Local realism ruled out? (was: Photon entanglement and )

[akhmeteli]

Why don't you start a separate thread on the subject? Then we could discuss the evidence for your perspective.

Thank you for the suggestion. I should say this is the first thread I am starting since I joined physics forums four years ago.

So this thread has branched from another one -"Photon entanglement and fair sampling assumption". I noted there that, on the one hand, so far no experiments demonstrating violations of the Bell inequalities have been free from some significant loopholes, such as the detection loophole and the locality loophole, on the other hand, 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 both on the theoretical and on the experimental level. I was not taking sides with or against local realism, but pointed out that it has not been ruled out, however prevalent the opposite point of view can be.

My posts followed in part those of nightlight, and I did not offer any original research (otherwise the posts would have been inappropriate for this forum). These issues were also discussed in some prevous threads (https://www.physicsforums.com/showthread.php?t=245242 and https://www.physicsforums.com/showthread.php?t=230461 ).

My posts were criticized by knowledgeable opponents, but I'd say until recently their factual basis was not challenged. So I'll start with replying to DrChinese's posts

Apparently not as well known as you seem to think. I probably saw 10 papers last year on that subject (measurement problems), compared to perhaps 1000 on entanglement. So I would say the problem you identify is much less of a problem for the practicing physicist than you suggest.

I was not trying to say that the measurement problem is more or less important than, say, entanglement. All I was saying it is not some problem that arose yesterday, let alone was first raised by me. In this respect it is indeed "well-known" (Google gives 184000 links for the exact phrase "measurement problem in quantum mechanics", which is, by the way, pretty much the same as the result for "quantum entanglement" - 194000).

I'll try to reply to other DrC's remarks later.

 

[ZapperZ]

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.

 

[DrChinese]

My posts were criticized by knowledgeable opponents, but I'd say until recently their factual basis was not challenged. So I'll start with replying to DrChinese's posts

I was not trying to say that the measurement problem is more or less important than, say, entanglement. All I was saying it is not some problem that arose yesterday, let alone was first raised by me. In this respect it is indeed "well-known" (Google gives 184000 links for the exact phrase "measurement problem in quantum mechanics", which is, by the way, pretty much the same as the result for "quantum entanglement" - 194000).

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.

I would say that it is NOT generally accepted that QM is inconsistent. 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. 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.

 

[akhmeteli]

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.

Dear ZapperZ,

Thank you for the reference. I have read the paper. I am not sure you have read it, though. I have not found anything there ruling out local realism, and a host of quotes confirming that there have been no experimental results conclusively ruling out local realism. Maybe you could indicate some specific quote?

I won't give you all the quotes here. Let me just emphasize that EPR-type experiments typically cannot rule out local realism:

"The predictions of quantum mechanics and local hidden variable theories are shown to be incompatible in Bell’s work. This is not shown by the EPR paradox."

So the experiments reviewed in the Reid's work are, strictly speaking, not relevant, as they relate to EPR.

Let me emphasize that neither the above quote rules out local realism: Reid specifically italicizes the word "predictions". As for actual experiments, I gave the quotes by Shimony and Zeilinger, confirming that no experiments "ruling out" LR have been free from loopholes. As you want more quotes:

"a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing" (M. Genovese, Phys. Rep. 85, 166,180 (2005).)"

So there is a consensus among experts that existing experiments do not rule out local realism (and I suspect you know that). If you state the opposite (although I am almost sure you know better than that), then you are proposing your own personal theory. But you're a mentor, so that must be OK anyway:-)

 

[DrChinese]

"The predictions of quantum mechanics and local hidden variable theories are shown to be incompatible in Bell’s work. This is not shown by the EPR paradox."

So the experiments reviewed in the Reid's work are, strictly speaking, not relevant, as they relate to EPR.

Let me emphasize that neither the above quote rules out local realism: Reid specifically italicizes the word "predictions". As for actual experiments, I gave the quotes by Shimony and Zeilinger, confirming that no experiments "ruling out" LR have been free from loopholes. As you want more quotes:

"a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing" (M. Genovese, Phys. Rep. 85, 166,180 (2005).)"

So there is a consensus among experts that existing experiments do not rule out local realism (and I suspect you know that)...

You are misreading the quotes to your own position, there is NO SUCH CONSENSUS. 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.

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.

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.

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.

 

[akhmeteli]

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".

DrChinese, let us try to sort it out. First, let me emphasize that my statement on the contradiction between unitary evolution (UE) and the projection postulate (PP) is not new, furthermore, it was published in peer-reviewed journals. Therefore, it’s not some independent research and thus does not break the forum’s rules. To prove this, I don’t need to prove that QM is generally considered self-contradictory, I just need to give a reference: L.E. Ballentine, Found. Phys., vol. 20, p. 1329 (1990). Of course, that does not necessarily mean Ballentine is correct. However, you don’t seem to challenge the statement that UE and PP are mutually contradictory (if you do, please advise). My reasoning was that PP introduces irreversibility, whereas UE cannot produce irreversibility.

Now, I am afraid I have to disagree that “that is 100% irrelevant to Bell's Theorem”. I explained how it is relevant: in fact, the proof of the Bell’s theorem significantly uses both UE (as the spin projections are conserved) and PP (to calculate the correlations in QM and prove that QM can indeed violate the Bell inequalities. Thus, I am not sure “it is plain wrong to say "Bell is inconsistent because QM is inconsistent"”. I gave you my reasoning, but I haven’t seen yours so far.

I’ll try to reply to your other remarks later.

 

[ZapperZ]

This is utterly confusing.

First, you argue that Bell, etc. theorem does NOT rule out local realism.

Then you argue that even if they did, the absence of loophole-free experiments would not rule out local realism anyway!

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.

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].

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).

 

[zonde]

All of the EPR-type test papers have argued for that

Either this is plain wrong or I have misunderstood the statement (all papers argue that particular experiment rule out local realism).

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

 

[ZapperZ]

Either this is plain wrong or I have misunderstood the statement (all papers argue that particular experiment rule out local realism).

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

But that paper IS trying to argue for it based on the principle that it is trying to test or demonstrate. The inability to make a slam-dunk closure on local realism in that case is not based on the intrinsic property of the inequality, as what is trying to be argued in this thread, but rather the inability to close all the loopholes. Note also that there are various classes of local realism, one of which was definitely falsified via the most recent test of the Leggett's inequality.

The point here is that this thread appears to indicate that even IF all the loopholes are closed (and I will make MY prediction here that in the near future, say within 3 years, ALL the loopholes will be closed in one single experiment), the intrinsic nature of the theory will STILL not falsify local realism.

Zz.

 

[zonde]

The inability to make a slam-dunk closure on local realism in that case is not based on the intrinsic property of the inequality, as what is trying to be argued in this thread, but rather the inability to close all the loopholes.

Basically you are saying that the problem is not in theory but rater that we have not yet done what should be possible do based on what theory says, right?

 

[ZapperZ]

Basically you are saying that the problem is not in theory but rater that we have not yet done what should be possible do based on what theory says, right?

Maybe, but I'm already quite convinced. It takes such a tremendous amount of coincidence for (i) ALL (and I mean 100%) of the experiments to violate those inequalities and (ii) different experiments that closed different loopholes all come up with the same, identical conclusions. And these experiments are being done with greater and greater precisions with ridiculous standard deviation confidence.

Zz.

 

[DrChinese]

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

The Unfair Sampling Assumption is that discovery of an unfair sample can save local realism. Keep in mind even that is speculative. What if the unfair sample did not trend from local realism to QM? Perhaps even larger violations of Bell's Inequality would be seen instead. Heh.

Please note the words he uses: "however unlikely". That pretty much sums it up. A lot of things are unlikely but possible. The sun could burn out tomorrow. That does not mean that scientists are unsure whether the sun will shine tomorrow. So, let's use language fairly. Bell is accepted, and so are Bell test results.

 

[yoda jedi]

why the glue ?

LOCAL REALISM ruled out?

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

 

[Dmitry67]

none.
they are just inconsistent
local non-realistic theory or non-local realistic theory (or local realistic theory with backward causality - TI)

 

[DrChinese]

why the glue ?

LOCAL REALISM ruled out?

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

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.

 

[Count Iblis]

The http://arxiv.org/abs/0908.3408" won't be ruled out anytime soon.

 

[Matterwave]

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.

It could also be that induction fails. But if we do that, we would hafta get rid of almost all of science, so let's not.

 

[akhmeteli]

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]

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]

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]

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]

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

 

[MaxwellsDemon]

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?

 

[ZapperZ]

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:

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

and this:

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

and one more:

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

Zz.

 

[Maaneli]

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:

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

and this:

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

and one more:

https://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]

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]

"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]

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]

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]

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]

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]

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]

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]

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]

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]

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. 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]

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]

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]

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]

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]

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]

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]

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]

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]

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?

 

[akhmeteli]

That's funny! You should really re-read what you are writing first. 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 https://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]

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]

...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.



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]

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]

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

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.