics you'd have if you assumed the earlier measurements (the ones which resulted in the records) collapsed the wavefunction of the system being measured according to the projection postulate.
Sorry, JesseM, I cannot accept this argument. The reason is as follows. If you take unitary evolution seriously (and I suspect you do), then you may agree that unitary evolution does not allow irreversibility, so, strictly speaking, no “record” can be permanent, so a magnetic domain on a hard disk can flip, furthermore, ink in a lab log can disappear, however crazy that may sound.
I agree, but I think you misunderstand my point. Any comparison of the predictions of the "standard pragmatic recipe" with another interpretation like the MWI's endless unitary evolution must be done at some particular time--what happens in the future of that time doesn't affect the comparison! My point is that if we consider any series of experiments done in some finite time window ending at time T1, and at T1 we look at all records existing at that time in order to find the statistics, then both of the following two procedures should yield the same predictions about these statistics:

1) Assume that unitary evolution applied until the very end of the window, so any measurements before T1 simply created entanglement with no "wavefunction collapse", then take the quantum state at the very end and use the Born rule to see what statistics will be expected for all records at that time

2) Assume that for each measurement that left an (error-free) record which survived until T1, that measurement did collapse the wavefunction according to the projection postulate, with unitary evolution holding in between each collapse, and see what predictions we get about the statistics at the end of this series of collapses-with-unitary-evolution-in-between.

Would you agree the predicted statistics would be the same regardless of which of these procedures we use? If you do agree, then I'd say that means the standard pragmatic recipe involving the projection postulate should work just fine for any of the types of experiments physicists typically do, including Aspect-type experiments. The only time the projection postulate may give incorrect statistical predictions about observations is if you treat some measurement as inducing a "collapse" even though the information about that measurement was later "erased" in a quantum sense (not just burning the records or something, which might make the information impossible to recover in practice but not necessarily in principle), but in any case the rules for using the projection postulate are not really spelled out and most physicists would understand that it wouldn't be appropriate in such a case.
If you challenge that, you challenge unitary evolution, if you challenge unitary evolution, there’s little left of quantum theory. Furthermore, in our previous discussion, I argued that even death (we were talking abot Schroedinger’s cat), strictly speaking, cannot be permanent because of unitary evolution and the quantum recurrence theorem.
Quantum recurrence isn't really relevant, the question is just whether there was a unique truth about whether the cat was alive or dead at some specific time, not whether the cat may reappear in the distant future. As long as there is some record of whether the cat was alive or dead at time T it's fine for us to say there was a definite truth (relative to our 'world' at least), but if the records are thoroughly erased we can't say this.
It is not so important for this thread how the “pragmatic recipe” is used in general, it is important how the projection postulate is used in the proof of the Bell theorem: it is supposed that as soon as you measure the spin projection of one particle, the spin projection of the other particle becomes definite immediately, according to the projection postulate. So the projection postulate is not "only" used here “at the very end of the complete experiment”, so you have highlighted an important point.
Well, see my point about the agreement in statistical predictions between method 1) and 2) above.

akhmeteli

Jul27-10, 03:58 PM

It is clear to a lot of people that it is possible to construct models that emulate *some* of the predictions of QM in a local realistic manner. Cleaning up one tiny item (which I guess is your perceived inconsistency in QM) but breaking 2 more major ones (such as HUP, entanglement) is not a profitable start, in my opinion.

I cannot address all your comments right now, but why do you think I am breaking HUP and entanglement? HUP is valid for scalar electrodynamics, and the projections of the generalized coherent states on (say) two-particle subspace of the Fock space are entangled states, so your statement is at least not obvious.

DrChinese

Jul27-10, 04:30 PM

I cannot address all your comments right now, but why do you think I am breaking HUP and entanglement? HUP is valid for scalar electrodynamics, and the projections of the generalized coherent states on (say) two-particle subspace of the Fock space are entangled states, so your statement is at least not obvious.

That is a reasonable comment.

1. I am guessing that for you, entangled particles have states in common due to their earlier interaction. Further, that entangled particles are in fact discrete and are not in communication with each other in any ongoing manner. And yet, it is possible to entangle particles that have never existed in a common light cone. My point is that won't go hand in hand with any local realistic view.

2. EPR argued that the HUP could be beaten with entangled particles. You could learn the value of position on Alice and the momentum of Bob. And yet, a subsequent observation of Alice's momentum cannot be predicted using Bob's value. (Of course this applies to all non-commuting pairs, including spin). So EPR is wrong in that regard. That implies that the reality of Alice is somehow affected by the nature of the observation of Bob. I assume you deny this.

JesseM

Jul27-10, 04:56 PM

I'm willing to spend time trying to figure out what you're saying unless it involves Many Worlds. The reason I dismiss Many Worlds is that if it's true, there's no way to do science. That is, if all possible outcomes are always realized, there are universes in which the participants don't get the right statistics, i.e., those that are dictating the split rates. And, there's no way any participant in any of the splits can know whether his results are the "correct" results or not. Therefore, you can't do science.
This seems more like a philosophical objection than a scientific one. Besides, according to the frequentist view of probability, it is always possible for the statistics seen on a finite number of trials to differ from the "true" probabilities that would obtain in the limit of an infinite number of trials (which are, if QM is correct, the probabilities given by applying the Born rule to the state of the wavefunction at the time of measurement), so the problem you point to isn't specific to a many-worlds framework. For example, if I run an experiment with 100 trials to collect statistics, if we looked at all trials of an experiment of this type that will ever be performed in human history, the number might be millions or billions, which means there will be a few cases where experimenters did a run of 100 or more trials and got statistics which differed significantly from the "correct" ones--how do I know my run wasn't one of those cases? The problem is even worse if we assume the universe is spatially infinite (as many cosmological models suppose), in which case it seems reasonable to postulate an infinite number of planets where intelligent life arises and performs the same sort of experiment--in this case even if we consider every trial of this type of experiment that has been done in the history of our planet, there should be some (very rare) civilizations where the statistics in every trial of the same type of experiment are badly off from the "correct" ones due to random statistical fluctuations, how can we know that we don't happen to be one of these? (philosophically I think the solution lies in adopting something along the lines of the self-sampling assumption (http://www.anthropic-principle.com/)) Do you think that the mere assumption of an infinite universe with an infinite number of civilizations makes it impossible to "do science"? If not, how is the many-worlds interpretation different?

JesseM

Jul27-10, 05:47 PM

And yet, it is possible to entangle particles that have never existed in a common light cone. My point is that won't go hand in hand with any local realistic view.
Just curious, how would this work?

DevilsAvocado

Jul27-10, 07:09 PM

Me too! I’m looking for it on PF but can’t find it!?

DevilsAvocado

Jul27-10, 07:41 PM

but let me ask you, DevilsAvocado, what is your personal opinion?

Okay, you asked for it. But first let’s make it perfectly clear: I’m only a layman. I trust people who are smarter than me 99% of the time. The last 1% is reserved for human errors, nobody is perfect, and even Einstein made mistakes. When it comes to the Scientific community (http://en.wikipedia.org/wiki/Scientific_community), these numbers naturally diverse even more.

My personal advice to an independent researcher:
1) Question your own work more than others, every day, especially if you are working alone.

2) Write down this quote and read it at least once every day:
"One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision." -- Bertrand Russell

3) Make sure you have read and understand every word in the article Wikipedia – Scientific method (http://en.wikipedia.org/wiki/Scientific_method) and especially the understanding of the four essential elements:

Characterizations
Hypotheses
Predictions
Experiments

I’m not saying this to be rude, just to tell you the truth – it looks like you have to work very hard on every advice.

Now, what’s my personal opinion on EPR-Bell experiments and loopholes? Well, I think you are presenting a terrible biased picture of the situation. You want us to believe that current experts in EPR-Bell experiments have the same bizarre valuation of their experiments as you have. Namely, that every performed EPR-Bell experiment so far is worth nothing?? Zero, zip, nada, zilch, 0!? :eek:

By your logic, Anton Zeilinger is going to work every day, and starts working on new experiments, which he already knows is not going to prove anything, once again, year after year...?:bugeye:?

This tells me that either your logic or Anton Zeilinger’s logic is extremely obtuse. And I already know where to place my bet...

Please, read this article (http://en.wikipedia.org/wiki/Dunning–Kruger_effect) and reevaluate your conclusion.

You are also trying to apply this faulty logic on RUTA:
Again, Ruta is no fan of local realism either, but he also admits that there are no such experiments.

Yes, RUTA is an honest scientist and he would never lie and say that a 100% loophole-free Bell experiment has been performed, when it hasn’t yet.

But where do you see RUTA saying that performed Bell experiments so far is worth absolutely nothing, nil!?!? Your twist is nothing but a scam:
Given the preponderance of experimental evidence and the highly contrived nature by which loop holes must exist to explain away violations of Bell inequalities, the foundations community has long ago abandoned any attempt to save local realism. But, you're right, there are no truly "loop hole free" experiments, so die hard local realists can cling to hope.
1) Yes, but the loop holes that exist, if realized in Nature, would mean Nature is extremely contrived -- a giant conspiracy to "trick" us. No one that I know in the foundations community believes this is the case.

This is of course exactly the same standpoint as Zeilinger et al. has, that you are quoting to "prove" something completely different!!

These are honest scientist that you are exploiting in a dishonest way to "prove" the opposite. What’s your excuse?? :grumpy:

I can guarantee you that RUTA, Zeilinger or any other real scientist in the community all agree that all performed EPR-Bell experiments so far has proven with 99.99% certainty that all local realistic theories are doomed. But they are fair, and will never lie, and say 100%, until they are 100%.

You are exploiting this fact in a very deceive way, claiming that they are saying that there is 0% proof of local realistic theories being wrong.

And then comes the "Grand Finale", where you use a falsification of Anton Zeilinger’s standpoint, as the "foundation" for this personal cranky statement:
"there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory, EVER"

Outrageous :mad:

RUTA

Jul27-10, 09:29 PM

This seems more like a philosophical objection than a scientific one. Besides, according to the frequentist view of probability, it is always possible for the statistics seen on a finite number of trials to differ from the "true" probabilities that would obtain in the limit of an infinite number of trials (which are, if QM is correct, the probabilities given by applying the Born rule to the state of the wavefunction at the time of measurement), so the problem you point to isn't specific to a many-worlds framework. For example, if I run an experiment with 100 trials to collect statistics, if we looked at all trials of an experiment of this type that will ever be performed in human history, the number might be millions or billions, which means there will be a few cases where experimenters did a run of 100 or more trials and got statistics which differed significantly from the "correct" ones--how do I know my run wasn't one of those cases? The problem is even worse if we assume the universe is spatially infinite (as many cosmological models suppose), in which case it seems reasonable to postulate an infinite number of planets where intelligent life arises and performs the same sort of experiment--in this case even if we consider every trial of this type of experiment that has been done in the history of our planet, there should be some (very rare) civilizations where the statistics in every trial of the same type of experiment are badly off from the "correct" ones due to random statistical fluctuations, how can we know that we don't happen to be one of these? (philosophically I think the solution lies in adopting something along the lines of the self-sampling assumption (http://www.anthropic-principle.com/)) Do you think that the mere assumption of an infinite universe with an infinite number of civilizations makes it impossible to "do science"? If not, how is the many-worlds interpretation different?

In the Single World, the predicted distribution is what each experimentalist should find and, indeed, our QM predictions match said distributions. In the Single World, a scientifically predicted distribution that didn't match experimentally obtained results would not be accepted. No scientist would say,"Hey, maybe we're just in that weird spot in an infinite universe?" No way, the theory is toast.

But, in Many Worlds, you're saying any unobserved outcomes in our universe are observed in other universes, so you automatically create aberrant distributions. In Many Worlds, unrealized outcomes aren't mere counterfactuals, they're instantiated. So, if you REALLY believe in Many Worlds, the best you can do is believe we're in that special universe where the REAL QM distributions obtain. But, you'd have to admit that there's no way to know.

Why would any scientist buy into a philosophy like that?

zonde

Jul28-10, 03:22 AM

You can prevent or destroy entangled states very easily -- making and keeping them entangled is the difficult part. There is no getting around violations of Bell inequalities by entangled states in certain situations unless you destroy the situations, which is, again, easy to do.
The point was not about that entangled states can be destroyed. The point is what you get after you destroy entangled state in a certain way. And it is not complete absence of any correlation but rater purely classical correlation that obeys local realism (not really predicted by QM prediction a la Bell).

Your point was that it would be contrived to assume that entangled state would disappear as we extend inefficient detection case toward efficient detection.
I gave you an example how this can happen in quite elegant way.

You used the phrase "in the case of measurement." That is the problem, we don't have a definition for what constitutes a "measurement." We know it when we see it, so we know how to use QM, that's not the problem.
Sorry, poor formulation. Let me rewrite it.
If all particles from ensemble are preserved that is unitary evolution.
If ensemble is reduce to subensemble this is measurement or decoherence (depends from analysis performed by experimenter).

zonde

Jul28-10, 03:34 AM

If "Unitary evolution and projection postulate are not contradicting", then the results for the subensemble should not contradict the results for the ensemble, however, they do contradict, as, unlike unitary evolution, the projection postulate destroys superposition and introduces irreversibility.
You consider ensemble as statistical ensemble of completely independent members where each member possess all the properties of ensemble as a whole, right?
Otherwise I do not understand how you can justify your statement.

DevilsAvocado

Jul28-10, 06:07 AM

Why would any scientist buy into a philosophy like that?

RUTA, since no one has showed me a "postcard" from one of the other myriads of MWI worlds, I’m on "your side" – but I think the answer is: Yes

And it’s not a bunch of unknown geniuses in Mongolia – it’s Stephen Hawking (http://en.wikipedia.org/wiki/Stephen_Hawking) & Steven Weinberg (http://en.wikipedia.org/wiki/Steve_Weinberg)!! :surprised

This makes me wonder if (maybe) I could be wrong... :smile:

RUTA

Jul28-10, 07:57 AM

RUTA, since no one has showed me a "postcard" from one of the other myriads of MWI worlds, I’m on "your side" – but I think the answer is: Yes

And it’s not a bunch of unknown geniuses in Mongolia – it’s Stephen Hawking (http://en.wikipedia.org/wiki/Stephen_Hawking) & Steven Weinberg (http://en.wikipedia.org/wiki/Steve_Weinberg)!! :surprised

This makes me wonder if (maybe) I could be wrong... :smile:

My question was rhetoric, of course. Most physicists subscribe to Mermin's "Shut up and calculate!" but of those (few) physicists who care about foundational issues, most subscribe to some variant of Many Worlds (no-collapse models). The reason is simple -- they're more concerned with issues of formalism and no-collapse models solve the measurement problem.

RUTA

Jul28-10, 07:59 AM

Sorry, poor formulation. Let me rewrite it.
If all particles from ensemble are preserved that is unitary evolution.
If ensemble is reduce to subensemble this is measurement or decoherence (depends from analysis performed by experimenter).

When you understand the measurement problem, come back and we'll talk about it.

DevilsAvocado

Jul28-10, 10:26 AM

When you understand the measurement problem, come back and we'll talk about it.

Could this maybe be helpful to zonde?

http://upload.wikimedia.org/wikipedia/en/thumb/b/b0/Observer-observed.gif/350px-Observer-observed.gif
Observer O measures the state of the quantum system S

:rolleyes:

DevilsAvocado

Jul28-10, 10:27 AM

My question was rhetoric, of course.

Okidoki, thanks.

DevilsAvocado

Jul28-10, 10:45 AM

MWI has a problem with Born rule.
It is not clear why, while ALL weird world exist, the ones with low 'intensity' are somehow less important.

... For example, if I run an experiment with 100 trials to collect statistics, if we looked at all trials of an experiment of this type that will ever be performed in human history, the number might be millions or billions, which means there will be a few cases where experimenters did a run of 100 or more trials and got statistics which differed significantly from the "correct" ones--how do I know my run wasn't one of those cases?

The problem I have with MWI is that: Yes, most of the times we will of course see the "correct" statistics. But to me it’s not clear how the "weird stuff" is always split into the few "weird worlds". This "weird stuff" should be "distributed" evenly among all worlds... if we stick to QM probability.

Then we should see some really unbelievable and crazy stuff now and then – but we don’t...??

DevilsAvocado

Jul28-10, 10:58 AM

Could someone please explain what’s "mutually contradicting" in this?
cos^2(a-b)

Even I can solve this 'equation' without any contradictions...

JesseM

Jul28-10, 01:29 PM

In the Single World, the predicted distribution is what each experimentalist should find and, indeed, our QM predictions match said distributions.
That's just not true, a finite number of trials will not always yield exactly the same statistics as the ideal probability distribution, statistical fluctuations are always possible. If you flip a coin 100 times, and the coin's physical properties are such that it has a 50% chance of landing heads or tails on a given flip, that doesn't imply you are guaranteed to get exactly 50 heads and 50 tails! In fact, if you have a very large collection of series of 100 flips, a small fraction of the series will have statistics that differ significantly from the true probabilities (the greater the 'significant' difference, the smaller the fraction)--eventually you might see some series where 100 flips of a fair coin yielded 80 heads and 20 tails. Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities. This might be a very tiny fraction, but then it's no smaller than the fraction of "worlds" that see the same type of departure from the true probabilities.

Do you disagree with any of the statements above? If so, what's the first one you would disagree with? If you don't disagree with any, perhaps you would indeed say it's impossible to "do science" in a universe where the number of civilizations is infinite (assuming there is indeed a random element to experiments that can't be eliminated with better experimental techniques, which would even be true in a deterministic hidden-variable model like Bohmian mechanics if it's impossible to measure/control the hidden variables). But I think this would be a pretty strange position to take, philosophically.

RUTA

Jul28-10, 01:55 PM

That's just not true, a finite number of trials will not always yield exactly the same statistics as the ideal probability distribution, statistical fluctuations are always possible. If you flip a coin 100 times, and the coin's physical properties are such that it has a 50% chance of landing heads or tails on a given flip, that doesn't imply you are guaranteed to get exactly 50 heads and 50 tails! In fact, if you have a very large collection of series of 100 flips, a small fraction of the series will have statistics that differ significantly from the true probabilities (the greater the 'significant' difference, the smaller the fraction)--eventually you might see some series where 100 flips of a fair coin yielded 80 heads and 20 tails. Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities. This might be a very tiny fraction, but then it's no smaller than the fraction of "worlds" that see the same type of departure from the true probabilities.

Do you disagree with any of the statements above? If so, what's the first one you would disagree with? If you don't disagree with any, perhaps you would indeed say it's impossible to "do science" in a universe where the number of civilizations is infinite (assuming there is indeed a random element to experiments that can't be eliminated with better experimental techniques, which would even be true in a deterministic hidden-variable model like Bohmian mechanics if it's impossible to measure/control the hidden variables). But I think this would be a pretty strange position to take, philosophically.

You obtain results with an uncertainty in experimental physics, so you only need the result to agree with theory within a certain range (that's the source of statements having to do with "confidence level"). For an introductory paper on how QM statistics are obtained (they even supply the data so you can reproduce the results yourself) see: "Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory," Dietrich Dehlinger and M. W. Mitchell, Am. J. Phys. v70, Sep 2002, 903-910. Here is how they report their result in the abstract, for example:

"Bell’s idea of a hidden variable theory is presented by way of an example and compared to the quantum prediction. A test of the Clauser, Horne, Shimony, and Holt version of the Bell inequality finds S = 2.307 +/- 0.035, in clear contradiction of hidden variable theories. The experiments described can be performed in an afternoon."

According to your view, they can't say "in clear contradiction," but that's standard experimental physics. And, if you were right, we couldn't do experimental physics. Thankfully, you're wrong :-)

JesseM

Jul28-10, 02:24 PM

You obtain results with an uncertainty in experimental physics, so you only need the result to agree with theory within a certain range (that's the source of statements having to do with "confidence level").
Yes, and no matter how many trials you do, as long as the number is finite there is some small probability that your results will differ wildly from the "true" probabilities determined by the laws of QM. For example, if in a particular experiment the QM prediction is that there is a 25% chance of seeing a particular result, then even if the experiment is done perfectly and QM is a correct description of the laws of physics, and even if you did a huge number of trials, there is some nonzero probability you would get that particular result on more than 90% of all trials, due to nothing but a statistical fluctuation. If the number of trials is large enough the probability of such a large statistical fluctuation may be tiny--say, one in a googol--but as long as the number of trials is finite the probability is nonzero.

If continue to disagree with what I'm saying about the situation with the MWI being no worse than the situation with an infinite universe containing an infinite number of civilizations, I'd appreciate an answer to my question about what specific statement in the chain of argument you disagree with:
That's just not true, a finite number of trials will not always yield exactly the same statistics as the ideal probability distribution, statistical fluctuations are always possible. If you flip a coin 100 times, and the coin's physical properties are such that it has a 50% chance of landing heads or tails on a given flip, that doesn't imply you are guaranteed to get exactly 50 heads and 50 tails! In fact, if you have a very large collection of series of 100 flips, a small fraction of the series will have statistics that differ significantly from the true probabilities (the greater the 'significant' difference, the smaller the fraction)--eventually you might see some series where 100 flips of a fair coin yielded 80 heads and 20 tails. Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities. This might be a very tiny fraction, but then it's no smaller than the fraction of "worlds" that see the same type of departure from the true probabilities.

Do you disagree with any of the statements above? If so, what's the first one you would disagree with?
For an introductory paper on how QM statistics are obtained (they even supply the data so you can reproduce the results yourself) see: "Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory," Dietrich Dehlinger and M. W. Mitchell, Am. J. Phys. v70, Sep 2002, 903-910. Here is how they report their result in the abstract, for example:

"Bell’s idea of a hidden variable theory is presented by way of an example and compared to the quantum prediction. A test of the Clauser, Horne, Shimony, and Holt version of the Bell inequality finds S = 2.307 +/- 0.035, in clear contradiction of hidden variable theories. The experiments described can be performed in an afternoon."
Presumably there was some confidence interval they used to get the error bars of +/- 0.035. For example, they might have calculated that the probability that S is greater than 2.307 + 0.035 or less than 2.307 - 0.035 is less than 5 sigma, or about an 0.00005% chance (perhaps based on considering a null hypothesis where S was outside of that range, and finding an 0.00005% that the null hypothesis would give a result of 2.307 in their experiment).
According to your view, they can't say "in clear contradiction," but that's standard experimental physics.
Whatever gave you the idea that I would say they can't say "in clear contradiction"? If the probability of getting statistics that depart appreciably from the true probabilities is miniscule, then we can be very confident our results are close to the true probabilities. This is true in an infinite universe with an infinite number of civilizations (you haven't told me what you think about this scenario), and it's just as true in the MWI.

RUTA

Jul28-10, 03:31 PM

Yes, and no matter how many trials you do, as long as the number is finite there is some small probability that your results will differ wildly from the "true" probabilities determined by the laws of QM. For example, if in a particular experiment the QM prediction is that there is a 25% chance of seeing a particular result, then even if the experiment is done perfectly and QM is a correct description of the laws of physics, and even if you did a huge number of trials, there is some nonzero probability you would get that particular result on more than 90% of all trials, due to nothing but a statistical fluctuation. If the number of trials is large enough the probability of such a large statistical fluctuation may be tiny--say, one in a googol--but as long as the number of trials is finite the probability is nonzero.

If continue to disagree with what I'm saying about the situation with the MWI being no worse than the situation with an infinite universe containing an infinite number of civilizations, I'd appreciate an answer to my question about what specific statement in the chain of argument you disagree with:

I disagree with this statement:

"Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities. This might be a very tiny fraction, but then it's no smaller than the fraction of "worlds" that see the same type of departure from the true probabilities."

In science, we expect every experiment to realize the proper distribution. You would never hear someone present aberrant data as "to be expected, based on the fact that an infinite number of civilizations are doing this very experiment." Most scientists would take this as a reductio against your particular interpretation of statistics in science.

Many Worlds is de facto in agreement with your interpretation. That's why I said (rhetorically), "Why would any scientist subscribe to Many Worlds?"

JesseM

Jul28-10, 06:02 PM

I disagree with this statement:

"Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities. This might be a very tiny fraction, but then it's no smaller than the fraction of "worlds" that see the same type of departure from the true probabilities."

In science, we expect every experiment to realize the proper distribution.
Are you saying we expect every experiment to exactly realize the proper distribution? If the probability of detecting some result (say, spin-up) is predicted by QM to be 0.5, would you expect that a series of 100 trials would yield exactly 50 instances of that result?

I would say instead that in science, we recognize that, given a large enough number of trials, the probability is very tiny that the statistics will differ significantly from the proper distribution (the law of large numbers (http://en.wikipedia.org/wiki/Law_of_large_numbers)). This "very tiny" chance can be quantified precisely in statistics, and it is always nonzero for any finite number of trials. But with enough trials it may become so small we don't have to worry about it, say a 1 in 10^100 chance that the observed statistics differ from the true probabilities by more than some amount epsilon (and in that case, we should expect that 1 in 10^100 civilizations that do the same number of trials will indeed observe statistics that differ from the true probabilities by more than that amount epsilon). From a purely statistical point of view (ignoring what assumptions we might make pragmatically for the purposes of doing science), do you think what I say here is incorrect?
You would never hear someone present aberrant data as "to be expected, based on the fact that an infinite number of civilizations are doing this very experiment."
No, but that's because it's extremely unlikely that our civilization would happen to be one of those that gets the aberrant result. That doesn't change the fact that in a universe with an infinite number of civilizations doing scientific experiments, any aberrant result will in fact occur occasionally.
Most scientists would take this as a reductio against your particular interpretation of statistics in science.
I disagree, I think this is a rather idiosyncratic perspective that you hold. Most scientists would not say that an infinite universe with an infinite number of civilizations, a very small fraction of which will see aberrant results throughout their history due to random statistical fluctuations, presents any problem for normal science, because again it's vanishingly unlikely that we happen to be living in one of those unlucky civilizations.

RUTA

Jul28-10, 08:51 PM

Are you saying we expect every experiment to exactly realize the proper distribution? If the probability of detecting some result (say, spin-up) is predicted by QM to be 0.5, would you expect that a series of 100 trials would yield exactly 50 instances of that result?

I assume that's rhetorical.

No, but that's because it's extremely unlikely that our civilization would happen to be one of those that gets the aberrant result. That doesn't change the fact that in a universe with an infinite number of civilizations doing scientific experiments, any aberrant result will in fact occur occasionally.

Just not here, right? Suppose X claims to have a source that produces 50% spin up and 50% spin down and X reports, "I have a 50-50 up-down source that keeps producing pure up results." If you REALLY believe that your interpretation of statistics in science is correct, then you would HAVE to admit that perhaps X is right. But, what will MOST scientists say? Of course, X is mistaken, he doesn't have a 50-50 source. Why? Because our theory is empirically driven, not the converse.

I disagree, I think this is a rather idiosyncratic perspective that you hold. Most scientists would not say that an infinite universe with an infinite number of civilizations, a very small fraction of which will see aberrant results throughout their history due to random statistical fluctuations, presents any problem for normal science, because again it's vanishingly unlikely that we happen to be living in one of those unlucky civilizations.

If your view is correct, you could find me a paper published with aberrant results. Can you find me a published paper with claims akin to X supra? Why not? Because the weird stuff only happens in "other places?" Not here?

JesseM

Jul28-10, 09:09 PM

I assume that's rhetorical.
Yes, but a literal interpretation of your statement "In science, we expect every experiment to realize the proper distribution" would imply every experiment should yield precisely the correct statistics. I was illustrating that this statement doesn't really make any sense to me. If you didn't mean it in the literal sense that the observed statistics should precisely equal the correct probabilities, what did you mean?
Just not here, right? Suppose X claims to have a source that produces 50% spin up and 50% spin down and X reports, "I have a 50-50 up-down source that keeps producing pure up results." If you REALLY believe that your interpretation of statistics in science is correct
Are you saying my statements are incorrect on a purely statistical level? If so, again, can you pinpoint which statement in the second paragraph of my last post is statistically incorrect?
then you would HAVE to admit that perhaps X is right.
If "perhaps" just means "the probability is zero", then yes. But if I can show the chance X is right is astronomically small, say only a 1 in 10^100 chance that a 50-50 source would actually produce so many up results in a row, then on a pragmatic level I won't believe him. Do you deny that statistically, the probability of getting N heads in a row with a fair coin is always nonzero, though it may be astronomically small if N is very large? If not, do you deny that in an infinite universe with an infinite number of civilizations flipping fair coins, there will be some that do see N heads in a row? These aren't rhetorical questions, I am really having trouble what part of my argument, specifically, you object to.
But, what will MOST scientists say? Of course, X is mistaken, he doesn't have a 50-50 source.
Of course, I'll say that too. Why wouldn't I? If it would require a statistical fluctuation with a probability of 1 in 10^100 for his theory to be right, then we can say his theory is wrong beyond all reasonable doubt, even if we can't have perfect philosophical certainty that his theory is wrong.
If your view is correct,
My view of what? Again, on a purely statistical sense are any of my statements incorrect? If so, which ones?
you could find me a paper published with aberrant results.
It depends what you mean by "aberrant". If you mean the sort of massive statistical fluctuation that probability theory would say has an astronomically small probability like 1 in 10^40 or whatever, then this is much larger than the number of scientific experiments that have been done in human history so I wouldn't expect any such aberrant results. If you just mean papers with good experimental design found some result to a confidence of two sigma or something, but later experiments showed the result was incorrect, I don't think it'd be that hard to find such a paper.

billschnieder

Jul28-10, 09:52 PM

Yes, but a literal interpretation of your statement "In science, we expect every experiment to realize the proper distribution" would imply every experiment should yield precisely the correct statistics.

Your argument does not make any sense to me so I am hoping you could clarify your understanding of the meaning of "probability". If a source has a 0.1-0.9 up-down probability, what does that mean in your understanding according to MWI. Does it mean 10% of the worlds will obtain 100% up and 90% of the worlds will obtain 100% down, or does it mean in every world, there will be 10% up and 90% down? It is not clear from your statements what you mean and what it has that got to do with "correct statistics"?

If I calculate the probability that the sun will explode tomorrow to be 0.00001, what does that mean in MWI. Is your understanding that I am calculating the probability of the sun in "my" world, exploding, or all the suns in the multiverse exploding or what exactly? Or do you think such a probability result does not make sense in science.

I think after attempting to respond to this issues you may appreciate why many wonder "Why would any scientist subscribe to Many Worlds?"

akhmeteli

Jul28-10, 10:24 PM

But there are two aspects of this question--the first is whether local realism can be ruled out given experiments done so far, the second is whether local realism is consistent with the statistics predicted theoretically by QM. Even if you don't use the projection postulate to generate predictions about statistics, you need some real-valued probabilities for different outcomes, you can't use complex amplitudes alone since those are never directly measured empirically. And if we understand local realism to include the condition that each measurement has a unique outcome, then it is impossible to get these real-valued statistics from a local realist model.
But I certainly don’t “understand local realism to include the condition that each measurement has a unique outcome”, not necessarily. You may believe that my understanding of local realism is not reasonable, but you may agree that “my” model is local realistic within common understanding of this term. I already said that you can define probability density in the model using the expression for the charge density.
No idea where you got the idea that I would be talking about "approximate" locality from anything in my posts. I was just talking about QM being a "pragmatic" recipe for generating statistical predictions, I didn't say that Bell's theorem and the definition of local realism were approximate or pragmatic. Remember, Bell's theorem is about any black-box experiment where two experimenters at a spacelike separation each have a random choice of detector setting, and each measurement must yield one of two binary results--nothing about the proof specifically assumes they are measuring anything "quantum", they might be choosing to ask one of three questions with yes-or-no answers to a messenger sent to them or something. Bell's theorem proves that according to local realism, any experiment of this type must obey some Bell inequalities. So then if you want to show that QM is incompatible with local realism, the only aspect of QM you should be interested in is its statistical predictions about some experiment of this type, all other theoretical aspects of QM are completely irrelevant to you. Unless you claim that the "pragmatic recipe" I described would actually make different statistical predictions about this type of experiment than some other interpretation of QM like Bohmian mechanics or the many-worlds-interpretation, then it's pointless to quibble with the pragmatic recipe in this context.
I don’t quite get it. First off, I concede that the Bell inequalities cannot be violated in local realistic theories. I don’t question this part of the Bell theorem. The second part of the Bell theorem states that the inequalities can be violated in QM. I don’t question the derivation of this statement, but I insist that its assumptions are mutually contradictory, making this statement questionable. You tell me that measurements typically involve environmental decoherence. I read the following implication from that (may be I was wrong): so there is no contradiction between unitary evolution (UI) and the projection postulate (PP). If you say that the difference between UI and PP has its root in environmental decoherence, I don’t have problems with that, but that does not eliminate the difference, or contradiction, between them. What I tried to emphasize, is you cannot declare this decoherence or any other root cause of the contradiction negligible, you cannot use any approximations to rule out local realism.
But that won't produce a local realist theory where each measurement has a unique outcome. Suppose you have two separate computers, one modeling the amplitudes for various measurements which could be performed in the local region of one simulated experimenter "Alice", another modeling the amplitudes for various measurements which could be performed in the local region of another simulated experimenter "Bob", with the understanding that these amplitudes concerned measurements on a pair of entangled particles that were sent to Alice and Bob (who make their measurements at a spacelike separation). If you want to simulate Alice and Bob making actual measurements, and you must assume that each measurement yields a unique outcome (i.e. Alice and Bob don't each split into multiple copies as in the toy model I linked to at the end of my last post), then if the computers running the simulation are cut off from communicating with one another and neither computer knows in advance what measurement will be performed by the simulated experimenter on the other computer, then there is no way that such a simulation can yield the same Bell-inequality-violating statistics predicted by QM, even if you program the Born rule into each computer to convert amplitudes into probabilities which are used to generate the simulated outcome of each measurement. Do you disagree that there is no way to get the correct statistics predicted by any interpretation of QM in a setup like this where the computers simulating each experimenter are cut off from communicating? (which corresponds to the locality condition that events in regions with a spacelike separation can have no causal effect on one another)
Again, I don’t need unique outcomes – no measurement is final
The problem is that there is no agreement on how the many-worlds interpretation can be used to derive any probabilities. If we're not convinced it can do so then we might not view it as being a full "interpretation" of QM yet, rather it'd be more like an incomplete idea for how one might go about constructing an interpretation of QM in which measurement just caused the measuring-system to become entangled with the system being measured.
Well, I don’t know much about many worlds, but anyway – it seems this problem does not prevent you from favoring many worlds.
See my comments above about the Wigner's friend type thought experiment. I am not convinced that you can actually find a situation where a series of measurements are made that each yield records of the result, such that using the projection postulate for each measurement gives different statistical predictions then if we just treat this as a giant entangled system which evolves in a unitary way, and then at the very end use the Born rule to find statistical expectations for the state of all the records of prior measurements. And as I said there as well, the projection postulate does not actually specify whether in a situation like this you should treat each successive measurement as collapsing the wavefunction onto an eigenstate or whether you should save the "projection" for the very last measurement.
I already said, first, that I disagree with your reading of this experiment, second, it is important how the projection postulate is used to prove violations in QM.

I wasn't guessing what he said, I was guessing what he meant by what he said. What he said was only the very short statement "Yes, it is an approximation. However, due to decoherence, this is an extremely good approximation. Essentially, this approximation is as good as the second law of thermodynamics is a good approximation." I think this statement is compatible with my interpretation of what he may have meant, namely "in Bohmian mechanics the collapse is not 'real' (i.e. the laws governing measurement interactions are exactly the same as the laws governing other interactions) but just a pragmatic way of getting the same predictions a full Bohmian treatment would yield." Nowhere did he say that using the projection postulate will yield different statistical predictions about observed results than those predicted by Bohmian mechanics.

If it’s an approximation, it is not precise, if it is not precise, there must be difference.

I think they are different only if you assume multiple successive measurements, and understanding "the projection postulate" to imply that each measurement collapses the wavefunction onto an eigenstate, and assuming that for some of the measurements the records of the results are "erased" so that it cannot be known later what the earlier result was. If you are dealing with a situation where none of the measurement records are erased, I'm pretty sure that the statistics for the measurement results you get using the projection postulate will be exactly the same as the statistics you get if you model the whole thing as a giant entangled system and then use the Born rule at the very end to find the probabilities of different combinations of recorded measurement results. And once again, the "projections postulate" does not precisely define when projection should occur anyway, you are free to interpret the projection postulate to mean that only the final measurement of the records at the end of the entire experiment actually collapses the wavefunction.

I don’t quite see what the status of all these statements is. Anyway, I don’t see any reason to agree with them until they are substantiated. substantiation.

akhmeteli

Jul28-10, 11:05 PM

(continued from previous post)
I think you misunderstood what I meant by "any" above, I wasn't asking if your model could reproduce any arbitrary prediction made by the "standard pragmatic recipe" (i.e. whether it would agree with the standard pragmatic recipe in every possible case, as I think Bohmian mechanics does). Rather, I was using "any" in the same sense as it's used in the question priests used to ask at weddings, "If any person can show just cause why they may not be joined together, let them speak now or forever hold their peace"--in other words, I was asking if there was even a single instance of a case where your model reproduces the probabilistic predictions of standard QM, or whether your model only deals with complex amplitudes that result from unitary evolution.

I got that about "any" the first time:-) Probabilities can be introduced in "my" model using the expression for current density, the same way it is done in the Bohm interpretation - so it's pretty much the Born rule, but again, it should be used just as an operational rule.

The reason I asked this is that the statement of yours I was responding to was rather ambiguous on this point:

If your model does predict actual measurement results, then if the model was applied to an experiment intended to test some Bell inequality, would it in fact predict an apparent violation of the inequalites in both experiments where the locality loophole was closed but not the detector efficiency loophole, and in experiments where the efficiency loophole was closed but not the locality loophole?

I hope and think so, but I am not sure - as I said, I am not sure to what extent it describes experimental results correctly.

I think you said your model would not predict violations of Bell inequalities in experiments with all loopholes closed--would you agree that if we model such experiments using unitary evolution plus the Born rule (perhaps applied to the records at the very end of the full experiment, after many trials had been performed, so we don't have to worry about whether applying the Born rule means we have to invoke the projection postulate), then we will predict violations of Bell inequalities even in loophole-free experiments?

I am not sure - you need correlations, so you need to use the Born rule twice in each event, and this is pretty much equivalent to the projection postulate. You said very well (I hope I understood you correctly) that the Born rule should be applied at the end of each experiment - that means, I think, you cannot use it twice in each experiment.

Likewise, would you agree that Bohmian mechanics also predicts violations in loophole-free experiments, and many-worlds advocates would expect the same prediction even if there is disagreement on how to derive it?

I have nothing to say about many worlds, and I am not sure about Bohmian mechanics - Demystifier said that it does predict violations in ideal experiments, but then it seemed he was less categorical about that (see his post 303 in this thread). So I don't know. My guess you cannot prove violations in Bohmian mechanics using just unitary evolution, otherwise the relevant proof could be "translated" into a proof in standard QM.

akhmeteli

Jul28-10, 11:54 PM

Disagree, as we have already been through this many times. There is nothing BUT evidence of violation of Bell Inequalities. To use a variation on your 34 year old virgin example:

Prosecutor: "We found the suspect over the victim, holding the murder weapon. The victim's last words identified the suspect as the perp. The murder weapon was recently purchased by the suspect, and there are witnesses who testified that the suspect planned to use it to kill the victim." Ah, says the defense attorney, but where is the photographic evidence of the crime itself? This failure is proof of the suspect's innocence!

The problem is you could write an equally winning speech for the prosecutor, proving that the sum of the angles of a planar triangle is not 180 degrees.

There is another thing. There is a huge difference between " beyond reasonable doubt" in court and in science. You know that DNA testing led to acquittal of maybe hundreds people or more. It's not so different to imprison or execute an innocent. I even heard that prosecutors try to exclude mathematicians from their future juries because mathematicians' requirement for "beyond any doubt" is much stricter than that of the nation on the average (whether this is true or not is not important, it's a good illustration anyway).

I'd say there is some sound reason between this difference: crime is not reproducible, and science is supposed to be. However, 46 years of looking for violations of the genuine inequalities have demonstrated no such violations.

The difference is especially clear in this case, as elimination of local realism is an extremely radical idea, so the burden of proof is very high.

You can always demand one more nail in the coffin. In fact, it is good science to seek it. But the extra nail does not change it from "no experimental evidence" (as you claim) to "experimental evidence". It changes it from "overwhelming experimental evidence" (my claim) to "even more overwhelming experimental evidence".

I fail to see how total absence of violations of the genuine Bell inequalities can serve as "overwhelming experimental evidence" of such violations, but obviously you have no such problems.

As to the second of your assertions: how QM arrives at its predictions may be "inconsistent" in your book. But it does not cause a local realistic theory to be any more valid. If QM is wrong, so be it. That does not change the fact that all local realistic theories are excluded experimentally.

All local realistic theories can only be ruled out by a demonstration of violation of the genuine Bell inequalities, period. Sorry to disappoint you, but no such demonstration available. Furthermore, the proof of such violations in quantum theory requires mutually contradicting assumptions. Therefore, violations of the Bell inequalities are on shaky grounds, to put it mildly, both theoretically and experimentally.

akhmeteli

Jul29-10, 12:06 AM

akhmeteli

Jul29-10, 12:15 AM

Great point. So there is no evidence for GR either. :biggrin:

There is another issue with akhmeteli's line of reasoning IF CORRECT: there is a currently unknown local force which connects Alice and Bob. This kicks in on Bell tests like Rowe et al which closes the detection loophole. But not otherwise as far as we know.

There is also a strong bias - also previously unknown and otherwise undetected - which causes an unrepresentative sample of entangled pairs to be detected. This kicks in on Bell tests such as Weihs et al, which closes the locality loophole. Interestingly, this special bias does NOT appear when all pairs are considered such as in Rowe, however, the effect of the unknown local force is exactly identical. What a happy coincidence!

And so on for every loophole when closed individually. All the loopholes have exactly the same effect at every angle setting! And if you leave 2 open instead of 1, you also get the same effect! (I.e. if you leave the locality and detection loopholes open simultaneously, the effect is the same as either one individually.)

Great sample of eloquence and logic. Again, just a tiny problem: it's no sweat to rewrite your post to prove that the sum of the angles of a planar triangle is not 180 degrees. But maybe it isn't?

Stangely, the entanglement effect (remember that this is just a coincidence per Local Realism) completely disappears if you learn the values of Alice and Bob. Just as QM predicts, but surprisingly, quite contrary to the ideals of Local Realism. After all, EPR thought that you could beat the HUP with entangled particle pairs, and yet you can't!

I don't challenge HUP at all.

So to summarize: akhmeteli is essentially asserting that a) 2 previously unknown and otherwise undetected effects exist (accounting for the loopholes); b) these effects are not only exactly equal to each other but are also equal to their combined impact; and c) an expected ability to beat the HUP (per EPR's local realism) has not materialized.

See above

akhmeteli

Jul29-10, 12:22 AM

You apparently cannot, as you put forth your opinions as fact. Further, you apparently cannot tell the difference between ad hoc speculation and evidence based opinions. To reasonable people, there is a difference.

I cannot comment on something lacking any specifics.

There is a huge difference in your speculation on loopholes (notice how you cannot model the behavior of these despite your unsupported claims) and RUTA's opinions (which he can model nicely using both standard and original science).

Again, how about specifics? What unsupported claims, exactly? I did not claim I can model loopholes within a reasonable time frame.

akhmeteli

Jul29-10, 01:30 AM

So basically, this version is useless as is (since it cannot predict anything new and cannot explain existing well); but you want us to accept that a future version might be valuable. That may be reasonable, I can see the concept and that is certainly a starting point for some good ideas. But it is a far cry to go from here to saying your point is really made.

What point related to the model I claimed I made and in fact did not?

You call my model useless. I respectfully disagree. Irrespective of any interpretation of quantum theory, it adds some rigorous, and therefore valuable, results to mathematical physics, for example, it demonstrates a surprising and simple result: matter field can be naturally eliminated from scalar electrodynamics.

No, I don't have time to "explain existing well" using the model, but the model does not belong to me anymore, so those who wish can find out whether it's good or bad at explaining. I think the model adds a meaningful and specific material for discussions of interpretation of quantum theory. Anybody can use it to support their own points or question other people's points. For example, it can be used to analyze such no-go theorems as the Bell theorem. For example, it shows that not all quantum field theories are "non-local-realistic". I guess this is a new and interesting result, no matter what interpretation you favor.

No, the model perhaps cannot predict anything new. However, if it had the same unitary evolution as quantum electrodynamics, rather than "a" quantum field theory, it would be much more valuable, although in that case it would certainly could not predict anything new. Therefore, the inability to predict something new may be the least of the model's problem.

Santos, Hess and many others have gone down similar paths with similar arguments for years. Where did they end up?

For example, according to you, Santos "ended up" "convincing a few good people that "all loopholes should be closed simultaneously"", you call it a "questionable conclusion", I see that a genuine contribution to our body of knowledge.

Please keep in mind that you should not expect to post speculative ideas in this forum with impunity. This forum is for generally accepted science.

What speculative ideas? Until recently, practically everything I said was published in peer-reviewed journals by others. Now that my article was accepted for publication, I just added a discussion of some of my mathematical results from that article.

With all due respect, I believe you post speculative ideas in this forum with impunity when you question the mainstream fact (not opinion) that there have been no experimental demonstrations of the genuine Bell inequalities.

DevilsAvocado

Jul29-10, 06:57 AM

Similarly, if space is infinite and there are an infinite number of different civilizations doing the same type of quantum experiment, there will be some small fraction of the civilizations where the statistics they get on every trial of that experiment throughout their history differ significantly from the true probabilities.

But this doesn’t make sense, does it? If there’s 1 in 10^100 MWI civilizations...

I would say instead that in science, we recognize that, given a large enough number of trials, the probability is very tiny that the statistics will differ significantly from the proper distribution (the law of large numbers (http://en.wikipedia.org/wiki/Law_of_large_numbers)). This "very tiny" chance can be quantified precisely in statistics, and it is always nonzero for any finite number of trials. But with enough trials it may become so small we don't have to worry about it, say a 1 in 10^100 chance that the observed statistics differ from the true probabilities by more than some amount epsilon (and in that case, we should expect that 1 in 10^100 civilizations that do the same number of trials will indeed observe statistics that differ from the true probabilities by more than that amount epsilon). From a purely statistical point of view (ignoring what assumptions we might make pragmatically for the purposes of doing science), do you think what I say here is incorrect?

That gets 'unlucky' aberrant result...

... it's extremely unlikely that our civilization would happen to be one of those that gets the aberrant result. That doesn't change the fact that in a universe with an infinite number of civilizations doing scientific experiments, any aberrant result will in fact occur occasionally.

Q: Why on earth are these aberrant results ALWAYS measured in the SAME 'unlucky' civilization!?!?

JesseM, do you get what I’m saying? Your example probably works for ONE experiment, flipping coins, but our whole world is built on an extremely large amount of microscopic "experiments" with different probabilities being realized every nanosecond.

So JesseM, you must explain why this "googolplexian unluckiness" ALWAYS hits the same poor civilization EVERY TIME, and are not evenly spread out over all MWI civilizations, including ours...?:bugeye:?:bugeye:?

DevilsAvocado

Jul29-10, 07:51 AM

I just found out that also this is probably false:
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

Wikipedia - The problem of measurement (http://en.wikipedia.org/wiki/Mathematical_formulations_of_quantum_mechanics#The _problem_of_measurement)
...
note, however, that von Neumann's description dates back to the 1930s and is based on experiments as performed during that time – more specifically the Compton–Simon experiment (http://en.wikipedia.org/wiki/Compton_scattering); it is not applicable to most present-day measurements within the quantum domain

Zarqon

Jul29-10, 07:59 AM

So JesseM, you must explain why this "googolplexian unluckiness" ALWAYS hits the same poor civilization EVERY TIME, and are not evenly spread out over all MWI civilizations, including ours...?:bugeye:?:bugeye:?

Who knows what improbable events occur here though? There might even be a universe out there where such crazy stuff as an octopus that can correctly predict the result of all football games exist. :wink:

On another note, most interpretations discussed here seems to be ones with a deterministic core, but why do so many feel the need for the world to be determinstic? Is there really no serious/valid interpretation candidate that describe things as they are seen in the lab, i.e. random and non-local? (shut up and calculate is no interpretation)

Dmitry67

Jul29-10, 08:07 AM

Q: Why on earth are these aberrant results ALWAYS measured in the SAME 'unlucky' civilization!?!?

Do you want a crazy idea? Note: it is just an idea, a model, I dont claim anything.

So, MWI. There are 'normal', 'regular' bracnhes. There are also 'weird' branches, where rare things are happening all the time or sometimes. Among them there are strange branches, where rare things are heppening based on some rule, we can call a pseudo-law.

For example, there is a branch where Uranium nuclei are not decaying on Fridays - at all. Just by pure chance. So far there is no value in what I said - yes, there are some branches, so what?

But now lets assume that consciousness is not possible in 'bare' Universe, but it is possible in Universe + some pseudo-laws. Then only weird branches with psedo-laws are observed! What a conspiracy from nature!

DevilsAvocado

Jul29-10, 08:25 AM

Who knows what improbable events occur here though? There might even be a universe out there where such crazy stuff as an octopus that can correctly predict the result of all football games exist. :wink:

LOL! Yeah, and why doesn’t that weird thing happen here!? :biggrin: And why doesn’t the same octopus settle the FIFA World Cup by simultaneously shooting with all his eight feet in the last penalty shootout!?!? :rofl:

On another note, most interpretations discussed here seems to be ones with a deterministic core, but why do so many feel the need for the world to be determinstic? Is there really no serious/valid interpretation candidate that describe things as they are seen in the lab, i.e. random and non-local? (shut up and calculate is no interpretation)

I’m with you all the way Broo. :approve:

DevilsAvocado

Jul29-10, 08:33 AM

But now lets assume that consciousness is not possible in 'bare' Universe, but it is possible in Universe + some pseudo-laws. Then only weird branches with psedo-laws are observed! What a conspiracy from nature!

Yeah! And I think there is a name for that conspiracy... the Anthropic principle (http://en.wikipedia.org/wiki/Anthropic_principle)! :wink:

RUTA

Jul29-10, 08:52 AM

Alright, JesseM, I’m going to provide a detailed response in hopes of ending the confusion.

First, I assume by “flipping a coin” you mean a phenomenon with an unequivocally 50-50 outcome. According to Newton’s laws, the literal flipping of a coin will produce a deterministic outcome, so the 50-50 outcome is not ontological, but epistemological. I do science in an effort to explore ontology, not epistemology. In order to do this, I have to make epistemological assumptions. It is one of those assumptions that you and I differ on.

I assume we both agree that there are statistical regularities in Nature. The question is, how are they instantiated? The answer to this question tells us whether or not such regularities can be discovered scientifically. I will argue that, according the JesseM belief (what you call “pure statistics”), it is impossible to know whether or not you have discovered any such regularity. In contrast, according to the RUTA belief, science can discover these regularities. Conclusion: Most scientists probably subscribe to the RUTA belief (either tacitly or explicitly, but at least pragmatically).

Consider a series of experiments designed to find a statistical regularity of Nature (SRN). Each experiment conducts many trials, each with a distribution of outcomes. Many experiments produce many distributions, so that we have a distribution of distributions at any given location in the universe (assumed infinite).

According to the JesseM belief, all conceivable distributions of distributions are instantiated in the universe and only collectively do they yield the SRN being investigated.

According to the RUTA belief, each distribution of distributions yields the SRN being investigated.

P1. We don’t know the SRN under investigation, that’s why we’re doing the experiment.
P2. If JesseM is right, there are distributions of distributions nowhere “near” the SRN. [Define this proximity per a number of “standard deviations” obtained over the distribution of distributions itself. Pick any number you like, since, according to JesseM, all conceivable distributions of distributions are realized.]
C1. Any particular location in the universe doesn’t (and can’t) know whether or not their distribution of distributions is “near” the SRN.
P3. Most scientists believe (tacitly or explicitly, but at least pragmatically) that the distribution of distributions they discover on Earth is “near” the SRN.
P4. The scientists of P3 don’t believe Earth occupies a “special” or “privileged” place in the universe.
C2. Most scientists subscribe to the RUTA belief, not the JesseM belief.

Of course, the point isn’t really about popularity, but epistemological assumptions (tacit or explicit) in an empirically-based exploration of ontology.

Now you should be able to easily and accurately infer my answer to your question about getting “all heads” when “flipping a coin” somewhere in an infinite universe.

JesseM

Jul29-10, 09:47 AM

Q: Why on earth are these aberrant results ALWAYS measured in the SAME 'unlucky' civilization!?!?
They're not, you could easily have civilizations which are unlucky for some period of time but whose results then return to the mean. But I was specifically defining "aberrant" relative to a civilization's entire run of experiments over their entire history. In an infinite universe, we might consider the set of all civilizations that do 1 billion runs of a particular experiment in their entire history before their species dies off, for example. For any quantum experiment, do you agree there's some nonzero probability that 1 billion runs of the experiment would yield statistics that are off from the true quantum probabilities by more than some significant amount epsilon? And whatever probability that is, do you agree that in an infinite set of civilizations that do 1 billion runs in their entire history before dying off, that will be the fraction of the set that does get statistics off from the true quantum probabilities by more than epsilon?
So JesseM, you must explain why this "googolplexian unluckiness" ALWAYS hits the same poor civilization EVERY TIME, and are not evenly spread out over all MWI civilizations, including ours...?:bugeye:?:bugeye:?
See above. And remember I wasn't talking about MWI civilizations, just about an infinite number of civilizations in a single spatially infinite universe...my point was that RUTA's criticism of the MWI would apply equally to this single-universe case.

JesseM

Jul29-10, 10:48 AM

First, I assume by “flipping a coin” you mean a phenomenon with an unequivocally 50-50 outcome. According to Newton’s laws, the literal flipping of a coin will produce a deterministic outcome, so the 50-50 outcome is not ontological, but epistemological.
The 50/50 probability on an individual trial is not ontological in a deterministic universe, but even in a deterministic universe, for a large set of trials where we flip a coin N times, we should expect that all possible sequences of results occur with equal frequency (for example, if we do 8 million trials where we flip the coin three times and record the result, we'd expect HHH, HHT, HTH, HTT, THH, THT, TTH, and TTT to each occur on about 1 million of the trials). This can be justified using arguments analogous to those in classical statistical mechanics, where we assume all the possible "microstates" associated with a given "macrostate" would occur with equal frequency in the limit of a very large number of trials with the same macrostate.

Do you disagree that for some phenomena with a 50/50 outcome, regardless of whether the uncertainty is epistemological or ontological, we would expect that if a near-infinite number of civilizations were doing a sequence of N tests of that phenomena, all specific sequences of N results would occur with the same frequency relative to this near-infinite set? For example, if each civilization is doing 20 flips of a fair coin, we should expect that about 2-20 of these civilizations get the sequence HTHHTTTHTHHHHTTHTTHT, while about 2-20 of these civilizations get the sequence HHHHHHHHHHHHHHHHHHHH? Each specific sequence occurs with equal frequency, but there are far more possible sequences with close to 10 heads and 10 tails then there are possible sequences with more asymmetrical ratios of heads to tails, and this explains why the average civilization is a lot more likely to see something close to a 50/50 ratio.

It would really help if you would give me a specific answer to whether you agree that the above is statistically correct. If you don't think it's correct, do you think it would still be incorrect if we reduced N from 20 to 3, and replaced multiple civilizations with a single experimenter doing a large run of sequences of 3 tests? If a single experimenter does 8000 sequences of 3 tests, do you disagree with the prediction that about 1000 sequences will give result HHH, about 1000 will give result HHT, and so on for all 8 possible combinations?
I assume we both agree that there are statistical regularities in Nature. The question is, how are they instantiated? The answer to this question tells us whether or not such regularities can be discovered scientifically. I will argue that, according the JesseM belief (what you call “pure statistics”)
But you still aren't telling me what specific statement about "pure statistics" you think is incorrect, you're just disagreeing with my argument as a whole. I laid out my argument in a step-by-step fashion so we could pinpoint where precisely you think the argument goes off the rails, rather than you just telling me you disagree with the conclusion. Can you pinpoint what specific sentences in the paragraphs above (starting with 'Do you disagree' and 'It would really help') you believe to be incorrect?
it is impossible to know whether or not you have discovered any such regularity.
It is impossible to "know" with perfect 100% certainty that a given equation accurately describes nature. But science isn't about perfect 100% certainty in anything! It's just about accumulating stronger and stronger evidence for some theories, and I'd say that if we can show that if we are comparing some hypothesis to a null hypothesis, and we find that the null hypothesis would require us to believe a statistical fluctuation with probability 1 in 10^100 had occurred, that's extremely strong evidence that the null hypothesis is false. Perfect 100% certainty only occurs in pure mathematical proofs.
Conclusion: Most scientists probably subscribe to the RUTA belief (either tacitly or explicitly, but at pragmatically).
I disagree, most scientists would probably agree that we can never have complete 100% certainty in any theory, only accumulate strong evidence for some theories and evidence against others. And most scientists would agree that if a given set of results would only have a probability of 1 in 10^100 according to some null hypothesis, that's very strong evidence against the null hypothesis.
Consider a series of experiments designed to find a statistical regularity of Nature (SRN). Each experiment conducts many trials, each with a distribution of outcomes. Many experiments produce many distributions, so that we have a distribution of distributions at any given location in the universe (assumed infinite).

According to the JesseM belief, all conceivable distributions of distributions are instantiated in the universe
Well, only if it is in fact true that the universe is infinite in size with an infinite number of civilizations running the same type of experiment. It's possible the universe is actually finite in size. The standard frequentist view of probability is that probabilities represent the statistics that would be seen in an infinite collection of trials of the same experiment, regardless of whether such an infinite collection is actually performed in the real physical universe.
and only collectively do they yield the SRN being investigated.

According to the RUTA belief, each distribution of distributions yields the SRN being investigated.[/quote]
But a "distribution of distributions" is just a larger distribution. Do you think that the laws of statistics would work differently in these two case?

1) A single long-lived civilization does a large number of trials where each trial consists of N tests (like a coin flip), each trial giving a distribution.
2) A large number of short-lived civilizations do m trials where each trial consists of n tests, each trial giving a distribution, after which these civilizations collapse (due to nuclear war or global warming or whatever). As it so happens, m*n=N, so for each of these short-lived civilizations, their "distribution of distributions" consists of a total of N tests.

Your argument would seem to imply that in case 1), since a given series of N tests is just a single distribution from many collected by that civilization, you accept that a given series might show aberrant results; but somehow in case 2), since the "distribution of distributions" for each of the short-lived civilizations consists of N tests, not one of these civilizations will get aberrant statistics on those N tests (which consists of all tests of a given experiment in their entire history, perhaps lasting hundreds of years before they finally die off). This would be something of a statistical miracle!

If you don't think your argument would actually imply this statistically miraculous conclusion, please clarify.
P1. We don’t know the SRN under investigation, that’s why we’re doing the experiment.
P2. If JesseM is right, there are distributions of distributions nowhere “near” the SRN. [Define this proximity per a number of “standard deviations” obtained over the distribution of distributions itself. Pick any number you like, since, according to JesseM, all conceivable distributions of distributions are realized.]
C1. Any particular location in the universe doesn’t (and can’t) know whether or not their distribution of distributions is “near” the SRN.
Again, they can't "know" with 100% certainty, but they can be very very confident. If some aberrant "distribution of distributions" would only occur in 1 out of 10^100 civilizations, it's reasonable for any given civilization to conclude there's only a 1 in 10^100 chance that their civilization is one of the ones that gets the aberrant statistics.
P3. Most scientists believe (tacitly or explicitly, but at least pragmatically) that the distribution of distributions they discover on Earth is “near” the SRN.
P4. The scientists of P3 don’t believe Earth occupies a “special” or “privileged” place in the universe.
Yes, and according to my view of statistics, both beliefs are perfectly reasonable. You seem to think that somehow my view implies such beliefs aren't reasonable, but you've never given a clear explanation as to why that should be the case.
C2. Most scientists subscribe to the RUTA belief, not the JesseM belief.
I don't believe that. Most scientists would believe the same laws of statistics apply to collections of trials with N tests in cases 1) and 2) above, despite the fact that in 2) each trial represents a "distribution of distributions" for an entire civilization while in 1) a single civilization is doing many such trials with N tests.
Now you should be able to easily and accurately infer my answer to your question about getting “all heads” when “flipping a coin” somewhere in an infinite universe.
No, I actually am not sure, so please state it outright. Do you really believe that different statistics would apply in a collection of trials with N tests each in case 1) and 2) above, even though the only difference is that in case 1) we are considering a large number of trials done by a single civilization, and in case 2) we are considering a large number of civilizations which each do N tests before dying off?

DrChinese

Jul29-10, 10:51 AM

1. For example, according to you, Santos "ended up" "convincing a few good people that "all loopholes should be closed simultaneously"", you call it a "questionable conclusion", I see that a genuine contribution to our body of knowledge.

2. With all due respect, I believe you post speculative ideas in this forum with impunity when you question the mainstream fact (not opinion) that there have been no experimental demonstrations of the genuine Bell inequalities.

1. That's what you call a contribution? I guess I have a different assessment of that. Better Bell tests will always be on the agenda and I would say Zeilinger's agreement on that represents no change in his overall direction.

2. I consider your comment in 1. above to be acknowledgement of the obvious, which is that it is generally agreed that Bell Inequality violations have been found in every single relevant test performed to date. "Gen-u-wine" ones at that! So you can try and misrepresent the mainstream all you want, but you are 180 degrees off.

Why don't you call it for what it is: you are part of a very small minority regarding Bell. Where's the disrespect in that? If you are confident, just call yourself a rebel and continue your research.

JesseM

Jul29-10, 11:04 AM

Your argument does not make any sense to me so I am hoping you could clarify your understanding of the meaning of "probability". If a source has a 0.1-0.9 up-down probability, what does that mean in your understanding according to MWI. Does it mean 10% of the worlds will obtain 100% up and 90% of the worlds will obtain 100% down, or does it mean in every world, there will be 10% up and 90% down? It is not clear from your statements what you mean and what it has that got to do with "correct statistics"?
To be clear, the actual MWI doesn't give a straightforward explanation of probabilities in terms of a frequentist notion of a fraction of worlds where something occurs, instead MWI have to use more subtle arguments involving things like decision theory (http://en.wikipedia.org/wiki/Decision_theory). When I talked about fractions of worlds or fractions of copies that see some result, I was talking about my "toy model" from post #11 of this thread (http://www.physicsforums.com/showthread.php?t=221870) which was showing how in principle it would be possible to explain Bell inequality violations using a local model where each measurement splits the experimenter into multiple copies. Perhaps someday someone will develop a variant of the MWI that explains probabilities in terms of fractions of copies, but it doesn't exist yet.

Anyway, in terms of a model along the lines of my toy model, if there is a ninety percent chance of getting result N and a ten percent chance of getting result T, that would mean that if an experimenter did a trial involving three tests in a row, after it was done there'd be an ensemble of copies of the experimenter, with (0.9)(0.9)(0.9) = 0.729 of the copies having recorded result "NNN", (0.9)(0.9)(0.1) = 0.081 of the copies having recorded result "NNT", (0.1)(0.1)(0.9) = 0.009 having recorded result "TTN", and so on for all eight possible combinations of recorded results.
If I calculate the probability that the sun will explode tomorrow to be 0.00001, what does that mean in MWI. Is your understanding that I am calculating the probability of the sun in "my" world, exploding, or all the suns in the multiverse exploding or what exactly? Or do you think such a probability result does not make sense in science.
Assuming your calculation was correct according to a full QM treatment of the problem, and it represented the probability that our Sun would explode tomorrow given its history up until today, then that would mean tomorrow, in the collection of copies of our solar system that had the same history up until today, the Sun would have exploded in 0.00001 of these copies.

RUTA

Jul29-10, 11:24 AM

JesseM

Jul29-10, 12:18 PM

The 50/50 probability on an individual trial is not ontological in a deterministic universe, but even in a deterministic universe, for a large set of trials where we flip a coin N times, we should expect that all possible sequences of results occur with equal frequency
Are we talking about assumed statistical or definite outcomes?
In the limit as the number of trials approaches infinity, the statistics in the actual outcomes should approach the "true" probabilities determined by the laws of nature with probability 1, that's the law of large numbers (http://en.wikipedia.org/wiki/Law_of_large_numbers). So, I'm talking about actual outcomes.
Are you ascribing the 50-50 outcomes to ontology or epistemology?
I'm saying that, as an ontological fact, the nature of the laws of physics and the experiment are such that if the experiment was repeated under the same conditions many times, in the limit as the number of trials went to infinity the ratio of one outcome to another would approach 50/50. But this does not mean that there is any true ontological randomness on individual trials, since it may be that the outcome on each trial is completely determined by the initial "microstate" of the coin, coinflipper, and nearby environment. That's what I meant when I said:
This can be justified using arguments analogous to those in classical statistical mechanics, where we assume all the possible "microstates" associated with a given "macrostate" would occur with equal frequency in the limit of a very large number of trials with the same macrostate.
I assume you're probably familiar with how probabilities are derived from an ensemble of microstates in classical statistical mechanics, where the laws of physics are assumed to be completely deterministic?
Do you disagree that for some phenomena with a 50/50 outcome
Where this means the TRUE outcome, not what any particular civilization finds, but the REAL underlying principle of Nature. [Which, we tacitly, explicitly or pragmatically assume exists and can be discovered empirically when we do science.]
Sure, you're free to assume that indeterminism is fundamental and that the most fundamental laws of nature can only tell you there's a 50/50 chance on each trial. Although as I said above, you're also free to assume a deterministic universe where the future evolution is totally determined by the initial microstate, but as the number of trials approaches infinity each microstate compatible with the experiment's initial macrostate would occur with equal frequency. Still, for the sake of this discussion let's go with the first option and say the indeterminism is fundamental.
regardless of whether the uncertainty is epistemological or ontological, we would expect that if a near-infinite number of civilizations were doing a sequence of N tests of that phenomena, all specific sequences of N results would occur with the same frequency relative to this near-infinite set?
This is precisely where we disagree. I say ALL civilizations will empirically deduce the 50-50 law.
OK, so to be clear, if the laws of physics do indeed give a 50/50 law, you're saying that if a single series of N tests is done by a very long-lived civilization which has time to do many additional series of N tests, then that individual series is not guaranteed to yield N/2 of result #1 and N/2 of result #2? But if a series of N tests is done by a civilization which only has time to do N tests before it dies out, you think they are guaranteed to find N/2 of result #1 and N/2 of result #2?

If so, is this just an assumption you think each civilization much make for epistemological purposes, or do you think if we could actually travel through the universe and surreptitiously observe many civilizations over the course of their entire histories, we would actually see that this was the case?
For some reason you think it's innane to believe that the REAL underlying statistical law of Nature is discovered by ALL civilizations in an infinite universe.
Yes, just because I believe that same laws of statistics apply to multiple civilizations as would apply to multiple series of experiments performed by a single long-lived civilization. To suggest otherwise would be seem nothing short of supernatural, as if the fundamental laws of physics could anticipate how long each civilization was going to last and would tailor their statistics to that.
But, as a scientist who doesn't believe he lives in a "special" or "privileged" civiliation
I don't either. I just think that if some anomalous results would only be seen by 1 out of 10^100 civilizations (or some other astronomically small probability), then there is only a 1 out of 10^100 probability that my civilization happens to be one that's getting such an anomalous result. It's the civilizations that get anomalous results over huge numbers of trials that are "special", not the ones that get results very close to the true probabilities.
and does believe it's possible to do science, i.e., discover empirically the REAL underlying statistical law of Nature
So do I, unless by "discover empirically" you mean "know with absolute 100% certainty" as opposed by "be confident beyond all reasonable doubt". As I said, only in math can you know anything with perfect 100% certainty, we cannot even be 100% sure that the Earth is round, only 99.999999% (or whatever) sure.
If I REALLY believed in your interpretation, I would HAVE to admit that doing science is impossible.
Why? You just keep saying this but never explain what you mean by "doing science", or why you think I am not "doing science" if I show that there is only a 1 in 10^100 chance that my experimental results differ from the true probabilities by more than some small amount epsilon.
So, why would I subscribe to your belief when there's no more argument for it than mine
The argument for mine is just that the same laws of statistics apply everywhere, that the fundamental laws of physics don't have high-level knowledge of what a "civilization" is and how long each civilization will last, and use this to give different results in a series of N tests depending on whether they are done in a civilization that only does N tests before dying out or a civilization that is more long-lived.

RUTA

Jul29-10, 12:45 PM

JesseM

Jul29-10, 01:25 PM

"OK, so to be clear, if the laws of physics do indeed give a 50/50 law, you're saying that if a single series of N tests is done by a very long-lived civilization which has time to do many additional series of N tests, then that individual series is not guaranteed to yield N/2 of result #1 and N/2 of result #2? But if a series of N tests is done by a civilization which only has time to do N tests before it dies out, you think they are guaranteed to find N/2 of result #1 and N/2 of result #2?

If so, is this just an assumption you think each civilization much make for epistemological purposes, or do you think if we could actually travel through the universe and surreptitiously observe many civilizations over the course of their entire histories, we would actually see that this was the case?"

Both civilizations will deduce the 50-50 law (or whatever the REAL law is). That's MY assumption and it is made precisely for the reasons I stated (and will not repeat).
OK, but just saying that both civilizations will deduce it does not tell me if you actually believe that if a civilization does a test exactly N times before collapsing, it will get exactly N/2 with each result. After all, part of the way we deduce laws of nature is just by looking for elegant and simple equations that agree closely with all experiments--even if someone did a meta-analysis of all experiments every done measuring spin of fermions and found that it was actually 50.000001% of experiments that gave spin-up, that wouldn't cause them to change the equations of quantum physics which would become more ungainly and inelegant if you tried to make them agree with this result.

So, can you please tell me if you think that if an experiment does the experiment N times in its history before civilization ends, they will get exactly N/2 of each outcome? Yes or no?

Incidentally, it occurs to me that the laws of quantum physics don't just give probability distributions for single measurements, they also give probability distributions for the possible statistics seen on a series of N measurements, even if N is very large. Would you disagree that for an experiment with spin that QM predicts has a 1/2 chance of yielding either result, it's also a prediction of QM that there is a probability of 1/2N that a series of N spin measurements on different particles (whose spin is unknown until measurement) will yield the result spin-up every time? So in other words, if you say the probability is zero that this will happen whenever N is the total number of experiments performed by a given civilization, you are saying that the equations of QM actually give incorrect predictions in this case?
I can't be any clearer, JesseM. If you still don't get it, you probably never will -- no pun intended :-)
I get that you believe it would be impossible to "do science" if there was the slightest chance (even 1 in 10^100 or whatever) that the statistics collected over our entire history could be badly off from the true probabilities due to random statistical fluctuation, but I don't get why you believe this, because you haven't defined what you mean by "do science" (for example, you haven't told me whether you think that science requires us to be able to be 100% certain a theory is empirically correct, or whether you agree that strong evidence which convinces us the theory is correct beyond all reasonable doubt is the best that empirical science can hope to achieve...and if the latter, I don't see why a 1 in 10^100 chance that the null hypothesis could give the observed results doesn't qualify as strong evidence which convinces beyond all reasonable doubt that the null hypothesis is empirically false)

RUTA

Jul29-10, 02:15 PM

OK, but just saying that both civilizations will deduce it does not tell me if you actually believe that if a civilization does a test exactly N times before collapsing, it will get exactly N/2 with each result. After all, part of the way we deduce laws of nature is just by looking for elegant and simple equations that agree closely with all experiments--even if someone did a meta-analysis of all experiments every done measuring spin of fermions and found that it was actually 50.000001% of experiments that gave spin-up, that wouldn't cause them to change the equations of quantum physics which would become more ungainly and inelegant if you tried to make them agree with this result.

So, can you please tell me if you think that if an experiment does the experiment N times in its history before civilization ends, they will get exactly N/2 of each outcome? Yes or no?

In the experiment I referenced (Dehlinger & Mitchell), the result was quoted as S = 2.307 +/- 0.035. Have you done experimental physics? Do you understand where the +/- 0.035 comes from? If so, then it should be abundantly clear to you what I mean by " every civilization is able to empirically determine the REAL law." If not, do some experimental physics then come back and we'll talk.

Incidentally, it occurs to me that the laws of quantum physics don't just give probability distributions for single measurements, they also give probability distributions for the possible statistics seen on a series of N measurements, even if N is very large. Would you disagree that for an experiment with spin that QM predicts has a 1/2 chance of yielding either result, it's also a prediction of QM that there is a probability of 1/2N that a series of N spin measurements on different particles (whose spin is unknown until measurement) will yield the result spin-up every time? So in other words, if you say the probability is zero that this will happen whenever N is the total number of experiments performed by a given civilization, you are saying that the equations of QM actually give incorrect predictions in this case?

Again, you are conflating "conceivable" with "realizable." Just because you imagine it to be so, and indeed may even USE these numbers to do a computation, doesn't entail the results will be realized by any particular civilization. There's nothing in the analysis that says all conceivable distributions will be realized given an infinite number of trials. You are adding that to the formalism as an assumption.

I get that you believe it would be impossible to "do science" if there was the slightest chance (even 1 in 10^100 or whatever) that the statistics collected over our entire history could be badly off from the true probabilities due to random statistical fluctuation, but I don't get why you believe this, because you haven't defined what you mean by "do science" (for example, you haven't told me whether you think that science requires us to be able to be 100% certain a theory is empirically correct, or whether you agree that strong evidence which convinces us the theory is correct beyond all reasonable doubt is the best that empirical science can hope to achieve...and if the latter, I don't see why a 1 in 10^100 chance that the null hypothesis could give the observed results doesn't qualify as strong evidence which convinces beyond all reasonable doubt that the null hypothesis is empirically false)

I did define "doing science." Here is the bottom line: I'm a theoretical physicist, but I have done and taught experimental physics to include error analysis. Perhaps you have also engaged in these activities, maybe you're even an experimental physicist, but the bottom line is that we possess different underlying assumptions as to what the nature of reality allows us to conclude about our theories and experiments. My underlying assumption: All civilizations will observe the same distribution (in accord with the REAL law) when conducting the same experiments, even if there are an infinite number of such civilizations. Your underlying assumption: The distributions obtained by all civilizations will mirror all those that are conceivable per the REAL law.

You can keep asking me the same questions (just reworded), and I can keep giving you the same answers (just reworded), but at this point, if you don't understand, you'll just have to live with it. I'm done.

JesseM

Jul29-10, 05:27 PM

In the experiment I referenced (Dehlinger & Mitchell), the result was quoted as S = 2.307 +/- 0.035. Have you done experimental physics? Do you understand where the +/- 0.035 comes from?
Without seeing the details of their error analysis I don't know exactly, but from my understanding of significance testing, the usual procedure would be to take the experimental mean E (like E=2.307), then pick a confidence interval--say, two standard deviations or 95%--and then pick some a statistical distribution that makes sense for the experiment like the normal distribution, and find two different normal distributions with different means, one with a mean M1 lower than E such that exactly 95% of the area under the curve is between (2M1 - E) and E (note that the midpoint between 2M1-E and E is M1), and another with a mean M2 greater than E such that exactly 95% of the area under the curve is between between E and (2M2 - E) (the midpoint between E and 2M2-E is M2). So, in effect you're considering an infinite set of null hypotheses with different means, and then looking for the ones with the lowest and highest possible means M1 and M2 such that the experimentally-observed mean E would not lie outside the middle 95% of your null hypothesis (causing you to reject it). If you are considering a set of normal distributions with different means as your null hypotheses, then this is actually equivalent to just finding a single normal distribution centered on E and then finding an M1 and M2 such that 95% of the area under the curve lies between M1 and M2, but in general if you aren't necessarily assuming normal distributions as your null hypotheses, you have to consider two different distributions which are not centered on E as described above. See the discussion on p. 4-6 of this book on confidence intervals (http://books.google.com/books?id=1ZEMXC-Xc9gC&lpg=PP1&ots=hjJbAcFCfC&dq=confidence%20interval&pg=PA4#v=onepage&q=confidence%20interval&f=false) along with the "two-distribution representation on page 9 (http://books.google.com/books?id=1ZEMXC-Xc9gC&lpg=PP1&ots=hjJbAcFCfC&dq=confidence%20interval&pg=PA9#v=onepage&q=confidence%20interval&f=false).

Anyway, the point is that if the authors used this type of procedure, then it doesn't mean they are 100% confident that the true mean lies in the range 2.307 +/- 0.035. Rather, it just means that if the true distribution is of the type they assumed in calculating the confidence interval (most likely a normal distribution), and if the true mean M of the distribution lies in the range 2.307 +/- 0.035, then 95% of all samples from this distribution will lie within a region centered on M which includes the experimentally observed value of 2.307 (which for a normal distribution is equivalent to saying that if a large number of samples are taken from a distribution with mean M, and each sample is used to construct a 95% confidence interval, then 95% of the confidence intervals will include the value M--see the bottom of p. 1 in this pdf (http://philosophy.ucsd.edu/Courses/winter06/WhatisConfIntervalSober.pdf)). But if the true mean M lies outside the range 2.307 +/- 0.035, then it'd still be true that 5% of all samples from this distribution will be in the "tails" of the distribution, and the tails would include the experimentally observed value of 2.307. So, you have no basis for being totally certain the true mean M lies in the range 2.307 +/- 0.035, since even if it isn't there is still some nonzero chance of getting the experimental result 2.307.
If so, then it should be abundantly clear to you what I mean by " every civilization is able to empirically determine the REAL law."
No, it isn't. If you are engaging in good-faith intellectual discussion rather than just using rhetoric to make a case against my position, I think it is reasonable to ask that you actually give me a straight answer to a simple yes-or-no question like the one I asked:
So, can you please tell me if you think that if a civilization does the experiment N times in its history before civilization ends, they will get exactly N/2 of each outcome? Yes or no?
Again, you are conflating "conceivable" with "realizable." Just because you imagine it to be so, and indeed may even USE these numbers to do a computation, doesn't entail the results will be realized by any particular civilization.
Would you agree with the claim that the law of large numbers (http://en.wikipedia.org/wiki/Law_of_large_numbers) says that as the number of trials approaches infinity, the observed statistics should approach the true probabilities given by the fundamental laws of physics with probability 1? (so if theoretical QM says the probability of getting N spin-ups in a row is 1/2N, then in the limit as the number of civilizations that perform N spin measurements approaches infinity, the fraction that get all spin-ups should approach 1/2N) Or perhaps you would agree that this should be true according to the law of large numbers, but you don't believe the law of large numbers would actually hold even in an infinite universe with an infinite number of trials of any experiment?
There's nothing in the analysis that says all conceivable distributions will be realized given an infinite number of trials. You are adding that to the formalism as an assumption.
But it's just the assumption that the law of large numbers is correct, which is a founding assumption in statistics. Without it I don't see how you could justify the claim that a large set of trials is more likely to give statistics close to the "true" values than a small number! Perhaps you can think of some way of justifying it in terms of your own statistical philosophy, but if you are arguing that most other physicists would agree that the law of large numbers does not apply in any case where the number of trials approaches infinity (including an infinite universe where each civilization does a finite number of trials but the number of civilizations is infinity), I think that's extremely unlikely.
I did define "doing science."
In what post? Did you define it in such a way that would tell me whether you think we need to be able to have perfect 100% certainty in some result or we aren't "doing science", or whether you agree that we are still "doing science" if we reject hypotheses based on the fact that they are astronomically unlikely to produce the experimentally-observed results?
My underlying assumption: All civilizations will observe the same distribution (in accord with the REAL law) when conducting the same experiments, even if there are an infinite number of such civilizations.
But that's not in accord with the "REAL law" as I understand it, because a statistical law like QM doesn't just predict the average expected value, it also predicts a specific probability distribution on any sequence of results.
You can keep asking me the same questions (just reworded), and I can keep giving you the same answers (just reworded), but at this point, if you don't understand, you'll just have to live with it. I'm done.
You may think that your answer to the questions I ask should be obvious from your previous answers, but to me they aren't, because I can think of various alternatives that seem consistent with your previous answers. For example, to the question of whether a 50/50 probability implies that a civilization that does exactly N trials in its history will get exactly N/2 of each result, it would be consistent with your previous answers if you said "yes, I think the number must be precisely N/2, not one more or less" but it would also seem consistent with your previous answers if you said "no, I just think that if they use their data to construct a confidence interval, the true value is guaranteed to lie in that confidence interval." Likewise, to the question about the law of large numbers, you might say "I agree that the law of large numbers applies to the probabilities in QM, but I think the theory of QM only deals with probabilities of individual measurements, it doesn't even define a probability distribution on the 2N conceivable results for a sequence of N measurements" or "no, I reject the law of large numbers altogether". To the question of whether you think we'd see different statistics on a bunch of sequences of N trials depending on whether each sequence represented the entire history of a bunch of short-lived civilizations or they were each just a fraction of the trials done by a long-lived civilization, you might say "yes, I think the statistics would be different" or "no, I think that for any sufficiently large N, you're guaranteed to see statistics equal to the true probabilities, or at least statistics where if you use them to build a confidence interval the true probabilities are guaranteed to be in that confidence interval." And to the question of whether "doing science" requires perfect certainty you might say "yes, unless we can achieve perfect certainty some theory is correct there can be no science" or "no, showing that it's astronomically unlikely a given theory would produce the observed results is fine, I just don't believe that even an astronomically small fraction of civilizations will get data that forces them to conclude that about a theory that's actually correct". I could go on, but the point is that my uncertainty is genuine, and I don't think it's due to poor reading comprehension on my part, I think others reading your posts and looking at the alternative possible answers I suggest would also be unsure of which answer you'd give, based on your previous statements.

metacristi

Jul29-10, 06:08 PM

Local realism ruled out?

Einstein's dream is definitely a degenerative scientific program (at least it seems so at this moment in time). But locality (via the idea that nature conspire somehow - strong determinism at planck level is one radical version - to produce the results seen in Aspect et altri types of experiments) is still perene. Counterfactual definiteness is definitely a weak link in the chain of reasoning behind the rejection of locality, accepting it in the premises is indeed of 'bon sens' at this moment in time but this in no way make its rejection a dead end. So even if this kind of hypothesis is situated rather low now on a not (strongly) prescriptive list of viable scientific programs (one can argue that it is stagnant) it is a mistake to jump to the much stronger conclusion that locality is dead. The future may still be full of surprises.

akhmeteli

Jul30-10, 08:00 PM

You apparently cannot, as you put forth your opinions as fact. Further, you apparently cannot tell the difference between ad hoc speculation and evidence based opinions. To reasonable people, there is a difference.

Whatever you say, it is a mainstream fact that there has been no experimental evidence of violations of the genuine Bell inequalities. I supported this statement with quotes. Your denial of this fact does not seem reasonable. It just does not seem reasonable. Zeilinger does not know about such evidence, Shimony does not know about such evidence, Genovese does not know about such evidence, however you do know about it. Why don't you enlighten them? I am sure they will be grateful.

There is a huge difference in your speculation on loopholes (notice how you cannot model the behavior of these despite your unsupported claims) and RUTA's opinions (which he can model nicely using both standard and original science).

Look, neither you nor RUTA think local realism has a snowball's chance in hell. I have no problems with that. But, unlike you, RUTA does not deny two facts (his post 618 in this thread):

1) There is no experimental evidence of violations of the genuine Bell inequalities so far;
2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.

So, while our opinions differ wildly, our facts don't. Whereas you deny at least one of them (your post 621 in this thread), although you seem to know about Bell experiments much more than I do. The situation is very simple. In all experiments, either spatial separation is not sufficient, so the Bell inequalities can be violated in local realistic theories as well, or the Bell inequalities are doctored using the fair sampling assumption, so it's not the genuine Bell inequalities that are violated.

I am not even sure if you deny the second statement. On the one hand, your "disagree" may relate to both statements, on the other hand, you say for some reason that "If QM is wrong, so be it."

Anyway, I just cannot understand why you choose to deny a mainstream fact. Are you trying to be "holier than thou"? But we are not discussing religious issues, for god's sake.

And, by the way, what unsupported claims exactly?

JesseM

Jul30-10, 08:16 PM

2) Proofs of the Bell theorem use two mutually contradicting postulates of the standard quantum theory (unitary evolution and projection postulate) to prove that the Bell inequalities are indeed violated in quantum theory.
Since you distinguish the projection postulate from the Born rule, would you acknowledge that Bell's proof of the incompatibility between QM and local realism only depends on the idea that empirical observations will match those given by applying the Born rule to the wavefunction at the moment the observations are made? Also, do you agree that other "interpretations" of QM that don't require any special postulate about measurement, like Bohmian mechanics, also predict Bell inequality violations in the type of experiment examined by Bell? Since Bell's proof is just based on deducing the consequences of local realism for these types of experiments, and only at the end does he need to make reference to QM to compare its predictions to those of local realism, you could easily modify the proof to show "local realism's predictions about these experiments are inconsistent with any model whose predictions about empirical results match those of Bohmian mechanics".

akhmeteli

Jul30-10, 10:19 PM

Since you distinguish the projection postulate from the Born rule, would you acknowledge that Bell's proof of the incompatibility between QM and local realism only depends on the idea that empirical observations will match those given by applying the Born rule to the wavefunction at the moment the observations are made? Also, do you agree that other "interpretations" of QM that don't require any special postulate about measurement, like Bohmian mechanics, also predict Bell inequality violations in the type of experiment examined by Bell? Since Bell's proof is just based on deducing the consequences of local realism for these types of experiments, and only at the end does he need to make reference to QM to compare its predictions to those of local realism, you could easily modify the proof to show "local realism's predictions about these experiments are inconsistent with any model whose predictions about empirical results match those of Bohmian mechanics".

JesseM,

Sorry, I owe you replies to your previous posts, as, on the one hand, I am busy at work right now, on the other hand, some of your posts take quite some time to reply.

But let me try to reply to this post so far.

No, I don't agree "that Bell's proof of the incompatibility between QM and local realism only depends on the idea that empirical observations will match those given by applying the Born rule to the wavefunction at the moment the observations are made". As I said, to prove that the inequalities can be violated in quantum theory, you need to calculate correlations. In the process, you use the projection postulate, assuming that as soon as you measured the spin projection for one particle to be +1, the spin projection for the other particle immediately becomes definite and equal to -1. This postulate introduces nonlocality directly and shamelessly:-) I don't know a proof that would use the Born rule only. And in the experiment, you actually conduct two measurements for two particles.

And I don't agree that, say, "Bohmian mechanics also predicts Bell inequality violations in the type of experiment examined by Bell", not without using something like the projection postulate. I wrote about that in my post 660 in this thread (at the end). I said there "I don't know", and I don't, but I won't agree with that until I see a reference to a proof. As I said, I very much doubt that this can be proven in Bohmian mechanics without something like the projection postulate. If it could be done, it seems there would be no problem to translate this proof into a proof for standard quantum theory. As I said, according to Demystifier, for example, the projection postulate is an approximation in Bohmian mechanics. And as Bohmian mechanics embraces unitary evolution, and as unitary evolution contradicts the projection postulate, I am sure the latter cannot be anything but an approximation in Bohmian mechanics. Otherwise Bohmian mechanics would inherit the contradictions of the standard quantum theory.

JesseM

Jul31-10, 12:13 AM

JesseM,

Sorry, I owe you replies to your previous posts, as, on the one hand, I am busy at work right now, on the other hand, some of your posts take quite some time to reply.
No problem.
No, I don't agree "that Bell's proof of the incompatibility between QM and local realism only depends on the idea that empirical observations will match those given by applying the Born rule to the wavefunction at the moment the observations are made". As I said, to prove that the inequalities can be violated in quantum theory, you need to calculate correlations. In the process, you use the projection postulate, assuming that as soon as you measured the spin projection for one particle to be +1, the spin projection for the other particle immediately becomes definite and equal to -1.
Why is that necessary? The wavefunction for an entangled system assigns an amplitude to joint states like |01> and |00>, no? So can't you just apply the Born rule once to find the probability of a given joint state?
And I don't agree that, say, "Bohmian mechanics also predicts Bell inequality violations in the type of experiment examined by Bell", not without using something like the projection postulate.
Bohmian mechanics doesn't require the projection postulate. It just says that the particles have a well-defined position at all times, and measurement outcomes all depend on that position. Have you read the full Stanford Encyclopedia article on Bohmian mechanics (http://plato.stanford.edu/entries/qm-bohm/)? From section 4:
In the Bohmian mechanical version of nonrelativistic quantum theory, quantum mechanics is fundamentally about the behavior of particles; the particles are described by their positions, and Bohmian mechanics prescribes how these change with time. In this sense, for Bohmian mechanics the particles, described by their positions, are primary, or primitive, while the wave function is secondary, or derivative.

...

This demonstrates that all claims to the effect that the predictions of quantum theory are incompatible with the existence of hidden variables, with an underlying deterministic model in which quantum randomness arises from averaging over ignorance, are wrong. For Bohmian mechanics provides us with just such a model: For any quantum experiment we merely take as the relevant Bohmian system the combined system that includes the system upon which the experiment is performed as well as all the measuring instruments and other devices used in performing the experiment (together with all other systems with which these have significant interaction over the course of the experiment) ... The initial configuration is then transformed, via the guiding equation for the big system, into the final configuration at the conclusion of the experiment. It then follows that this final configuration of the big system, including in particular the orientation of instrument pointers, will also be distributed in the quantum mechanical way, so that this deterministic Bohmian model yields the usual quantum predictions for the results of the experiment.
So the idea is that the same dynamical equation guides the behavior of all components of the system from beginning to end (which each have a single well-defined position at all times, no superpositions involved), with no discontinuities along the lines of the projection postulate. And at the end, the state of the system includes the state of all "instrument pointers", so that gives you the Bohmian predictions about empirical results, which always agree with "the usual quantum predictions for the results of the experiment" (which I think would just mean the predictions you get by taking the wavefunction for the whole system, evolving it to the time of the end of the experiment, and using the Born rule on the amplitudes for different joint outcomes).

The article repeats the idea that Bohmian mechanics deals fundamentally with position in section 5:
Bohmian mechanics has been presented here as a first-order theory, in which it is the velocity, the rate of change of position, that is fundamental: it is this quantity, given by the guiding equation, that is specified by the theory, directly and simply
And in section 7:
By contrast, if, like Einstein, we regard the description provided by the wave function as incomplete, the measurement problem vanishes: With a theory or interpretation like Bohmian mechanics, in which the description of the after-measurement situation includes, in addition to the wave function, at least the values of the variables that register the result, there is no measurement problem. In Bohmian mechanics pointers always point.
Sections 7 and 8 also explain why Bohmian predictions end up being the same as predictions made using the standard pragmatic recipe involving "collapse" during measurement, in spite of the fact that Bohmian mechanics says nothing new or different really happens during measurement (the answer seems to involve the Bohmian version of decoherence).

Section 14 explains that the guiding equation of Bohmian dynamics describes the evolution of "configurations", and configurations are just specifications of the positions of every part of the system (which may be 'hidden variables' if we haven't measured the position of any given part at any given moment):
Nor can Bohmian mechanics easily be modified to become Lorentz invariant. Configurations, defined by the simultaneous positions of all particles, play too crucial a role in its formulation, the guiding equation defining an evolution on configuration space.
And section 15 says:
The Bohmian account of the two-slit experiment, in Section 6, and its resolution of the measurement problem (or the paradox of Schrödinger's cat), in Section 7, are simple and straightforward. With regard to the latter, in Bohmian mechanics particles always have definite positions, and hence pointers, which are made of particles, always point.
Anyway, I think you get the idea: Bohmian mechanics doesn't require anything like the projection postulate because it just gives a deterministic equation for the positions of all the particles in a given system, including the particles in measuring-devices ('pointers'). If you haven't read the full article I really recommend doing so, it's very informative.
I wrote about that in my post 660 in this thread (at the end). I said there "I don't know", and I don't, but I won't agree with that until I see a reference to a proof. As I said, I very much doubt that this can be proven in Bohmian mechanics without something like the projection postulate.
As noted above, you seem to be misunderstanding something very basic about Bohmian mechanics, it has no need of the projection postulate because it assumes all particles have unique positions at all times (no spread-out superpositions), including particles in measuring-devices, and the evolution of these positions is given by a deterministic "guiding equation". So, the statistics it predicts for multiple trials of some experiment would just be derived in a straightforward way from the statistics it predicts for pointer states on multiple trials (and as discussed in section 9, the reason it can be used to derive statistical predictions despite having a deterministic guiding equation is basically identical to how you get statistical predictions in classical statistical mechanics--just as there are multiple microstates (http://en.wikipedia.org/wiki/Microstate_(statistical_mechanics)) compatible with a given observed macrostate in statistical mechanics, and we assume each possible microstate is equally probable, similarly in Bohmian mechanics there are multiple hidden-variable configurations compatible with a given observed quantum state, and it's assumed that each of those is equally likely).

As for whether these Bohmian predictions agree with those made using the usual recipe of wavefunction evolution + Born rule, I already quoted section 4 saying "so that this deterministic Bohmian model yields the usual quantum predictions for the results of the experiment", and the last paragraph of section 13 says:
The nonlocality of Bohmian mechanics has a remarkable feature: it is screened by quantum equilibrium. It is a consequence of the quantum equilibrium hypothesis that the nonlocal effects in Bohmian mechanics don't yield observable consequences that are also controllable — we can't use them to send instantaneous messages. This follows from the fact that, given the quantum equilibrium hypothesis, the observable consequences of Bohmian mechanics are the same as those of orthodox quantum theory, for which instantaneous communication based on quantum nonlocality is impossible (see Eberhard 1978).
If it could be done, it seems there would be no problem to translate this proof into a proof for standard quantum theory.
Proof of what? Are you still talking about my statement "Bohmian mechanics also predicts Bell inequality violations in the type of experiment examined by Bell"? And what would the analogous "proof for standard quantum theory" be--just a proof that standard quantum theory predicts Bell inequality violations? (again, you can show this by just applying the Born rule to joint states, which are assigned amplitudes by the wavefunction)
As I said, according to Demystifier, for example, the projection postulate is an approximation in Bohmian mechanics.
Well, as I said, the meaning of his words is unclear, he might have just meant that Bohmian mechanics reproduces the exact same statistics as you'd get using the projection postulate, but that it does so using a different fundamental equation and without assuming anything special actually happens during measurement. It's also possible Demystifier would distinguish between the procedure of repeatedly applying the projection postulate for multiple measurements vs. assuming unitary evolution until the very end of a series of measurements and then applying the Born rule to find the probabilities for different possible combinations of recorded outcomes for all the previous measurements, and that he would say there are cases where Bohmian mechanics would predict slightly different statistics from the first case but not from the second case.

In any case, the Stanford Encyclopedia article was written by a professional physicist, Sheldon Goldstein, who advocates Bohm's interpretation, and in it he makes some quite ambiguous statements like "given the quantum equilibrium hypothesis, the observable consequences of Bohmian mechanics are the same as those of orthodox quantum theory". If Demystifier would actually disagree with statements like that (and I don't think he would), I would tend to trust Goldstein's expertise over Demystifier's. Also, p. 50 of this book (http://books.google.com/books?id=xcQNyP2nzRsC&lpg=PA49&dq=%22quantum%20equilibrium%22%20bohm%20prediction s&pg=PA50#v=onepage&q=%22quantum%20equilibrium%22%20bohm%20predictions&f=false) says that in any situation where the standard version of QM makes definite predictions, Bohmian mechanics makes the same predictions (though the author considers the possibility there might be situations where the standard version doesn't make clear predictions, like an observable which can't be represented as a Hermitian operator):
The important question remains (quite crucial particularly from the pragmatic point of view) of whether or not Bohm's model and the standard interpretation are indeed observationally completely equivalent. Of course in typical experiments if the calculation of any measurable quantity is unambiguously formulated, then both these interpretations yield the same predictions when the (common) formalism is applied. In an interview with Home [132] in 1986, when asked whether there were new predictions from his model, Bohm responded: "Not the way it's done." Bell [133] made a similar point but a bit more circumspectly: "It (de Broglie-Bohm version of nonrelativistic quantum mechanics) is experimentally equivalent to the usual version insofar as the latter is unambiguous."

akhmeteli

Jul31-10, 01:01 AM

No problem.

Why is that necessary? The wavefunction for an entangled system assigns an amplitude to joint states like |01> and |00>, no? So can't you just apply the Born rule once to find the probability of a given joint state?

I'll try to answer your questions one at a time, otherwise I'll never be able to handle them:-)

I don't quite get it. In Bell experiments, you need correlations. You need two measurements on the entangled system (maybe you could design some measurement to measure the correlation directly in one measurement, but practical Bell experiments require two measurements). Therefore, you need to apply the Born rule twice to predict something for these measurements.

akhmeteli

Jul31-10, 01:42 AM

I will skip a large part of the quote

Sections 7 and 8 also explain why Bohmian predictions end up being the same as predictions made using the standard pragmatic recipe involving "collapse" during measurement, in spite of the fact that Bohmian mechanics says nothing new or different really happens during measurement (the answer seems to involve the Bohmian version of decoherence).

As for whether these Bohmian predictions agree with those made using the usual recipe of wavefunction evolution + Born rule, I already quoted section 4 saying "so that this deterministic Bohmian model yields the usual quantum predictions for the results of the experiment", and the last paragraph of section 13 says:

Well, as I said, the meaning of his words is unclear, he might have just meant that Bohmian mechanics reproduces the exact same statistics as you'd get using the projection postulate, but that it does so using a different fundamental equation and without assuming anything special actually happens during measurement. It's also possible Demystifier would distinguish between the procedure of repeatedly applying the projection postulate for multiple measurements vs. assuming unitary evolution until the very end of a series of measurements and then applying the Born rule to find the probabilities for different possible combinations of recorded outcomes for all the previous measurements, and that he would say there are cases where Bohmian mechanics would predict slightly different statistics from the first case but not from the second case.

In any case, the Stanford Encyclopedia article was written by a professional physicist, Sheldon Goldstein, who advocates Bohm's interpretation, and in it he makes some quite ambiguous statements like "given the quantum equilibrium hypothesis, the observable consequences of Bohmian mechanics are the same as those of orthodox quantum theory". If Demystifier would actually disagree with statements like that (and I don't think he would), I would tend to trust Goldstein's expertise over Demystifier's. Also, p. 50 of this book (http://books.google.com/books?id=xcQNyP2nzRsC&lpg=PA49&dq=%22quantum%20equilibrium%22%20bohm%20prediction s&pg=PA50#v=onepage&q=%22quantum%20equilibrium%22%20bohm%20predictions&f=false) says that in any situation where the standard version of QM makes definite predictions, Bohmian mechanics makes the same predictions (though the author considers the possibility there might be situations where the standard version doesn't make clear predictions, like an observable which can't be represented as a Hermitian operator):

In the same article Goldstein writes:
"The second formulation of the measurement problem, though basically equivalent to the first one, suggests an important question: Can Bohmian mechanics itself provide a coherent account of how the two dynamical rules might be reconciled? How does Bohmian mechanics justify the use of the "collapsed" wave function in place of the original one? This question was answered in Bohm's first papers on Bohmian mechanics (Bohm 1952, Part I, Section 7, and Part II, Section 2). What would nowadays be called effects of decoherence, produced by interaction with the environment (air molecules, cosmic rays, internal microscopic degrees of freedom, etc.), make it extremely difficult for the component of the after-measurement wave function corresponding to the actual result of the measurement to develop significant overlap — in the configuration space of the very large system that includes all systems with which the original system and apparatus come into interaction — with the other components of the after-measurement wave function. But without such overlap the future evolution of the configuration of the system and apparatus is generated, to a high degree of accuracy, by that component all by itself. The replacement is thus justified as a practical matter. (See also Dürr et al. 1992, Section 5.)"

"To a high degree of accuracy"! So Goldstein says exactly the same as Demystifier (or, if you wish, Demystifier says exactly the same as Goldstein:-) ), namely: collapse is an approximation. The overlap does not disappear!

JesseM

Jul31-10, 09:25 AM

I'll try to answer your questions one at a time, otherwise I'll never be able to handle them:-)

I don't quite get it. In Bell experiments, you need correlations. You need two measurements on the entangled system (maybe you could design some measurement to measure the correlation directly in one measurement, but practical Bell experiments require two measurements). Therefore, you need to apply the Born rule twice to predict something for these measurements.
But in terms of the formalism, do you agree that you can apply the Born rule once for the amplitude of a joint state? One could consider this as an abstract representation of a pair of simultaneous measurements made at the same t-coordinate, for example. Even if the measurements were made at different times, one could assume unitary evolution for each measurement so that each measurement just creates entanglement between the particles and the measuring devices, but then apply the Born rule once to find the probability for the records of the previous measurements ('pointer states' in Bohmian lingo)

JesseM

Jul31-10, 09:38 AM

I will skip a large part of the quote

In the same article Goldstein writes:
"The second formulation of the measurement problem, though basically equivalent to the first one, suggests an important question: Can Bohmian mechanics itself provide a coherent account of how the two dynamical rules might be reconciled? How does Bohmian mechanics justify the use of the "collapsed" wave function in place of the original one? This question was answered in Bohm's first papers on Bohmian mechanics (Bohm 1952, Part I, Section 7, and Part II, Section 2). What would nowadays be called effects of decoherence, produced by interaction with the environment (air molecules, cosmic rays, internal microscopic degrees of freedom, etc.), make it extremely difficult for the component of the after-measurement wave function corresponding to the actual result of the measurement to develop significant overlap — in the configuration space of the very large system that includes all systems with which the original system and apparatus come into interaction — with the other components of the after-measurement wave function. But without such overlap the future evolution of the configuration of the system and apparatus is generated, to a high degree of accuracy, by that component all by itself. The replacement is thus justified as a practical matter. (See also Dürr et al. 1992, Section 5.)"

"To a high degree of accuracy"! So Goldstein says exactly the same as Demystifier (or, if you wish, Demystifier says exactly the same as Goldstein:-) ), namely: collapse is an approximation. The overlap does not disappear!
But here he is talking about the assumption of a collapse followed by another measurement later. What I said before about Demystifier applies to Goldstein too:
It's also possible Demystifier would distinguish between the procedure of repeatedly applying the projection postulate for multiple measurements vs. assuming unitary evolution until the very end of a series of measurements and then applying the Born rule to find the probabilities for different possible combinations of recorded outcomes for all the previous measurements, and that he would say there are cases where Bohmian mechanics would predict slightly different statistics from the first case but not from the second case.
If you assume unitary evolution and only apply the Born rule once at the very end, then the probabilities for different final observed states should be exactly equal to the probabilities given by Bohmian mechanics + the quantum equilibrium hypothesis. See for example the beginning of section 9 where he writes:
According to the quantum formalism, the probability density for finding a system whose wave function is ψ in the configuration q is |ψ(q)|2. To the extent that the results of measurement are registered configurationally, at least potentially, it follows that the predictions of Bohmian mechanics for the results of measurement must agree with those of orthodox quantum theory (assuming the same Schrödinger equation for both) provided that it is somehow true for Bohmian mechanics that configurations are random, with distribution given by the quantum equilibrium distribution |ψ(q)|2.
Would you agree that if we assume unitary evolution and then apply the Born rule once, at the very end, the probability that this last measurement will find the system in configuration q will be exactly |ψ(q)|2? And here Goldstein is saying that according to the quantum equilibrium hypothesis, at any given time the probability that a system's full configuration has an arrangement of positions corresponding to the observable state 1 is also exactly |ψ(q)|2. He says something similar in this paper (http://philpapers.org/rec/GOLQEA) where he writes:
Bohmian mechanics is arguably the most naively obvious embedding imaginable of Schr¨ odinger’s equation into a completely coherent physical theory. It describes a world in which particles move in a highly non-Newtonian sort of way, one which may at first appear to have little to do with the spectrum of predictions of quantum mechanics. It turns out, however, that as a consequence of the defining dynamical equations of Bohmian mechanics, when a system has wave function ψ its configuration is typically random, with probability density ρ given by |ψ|2, the quantum equilibrium distribution.
In any case, I want to be clear on one point: are you really arguing that Bohmian mechanics, when used the predict statistics for observable pointer states (which it can do assuming the same dynamical equation guides particle positions at all times, with no special rule for measurement), might not predict Bell inequality violations in an experiment of the type imagined by Bell? I don't think anyone would argue that Bohmian mechanics gives "approximately" the same results as the standard QM formalism if this were the case, that would be a pretty huge difference! And note section 13 of the Stanford article where Goldstein notes that Bohmian mechanics is explicitly nonlocal--the motions of each particle depend on the instantaneous positions of every other particle in the system.

akhmeteli

Jul31-10, 03:41 PM

But in terms of the formalism, do you agree that you can apply the Born rule once for the amplitude of a joint state? One could consider this as an abstract representation of a pair of simultaneous measurements made at the same t-coordinate, for example. Even if the measurements were made at different times, one could assume unitary evolution for each measurement so that each measurement just creates entanglement between the particles and the measuring devices, but then apply the Born rule once to find the probability for the records of the previous measurements ('pointer states' in Bohmian lingo)

I am not quite sure. Could you write down the amplitude you have in mind? It should be relevant to the correlation, shouldn't it? As I said, maybe you can design just one measurement to measure the correlation directly (it would probably be some nonlocal measurement), but that has nothing to do with what is done in Bell experiments and, therefore, is not useful for analysis of experiments. So you can do a lot as a matter of formalism, but the issue at hand is if what we do is relevant to Bell experiments. I don't accept the procedure you offer as it has nothing to do with practical measurements, which are performed on both particles. As I said, records are not even permanent. And measurements are never final. That is the curse of unitary evolution.

Furthermore, I am not sure the Born rule can be used as anything more than an operating principle, because I don't have a clear picture of how the Born rule arises from dynamics (unitary evolution).

Let me explain my problem with the derivation for quantum theory in more detail. Say, you are performing a measurement on one particle. If we take unitary evolution seriously, the measurement cannot destroy the superposition, therefore, the probability is not zero for each sign of the measured spin projection even after the measurement. Therefore, the same is true for the second particle. So, technically, the probability should not be zero for both particles having the same spin projection? You cannot eliminate this possibility, at least not if you perform just one measurement.

akhmeteli

Jul31-10, 04:28 PM

I skipped a large part of the quote again

In any case, I want to be clear on one point: are you really arguing that Bohmian mechanics, when used the predict statistics for observable pointer states (which it can do assuming the same dynamical equation guides particle positions at all times, with no special rule for measurement), might not predict Bell inequality violations in an experiment of the type imagined by Bell?

The probability density may be the same in Bohmian and standard theory for the entire system. But nobody models the instruments in the Bell proof. So you need something more to calculate the correlation in quantum theory and prove the violations. You have two measurements in experiments (so it is sufficient to use your understanding of Goldstein and Demystifier's words on approximation: "collapse followed by another measurement later") . To get the result, you can use the projection postulate in standard quantum mechanics, or you can say in Bohmian mechanics that collapse is a good approximation there. I am not aware of any proofs that do not use tricks of this kind. So yes, I do think that if you do not use such trick, you cannot prove violations in Bohmian mechanics. If you can offer a derivation that does not use something like this, I am all ears.

I don't think anyone would argue that Bohmian mechanics gives "approximately" the same results as the standard QM formalism if this were the case, that would be a pretty huge difference! And note section 13 of the Stanford article where Goldstein notes that Bohmian mechanics is explicitly nonlocal--the motions of each particle depend on the instantaneous positions of every other particle in the system.

Goldstein and Demystifier seem to say just that: collapse (part and parcel of standard quantum mechanics (SQM) so far) is just an approximation in Bohmian mechanics. So don't shoot the messenger (me:-) ). Again, if collapse were precise in Bohmian mechanics (BM), that would mean that BM contains the same internal contradictions as SQM.

And yes, Bohmian mechanics is explicitly nonlocal, but for some reason, there is no faster-than-light signaling there, for example (for the standard probability density). "My" model may have the same unitary evolution as an explicitly nonlocal theory (a quantum field theory), but it's local.

JesseM

Jul31-10, 04:39 PM

I am not quite sure. Could you write down the amplitude you have in mind?
The amplitude would depend on the experimental setup, but see the bottom section of p. 155 of this book (http://books.google.com/books?id=bDXwFHJNKFAC&lpg=PA155&dq=%22bell%20basis%22&pg=PA155#v=onepage&q=%22bell%20basis%22&f=false), which says:
If we denote the basis states for Alice as \mid a_i \rangle and the basis states for Bob by \mid b_j \rangle , then the basis states for the composite system are found by taking the tensor product of the Alice and Bob basis states:

\mid \alpha_{ij} \rangle = \mid a_i \rangle \otimes \mid b_j \rangle = \mid a_i \rangle \mid b_j \rangle = \mid a_i b_j \rangle
So in an experiment where the \mid a_i \rangle basis states represent eigenstates of spin for the particle measured by Alice, and the \mid b_j \rangle basis states represent eigenstates of spin for the particle measured by Bob, you can have basis states for the composite system like \mid a_i b_j \rangle and these states will naturally be assigned some amplitude by the wavefunction of the whole system.

Also see p. 194 of this book (http://books.google.com/books?id=-xCxg-yCvBcC&lpg=PA191&dq=spin%20bra%20ket%20entangled&pg=PA194#v=onepage&q=spin%20bra%20ket%20entangled&f=false) where they say:
In contrast with the classical physics, where the state of a system is completely defined by describing the state of each of its component pieces separately, in a quantum system the state cannot always be described considering only the component pieces. For instance, the state

\frac{1}{\sqrt{2}} (\mid 00 \rangle + \mid 11 \rangle )

cannot be decomposed into separate states for each of the two bits.

It should be relevant to the correlation, shouldn't it? As I said, maybe you can design just one measurement to measure the correlation directly (it would probably be some nonlocal measurement), but that has nothing to do with what is done in Bell experiments and, therefore, is not useful for analysis of experiments. So you can do a lot as a matter of formalism, but the issue at hand is if what we do is relevant to Bell experiments.
Suppose "as a matter of formalism" we adopt the procedure of applying unitary evolution to the whole experiment and then applying the Born rule to joint states (which includes measurement records/pointer states) at the very end. And suppose this procedure gives predictions which agree with the actual statistics we see when we examine records of experiments done in real life. Then don't we have a formalism which has a well-defined procedure for making predictions and whose predictions agree with experiment? It doesn't matter that the formalism doesn't make predictions about each individual measurement at the time it's made, as long as it makes predictions about the final results at the end of the experiment which we can compare with the actual final results (or compared with the predictions about the final results that any local realist theory would make).
As I said, records are not even permanent. And measurements are never final.
No, but forget what you know theoretically about QM, do you agree that in real life we can write down and share the results we have found at the end of an experiment? The fact that these records may no longer exist in 3000 AD doesn't mean we can't compare the records we see now with the predictions of some formal model.
Furthermore, I am not sure the Born rule can be used as anything more than an operating principle, because I don't have a clear picture of how the Born rule arises from dynamics (unitary evolution).
As a theoretical problem you may be interested in how it arises from dynamics, but if you just want a formal model that makes well-defined predictions that can be compared with reality, you don't need to know. That's why I keep calling it a pragmatic recipe--it doesn't need to have any theoretical elegance! All it needs to be is a procedure that always gives a prediction about the sort of quantitative results human experimenters obtain from real experiments.
Let me explain my problem with the derivation for quantum theory in more detail. Say, you are performing a measurement on one particle. If we take unitary evolution seriously,
On a theoretical level I agree it's good to "take unitary evolution seriously", but not in terms of the pragmatic recipe. If the pragmatic recipe says to apply unitary evolution until some time T when all measurement results have been recorded, then apply the Born rule to the pointer states at time T, that's a perfectly well-defined procedure whose predictions can be compared with the actual recorded results at T, even if we have no theoretical notion of how to justify this application of the Born rule.
the measurement cannot destroy the superposition, therefore, the probability is not zero for each sign of the measured spin projection even after the measurement. Therefore, the same is true for the second particle. So, technically, the probability should not be zero for both particles having the same spin projection?
If they are entangled in such a way that QM predicts you always get opposite spins, that would mean the amplitude for joint states \mid 11 \rangle and \mid 00 \rangle is zero. But since there is a nonzero amplitude for \mid 01 \rangle and \mid 10 \rangle, that means there's some nonzero probability for Alice to get result 1 and also some nonzero probability for her to get result 0, and likewise for Bob.

akhmeteli

Jul31-10, 04:50 PM

You consider ensemble as statistical ensemble of completely independent members where each member possess all the properties of ensemble as a whole, right?
Otherwise I do not understand how you can justify your statement.

What's your definition of ensemble? I just think that however you consider an ensemble, you cannot neglect the effect of one of its part on another. If you mean that a measurement is averaging over the particles beyond the subensemble or approximation, say so. In both cases the predictions of unitary evolution and projection postulate differ, hence the contradiction.

akhmeteli

Jul31-10, 04:57 PM

1. That's what you call a contribution? I guess I have a different assessment of that. Better Bell tests will always be on the agenda and I would say Zeilinger's agreement on that represents no change in his overall direction.

Yes, this is what I call a contribution

2. I consider your comment in 1. above to be acknowledgement of the obvious, which is that it is generally agreed that Bell Inequality violations have been found in every single relevant test performed to date. "Gen-u-wine" ones at that! So you can try and misrepresent the mainstream all you want, but you are 180 degrees off.

Why don't you call it for what it is: you are part of a very small minority regarding Bell. Where's the disrespect in that? If you are confident, just call yourself a rebel and continue your research.[/QUOTE]

No, it's no acknowledgement. Is it really "generally agreed", but not by Zeilinger, Shimony and Genovese?

akhmeteli

Jul31-10, 05:12 PM

That is a reasonable comment.

1. I am guessing that for you, entangled particles have states in common due to their earlier interaction. Further, that entangled particles are in fact discrete and are not in communication with each other in any ongoing manner. And yet, it is possible to entangle particles that have never existed in a common light cone. My point is that won't go hand in hand with any local realistic view.

Again, do entangled "particles that have never existed in a common light cone" present a loophole-free evidence of nonlocality? At last? As far as I know, nobody claimed that. Except maybe you. And entanglement exists in some form in the model.

2. EPR argued that the HUP could be beaten with entangled particles. You could learn the value of position on Alice and the momentum of Bob. And yet, a subsequent observation of Alice's momentum cannot be predicted using Bob's value. (Of course this applies to all non-commuting pairs, including spin). So EPR is wrong in that regard. That implies that the reality of Alice is somehow affected by the nature of the observation of Bob. I assume you deny this.

It is affected. But not instantaneously. At least it has not been demonstrated experimentally that the effect propagates faster than light. And again, I just don't question HUP, and HUP is valid for the model.

JesseM

Jul31-10, 05:22 PM

The probability density may be the same in Bohmian and standard theory for the entire system. But nobody models the instruments in the Bell proof.
You can include the state of the measuring device in a quantum analysis (simplifying its possible states so you don't actually consider it as composed of a vast number of particles), see this google scholar search for "state of the measuring" and "quantum" (http://scholar.google.com/scholar?hl=en&q=quantum+%22state+of+the+measuring%22&btnG=Search&as_sdt=1000000000000&as_ylo=&as_vis=0).
You have two measurements in experiments (so it is sufficient to use your understanding of Goldstein and Demystifier's words on approximation: "collapse followed by another measurement later") . To get the result, you can use the projection postulate in standard quantum mechanics
Or just include the measuring device in the quantum state, and apply the Born rule to the joint state of all the measuring devices/pointer states at some time T after the experiment is finished. Goldstein's point about the Bohmian probability being |ψ(q)|^2 means the probabilities for different joint pointer states at T should be exactly equal to the Bohmian prediction about the pointer states at T.
or you can say in Bohmian mechanics that collapse is a good approximation there.
Huh? My understanding is that a purely Bohmian analysis of any physical situation will never make use of "collapse", it'll only find the probabilities for the particles to end up in different positions according to the quantum equilibrium hypothesis. The idea that "collapse is a good approximation" would only be used if you wanted to compare Bohmian predictions to the predictions of a QM recipe which uses the collapse assumption, but if you were just interested in what Bohmian mechanics predicted, you would have no need for anything but the Bohmian guiding equation which tells you how particle positions evolve.
I am not aware of any proofs that do not use tricks of this kind.
OK, but have you actually studied the math of Bohmian mechanics and looked at how it makes predictions about any experiments, let alone Bell-type experiments? I haven't myself, but from what I've read I'm pretty sure that no purely Bohmian derivation of predictions would need to make use of any "trick" involving collapse.
So yes, I do think that if you do not use such trick, you cannot prove violations in Bohmian mechanics. If you can offer a derivation that does not use something like this, I am all ears.
Well, take a look at section 7.5 of Bohm's book The Undivided Universe, which is titled "The EPR experiment according to the causal interpretation" (another name for Bohmian mechanics), which can be read in its entirety on google books here (http://books.google.com/books?id=Erp0kUhm_NwC&lpg=PA1&ots=SKlzBrjAIU&dq=de%20broglie%20bohm%20bell%20inequality&lr&pg=PA147#v=onepage&q&f=false). Do you see any mention of a collapse assumption there?
Goldstein and Demystifier seem to say just that: collapse (part and parcel of standard quantum mechanics (SQM) so far) is just an approximation in Bohmian mechanics. So don't shoot the messenger (me:-) ).
But Goldstein also says that the probabilities predicted by Bohmian mechanics are just the same as those predicted by QM. Again, I think the seeming inconsistency is probably resolved if by assuming that when he talks of agreement he's talking of a single application of the Born rule to a quantum system which has been evolving in a unitary way, whereas when he talks about "approximation" he's talking about a repeated sequence of unitary evolution, projection onto an eigenstate by measurement, unitary evolution starting again from that eigenstate, another projection, etc.

GeorgCantor

Jul31-10, 05:35 PM

Do you know of a totally 100% loophole-free experiement from anywhere in the universe?

I can just repeat what I said several times: for some mysterious reason, Shimony is not quite happy about experimental demonstration of violations, Zeilinger is not quite happy... You are quite happy with it? I am happy for you. But that's no reason for me to be happy about that demonstration. Again, the burden of proof is extremely high for such radical ideas as elimination of local realism.

Yes, they aren't quite happy yet. The departure from the old concepts is just too great.

This isn't much different than Darwin's TOE in the mid-nineteen century. Not everyone would immediately recognize the evidence(no matter what), for the idea of a fish turning into a human being was just too radical, as you are saying about local realism. The TOE turned the world upside down, but we made do with it. Controversial or not, the theory of evolution is here to stay and so is the death of classical realism.

DevilsAvocado

Jul31-10, 05:44 PM

Controversial or not, the theory of evolution is here to stay and so is the death of classical realism.

Agree! :approve:

(Very good answer GC!)

JesseM

Jul31-10, 05:57 PM

So yes, I do think that if you do not use such trick, you cannot prove violations in Bohmian mechanics. If you can offer a derivation that does not use something like this, I am all ears.
Well, take a look at section 7.5 of Bohm's book The Undivided Universe, which is titled "The EPR experiment according to the causal interpretation" (another name for Bohmian mechanics), which can be read in its entirety on google books here (http://books.google.com/books?id=Erp0kUhm_NwC&lpg=PA1&ots=SKlzBrjAIU&dq=de%20broglie%20bohm%20bell%20inequality&lr&pg=PA147#v=onepage&q&f=false). Do you see any mention of a collapse assumption there?

And here's another:

A causal account of non-local Einstein-Podolsky-Rosen spin correlations (http://www.psiquadrat.de/downloads/dewdney1987.pdf)

Section 5 on p.12-13 of the pdf says:
The preceding analysis enables us to see clearly the manner in which the assumptions made by Bell [7] in his derivation of an inequality that any local hidden variables theory must apparently satisfy are violated in the causal interpretation ...

In the causal interpretation the probability distribution of positions is derived from the quantum mechanical wavefunction which is a function of all the contributing parts of the process, including the orientation of the magnets ...

Bell's inequality is therefore violated because the hidden variables are non-locally interconnected by the quantum potential derived from the total quantum state. It is in this sense that the causal interpretation implies non-local correlations in the properties of distantly separated systems.
So it seems that the analysis is based only on the positions of the parts of the system (including which direction the particles are deflected by the magnets, which is what a determination of 'spin' is based on), and that "the system" explicitly includes the magnets and their orientations. And this Bohmian analysis does apparently show that Bell's inequality can be violated.

akhmeteli

Jul31-10, 06:18 PM

My personal advice to an independent researcher:

Thank you for your advice, but I think it's completely misplaced. Let me explain.

Now, what’s my personal opinion on EPR-Bell experiments and loopholes? Well, I think you are presenting a terrible biased picture of the situation. You want us to believe that current experts in EPR-Bell experiments have the same bizarre valuation of their experiments as you have. Namely, that every performed EPR-Bell experiment so far is worth nothing?? Zero, zip, nada, zilch, 0!? :eek:

Before you start another episode of your soap opera here, why don't you just read the question you were asked?

I wrote the following:

"Those experts are telling us, mere mortals, that there have been no loophole-free Bell experiments. You are certainly free to disagree with them, but then why don’t you just pinpoint that loophole-free experiment? And it would be most helpful if you could explain how it so happened that Shimony, Zeilinger and Genovese have no knowledge whatsoever about this experiment.
Again, Ruta is no fan of local realism either, but he also admits that there are no such experiments.
So, to summarize, it seems obvious that there have been no such experiments so far (DrChinese will strongly disagree, but let me ask you, DevilsAvocado, what is your personal opinion?)"

So it should be clear that I asked you the following question: "Do you agree that there have been no loophole-free Bell experiments?" Did I say "that every performed EPR-Bell experiment so far is worth nothing", as you imply? No, I did not. In my opinion, those experiments are very valuable as they explored the new area of parameters, so we know now what Nature is like in this area. Why are you substituting my question with something very different? Why are you ascribing me an opinion that I don't share?

So let me ask you again:

"Do you agree that there have been no loophole-free Bell experiments?"

You are also trying to apply this faulty logic on RUTA:

Yes, RUTA is an honest scientist and he would never lie and say that a 100% loophole-free Bell experiment has been performed, when it hasn’t yet.

So you agree that a loophole-free Bell experiment has not been performed? Or not?

But where do you see RUTA saying that performed Bell experiments so far is worth absolutely nothing, nil!?!? Your twist is nothing but a scam:

But where do you see me saying that performed Bell experiments so far is worth absolutely nothing, nil!?!? Your twist is nothing but a scam

I can guarantee you that RUTA, Zeilinger or any other real scientist in the community all agree that all performed EPR-Bell experiments so far has proven with 99.99% certainty that all local realistic theories are doomed. But they are fair, and will never lie, and say 100%, until they are 100%.

You are exploiting this fact in a very deceive way, claiming that they are saying that there is 0% proof of local realistic theories being wrong.

And where am I "claiming that they are saying that there is 0% proof of local realistic theories being wrong"? I give their direct quotes confirming that there have been no loophole-free Bell experiments. Why twist my words again? They do believe there is little or no chance for local realism, but this is their opinion. The fact (that they admit) is, however, that there have been no loophole-free experiments ruling out local realism.

And then comes the "Grand Finale", where you use a falsification of Anton Zeilinger’s standpoint, as the "foundation" for this personal cranky statement:

Outrageous :mad:

Since when a literal quote is a falsification?

And I gave you the reasons, so there are indeed "some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory, EVER". If you are outraged by this statement, that does not mean there are no such reasons.

akhmeteli

Jul31-10, 06:38 PM

You can include the state of the measuring device in a quantum analysis (simplifying its possible states so you don't actually consider it as composed of a vast number of particles), see this google scholar search for "state of the measuring" and "quantum" (http://scholar.google.com/scholar?hl=en&q=quantum+%22state+of+the+measuring%22&btnG=Search&as_sdt=1000000000000&as_ylo=&as_vis=0).

So was the violation in quantum theory derived in this way?

Or just include the measuring device in the quantum state, and apply the Born rule to the joint state of all the measuring devices/pointer states at some time T after the experiment is finished. Goldstein's point about the Bohmian probability being |ψ(q)|^2 means the probabilities for different joint pointer states at T should be exactly equal to the Bohmian prediction about the pointer states at T.

So was the violation in quantum theory derived without PP or something like that? Mind that "different joint pointer states" overlap in principle.

Huh? My understanding is that a purely Bohmian analysis of any physical situation will never make use of "collapse", it'll only find the probabilities for the particles to end up in different positions according to the quantum equilibrium hypothesis. The idea that "collapse is a good approximation" would only be used if you wanted to compare Bohmian predictions to the predictions of a QM recipe which uses the collapse assumption, but if you were just interested in what Bohmian mechanics predicted, you would have no need for anything but the Bohmian guiding equation which tells you how particle positions evolve.

So were violations proven in "a purely Bohmian analysis"? I am not aware of that.

OK, but have you actually studied the math of Bohmian mechanics and looked at how it makes predictions about any experiments, let alone Bell-type experiments? I haven't myself, but from what I've read I'm pretty sure that no purely Bohmian derivation of predictions would need to make use of any "trick" involving collapse.

Again, same question, is there a "purely Bohmian derivation of" violations? I am not aware of that.

Well, take a look at section 7.5 of Bohm's book The Undivided Universe, which is titled "The EPR experiment according to the causal interpretation" (another name for Bohmian mechanics), which can be read in its entirety on google books here (http://books.google.com/books?id=Erp0kUhm_NwC&lpg=PA1&ots=SKlzBrjAIU&dq=de%20broglie%20bohm%20bell%20inequality&lr&pg=PA147#v=onepage&q&f=false). Do you see any mention of a collapse assumption there?

Yes: "Using the theory of measurement..." and "do not overlap for different j"

But Goldstein also says that the probabilities predicted by Bohmian mechanics are just the same as those predicted by QM. Again, I think the seeming inconsistency is probably resolved if by assuming that when he talks of agreement he's talking of a single application of the Born rule to a quantum system which has been evolving in a unitary way, whereas when he talks about "approximation" he's talking about a repeated sequence of unitary evolution, projection onto an eigenstate by measurement, unitary evolution starting again from that eigenstate, another projection, etc.

Very well, and this is what we have in Bell experiments, as there are two measurements.

DevilsAvocado

Jul31-10, 06:55 PM

... And where am I "claiming that they are saying that there is 0% proof of local realistic theories being wrong"? I give their direct quotes confirming that there have been no loophole-free Bell experiments. Why twist my words again? They do believe there is little or no chance for local realism, but this is their opinion. The fact (that they admit) is, however, that there have been no loophole-free experiments ruling out local realism.

You are a funny guy, not a scientist.

Is this really so hard? You are continuously making the same cranky INSINUATIONS – as if all the hard work by one of the most famous experts in EPR-Bell experiments, Anton Zeilinger, has only resulted in a PERSONAL OPINION!?

You are way out my friend, and alone on your twisted road:
When I first entered the foundations community (1994), there were still a few conference presentations arguing that the statistical and/or experimental analyses of EPR-Bell experiments were flawed. SUCH TALKS HAVE GONE THE WAY OF THE DINOSAURS. VIRTUALLY EVERYONE AGREES THAT THE EPR-BELL EXPERIMENTS AND QM ARE LEGIT, SO WE NEED A SIGNIFICANT CHANGE IN OUR WORLDVIEW. There is a proper subset who believe this change will be related to the unification of QM and GR :-)
Stanford Encyclopedia of Philosophy – Bell's Theorem
...
In the face of the spectacular experimental achievement of Weihs et al. and the anticipated result of the experiment of Fry and Walther THERE IS LITTLE THAT A DETERMINED ADVOCATE OF LOCAL REALISTIC THEORIES CAN SAY except that, despite the spacelike separation of the analysis-detection events involving particles 1 and 2, the backward light-cones of these two events overlap, and it is conceivable that some controlling factor in the overlap region is RESPONSIBLE FOR A CONSPIRACY AFFECTING THEIR OUTCOMES. THERE IS SO LITTLE PHYSICAL DETAIL IN THIS SUPPOSITION that a discussion of it is best delayed until a methodological discussion in Section 7.

I made the important parts in upper-case + bold, since you seem to having trouble understanding simple English.

akhmeteli

Jul31-10, 06:56 PM

Yes, they aren't quite happy yet. The departure from the old concepts is just too great.

This isn't much different than Darwin's TOE in the mid-nineteen century. Not everyone would immediately recognize the evidence(no matter what), for the idea of a fish turning into a human being was just too radical, as you are saying about local realism. The TOE turned the world upside down, but we made do with it. Controversial or not, the theory of evolution is here to stay and so is the death of classical realism.

So TOE has been confirmed by now. So what? Should we consider that a confirmation of elimination of local realism? No way. This elimination must be confirmed independently. Has it been confirmed experimentally so far? As there are no experimental demonstrations of violations of genuine Bell inequalities, local realism has not been ruled out so far. What should we expect? In 10 years? In fifty years? It's a matter of opinion. You believe local realism will be eliminated by future experiments, I don't expect that. But both of us will have to accept the results of the future experiments, whether we'll like them or dislike them.
We have yet to see decisive experiments, so we both still have the right to have our opinions.

JesseM

Jul31-10, 11:30 PM

You can include the state of the measuring device in a quantum analysis (simplifying its possible states so you don't actually consider it as composed of a vast number of particles), see this google scholar search for "state of the measuring" and "quantum".
So was the violation in quantum theory derived in this way?
I'm pretty sure you can derive any quantum statistics in this way. Doing a little research, it turns out this was essentially Von Neumann's approach to the measurement problem--he conceived of two stages of the measurement process, a first where the system being measured simply becomes entangled with the measuring-device, and a second where the measuring-device is "observed" and found to be in some definite pointer state, with the probability of different pointer states determined by the Born rule. See this paper (http://arxiv.org/abs/quant-ph/9605002) where on page 3 they write:
The crucial step to describe the measurement process as an interaction of two quantum systems [as is implicit in (2.2)] was made by von Neumann [6], who recognized that an interaction between a classical and a quantum system cannot be part of a consistent quantum theory. In his Grundlagen, he therefore proceeded to decompose the quantum measurement into two fundamental stages. The first stage (termed "von Neumann measurement") gives rise to the wavefunction (2.2). The second stage (which von Neumann termed "observation" of the measurement) involves the collapse described above, i.e., the transition from (2.2) to (2.3).
The same authors have another paper here (http://arxiv.org/abs/quant-ph/9605039) where they apply this sort of analysis to "Bell-type measurements" on p. 16, with two quantum particles Q1 and Q2 along with two measuring-devices or "ancillae" A1 and A2, such that after the ancillae interact with the particles they are all in one entangled state \mid Q_1 Q_2 A_1 A_2 \rangle = \frac{1}{\sqrt{2}} (\mid \uparrow \uparrow 1 1 \rangle + \mid \downarrow \downarrow 0 0 \rangle ). They then say that "after observing A1, for instance, the state of A2 can be inferred without any uncertainty". Unfortunately they don't give explicit calculations for the probabilities of different results on A1 and A2 when the ancillae aren't measuring spin on the same axis, so they don't clearly show how von Neumann's approach predicts Bell inequality violations. And although I came across a lot of other papers that model measurement in terms of measuring-devices becoming entangled with measuring-systems, like this one (http://www.hep.princeton.edu/~mcdonald/examples/QM/zurek_prd_24_1516_81.pdf), most did not use von Neumann's approach of assuming a collapse at the very end when the measuring devices were all "observed", instead they were generally trying to show how one could make meaningful statements about measurement results without making use of even a single "collapse" or application of the Born rule (perhaps part of the problem is that von Neumann's approach is rather old hat so most physicists would just consider it pedantic to explicitly demonstrate what predictions it would give for a Bell-type experiment). But anyway, given that this approach has been around for so many years, I seriously doubt that it would fail to predict Bell inequality violations without anyone having noticed this fact! (or without it being widely commented-on in these sorts of papers if it was known that it failed to predict BI violations)

Also, I found one other interesting paper here (http://www.lps.uci.edu/barrett/publications/SuggestiveProperties.pdf) which discusses what happens if we assume measurement just creates entanglement between pointer states and particle states with no collapse ever (what the author calls the 'bare theory' of QM0, and then we consider the limit as an observer makes an infinite series of measurements in an EPR type experiment. On p. 13-14 the author discusses the result:
For another example suppose that two systems SA and SB are initially in the EPR state (2) and that A and B make space-like measurements of their respective systems ... What does the bare theory predict in the limit as this experiment is performed an infinite number of times? ... given the general limiting property, A and B will approach an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts .. if they perform an appropriate sequence of different experiments, then they will approach an eigenstate of reporting that their results fail to satisfy the Bell-type inequalities.
Again, same question, is there a "purely Bohmian derivation of" violations? I am not aware of that.
I believe so, the section of Bohm's book I linked to and the paper I linked to in post #701 both appeared to analyze EPR-type experiments from a purely Bohmian perspective.
Well, take a look at section 7.5 of Bohm's book The Undivided Universe, which is titled "The EPR experiment according to the causal interpretation" (another name for Bohmian mechanics), which can be read in its entirety on google books here. Do you see any mention of a collapse assumption there?
Yes: "Using the theory of measurement..." and "do not overlap for different j"
I think you're probably misunderstanding the import of those phrases. When Bohm wrote on p. 122 (http://books.google.com/books?id=vt9XKjc4WAQC&lpg=PA122&dq=%22using%20the%20theory%20of%20measurement%22%2 0bohm&pg=PA122#v=onepage&q&f=false) "Using the theory of measurement described in chapters 2 and 6, we may assume an interaction Hamiltonian..." and gives an equation, that's the Hamiltonian equation which guides the continuous time evolution of the system, I don't see how it has anything to do with discontinuous collapse. And the "theory of measurement" described in chapter 6 appears to be one that does not involve collapse--scroll down to p. 104 here (http://www.scribd.com/doc/33838548/The-Undivided-Universe-An-Ontological-Interpretation-of-Quantum-pdf) to look at that chapter, he says on p. 109:
At this stage we can say that everything has happened as if the overall wave function had 'collapsed' to one corresponding to the actual result obtained in the measurement. We emphasise, however, that in our treatment there is no actual collapse; there is merely a process in which the information represented by the unoccupied packets effectively loses all potential for activity ... It follows that in this regard measurement is indeed just a special case of a transition process in which the two systems interact and then come out in correlated states. It is this correlation that enables us, from the observed result, to attribute a corresponding property to the final state of the observed system.

In the transition process that takes place in a measurement, it is clear that (as happens indeed in all transition processes) there is no need to place any 'cuts' or arbitrary breaks in the description of reality, such as that, for example, introduced by von Neumann between the quantum and classical levels.
I also don't see why "\alpha \Delta t must be large enough so that the \Phi_A (y - j \alpha \Delta t ) do not overlap for different j" lower on the same page has anything to do with collapse, \Phi_A (y) is supposed to represent the "initial wave packet of the apparatus" so this condition also may express some constraint on the design of the apparatus (maybe something like the idea that it should be designed so there isn't significant interference between different possible pointer states), I'm not sure. Do you actually understand the detailed meaning of the math in this section or are you just looking at the verbal descriptions of Bohmian calculations like me? You didn't answer the question I asked earlier:
OK, but have you actually studied the math of Bohmian mechanics and looked at how it makes predictions about any experiments, let alone Bell-type experiments? I haven't myself, but from what I've read I'm pretty sure that no purely Bohmian derivation of predictions would need to make use of any "trick" involving collapse.
But Goldstein also says that the probabilities predicted by Bohmian mechanics are just the same as those predicted by QM. Again, I think the seeming inconsistency is probably resolved if by assuming that when he talks of agreement he's talking of a single application of the Born rule to a quantum system which has been evolving in a unitary way, whereas when he talks about "approximation" he's talking about a repeated sequence of unitary evolution, projection onto an eigenstate by measurement, unitary evolution starting again from that eigenstate, another projection, etc.
Very well, and this is what we have in Bell experiments, as there are two measurements.
Have you not been paying attention to the distinction I've been making in previous posts between two procedures for calculating probabilities in QM? I have been saying over and over that if you have a series of measurements, you don't have to treat each measurement as leading to a collapse, you can instead treat each measurement as just creating entanglement between measuring apparatus and system being measured, and then apply the Born rule once to the final pointer states after a long series of measurements. That seems to be exactly the approach von Neumann used to deal with measurement too, as noted at the top. So my point is that as long as you only apply the Born rule once in this way, I think there is perfect agreement in the probabilities for different pointer states between this approach and Bohmian mechanics; it's only when you use the projection postulate repeatedly at the moment of each measurement that the agreement with Bohmian mechanics may only be "approximate".

akhmeteli

Aug1-10, 08:13 AM

I'm pretty sure you can derive any quantum statistics in this way.

Being pretty sure is one thing. Giving a proof or a reference is something else. I comment on your references below.

Doing a little research, it turns out this was essentially Von Neumann's approach to the measurement problem--he conceived of two stages of the measurement process, a first where the system being measured simply becomes entangled with the measuring-device, and a second where the measuring-device is "observed" and found to be in some definite pointer state, with the probability of different pointer states determined by the Born rule.

Again, we may have some opinion about adequacy of this procedure, but it is not quite relevant. This procedure is about just one measurement, the Bell theorem is about two measurements.

See this paper (http://arxiv.org/abs/quant-ph/9605002) where on page 3 they write:

The same authors have another paper here (http://arxiv.org/abs/quant-ph/9605039) where they apply this sort of analysis to "Bell-type measurements" on p. 16, with two quantum particles Q1 and Q2 along with two measuring-devices or "ancillae" A1 and A2, such that after the ancillae interact with the particles they are all in one entangled state \mid Q_1 Q_2 A_1 A_2 \rangle = \frac{1}{\sqrt{2}} (\mid \uparrow \uparrow 1 1 \rangle + \mid \downarrow \downarrow 0 0 \rangle ). They then say that "after observing A1, for instance, the state of A2 can be inferred without any uncertainty". Unfortunately they don't give explicit calculations for the probabilities of different results on A1 and A2 when the ancillae aren't measuring spin on the same axis, so they don't clearly show how von Neumann's approach predicts Bell inequality violations.

So no proof.

And although I came across a lot of other papers that model measurement in terms of measuring-devices becoming entangled with measuring-systems, like this one (http://www.hep.princeton.edu/~mcdonald/examples/QM/zurek_prd_24_1516_81.pdf), most did not use von Neumann's approach of assuming a collapse at the very end when the measuring devices were all "observed", instead they were generally trying to show how one could make meaningful statements about measurement results without making use of even a single "collapse" or application of the Born rule (perhaps part of the problem is that von Neumann's approach is rather old hat so most physicists would just consider it pedantic to explicitly demonstrate what predictions it would give for a Bell-type experiment).

So no proof.

But anyway, given that this approach has been around for so many years, I seriously doubt that it would fail to predict Bell inequality violations without anyone having noticed this fact! (or without it being widely commented-on in these sorts of papers if it was known that it failed to predict BI violations)

In this case you are right to seriously doubt it:-), as "someone" has indeed noticed this fact, and it was not me! You see, I clearly said in this thread and in my article that I have little, if anything new to say about the Bell theorem, I just repeat other people's analysis. These people are nightlight and Santos (nightlight told me that they corresponded for years via emails). I give the references in my article. If you feel the references are not specific enough, let me know, I'll try to do something about that.

I'll try to address the other points of your post later.

JesseM

Aug1-10, 10:20 AM

akhmeteli

Aug1-10, 02:00 PM

Also, I found one other interesting paper here (http://www.lps.uci.edu/barrett/publications/SuggestiveProperties.pdf) which discusses what happens if we assume measurement just creates entanglement between pointer states and particle states with no collapse ever (what the author calls the 'bare theory' of QM0, and then we consider the limit as an observer makes an infinite series of measurements in an EPR type experiment. On p. 13-14 the author discusses the result:

JesseM, with all due respect, a couple of lines later the author writes: "Note, however, that since the linear dynamics can be written in a perfectly local form, there are in fact no nonlocal causal connections in the bare theory. ...Just as reports of determinate results, relative frequencies, and randomness would generally be explained by the bare theory as illusions the apparent nonlocality here would be just that, apparent." :-) And on page 4: "According to the bare theory,
an observer who begins in an eigenstate of being ready to make a
measurement would end up in an eigenstate of reporting that he has
an ordinary, determinate result to his measurement. This might mean
that the observer believes that he has a determinate measurement
result, but in the context of the bare theory this would not generally
mean that there is any determinate result that the observer believes he
has. Contrary to what Everett and others have claimed, the bare theory
does not make the same empirical predictions as the standard theory;
rather, the bare theory at best provides an explanation for why it might
appear to an observer that the standard theory's empirical predictions
are true when they are in fact false. That is, the bare theory provides
the basis for claiming in some circumstances that some of one's beliefs
are the result of an illusion." So no, this link, while indeed interesting, does not prove what you want.

I believe so, the section of Bohm's book I linked to and the paper I linked to in post #701 both appeared to analyze EPR-type experiments from a purely Bohmian perspective.

I commented on the Bohm's book, and in the paper by Dewdney e.a., they take their formulae for correlations 3.2 and 3.2a from nowhere, just as "well known expectation value for the correlations". After that, the inequalities are violated. But you cannot get these formulae without the projection postulate, at least that's what I think so far.

I think you're probably misunderstanding the import of those phrases. When Bohm wrote on p. 122 (http://books.google.com/books?id=vt9XKjc4WAQC&lpg=PA122&dq=%22using%20the%20theory%20of%20measurement%22%2 0bohm&pg=PA122#v=onepage&q&f=false) "Using the theory of measurement described in chapters 2 and 6, we may assume an interaction Hamiltonian..." and gives an equation, that's the Hamiltonian equation which guides the continuous time evolution of the system, I don't see how it has anything to do with discontinuous collapse. And the "theory of measurement" described in chapter 6 appears to be one that does not involve collapse--scroll down to p. 104 here (http://www.scribd.com/doc/33838548/The-Undivided-Universe-An-Ontological-Interpretation-of-Quantum-pdf) to look at that chapter, he says on p. 109:

I also don't see why "\alpha \Delta t must be large enough so that the \Phi_A (y - j \alpha \Delta t ) do not overlap for different j" lower on the same page has anything to do with collapse, \Phi_A (y) is supposed to represent the "initial wave packet of the apparatus" so this condition also may express some constraint on the design of the apparatus (maybe something like the idea that it should be designed so there isn't significant interference between different possible pointer states), I'm not sure. Do you actually understand the detailed meaning of the math in this section or are you just looking at the verbal descriptions of Bohmian calculations like me?

While you may regard the mention of measurement theory as purely formal (I did not check it), the "overlap" phrase is critical. No overlap - no interference. This is where they get rid of superposition. And no condition can prevent overlap. The word "significant" is not good enough.

I did not check the "proof" in detail, but I know Bohm's theory of measurement and know where they get rid of superposition to get "appearance of collapse".

You didn't answer the question I asked earlier:

Sorry, as I said, I am struggling trying to keep up with you:-)

Yes, I studied their math, and it is my understanding that the neglect of the overlap takes care of superpositions, so I disagree with your "pretty sure".

Have you not been paying attention to the distinction I've been making in previous posts between two procedures for calculating probabilities in QM? I have been saying over and over that if you have a series of measurements, you don't have to treat each measurement as leading to a collapse, you can instead treat each measurement as just creating entanglement between measuring apparatus and system being measured, and then apply the Born rule once to the final pointer states after a long series of measurements. That seems to be exactly the approach von Neumann used to deal with measurement too, as noted at the top. So my point is that as long as you only apply the Born rule once in this way, I think there is perfect agreement in the probabilities for different pointer states between this approach and Bohmian mechanics; it's only when you use the projection postulate repeatedly at the moment of each measurement that the agreement with Bohmian mechanics may only be "approximate".

I got your idea, but, as I said, the procedure you describe has nothing to do with real Bell experiments, where measurements are done separately on each particle, they actually use the results of two measurements. So your procedure applying the Born rule once does not seem relevant to experiments. How do you get the correlation in your procedure?

akhmeteli

Aug1-10, 02:37 PM

Yes, I haven't linked to a proof, and I don't feel like spending hours combing through papers looking for one (as I said, most modern papers would probably just consider the result too trivial to explicitly demonstrate).

I fully understand.

Are you just being pedantic in noting I haven't proved it, or do you actually believe it is plausible that von Neumann's approach to QM measurement, which has been around for decades, would fail to predict Bell inequality violations without anyone noticing this fact? (or if physicists had noticed, without it being a widely discussed result?)

I would like to be accurate here, as it is my understanding that the projection postulate was also introduced by Neumann. But I believe you have in mind an approach where actual measurement is performed only once. I just don't understand how this approach is relevant to Bell experiments where measurements are performed twice. And I really don't think you can get theoretical violations in standard QM or in Bohmian mechanics without the projection postulate or something like that.

Or does your claim here:

...mean that you believe "nightlight and Santos" have actually proved that von Neumann's approach, where we model measurements as just creating entanglement and we then "observe" the measurement records later (using the Born rule on the records), fails to predict violations of Bell inequalities in those records?

See my comment above on "Neumann's approach". I cannot say in good faith that nightlight or Santos "proved" that violations in QM cannot be proven without using the projection postulate or something like that (maybe they did, but I am not sure). What they did do (at least this is my understanding), they noted that the projection postulate is used in standard proofs of the Bell theorem where it is proven that the inequalities can be violated in QM, and they also noted that the projection postulate contradicts unitary evolution. Can you prove the violations without this postulate? I cannot eliminate such a possibility, but I don't think it is possible. I perfectly understand that you don't want to spend hours to find a proof of what you think is true, but I hope you'll understand that neither I want to spend hours to find a proof of what you think is true and I think is false:-) My logic is as follows. Violations spell nonlocality, the projection postulate spells nonlocality (as soon as the spin projection of one particle is measured, the spin projection of the other particle, however remote, becomes determinate - this stinks to heaven!), so a suspicion that this is the only source of nonlocality seems quite natural.

Also, note the paper here (http://www.lps.uci.edu/barrett/publications/SuggestiveProperties.pdf) I linked to above, which shows that in the limit as the number of measurements (without collapse) in an EPR type experiment goes to infinity the state vector will approach "an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts". This does at least imply that in the limit as the number of measurements goes to infinity, if we "collapse" the records at the very end, the probability that the records will show measurement results that were "randomly distributed and statistically correlated in just the way the standard theory predicts" should approach 1 in this limit. Do you disagree?

I commented on that in my post 709.

DevilsAvocado

Aug1-10, 03:41 PM

My logic is as follows. Violations spell nonlocality, the projection postulate spells nonlocality (as soon as the spin projection of one particle is measured, the spin projection of the other particle, however remote, becomes determinate - this stinks to heaven!), so a suspicion that this is the only source of nonlocality seems quite natural.

What also stinks to heaven, is when wannabes pretend to have "serious proof" that dismiss all work of John Bell, and all serious scientist who worked on EPR-Bell experiments for decades – without even a basic understanding of Bell's Theorem!?

EPR-Bell experiments is not about "the other particle, however remote, becomes determinate"! This is only the case when the polarizers are aligned parallel!! EPR-Bell experiments are all about statistics, and there is no way one could violate Bell's Inequality when the polarizers are aligned parallel only, JesseM can verify this.

What is also hilarious is that when the polarizers are aligned parallel, and the correlation is 100%, anyone can easily construct LHV that explains this in a LR model, except you.

But I’m not surprised you have missed this. You seem to spend all your time looking for irrelevant "stuff" to discredit the work of John Bell.

JesseM

Aug1-10, 03:46 PM

I would like to be accurate here, as it is my understanding that the projection postulate was also introduced by Neumann. But I believe you have in mind an approach where actual measurement is performed only once. I just don't understand how this approach is relevant to Bell experiments where measurements are performed twice.
You seem to be misunderstanding something really basic about my argument--you are conflating "measurement" with "projection", but my whole point is that they don't need to be treated as equivalent! You can instead assume that each interaction between the quantum system and the measuring-device can be treated in a purely unitary way--i.e. these measurements do not involve projection--and that after all the measurements in your experiment are done, you have a pure state where all the records of the previous measurements are in a massive superposition, and only then do you use the projection postulate once on the whole collection of records (records of many different prior measurements). I've already explained this several times in the past but you continue to misunderstand...for example, from post #706:
Have you not been paying attention to the distinction I've been making in previous posts between two procedures for calculating probabilities in QM? I have been saying over and over that if you have a series of measurements, you don't have to treat each measurement as leading to a collapse, you can instead treat each measurement as just creating entanglement between measuring apparatus and system being measured, and then apply the Born rule once to the final pointer states after a long series of measurements. That seems to be exactly the approach von Neumann used to deal with measurement too, as noted at the top. So my point is that as long as you only apply the Born rule once in this way, I think there is perfect agreement in the probabilities for different pointer states between this approach and Bohmian mechanics; it's only when you use the projection postulate repeatedly at the moment of each measurement that the agreement with Bohmian mechanics may only be "approximate".
And post #694:
Suppose "as a matter of formalism" we adopt the procedure of applying unitary evolution to the whole experiment and then applying the Born rule to joint states (which includes measurement records/pointer states) at the very end. And suppose this procedure gives predictions which agree with the actual statistics we see when we examine records of experiments done in real life. Then don't we have a formalism which has a well-defined procedure for making predictions and whose predictions agree with experiment? It doesn't matter that the formalism doesn't make predictions about each individual measurement at the time it's made, as long as it makes predictions about the final results at the end of the experiment which we can compare with the actual final results (or compared with the predictions about the final results that any local realist theory would make).
post #690:
But in terms of the formalism, do you agree that you can apply the Born rule once for the amplitude of a joint state? One could consider this as an abstract representation of a pair of simultaneous measurements made at the same t-coordinate, for example. Even if the measurements were made at different times, one could assume unitary evolution for each measurement so that each measurement just creates entanglement between the particles and the measuring devices, but then apply the Born rule once to find the probability for the records of the previous measurements ('pointer states' in Bohmian lingo)
So, after reviewing these comments, do you understand what I mean now? That if we want to make predictions about what our records will show at the end of a series of N measurements, we can assume unitary evolution until after all N measurements are complete, and then just apply the Born rule to the records at that time to get a prediction about the statistics?

If you do understand this, note that this is exactly what von Neumann's approach was. In his approach we do not assume that each measurement collapses the wavefunction, instead it just causes entanglement, and then only later are the measurement records "observed". In post #706 I quoted this paper (http://arxiv.org/abs/quant-ph/9605002) which described his approach on p. 3:
The crucial step to describe the measurement process as an interaction of two quantum systems [as is implicit in (2.2)] was made by von Neumann [6], who recognized that an interaction between a classical and a quantum system cannot be part of a consistent quantum theory. In his Grundlagen, he therefore proceeded to decompose the quantum measurement into two fundamental stages. The first stage (termed "von Neumann measurement") gives rise to the wavefunction (2.2). The second stage (which von Neumann termed "observation" of the measurement) involves the collapse described above, i.e., the transition from (2.2) to (2.3).
Similarly, consider the paper Quantum Mechanics and Reality (http://arxiv.org/abs/quant-ph/0412148) which discusses different approaches to "measurement", and on p. 16 describes von Neumann's approach:
In contrast to Bohr, the measuring apparatus A as well as systems S are both to be described by quantum mechanics.

...

The state \sum c_n \phi_n f(a_n) is a linear superposition of states with different pointer states. It is a grotesque state. We still have not obtained a definite value of the pointer reading. Von-Neumann now postulates that when the measurement is completed, and not before that, the wave function collapses to one of the terms in the linear superposition e.g. to \phi_N f(a_N). It is this collapse postulate which adds an extra ingredient to Quantum mechanics and making quantum mechanical description nonclosed.

In an elaboration of von-Neumann view by London and Bauer, and also subscribed to by Wigner and Stapp, this final collapse of wave function takes place when the result of measurement is recorded in a human mind.
Anyway, if you now understand the approach I'm suggesting but aren't convinced that von Neumann's was the same, I can try to find more sources explaining his approach. But I want to make sure that you actually do understand my approach now, given that you still seem to be conflating "measurement" with "collapse"...

akhmeteli

Aug1-10, 04:57 PM

You seem to be misunderstanding something really basic about my argument--you are conflating "measurement" with "projection", but my whole point is that they don't need to be treated as equivalent! You can instead assume that each interaction between the quantum system and the measuring-device can be treated in a purely unitary way--i.e. these measurements do not involve projection--and that after all the measurements in your experiment are done, you have a pure state where all the records of the previous measurements are in a massive superposition, and only then do you use the projection postulate once on the whole collection of records (records of many different prior measurements). I've already explained this several times in the past but you continue to misunderstand...for example, from post #706:

OK, so you just use the projection postulate, not the Born rule? Then I agree that you can prove violations in quantum mechanics. But this is exactly where you introduce nonlocality. Remember that actual records are not even permanent. Where exactly do you perform this second stage of your procedure, the "observation"? Near the point where the first particle is? Or where the second particle is? If where the first particle is, as soon as you "observe" its spin projection, the spin projection of the second one becomes immediately determinate, according to the projection postulate, and remember that you can choose on the spot which spin projection you want to determine. So you do introduce nonlocality. Or are you trying to say that the Born rule and the projection postulate are one and the same thing? But as far as I understand, the Born rule does not state that after the measurement the system is in a certain eigenstate, it just gives the probability of a certain measurement result.

So, after reviewing these comments, do you understand what I mean now? That if we want to make predictions about what our records will show at the end of a series of N measurements, we can assume unitary evolution until after all N measurements are complete, and then just apply the Born rule to the records at that time to get a prediction about the statistics?

No, I don't understand what you mean. Now you're telling me that you use the Born rule. A few lines before you said you were using the projection postulate. Please explain.

akhmeteli

Aug1-10, 05:11 PM

EPR-Bell experiments is not about "the other particle, however remote, becomes determinate"! This is only the case when the polarizers are aligned parallel!! EPR-Bell experiments are all about statistics, and there is no way one could violate Bell's Inequality when the polarizers are aligned parallel only, JesseM can verify this.

With all due respect, you did not understand anything I said. I did not speak about two polarizers at all. Let me try to explain. Suppose you have two particles of a singlet, and you are measuring the spin projection of the first particle, so you need just one polarizer. The projection postulate says that after you measure the spin projection on some axis, say, it is +1, the wavefunction immediately collapses into an eigenstate of this spin projection of the first particle. That means that the spin projection of the second particle on the same axis immediately becomes determinate, it equals -1. That's where nonlocality is introduced through the projection postulate. Then you may measure the spin projection of the second particle on a different axis using another polarizer to prove violations or for whatever purpose you want, but that is a different story.

DevilsAvocado

Aug1-10, 06:03 PM

With all due respect, you did not understand anything I said.

With all due respect, I think you are talking bull. If it’s one thing Bell showed, it’s that the Einsteinian argument fails:

no action on a distance (polarisers parallel) ⇒ determinism
determinism (polarisers nonparallel) ⇒ action on a distance

Determinism is stone dead.

That's where nonlocality is introduced through the projection postulate.

Are you talking about John von Neumann and the "wavefunction collapse" from 1932?? The collapse of the wavefunction is just an interpretation?? And AFAICT, it not very "hot" either?? Are you saying that John von Neumann, who died in 1957, proved John Bell wrong in 1964?? Or are you saying that you have discovered "something" that John Bell and the whole scientific community totally missed??
Wikipedia - Wavefunction collapse (http://en.wikipedia.org/wiki/Wave_function_collapse#History_and_context)
...
Although von Neumann's projection postulate is often presented as a normative description of quantum measurement, it was conceived by taking into account experimental evidence available during the 1930s (in particular the Compton-Simon experiment has been paradigmatic), and that many important present-day measurement procedures (http://en.wikipedia.org/wiki/Measurement_in_quantum_mechanics#Wavefunction_coll apse) do not satisfy it (so-called measurements of the second kind).[4]

The existence of the wave function collapse is required in

the Copenhagen interpretation
the objective collapse interpretations
the so-called transactional interpretation
in a "spiritual interpretation" in which consciousness causes collapse.

On the other hand, the collapse is considered as a redundant or optional approximation in

interpretations based on Consistent Histories
the Many-Worlds Interpretation
the Bohm interpretation
the Ensemble Interpretation

Dunning–Kruger effect (http://en.wikipedia.org/wiki/Dunning–Kruger_effect)

JesseM

Aug1-10, 06:22 PM

OK, so you just use the projection postulate, not the Born rule?
If you only use it once, at the very end, and then don't attempt to predict anything about what happens to the records afterwards, I don't see the difference. For example, if there were three measurements which could each yield result 1 or 0, then at the end right before "observation" the records will be a single quantum state which can be expressed as a sum of eigenstates:

\alpha_1 \mid 000 \rangle + \alpha_2 \mid 001 \rangle + \alpha_3 \mid 010 \rangle + \alpha_4 \mid 011 \rangle +\alpha_5 \mid 100 \rangle + \alpha_6 \mid 101 \rangle + \alpha_7 \mid 110 \rangle + \alpha_8 \mid 111 \rangle

where the \alpha_i are complex amplitudes. Then if you apply the "projection postulate", you're saying the quantum state will randomly become one of those eigenstates, with the probability of it going to a given eigenstate like \mid 010 \rangle being \alpha_3 \alpha_3* (i.e. the amplitude times its complex conjugate). And the "Born rule" just tells you that the probability of getting a given result like 010 is \alpha_3 \alpha_3*. So if you're not interested in what happens to the quantum state later, but just in the probabilities of seeing different combinations of measurement records at some time T after all the measurements are complete, I don't see the distinction between applying the "projection postulate" at T to get these probabilities vs. applying the "Born rule" at T. What difference are you seeing?
But this is exactly where you introduce nonlocality. Remember that actual records are not even permanent. Where exactly do you perform this second stage of your procedure, the "observation"? Near the point where the first particle is?
If you see a paper listing a bunch of results taken at different places, how do you think they got into that one paper? Presumably the information from each measuring device was transferred to a common location at some point, so you're free to assume that each measuring-device was transferred to a common location before the "observation" of their records happened, or that each sent an email to a common location before "observation", whatever.

akhmeteli

Aug1-10, 06:22 PM

With all due respect, I think you are talking bull. If it’s one thing Bell showed, it’s that the Einsteinian argument fails:

no action on a distance (polarisers parallel) ⇒ determinism
determinism (polarisers nonparallel) ⇒ action on a distance

Determinism is stone dead.

Are you talking about John von Neumann and the "wavefunction collapse" from 1932?? The collapse of the wavefunction is just an interpretation?? And AFAICT, it not very "hot" either?? Are you saying that John von Neumann, who died in 1957, proved John Bell wrong in 1964?? Or are you saying that you have discovered "something" that John Bell and the whole scientific community totally missed??

Dunning–Kruger effect (http://en.wikipedia.org/wiki/Dunning–Kruger_effect)

I give up. You have no use for any explanations, and I have no use for your soap opera.

DevilsAvocado

Aug1-10, 06:34 PM

I give up.

This is often the case when frauds are proven wrong:
Wikipedia - Wavefunction collapse (http://en.wikipedia.org/wiki/Wave_function_collapse#History_and_context)
...
Although von Neumann's projection postulate is often presented as a normative description of quantum measurement, it was conceived by taking into account experimental evidence available during the 1930s (in particular the Compton-Simon experiment has been paradigmatic), and that many important present-day measurement procedures (http://en.wikipedia.org/wiki/Measurement_in_quantum_mechanics#Wavefunction_coll apse) do not satisfy it (so-called measurements of the second kind).[4]

The existence of the wave function collapse is required in

the Copenhagen interpretation
the objective collapse interpretations
the so-called transactional interpretation
in a "spiritual interpretation" in which consciousness causes collapse.

On the other hand, the collapse is considered as a redundant or optional approximation in

interpretations based on Consistent Histories
the Many-Worlds Interpretation
the Bohm interpretation
the Ensemble Interpretation

akhmeteli

Aug1-10, 06:43 PM

If you only use it once, at the very end, and then don't attempt to predict anything about what happens to the records afterwards, I don't see the difference. For example, if there were three measurements which could each yield result 1 or 0, then at the end right before "observation" the records will be a single quantum state which can be expressed as a sum of eigenstates:

\alpha_1 \mid 000 \rangle + \alpha_2 \mid 001 \rangle + \alpha_3 \mid 010 \rangle + \alpha_4 \mid 011 \rangle +\alpha_5 \mid 100 \rangle + \alpha_6 \mid 101 \rangle + \alpha_7 \mid 110 \rangle + \alpha_8 \mid 111 \rangle

where the \alpha_i are complex amplitudes. Then if you apply the "projection postulate", you're saying the quantum state will randomly become one of those eigenstates, with the probability of it going to a given eigenstate like \mid 010 \rangle being \alpha_3 \alpha_3* (i.e. the amplitude times its complex conjugate). And the "Born rule" just tells you that the probability of getting a given result like 010 is \alpha_3 \alpha_3*. So if you're not interested in what happens to the quantum state later, but just in the probabilities of seeing different combinations of measurement records at some time T after all the measurements are complete, I don't see the distinction between applying the "projection postulate" at T to get these probabilities vs. applying the "Born rule" at T. What difference are you seeing?

I don't know. Generally speaking, the projection postulate immediately introduces nonlocality. Right now I don't quite know how the procedure you describe is supposed to be used to prove the violations in quantum mechanics. Before I see the proof, I cannot tell you if there is any difference or not. Anyway, strictly speaking, the projection postulate is not compatible with unitary evolution, whether you use the postulate at the end, at the beginning, or in the middle.

If you see a paper listing a bunch of results taken at different places, how do you think they got into that one paper? Presumably the information from each measuring device was transferred to a common location at some point, so you're free to assume that each measuring-device was transferred to a common location before the "observation" of their records happened, or that each sent an email to a common location before "observation", whatever.

Then problems with spatial separation may arise. Again, until I see how your procedure is used in a proof of violations, it is difficult to say what is important and what isn't. And remember, in principle, records are not permanent.

DevilsAvocado

Aug1-10, 07:22 PM

I give up.

Ohh! Sorry, I missed the most important part:
Wikipedia - Measurements of the second kind (http://en.wikipedia.org/wiki/Measurement_in_quantum_mechanics#Measurements_of_t he_second_kind)
...
Note that many present-day measurement procedures are measurements of the second kind, some even functioning correctly only as a consequence of being of the second kind (for instance, a photon counter, detecting a photon by absorbing and hence annihilating it, thus ideally leaving the electromagnetic field in the vacuum state rather than in the state corresponding to the number of detected photons; also the Stern-Gerlach experiment (http://en.wikipedia.org/wiki/Stern-Gerlach_experiment) would not function at all if it really were a measurement of the first kind).

JesseM

Aug1-10, 07:32 PM

I don't know. Generally speaking, the projection postulate immediately introduces nonlocality.
Is there something wrong with "introducing nonlocality" in this context? All I'm claiming is that the rule of assuming unitary evolution, and then applying the Born rule/projection postulate at the very end to determine probabilities of different recorded outcomes, is a well-defined pragmatic procedure for generating theoretical predictions about experiments which can be compared with the actual results you find when the experiment is done in real life and the measurement results all written down somewhere. As always, it's just a pragmatic rule for generating predictions about the kinds of results we can write down, it's not meant to be a coherent description of what actually goes on physically at all moments.

Do you disagree that this is a well-defined procedure for generating predictions about the actual results seen in quantum experiments?
Right now I don't quite know how the procedure you describe is supposed to be used to prove the violations in quantum mechanics. Before I see the proof, I cannot tell you if there is any difference or not.
Again, I don't feel like spending a lot of time looking for a paper that specifically uses the von Neumann approach to derive theoretical predictions about EPR type experiments. But do you disagree that the procedure I'm using is the same one von Neumann was proposing? If you don't disagree, don't you think it's fairly implausible that this procedure would fail to predict Bell inequality violations, but no one would have noticed this before despite the procedure being known for decades?

Also, now that you hopefully understand that I'm not talking about applying to projection postulate to each measurement but only once at the very end to all the records, you might reconsider the comment I made about one of the papers I linked to:
Also, note the paper here (http://www.lps.uci.edu/barrett/publications/SuggestiveProperties.pdf) I linked to above, which shows that in the limit as the number of measurements (without collapse) in an EPR type experiment goes to infinity the state vector will approach "an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts". This does at least imply that in the limit as the number of measurements goes to infinity, if we "collapse" the records at the very end, the probability that the records will show measurement results that were "randomly distributed and statistically correlated in just the way the standard theory predicts" should approach 1 in this limit. Do you disagree?
To put it another way, applying only unitary evolution to a series of N measurements and looking at the state S at the end means that, in the limit as N approaches infinity, S approaches "an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts". So, this implies that if we apply unitary evolution to a series of N measurements and then apply the projection postulate/Born rule at the very end, then in the limit as N approaches infinity, the probability that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts" must approach 1. This isn't quite what I wanted to prove (that even for a small number of measurements, the von Neumann rule gives probabilities which violate Bell inequalities) but it's close.
Anyway, strictly speaking, the projection postulate is not compatible with unitary evolution, whether you use the postulate at the end, at the beginning, or in the middle.
Who cares if it's incompatible when it's just a pragmatic rule for making predictions, not intended to be a coherent theoretical description of what's really going on at all times? The pragmatic rule says that you model the system as evolving in a unitary way until all the measurements are done, then at the end you apply the projection postulate/Born rule to get predictions about the statistics of measurement records. If you see this final application of the projection postulate/Born rule as a violation of unitary evolution, fine, the pragmatic rule says you apply unitary evolution up to the final time T, then at time T you discard unitary evolution and apply the projection postulate. That's a coherent pragmatic rule (nothing wrong with requiring different rules at different times, as long as you know which to use when) even if it makes little sense as a theoretical picture.

akhmeteli

Aug2-10, 01:57 AM

Is there something wrong with "introducing nonlocality" in this context?

JesseM, everything is wrong with it. Let us remember what we are talking about, in the first place. The question in the title of this thread is "Local realism ruled out?" I offered two arguments (sorry that I have to repeat them one more time):

1. There has been no experimental evidence of violations of the genuine Bell inequalities.
2. The violation of the inequalities in quantum theory is theoretically proven using mutually contradictory assumptions.

And then the conclusion: both experimental and theoretical arguments in favor of nonlocality are controversial, to say the least.

Now, what are trying to prove?

That it is possible to theoretically prove the violations in quantum theory, if you preliminarily introduce nonlocality in the measurement procedure? I could not agree more! But how does this proves nonlocality? This is circular reasoning, for crying out loud!

I fully agree that you can theoretically prove violations if you use the projection postulate! But I reject the projection postulate as anything but an approximation, because it contradicts unitary evolution! Take a standard proof of the Bell theorem, and it proves violations in quantum theory using the projection postulate! No need to spend hours looking for the proof!

All I'm claiming is that the rule of assuming unitary evolution, and then applying the Born rule/projection postulate at the very end to determine probabilities of different recorded outcomes, is a well-defined pragmatic procedure for generating theoretical predictions about experiments which can be compared with the actual results you find when the experiment is done in real life and the measurement results all written down somewhere. As always, it's just a pragmatic rule for generating predictions about the kinds of results we can write down, it's not meant to be a coherent description of what actually goes on physically at all moments.

Do you disagree that this is a well-defined procedure for generating predictions about the actual results seen in quantum experiments?

I do agree that this is is a well-defined procedure for generating... But what does this prove? Let me give you an example of a well-defined procedure: at the end of any experiment aimed at measuring some value you don't bother to read any records and just declare that this value is equal to 5 (in your favorite system of units). Do you agree that this is a well-defined procedure? I bet you do! It cannot even be disproven by experiments! What's wrong then with this procedure? Everything! I don't even know where to start to criticize it! Your procedure is not so absurd, as the projection postulate is at least an approximation, but strictly speaking it's still absurd, as the projection postulate contradicts unitary evolution.

Another thing. I suspect that you can prove nonlocality of classical electromagnetism if you introduce nonlocality in the measurement procedure. But is this what you really want?

Again, I don't feel like spending a lot of time looking for a paper that specifically uses the von Neumann approach to derive theoretical predictions about EPR type experiments. But do you disagree that the procedure I'm using is the same one von Neumann was proposing? If you don't disagree, don't you think it's fairly implausible that this procedure would fail to predict Bell inequality violations, but no one would have noticed this before despite the procedure being known for decades?

I agree that you can prove violations if you use the projection postulate. And no need to look for such a proof - a standard proof of the Bell inequality will do. But how does this undermine my arguments?

Also, now that you hopefully understand that I'm not talking about applying to projection postulate to each measurement but only once at the very end to all the records, you might reconsider the comment I made about one of the papers I linked to:

To put it another way, applying only unitary evolution to a series of N measurements and looking at the state S at the end means that, in the limit as N approaches infinity, S approaches "an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts". So, this implies that if we apply unitary evolution to a series of N measurements and then apply the projection postulate/Born rule at the very end, then in the limit as N approaches infinity, the probability that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts" must approach 1. This isn't quite what I wanted to prove (that even for a small number of measurements, the von Neumann rule gives probabilities which violate Bell inequalities) but it's close.

I commented on this article in post 709.

Who cares if it's incompatible when it's just a pragmatic rule for making predictions, not intended to be a coherent theoretical description of what's really going on at all times? The pragmatic rule says that you model the system as evolving in a unitary way until all the measurements are done, then at the end you apply the projection postulate/Born rule to get predictions about the statistics of measurement records. If you see this final application of the projection postulate/Born rule as a violation of unitary evolution, fine, the pragmatic rule says you apply unitary evolution up to the final time T, then at time T you discard unitary evolution and apply the projection postulate. That's a coherent pragmatic rule (nothing wrong with requiring different rules at different times, as long as you know which to use when) even if it makes little sense as a theoretical picture.

You can say the same about my "5-procedure". And that's not very good for your procedure.

I'd say your procedure's viability hinges on how good an approximation the projection postulate is. But when you start to use this procedure in the area where the projection postulate is not a good approximation, your procedure will probably no better than my "5-procedure". And, as I said, I doubt that you can use approximations, such as the projection postulate, to prove nonlocality, as "approximate nonlocality" does not make much sense.

JesseM

Aug2-10, 09:23 AM

JesseM, everything is wrong with it. Let us remember what we are talking about, in the first place. The question in the title of this thread is "Local realism ruled out?" I offered two arguments (sorry that I have to repeat them one more time):

1. There has been no experimental evidence of violations of the genuine Bell inequalities.
2. The violation of the inequalities in quantum theory is theoretically proven using mutually contradictory assumptions.

And then the conclusion: both experimental and theoretical arguments in favor of nonlocality are controversial, to say the least.

Now, what are trying to prove?

That it is possible to theoretically prove the violations in quantum theory, if you preliminarily introduce nonlocality in the measurement procedure? I could not agree more! But how does this proves nonlocality? This is circular reasoning, for crying out loud!
How could a proof possibly prove an empirical result? The proof is just intended to show that the statistical predictions of a local realist theory would differ from the statistical predictions of QM. If everyone agrees the pragmatic procedure I described is one way to define the "predictions of QM", then if that procedure predicts Bell inequality violations, that's all you need for the proof. No one would claim that the proof alone shows that QM's predictions will turn out to be empirically true, that of course is a matter for experiment.
I fully agree that you can theoretically prove violations if you use the projection postulate! But I reject the projection postulate as anything but an approximation, because it contradicts unitary evolution! Take a standard proof of the Bell theorem, and it proves violations in quantum theory using the projection postulate! No need to spend hours looking for the proof!
Sure, if you apply the projection postulate multiple times. I was just making the point that I think you can just apply it (or the Born rule, whichever) once at the very end, once all the measurements have been completed. The advantage of this is twofold:

1. You don't have to worry about the definition of which interactions constitute "measurements" and which don't, so there isn't the same ambiguity about how to apply the pragmatic rule

2. If you take a quantum system and model it as evolving in a unitary rule throughout some time interval, then apply the Born rule once at the very end to find the probability it'll be in different states, my understanding is that the probabilities you derive should be identical to those predicted by Bohmian mechanics (where there is no need for the Born rule since the measuring-device pointers have well-defined positions at all times, and the wavefunction is just understood as a classical ensemble of possible arrangements of positions with different probabilities). I believe it's only if you model each measurement as causing a separate "collapse" according to the projection postulate that your predictions would only be "approximately" equal to those given by the Bohmian analysis of the same situation.
I do agree that this is is a well-defined procedure for generating... But what does this prove? Let me give you an example of a well-defined procedure: at the end of any experiment aimed at measuring some value you don't bother to read any records and just declare that this value is equal to 5 (in your favorite system of units). Do you agree that this is a well-defined procedure? I bet you do!
No, it's not solely a procedure "for generating predictions about the actual results seen in quantum experiments", because you've also added a rule about what we must do when conducting the actual experiments (not look at the results). My procedure didn't tell you anything about how the experiments should be conducted, it was just a procedure to generate theoretical predictions about any quantum experiment (or at least any where you have measured the initial state of the system so you can evolve it forward) which could be compared with the empirical results of that experiment.
Another thing. I suspect that you can prove nonlocality of classical electromagnetism if you introduce nonlocality in the measurement procedure. But is this what you really want?
In classical electromagnetism all the local variables have well-defined values at all times (just like Bohmian mechanics), and their values evolve in a local way, so even if we assume we can magically become aware of all the values throughout space at a single instant, there will be no Bell inequality violations in the statistics. Of course if you imagined a "measurement procedure" that instantly changed all the local values at the moment of measurement, just like the projection postulate instantly changes the system's quantum state, then you might get Bell inequality violations depending on the nature of this change, but this theory would no longer resemble what we mean by "classical electromagnetism". In contrast, the procedure I describe above where you use the Born rule to get predictions about measurement-records is one that everyone would agree matches what physicists mean when they talk about the predictions of "QM". And again, Bell was just trying to prove that local realism is inconsistent with what everyone understands to be the predictions of "QM." You seem to be making some theoretical point that you don't find this surprising since the predictions of "QM" involve a nonlocal rule, but who cares? The proof is not intended to show that this result is surprising.
Also, now that you hopefully understand that I'm not talking about applying to projection postulate to each measurement but only once at the very end to all the records, you might reconsider the comment I made about one of the papers I linked to:

To put it another way, applying only unitary evolution to a series of N measurements and looking at the state S at the end means that, in the limit as N approaches infinity, S approaches "an eigenstate of reporting that their measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts". So, this implies that if we apply unitary evolution to a series of N measurements and then apply the projection postulate/Born rule at the very end, then in the limit as N approaches infinity, the probability that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts" must approach 1. This isn't quite what I wanted to prove (that even for a small number of measurements, the von Neumann rule gives probabilities which violate Bell inequalities) but it's close.
I commented on this article in post 709.
Yes, but your comment was made when you still seemed confused about the procedure I was suggesting, that's why I re-introduced it with the comment in bold. Your comments in post #709 were:
JesseM, with all due respect, a couple of lines later the author writes: "Note, however, that since the linear dynamics can be written in a perfectly local form, there are in fact no nonlocal causal connections in the bare theory. ...Just as reports of determinate results, relative frequencies, and randomness would generally be explained by the bare theory as illusions the apparent nonlocality here would be just that, apparent." :-)
Of course, the "bare theory" is local, but it also doesn't make any well-defined statistical predictions about empirical results. My point was that if you combined their conclusion about the "bare theory" with the procedure I (and von Neumann) suggest where you do introduce a single application of the Born rule/projection postulate at the very end of a series of measurements, then you can show that in the limit as the number of measurements approaches infinity, the von Neumann procedure will predict with probability 1 that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts".

Now, it may be that you have no objection to the idea that this procedure will predict Bell inequality violations, as suggested by your comment "I fully agree that you can theoretically prove violations if you use the projection postulate!" I thought, though, that previously when you were asking me to "prove it", you were asking for a proof that the procedure I described (unitary evolution with a single application of the Born rule at the very end) would predict Bell inequality violations. That's why I brought up this paper, since it helps justify the conclusion that this is almost certainly true, even if I can't provide a detailed proof.
Who cares if it's incompatible when it's just a pragmatic rule for making predictions, not intended to be a coherent theoretical description of what's really going on at all times? The pragmatic rule says that you model the system as evolving in a unitary way until all the measurements are done, then at the end you apply the projection postulate/Born rule to get predictions about the statistics of measurement records. If you see this final application of the projection postulate/Born rule as a violation of unitary evolution, fine, the pragmatic rule says you apply unitary evolution up to the final time T, then at time T you discard unitary evolution and apply the projection postulate. That's a coherent pragmatic rule (nothing wrong with requiring different rules at different times, as long as you know which to use when) even if it makes little sense as a theoretical picture.
You can say the same about my "5-procedure". And that's not very good for your procedure.
Except that your procedure is useless for making predictions about the sort of experiments physicists actually do in quantum physics (since your procedure requires that physicists discard measurement results without looking at them), while mine works just fine for this pragmatic purpose.
I'd say your procedure's viability hinges on how good an approximation the projection postulate is.
As I said, I think my (and von Neumann's) procedure would exactly agree with the predictions of Bohmian mechanics for a given system at the end of a given time period, and Bohmian mechanics does not require the projection postulate. I think you'll probably disagree with that statement about Bohmian mechanics, though, so I need to go back and address your most recent posts on that subject.

akhmeteli

Aug2-10, 02:30 PM

How could a proof possibly prove an empirical result? The proof is just intended to show that the statistical predictions of a local realist theory would differ from the statistical predictions of QM.
I fully agree. But QM is a well established (experimentally as well) theory, so such a proof of difference, generally speaking, could be an argument against all local realistic theories.
If everyone agrees the pragmatic procedure I described is one way to define the "predictions of QM", then if that procedure predicts Bell inequality violations, that's all you need for the proof. No one would claim that the proof alone shows that QM's predictions will turn out to be empirically true, that of course is a matter for experiment.
I agree (subject to your “ifs”).
Sure, if you apply the projection postulate multiple times. I was just making the point that I think you can just apply it (or the Born rule, whichever) once at the very end, once all the measurements have been completed. The advantage of this is twofold:

1. You don't have to worry about the definition of which interactions constitute "measurements" and which don't, so there isn't the same ambiguity about how to apply the pragmatic rule

2. If you take a quantum system and model it as evolving in a unitary rule throughout some time interval, then apply the Born rule once at the very end to find the probability it'll be in different states, my understanding is that the probabilities you derive should be identical to those predicted by Bohmian mechanics (where there is no need for the Born rule since the measuring-device pointers have well-defined positions at all times, and the wavefunction is just understood as a classical ensemble of possible arrangements of positions with different probabilities). I believe it's only if you model each measurement as causing a separate "collapse" according to the projection postulate that your predictions would only be "approximately" equal to those given by the Bohmian analysis of the same situation.
JesseM, my response still crucially depends on what exactly you use –the projection postulate or the Born rule.
If you use the projection postulate, no matter one time or a billion times, you manually introduce nonlocality. In this case I immediately concede that you can prove violations in QM (it does not matter if I am right or wrong about it), but I refuse to accept this proof as an argument against local realism, as this proof a) contains mutually contradictory assumptions, and 2) uses nonlocality as one of its assumptions.
If you use the Born rule… Well, the objections I offered above would not look equally strong (although it is not quite clear to me how compatible with dynamics the Born rule is). But then another issue arises: can you get a proof of violations in QM? I am not ready to concede this point. Again, I fully understand that you have better things to do than to look for such a proof, but that does not mean I must concede this point. I think the burden of proof of nonlocality is on those who want nonlocality. The Bell theorem, on the face of it, looks like such a proof, but, as I said repeatedly, it contains mutually contradictory assumptions. If you want to convince me that it is possible to cure this defect, or to prove violations in Bohmian mechanics without using the projection postulate or something similar, I need more than your word, sorry.
No, it's not solely a procedure "for generating predictions about the actual results seen in quantum experiments", because you've also added a rule about what we must do when conducting the actual experiments (not look at the results). My procedure didn't tell you anything about how the experiments should be conducted, it was just a procedure to generate theoretical predictions about any quantum experiment (or at least any where you have measured the initial state of the system so you can evolve it forward) which could be compared with the empirical results of that experiment.
I disagree. This “rule” is not essential and can be removed (so, if you wish, you can look at the results and still say that the value equals 5 :-) ). My idiotic procedure still has something in common with your much more decently looking procedure: it is not compatible with dynamics.
In classical electromagnetism all the local variables have well-defined values at all times (just like Bohmian mechanics), and their values evolve in a local way, so even if we assume we can magically become aware of all the values throughout space at a single instant, there will be no Bell inequality violations in the statistics. Of course if you imagined a "measurement procedure" that instantly changed all the local values at the moment of measurement, just like the projection postulate instantly changes the system's quantum state, then you might get Bell inequality violations depending on the nature of this change, but this theory would no longer resemble what we mean by "classical electromagnetism".
I am certainly not trying to prove that classical electrodynamics is nonlocal, I am just trying to say that you can prove nonlocality where there is no trace of it, if you use a nonlocal measurement procedure.
In contrast, the procedure I describe above where you use the Born rule to get predictions about measurement-records is one that everyone would agree matches what physicists mean when they talk about the predictions of "QM".
Again, if it’s the Born rule, I could tentatively agree (but then you don’t have a proof of violations in QM), but if it’s the projection postulate, I stand by my objections.
And again, Bell was just trying to prove that local realism is inconsistent with what everyone understands to be the predictions of "QM." You seem to be making some theoretical point that you don't find this surprising since the predictions of "QM" involve a nonlocal rule, but who cares? The proof is not intended to show that this result is surprising.
It does not matter much if this inconsistency is surprising or not. It does matter though if Nature is local realistic or not (at least it matters for me; that does not mean that I won’t be able to accept nonlocality if and when it is thoroughly confirmed experimentally). So I am trying to make point that the proof of inconsistency is dubious, as it uses mutually contradictory assumptions. I am also trying to make a point that it is not possible to reasonably embrace those contradictory assumptions anyway, and I put my bet on unitary evolution and against the projection postulate. You see, irrespective of the results of future experiments, we’ll have to modify either unitary evolution or the projection postulate anyway, local realism or no local realism. A logical contradiction is just not acceptable.

Yes, but your comment was made when you still seemed confused about the procedure I was suggesting, that's why I re-introduced it with the comment in bold. Your comments in post #709 were:

Of course, the "bare theory" is local, but it also doesn't make any well-defined statistical predictions about empirical results. My point was that if you combined their conclusion about the "bare theory" with the procedure I (and von Neumann) suggest where you do introduce a single application of the Born rule/projection postulate at the very end of a series of measurements, then you can show that in the limit as the number of measurements approaches infinity, the von Neumann procedure will predict with probability 1 that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts".

Now, it may be that you have no objection to the idea that this procedure will predict Bell inequality violations, as suggested by your comment "I fully agree that you can theoretically prove violations if you use the projection postulate!" I thought, though, that previously when you were asking me to "prove it", you were asking for a proof that the procedure I described (unitary evolution with a single application of the Born rule at the very end) would predict Bell inequality violations. That's why I brought up this paper, since it helps justify the conclusion that this is almost certainly true, even if I can't provide a detailed proof.
Again, I don’t care about any proof if you use the projection postulate (as in this case the proof of nonlocality contains circular reasoning anyway), but I need a proof if you use the Born rule. As confirmed by my quotes from the article, the latter does not contain anything like such proof.

Except that your procedure is useless for making predictions about the sort of experiments physicists actually do in quantum physics (since your procedure requires that physicists discard measurement results without looking at them), while mine works just fine for this pragmatic purpose.

Yes, but just because it uses a better approximation than my procedure. Where this approximation fails (and it cannot but fail somewhere, as, strictly speaking, it is incompatible with unitary evolution), your procedure will fail.

As I said, I think my (and von Neumann's) procedure would exactly agree with the predictions of Bohmian mechanics for a given system at the end of a given time period, and Bohmian mechanics does not require the projection postulate. I think you'll probably disagree with that statement about Bohmian mechanics, though, so I need to go back and address your most recent posts on that subject.
Again, if you use the Born rule in your procedure, I could tentatively agree, if it’s the projection postulate, then I disagree, as there is no collapse in Bohmian mechanics

JesseM

Aug2-10, 03:33 PM

I fully agree. But QM is a well established (experimentally as well) theory, so such a proof of difference, generally speaking, could be an argument against all local realistic theories.
Well, yes--exactly! If you take "QM" to just mean the pragmatic procedure for making predictions that I describe, then this procedure has a great track record of agreement with experiment. So, even if this pragmatic procedure makes little sense as an ontological picture of what's "really going on", it should be inherently interesting to physicists to know whether the predictions of the pragmatic procedure are compatible with local realism. Of course showing that they're incompatible doesn't prove local realism is false in the real world, since it's possible you could have some local realist model whose predictions matched those of the pragmatic procedure in all the experiments that have been done to date, but which would differ from the pragmatic procedure in an ideal Bell test. Still most physicists would consider this unlikely, owing to the fact that most would agree such a model would almost certainly be very contrived and inelegant.
JesseM, my response still crucially depends on what exactly you use –the projection postulate or the Born rule.
But I already explained in post #716 (http://www.physicsforums.com/showpost.php?p=2823021&postcount=716) that I didn't see a difference between the two if it was only done once at the end, they are both just ways of getting the same probabilities for the end results. I concluded by asking "So if you're not interested in what happens to the quantum state later, but just in the probabilities of seeing different combinations of measurement records at some time T after all the measurements are complete, I don't see the distinction between applying the "What difference are you seeing?" and your response in post #719 (http://www.physicsforums.com/showpost.php?p=2823048&postcount=719) was "I don't know." So I would still say that there's no meaningful difference between them--if you want to say that the Born rule itself introduces nonlocality since it gives probabilities for a combination of simultaneous physical facts at different spatial locations, that's fine with me!
But then another issue arises: can you get a proof of violations in QM? I am not ready to concede this point.
I think so, if by "QM" you mean the pragmatic rule for generating predictions that I described (and which is the same as von Neumann's rule), which requires a single application of the Born rule to the quantum state of the system at some time after all measurements are completed and recorded. Are you actually suggesting that von Neumann's procedure might not actually predict Bell inequality violations, and that this has just gone unnoticed by physicists for decades? Or are you using "QM" to mean unitary evolution only, with no invoking the projection postulate or the Born rule? (unless the Born rule can somehow be derived from unitary evolution, which is what many-worlds advocates often try to do)
Again, I fully understand that you have better things to do than to look for such a proof
See above, I'm not even clear on what you're asking me to prove here.
The Bell theorem, on the face of it, looks like such a proof, but, as I said repeatedly, it contains mutually contradictory assumptions.
Bell's theorem has two parts: 1) in the type of experiment he specifies, local realism predicts that some Bell inequality will be obeyed, and 2) in the type of experiment he specifies, the predictions of "QM" as understood by physicists are that the Bell inequality will be violated. Your objection about "mutually contradictory assumptions" only seems to be an objection to 2), correct? But isn't it basically just a semantic disagreement, since you seem to define "QM" to mean "unitary evolution only" (which cannot be used to make predictions about any real-world experiment, since unitary evolution only gives complex amplitudes and empirically we never measure complex amplitudes), whereas most physicists would understand "QM" to mean the sort of pragmatic rule for making predictions that I describe.
If you want to convince me that it is possible to cure this defect, or to prove violations in Bohmian mechanics without using the projection postulate or something similar, I need more than your word, sorry.
Even if I could show that Bohmian mechanics can produce predictions of Bell inequality violations without invoking the projection postulate (and I think the links I gave already do this, despite your objections), what difference would it make to your argument? After all the guiding equation of Bohmian mechanics is explicitly nonlocal, so if you objected to the use of the projection postulate because it's nonlocal wouldn't you have the same objection to Bohmian mechanics?
I disagree. This “rule” is not essential and can be removed (so, if you wish, you can look at the results and still say that the value equals 5 :-) ).
But then you aren't comparing theoretical predictions with measurement results, you're comparing them with what you "say" about measurement results, where what you say is in most cases a lie.
I am certainly not trying to prove that classical electrodynamics is nonlocal, I am just trying to say that you can prove nonlocality where there is no trace of it, if you use a nonlocal measurement procedure.
Again, if by "nonlocal measurement procedure" you just mean instantly learn the values of the electromagnetic field at different locations without actually changing them in the process, then no, this won't lead to any Bell inequality violations in the results you learn.
Again, if it’s the Born rule, I could tentatively agree (but then you don’t have a proof of violations in QM), but if it’s the projection postulate, I stand by my objections.
But you never gave a coherent reason for disagreeing that there is no reason for distinguishing the two if we just make one "observation" of the records at the end of all measurements. Do you agree that if at the time we make an observation the quantum state of the records (obtained by unitary evolution) is \alpha_1 \mid 000 \rangle + \alpha_2 \mid 001 \rangle + \alpha_3 \mid 010 \rangle + \alpha_4 \mid 011 \rangle +\alpha_5 \mid 100 \rangle + \alpha_6 \mid 101 \rangle + \alpha_7 \mid 110 \rangle + \alpha_8 \mid 111 \rangle then if we "observe" these records, regardless of whether we apply the Born rule or the projection postulate we will predict that the probability of a given result like 010 will just be the amplitude for that eigenstate times its complex conjugate, i.e. \alpha_3 \alpha_3*? Please tell me clearly whether you agree or disagree that the probability of 010 is going to be \alpha_3 \alpha_3* either way. If you don't disagree, then obviously the Born rule and the projection postulate are both making the exact same predictions about the statistics seen in the records at this time, so the probability of statistics that violate the Bell inequalities is the same either way.
So I am trying to make point that the proof of inconsistency is dubious, as it uses mutually contradictory assumptions. I am also trying to make a point that it is not possible to reasonably embrace those contradictory assumptions anyway, and I put my bet on unitary evolution and against the projection postulate. You see, irrespective of the results of future experiments, we’ll have to modify either unitary evolution or the projection postulate anyway, local realism or no local realism. A logical contradiction is just not acceptable.
But you never really addressed my point in post #721 that the "contradiction" only arises if you take the procedure as an ontological description of reality, that purely as a pragmatic procedure it's not contradictory since it's just telling you to use different rules at different times. Your response was just to compare this with your silly "pretend the answer is always 5" procedure, but of course that procedure doesn't have a long track record of accurately predicting experimental results like the QM procedure.
Again, I don’t care about any proof if you use the projection postulate (as in this case the proof of nonlocality contains circular reasoning anyway), but I need a proof if you use the Born rule.
Do you disagree that if a system's state is in an eigenstate of some operator, the Born rule says that on "observation" you are guaranteed to find the value associated with that eigenstate with probability 1? So, that means their conclusion (if we do N measurements, pure unitary evolution predicts that in the limit as N approaches infinity, the measurement records approach an eigenstate where "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts") implies the conclusion (if we do N measurements modeled by unitary evolution and then at the end apply the Born rule to the measurement records, in the limit as N approaches infinity the probability of finding that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts" approaches 1)
As I said, I think my (and von Neumann's) procedure would exactly agree with the predictions of Bohmian mechanics for a given system at the end of a given time period, and Bohmian mechanics does not require the projection postulate. I think you'll probably disagree with that statement about Bohmian mechanics, though, so I need to go back and address your most recent posts on that subject.
Again, if you use the Born rule in your procedure, I could tentatively agree, if it’s the projection postulate, then I disagree, as there is no collapse in Bohmian mechanics
And again, if you assume unitary evolution until some time T, then regardless of whether you invoke "the Born rule" or "the projection postulate" at time T, the probabilities of finding different possible combinations of measurement results at time T will be exactly the same. And my argument is that Bohmian mechanics will also yield exactly the same predictions for probabilities of different possible combinations of measurement results at time T.

akhmeteli

Aug2-10, 06:41 PM

Well, yes--exactly! If you take "QM" to just mean the pragmatic procedure for making predictions that I describe, then this procedure has a great track record of agreement with experiment. So, even if this pragmatic procedure makes little sense as an ontological picture of what's "really going on", it should be inherently interesting to physicists to know whether the predictions of the pragmatic procedure are compatible with local realism. Of course showing that they're incompatible doesn't prove local realism is false in the real world, since it's possible you could have some local realist model whose predictions matched those of the pragmatic procedure in all the experiments that have been done to date, but which would differ from the pragmatic procedure in an ideal Bell test. Still most physicists would consider this unlikely, owing to the fact that most would agree such a model would almost certainly be very contrived and inelegant.
So it’s a matter of opinion. Note that this pragmatic procedure is doomed to fail somewhere anyway, as it contradicts the unitary evolution.
But I already explained in post #716 (http://www.physicsforums.com/showpost.php?p=2823021&postcount=716) that I didn't see a difference between the two if it was only done once at the end, they are both just ways of getting the same probabilities for the end results. I concluded by asking "So if you're not interested in what happens to the quantum state later, but just in the probabilities of seeing different combinations of measurement records at some time T after all the measurements are complete, I don't see the distinction between applying the "What difference are you seeing?" and your response in post #719 (http://www.physicsforums.com/showpost.php?p=2823048&postcount=719) was "I don't know." So I would still say that there's no meaningful difference between them
If you believe there is no difference, why don’t you choose just one of those two that you like more, even if just to give some focus to the discussion? But I explained to you how my reasoning will depend on your choice: if you choose the projection postulate, I’ll say that your proof of nonlocality in QM contains circular reasoning; if you choose the Born rule, then I’ll say that you don’t have a proof of nonlocality. So the difference is in how the discussion will develop depending on your choice. You may call this difference meaningful or not meaningful, but it is at least important for the course of further discussion.
--if you want to say that the Born rule itself introduces nonlocality since it gives probabilities for a combination of simultaneous physical facts at different spatial locations, that's fine with me!
On the face of it, this may be a possibility, but I think I won’t try to formulate my opinion on this issue at this point, because right now it does not look critical for the discussion.

I think so, if by "QM" you mean the pragmatic rule for generating predictions that I described (and which is the same as von Neumann's rule), which requires a single application of the Born rule to the quantum state of the system at some time after all measurements are completed and recorded. Again, if you use the Born rule, rather than the projection postulate in your procedure, it’s not at all obvious that you’ll be able to prove violations in QM.
Are you actually suggesting that von Neumann's procedure might not actually predict Bell inequality violations, and that this has just gone unnoticed by physicists for decades?
Yes, I am actually suggesting that (again, provided you use the Born rule, not the projection postulate). As for “gone unnoticed”… I don’t know. For many people, the difference between the Born rule and the projection postulate may be just a meaningless subtlety :-)
Or are you using "QM" to mean unitary evolution only, with no invoking the projection postulate or the Born rule? (unless the Born rule can somehow be derived from unitary evolution, which is what many-worlds advocates often try to do)
This is an interesting question. I cannot exclude a possibility that my criticism of the projection postulate is actually valid for the Born rule as well (or maybe just for some forms of the Born rule), but I am not sure. There is no doubt that the projection postulate is incompatible with unitary evolution as it destroys superpositions and creates irreversibility. Is the Born rule compatible with unitary evolution? I don’t know. Let me just mention that an acquaintance of mine, who coauthored a series of articles describing the quantum measurement procedure by a rigorous model (http://arxiv.org/abs/quant-ph/0702135), told me that, according to the results for their model, the Born rule is also just an approximation. But it does not look like the Born rule in its simplest form (i.e. as it is used in Bohmian mechanics, for example) introduces nonlocality.
See above, I'm not even clear on what you're asking me to prove here.
I am just saying that I do not accept without proof that it is possible to prove violations in QM using just unitary evolution and the Born rule.
Bell's theorem has two parts: 1) in the type of experiment he specifies, local realism predicts that some Bell inequality will be obeyed, and 2) in the type of experiment he specifies, the predictions of "QM" as understood by physicists are that the Bell inequality will be violated. Your objection about "mutually contradictory assumptions" only seems to be an objection to 2), correct?
Correct.
But isn't it basically just a semantic disagreement, since you seem to define "QM" to mean "unitary evolution only" (which cannot be used to make predictions about any real-world experiment, since unitary evolution only gives complex amplitudes and empirically we never measure complex amplitudes), whereas most physicists would understand "QM" to mean the sort of pragmatic rule for making predictions that I describe.
As I said, to make predictions, you may use some form of the Born rule as a purely operational principle.
Even if I could show that Bohmian mechanics can produce predictions of Bell inequality violations without invoking the projection postulate (and I think the links I gave already do this, despite your objections), what difference would it make to your argument?
I do not agree that your links do that, and I offered specific arguments.
As for what difference it would make to my argument… I’d say significant difference. Right now my argument is quite simple: violations in quantum mechanics are proven using 1) unitary evolution and 2) the projection postulate, and 1) and 2) are mutually contradictory. If you prove violations in Bohmian mechanics without using the projection postulate or something similar, this proof could be translated into a proof for standard QM, so my argument in its current form will not hold, and I’ll have to analyze the Born rule trying to find out if it is compatible with unitary evolution.
After all the guiding equation of Bohmian mechanics is explicitly nonlocal, so if you objected to the use of the projection postulate because it's nonlocal wouldn't you have the same objection to Bohmian mechanics?
It is explicitely nonlocal, but it is not obvious that it cannot have a local form. For example, there is no faster-than-light signaling in Bohmian mechanics, if we assume the standard equivariant distribution. Furthermore, the evolution there is the same unitary evolution as in standard quantum mechanics, which has a solid experimental basis. I reject the projection postulate not just because it is nonlocal, but because it contradicts unitary evolution. Let me also mention that “my” model, while local, can have a seemingly nonlocal form (that of a quantum field theory).
But then you aren't comparing theoretical predictions with measurement results, you're comparing them with what you "say" about measurement results, where what you say is in most cases a lie.
But still, using your wording, it “is a well-defined pragmatic procedure for generating theoretical predictions about experiments which can be compared with the actual results you find when the experiment is done in real life and the measurement results all written down somewhere.” I just wanted to show you that this is not enough. The procedure must make sense.
Again, if by "nonlocal measurement procedure" you just mean instantly learn the values of the electromagnetic field at different locations without actually changing them in the process, then no, this won't lead to any Bell inequality violations in the results you learn.
But the projection postulate changes the values in the process.

But you never gave a coherent reason for disagreeing that there is no reason for distinguishing the two if we just make one "observation" of the records at the end of all measurements. Do you agree that if at the time we make an observation the quantum state of the records (obtained by unitary evolution) is \alpha_1 \mid 000 \rangle + \alpha_2 \mid 001 \rangle + \alpha_3 \mid 010 \rangle + \alpha_4 \mid 011 \rangle +\alpha_5 \mid 100 \rangle + \alpha_6 \mid 101 \rangle + \alpha_7 \mid 110 \rangle + \alpha_8 \mid 111 \rangle then if we "observe" these records, regardless of whether we apply the Born rule or the projection postulate we will predict that the probability of a given result like 010 will just be the amplitude for that eigenstate times its complex conjugate, i.e. \alpha_3 \alpha_3*? If you don't disagree, then obviously the Born rule and the projection postulate are both making the exact same predictions about the statistics seen in the records at this time, so the probability of statistics that violate the Bell inequalities is the same either way.
Please see the answer above in this post starting with words “If you believe there is no difference,”
But you never really addressed my point in post #721 that the "contradiction" only arises if you take the procedure as an ontological description of reality, that purely as a pragmatic procedure it's not contradictory since it's just telling you to use different rules at different times. Your response was just to compare this with your silly "pretend the answer is always 5" procedure, but of course that procedure doesn't have a long track record of accurately predicting experimental results like the QM procedure.
No, it does not, and it is extremely silly indeed, but its mere existence suggests that if you use some nonsense as a measurement procedure, there is always a risk of getting some nonsense as a result. I just cannot embrace logical contradictions, sorry. There is a theorem in logic that if you assume that some false statement is true, that implies that any false statement is true.
Do you disagree that if a system's state is in an eigenstate of some operator, the Born rule says that on "observation" you are guaranteed to find the value associated with that eigenstate with probability 1? So, that means their conclusion (if we do N measurements, pure unitary evolution predicts that in the limit as N approaches infinity, the measurement records approach an eigenstate where "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts") implies the conclusion (if we do N measurements modeled by unitary evolution and then at the end apply the Born rule to the measurement records, in the limit as N approaches infinity the probability of finding that "the measurement results were randomly distributed and statistically correlated in just the way the standard theory predicts" approaches 1)
I gave the quote from his article suggesting that those records may be an illusion. Rather damning:-) If you think such an illusion may be OK, then what exactly is wrong with my 5-procedure?:-)

And again, if you assume unitary evolution until some time T, then regardless of whether you invoke "the Born rule" or "the projection postulate" at time T, the probabilities of finding different possible combinations of measurement results at time T will be exactly the same. And my argument is that Bohmian mechanics will also yield exactly the same predictions for probabilities of different possible combinations of measurement results at time T.

Please see the answer above in this post starting with words “If you believe there is no difference,”

JesseM

Aug4-10, 03:46 PM

So it’s a matter of opinion. Note that this pragmatic procedure is doomed to fail somewhere anyway, as it contradicts the unitary evolution.
Why is it doomed to fail? You think nature must obey unitary evolution? Isn't it possible nature follows some other nonlocal rule like the guiding equation of Bohmian mechanics, and that the predictions of this nonlocal rule about measurement records would happen to agree mathematically with the pragmatic procedure of calculating a "wavefunction" for the system, evolving it in a unitary way according to the Schroedinger equation, and then applying the Born rule/projection postulate to the records once all measurements in the experiment are finished?
If you believe there is no difference, why don’t you choose just one of those two that you like more, even if just to give some focus to the discussion? But I explained to you how my reasoning will depend on your choice: if you choose the projection postulate, I’ll say that your proof of nonlocality in QM contains circular reasoning; if you choose the Born rule, then I’ll say that you don’t have a proof of nonlocality.
That still doesn't make sense to me. If we find that unitary evolution predicts a system's wavefunction is in state S at time T, then if we apply "the Born rule" at time T to find probabilities for different possible combinations of measurement results at T, we are guaranteed mathematically to get exactly the same probabilities as if we applied the "projection postulate" to S at time T. Thus, if applying the "projection postulate" predicts statistics which violate Bell inequalities, applying the "Born rule" is guaranteed to do so as well. Do you have the slightest doubt that this is true? If so that would suggest to me that you just aren't very well-versed in the mathematical formalism of QM, that your understanding is more conceptual. There's no shame in that, I said before that this was true of my understanding of Bohmian mechanics (and my knowledge of QM math doesn't go beyond the undergrad level), but if that's the case it would help me understand your doubts about my argument if you would say so. On the other hand, if you do claim to understand the mathematical meaning of things like wavefunction evolution, expressing the wavefunction as a sum of eigenstates of a particular measurement operator, and of the projection postulate and the Born rule, then please tell me if you have any mathematical doubts about this argument from post #716, and if so what they are:
For example, if there were three measurements which could each yield result 1 or 0, then at the end right before "observation" the records will be a single quantum state which can be expressed as a sum of eigenstates:

\alpha_1 \mid 000 \rangle + \alpha_2 \mid 001 \rangle + \alpha_3 \mid 010 \rangle + \alpha_4 \mid 011 \rangle +\alpha_5 \mid 100 \rangle + \alpha_6 \mid 101 \rangle + \alpha_7 \mid 110 \rangle + \alpha_8 \mid 111 \rangle

where the \alpha_i are complex amplitudes. Then if you apply the "projection postulate", you're saying the quantum state will randomly become one of those eigenstates, with the probability of it going to a given eigenstate like \mid 010 \rangle being \alpha_3 \alpha_3* (i.e. the amplitude times its complex conjugate). And the "Born rule" just tells you that the probability of getting a given result like 010 is \alpha_3 \alpha_3*.
Would you disagree with the idea that if the measurement records constitute an "observable" we can express the quantum state as a sum of eigenstates of that observable? Would you disagree that both the Born rule and the projection postulate would say the probability of getting a given value for an observable is found by taking the amplitude associated with the corresponding eigenstate (when you express the quantum state as a sum of eigenstates for that observable) and multiplying it by its complex conjugate?

akhmeteli

Aug8-10, 11:32 PM

Sorry, I have not replied for some time – was a bit busy.
Why is it doomed to fail? You think nature must obey unitary evolution? Isn't it possible nature follows some other nonlocal rule like the guiding equation of Bohmian mechanics, and that the predictions of this nonlocal rule about measurement records would happen to agree mathematically with the pragmatic procedure of calculating a "wavefunction" for the system, evolving it in a unitary way according to the Schroedinger equation, and then applying the Born rule/projection postulate to the records once all measurements in the experiment are finished?
Well, generally speaking, a lot of things are possible, but I am pretty conservative and try to preserve as much of what we have as possible. Unitary evolution has been thoroughly tested, and I don’t see any reason to discard it. It may happen that the projection postulate is correct, and unitary evolution is wrong, but my bet is on unitary evolution.

That still doesn't make sense to me. If we find that unitary evolution predicts a system's wavefunction is in state S at time T, then if we apply "the Born rule" at time T to find probabilities for different possible combinations of measurement results at T, we are guaranteed mathematically to get exactly the same probabilities as if we applied the "projection postulate" to S at time T. Thus, if applying the "projection postulate" predicts statistics which violate Bell inequalities, applying the "Born rule" is guaranteed to do so as well. Do you have the slightest doubt that this is true? If so that would suggest to me that you just aren't very well-versed in the mathematical formalism of QM, that your understanding is more conceptual. There's no shame in that, I said before that this was true of my understanding of Bohmian mechanics (and my knowledge of QM math doesn't go beyond the undergrad level), but if that's the case it would help me understand your doubts about my argument if you would say so. On the other hand, if you do claim to understand the mathematical meaning of things like wavefunction evolution, expressing the wavefunction as a sum of eigenstates of a particular measurement operator, and of the projection postulate and the Born rule, then please tell me if you have any mathematical doubts about this argument from post #716, and if so what they are:
OK, so you refuse to choose just one of those: either the Born rule or the projection postulate. Then I have to retract (or caveat, if you wish:-) ) my concession that it is possible to prove nonlocality using the projection postulate. Indeed, I am inclined to agree that “if we apply "the Born rule" at time T to find probabilities for different possible combinations of measurement results at T, we are guaranteed mathematically to get exactly the same probabilities as if we applied the "projection postulate" to S at time T.” However, I don’t think you can prove the violations using just probabilities from the projection postulate, but not the collapse, so we have not moved any further.
Would you disagree with the idea that if the measurement records constitute an "observable"
I am not sure about this “if”, as records are not permanent.
we can express the quantum state as a sum of eigenstates of that observable? Would you disagree that both the Born rule and the projection postulate would say the probability of getting a given value for an observable is found by taking the amplitude associated with the corresponding eigenstate (when you express the quantum state as a sum of eigenstates for that observable) and multiplying it by its complex conjugate?
I would agree with that, but, as I explained above, this does not seem to lead to any progress in our discussion. If you remove collapse from the projection postulate, I don’t think you’ll be able to prove the violations.

JesseM

Aug9-10, 10:21 PM

OK, so you refuse to choose just one of those: either the Born rule or the projection postulate. Then I have to retract (or caveat, if you wish:-) ) my concession that it is possible to prove nonlocality using the projection postulate. Indeed, I am inclined to agree that “if we apply "the Born rule" at time T to find probabilities for different possible combinations of measurement results at T, we are guaranteed mathematically to get exactly the same probabilities as if we applied the "projection postulate" to S at time T.” However, I don’t think you can prove the violations using just probabilities from the projection postulate, but not the collapse, so we have not moved any further.
That doesn't make sense to me either. The "probabilities from the projection postulate" are precisely the probabilities that the state will "collapse" onto each possible eigenstate, which is supposed to be the eigenstate corresponding to what's actually observed. So if at time T the amplitude for \mid 010 \rangle is \alpha_3 (obtained via unitary evolution), that means that if you observe the records at time T there is a probability of \alpha_3 \alpha_3* that the state will collapse to the eigenstate \mid 010 \rangle and that you will observe results 010.

And remember, the Bell inequalities deal with probabilities too! For example, one inequality says that if two experimenters are measuring spins of entangled particles, and each experimenter has a choice of three possible angles to measure spin along, then if there is a probability 1 that they see opposite results when they measure spin along the same axis, that means there must be a probability of at least 1/3 that they see opposite results when they measure along different axes, according to local realism. Meanwhile for a certain choice of detector angles the QM prediction is that the probability of seeing opposite results for different angles is only 1/4, so QM is understood to be incompatible with local realism. If we pick a time T shortly after both particles' spins have been measured and recorded, and "observe" the measurement records at T, then if the "projection postulate" predicts a probability 1 of opposite results for detectors set to the same angle but a probability 0.25 of opposite results for detectors set to different angles, that prediction is incompatible with local realism.

Meanwhile, it would help me if you would tell me whether you do have a good working understanding of the QM math or if your understanding is more conceptual...like I asked before, do you understand the mathematical meaning of "things like wavefunction evolution, expressing the wavefunction as a sum of eigenstates of a particular measurement operator, and of the projection postulate and the Born rule"?

Eye_in_the_Sky

Aug12-10, 07:09 PM

I rather see QM as non-separable, causally local ...
Exactly what we believe ...

It sounds to me like the two of you are agree upon (... among other things) the following:

The entanglement phenomenon exhibited in the Alice-and-Bob scenario can be construed as:

(i) "nonseparable" ,

and

(ii) obeying the principle of "local causality" .

... Am I correct in this assessment?

RUTA

Aug12-10, 07:33 PM

It sounds to me like the two of you are agree upon (... among other things) the following:

The entanglement phenomenon exhibited in the Alice-and-Bob scenario can be construed as:

(i) "nonseparable" ,

and

(ii) obeying the principle of "local causality" .

... Am I correct in this assessment?

I can't speak for jambaugh, but this is correct for Relational Blockworld.

akhmeteli

Sep4-10, 03:55 PM

Sorry, it has taken me a long time to reply – was a bit busy.
That doesn't make sense to me either. The "probabilities from the projection postulate" are precisely the probabilities that the state will "collapse" onto each possible eigenstate, which is supposed to be the eigenstate corresponding to what's actually observed. So if at time T the amplitude for \mid 010 \rangle is \alpha_3 (obtained via unitary evolution), that means that if you observe the records at time T there is a probability of \alpha_3 \alpha_3* that the state will collapse to the eigenstate \mid 010 \rangle and that you will observe results 010.
I agree, if you use the projection postulate, you can prove the violation of the Bell inequalities in QM. The question is can you prove that using the Born rule? It is my understanding that the Born rule gives the probability that the system is in a certain state, And I conceded that these probabilities may be the same that you get from the projection postulate. However, to prove the violation of the Bell inequalities you need the correlations. To get the correlations, you need the values of the observables. If, according to measurement results, the system is in the eigenstate \mid 010 \rangle, that does not mean automatically that you will observe results 010. This may sound outrageous, but what can I do? This is a direct consequence of unitary evolution: measurement cannot turn a superposition into a mixture. You need the projection postulate to get the values of the observables, and what projection postulate states directly contradicts unitary evolution.

Meanwhile, it would help me if you would tell me whether you do have a good working understanding of the QM math or if your understanding is more conceptual...like I asked before, do you understand the mathematical meaning of "things like wavefunction evolution, expressing the wavefunction as a sum of eigenstates of a particular measurement operator, and of the projection postulate and the Born rule"?
I am not enthusiastic about broadcasting details of my background, so I’ll try to PM you.

JesseM

Sep4-10, 05:40 PM

I agree, if you use the projection postulate, you can prove the violation of the Bell inequalities in QM. The question is can you prove that using the Born rule? It is my understanding that the Born rule gives the probability that the system is in a certain state,
Depends what you mean by that--the Born rule gives probabilities of measurement results, not of quantum states.
And I conceded that these probabilities may be the same that you get from the projection postulate. However, to prove the violation of the Bell inequalities you need the correlations. To get the correlations, you need the values of the observables. If, according to measurement results, the system is in the eigenstate \mid 010 \rangle, that does not mean automatically that you will observe results 010.
But the measurement results are the "results 010". We never measure the quantum state directly, we measure observables like position (including the position of pointers), it's only if we use the projection postulate that we can infer a measurement of result 010 implies the system is in an eigenstate \mid 010 \rangle (in an everett interpretation where there is no 'collapse', this inference would be unjustified since there might be some other versions of ourselves who got different measurement results, so the system can still be in a superposition of different eigenstates).
This may sound outrageous, but what can I do? This is a direct consequence of unitary evolution: measurement cannot turn a superposition into a mixture. You need the projection postulate to get the values of the observables
...or the Born rule.
and what projection postulate states directly contradicts unitary evolution.
While the Born rule does not as explicitly contradict unitary evolution, it also seems that no one has a very convincing way of deriving it from unitary evolution alone (and those that attempt to do so usually assume a many-worlds type framework where parallel versions of the experimenter experience different outcomes). So you're free to say that the Born rule doesn't really make sense given the hypothesis of unitary evolution alone, but I don't think there's any good basis for denying that modeling Aspect-type experiments using unitary evolution until time T, then applying the Born rule to find the probabilities of different combinations of observable measurement records, yields probabilistic predictions that violate Bell inequalities.
I am not enthusiastic about broadcasting details of my background, so I’ll try to PM you.
Thanks. But to be clear, I wasn't asking for personal information about universities attended and so forth, just a general statement about your level of technical knowledge in this subject (and your PM suggests that you do have an in-depth knowledge of the math).

akhmeteli

Sep6-10, 03:35 AM

Depends what you mean by that--the Born rule gives probabilities of measurement results, not of quantum states.
Sometimes the Born rule is defined in terms of probabilities of states – see, e.g. http://plato.stanford.edu/entries/qm/.

But the measurement results are the "results 010". We never measure the quantum state directly, we measure observables like position (including the position of pointers), it's only if we use the projection postulate that we can infer a measurement of result 010 implies the system is in an eigenstate \mid 010 \rangle (in an everett interpretation where there is no 'collapse', this inference would be unjustified since there might be some other versions of ourselves who got different measurement results, so the system can still be in a superposition of different eigenstates).
OK, so you define the Born rule in terms of probabilities of outcomes of measurements and, in particular, use it for measurement of more than one observable.

...or the Born rule.
Perhaps I could agree that if you formally apply this definition of the Born rule, you can get violations in quantum mechanics, but this has little to do with the actual measurements in Bell experiments (see below), so the Born rule for several measurements is little if at all better than the projection postulate.
While the Born rule does not as explicitly contradict unitary evolution, it also seems that no one has a very convincing way of deriving it from unitary evolution alone (and those that attempt to do so usually assume a many-worlds type framework where parallel versions of the experimenter experience different outcomes). So you're free to say that the Born rule doesn't really make sense given the hypothesis of unitary evolution alone, but I don't think there's any good basis for denying that modeling Aspect-type experiments using unitary evolution until time T, then applying the Born rule to find the probabilities of different combinations of observable measurement records, yields probabilistic predictions that violate Bell inequalities.
I think there is such a basis. Indeed, there is nothing either in unitary evolution or in the Born rule about “observable measurement records”. As I said, those “records” are not even permanent. The Born rule only tells us about some abstract results of some abstract measurements. So you should modify your statement. In Bell experiments, the spin projections of the two particles of the singlet are measured independently. I cannot imagine how the spin projections of two spatially separated particles can be measured in one measurement. If, however, you apply the Born rule to the actual measurements, you get something that contradicts unitary evolution. Indeed, after the measurement on the first particle, whatever “record” you get, the system is still in a superposition, so you can get both results for the other particle.
So I’d say the replacement of the projection postulate by the Born rule for several variables does not change the reasoning: the Born rule still contradicts unitary evolution, at least for the actual Bell experiments. And it is difficult to agree with your approach. As far as I understand, you are saying that yes, there is a contradiction, but it’s OK for some reason. I see this differently. While for some purposes this may be "OK", it's not "OK" when we are trying to decide, for example, the issue in the title of this thread: Has local realism been ruled out? What happens is people first adopt assumptions that contradict both unitary evolution and local realism, such as the projection postulate or the Born rule for several variables, and then “rule out” local realism.

JesseM

Sep6-10, 10:31 PM

Sometimes the Born rule is defined in terms of probabilities of states – see, e.g. http://plato.stanford.edu/entries/qm/.
No, I don't think so. If you look at the actual equation they give for the Born rule in section 3.4 (http://plato.stanford.edu/entries/qm/#Dyn), the equation is giving a probability of getting a given eigenvalue, not a given eigenstate/eigenvector. The verbal discussion in the paragraph preceding that equation is a bit confusing because they assume the Born rule is always coupled with the collapse postulate, so that the probability of getting a given eigenvalue would be the same as the probability of collapsing to the corresponding eigenstate, but the two assumptions are logically separable, and the article follows every other source I've seen in defining the Born rule in terms of the probability of getting a particular eigenvalue (which is understood as a possible measurement result).
OK, so you define the Born rule in terms of probabilities of outcomes of measurements and, in particular, use it for measurement of more than one observable.
Applying the Born rule to pointer states at the end of the experiment is just the von Neumann procedure, as I pointed out before.
I think there is such a basis. Indeed, there is nothing either in unitary evolution or in the Born rule about “observable measurement records”.
I don't understand what you mean by "nothing in" them "about" measurement records. Unitary evolution and the Born rule apply the same way to all quantum systems, they don't give specific rules for pointer states so I guess in that sense you could say there is "nothing in" them about pointer states, but nor do they give specific rules for electrons going through a double-slit or for any other particular quantum system, would you say "there is nothing in unitary evolution or in the Born rule about electrons"? The point is that unitary evolution and the Born rule can be applied in exactly the same way to any quantum system you like, so why not apply them to the macroscopic measuring devices and their records/pointer states in just the way you'd apply them to microscopic systems?
As I said, those “records” are not even permanent.
Who said they had to be permanent? The point is just to pick some time T shortly after all the experiments have been done, and apply the Born rule at T to find the probabilities of observing different measurement records at T. Maybe in the distant future all records of this experiment will be lost and no one will remember what the actual results were, but so what? This is just a procedure for making predictions about empirical results in the here-and-now.
The Born rule only tells us about some abstract results of some abstract measurements.
Don't know what you mean by that. Any time you use a theoretical model to make predictions about a real-world experiment, the model is always simplified, you couldn't possibly model the precise behavior of every single particle involved in the experiment, so in that sense all models are "abstract", but they are nevertheless highly useful in making predictions about real-world experiments, otherwise we'd just be doing pure math and not physics!
So you should modify your statement. In Bell experiments, the spin projections of the two particles of the singlet are measured independently. I cannot imagine how the spin projections of two spatially separated particles can be measured in one measurement.
I think you need to review the links I gave you earlier about von Neumann's procedure for calculating probabilities (see post #706 in particular). Again, there is no problem with measurements being made prior to the moment we apply the Born rule, it's just that each measurement is modeled as causing the measuring-device to become entangled with the system being measured exactly as you'd expect from unitary evolution, with no attempt to talk about probabilities at that point. Then at some time T after all measurements have already been performed, the Born ruler is applied to the pointer states of all the measuring devices. Obviously in the a real Bell experiment, at some point all the data will be collected in one place so scientists can review it, what's wrong with waiting until then to apply the Born rule to find the probability that a scientist will see different combinations of results on their computer screen?
If, however, you apply the Born rule to the actual measurements,
Any time someone looks at data you could call it a type of "measurement", including looking at a computer screen where the results of some prior measurements at different locations have been collected. The point of von Neumann's procedure is not to apply the Born rule to those prior measurements, to just model them according to standard unitary evolution, and just apply the Born rule at the very end to the collected measurement records.
you get something that contradicts unitary evolution.
How so?
Indeed, after the measurement on the first particle, whatever “record” you get, the system is still in a superposition, so you can get both results for the other particle.
But von Neumann's approach doesn't involve multiple successive applications of the Born rule, just a single one after all the experiments have been completed.
So I’d say the replacement of the projection postulate by the Born rule for several variables does not change the reasoning: the Born rule still contradicts unitary evolution, at least for the actual Bell experiments.
You haven't really explained why you think it contradicts unitary evolution. Many advocates of the many-worlds interpretation have tried to argue that the Born rule would still work for a "typical" observer in that interpretation, despite the fact that in the MWI unitary evolution goes on forever and thus each experiment just results in a superposition of different versions of the same experimenter seeing different results. Also, have a look at the paper at http://www.math.ru.nl/~landsman/Born.pdf which I found linked in wikipedia's article on the Born rule, the concluding paragraph says "The conclusion seems to be that no generally accepted derivation of the Born rule has been given to date, but this does not imply that such a derivation is impossible in principle."

Besides, you talk as though "unitary evolution" were a sacred inviolate principle, but in fact all the empirical evidence in favor of QM depends on the fact that we can connect the abstract formalism of wavefunction evolution to actual empirical observations via either the Born rule or the collapse postulate--without them you can't point to a single scrap of empirical evidence in favor of unitary evolution! Of course if unitary evolution + collapse/Born rule produces a lot of successful predictions, then on the grounds of elegance there seems to be a good basis for hoping that the same unitary evolution that governs interactions between particles between measurements also governs interactions between particles and measuring devices (since measuring devices are just very large and complex collections of particles)...that's why my hope is that a totally convincing derivation of the Born rule from the MWI will eventually be found. But to just say "the Born rule and the collapse postulate violate the sacred principle of unitary evolution, therefore they must be abandoned", and to not even attempt to show how "unitary evolution" alone can yield a single solitary prediction about any empirical experiment ever performed, seems to be turning unitary evolution into a religious creed rather than a scientific theory.
I see this differently. While for some purposes this may be "OK", it's not "OK" when we are trying to decide, for example, the issue in the title of this thread: Has local realism been ruled out?
If the predictions of "quantum mechanics" are understood in von Neumann's way, then we can say that local realism is incompatible with the predictions of "quantum mechanics", and that "quantum mechanics" has a perfect track record so far in all experimental tests that have been done (including Aspect-type experiments, although none so far have done a perfect job of closing all loopholes (http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments)). If on the other hand you choose to define "quantum mechanics" as unitary evolution alone, then unless you have some argument for why the Born rule should still work as MWI advocates do, your version of "quantum mechanics" is a purely abstract mathematical notion that makes no predictions about any real-world empirical experiments whatsoever.

akhmeteli

Sep7-10, 10:28 PM

No, I don't think so. If you look at the actual equation they give for the Born rule in section 3.4 (http://plato.stanford.edu/entries/qm/#Dyn), the equation is giving a probability of getting a given eigenvalue, not a given eigenstate/eigenvector. The verbal discussion in the paragraph preceding that equation is a bit confusing because they assume the Born rule is always coupled with the collapse postulate, so that the probability of getting a given eigenvalue would be the same as the probability of collapsing to the corresponding eigenstate, but the two assumptions are logically separable, and the article follows every other source I've seen in defining the Born rule in terms of the probability of getting a particular eigenvalue (which is understood as a possible measurement result).
It is not obvious that b_i is an eigenvalue, not an eigenstate. While b_i was defined earlier in the text, it was defined as an expansion coefficient, not as an eigenvalue. And the narrative suggests that the author is talking about the probability of the eigenstate. But anyway, let’s use your definition.
I don't understand what you mean by "nothing in" them "about" measurement records. Unitary evolution and the Born rule apply the same way to all quantum systems, they don't give specific rules for pointer states so I guess in that sense you could say there is "nothing in" them about pointer states, but nor do they give specific rules for electrons going through a double-slit or for any other particular quantum system, would you say "there is nothing in unitary evolution or in the Born rule about electrons"? The point is that unitary evolution and the Born rule can be applied in exactly the same way to any quantum system you like, so why not apply them to the macroscopic measuring devices and their records/pointer states in just the way you'd apply them to microscopic systems?
I mean the Born rule is not about “records”, either observable or not, it is about the final results of observation (please advise if you disagree). These are two different things, as, for example, "records” are never final.
Who said they had to be permanent? The point is just to pick some time T shortly after all the experiments have been done, and apply the Born rule at T to find the probabilities of observing different measurement records at T. Maybe in the distant future all records of this experiment will be lost and no one will remember what the actual results were, but so what? This is just a procedure for making predictions about empirical results in the here-and-now.
As I said, this procedure can be satisfactory for one purpose and unsatisfactory for another one. We are talking about the Born rule as applied to Bell experiments. In this case your procedure should be as follows: you have to take the records of measurements for two spatially separated particles and observe them simultaneously to obtain the input to the correlation. If you observe the records simultaneously (and that means in the same place), you cannot do that fast enough to eliminate the possibility of subluminal signaling (i.e. to close the locality loophole). On the other hand, you cannot be sure the records were the same at the time of the measurement, as the records are not permanent.
Don't know what you mean by that. Any time you use a theoretical model to make predictions about a real-world experiment, the model is always simplified, you couldn't possibly model the precise behavior of every single particle involved in the experiment, so in that sense all models are "abstract", but they are nevertheless highly useful in making predictions about real-world experiments, otherwise we'd just be doing pure math and not physics!
I mean the following. You cannot apply the Born rule in a specific form to an arbitrary measurement. For example, you cannot apply the Born rule defining the probability of the system having certain coordinates to a momentum measurement. In the same way, if you apply the Born rule for spin projections of two spatially separated particles, strictly speaking, the measurement should be designed to measure the two spin projections simultaneously, so perhaps you need some nonlocal measurement arrangement (nightlight said something to this effect). That’s not what happens in Bell experiments, where you measure the spin projections separately, and then combine the results. As I said above, this is something different.

I think you need to review the links I gave you earlier about von Neumann's procedure for calculating probabilities (see post #706 in particular). Again, there is no problem with measurements being made prior to the moment we apply the Born rule, it's just that each measurement is modeled as causing the measuring-device to become entangled with the system being measured exactly as you'd expect from unitary evolution, with no attempt to talk about probabilities at that point. Then at some time T after all measurements have already been performed, the Born ruler is applied to the pointer states of all the measuring devices. Obviously in the a real Bell experiment, at some point all the data will be collected in one place so scientists can review it, what's wrong with waiting until then to apply the Born rule to find the probability that a scientist will see different combinations of results on their computer screen?
I disagree that “there is no problem” – “at some time T after all measurements have already been performed” you cannot close the locality loophole, as “all the data will be collected in one place”, and you cannot state with certainty that the records have not changed. And that is “what's wrong with waiting until then”.
How so?
On the one hand, the probability of nonzero sum of spin projections is zero, according to the Born rule. On the other hand, according to unitary evolution, the spin projection measurement cannot turn the superposition into a mixture, so the spin projection measurement on the second particle can yield any value, so, according to the Born rule, the probability of nonzero sum of spin projections is not zero.
But von Neumann's approach doesn't involve multiple successive applications of the Born rule, just a single one after all the experiments have been completed.
But Bell experiments involve independent measurements on the two spatially separated particles.
You haven't really explained why you think it contradicts unitary evolution. Many advocates of the many-worlds interpretation have tried to argue that the Born rule would still work for a "typical" observer in that interpretation, despite the fact that in the MWI unitary evolution goes on forever and thus each experiment just results in a superposition of different versions of the same experimenter seeing different results.
See above
Also, have a look at the paper at http://www.math.ru.nl/~landsman/Born.pdf which I found linked in wikipedia's article on the Born rule, the concluding paragraph says "The conclusion seems to be that no generally accepted derivation of the Born rule has been given to date, but this does not imply that such a derivation is impossible in principle."
I am not trying to say that the Born rule per se contradicts unitary evolution (I am not sure about that), it’s the Born rule as applied for Bell experiments that contradicts unitary evolution (see above).
Besides, you talk as though "unitary evolution" were a sacred inviolate principle, but in fact all the empirical evidence in favor of QM depends on the fact that we can connect the abstract formalism of wavefunction evolution to actual empirical observations via either the Born rule or the collapse postulate--without them you can't point to a single scrap of empirical evidence in favor of unitary evolution!
My reasoning is as follows: yes, a local realistic theory cannot produce all the predictions of standard quantum mechanics, however, the postulates of standard quantum mechanics are mutually contradictory, so you cannot blame local realistic theories for failing to reproduce all predictions of standard quantum theory. So if you question unitary evolution, you also question standard quantum mechanics, therefore you cannot reasonably blame local realistic theories for failing to reproduce all predictions of standard quantum theory. And I can use unitary evolution with the Born rule for just one observable as an operational rule to get empirical evidence in favor of unitary evolution.
Of course if unitary evolution + collapse/Born rule produces a lot of successful predictions, then on the grounds of elegance there seems to be a good basis for hoping that the same unitary evolution that governs interactions between particles between measurements also governs interactions between particles and measuring devices (since measuring devices are just very large and complex collections of particles)...that's why my hope is that a totally convincing derivation of the Born rule from the MWI will eventually be found. But to just say "the Born rule and the collapse postulate violate the sacred principle of unitary evolution, therefore they must be abandoned", and to not even attempt to show how "unitary evolution" alone can yield a single solitary prediction about any empirical experiment ever performed, seems to be turning unitary evolution into a religious creed rather than a scientific theory.
See above

If the predictions of "quantum mechanics" are understood in von Neumann's way, then we can say that local realism is incompatible with the predictions of "quantum mechanics", and that "quantum mechanics" has a perfect track record so far in all experimental tests that have been done (including Aspect-type experiments, although none so far have done a perfect job of closing all loopholes (http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments)).
You see, thermodynamics also “has a perfect track record so far in all experimental tests that have been done”, however, irreversibility is at odds with dynamics, be it classical or quantum dynamics
If on the other hand you choose to define "quantum mechanics" as unitary evolution alone, then unless you have some argument for why the Born rule should still work as MWI advocates do, your version of "quantum mechanics" is a purely abstract mathematical notion that makes no predictions about any real-world empirical experiments whatsoever.
Again, you can use unitary evolution with the Born rule for just one observable, as an operational rule.

yoda jedi

Nov9-10, 01:15 PM

100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

not yet.

There have been experiments that closed the detector efficiency loophole

wrong.

----------------

........."detection-loophole-freeBell experiment seems possible in the near future"............

akhmeteli

Apr9-11, 07:20 PM

Let me add (belatedly) that the article mentioned in post 574 of this thread has just been published (you may wish to look at the postprint of the article and the exact reference to it at http://www.akhmeteli.org/akh-prepr-ws-ijqi2.pdf ).

It should be noted that some results of the article have already been significantly improved. For example, the elimination of the matter field from scalar electrodynamics has been done somewhat cleaner. Furthermore, while the extension to spinor electrodynamics in the article is much less general, some surprising new results suggest that the results for scalar electrodynamics can be fully valid for spinor electrodynamics.

JesseM

Apr9-11, 07:30 PM

here have been experiments that closed the detector efficiency loophole
wrong.

----------------

........."detection-loophole-freeBell experiment seems possible in the near future"............
Didn't notice this post before. For some examples of experiments with ions that have already closed the detection loophole (without simultaneously closing the locality loophole, as I noted), see here (http://deepblue.lib.umich.edu/bitstream/2027.42/62731/1/409791a0.pdf) (pdf file) and here (http://prl.aps.org/abstract/PRL/v100/i15/e150404).

yoda jedi

Apr10-11, 06:23 PM

Photonic.

Phys. Rev. A 83, 032123 (2011)
Detection loophole in Bell experiments: How postselection modifies the requirements to observe nonlocality
http://arxiv.org/pdf/1010.1178
http://pra.aps.org/abstract/PRA/v83/i3/e032123

A common problem in Bell-type experiments is the well-known detection loophole: if the detection efficiencies are not perfect and if one simply postselects the conclusive events, one might observe a violation of a Bell inequality, even though a local model could have explained the experimental results. In this paper, we analyze the set of all postselected correlations that can be explained by a local model, and show that it forms a polytope, larger than the Bell local polytope. We characterize the facets of this postselected local polytope in the Clauser-Horne-Shimony-Holt scenario, where two parties have binary inputs and outcomes. Our approach gives interesting insights on the detection loophole problem.

.

akhmeteli

Jul21-11, 01:24 AM

Let me make a quick update, as the thread drew a lot of interest.

In post 574 in this thread, I announced some results for scalar electrodynamics published by now in the International Journal of Quantum Information (http://www.akhmeteli.org/akh-prepr-ws-ijqi2.pdf) and relevant to this thread. However, the results of that article for spinor electrodynamics (which is more realistic) were much less general and less satisfactory. Since then I obtained some surprising results for spinor electrodynamics and the Dirac equation: http://arxiv.org/abs/1008.4828 (accepted for publication in the Journal of Mathematical Physics), which opened a way for extension of the results of my previous article to spinor electrodynamics in its entirety.

akhmeteli

Aug16-11, 10:11 PM

I obtained some surprising results for spinor electrodynamics and the Dirac equation: http://arxiv.org/abs/1008.4828 (accepted for publication in the Journal of Mathematical Physics), which opened a way for extension of the results of my previous article to spinor electrodynamics in its entirety.

So here's the link to the published version of the article - http://akhmeteli.org/wp-content/uploads/2011/08/JMAPAQ528082303_1.pdf , and the abstract:

"Three out of four complex components of the Dirac spinor can be algebraically eliminated from the Dirac equation (if some linear combination of electromagnetic fields does not vanish), yielding a partial differential equation of the fourth order for the remaining complex component. This equation is generally equivalent to the Dirac equation. Furthermore, following Schrödinger [Nature (London), 169, 538 (1952)], the remaining component can be made real by a gauge transform, thus extending to the Dirac field the Schrödinger conclusion that charged fields do not necessarily require complex representation. One of the two resulting real equations for the real function describes current conservation and can be obtained from the Maxwell equations in spinor electrodynamics (the Dirac-Maxwell electrodynamics). As the Dirac equation is one of the most fundamental equations, these results both belong in textbooks and can be used for development of new efficient methods and algorithms of quantum chemistry."

akhmeteli

May11-12, 09:42 PM

Gordon Watson

May12-12, 12:37 AM

Another quick update: the extension to spinor electrodynamics (which is more realistic than scalar electrodynamics) has been described in a short article in Journal of Physics: Conference Series ( http://dx.doi.org/10.1088/1742-6596/361/1/012037 - free access):

"2. After introduction of a complex 4-potential (producing the same electromagnetic field as the standard real 4-potential), the spinor field can be algebraically eliminated from spinor electrodynamics; the resulting equations describe independent evolution of the electromagnetic field.

3. The resulting theories for the electromagnetic field can be embedded into quantum field
theories."

The details can be found in the references of the article.

NB: To avoid side-tracking this thread, I've reproduced this post at http://www.physicsforums.com/showpost.php?p=3909153&postcount=289 :- I suggest any discussion-arising should be done there. GW

Hi Andrey, and congratulations on the publication of another advance in your work. However, with respect to the passage copied below AND your concern about breaching Bell inequalities, I suggest that you need to carefully distinguish this dichotomy, imho:

The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism".

I am certain that valid experiments (and good theory) will continue to deliver (1): a violation of Bell inequalities. I am confident that no experiments will ever falsify (2): local realism (properly defined).

To these ends, and to this latter end in particular, I'd welcome your comments on the breaching of Bell inequalities AND the explicit local realism (and any other matter) in http://www.physicsforums.com/showpost.php?p=3905795&postcount=287

PS: As previously discussed, I believe that the BOLD-ed sentence below greatly weakens your work. Me believing it to be a FALSE hope :frown: (as opposed to Bell's positive one, as discussed and delivered in the above link). :smile:

With best regards,

Gordon
.............

From http://iopscience.iop.org/1742-6596/361/1/012037/pdf/1742-6596_361_1_012037.pdf -- "Of course, the Bell inequalities cannot be violated in such a theory. But there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory. Indeed, there seems to be a consensus among experts that “a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing” [4]. On the other hand, to prove theoretically that the inequalities can be violated in quantum theory, one needs to use the projection postulate (loosely speaking, the postulate states that if some value of an observable is measured, the resulting state is an eigenstate of the relevant operator with the relevant eigenvalue). However, such postulate, strictly speaking, is in contradiction with the standard unitary evolution of the larger quantum system that includes the measured system and the measurement device, as such postulate introduces irreversibility and turns a superposition of states into their mixture. Therefore, mutually contradictory assumptions are required to prove the Bell theorem, so it is on shaky grounds both theoretically and experimentally and can be circumvented if, for instance, the projection postulate is rejected. [Emphasis added by GW: other issues arising not addressed here.]

NB: To avoid side-tracking this thread, I've reproduced this post at http://www.physicsforums.com/showpost.php?p=3909153&postcount=289 :- I suggest any discussion-arising should be done there. GW

akhmeteli

May12-12, 12:58 PM

NB: To avoid side-tracking this thread, I've reproduced this post at http://www.physicsforums.com/showpost.php?p=3909153&postcount=289 :- I suggest any discussion-arising should be done there. GW

Dear Gordon Watson,

Thank you for your comment. I think it is relevant to this thread as well.

[QUOTE=Gordon Watson]Hi Andrey, and congratulations on the publication of another advance in your work.

Thank you

However, with respect to the passage copied below AND your concern about breaching Bell inequalities, I suggest that you need to carefully distinguish this dichotomy, imho:

The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism".

I guess this statement is technically correct, as, for example, violations of the Bell inequalities cannot exclude superdeterministic theories.

I am certain that valid experiments (and good theory) will continue to deliver (1): a violation of Bell inequalities.

With all due respect, this is just your opinion, not a fact. For example, there is no loophole-free experimental evidence of violations. I am not ready to concede this point, sorry.

I am confident that no experiments will ever falsify (2): local realism (properly defined).

I would also be surprised to hear about such experiments falsifying local realism, but who knows...

To these ends, and to this latter end in particular, I'd welcome your comments on the breaching of Bell inequalities AND the explicit local realism (and any other matter) in http://www.physicsforums.com/showpost.php?p=3905795&postcount=287

I will look at that thread, but I am not sure I will be able to comment - these are difficult and sometimes controversial issues.

PS: As previously discussed, I believe that the BOLD-ed sentence below greatly weakens your work. Me believing it to be a FALSE hope :frown: (as opposed to Bell's positive one, as discussed and delivered in the above link). :smile:

From http://iopscience.iop.org/1742-6596/361/1/012037/pdf/1742-6596_361_1_012037.pdf -- "Of course, the Bell inequalities cannot be violated in such a theory. But there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory. Indeed, there seems to be a consensus among experts that “a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing” [4]. On the other hand, to prove theoretically that the inequalities can be violated in quantum theory, one needs to use the projection postulate (loosely speaking, the postulate states that if some value of an observable is measured, the resulting state is an eigenstate of the relevant operator with the relevant eigenvalue). However, such postulate, strictly speaking, is in contradiction with the standard unitary evolution of the larger quantum system that includes the measured system and the measurement device, as such postulate introduces irreversibility and turns a superposition of states into their mixture. Therefore, mutually contradictory assumptions are required to prove the Bell theorem, so it is on shaky grounds both theoretically and experimentally and can be circumvented if, for instance, the projection postulate is rejected. [Emphasis added by GW: other issues arising not addressed here.]

[/B]

Again, with all due respect, you offer your opinion, not your reasons.

Gordon Watson

May12-12, 07:35 PM

Dear Gordon Watson,

Thank you for your comment. I think it is relevant to this thread as well.

Thank you

Thanks Andrey, I'm happy to discuss it here, and in detail. [That suggestion came from the concern that a focus on classical probability theory and Malus' Method (i.e., on what is essentially high-school maths and logic; with little more required) would distract from the maths that you're working with in your papers.]

Now, wrt this statement: The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism", you say:
I guess this statement is technically correct, as, for example, violations of the Bell inequalities cannot exclude superdeterministic theories.

However, understanding the point at issue, you would NOT be able to offer this response; imho!

[EDIT: this emphasised above to clearly identify that the response's reference to "I guess ... technically correct ... cannot exclude super deterministic theories" is inadequate in the face of what can be clearly shown: that a DEFINITE local realistic formulation demolishes your escape clause. That is "I guess ... " to a TRUISM is not acceptable. Agree; or refute the truism, please. /EDIT]

For it can be clearly shown, with neither mystery nor complication, that a DEFINITE local realistic formulation demolishes your escape clause. MOREOVER, the formulation is right in line with Bell's hope: It begins with the acceptance of Einstein-locality (EL). It continues with Bell's hope:

"... the explicit representation of quantum nonlocality [in 'the de Broglie-Bohm theory'] ... started a new wave of investigation in this area. Let us hope that these analyses also may one day be illuminated, perhaps harshly, by some simple constructive model. However that may be, long may Louis de Broglie continue to inspire those who suspect that what is proved by impossibility proofs is lack of imagination," (Bell 2004: 167). "To those for whom nonlocality is anathema, Bell's Theorem finally spells the death of the hidden variables program.31 But not for Bell. None of the no-hidden-variables theorems persuaded him that hidden variables were impossible," (Mermin 1993: 814). [All emphasis and [.] added by GW; see http://www.physicsforums.com/showpos...&postcount=287]

Bell (2004): Speakable and Unspeakable in Quantum Mechanics; 2nd edition. CUP, Cambridge.

Mermin (1993): Rev. Mod. Phys. 65, 3, 803-815. Footnote #31: "Many people contend that Bell's Theorem demonstrates nonlocality independent of a hidden-variables program, but there is no general agreement about this."

So, this suggests that you are up against a proven fact (and not just an opinion :smile:); this TRUISM:

"The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism."

... reinforcing a conclusion held by many, for many years.

Next, in response to: "I am certain that valid experiments (and good theory [including current QM]) will continue to deliver (1): a violation of Bell inequalities," you say:
With all due respect, this is just your opinion, not a fact. For example, there is no loophole-free experimental evidence of violations. I am not ready to concede this point, sorry.

The point is this (if you seek to down-play the good theories): VALID EXPERIMENTS already violate Bell's Theorem (with loopholes for the desperate)! Moreover, such loopholes are being reduced almost daily! Why then would better experiments reverse that trend AND suddenly NOT-violate Bell's Theorem? AGAINST the whole history of VALID QM experimentation? Especially WHEN the idealised maths (that you're to examine) show that ideal experiments WILL continue the violation!

To put the position clearly: You will one day concede this point; imho. So why not see what needs be adjusted in your work NOW to avoid this later capitulation with its consequent complications?

I would also be surprised to hear about such experiments falsifying local realism, but who knows...

Good! Do we agree then, that Einstein-locality remains at the core of our personal world-views?

I will look at that thread, but I am not sure I will be able to comment - these are difficult and sometimes controversial issues.

Thanks; that's all that is asked! In an attempt to be helpful wrt to your work; with any and all critiques of my work most welcome.

You write: "But there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory." AGAINST which, in effect, the message is: "Please, abandon this false hope!" You respond:

Again, with all due respect, you offer your opinion, not your reasons.

Please: Reasons are clearly given, at the level of high-school maths and logic, here: http://www.physicsforums.com/showpos...&postcount=287

With best regards, Gordon

lugita15

May12-12, 10:23 PM

Gordon Watson

May12-12, 10:59 PM

Gordon, do you agree or disagree with akhmeteli's point that the only way you can have viable local hidden-variable model in the face of a Bell inequality violation (with no experimental loopholes) is if your hidden-variable model is superdeterministic, i.e. violates the no-conspiracy condition?

Hi lugita, DISAGREE: on the understanding that by "super-determinism" you mean "NO free-will on the part of Alice and Bob."

As to "violating the no-conspiracy condition" -- best you spell that out for me, please.

As to my reason: see

Q_{\textit{0.2}} http://www.physicsforums.com/showpost.php?p=3905795&postcount=287 with critical comments, etc., most welcome.

For there you'll find a viable local hidden-variable model AND Bell inequality violations (with no experimental loopholes)! The plural arising from "a viable local hidden-variable model" of both EPRB-Bell (1964) and Aspect's experiment (his 2004 paper), equally applicable to CHSH, CRB, GHSZ, GHZ, etc.

Thanks, Gordon

lugita15

May12-12, 11:31 PM

Hi lugita, DISAGREE: on the understanding that by "super-determinism" you mean "NO free-will on the part of Alice and Bob."

As to "violating the no-conspiracy condition" -- best you spell that out for me, please.The no-conspiracy condition, which is one of the assumptions used in Bell's proof, states that the result Alice observes by measuring her photon is independent of the angle setting at which Bob measures his photon. This assumption rules out several possibilities at once:
1. The Universe conspires to make Alice and Bob make the exact measurement decisions needed to make Bell's inequality appear violated when it would really not be if Alice and Bob's measurement decisions were totally random.
2. The universe tells the photons what Alice and Bob are going to do, so that the photons can plan their strategy to anticipate the measurement decisions

Etc. Someone who believes in local hidden variables but denies no-conspiracy is called a superdeterminist. Given this, are you one?

Concerning your "classical challenge", I think your time may be better spent trying to understand the core of Bell's reasoning, which is only a few steps of simple logic, rather than focusing on the gory details of his original proof, which discusses things like factorization of conditional probability and integrating over lambda. Why don't you take a look at Herbert's version of Bell's proof, which is simpler by leaps and bounds than Bell's original paper and can thus allow us to identify the locus of your disagreement with Bell.

EDIT: Sorry, I forgot the link:

http://quantumtantra.com/bell2.html

akhmeteli

May12-12, 11:59 PM

Gordon, do you agree or disagree with akhmeteli's point that the only way you can have viable local hidden-variable model in the face of a Bell inequality violation (with no experimental loopholes) is if your hidden-variable model is superdeterministic, i.e. violates the no-conspiracy condition?

Dear lugita15,

I am afraid I have to disagree with your interpretation of my words in the answer to Gordon Watson. I only agreed with GW that
"violation of a Bell inequality" is NOT the same as (2) "falsifying local realism"
, and I mentioned superdeterminism just as an example to explain why I had to agree with GW's statement. I did not say that superdeterminism is "the only way you can have viable local hidden-variable model in the face of a Bell inequality violation (with no experimental loopholes)". I may have conceded this point elsewhere for the sake of argument, but I don't want to take sides on this issue - I just don't know enough about it.

lugita15

May13-12, 12:03 AM

Dear lugita15,

I am afraid I have to disagree with your interpretation of my words in the answer to Gordon Watson. I only agreed with GW that

, and I mentioned superdeterminism just as an example to explain why I had to agree with GW's statement. I did not say that superdeterminism is "the only way you can have viable local hidden-variable model in the face of a Bell inequality violation (with no experimental loopholes)". I may have conceded this point elsewhere for the sake of argument, but I don't want to take sides on this issue - I just don't know enough about it.Sorry for putting words in your mouth, akhmeteli! Let me state that as my point, then.

akhmeteli

May13-12, 12:25 AM

Sorry for putting words in your mouth, akhmeteli! Let me state that as my point, then.

OK, no problem

akhmeteli

May13-12, 01:49 AM

Now, wrt this statement: The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism", you say:

However, understanding the point at issue, you would NOT be able to offer this response; imho! For it can be clearly shown, with neither mystery nor complication, that a DEFINITE local realistic formulation demolishes your escape clause. MOREOVER, the formulation is right in line with Bell's hope: It begins with the acceptance of Einstein-locality (EL). It continues with Bell's hope:
So, this suggests that you are up against a proven fact (and not just an opinion :smile:); this TRUISM:

"The (1) "violation of a Bell inequality" is NOT the same as (2) "falsifying local realism."

... reinforcing a conclusion held by many, for many years.
Dear Gordon Watson,

I am afraid I am royally confused :-( I actually AGREED with your TRUISM in my previous post (745), so what are you talking about?
Next, in response to: "I am certain that valid experiments (and good theory [including current QM]) will continue to deliver (1): a violation of Bell inequalities," you say:

The point is this (if you seek to down-play the good theories): VALID EXPERIMENTS already violate Bell's Theorem (with loopholes for the desperate)!
You believe that loopholes are “for the desperate”, but I am afraid this is just your opinion, and I don’t have to agree with such an opinion. For example, even Zeilinger, who is no fan of local theories, calls the loopholes “essential” (you can find the quote in this post: http://www.physicsforums.com/showpost.php?p=1705826&postcount=65 ).

As for “good theory [including current QM]”, I explained in the very first post in this thread why I have problems with this THEORETICAL argument. Briefly: the proof of the possibility of violations of the Bell inequalities in quantum mechanics (which proof is an important part of the Bell theorem proof) typically uses two major assumptions of standard QM: unitary evolution and theory of measurements (e.g., the projection postulate). However, these assumptions are mutually contradictory, as unitary evolution, unlike the projection postulate, cannot provide irreversibility or turn a pure state into a mixture.
Moreover, such loopholes are being reduced almost daily! Why then would better experiments reverse that trend AND suddenly NOT-violate Bell's Theorem? AGAINST the whole history of VALID QM experimentation?
I explained why such reasoning does not impress me in post 34 in this thread: “what’s wrong with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees. Or do you think there is nothing wrong with it? In both cases we are talking about a theorem, remember? If you have not made sure that all assumptions of the theorem are fulfilled simultaneously, you cannot demand that the statement of the theorem hold true.” So, up to now, experiments demonstrate violations only when the assumptions of the Bell theorem are not fulfilled. Until loophole-free violations are demonstrated, I don’t buy your conclusion on violations, sorry.
Especially WHEN the idealised maths (that you're to examine) show that ideal experiments WILL continue the violation!
If you are talking about standard QM, see above (starting with “As for “good theory [including current QM]””). If, however, you are talking about your own model… OK, let us assume for the sake of argument that your model is indeed local and predicts violations. Does this prove that violations are for real? No way, as the status of your model is unknown – I don’t know if your model is correct or not. If your model has the same predictions for all experiments as standard QM, it means it is also self-contradictory. If, however, your model’s predictions are different from those of QM, the experimental status of your model is dubious in the best case.

To put the position clearly: You will one day concede this point; imho. So why not see what needs be adjusted in your work NOW to avoid this later capitulation with its consequent complications?
Maybe I’ll concede this point in the future, for example, if and when new experiments provide results that I do not expect. But right now I don’t see valid reasons to concede it or adjust my work.

Good! Do we agree then, that Einstein-locality remains at the core of our personal world-views?
If you mean locality of special theory of relativity, then yes, if you mean locality of EPR, then perhaps no.

You write: "But there are some reasons to believe these inequalities cannot be violated either in experiments or in quantum theory." AGAINST which, in effect, the message is: "Please, abandon this false hope!" You respond:

Please: Reasons are clearly given, at the level of high-school maths and logic, here: http://www.physicsforums.com/showpos...&postcount=287
I did not study that post in detail, but it looks like you use Malus law as an assumption. I cannot accept this law as a precise one for reasons given in post 41 in this thread (PP and UE there stand for “projection postulate” and “unitary evolution”, respectively.)

Gordon Watson

May13-12, 04:26 AM

Dear Gordon Watson,

I am afraid I am royally confused :-( I actually AGREED with your TRUISM in my previous post (745), so what are you talking about?

Dear akhmeteli: Sorry for any confusion on my part. (I've now added to my remark in an attempt to be very clear). Your " I guess ... " response was so highly and incorrectly conditional that I saw no AGREEMENT of the KIND warranted by the data that I referred you to! It is a TRUISM, so please: AGREE unconditionally, or reject it (with grounds)! That's what I was talking about. The days of your response being seen as in any way relevant are passed, imho. That's all that was meant; and REMAINS!

You believe that loopholes are “for the desperate”, but I am afraid this is just your opinion, and I don’t have to agree with such an opinion. For example, even Zeilinger, who is no fan of local theories, calls the loopholes “essential” (you can find the quote in this post: http://www.physicsforums.com/showpost.php?p=1705826&postcount=65 ).

I stand by my opinion.

As for “good theory [including current QM]”, I explained in the very first post in this thread why I have problems with this THEORETICAL argument. Briefly: the proof of the possibility of violations of the Bell inequalities in quantum mechanics (which proof is an important part of the Bell theorem proof) typically uses two major assumptions of standard QM: unitary evolution and theory of measurements (e.g., the projection postulate). However, these assumptions are mutually contradictory, as unitary evolution, unlike the projection postulate, cannot provide irreversibility or turn a pure state into a mixture.

OK; so you "dismiss" current QM. That's fine; I simply re-interpret it in the light of the "good theory" that remains: The one that you leave unaddressed and thus intact. The one that is the sole basis for my suggestion that you need to "tweak" your theory and correct (or remove) references to the items that I highlighted.

I explained why such reasoning does not impress me in post 34 in this thread: “what’s wrong with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees. Or do you think there is nothing wrong with it? In both cases we are talking about a theorem, remember? If you have not made sure that all assumptions of the theorem are fulfilled simultaneously, you cannot demand that the statement of the theorem hold true.” So, up to now, experiments demonstrate violations only when the assumptions of the Bell theorem are not fulfilled. Until loophole-free violations are demonstrated, I don’t buy your conclusion on violations, sorry.

Sorry? But if you do not examine the free data; the data that I suggest leaves these OLD arguments of yours behind; the data THAT STARTS WITH Bell's primary assumptions fulfilled ... well, "sorry" doesn't seem to cut it. A suggestion re "avoidance" would fit the situation better. :frown:

If you are talking about standard QM, see above (starting with “As for “good theory [including current QM]””). If, however, you are talking about your own model… OK, let us assume for the sake of argument that your model is indeed local and predicts violations. Does this prove that violations are for real? No way, as the status of your model is unknown – I don’t know if your model is correct or not. If your model has the same predictions for all experiments as standard QM, it means it is also self-contradictory. If, however, your model’s predictions are different from those of QM, the experimental status of your model is dubious in the best case.

If I sincerely offer a model that might help you correct errors in your papers (as I have done sincerely, and privately, from the start), MAYBE you should revisit high-school maths and logic and check it out. For that's the hint I gave; assuring you it was not very heavy-duty analysis: JUST heavy-duty conclusions .. and heavy-duty consequences for some of your statements.

Maybe I’ll concede this point in the future, for example, if and when new experiments provide results that I do not expect. But right now I don’t see valid reasons to concede it or adjust my work.

Just study that data that I offered, please. IT IS certainly beyond your expectations thus far, in our discussions to-date. It is not beyond your ability; nor, as I see it, is it beyond the direction that your research is taking you. (That's the why of why-I'm-here.)

If you mean locality of special theory of relativity, then yes, if you mean locality of EPR, then perhaps no.

I mean Einstein-locality. Please: HOW does that differ from (your once again) seeming conditional hedge? Please elaborate on the "locality of EPR" -- for I may have missed something there.

I did not study that post in detail, but it looks like you use Malus law as an assumption. I cannot accept this law as a precise one for reasons given in post 41 in this thread (PP and UE there stand for “projection postulate” and “unitary evolution”, respectively.) [Emphasis added by GW.]

If I send you some data and you do not study it IN ANY meaningful WAY, what more can I say?

Just this, perhaps:

Every phrase emBOLDed (by me) is wrong, irrelevant or lazy. Which hardly seems fair comment on a model that delivers on Bell's hope for a simple constructive model: one that is (as he surmised) perhaps harshly illuminative.

................

PS: Re Zeilinger: "Expecting that any improved experiment will also agree with quantum theory, a shift of our classical philosophical positions seems necessary. Among the possible implications are nonlocality or complete determinism or the abandonment of counterfactual conclusions. Whether or not this will finally answer the eternal question: “Is the moon there, when nobody looks?” ... is certainly up to the reader’s personal judgement. [Emphasis by GW.]"

The bold-emphasised piece agrees with me. The shift in "classical philosophical positions" is delivered, courtesy of Malus' Method, in the data to which you were directed. It's worth a good hard read.

......................

With best regards,

Gordon
..

akhmeteli

May13-12, 12:01 PM

Dear akhmeteli: Sorry for any confusion on my part. (I've now added to my remark in an attempt to be very clear). Your " I guess ... " response was so highly and incorrectly conditional that I saw no AGREEMENT of the KIND warranted by the data that I referred you to! It is a TRUISM, so please: AGREE unconditionally, or reject it (with grounds)! That's what I was talking about. The days of your response being seen as in any way relevant are passed, imho. That's all that was meant; and REMAINS!

Dear Gordon Watson,

I just don't want to say more about your statement than I said. As for your data, I have looked at it and decided against studying it in detail, as, on the one hand, that would require quite some time, and I have other priorities (I have a day job and three different physics projects on my hands), on the other hand, the data does not look properly published (with all due respect, Physics Essays is not a source I would rely on). Looks like mentors agree, as they have just closed your thread. Again, I don't comment on correctness or incorrectness of your model, but, with all due respect, if you cannot publish it properly, it's not my problem.The world of physics is ruthless.

I stand by my opinion.

No problem. But again, it's just your opinion, not a fact.

OK; so you "dismiss" current QM. That's fine; I simply re-interpret it in the light of the "good theory" that remains: The one that you leave unaddressed and thus intact. The one that is the sole basis for my suggestion that you need to "tweak" your theory and correct (or remove) references to the items that I highlighted.

I dismiss the projection postulate, as it contradicts unitary evolution anyway, but I fully adopt unitary evolution. And I agree, I leave your theory unaddressed (for the above reasons) and intact (as I don't comment on its correctness). Again, even assuming that your theory is correct as a theory, that would not mean that I have to adjust my work, as the experimental status of your theory is unknown (unless its predictions coincide with those of standard QM, in which case your theory is also self-contradictory).

Sorry? But if you do not examine the free data; the data that I suggest leaves these OLD arguments of yours behind; the data THAT STARTS WITH Bell's primary assumptions fulfilled ... well, "sorry" doesn't seem to cut it. A suggestion re "avoidance" would fit the situation better. :frown:

As I said, Bell's primary assumptions are mutually contradictory, so if you START with them, your conclusions cannot impress me. And yes, I do avoid studying your theory in detail for reasons given above.

If I sincerely offer a model that might help you correct errors in your papers (as I have done sincerely, and privately, from the start), MAYBE you should revisit high-school maths and logic and check it out. For that's the hint I gave; assuring you it was not very heavy-duty analysis: JUST heavy-duty conclusions .. and heavy-duty consequences for some of your statements.

Again, I tried to explain why I don't see how your material can affect my work. If you don't accept my explanations, just tell me: do experimental predictions of your model fully coincide with those of standard QM?

Just study that data that I offered, please. IT IS certainly beyond your expectations thus far, in our discussions to-date. It is not beyond your ability; nor, as I see it, is it beyond the direction that your research is taking you. (That's the why of why-I'm-here.)

See above.

I mean Einstein-locality. Please: HOW does that differ from (your once again) seeming conditional hedge? Please elaborate on the "locality of EPR" -- for I may have missed something there.

I just don't think we need noncontextual variables.

If I send you some data and you do not study it IN ANY meaningful WAY, what more can I say?

Just this, perhaps:

Every phrase emBOLDed (by me) is wrong, irrelevant or lazy. Which hardly seems fair comment on a model that delivers on Bell's hope for a simple constructive model: one that is (as he surmised) perhaps harshly illuminative.

You may call my phrases wrong and irrelevant, but, with all due respect, you're not my boss, so my laziness is none of your business. As I said, I have other priorities and obligations. Again, I fail to see how your model can affect my work. As for fairness... I owe fairness to my co-authors, who expect me to contribute to our mutual work in a timely manner.

PS: Re Zeilinger: "Expecting that any improved experiment will also agree with quantum theory, a shift of our classical philosophical positions seems necessary. Among the possible implications are nonlocality or complete determinism or the abandonment of counterfactual conclusions. Whether or not this will finally answer the eternal question: “Is the moon there, when nobody looks?” ... is certainly up to the reader’s personal judgement. [Emphasis by GW.]"

The bold-emphasised piece agrees with me. The shift in "classical philosophical positions" is delivered, courtesy of Malus' Method, in the data to which you were directed. It's worth a good hard read.

I cannot reasonably expect "that any improved experiment will also agree with quantum theory" as some assumptions of standard quantum theory (unitary evolution and the theory of measurements) flatly contradict each other. As for your data... I am of no consequence anyway, whereas mentors do not believe your data belongs here. Publish your data properly, then discuss it here. I know first-hand that it is not always easy to publish your work, but nobody else can do that for you. If people are not enthusiastic about our work, it's our problem, not theirs.

Gordon Watson

May15-12, 07:54 AM

Dear Gordon Watson,

I just don't want to say more about your statement than I said. As for your data, I have looked at it and decided against studying it in detail, as, on the one hand, that would require quite some time, ... [Emphasis below added by GW.]

30 minutes, max; plus or minus! :smile: The equations and their reductions are all done for you; step by step; the experimental results, which you should recognise like the back of your hand, are ALL there too. They should draw you into and through the simple maths. There are no maths tricks or errors, AFAIK! (That's why I brought my ideas to PF as a question; to see if I had missed something.)

I dismiss the projection postulate, as it contradicts unitary evolution anyway, but I fully adopt unitary evolution. And I agree, I leave your theory unaddressed (for the above reasons) and intact (as I don't comment on its correctness). Again, even assuming that your theory is correct as a theory, that would not mean that I have to adjust my work, as the experimental status of your theory is unknown (unless its predictions coincide with those of standard QM, in which case your theory is also self-contradictory).

LOL! :tongue2: The experimental status of my work is exactly that of QM = my work and QM share the same predictions! (I am NOT so radical as to dispute valid experiments and theory. NB: My focus is on Bell's Theorem, which (AFAIK) is NOT a property of quantum theory; Peres text-book (1995: 162) and I in agreement on this point. AND THAT's why I'm encouraging you to reassess your published statements about BT and its impact on your theory. You are bringing into your physics an issue that ... ... ... me leaving you to complete the sentence.)

Self-contradictory? Sorry, not so. That 30 minutes gotta be looking like a good investment.

Make it 25 minutes: You might be surprised to see (so-called) "projection" and "unitary evolution" united in my simple equations!

Please note how the so-called "quantum jumps" are handled there. Again, in line with Bell's direct appeal, as I read him, I write: This may be seen as "a development towards greater physical precision … to have the 'jump' in the equations and not just the talk," Bell (2004: 118), "so that it would come about as dynamical process in dynamically defined conditions." This latter hope being delivered expressly, and smoothly, in my equation (11).

As I said, Bell's primary assumptions are mutually contradictory, so if you START with them, your conclusions cannot impress me. ...

Amazing. In your terms: What you're allowed to say versus what I'm not allowed to question!

Let me STRESS this important point: I am on Bell's side in this matter: and vice-versa, AFAIK. And, to be clear about my advocacy for Bell and QM: I'll back him against your colleagues, supervisors, etc; me taking the view (not lightly) that I am one of Bell's keenest 'disciples', :cool: disagreeing (AFAIK) only with a supplementary assumption that he made in arriving at his 'theorem'. An assumption that is not included in the excellent (imho) "primary" assumptions that he began with.

That is: NO contradiction arises if you take Bell's primary assumptions to be: Bell (1964: eqns (1), (2), (3), (12), (13), (14))! And, Yes; I do start with them: for I'm not playing games -- AND I accept Einstein-locality as my starting point, as did Bell (e.g., 1964).

Again, I tried to explain why I don't see how your material can affect my work. If you don't accept my explanations, just tell me: do experimental predictions of your model fully coincide with those of standard QM?

Of course! Fully! As shown in equations (9) and (10). Make it 20 minutes; you've just been told, to the best of my ability.

... Again, I fail to see how your model can affect my work. ...

I cannot reasonably expect "that any improved experiment will also agree with quantum theory" as some assumptions of standard quantum theory (unitary evolution and the theory of measurements) flatly contradict each other. ...

Andrey: it is well known that any result you like can be drawn from a contradiction. I suggest that the (SEROUS) contradiction that you see (and cite) ARISES from an erroneous interpretation of mathematical terms. I suggest that the reason that I see NO contradiction is that my own work gives me access to a very different (physically significant) interpretation.

So, in closing: the essence of my intended-to-be-helpful message to you (from day one) is this:

1. IF your theory requires you to take the stance on Bell's Theorem that you do, THEN:

2. Imho, your theory is defective. BUT:

3. Imho, it may equally be the case, from my experience, that such a defect might be readily and easily remedied.

4. That's it; that's all; still wishing you the best of good luck with every project,

PS: Excuse any fun above; it was late; I tend to mix fun and physics; and I love wrestling with, and very much appreciate, your feisty spirit.

With best regards; expecting us to agree one day, soon :smile:

Gordon

akhmeteli

May15-12, 10:07 PM

LOL! :tongue2: The experimental status of my work is exactly that of QM = my work and QM share the same predictions! (I am NOT so radical as to dispute valid experiments and theory. NB: My focus is on Bell's Theorem, which (AFAIK) is NOT a property of quantum theory; Peres text-book (1995: 162) and I in agreement on this point. AND THAT's why I'm encouraging you to reassess your published statements about BT and its impact on your theory. You are bringing into your physics an issue that ... ... ... me leaving you to complete the sentence.)

Self-contradictory? Sorry, not so. That 30 minutes gotta be looking like a good investment.

Make it 25 minutes: You might be surprised to see (so-called) "projection" and "unitary evolution" united in my simple equations!

Amazing. In your terms: What you're allowed to say versus what I'm not allowed to question!

Let me STRESS this important point: I am on Bell's side in this matter: and vice-versa, AFAIK. And, to be clear about my advocacy for Bell and QM: I'll back him against your colleagues, supervisors, etc; me taking the view (not lightly) that I am one of Bell's keenest 'disciples', :cool: disagreeing (AFAIK) only with a supplementary assumption that he made in arriving at his 'theorem'. An assumption that is not included in the excellent (imho) "primary" assumptions that he began with.

That is: NO contradiction arises if you take Bell's primary assumptions to be: Bell (1964: eqns (1), (2), (3), (12), (13), (14))! And, Yes; I do start with them: for I'm not playing games -- AND I accept Einstein-locality as my starting point, as did Bell (e.g., 1964).

Of course! Fully! As shown in equations (9) and (10). Make it 20 minutes; you've just been told, to the best of my ability.

Andrey: it is well known that any result you like can be drawn from a contradiction. I suggest that the (SEROUS) contradiction that you see (and cite) ARISES from an erroneous interpretation of mathematical terms. I suggest that the reason that I see NO contradiction is that my own work gives me access to a very different (physically significant) interpretation.

So, in closing: the essence of my intended-to-be-helpful message to you (from day one) is this:

1. IF your theory requires you to take the stance on Bell's Theorem that you do, THEN:

2. Imho, your theory is defective. BUT:

3. Imho, it may equally be the case, from my experience, that such a defect might be readily and easily remedied.

4. That's it; that's all; still wishing you the best of good luck with every project,

PS: Excuse any fun above; it was late; I tend to mix fun and physics; and I love wrestling with, and very much appreciate, your feisty spirit.

Dear Gordon Watson,

Thank you for your reply.

You did clarify your position. If I understood you correctly, you believe that

1) your theory's experimental predictions fully coincide with those of standard quantum mechanics;

2) your theory is not self-contradictory and unites "projection" and "unitary evolution".

Let me tell you what. I wrote nothing or almost nothing original about the Bell theorem in my published articles. I just had to define my position, as the issue of the Bell theorem would have arisen anyway.

In particular, I wrote, following other authors, that:

1) Unitary evolution and quantum theory of measurements (e.g., the projection postulate) are mutually contradictory.

2) Both unitary evolution and the projection postulate are used to prove that the Bell inequalities can be violated in standard quantum mechanics (SQM).

Neither of these points is new or belongs to me. If your theory adopts both unitary evolution and the projection postulate of SQM, but not its contradiction, then you seem to have solved the 80-year-old measurement problem of quantum mechanics ( http://plato.stanford.edu/entries/qt-measurement/ and published work cited there, such as Albert's, or Bassi/Ghirardi's ). I congratulate you with this achievement, and suggest that you don't waste time on me (I was dead serious saying that I am of no consequence anyway) and publish your result (it does not matter if I see contradiction or not; what matters is that the measurement problem in quantum mechanics is generally recognized as such, no matter if I am dead or alive). Until properly published, your great result does not belong here, and, with all due respect, on the one hand, I don't believe your claims, on the other hand, I don't want to and don't have to check your derivation.

Let me assure you that I have no intention to offend you. Let me emphasize that I am not an expert in the Bell theorem. If I had more time to go into details, I would have started with reading (more) published articles of other people who defend local realism against the Bell theorem :-). Somehow they are able to publish their work, although, in general, local realism is not very popular:-).

lugita15

May15-12, 10:14 PM

Unitary evolution and quantum theory of measurements (e.g., the projection postulate) are mutually contradictory. Why do you think they're mutually contradictory? They have been used together for nearly a century, and have produced amazing theoretical and experimental results. Now you may believe that the combination of the two is philosophically problematic, because of the measurement problem, but logically they seem to go together just fine. There are a variety of interpretations of QM that embrace or explain these two features of quantum mechanics: Copenhagen, de Broglie-Bohm, Many Worlds, etc. Are you saying that all of these views are inconsistent/incoherent?

scijeebus

May15-12, 10:26 PM

There isn't much of a violation of anything, things in quantum mechanics aren't really causally related, they are related via correlation. Because of this, entanglement doesn't have to violate that things are independent from us, because before measurement the particles are still entangled, otherwise we wouldn't be able to disentangle them. When we disentangle particles, there is no causality of information being sent between points. When particles are entangled, the plural form is meaningless, they are the same particle by the properties of correlation, and it is this same correlation that breaks the entanglement, for when particles become dis-entangled, all that is really happening is their probabilities adjust to correlate to specific but different values, and that's it. This same property of correlation also explains the quantum erasure. Paths aren't ever destroyed, the probability of an electron in a double slit experiment just correlates to that of a single path upon measurement.
Of course, there we can't be 100% sure of anything in the first place because we aren't ever even observing photons, we are observing the electrical impulses in our brain.
But, because things aren't causally connected, there isn't a causation that can be violated. This leaves room for the principal of locality but also for realism because things can still be logically correlated to show a sequence of events.

akhmeteli

May15-12, 11:30 PM

Why do you think they're mutually contradictory?

Because, for example, unitary evolution cannot provide irreversibility or turn a pure state into a mixture, whereas the projection postulate mandates just that.

They have been used together for nearly a century, and have produced amazing theoretical and experimental results.

Thermodynamics has been used for much longer than a century and has produced amazing theoretical and experimental results. However, there is a contradiction between themodynamics and its underlying theories - classical or quantum mechanics: for example, unitary evolution cannot provide irreversibility, which is a basic assumption of thermodynamics.

Furthermore, the Bell theorem drives the assumptions of standard quantum mechanics to their extremes, which are currently inaccessible in experiment - loophole-free experiments are not possible right now (I am not saying that they won't be possible tomorrow, or in a year, or in ten years from now) - so that may be a reason why the theorem's conclusions have not been disproved experimentally yet. I do appreciate that loophole-free experimental demonstration of violations of the Bell inequalities can be achieved in the future, but we are living and discussing right now. As they say, it is difficult to make forecasts, especially for the future:-)

Now you may believe that the combination of the two is philosophically problematic, because of the measurement problem, but logically they seem to go together just fine.

I did not say anything about philosophical problems, and logically they are mutually contradictory (see above). I am not trying to sell you something that I invented or something that was invented yesterday - the contradiction has been recognized 80 years ago by von Neumann - see more details at http://plato.stanford.edu/entries/qt-measurement/ or at http://en.wikipedia.org/wiki/Measurement_problem and references there.

There are a variety of interpretations of QM that embrace or explain these two features of quantum mechanics: Copenhagen, de Broglie-Bohm, Many Worlds, etc. Are you saying that all of these views are inconsistent/incoherent?

Not exactly. I am saying that standard quantum mechanics is indeed inconsistent (there are many versions of Copenhagen interpretation, so I cannot be sure this is true for all of its versions).

In de Broglie-Bohm interpretation, the projection postulate (PP) is just an approximation (see, e.g., Demystifier's post http://www.physicsforums.com/showpost.php?p=2167542&postcount=19 - he wrote dozens of articles on dBB interpretation. If you need, I think I'll be able to find other quotes confirming that). If it's an approximation, not a rigorous result, on the one hand, I cannot say that dBB is inconsistent, on the other hand, I don't need to waste my breath trying to prove that PP is, strictly speaking, incorrect.

As for Many Worlds, although some people state that the measurement problem has been solved in that interpretation, this statement is not generally recognized, as far as I understand. While there is no wave function collapse in that interpretation, "There is a serious difficulty with the concept of probability in the context of the MWI." (plato.stanford.edu/entries/qm-manyworlds ).

Gordon Watson

May15-12, 11:37 PM

Dear Gordon Watson,

Thank you for your reply.

You did clarify your position. If I understood you correctly, you believe that

1) your theory's experimental predictions fully coincide with those of standard quantum mechanics;

2) your theory is not self-contradictory and unites "projection" and "unitary evolution".

Let me tell you what. I wrote nothing or almost nothing original about the Bell theorem in my published articles. I just had to define my position, as the issue of the Bell theorem would have arisen anyway.

In particular, I wrote, following other authors, that:

1) Unitary evolution and quantum theory of measurements (e.g., the projection postulate) are mutually contradictory.

2) Both unitary evolution and the projection postulate are used to prove that the Bell inequalities can be violated in standard quantum mechanics (SQM).

Neither of these points is new or belongs to me. If your theory adopts both unitary evolution and the projection postulate of SQM, but not its contradiction, then you seem to have solved the 80-year-old measurement problem of quantum mechanics ( http://plato.stanford.edu/entries/qt-measurement/ and published work cited there, such as Albert's, or Bassi/Ghirardi's ). I congratulate you with this achievement, and suggest that you don't waste time on me (I was dead serious saying that I am of no consequence anyway) and publish your result (it does not matter if I see contradiction or not; what matters is that the measurement problem in quantum mechanics is generally recognized as such, no matter if I am dead or alive). Until properly published, your great result does not belong here, and, with all due respect, on the one hand, I don't believe your claims, on the other hand, I don't want to and don't have to check your derivation.

Let me assure you that I have no intention to offend you. Let me emphasize that I am not an expert in the Bell theorem. If I had more time to go into details, I would have started with reading (more) published articles of other people who defend local realism against the Bell theorem :-). Somehow they are able to publish their work, although, in general, local realism is not very popular:-).

Many thanks Andrey: nice to see there is much we can agree upon. BUT please: there is no way that you have given any offence; your engagement is most refreshing; I admire your spirit and your mathematical adventures!

And, Yes, expanding your neat summary; I believe (1), (2) and (3). That is:

(1) the theory's experimental predictions fully coincide with those of standard quantum mechanics;

(2) the theory is not self-contradictory;

(3) the theory unites "projection" and "unitary evolution".

I am certain re (1) and (2). However (3) uses terms that are not mine. So, being cautious, my contribution is to have the 'jump' (after Bell (2004: 118)) in the equations (not just in the talk), and to then show (equation (11)) that such "jumps" may be associated with smooth dynamical transitions. That is, by way of illustration only, in dynamical classical terms, think of spin, torque, precession.

As for formal publication in a recognised journal: I've given up on that and will now direct my efforts toward on-line publication via sites that give such as me a go. Where helpful people engage with you in the strongest possible terms; and there are no concerns re loss of face, etc.

PS: My first supporter, a Russian-born physicist in USA, told me: "You'll never be published; you have no sponsor; someone to get the credit for discovering you." This was the truth for 9 years. But under his terms, my "sponsor" from 1998 is a former student and close associate of Louis de Broglie! A nicer person you should never expect to meet; I trust there's one in your work somewhere.

With best regards, and thanks again,

Gordon