Entanglement, causality and local realism

[karatemonkey]

I have been walking around with the notion that "quantum entanglement implies a sort
causal relationship due to the states having a shared history". I am now not so
sure that this is correct.
When I talk about entanglement, I use the argument that the preparation of the entangled state places information in the entangled state at the time of preparation and this "influences" future measurements. Where "this influences future measurements" in the last sentence means that the entangled states share a Hilbert space containing the eigenvectors of the joint Hamiltonian of the entangled objects. I'm not sure if I am way off course in my comprehension or if I have a problem with my language.

 

[mn4j]

In QM, an entangled system of particles is treated as a single entity. Observables calculated for the system CAN NOT and SHOULD NOT be attributed to parts of the system independently. Doing so leads us to silly paradoxes such as spokey action at a distance. Non-locality is inherent in the decision to consider distant particles as a single entity. There is nothing mysterious here.

Just like if the system is "The sun, and an observer with a series of colored goggles", an observable could be the color seen by the observer. This color can not be attributed to the observer only or to the sun only without leading to paradoxes. For example, if you say the color seen by the observer belongs to the sun, then the observer will be able to change the "color of the sun" superluminally by changing the goggles they are wearing.

 

[karatemonkey]

Thank you for your help. I'm still working on getting the concepts clear. I appreciate the help. I have found that the short answer is NO, entanglement doesn't imply causality. I was referred to a paper http://arxiv.org/abs/quant-ph/9904042 that goes to the question of causality and entanglement.

 

[canoe]

I have been walking around with the notion that "quantum entanglement implies a sort
causal relationship due to the states having a shared history". I am now not so
sure that this is correct.
When I talk about entanglement, I use the argument that the preparation of the entangled state places information in the entangled state at the time of preparation and this "influences" future measurements. Where "this influences future measurements" in the last sentence means that the entangled states share a Hilbert space containing the eigenvectors of the joint Hamiltonian of the entangled objects. I'm not sure if I am way off course in my comprehension or if I have a problem with my language.

Just to add a little to mn4j's comments...When you say "...that preparation of the entangled state places information in the entangled state at the time of preparation..." your argument sounds remarkably similar QM arguments involving "hidden variables". This was essentially what Einstein,etal had stated in the EPR paper, so you are in good company. However, Aspect's experimental violation of Bell's Inequality has pretty much ruled out any explanation of non-locality (spooky action at a distance) that might be attributed to hidden variables.

 

[mn4j]

However, Aspect's experimental violation of Bell's Inequality has pretty much ruled out any explanation of non-locality (spooky action at a distance) that might be attributed to hidden variables.

I strongly disagree with the above. Comparing Aspect's experiment to Bell's inequality is apples to rocks. The assumptions used by Bell in deriving his inequalities are so handicapped, that they amount to a straw man. Consequently, violation of said inequalities by Aspect type experiments, should not be surprising.

Note that it can be argued (and more reasonably so) that violation of Bell's inequalities by Aspect type experiments demonstrate the non-validity of Bell's inequality. Thus the issue of non-locality and causality does not even begin to come into the picture until Bell proponents can prove that the inequalities are accurate representations of all possible deterministic local and causal systems. This has not been done. However, there are numerous demonstrations of the errors of Bell's inequalities.

I will draw your attention to a recent one:
http://arxiv.org/abs/0904.4259
Where the author shows convincingly that Bell blundered right from his first equation by assuming the wrong topology for EPR experiment.

 

[canoe]

I strongly disagree with the above. Comparing Aspect's experiment to Bell's inequality is apples to rocks. The assumptions used by Bell in deriving his inequalities are so handicapped, that they amount to a straw man. Consequently, violation of said inequalities by Aspect type experiments, should not be surprising.

Note that it can be argued (and more reasonably so) that violation of Bell's inequalities by Aspect type experiments demonstrate the non-validity of Bell's inequality. Thus the issue of non-locality and causality does not even begin to come into the picture until Bell proponents can prove that the inequalities are accurate representations of all possible deterministic local and causal systems. This has not been done. However, there are numerous demonstrations of the errors of Bell's inequalities.

I will draw your attention to a recent one:
http://arxiv.org/abs/0904.4259
Where the author shows convincingly that Bell blundered right from his first equation by assuming the wrong topology for EPR experiment.

In deference to the author that originated the post...might we agree that the intention of the Aspect experiment was to test Bell's Theorem and that within the parameters of that test and at that time, it was accepted that Bell's Inequality was violated. Hence it is the preavailing belief (at this time) that Bell's Inequality was violated and that non-locality is a characteristic of the Quantum World...not to say that this is the final word on the subject.

I will review the archive in depth when I get a chance...I note that it seems to have been updated on nunmerous occasions due to challenges.

 

[karatemonkey]

I appreciate all the attention given to my question.
I am not trying to suggest there are hidden variables. That's where I run run into a problem with my language.
What I am grasping at is how to express Bell or CHSH violations. Causality in my mind has to figure somewhere in the framework of entanglement. Can you just make measurements on arbitrary systems and then decide after the fact to communicate your results and do the statistics and test for violation? That wouldn't make any sense. There has to be some prior agreement or knowledge or belief and a way to meaningfully correlate the measurements. This process of agreement prior to future measurements "feels" like the notion of causality. I understand that with or without any prior agreement the measurements inherently are unaffected. Admittedly, I am getting into epistemology here.

 

[mn4j]

Hence it is the preavailing belief (at this time) that Bell's Inequality was violated and that non-locality is a characteristic of the Quantum World...not to say that this is the final word on the subject.

That Bell's inequality was violated by experiment is the only fact here. The rest is conjecture, trying to answer the question "Why was Bell's inequality violated?". The issue I and many others have raised is the fact that the so-called "prevailing belief" is misguided and unjustified.

Think about the following silly example for a second:

1) Canoe comes up with a set of inequalities which we shall term "Canoe's inequality". It states that for all real numbers, n + n < 2n-1
2) Experiments are performed on real numbers showing that n + n = 2n
3) Canoe concludes that experimental violation of his inequalities prove that numbers are not real.

As you can see, the conclusion (3) neglects completely to discuss the validity of (1). It just so happens that in this case, the non-validity of (1) is obvious. However in the case of Bell's inequality, it is not so obvious to the untrained eye that Bell's inequalities are not valid. It is not surprising that nobody has EVER performed a macroscopic locally real experiment which proved the validity of Bell's inequalities.

What I am grasping at is how to express Bell or CHSH violations.

As I explained above, violations of the Bell of CHSH can only mean the inequalities do not correctly model the system being measured. The only way causality or locality come into the picture is IF and only IF, Bell or CHSH inequalities have been proven to EXHAUSTIVELY and ACCURATELY model all POSSIBLE locally causal systems. This has not been done. In almost half a century, since Bell's work, nobody has experimentally verified that Bell's inequalities are correct. So it is mind-boggling that Bell proponents purport to say how nature must be, based on an unverified mathematical theory such as Bell's or CHSH inequalities.

Causality in my mind has to figure somewhere in the framework of entanglement. Can you just make measurements on arbitrary systems and then decide after the fact to communicate your results and do the statistics and test for violation? That wouldn't make any sense. There has to be some prior agreement or knowledge or belief and a way to meaningfully correlate the measurements. This process of agreement prior to future measurements "feels" like the notion of causality. I understand that with or without any prior agreement the measurements inherently are unaffected. Admittedly, I am getting into epistemology here.

It seems to me you are trying hard to explain how causality comes into the picture. But all of this is irrelevant to the issue once you understand what I have explained above, because the idea that all possible hidden-variable theorems have been forbidden is just fantasy. In any case, you are right that is possible to have epistemological dependence (logical dependence) in a situation in which there is no ontological causal relationship.

For example consider two clocks located at opposite ends of the universe. They will be correlated by virtue of their being clocks, even if they run at different speeds. If time-tagged data of each clock were collected during the same time period and analysed together, a correlation will be observed even if it was impossible for information to travel from one to the other during the measurement.

 

[karatemonkey]

I appreciate all the responses. And I probably don't understand all of what is being said.

I am aware of the open question related to CHSH. My intuition also tells me that there are no hidden variables.
Your comment about clocks implies there has to be a notion of a clock and time and have these notions before make any observations. It also implies you know of the existence of both of these before hand and know to bring information together related to both of these. I don't see any hidden variables there. I do see a big belief system being brought to borne (sp?)

Maybe I don't really understand what causal means?

 

[Fredrik]

The assumptions used by Bell in deriving his inequalities are so handicapped, that they amount to a straw man.

That's an exaggeration at best, and crazy talk at worst. I'm still not sure where on that scale your comments are.

Note that it can be argued (and more reasonably so) that violation of Bell's inequalities by Aspect type experiments demonstrate the non-validity of Bell's inequality.

That doesn't make any sense.

Thus the issue of non-locality and causality does not even begin to come into the picture until Bell proponents can prove that the inequalities are accurate representations of all possible deterministic local and causal systems.

Wrong. Locality is still an issue, because when you derive the inequalities, you assume that the value of the quantity you're going to measure doesn't change when you rotate your measuring device.

I will draw your attention to a recent one:
http://arxiv.org/abs/0904.4259

Thanks for posting that. It looks interesting. Interesting enough to deserve its own thread actually. I think I'm going to start one.

Edit: I did, but it got deleted, and I got a formal warning for violating the forum rules.

Where the author shows convincingly that Bell blundered right from his first equation by assuming the wrong topology for EPR experiment.

That's not what he's saying. He's just saying that the set S⁰ appears (implicitly) in one step in Bell's argument, where e.g. S³ would have been an equally valid choice. (I still haven't understood why it is, but I'm working on it).

Think about the following silly example for a second:

1) Canoe comes up with a set of inequalities which we shall term "Canoe's inequality". It states that for all real numbers, n + n < 2n-1
2) Experiments are performed on real numbers showing that n + n = 2n
3) Canoe concludes that experimental violation of his inequalities prove that numbers are not real.

Come on, that's not even an argument. Do you think straw man arguments are valid when you use them?

It is not surprising that nobody has EVER performed a macroscopic locally real experiment which proved the validity of Bell's inequalities.

First of all, it isn't possible even in principle to "prove the validity of Bell's inequalities" by performing experiments. Second, I agree that it's not surprising, but for a very different reason. My reason is that QM predicts Bell inequality violations. If QM can kick CM's *** in every other way, we have no reason to expect the opposite when we do these experiments.

In almost half a century, since Bell's work, nobody has experimentally verified that Bell's inequalities are correct.

Again...not possible even in principle.

 

[karatemonkey]

Again thanks for all the replys.

Does anyone have any references on Quantum Mechanics, Probability and the notion of causality? (Preferably something outside the Copenhagen Interpretation.)

Does anyone know if the Quantum Bayesians have touched on the notion of causality yet?
I find their work really exciting.

I'm getting a very wild picture of the Universe the likes of which may knock my hair back. I haven't had that experience in a long time :) (Sorry, I had to mention that I really do get off on this stuff).

 

[ThomasT]

Bell's theorem assumes that any local hidden variable formulation of a GLOBAL experimental situation MUST be analyzable into its parts (expressable in factorable form) in order to be considered a local hidden variable formulation.

In effect, the data sets accumulating at A and B in the archetypal optical Bell test are to be treated as independent by any lhv formulation.

But of course this is, obviously, wrong. The data sets at A and B are not independent. Entanglement experiments are designed to produce dependent, spatially separated data sets -- the preparation of which entails some sort of common cause parameter/property which is the basis for the entanglement formulation (nonfactorable) and the data correlations.

So, what does an experimental violation of a Bell inequality tell us? Not much beyond the fact of the violation (though it can be used as a rough indicator of the presence of engtanglement). It doesn't mean that anything FTL is happening, or that nothing exists in the channels connecting emitters and detectors (the hidden variable thing). Obviously, something is going on between emission and detection -- it's just that nobody knows how to talk about it any more precisely than the standard QM formalism (which pretty much ignores the question of what's happening between emission and detection).

So, our intuitive notion of the meaning and cause of quantum entanglement is alive and well.

 

[Fredrik]

Does anyone have any references on Quantum Mechanics, Probability and the notion of causality? (Preferably something outside the Copenhagen Interpretation.)

The books by Ballentine and Isham both have good discussions about probability. Ballentine argues (convincingly in my opinion) that we shouldn't think of a state vector as representing an objective property of the system, and instead as a representation of an objective (statistical) property of an ensemble of identically prepared systems. (I prefer to say that a different way: QM doesn't describe the world. It's just an algorithm that tells us how to compute the probabilities of possible results of experiments, given the results of other experiments). Isham seems to agree with that, but he still makes an effort to always explain both how an "anti-realist" (like Ballentine) and a "realist" thinks. It's interesting to get both perspectives.

Does anyone know if the Quantum Bayesians have touched on the notion of causality yet?
I find their work really exciting.

I don't even know what that is.

I'm getting a very wild picture of the Universe the likes of which may knock my hair back. I haven't had that experience in a long time :) (Sorry, I had to mention that I really do get off on this stuff).

That's why we're here.

 

[canoe]

Again thanks for all the replys.

I'm getting a very wild picture of the Universe the likes of which may knock my hair back. I haven't had that experience in a long time :) (Sorry, I had to mention that I really do get off on this stuff).

A model of the Universe that could describe the causality of non-locality (among other things) would be very "wild" indeed. Some basic requirements would seem to have to be:

1) It would have to be Relativistic.
2) It would have to be Indeterministic.
3) It would have to be expanding at a rate that was ever-increasing.

Good luck with your search.

and...kudos to Fredrik for speaking up while I was absent. He is correct. We shouldn't be surprised by the violation of Bell's Inequality. It is what is predicted by QT..and QT is arguably the most successful theory ever (IMHO - not looking for a debate here).

 

[karatemonkey]

Fredrick thanks for the references. I'll check them out. What is causality I now is a bizarre question but, it's those simple ones that can be a real journey :)

The Bayesian are C.A. Fuchs, Carleton Caves, Asher Peres and others. The group is working on a new interpretation of QM. If you want to feel like a rebel follow their work :) (Admittedly, I'm a big fan of Fuchs' ideas, and the Bayesians. I've never been comfortable with the Copenhagen Interpretation, I don't know why but it always seemed inelegant Gasp! to me. It felt almost like the physics was so weird that there really wasn't language to express the ideas. That it seems to be beyond the reach of allot of people, even the smart ones

Thomas, thanks for the reply. And again, I do understand that CHSH hasn't been shown to work for all dimension Hilbert spaces. I agree with your views and I found your exposition very clear.
I do have an issue with talking about what happens during emission and detection. I don't think it makes sense to talk about what cannot be observed and observation counts as detection. To talk about what can't be observed and to go further an try to ascribe anything to such a situation really is more metaphysics than physics.

 

[karatemonkey]

Canoe thanks for the reply.

To connecting causality and non-locality, your reply about connecting the two being non-deterministic is intriguing. Why do you say that? I can see stochastic but not non-deterministic? Maybe this is semantics on my part?
In the end, I fear that even talking about causality and non-locality is very dangerous. I'm not thinking there is a direct connection between causality and entanglement like in hidden variables. I don't even think they communicate out side what the experimenters chose to communicate. And maybe that's all there is to it. Causality in this framework would be what is believed will happen or has happened. It's still constrained and not chaos. Then again I'm still wrestling with all this :)

I don't know why, other than physics has to fit experiment and be able to predict, you say the other things.

 

[canoe]

Canoe thanks for the reply.

To connecting causality and non-locality, your reply about connecting the two being non-deterministic is intriguing. Why do you say that? I can see stochastic but not non-deterministic? Maybe this is semantics on my part?
In the end, I fear that even talking about causality and non-locality is very dangerous. I'm not thinking there is a direct connection between causality and entanglement like in hidden variables. I don't even think they communicate out side what the experimenters chose to communicate. And maybe that's all there is to it. Causality in this framework would be what is believed will happen or has happened. It's still constrained and not chaos. Then again I'm still wrestling with all this :)

I don't know why, other than physics has to fit experiment and be able to predict, you say the other things.

I know I read somewhere (I can't remember quite where but I suspect i could locate it if need be) that Bohr went off at Heisenberg when the latter espoused the idea that the act of measuring caused uncertainty. In otherwords, there is an objective reality but we are just too clumsy to precisely measure it without causing a disturbance to the system. That would be stochastic.

However, conventional QT, whichever interpretation you favor, prescribes an underlying indeterminism to nature. Hence my very general comment that any successful model of the universe would seem to need to explain "Uncertainty".

As to the other things I mentioned:

A model of the universe that somehow would incorporate both indeterminism and relativity would, at some level, unify physics.

And as to my comments about the universe expanding at an ever-increasing rate, this has actually been observed and verified by astronomers in the last 10, or so, years. I think it would be a fair statement to say that astrophysicists are somewhat stumped by this discovery.

 

[karatemonkey]

Canoe, thanks for the reply. I don't know if I agree with the notion of an objective reality. I do believe in a consensus on reality.

 

[Max™]

I think one of the terms bandied around in this type of discussion is "counterfactual definite", which is a mouthful that basically says while observing something changes the outcome, there would have been a defined outcome if you had not observed it as well.

Essentially it can be summed up as realism, so the options are non-local but real (counterfactual definite), or local but without a definitely real state.

Either could fit the observations, but experiments, particularly Bell Inequality tests, show that the Universe does not fit BOTH of those parameters. One must be wrong, and it just so happens that modern quantum theory "makes more sense" under the non-local but real assumption, which also allows it to avoid hidden variable postulates.

 

[mn4j]

Again thanks for all the replys.

Does anyone have any references on Quantum Mechanics, Probability and the notion of causality? (Preferably something outside the Copenhagen Interpretation.)

Does anyone know if the Quantum Bayesians have touched on the notion of causality yet?
I find their work really exciting.

I'm getting a very wild picture of the Universe the likes of which may knock my hair back. I haven't had that experience in a long time :) (Sorry, I had to mention that I really do get off on this stuff).

Jaynes, E. T., 1990, `Probability in Quantum Theory,' in Complexity, Entropy, and the Physics of Information, W. H. Zurek (ed.), Addison-Wesley, Redwood City, CA, p. 381; http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf

 

[mn4j]

That's an exaggeration at best, and crazy talk at worst. I'm still not sure where on that scale your comments are.

I know, it is not fashionable to point out the problems with Bell's inequalities. If you can't tell already, I'm not fazed by however you may choose to characterize my comments.

Note that it can be argued (and more reasonably so) that violation of Bell's inequalities by Aspect type experiments demonstrate the non-validity of Bell's inequality.

That doesn't make any sense.

Then you must be talented at ignoring the obvious. Violation of Bell's inequality by real experiments means ONLY that Bell's inequality does not accurately model said experiments. What else did you think it meant?

[quote="mn4j]Thus the issue of non-locality and causality does not even begin to come into the picture until Bell proponents can prove that the inequalities are accurate representations of all possible deterministic local and causal systems.

Wrong. Locality is still an issue, because when you derive the inequalities, you assume that the value of the quantity you're going to measure doesn't change when you rotate your measuring device.[/quote]
Look, you need to study some basic logic.

Your argument goes like follows:
1) Bell's inequalities are valid for all local realist hidden variable theorems.
2) Violation of Bell's inequalities by experiments show that local realist hidden variable theorems are impossible.

I say claim (1) is unproven. If you think it has been proven, show me where. And until you can prove (1), discussion of (2) is a red-herring and completely irrelevant. On the contrary, there are published examples of local realist hidden variable theorems which violate the inequalities. You only need one such example to crush Bell's dreams. I will give you three:
* Clifford Algebra Valued Local Variables violate Bell's inequalities: Adv. Studies Theor. Phys., Vol. 1, 2007, no. 12, 603 - 610
* Event-by-Event Simulation of Einstein-Podolsky-Rosen-Bohm Experiments: Foundations of Physics, Vol. 38, Issue 4, p.433, 2008.
* Exclusion of time in the theorem of Bell. K. Hess et al 2002 Europhys. Lett. 57 775-781 ; "Breakdown of Bell's theorem for certain objective local parameter spaces", PNAS February 17, 2004 vol. 101 no. 7 1799-1805

That's not what he's saying. He's just saying that the set S⁰ appears (implicitly) in one step in Bell's argument, where e.g. S³ would have been an equally valid choice. (I still haven't understood why it is, but I'm working on it).

No! He is saying S⁰ is not valid. Read it when you get a chance.

Come on, that's not even an argument. Do you think straw man arguments are valid when you use them?

Interesting that you said that because I was showing how straw-man arguments are not valid. And Bell's theorem is a giant straw-man.

First of all, it isn't possible even in principle to "prove the validity of Bell's inequalities" by performing experiments.

If Bell's inequalities can not be proven, then we never get to claim (2) and Bell's theorem therefore fails.

My reason is that QM predicts Bell inequality violations.

Hehe, I like the way you phrased this one. I will say rather that Bell's inequalities FAIL to account for the predictions of QM, and the results of real experiments. Isn't it obvious that the only odd man out is Bell's inequalities. Everything else agrees with each other. (QM agrees with experiments and vice versa). Bell's inequalities are beginning to look like a trojan horse.

If QM can kick CM's *** in every other way, we have no reason to expect the opposite when we do these experiments.

Now I begin to understand where you are coming from. It's probably all about kicking CM's *** to you. Experimentalists can not only measure individual events in a double slit diffraction with electrons, they can also measure very accurately the time-order in which they arrive on the screen. I will only entertain such boasting and fanboyism when QM is able to predict those details which have been known for decades. For the moment though, the logic of the argument in favor of Bell's theorem is seriously lacking.

 

[DrChinese]

Look, you need to study some basic logic.

Your argument goes like follows:
1) Bell's inequalities are valid for all local realist hidden variable theorems.
2) Violation of Bell's inequalities by experiments show that local realist hidden variable theorems are impossible.

I say claim (1) is unproven. If you think it has been proven, show me where.

Bell designed his assumptions to match normal, reasonable definitions of locality and realism. That is why you are in the minority. Since Bell, virtually every physically possible test of entanglement has told us the exact same thing. Namely, that nature is not local realistic.

Like you, I have references for "disproofs" of Bell. Those would be dwarfed by the repeatable experiments supporting Bell, which are easily over a thousand at this point. And please note this: there is not a single experiment yielding a value for entangled correlations that is NOT in substantial agreement with the predictions of QM and in violation of the predictions of ANY proposed local realistic theory. That includes all of the references you provided.

 

[zonde]

Bell designed his assumptions to match normal, reasonable definitions of locality and realism. That is why you are in the minority. Since Bell, virtually every physically possible test of entanglement has told us the exact same thing. Namely, that nature is not local realistic.

virtually every physically possible test of entanglement - would be quite a stretch.
Haven't heard of entanglement experiments that had taken detection loophole into consideration.

 

[mn4j]

Bell designed his assumptions to match normal, reasonable definitions of locality and realism.

Prove it. Show me a single experiment with locally real macroscopic objects which validates this claim, failing which it is a mass of hot air. And this is the crucial point. Unless you can prove that Bell's assumptions are exhaustive and inclusive of all possible local hidden variable theorems, you can't even begin to attribute any validity to Bell's theorem.

That is why you are in the minority. Since Bell, virtually every physically possible test of entanglement has told us the exact same thing. Namely, that nature is not local realistic.

At one time, the majority also thought the Earth was flat. Like I thought, you have not even grasped the very basics of my argument you quoted above. Yes, experiments have validated the predictions of QM. So what? The issue before us is to show an experiment that has validated BELL's INEQUALITIES!

Like you, I have references for "disproofs" of Bell. Those would be dwarfed by the repeatable experiments supporting Bell, which are easily over a thousand at this point.

Hehe, you need to read my argument again and make sure you understand it before you purport to provide experiments (which all violated Bell's inequalities btw), as proofs of Bell's inequalities.

And please note this: there is not a single experiment yielding a value for entangled correlations that is NOT in substantial agreement with the predictions of QM and in violation of the predictions of ANY proposed local realistic theory. That includes all of the references you provided.

1) The agreement between QM and experiment has NEVER been an issue, so stop diverting attention to it as if it ever was.
2) All three references I provided show that local realist theories which agree with QM and experiments and VIOLATE Bell's inequalities are possible. Don't make claims about articles you have not read. If you want to discuss them in a non-hand-waving manner, let's do so.
3) Note this: There is not a single experiment confirming the validity of Bell's inequalities.

 

[Cthugha]

Haven't heard of entanglement experiments that had taken detection loophole into consideration.

Rowe et al, "Experimental violation of a Bell's inequality with efficient detection", Nature 409, 791-794 (15 February 2001)

 

[DrChinese]

virtually every physically possible test of entanglement - would be quite a stretch.
Haven't heard of entanglement experiments that had taken detection loophole into consideration.

Probably 10+ variations of that, depending on how you count it. In fact, the detection loophole was closed a number of years back. Here is one:

Entanglement
and Quantum Non-Locality[/url]

Now keep in mind this is not a Bell test. This is a test of GHZ, and GHZ strictly requires only a single sample to rule out local realism (of course they do a lot more :). Keep in mind that tests/theorems of GHZ, Hardy, Leggett, Kochen Specker also rule out local realism. Bell does not exist in a vacuum.

But there are Bell tests that also rule out the detection loophole too. The reason a lot of folks don't think it has been ruled out is because ALL loopholes were not closed simultaneously. They don't really need to be, but nonetheless we may be on the verge of a "loophole-free" test in the near future. I doubt that will satify folks like mn4j, since he/she rejects all contrary evidence.

 

[DrChinese]

Prove it. Show me a single experiment with locally real macroscopic objects which validates this claim, failing which it is a mass of hot air. And this is the crucial point. Unless you can prove that Bell's assumptions are exhaustive and inclusive of all possible local hidden variable theorems, you can't even begin to attribute any validity to Bell's theorem.

Well, you will be out there on your own as you are already. Local realists have been trying to exploit perceived weaknesses in Bell for years. To date, zero candidate local realistic theories remain standing. I would just love to see one candidate that answers this simple question: what is the true correlation rate for an entangled photon pair at 60 degrees? QM says it is .25 (i.e. cos^2 theta). LR requires it to be at least .333. Please, let's continue this discussion when you can find a theory that answers this. (Keep in mind that an LR theory must be able to provide the same predictions as QM across the board, not just in one area, and this is why there are NO remaining candidate theories... just vague concepts.)

For everyone else, you should be able to see why there won't be any such candidate theories.

 

[Fredrik]

Violation of Bell's inequality by real experiments means ONLY that Bell's inequality does not accurately model said experiments. What else did you think it meant?

You claimed that Bell inequalities aren't "valid". That could mean a lot of things. What you're saying now is probably the last thing I would have guessed, because it's something that every Bell "fanboy" would agree with: Bell inequalities don't represent a property of reality.

They do however represent a property of every member of some class of hidden variable theories. I don't know if that class includes all objective local theories, but has anyone ever said that it does? I mean, has anyone that matters ever said it without taking the assumptions that go into the derivation as the definition of the term "objective local theory"?

Your argument goes like follows:
1) Bell's inequalities are valid for all local realist hidden variable theorems.
2) Violation of Bell's inequalities by experiments show that local realist hidden variable theorems are impossible.
...
And until you can prove (1), discussion of (2) is a red-herring and completely irrelevant.

Don't tell me what my argument is. I would say that 1 holds given a definition of "objective local theory" (or whatever you'd like to call it) that most physicists agree is appropriate. You could argue that another definition that includes a larger class of theories is actually more appropriate, but even if that's the case, it wouldn't make any of this "a red-herring and completely irrelevant". We would just have to change 2 to say that we have ruled out a large class of objective local theories.

What exactly is it that you would like to change about the definition of "objective local theory", or equivalently, the assumptions that go into derivations of Bell inequalities? Here's an example of a derivation: 215,216. Do you see anything wrong with it?

No! He is saying S⁰ is not valid. Read it when you get a chance.

You're right about this. He does say that S⁰ is the wrong choice. I spent another hour or so staring at the first two pages today, and I have to say that it's amazing how badly written it is. If I had been his reviewer I would demand that he makes a clear argument before I even consider recommending it for publication. If it's true that S⁰ should be replaced by S³ in any derivation of Bell's theorem, and if Christian knows why, then it can't be difficult for him to prove it to us. And yet he fails to make any sense.

Interesting that you said that because I was showing how straw-man arguments are not valid.

No you made an attempt to show that, but it failed because your argument was a straw man.

And Bell's theorem is a giant straw-man.

That's just a crackpot claim that you have been unable to support.

Hehe, I like the way you phrased this one. I will say rather that Bell's inequalities FAIL to account for the predictions of QM, and the results of real experiments. Isn't it obvious that the only odd man out is Bell's inequalities. Everything else agrees with each other. (QM agrees with experiments and vice versa).

Yes, that's the point! And when the Bell inequalities fall, they take a large class of hidden variable theories with them.

 

[Fredrik]

Prove it. Show me a single experiment with locally real macroscopic objects which validates this claim
...
The issue before us is to show an experiment that has validated BELL's INEQUALITIES!
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3) Note this: There is not a single experiment confirming the validity of Bell's inequalities.

You keep coming back to this. I have already tried to tell you that it isn't possible, even in principle, to prove Bell inequalities by experiment. It wouldn't be possible even if nature did respect Bell inequalities, and it's even more silly to demand proof by experiment in a universe such as ours, where Bell inequalities are often violated.

 

[mn4j]

To date, zero candidate local realistic theories remain standing.

Again, you are handwaving here and avoiding to address the specific references I have provided.

I would just love to see one candidate that answers this simple question: what is the true correlation rate for an entangled photon pair at 60 degrees? QM says it is .25 (i.e. cos^2 theta). LR requires it to be at least .333.

Again you did not bother to look at the articles I quoted. Those hidden variable theorems reproduce the QM correlations exactly.

(Keep in mind that an LR theory must be able to provide the same predictions as QM across the board, not just in one area, and this is why there are NO remaining candidate theories... just vague concepts.)

A hidden variable theorem being just an interpretation of QM, does not independently have to reproduce all the predictions of QM. Again you are trying to divert the issue to one of LR vs QM. It has never been and never will be. Besides, all that is required of a LR theorem is that it provide a local realistic explanation of Aspect-type experiments. That is a sufficient condition, to falsify Bell's theorem. It has been done, again I point you to the articles I quoted, ie if you are ready to take your head out of the sand.

 

[mn4j]

Bell inequalities don't represent a property of reality.
They do however represent a property of every member of some class of hidden variable theories. I don't know if that class includes all objective local theories, but has anyone ever said that it does?

You need to look up Bell's theorem and what it says. If what you say is what Bell and his proponents believe, they should have saved everyone a lot of confusion by being explicit. Why would they make an extraordinary claim that "No local hidden variable theorem can reproduce the results of QM" , if they only meant to say some hidden variable theorems can not reproduce the results of QM?
It is interesting that you think there are no objective local theories for even classical objects even before QM was developed. Do you believe Bernoulli's Urn is non-local as well? Do you believe Bell's inequalities do not apply to any real system, quantum or classical? If you do, as your statement above implies, then I would be interested to hear on what basis, you compare the results of Aspect-type experiments to Bell's inequalities.

I mean, has anyone that matters ever said it without taking the assumptions that go into the derivation as the definition of the term "objective local theory"?

Take a look at Bell's theorem, it makes a categorical claim about all objective local theories. And every time anyone claims that Objective local theories are impossible, they are making the same claim. I'm sure if I had enough time, I could find one of your statements implying the same.

We would just have to change 2 to say that we have ruled out a large class of objective local theories.

Even that does not rescue Bell's theorem. For Bell's theorem to be valid, you have to rule out EVERY objective local hidden variable theory.

What exactly is it that you would like to change about the definition of "objective local theory", or equivalently, the assumptions that go into derivations of Bell inequalities?

I want you to admit that Bell's assumptions are not exhaustive of all objective local theories. You just admitted earlier that Bell's inequality does not apply to ALL local hidden variable theories, and yet you still believe Bell's assumptions are equivalent to the definition of objective local theory? You can't have it both ways. As you admitted above, Bell's inequalities do not apply to all possible local hidden variable theories. Therefore Bell's theorem, which is based on those inequalities, can not claim to make proclamations about what ALL objective local theories can or can not do.

Yes, that's the point! And when the Bell inequalities fall, they take a large class of hidden variable theories with them.

1) Yes, when Bell's inequalities fail, they take the class of hidden variables implied in Bell's assumptions with them. But by your own admission, those assumptions do not even apply to classical systems which are demonstrably local, so to characterize the class as large, is specious at best.
2) The viability of Bell's Theorem hangs on the increasingly hopeless wish that Bell's inequalities apply to ALL objective local theories.
3) Therefore, Bell's theorem is a fallacious argument.

 

[DrChinese]

Again, you are handwaving here and avoiding to address the specific references I have provided.

I can give you another 10 references to local realist theories, I am familiar with everything you mention. How about mentioning Matzkin, Christian, Nieuwenhuizen, Broda, Laudisa, etc. (Maybe you are one of these.) None of these are theories, sadly, they are ideas for theories at best and have mostly been directly addressed or otherwise have obvious glaring holes and are not worthy of specific critique. Hey, there is a Flat Earth Society and guess what? I don't bother to tell them the Earth is as flat as any other sphere.

So again, I ask the answer to a simple question: what is the true correlation rate for entangled photons at 60 degrees? Is it .25 or .333? A true theory - like QM - can answer this simple question (answer, experimentally verified, .25). (Oops, entangled particles don't exist in local realist theories... only pairs that share a common past...)

 

[DrChinese]

2) The viability of Bell's Theorem hangs on the increasingly hopeless wish that Bell's inequalities apply to ALL objective local theories.

I am disappointed to hear you say this, as a number of non-Bell theories and associated experiments come to exactly the same conclusion as Bell. Those being GHZ, Hardy, etc. Come on, every modern theory and related experiment says exactly the same thing. Realism is not tenable, at least when coupled with locality.

 

[Fredrik]

Why would they make an extraordinary claim that "No local hidden variable theorem can reproduce the results of QM" , if they only meant to say some hidden variable theorems can not reproduce the results of QM?
...
Take a look at Bell's theorem, it makes a categorical claim about all objective local theories.
...
etc.

I'm guessing that they were assuming that their readers would understand that "local hidden variable theory" is a phrase that needs to be defined, and that the theorem is valid for the class of theories covered by the definition.

Don't you see that a term like "objective local theory" is meaningless without a definition? If you think the people who defined the term are talking about theories that aren't covered by their definition, then that's a problem on your end, not theirs.

It is interesting that you think there are no objective local theories for even classical objects even before QM was developed.
...
Do you believe Bell's inequalities do not apply to any real system, quantum or classical?
...
But by your own admission, those assumptions do not even apply to classical systems which are demonstrably local

I have no idea how you could get that impression. If you understand a derivation of a Bell inequality, such as the one in Isham's book, it's completely obvious that the inequality holds for simple classical systems.

 

[RUTA]

Thanks for posting that. It looks interesting. Interesting enough to deserve its own thread actually. I think I'm going to start one.

Edit: I did, but it got deleted, and I got a formal warning for violating the forum rules.

That's not what he's saying. He's just saying that the set S⁰ appears (implicitly) in one step in Bell's argument, where e.g. S³ would have been an equally valid choice. (I still haven't understood why it is, but I'm working on it).

I read your post starting that thread, then I read the arXiv paper. I logged in this morning excited to read contributions so I was, of course, frustrated :-)

So, we're not allowed to discuss the paper here? Please email what you find: stuckeym@etown.edu

Thanks!