A Bell Theorem with no locality assumption?

[DrChinese]

I am opening a new thread to continue discussion of some interesting ideas around EPR and Bell. Specifically, this is about the idea of realism, and whether it is tenable in light of Bell and other HV no-go theorems. Note: I usually use Hidden Variables (HV) and Realism interchangeably although some people see these as quite different. I also tend to use Realism as being an extension of EPR's "elements of reality" as a starting point for most discussions. After all, if a physical measurement can be predicted with certainty without disturbing what is measured... well, I would call that as real as it gets.

charlylebeaugossehad thrown out a few ideas in another thread - especially around some papers by Charles Tresser. So I suggest we discuss around these:

http://arxiv.org/abs/quant-ph/0608008
We prove here a version of Bell Theorem that does not assume locality. As a consequence classical realism, and not locality, is the common source of the violation by nature of all Bell Inequalities.

http://arxiv.org/abs/quant-ph/0503006
In Bohm's version of the EPR gedanken experiment, the spin of the second particle along any vector is minus the spin of the other particle along the same vector. It seems that either the choice of vector along which one projects the spin of the first particle influences at superluminal speed the state of the second particle, or naive realism holds true i.e., the projections of the spin of any EPR particle along all the vectors are determined before any measurement occurs). Naive realism is negated by Bell's theory that originated and is still most often presented as related to non-locality, a relation whose necessity has recently been proven to be false. I advocate here that the solution of the apparent paradox lies in the fact that the spin of the second particle is determined along any vector, but not along all vectors. Such an any-all distinction was already present in quantum mechanics, for instance in the fact that the spin can be measured along any vector but not at once along all vectors, as a result of the Uncertainty Principle. The time symmetry of the any-all distinction defended here is in fact reminiscent of (and I claim, due to) the time symmetry of the Uncertainty Principle described by Einstein, Tolman, and Podolsky in 1931, in a paper entitled ``Knowledge of Past and Future in Quantum Mechanics" that is enough to negate naive realism and to hint at the any-all distinction. A simple classical model is next built, which captures aspects of the any-all distinction: the goal is of course not to have a classical exact model, but to provide a caricature that might help some people.

http://arxiv.org/abs/quant-ph/0501030
We prove here a version of Bell's Theorem that is simpler than any previous one. The contradiction of Bell's inequality with Quantum Mechanics in the new version is not cured by non-locality so that this version allows one to single out classical realism, and not locality, as the common source of all false inequalities of Bell's type.

[questions,yes]

Well ok, i'll start.

I'm a layman so the math is well over my head, a bit like the moon, unless I'm not looking at it, in which case it doesn't exist, until i look at it, and then it does, and did when i wasn't looking at it. Didn't it?

[charlylebeaugosse]

I am opening a new thread to continue discussion of some interesting ideas around EPR and Bell. Specifically, this is about the idea of realism, and whether it is tenable in light of Bell and other HV no-go theorems. Note: I usually use Hidden Variables (HV) and Realism interchangeably although some people see these as quite different. I also tend to use Realism as being an extension of EPR's "elements of reality" as a starting point for most discussions. After all, if a physical measurement can be predicted with certainty without disturbing what is measured... well, I would call that as real as it gets.

charlylebeaugossehad thrown out a few ideas in another thread - especially around some papers by Charles Tresser. So I suggest we discuss around these:

http://arxiv.org/abs/quant-ph/0608008
We prove here a version of Bell Theorem that does not assume locality. As a consequence classical realism, and not locality, is the common source of the violation by nature of all Bell Inequalities.

http://arxiv.org/abs/quant-ph/0503006
In Bohm's version of the EPR gedanken experiment, the spin of the second particle along any vector is minus the spin of the other particle along the same vector. It seems that either the choice of vector along which one projects the spin of the first particle influences at superluminal speed the state of the second particle, or naive realism holds true i.e., the projections of the spin of any EPR particle along all the vectors are determined before any measurement occurs). Naive realism is negated by Bell's theory that originated and is still most often presented as related to non-locality, a relation whose necessity has recently been proven to be false. I advocate here that the solution of the apparent paradox lies in the fact that the spin of the second particle is determined along any vector, but not along all vectors. Such an any-all distinction was already present in quantum mechanics, for instance in the fact that the spin can be measured along any vector but not at once along all vectors, as a result of the Uncertainty Principle. The time symmetry of the any-all distinction defended here is in fact reminiscent of (and I claim, due to) the time symmetry of the Uncertainty Principle described by Einstein, Tolman, and Podolsky in 1931, in a paper entitled ``Knowledge of Past and Future in Quantum Mechanics" that is enough to negate naive realism and to hint at the any-all distinction. A simple classical model is next built, which captures aspects of the any-all distinction: the goal is of course not to have a classical exact model, but to provide a caricature that might help some people.

http://arxiv.org/abs/quant-ph/0501030
We prove here a version of Bell's Theorem that is simpler than any previous one. The contradiction of Bell's inequality with Quantum Mechanics in the new version is not cured by non-locality so that this version allows one to single out classical realism, and not locality, as the common source of all false inequalities of Bell's type.

Those preprints where not published not rewritten to be more final so far, but someone posted the link to the paper that appeared on European J. of Phys. in the thread on action at a distance and EPR. One of the papers cited by DrC (thanks again for opening the thread)
relates more to the issue of ANY is not ALL in QM in the sense that in Classical Mechanics, ANY observation doable means ALL observation doable (at once) while this is not true in QM: in forward time because of the UP, in backward time, because of the time reversed UP of Einstein, Tolman, and Rosen (ETP). ETP also tels us that a single observale can hardly have a definite value before measurement, the first PROOF of non-realism, but his does not apply to EPR particles where two conjugate observable can pre-exist measurement if one measurement is made on each of the 2 particles. Then one had ANY but not ALL, while for generic particle, one does not even have any observable. Notice than the EPR case, the values are retrodictive (before the measurement, something that was accepted by Bohr and Heisenberg, at least until ETP showed that problematic). In some sense, the ANY is not ALL issue is a Bell-EPR type of issue but does not belong PRECISELY to this thread (but who cares?).

I have uploaded (after all, it's easy) two more recent things that I have about the title of the thread: a copy of the paper and a preprint that makes part of the paper more precise (in fact the Bell theorem part as the GHZ part remains untouched). People interested in this thread might need some time to go through these two papers (or at least the preprint as the paper has been out for a few weeks) before expressing opinions or asking questions.

This being said it seems to me that one essential ingredient in the "Bell Theory with no locality assumption" story is the hypothesis: Effect After Cause Principle. It states that for any Lorentz observer no effect can be observed and then be changed by a later caused. Yet the effect may happen after the cause (if one assumes Non-Locality to hold true, for instance), or one can ALSO assume Locality in which case of course the COMBINED hypothesis is not much different from locality. Once the EACP is recognized as not being nor implying locality, and in fact being weaker an hypothesis than locality, it remains of course to see if the proof is fine. As this is not math but physics, the issue does not reduce to a formal correctness issue.
CleBG

[charlylebeaugosse]

Well ok, i'll start.

I'm a layman so the math is well over my head, a bit like the moon, unless I'm not looking at it, in which case it doesn't exist, until i look at it, and then it does, and did when i wasn't looking at it. Didn't it?

The hardest math in there is trigonometry, a bit of proba, and simple considerations about convergence issues.Where is the block. As for the moon, that is another issue: should we really start on that here?

[ThomasT]

Hi DrC! Nice topic. Thanks, and to CleBG, for the links.

[nikman]

One so yearns for dots to be connected. For instance: how does Tresser relate to Leggett-Garg (specifically in re: the Gisin group and Zeilinger group experiments?). CleBG's remark about the Effect After Cause Principle feels so much like the Suarez (and Gisin) Before-Before stuff ...

[Dmitry67]

is the hypothesis: Effect After Cause Principle. It states that for any Lorentz observer no effect can be observed and then be changed by a later caused.

Could you provide a clear definition of that principle?
Lets forget about the definition of Cause and Effect: they both are Events, and the definition of Event in QM is interpretation-dependent. But this is irrelevant now. Just assume that Cause and Effect are 2 events in the BlockTime.

How you define the difference between Cause and Effect? For me, Effect is in the lightcone of Cause, nothing more. (In CTL it could be laso vice versa). But then (in flat spacetime) Effect is always after the Cause - just by definition!

Finally, the part about "then be changed..." denies the blocktime postulating (even imaginary) possibility of a "butterfly effect".

I would say, this "principle" is lyrics, not physics.

[Demystifier]

I would say, this "principle" is lyrics, not physics.
"In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite."
Paul Dirac

[DevilsAvocado]

Great quote Demystifier! And funny! :smile:

[DevilsAvocado]

I would say, this "principle" is lyrics, not physics.

I would say this "principle" is lyrics in the microscopic world, and physics in macroscopic world. Ever heard of the thermodynamic arrow of time (http://en.wikipedia.org/wiki/Arrow_of_time#Arrows)...?

[Demystifier]

Great quote Demystifier! And funny! :smile:
Thanks! If you want more, visit my blog. :smile:

[DevilsAvocado]

Thanks! If you want more, visit my blog. :smile:

Bin there, done that! :wink:

(And all your quotes are great!)

[charlylebeaugosse]

Could you provide a clear definition of that principle?
Lets forget about the definition of Cause and Effect: they both are Events, and the definition of Event in QM is interpretation-dependent. But this is irrelevant now. Just assume that Cause and Effect are 2 events in the BlockTime.

How you define the difference between Cause and Effect? For me, Effect is in the lightcone of Cause, nothing more. (In CTL it could be laso vice versa). But then (in flat spacetime) Effect is always after the Cause - just by definition!

Finally, the part about "then be changed..." denies the blocktime postulating (even imaginary) possibility of a "butterfly effect".

I would say, this "principle" is lyrics, not physics.

I'll answer to my best, as a physicist as I have a fair voice but lyrism is not my thing. Others may have better words to explain, and the question is nice but too bad to have it in an aggressive tone. While Chaos is really my main forte since the mid 1970's, I must say that I need explanation on what the butterfly effect is doing here. I'll answer to anon-aggressive version of the question/argument till the word "Finally".


I am not a non-localist, but the direct effect of non-locality is that effects (values of spin projection observed by Alice, or inferred as existing at Alice's location as a consequence of the chosen realism hypothesis (and I am not a realism believer either) ) depend on a cause
(the axis used by Bob to make his measurement) that is spatially remote. So by you position you refuse non-locality, and the paper also tries to recuse non-locality, but without starting from the opinion that locality is right.

So one starts from 2 hypothesis:
Effect After Cause Principle (formulated so that it is compatible with non-locality) and realism to get a Bell inequality incompatible with QM.The oddness that you see in the EACP are not new when compared to usual non-locality sort of consideration. Most people in awe of Bell Theorem tell that the way violation is avoided by Nature is that Locality is false. The goal of the mentioned paper (in the title of this thread) is not to tell people convinced of locality that only locality makes sense among locality and non-locality. The goal is to prove a Bell Theorem without using locality so that non-locality cannot save the day. Now I do believe that it is microscopic realism that is the issue among the hypotheses of Bell's inequality (and in all form of Bell's Theorem, with or without inequalities as GHZ). More particularly, I believe that microphysics does not allow two EPR-Bohm particles to have a total of at least 3 projections of the spin defined at once (or two projections on each side for a total of four direction in the CHSH form of Boole-Bell inequality (for the role of name of Boole, see the work of Pitowsky, for the stat theory behind that, see the papers of Fine in J. Math Phys and the paper in PRL at about the same time). With less than 3 projections making sense at once for the two EPR-B particles together, be it 0, one, or two, there is no Bell inequality: more precisely, there is no Boole type inequality incompatible with the correlations that are compatible with quantum mechanics.

But it was a question worse rising: hope the answer satisfied most people troubled by the question. It has been known for a long time (relatively) that non-locality violates the intuition of time we learned from Special Relativity. Gisin considers that since speed of light as a limit is new to physics, it i not too much a big deal if we have to abandon that. The worse part is that some time ago, he still had the support of very bizarre sects (perhaps still does). Physics is hill: the trauma brought to that science by people who like Bell (but also other masters) defended non-locality of QM, and realism in the case of Bell is very troublesome: for me it is as if Algebra would be under the control who tell you that equation must have both sides multiplied by zero to hold true, or some other non-sense.
The great Antony Leggett wrote, more than once, that among physicists, it is essentially consensual that out of the two hypotheses of Bell's Theorem, the one that is false is realism: statitics by people around Marland Scully tell us just the contrary. I would be troubled by one QM supporting classical microscopic realism in a major US university (or UK, or French, or German, or Italian, or Japanese (any country with some tradition of geat physics where no criminals came to power like in Argentina). Science is at risk: as it goes, this beautiful invention going back to the Greeks will disapear very soon: are physicists (who would be recognized as such by Einstein, Feynman, Bohr, etc...) an endangered specie??
What is clear to me is that with the level of lack of professionalism in citations and quotation, another discipline, in particular one using less science, would already have fully disappeared.

Sad, no? But do I have a pessimistic view?
Or am I about right?
And then what should we do?
CleBG

PS: Ask for specific uploads, and I'll provide what I can (i.e., what I have in soft form or what I know where to find in the www, but others have provided competent help in the threads that I have seen: uploading is a bit too hard for me to do it right away).

[charlylebeaugosse]

One so yearns for dots to be connected. For instance: how does Tresser relate to Leggett-Garg (specifically in re: the Gisin group and Zeilinger group experiments?). CleBG's remark about the Effect After Cause Principle feels so much like the Suarez (and Gisin) Before-Before stuff ...
Can you make precise what should be connected to what:papers and indications on what to look at said papers. For me Leggett-Garg is about realism consequences at the macroscopic level. Several people have participated to that debate following them. As for the massive production of the Switz and Austrian groups, they are so massive that pointers are unavoidable. The experiments are most often great, the theory often to par but Gisin has written many papers that are causes of confusion and the position of Zeilinger on realism and locality is hard for me to read so that I'd love to have pointers. I remember having seen things I id not like more that Gisin's but I was still much more new to the field. And when you say "Tresser relates", do you mean the person, or a particular point of the positions taken in the papers. Anyway, any mean to see better in the massive production that you have mentioned would be great, as well as understanding all of Leggett's contributions (alone or accompanied) to the subject.

Someone else has raised the issue of comparing the EACP with things of Gisin but the allusion is both lacking precision and lacking a precise reference (or several as appropriate).

[skippy1729]

I read the paper twice. I did not see any problems with it; which does not mean it is without problems!
What bothers me is that 1. It seems to rule out dBB (which most HV nogo theorems do not). 2. It is four years old and is not a BIG DEAL. What am I missing?

Skippy

[charlylebeaugosse]

I read the paper twice. I did not see any problems with it; which does not mean it is without problems!
What bothers me is that 1. It seems to rule out dBB (which most HV nogo theorems do not). 2. It is four years old and is not a BIG DEAL. What am I missing?

Skippy
Not sure of what dBB means. In such precise matters, guessing would be inappropriate.
The paper has just been published and went mostly unnoticed for a long time. What I got from the analysis of a very serious physicist whom I would not name here without his consent, is that in a first approximation, each time the paper was refused, any argument against it for one referee was mostly the main argument in favor for another referee who would also have his/her critics similarly matched. Frankly, the first version were very unclear to my opinion and even the version that got published still needed the corrections in the version for Pierre Coullet's 60th birthday where the EACP's compatibility with non-locality (and with locality, but this is not the issue, except to make clear that the EACP is neither of Locality ad Non-Locality) was more explicitly used and the effect of the other side on the pair is more carefully analyzed.

Now, if the paper is as right as you seem to consider, AND if enough people know what is in there and agree with you appreciation, then the impact should be visible as this paper
seriously support the viewpoint that it is classical realism and not locality that is the false hypothesis in Bell's theory, and that the old masters where right to support non existence of microscopic realism, on which the opinion of Einstein seems to have been dramatically miss-represented (in order to let people like Gisin and other present themselves as better than Einstein) if we believe the historical work of Jammer and Fine. Miss quotations and miss refereeing is rampant in this field as if it would be closer to politics than to science.
One useful thing that Gisin did (beside some nice experiments) was to lacye when it became kosher to write about Bell'sTheory and non-locality: a paer of Ekert that is patently false (as I explain in a pre-print that cries for a co-author to help me). A joint friend has proposed to Ekert (or so he told me) to write a paper with me to explain the mistake he did when invoking Bell theorem in his method for QM-based cryptography. I never heard back from Ekert who wrote the paper that made Bell's theory Kosher: his paper is in fact more cited than the original paper on Q-cryptography (Bennett-Brassard), but Bennett, with Brassard and with and without Mermin, made serious crimes of lack of scholarly acceptable
attitude.

Well to be short(er) at last, in a subject dominated by supporters of Bell (who often ignore that they defend a strong supporter of realism) a paper posted for 4 years on arXive and always refused has little chance of making an impact. Let's see if a published paper, and hopefully more to go, change the status of all that so the we can come back to real issues and advance physics in what is probably its main sub-discipline, i.e., QM and more precisely micro-physics in the non-relativistic and then in the relativistic regimes, with then progress in all issues that could benefit from a better understanding of the basics.

[DevilsAvocado]

Not sure of what dBB means.

dBB = de Broglie–Bohm theory (http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)

(also called the pilot-wave theory, Bohmian mechanics, and the causal interpretation)

[nikman]

Can you make precise what should be connected to what:papers and indications on what to look at said papers. For me Leggett-Garg is about realism consequences at the macroscopic level. Several people have participated to that debate following them. As for the massive production of the Switz and Austrian groups, they are so massive that pointers are unavoidable. The experiments are most often great, the theory often to par but Gisin has written many papers that are causes of confusion and the position of Zeilinger on realism and locality is hard for me to read so that I'd love to have pointers. I remember having seen things I id not like more that Gisin's but I was still much more new to the field. And when you say "Tresser relates", do you mean the person, or a particular point of the positions taken in the papers. Anyway, any mean to see better in the massive production that you have mentioned would be great, as well as understanding all of Leggett's contributions (alone or accompanied) to the subject.

Someone else has raised the issue of comparing the EACP with things of Gisin but the allusion is both lacking precision and lacking a precise reference (or several as appropriate).

The most illuminating Zeilinger paper IMO is one he did back in 2005 with Brukner. "Quantum Physics as a Science of Information". SpringerLink sits on it unless you want to give them money. But fortunately the gods have smiled it's available in toto via Google books:

http://tinyurl.com/2aoydkx

Leggett-Garg incorporates a nonlocality assumption and tests for "realism" (counterfactual definiteness, whatever). Inferentially or by default that's what Tresser also does. Or not? Anyway, how are they different?

Gisin indeed has become awfully hard to follow. He's hiking deep into the woods. As I read him (and this interpretation of mine may very well be of absolutely no value whatsoever) it's all somehow coming back to the measurement problem. Hopefully what he's up to will become clear in time.

[charlylebeaugosse]

The most illuminating Zeilinger paper IMO is one he did back in 2005 with Brukner. "Quantum Physics as a Science of Information". SpringerLink sits on it unless you want to give them money. But fortunately the gods have smiled it's available in toto via Google books:

http://tinyurl.com/2aoydkx

Leggett-Garg incorporates a nonlocality assumption and tests for "realism" (counterfactual definiteness, whatever). Inferentially or by default that's what Tresser also does. Or not? Anyway, how are they different?

Gisin indeed has become awfully hard to follow. He's hiking deep into the woods. As I read him (and this interpretation of mine may very well be of absolutely no value whatsoever) it's all somehow coming back to the measurement problem. Hopefully what he's up to will become clear in time.

With Leggett this paper shares the essential point that it is realsim and not locality that is the false asumption in Bell's theory. The author hope to soon write down "proofs" of that in terms of new experiments proposals and a discussion on the basis of the old superposition principle. One tool will be revisiting the Welcher Weg discussion, with views that are not new to Dirac, but new to Einstein, Bohr, Wheeler, Feyman, and many others, including Zeilinger whose views on locality are not fully clear, are they?

As for Gisin, he loves to explain why he is smarter than Einstein and is smart enough indeed to know that the paper that HE points out as THE start of the fashion for Bell theorem in PRL is a fraud.
Like many other localists, he cannot be (also) stupid enough despite his remarkable technical expertise in theory (beside experiments) for not let one think that he is not deeply lacking scientific honesty. Look at who support him: not so long ago (and for now I did not check) he had the support of some strange sect. This stinks, for me and I do not see any of that behind the paper being discussed. My understanding is that within a few month, another paper by the same author will be posted on QuantPh Arxive on
WW, superposition and taking the issue of local realism out of metaphysics into physics with application to interferences with or without delay. I am not privy of the title to look for, nor of the exact content. The Bell paper took about 4-5 years to be accepted (while long ago Pitowsky told the author that there were so many new ideas in there that the paper should appear anyway, or something of that sort).

[charlylebeaugosse]

dBB = de Broglie–Bohm theory (http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)

(also called the pilot-wave theory, Bohmian mechanics, and the causal interpretation)

That's what I thought, but I wanted to be sure: sonce that paper is anti-realist, it is as anti dBB as possible, siding strongly with Pauli and Einstein on that matter.

[nikman]

With Leggett this paper shares the essential point that it is realsim and not locality that is the false asumption in Bell's theory.

I genuinely don't get this. BOTH locality and realism may be false assumptions in Bell's theory. For a long time, in the wake of the Aspect experiments, it was thought that only one of them actually had to be a false assumption and the other (whichever other) might go free. Following that line of thinking Bell personally opted for the false assumption being locality, not realism, and went with Bohm and nonlocality in order to salvage realism. Then, much more recently, along come Leggett and Tresser who say okay, let's indeed assume locality is an unnecessary assumption. Accept nonlocality as read. But the Bell test results may indicate that realism is a false assumption also (Leggett is a scientist of genuine integrity: he's willing to help prove himself wrong if that's how things work out). Nothing in Bell forecloses that outcome. Both locality and realism could be false assumptions. So let's assume the truth of nonlocality and then see if realism can be tested independently.

Bell's brilliance had nothing to do with his initial belief (out of reverence for Einstein) that the conclusions of EPR ought to be correct, because they're not, nor with his acceptance of Bohmism. What he did was grasp how EPR might be tested by subjecting the assumptions of locality and realism to physical experiment. This was an unprecedented accomplishment. He was just never able to figure out how to unarguably separate locality and realism on the basis of experimental results because not even he could do everything.

[charlylebeaugosse]

I genuinely don't get this. BOTH locality and realism may be false assumptions in Bell's theory. For a long time, in the wake of the Aspect experiments, it was thought that only one of them actually had to be a false assumption and the other (whichever other) might go free. Following that line of thinking Bell personally opted for the false assumption being locality, not realism, and went with Bohm and nonlocality in order to salvage realism. Then, much more recently, along come Leggett and Tresser who say okay, let's indeed assume locality is an unnecessary assumption. Accept nonlocality as read. But the Bell test results may indicate that realism is a false assumption also (Leggett is a scientist of genuine integrity: he's willing to help prove himself wrong if that's how things work out). Nothing in Bell forecloses that outcome. Both locality and realism could be false assumptions. So let's assume the truth of nonlocality and then see if realism can be tested independently.

Bell's brilliance had nothing to do with his initial belief (out of reverence for Einstein) that the conclusions of EPR ought to be correct, because they're not, nor with his acceptance of Bohmism. What he did was grasp how EPR might be tested by subjecting the assumptions of locality and realism to physical experiment. This was an unprecedented accomplishment. He was just never able to figure out how to unarguably separate locality and realism on the basis of experimental results because not even he could do everything.

Bell+Aspect do not allow to distinguish the false hypothesis, you are right here, but there are many indication to the contrary (including in the papers of Leggett and Tresser), while both consider that the issue is not yet settled for good. Now the 1931 paper of Einstein, Tolman, and Podolsky (ETP) is quite often overlooked. It proves that for generic particles (although they do not make the distinction, but clearly their argument does not apply to EPR particles) there is a UP when going back in time, something that seems to me very hardly compatible with realism, and certainly not with realism of the form needed by Bell:
according to ETP, if one measurement is made, perhaps that observable pre-exist but not the conjugate ones. Now Bell, after Bohm, considers the case when one spin projection is measured on each particle: how can the other spin that he needs (or the two other spin needed by CHSH, hence also by Aspect et al.) make any sense. This is why I always tell that Einstein (as well as others of his size, and as Feynman apparently did by throwing
Clauser out of his office as told in a popular book: is that true???) would have laughed of Bell paper and dismissed it as being as naive as dBB theories.

- For Einstein making fun of dBB, see the correspondence with Born;
- For the opinion by Born in that book according to which Einstein beleived in HVs, see what I wrote recently about QM compatible HVs in the thread about "Is action at a distance possible as..." , and see in the Born-Einstein correspondence how much Born lacked any understanding of what Einstein was trying to tell him about EPR type issues.
Thus, I do not consider that Bell was fair when he cited Born against Einstein or that he was even decent in the way he responded to Jammer's remarks that Einstein did not defend (naive) HVs.

So Bell was surely a brilliant scientist but the way he quoted things was not exemplary, AND the 1931 ETP is certainly what should let us have a bit less consideration for that part of Bell's work (whose job at CERN was not to take care of foundational issues).

Now, while history is fun, the real issue is physics and yes, it is unknown whether it is locality, or realism or both that have to be blamed of the contradiction, but while research has to progress in a free way, there are good reasons to believe that realism (in the naive
and microscopic sense) is what is wrong. Personaly my scientific life contains alsmost as many proofs of what I thought false as proofs of what I thought right a few years (or weeks) before (of course "proofs" means arguments in favor of something when working as physicist,but I share my time between math and physics and else). The fact is that non-locality and other things of that kind have invaded physics and the sound foundations are melting away, all helped by the lack of professionalism of most contributors to the www culture.
Let us hope that reason and good science will win at the end. I'd love to be (again) convinced of non-locality. After all, that is the beauty of two forms of information (Classical and Quantum) traveling at different speed (c and infinity) that I "learned about" when talking to Charles Bennett that lead me back to Quantum Mechanics after a long carrier in Classical Physics. Unfortunately I began to see misquotations all over the places and then many false arguments. I have feared non-realism most of my life (forgetting that even a realist word is mostly empty, forgetting that we are mostly empty). Please convince me or anyone else a bit cautious that realism holds true,even if almost empty.

[DrChinese]

Let us hope that reason and good science will win at the end. ...

Of course they will and are! We aren't going backwards!! :smile:

There was a spirited debate many years back over Big Bang versus Continuous Creation. BB won after the 1965 discovery of the CMBR of course. That same year saw the publication of Bell. I think it is safe to say that future discoveries will help us to sort things out. I too have a slight bias towards throwing out realism, but could be swayed anytime by a good paper.

As nikman says, clearly separating locality and realism is not so simple given experimental setups. For example: even in situations in which non-locality appears to be demonstrated, there are ways to construe the "action" such that there are no FTL influences at all. But now we draw the causal direction of time into the equation, making things really strange.

[billschnieder]

There is so much confusion that I would like to start my participation in this thread by suggesting that we each define what we mean by "realism".

To me, realism means, "elements of reality" exist independent of observation, or observability. To me realism has nothing to do with instrumental behaviour or whether these "elements" can be directly observed without disturbance or not. To me, when you say a photon is emitted but not detected, you are admitting to my definition as above. As far as I can tell from this thread so far, all participants believe realism as defined above is true even if they haven't explicitly admitted it. If anyone else thinks realism as defined above is false, please state it and I will show using your own quotes that you are lying. However, you may think "realism" means something else and it is important we all agree what we are arguing for or against to avoid confusion.

Now some will argue that the EPR definition of realism is the idea that a single particle (or entangled pair) will have definite spin projections at 3 different angles. I do not agree that this is the EPR definition but I am willing to grant that definition for the sake of argument, so long as we are not later on drawing conclusions about the previous definition I gave above, based on this so called "EPR definition". In any case, I will suggest first that we present clearly the definition of realism we would like to argue, and then when all the parameters of this version of "realism" have been exposed, it will then make sense to question whether QM or Experiments in anyway tell us anything about the "realism" we are discussing.

[DevilsAvocado]

There was a spirited debate many years back over Big Bang versus Continuous Creation. BB won after the 1965 discovery of the CMBR of course. That same year saw the publication of Bell.

Yes, and the funny thing is that Sir Fred Hoyle, who coined the term "Big Bang", stuck to his own Steady State theory until he passed away in 2001, denying BB aggressively! :smile:

And what is almost funnier is that Hoyle promoted the theory that life evolved in space, spreading through the universe via panspermia (http://en.wikipedia.org/wiki/Panspermia), and that evolution on earth is driven by a steady influx of viruses arriving via comets. :biggrin:

It’s hard to be a heretic!


(P.S: Speak of the devil! :surprised)

[DrChinese]

1. To me, realism means, "elements of reality" exist independent of observation, or observability. To me realism has nothing to do with instrumental behaviour or whether these "elements" can be directly observed without disturbance or not. To me, when you say a photon is emitted but not detected, you are admitting to my definition as above. As far as I can tell from this thread so far, all participants believe realism as defined above is true even if they haven't explicitly admitted it.

2. Now some will argue that the EPR definition of realism is the idea that a single particle (or entangled pair) will have definite spin projections at 3 different angles. I do not agree that this is the EPR definition ...

1. I agree with this.

2. I miss how this is different than 1. EPR said it was reasonable to admit as "real" 2 or more elements even if they could not be predicted simultaneously. So 3 different angles would quality as EPR realism as I read it. So are you saying a) that you don't think EPR says this, or b) that you do not agree with this idea, regardless of whether EPR says it?

[DrChinese]

1. Yes, and the funny thing is that Sir Fred Hoyle, who coined the term "Big Bang", stuck to his own Steady State theory until he passed away in 2001, denying BB aggressively! :smile:

2. And what is almost funnier is that Hoyle promoted the theory that life evolved in space, spreading through the universe via panspermia (http://en.wikipedia.org/wiki/Panspermia), and that evolution on earth is driven by a steady influx of viruses arriving via comets. :biggrin:


1. That is sad.

2. I guess anything is possible. I have been called a virus by some people...

[billschnieder]

1. I agree with this.

2. I miss how this is different than 1. EPR said it was reasonable to admit as "real" 2 or more elements even if they could not be predicted simultaneously. So 3 different angles would quality as EPR realism as I read it. So are you saying a) that you don't think EPR says this, or b) that you do not agree with this idea, regardless of whether EPR says it?

1) I'm not sure I understand your point. Are you agreeing that my definition of "realism" in (1) is correct, or are you admitting that whatever that definition entails about the universe is true. There is a difference there. There are four possibilities

a) You agree that "realism" is defined as I did, but believe that "realism" so defined is false.
b) You disagree that "realism" is defined as I did, in which case you probably have your own definition. In addition you also believe what my definition implies about the universe, is false.
c) You disagree that realism is defined as I did but believe that, what my definition implies about the universe is true. In this case you will still have to provide your own definition of "realism".
d) You agree that realism is defined as I did, and what it implies about the universe is also True. In this case, we are in total agreement and the discussion around Bell's theorem will have to be about something other than "realism".

2) My definition of realism says nothing about predictability or observability. All it says is that "there exists, elements of reality independent of observation". If somebody says "The moon does not exist when no one is looking", they are rejecting my definition.

The so called "EPR definition" is more restrictive in the following sense. If a particle has a pre-existing attribute, which can never be directly measured, but which together with an attribute of the instrument, produce a measurable phenomenon, the so called "EPR definition" will classify this as "unreal", even though it is very real according to my definition. In other words, if you define realism as "observables" must "pre-exist" the act of "observation", then you are proposing a more restrictive view which ignores the obvious fact that some observables are created during the measurement process.

In the EPR scenario you have a spin, but you do not measure the spin, you measure it's projection. But the projection is meaningless unless you project it to something, and this something is defined by the instrument angle. Therefore the spin projection of a particle is just one example of an obvious case in which the observable is created on observation. So if you have defined realism in such a narrow way, you can not then conclude that the spin of the particle does not exist until it is measured. This is why I say we have to be clear about what definition of realism we are using. You do not need Bell to see that such a narrowly defined "realism" which is often erroneously ascribed to EPR, is a naive definition.

[DrChinese]

1) I'm not sure I understand your point. Are you agreeing that my definition of "realism" in (1) is correct, or are you admitting that whatever that definition entails about the universe is true. There is a difference there. There are four possibilities

a) You agree that "realism" is defined as I did, but believe that "realism" so defined is false.
b) You disagree that "realism" is defined as I did, in which case you probably have your own definition. In addition you also believe what my definition implies about the universe, is false.
c) You disagree that realism is defined as I did but believe that, what my definition implies about the universe is true. In this case you will still have to provide your own definition of "realism".
d) You agree that realism is defined as I did, and what it implies about the universe is also True. In this case, we are in total agreement and the discussion around Bell's theorem will have to be about something other than "realism".

2) My definition of realism says nothing about predictability or observability. All it says is that "there exists, elements of reality independent of observation". If somebody says "The moon does not exist when no one is looking", they are rejecting my definition.

The so called "EPR definition" is more restrictive in the following sense. If a particle has a pre-existing attribute, which can never be directly measured, but which together with an attribute of the instrument, produce a measurable phenomenon, the so called "EPR definition" will classify this as "unreal", even though it is very real according to my definition. In other words, if you define realism as "observables" must "pre-exist" the act of "observation", then you are proposing a more restrictive view which ignores the obvious fact that some observables are created during the measurement process.

In the EPR scenario you have a spin, but you do not measure the spin, you measure it's projection. But the projection is meaningless unless you project it to something, and this something is defined by the instrument angle. Therefore the spin projection of a particle is just one example of an obvious case in which the observable is created on observation. So if you have defined realism in such a narrow way, you can not then conclude that the spin of the particle does not exist until it is measured. This is why I say we have to be clear about what definition of realism we are using. You do not need Bell to see that such a narrowly defined "realism" which is often erroneously ascribed to EPR, is a naive definition.

1. I agree with your definition as stated. I don't necessarily agree that elements of reality exist independently of observation. I tend to reject that view.

2. According to EPR: if that spin's projection can be predicted with certainty, then the pre-existing spin must itself real - independent of the instrument by which it is measured.

If the EPR definition is more "restrictive" than yours: what does EPR define as unreal that you define as real? Because I cannot see the difference. EPR specifically defines as real observables whose values can be predicted - don't you? They say there is a matching element of reality to the observable. Not that the observable (projection) itself is real.

If your definition is less restrictive than EPR's, then more qualifies as real. Which would naturally make it easier to falsify. So I guess I see that point which you are making. But what evidence would you cite for us to accept your definition over EPR's? I mean, predicting with certainty seems like a pretty strong position.

(The EPR definition is LESS restrictive than the QM definition - which of course would be only those items which can be simultaneously predicted.)

[billschnieder]

1. I agree with your definition as stated. I don't necessarily agree that elements of reality exist independently of observation. I tend to reject that view.

Fair enough.

2. According to EPR: if that spin's projection can be predicted with certainty, then the pre-existing spin must itself real - independent of the instrument by which it is measured.

It is the spin which pre-exists the observation, not the "spin projection", yet it is the "spin projection" which is observable not the spin. So clearly, if the EPR definition is that "observables must pre-exist measurement", it is not a reasonable definition because as you have agreed in (1), realism simply means "elements of reality" (not "observables") pre-exist observation". In other words, it is possible for realism as defined and agreed in (1) to be true, in a completely contextual universe in which nothing can be directly observed, but in which pre-existing elements of reality always interact with instruments to reveal observables. But contextual observables are not allowed in a universe in which observables must pre-exist observation.

If the EPR definition is more "restrictive" than yours: what does EPR define as unreal that you define as real? Because I cannot see the difference.
If the EPR definition is that "observables must pre-exist observation", then contextual observables are not allowed. But in my definition, contextual observables are fully consistent with pre-existing "elements of reality". But if you are willing to agree that underlined text above is not the EPR definition, and will rather say that my original definition which you agreed to is the EPR definition, then that is a good point to start, and we can proceed to discuss the burden of proof required to disprove it.

[DevilsAvocado]

I have been called a virus by some people...

Caroline H. Thompson? :smile:

[zonde]

There is so much confusion that I would like to start my participation in this thread by suggesting that we each define what we mean by "realism".
It should definitely help to follow this discussion.

To me, realism means, "elements of reality" exist independent of observation, or observability. To me realism has nothing to do with instrumental behaviour or whether these "elements" can be directly observed without disturbance or not. To me, when you say a photon is emitted but not detected, you are admitting to my definition as above. As far as I can tell from this thread so far, all participants believe realism as defined above is true even if they haven't explicitly admitted it. If anyone else thinks realism as defined above is false, please state it and I will show using your own quotes that you are lying. However, you may think "realism" means something else and it is important we all agree what we are arguing for or against to avoid confusion.
I would say that while this definition is "true" it is not restrictive enough to have some value.
Because you can arrive at situation where "elements of reality" are completely independent from results of observations.
I think that definition should include some statement how "elements of reality" are related to observations. Say "elements of reality" ascribed to particle together with "elements of reality" ascribed to measurement equipment (conditions) determine observed result.

Now some will argue that the EPR definition of realism is the idea that a single particle (or entangled pair) will have definite spin projections at 3 different angles. I do not agree that this is the EPR definition but I am willing to grant that definition for the sake of argument, so long as we are not later on drawing conclusions about the previous definition I gave above, based on this so called "EPR definition". In any case, I will suggest first that we present clearly the definition of realism we would like to argue, and then when all the parameters of this version of "realism" have been exposed, it will then make sense to question whether QM or Experiments in anyway tell us anything about the "realism" we are discussing.
This is not EPR definition. EPR definition covers only the case when say projection of spin is predictable with certainty. And because this definition involves "prediction" it can start a looong discussion.

[zonde]

This violation of "Effect After Cause Principle" seems quite paradoxical. I think I agree with Dmitry:
For me, Effect is in the lightcone of Cause, nothing more. (In CTL it could be laso vice versa). But then (in flat spacetime) Effect is always after the Cause - just by definition!
If we can relate event that has happened before (memory) with another event that just happened (senses) then event in memory is cause by definition and event reported by senses is effect by definition and to say that effect and cause can swap places means that we should alter memory and simulate sensory information. But in that case we can't be sure about anything and I prefer to be sure about something rather than nothing.

[DrChinese]

Caroline H. Thompson? :smile:

Probably worse... :biggrin:

[DrChinese]

Fair enough.

It is the spin which pre-exists the observation, not the "spin projection", yet it is the "spin projection" which is observable not the spin. So clearly, if the EPR definition is that "observables must pre-exist measurement", it is not a reasonable definition because as you have agreed in (1), realism simply means "elements of reality" (not "observables") pre-exist observation". In other words, it is possible for realism as defined and agreed in (1) to be true, in a completely contextual universe in which nothing can be directly observed, but in which pre-existing elements of reality always interact with instruments to reveal observables. But contextual observables are not allowed in a universe in which observables must pre-exist observation.


If the EPR definition is that "observables must pre-exist observation", then contextual observables are not allowed. But in my definition, contextual observables are fully consistent with pre-existing "elements of reality". But if you are willing to agree that underlined text above is not the EPR definition, and will rather say that my original definition which you agreed to is the EPR definition, then that is a good point to start, and we can proceed to discuss the burden of proof required to disprove it.

I'm pretty much OK with that as a working definition.

I don't really see the distinction though. EPR does not insist that the spin "projection" preexist the measurement, merely that there is an element which does. Since the result is certain, there is little point in distinguishing the two. You call that a contextual measurement, and I do not define as such. Because the result is certain, it is non-contextual. I view contextual as meaning that the entire context, including spacelike separated components, is relevant. That would not be possible in a classically local world (but would in a quantum local world).

Now of course this is true only in the case where there is an undisputed element of reality. Where my dispute arises is in the definition of simultaneous elements of reality which cannot be individually predicted with certainty. That is what Bell attacked.

[billschnieder]

1) Since the result is certain, there is little point in distinguishing the two.

2)You call that a contextual measurement, and I do not define as such. Because the result is certain, it is non-contextual. I view contextual as meaning that the entire context, including spacelike separated components, is relevant. That would not be possible in a classically local world (but would in a quantum local world).

1) Well I think there is an important distinction. In modal logic, the certainty of a counter-factual statement can not be transferred to the events implied in the statement. The truth-value of an event can not pre-exist the event. The prediction is true, but the result is not certain until the event of measuring it actually occurs.

The counter-factual statement "if the Netherlands had scored 5 goals against Spain without conceding any, then they would have won the world-cup" is true, but the truth value of the statement can not be transferred to the events embodied in it. In fact, Netherlands lost and it is impossible to undo the event, but the counter-factual statement is still true even though the implied events will never be true. So it is possible to make a prediction of a counterfactual nature, even if it is impossible to actually realize it.

Similarly, the statement "If I had measured the projection along axis c, I would have obtained result C" is a perfectly valid statement, even when it is impossible to measure along axis c. The prediction, therefore is simply a clear description of the context, and what would be obtained in that context. The distinction above prevents us from erroneously assuming that not being able to measure "c" implies the counter-factual statement is wrong.

2) I don't know where you got your definition of contextual as I have never seen it defined as such. Essentially, you are saying contextual observables means they can not be predicted, or you are saying if it can be predicted definitely, then it is not contextual. I do not agree with this definition, but in any case I will keep it in mind that when you say contextual, that is what you mean.

Now continuing with the discussion about realism, since we have a working definition to continue with, I have a question:

If a single particle is real and has a pre-existing spin, according to realism, we would say measuring the spin-projection in a completely specified context, will result in a definite outcome. We can therefore define three or any number of different contexts "a", "b", "c", ... for the single particle for which we will obtain a definite result if we measure the single particle in that context. Do you agree that, this paragraph accurately. represents what a realist will say about the particle?

Non-realism will respond that it is not possible to predict what will be obtained even by completely specifying a contexts for the single particle, since it will not result in a definite outcome. Is this a correct representation of what a non-realism may say about the situation described in the previous paragraph? If not please could you rephrase it to your liking?

[DrChinese]

Now continuing with the discussion about realism, since we have a working definition to continue with, I have a question:

If a single particle is real and has a pre-existing spin, according to realism, we would say measuring the spin-projection in a completely specified context, will result in a definite outcome. We can therefore define three or any number of different contexts "a", "b", "c", ... for the single particle for which we will obtain a definite result if we measure the single particle in that context. Do you agree that, this paragraph accurately. represents what a realist will say about the particle?

Non-realism will respond that it is not possible to predict what will be obtained even by completely specifying a contexts for the single particle, since it will not result in a definite outcome. Is this a correct representation of what a non-realism may say about the situation described in the previous paragraph? If not please could you rephrase it to your liking?

I would say that the realist would agree, so yes. They would say the same even if these are not predictable.

The non-realist would say that the context would include the nature of a measurement, and there is no reality outside of that. They would say the same even if a, b and c were individually predictable but not simultaneously predictable.

[Pio2001]

So I suggest we discuss around these:

http://arxiv.org/abs/quant-ph/0608008
We prove here a version of Bell Theorem that does not assume locality. As a consequence classical realism, and not locality, is the common source of the violation by nature of all Bell Inequalities.

Hello, thanks for the links.

I read the above paper, and there is a point that I don't follow very well.

Page 3 § New Bell inequality, it is said "it follows from the EACP that the three sequences E, E' and P involved in (**) make sense".

For me, this is not true, for the obvious reason that the E' sequence does not exist.
In part C, it is said that E' is inferred to make sense, i.e. [...] (to [...] have well defined (albeit unknown) values) by using the augmentation of QM by A.

But since the orientations of E and P are not parallel, nor the ones of P and E', no definite value can be inferred for E'i.

I'd rather say "it follows from the EACP that the three probabilities p(Pi=Ei), p(Ei=E'i), and p(E'i=Pi) involved in (**) make sense".

It seems to me that this article just proves that Heisenberg's inequality is true. Not that realism is incompatible with quantum mechancis predictions.

The difference with Bell's inequality is that Bell's inequality applies to actual measurements, while this one applies to measurements that can't be done in practice (measuring both Ei and E'i).
Thus, EPR-Bell experiments show the incompatibility between experimentation and local hidden variable models, while this paper shows the incompatibility between measuring Ei and E'i.

Or am I missing something ?

[jk22]

Thus, EPR-Bell experiments show the incompatibility between experimentation and local hidden variable models

This is what I understood, about the local variables.


But how to make a no local assumption ? Does it is the case if we had made a 2-level variable system, by iterating the same approach :

a) local one k : C(A,B, g)=int[ A(thetA, k, g)B(thetB, k, g) ]dk (g left untouched)

the latter in fact equals C(A,B, g), where

b) g would remain as a kind of "non-localisable" variable, but seems not very physical.

then

CHSH = |C(A, B, g1) + C(A, B', g2)| + |C(A', B, g3) - C(A', B', g4)|

we could hide (under the moto : there will be always sthg hidden, the truth is somewhere else) the g's by setting values in function of some experimental parameter or results (but this seems not very physical)

does then the theorem hold : CHSH <= 2 forall g1,..g4

[Pio2001]

Hello jk22,
I was about to answer yes, but you made me read again CHSH's demonstration, and now I don't understand anything anymore.

I don't know how they can write such a thing as

\int d\lambda \, \rho (\lambda) \, \overline{A}(\alpha, \lambda) \, \overline{B}(\beta, \lambda)

http://3141592.pio2001.online.fr/pictures/physics/chsh.png

(taken from [1])

While lambda can depend on the measuring device. The lambdas in A and B should be able to be different.

[1] J.S.Bell, Introduction to the hidden-variable question, Societa Italiana di Fisica. Rendiconti della scuola internazionale di fisica "`Enrico Fermi"', Il corso fondamenti di mecanica quantistica, Academic Press, New York and London, 1972.

[charlylebeaugosse]

1) The quasi-triviality of the EACP is what made the set of hypothesis (i.e., EACP+ Locality) weaker, hence the overall result stronger. The price of the weaker hypothesis is a smaller set of Boole-Bell-like inequalities, but GHZ works without changing much of the proof (just using Lorentz observers the right way o get the needed spin projections, observed or for hidden variables. The main goal is to "prove" (this is not math) that hidden variable do not exist, at least the way Bell used them, but the proof is by contradiction, so that these variables are used in the proof of their non-existence, so to speak.

2) The EACP being causality extended to work on hidden variables if any existed, it is essentially only causality. Thus the contradiction coming from the inequalities is almost a complete proof that locality, the other a priori questionable part of the hypotheses.

3) Both papers are now published in the same journal (Eur. Phys. J. D 58, 385–396 (2010) and Eur. Phys. J. D 62, 139–154 (2011): in the first paper, see the GHZ part, the second paper being much more complete on the EPR-Bohm-Bell setting and more precise on the analysis of basic facts).

[charlylebeaugosse]

1) A bit surprising that one of the participants manipulates integrals but does not seem to understand what is a proof by contradiction. Assuming true what one hopes to prove false is well known practice since at least the proof that there are infinitely many prime numbers.

2) Besides, Bell's inequalities also use HVs, irreducibly for the proof of them, in an almost tautological way. Now, using extra hypotheses one can deduce an inequality relating measurable quantities, but then one only prove experimentally a correlation between two spins or polarizations for the members of a EPRB pair. To get deeper conclusions from these experiments, one has again to assume many things and the result is that locality and realism (in the sense of preexistence of observables to measurement, or HVs according to preference but the HVs statements are weaker).

3) Using the EACP, that is indeed almost only causality, one has almost a full proof that realism by itself is false (no HV's). The "almost" are there to cover the fact that there could be HVs that would not obey causality the way observables do. I do not know many physicists ready to swallow such pathologies, even among people inclined to believe in HVs.

4) Truth is: these papers are hard to read and the second should be read first, using the first one only for the GHZ part. But the issues are hard. Very deep and hard and dangerously close to philosophy, but philosophy is always there in the way we understand physics (and create it), even if we do not always see it.

[JordanL]

DrC: Does your personal inclination to reject objective realism lead you to any other assumptions or hypotheses?

Or, I suppose, does the collected work that has been done on that point of view have any other conclusions that might be testable? I would think that observational dependence in realism would imply a more fundamental interconnectedness of things that we observe to exist within our concept of reality. Would QM be sufficient to explain this greater connection? Or would a greater connection be unnecessary? If such a fundamental interdependence of existence were posited, how would it be tested?

I ask because this is an area I have not ventured very far into, and it seems you have given it more consideration.

[DrChinese]

DrC: Does your personal inclination to reject objective realism lead you to any other assumptions or hypotheses?

Or, I suppose, does the collected work that has been done on that point of view have any other conclusions that might be testable? I would think that observational dependence in realism would imply a more fundamental interconnectedness of things that we observe to exist within our concept of reality. Would QM be sufficient to explain this greater connection? Or would a greater connection be unnecessary? If such a fundamental interdependence of existence were posited, how would it be tested?

I ask because this is an area I have not ventured very far into, and it seems you have given it more consideration.

Welcome to PhysicsForums, JordanL!

I don't see rejecting realism as requiring any other assumptions. Keep in mind that there are several different interpretations that reject realism. I would say that "most" physicists reject realism in one fashion or another.

As to testing: there are "some" experiments which appear to support rejection of realism. There are a number of papers on the subject. I would say nothing to date is absolutely conclusive but that seems to be the direction. A lot of Bohmians reject realism too, or at a minimum reject non-contextuality (which to me is the same as objective realism).

[JordanL]

Welcome to PhysicsForums, JordanL!

I don't see rejecting realism as requiring any other assumptions. Keep in mind that there are several different interpretations that reject realism. I would say that "most" physicists reject realism in one fashion or another.

As to testing: there are "some" experiments which appear to support rejection of realism. There are a number of papers on the subject. I would say nothing to date is absolutely conclusive but that seems to be the direction. A lot of Bohmians reject realism too, or at a minimum reject non-contextuality (which to me is the same as objective realism).

Interesting. So ideas have been proposed that stop at simply rejecting realism, and ideas have also gone further than that? I'm opening up the links you provided in the first post now to give them a look through.

If observation itself presents a change in reality, there is some kind of information exchange between the observer and the observed. Is this a reasonable statement?

I have studied the ideas behind QM, GR and SR for a while, but I'm just teaching myself about the underlying math. Or rather, I'm just starting the process of teaching myself about the underlying math. I'm trying to check the understanding I have about the abstract ideas so that I have more context for the math I'm trying to learn.

EDIT: Also, thank you for the welcome. :) My first post got deleted because I guess I posted it in the wrong forum, but it was actually inspired by a similar thread about Bell's theorem that you posted on over a year ago.

[Demystifier]

A lot of Bohmians reject realism too, or at a minimum reject non-contextuality (which to me is the same as objective realism).
I would put it this way. Strong theorems (such as Kochen-Specker) rule out SIMULTANEOUS non-contextual/objective realism of non-commuting quantum observables. E.g., if spin in z-direction is real, then spin in x-direction is not. The Bohmian interpretation exploits the fact that at most one quantity may be real in the NON-CONTEXTUAL/OBJECTIVE sense, and this quantity is (usually) taken to be the particle position. Thus, in Bohmian mechanics spin indeed is not non-contextually/objectively real, but the particle position is. So when we measure spin, we don't really measure spin (because it is not real); what we really measure are some particle positions in the Stern-Gerlach apparatus.

Thus, it is not correct to say that Bohmians reject non-contextual realism. Instead, they reject non-contextual realism for almost all quantum observables, except one.

[Zarqon]

Haven't read the whole thread yet, but since the OP contained only refs to preprints, I though I would note that a PRL appeared on the subject a few days ago:

Waldherr et al. PRL 107, 090401 (2011) (http://prl.aps.org/abstract/PRL/v107/i9/e090401)

Quantum nonlocality has been experimentally investigated by testing different forms of Bell’s inequality, yet a loophole-free realization has not been achieved up to now. Much less explored are temporal Bell inequalities, which are not subject to the locality assumption, but impose a constraint on the system’s time correlations. In this Letter, we report on the experimental violation of a temporal Bell’s inequality using a nitrogen-vacancy (NV) defect in diamond and provide a novel quantitative test of quantum coherence. Such a test requires strong control over the system, and we present a new technique to initialize the electronic state of the NV with high fidelity, a necessary requirement also for reliable quantum information processing and/or the implementation of protocols for quantum metrology.


Is it true that since the temporal Bell inequalities do not depend on locality, a violation of the inequalities in this frame directly disproves realism? Or is it rather that there exists an equivalent notion of locality for time correlations instead, such that realism could still not be singled out even in this case. What's your thoughts on this?

[Demystifier]

Is it true that since the temporal Bell inequalities do not depend on locality, a violation of the inequalities in this frame directly disproves realism?
No, it doesn't disprove realism. It only disproves non-contextual realism, but the violation of original Bell inequalities also does that. Bell and many others emphasize nonlocality rather than contextuality because contextuality does not look so surprising to them, not because they thought contextuality could be avoided.

[DrChinese]

I would put it this way. Strong theorems (such as Kochen-Specker) rule out SIMULTANEOUS non-contextual/objective realism of non-commuting quantum observables. E.g., if spin in z-direction is real, then spin in x-direction is not. The Bohmian interpretation exploits the fact that at most one quantity may be real in the NON-CONTEXTUAL/OBJECTIVE sense, and this quantity is (usually) taken to be the particle position. Thus, in Bohmian mechanics spin indeed is not non-contextually/objectively real, but the particle position is. So when we measure spin, we don't really measure spin (because it is not real); what we really measure are some particle positions in the Stern-Gerlach apparatus.

Thus, it is not correct to say that Bohmians reject non-contextual realism. Instead, they reject non-contextual realism for almost all quantum observables, except one.

Thanks for clarifying that point, I wasn't certain I was getting it entirely correct. :smile:

[nikman]

A very recent interview with the Z of GHZ wherein he talks about local realism, progress in loophole closing and related stuff.

http://discovermagazine.com/2011/jul-aug/14-anton-zeilinger-teleports-photons-taught-the-dalai-lama

[jk22]

Is the detection loophole the fact that the experimental correlation function does not give -1 at angle 0, and a value of CHSH which is 2.38 and not 2.82 ?

This can be seen on the graph at the end of this paper :

http://arxiv.org/PS_cache/quant-ph/pdf/9806/9806043v1.pdf ?

[jk22]

If you want can we say in the formula used :
<AB> counts the matching pairs,
whereas <A><B> counts the non detected as pair, hence the loophole, so that the experimental result should give : <AB>-<A><B> if we take into account the detection loophole ?

[zonde]

Detection loophole is the fact that interpretation of Bell tests that use photons should relay on fair sampling assumption. This assumption means that correlations in photon pairs where one of two is not detected would be the same (if they would be detected) as for the pairs where both photons were detected.
If that is not so then correlations can be affected by detection of different subsamples under different settings of analyzer.

[DevilsAvocado]

http://discovermagazine.com/2011/jul-aug/14-anton-zeilinger-teleports-photons-taught-the-dalai-lama/article_view

So does that mean Einstein was wrong?

There are still some technical loopholes in the experiments testing Bell’s theorem that could allow for a local realistic explanation of entanglement. For instance, we don’t detect all the particles in an experiment, and therefore it is conceivable that, were we to detect every single particle, some would not be in agreement with quantum mechanics. There is *a very remote chance* that nature is really vicious and that it allows us to detect only particles that agree with quantum mechanics. If so, and if we could ever detect the others, then local realism could be saved. But I think we are close to closing all of these loopholes, which would be a significant achievement with practical implications for quantum technologies.
....

[zonde]

April 13, 2010:
NIST Detector Counts Photons With 99 Percent Efficiency (http://www.nist.gov/pml/div686/detector_041310.cfm)
So we are waiting ...

[DevilsAvocado]

... for that 1% to turn everything upside down ... :biggrin:

[zonde]

... for that 1% to turn everything upside down ... :biggrin:
Who is talking about 1%?
I am talking about 90% turning it into something slightly more classical.

Didn't you know that there are no reports about experiments that would aim for increased coincidence rates?

[DevilsAvocado]

Who is talking about 1%?

There must be something wrong with my calculator because I can’t even get the basic math right...
NIST Detector Counts Photons With 99 Percent Efficiency
...
Who is talking about 1%?
...
I am talking about 90%

So, are you saying (for real) that there is 90% chance for Local Reality to survive? :bugeye::bugeye::bugeye:

[zonde]

There is no problem with math.
The fact that we have detectors with 99% detection efficiency does not automatically solve question about detection loophole free photon Bell test.
Bell test still has to be performed using these detectors and should give high coincidence count rate while violating Bell inequalities by significant amount at the same time.

For example you can take a look at this experiment:
Ultra-bright source of polarization-entangled photons (http://arxiv.org/abs/quant-ph/9810003)
It says:
"After passing through adjustable irises, the light was collected using 35mm-focal length doublet lenses, and directed onto single-photon detectors — silicon avalanche photodiodes (EG&G #SPCM’s), with efficiencies of ∼ 65% and dark count rates of order 100s−1."
and:
"The collection irises for this data were both only 1.76 mm in diameter – the resulting collection efficiency (the probability of collecting one photon conditioned on collecting the other) is then ∼ 10%."

So while detector efficiency is around 65% coincidence rate was only around 10%. And it is this coincidence rate that is important if we want to speak about closing detection loophole.

[DevilsAvocado]

... coincidence rate was only around 10%


Okay, so I’m asking you again:

So, are you saying (for real) that there is 90% chance for Local Reality to survive?
:bugeye::bugeye::bugeye:

[zonde]

Make it 100%. I have no doubt that local realism holds at least as far as quantum entanglement is concerned.

[ThomasT]

Make it 100%. I have no doubt that local realism holds at least as far as quantum entanglement is concerned.That would mean that the qm predictions for all optical Bell tests are incorrect.

That's hard to accept, especially since the qm predicted correlation between the angular difference of the crossed polarizers and the rate of coincidental detection is also intuitively in line with classical optics principles, whereas that of the archetypal local realistic model isn't.

[DevilsAvocado]

Hey TT! Welcome back! http://planetsmilies.net/sign-smiley-506.gif


I’m sorry for that terrible "silly joke"... :blushing: pleeeeeeeeease tell me that this had absolutely nothing to do with your 'pause'...

[DevilsAvocado]

Make it 100%. I have no doubt that local realism holds at least as far as quantum entanglement is concerned.

zonde, you’re refuting the most precise theory we got, thousands of experiments, consensus in the global scientific community, the work and words by Anton Zeilinger et al., etc, etc, ...

How does it feel to be a heretic? Left all alone out in the cold?

[zonde]

That would mean that the qm predictions for all optical Bell tests are incorrect.
No, it doesn't mean that. QM predictions are tested and they work for inefficient detection case. Experiments with efficient detection can not change that.

But it would mean that QM predictions are incorrect for the limit of single photon.


That's hard to accept, especially since the qm predicted correlation between the angular difference of the crossed polarizers and the rate of coincidental detection is also intuitively in line with classical optics principles, whereas that of the archetypal local realistic model isn't.
I am not saying that "archetypal local realistic model" used by Bell is correct. It was successfully used to make mathematical argument but it is very poor as description of physical reality.

[zonde]

zonde, you’re refuting the most precise theory we got, thousands of experiments, consensus in the global scientific community, the work and words by Anton Zeilinger et al., etc, etc, ...

How does it feel to be a heretic? Left all alone out in the cold?
I can say the same as in the replay to Thomas.
Experiments with efficient detection can not change results of experiments with inefficient detection.

And I don't see that I am alone.
Idea that QM does not apply to single particles is quite common.

[DevilsAvocado]

And I don't see that I am alone.

In mainstream science you are, or you have to show me a least one reputable professor working at a reputable institute, preferably with one or two awards, accepted by the community – who agrees with you that local realism has 100% chance to survive.

And while you’re at it, you could maybe also explain to me why Zeilinger, Aspect and Clauser has won the Wolf Prize 2010 for Physics (http://www.wolffund.org.il/cat.asp?id=25&cat_title=PHYSICS) (one of the most prestigious in the world) along with 100,000 Euros "for their fundamental conceptual and experimental contributions to the foundations of quantum physics, specifically an increasingly sophisticated series of tests of Bell’s inequalities or extensions there of using entangled quantum states"...?

I mean... you could hardly claim that they’re just "nice" to Zeilinger, Aspect and Clauser, right?

And why are there speculations on a Nobel Prize in Physics to Zeilinger, Aspect and Clauser (http://blogs.scientificamerican.com/observations/2011/09/21/annual-nobel-predictions-announced-but-forecasting-prizes-remains-a-tricky-business/) for "their tests of Bell’s inequalities and research on quantum entanglement", if there are a lot of people like you who have "found out" that this is just "mumbo-jumbo"...?

[ThomasT]

No, it doesn't mean that. QM predictions are tested and they work for inefficient detection case. Experiments with efficient detection can not change that.Ok, but calculations assuming 100% efficient detection also indicate a measurable difference between qm predictions and LRHV predictions. So, I'm not sure what you're asserting wrt local realism.

But it would mean that QM predictions are incorrect for the limit of single photon.I'm not sure what you mean by this. Afaik, wrt the way I learned what I remember of qm :uhh:, it doesn't have to do with single photon detections, but only with photon flux wrt large number of trials. And isn't this is also what LRHV models of entanglement are concerned with predicting?

I am not saying that "archetypal local realistic model" used by Bell is correct. It was successfully used to make mathematical argument but it is very poor as description of physical reality.Ok, I think we agree on this. So exactly what are you referring to when you speak of "local realism"?

[DrChinese]

Ok, but calculations assuming 100% efficient detection also indicate a measurable difference between qm predictions and LRHV predictions. So, I'm not sure what you're asserting wrt local realism.

With LR nowhere near those results, which are 100% consistent with QM.

Don't make me come and beat you up! :smile:

[No-where-man]

I am opening a new thread to continue discussion of some interesting ideas around EPR and Bell. Specifically, this is about the idea of realism, and whether it is tenable in light of Bell and other HV no-go theorems. Note: I usually use Hidden Variables (HV) and Realism interchangeably although some people see these as quite different. I also tend to use Realism as being an extension of EPR's "elements of reality" as a starting point for most discussions. After all, if a physical measurement can be predicted with certainty without disturbing what is measured... well, I would call that as real as it gets.

charlylebeaugossehad thrown out a few ideas in another thread - especially around some papers by Charles Tresser. So I suggest we discuss around these:

http://arxiv.org/abs/quant-ph/0608008
We prove here a version of Bell Theorem that does not assume locality. As a consequence classical realism, and not locality, is the common source of the violation by nature of all Bell Inequalities.

http://arxiv.org/abs/quant-ph/0503006
In Bohm's version of the EPR gedanken experiment, the spin of the second particle along any vector is minus the spin of the other particle along the same vector. It seems that either the choice of vector along which one projects the spin of the first particle influences at superluminal speed the state of the second particle, or naive realism holds true i.e., the projections of the spin of any EPR particle along all the vectors are determined before any measurement occurs). Naive realism is negated by Bell's theory that originated and is still most often presented as related to non-locality, a relation whose necessity has recently been proven to be false. I advocate here that the solution of the apparent paradox lies in the fact that the spin of the second particle is determined along any vector, but not along all vectors. Such an any-all distinction was already present in quantum mechanics, for instance in the fact that the spin can be measured along any vector but not at once along all vectors, as a result of the Uncertainty Principle. The time symmetry of the any-all distinction defended here is in fact reminiscent of (and I claim, due to) the time symmetry of the Uncertainty Principle described by Einstein, Tolman, and Podolsky in 1931, in a paper entitled ``Knowledge of Past and Future in Quantum Mechanics" that is enough to negate naive realism and to hint at the any-all distinction. A simple classical model is next built, which captures aspects of the any-all distinction: the goal is of course not to have a classical exact model, but to provide a caricature that might help some people.

http://arxiv.org/abs/quant-ph/0501030
We prove here a version of Bell's Theorem that is simpler than any previous one. The contradiction of Bell's inequality with Quantum Mechanics in the new version is not cured by non-locality so that this version allows one to single out classical realism, and not locality, as the common source of all false inequalities of Bell's type.

What implications this could have on modern thoughts?
Does it mean universe is random and unpredictable or is it still the opposite?

[No-where-man]

Detection loophole is the fact that interpretation of Bell tests that use photons should relay on fair sampling assumption. This assumption means that correlations in photon pairs where one of two is not detected would be the same (if they would be detected) as for the pairs where both photons were detected.
If that is not so then correlations can be affected by detection of different subsamples under different settings of analyzer.


I thought the point of these experiments was to prove that objective reality doesn't exist, until we start to detect/measure it (although, this can't be/isn't true).

[ThomasT]

With LR nowhere near those results, which are 100% consistent with QM.

Don't make me come and beat you up! :smile:Well actually, at the risk of personal injury, I feel compelled to say that the predictions of the most sophisticated LRHV formulations aren't that far from the qm predictions. That is, they're more or less in line, just as the predictions of qm are, with what one might expect given the principles of classical optics. That is, the angular dependence is similar.

Nevertheless, the predicted results are still measurably different. So, I don't know what zonde is saying. I currently believe that the LR program is more or less dead, and I don't think that improving the detection efficiency will resurrect it, because, as I mentioned, even assuming 100% efficiency the qm predictions are still different from the LRHV predictions.

IMO, the stuff by Zeilinger et al. about the importance of closing the detection loophole is just a bunch of BS aimed at procuring contracts and grants from more or less ignorant investors. But then, what do I know?

We'll see what zonde has to say about this.

[ThomasT]

I thought the point of these experiments was to prove that objective reality doesn't exist, until we start to detect/measure it (although, this can't be/isn't true).I don't think that that's the point of the experiments -- although some otherwise very wise commenters have said this.

The experiments demonstrate that a certain class of models of quantum entanglement that conform to certain explicit expressions/forms of local realism are incapable of correctly predicting the results of entanglement preparations.

What this means wrt objective reality is still a matter of some dispute. However, the mainstream view seems to be that the experiments don't inform wrt objective reality, but only wrt the specific restrictions on the formulation of models of quantum entanglement.

So, if you're a local realist, then you can still be a local realist and neither qm nor experimental results contradict this view. It's just that you can't model entanglement in terms of the hidden variables that determine individual results -- because coincidental detection isn't determined by the variables that determine individual detection.

[zonde]

Ok, but calculations assuming 100% efficient detection also indicate a measurable difference between qm predictions and LRHV predictions. So, I'm not sure what you're asserting wrt local realism.
Can you say what does it means from perspective of QM that there is 100% efficient detection? Does it have anything to do with wave particle duality?
Then we can speak about calculations assuming 100% efficient detection.

I'm not sure what you mean by this. Afaik, wrt the way I learned what I remember of qm :uhh:, it doesn't have to do with single photon detections, but only with photon flux wrt large number of trials. And isn't this is also what LRHV models of entanglement are concerned with predicting?
There is difference between statistical ensemble and physical ensemble.
In statistical ensemble you have independent events and all statistics you calculate from statistical ensemble you can apply to individual events as probabilities.

Now what I mean is that QM predictions are not accurate for statistical ensemble of single photon events. It's gives basically the same as effect as making photons distinguishable at double slit i.e. no interference pattern.

Ok, I think we agree on this. So exactly what are you referring to when you speak of "local realism"?
I am referring to kind of (physical) ensemble interpretation. Or more exactly I mean that interference is effect of unfair sampling. I have tried to put together things from discussion into single coherent piece here (http://vixra.org/abs/1109.0052).

[DevilsAvocado]

... I have tried to put together things from discussion into single coherent piece here (http://vixra.org/abs/1109.0052).

Well, you ignore my question on mainstream science, and then you link to a "paper" on a site that has this policy:
ViXra.org is an e-print archive set up as an alternative to the popular arXiv.org service owned by Cornell University. It has been founded by scientists who find they are unable to submit their articles to arXiv.org because of Cornell University's policy of endorsements and moderation designed to filter out e-prints that they consider inappropriate.

ViXra is an open repository for new scientific articles. It does not endorse e-prints accepted on its website, neither does it review them against criteria such as correctness or author's credentials.

Nice.

[ThomasT]

Can you say what does it means from perspective of QM that there is 100% efficient detection? Does it have anything to do with wave particle duality? Then we can speak about calculations assuming 100% efficient detection.Regarding the assumption of 100% efficient detection, afaik, when qm and proposed LRHV models of entanglement are compared, this comparison is usually done on the basis of calculations "in the ideal", in order to simplify things and make the comparison more clear.

Anyway, what I was getting at had to do with my current understanding that qm and LRHV (wrt models that are clearly, explicitly local and realistic, ie., Bell-type models) entanglement predictions are necessarily different. And, if so, then if "local realism holds" for quantum entanglement, then it follows that qm doesn't hold for quantum entanglement.

But you noted in post #65 that "QM predictions are tested and they work for inefficient detection case". So, apparently, you're saying that qm holds for quantum entanglement. And what I surmise from this is that you think that there's an LRHV formulation of quantum entanglement that agrees with qm.

This is what I'm not clear about. Are you advocating an LRHV model that's compatible with qm, or are you saying something else?

Let me take a guess. There's an unnacceptable disparity between individual detection efficiency and coincidental detection efficiency. What you're saying is that as these converge, then qm and LRHV correlation ranges will converge, and the correlation curves will become more approximately congruent. Is that what you're saying?

... what I mean is that QM predictions are not accurate for statistical ensemble of single photon events.If by "statistical ensemble of single photon events" you're referring to either an accumulation of individual results or single individual results taken by themselves, then Bell has already shown that qm and local realism are compatible wrt this.

But you said in post #65 that if local realism holds for quantum entanglement "it would mean that QM predictions are incorrect for the limit of single photon." And you seem to be saying in post #66 that you agree with the idea that qm doesn't apply to single particles.

I don't know what that means. Don't we already know that neither qm nor LRHV models can predict the occurance of single photon detections in optical Bell tests (except when the angular difference of the polarizers is either 0 or 90 degrees and the result at one end is known)? For all other settings, the probability of individual detection is always 1/2 at both ends, ie., the results accumulate randomly.

I don't know if I'm parsing correctly what you're saying. Hopefully this post will enable further clarification. And thanks for the link to your paper. Maybe it will clear things up for me.

[zonde]

Regarding the assumption of 100% efficient detection, afaik, when qm and proposed LRHV models of entanglement are compared, this comparison is usually done on the basis of calculations "in the ideal", in order to simplify things and make the comparison more clear.

Anyway, what I was getting at had to do with my current understanding that qm and LRHV (wrt models that are clearly, explicitly local and realistic, ie., Bell-type models) entanglement predictions are necessarily different. And, if so, then if "local realism holds" for quantum entanglement, then it follows that qm doesn't hold for quantum entanglement.

But you noted in post #65 that "QM predictions are tested and they work for inefficient detection case". So, apparently, you're saying that qm holds for quantum entanglement. And what I surmise from this is that you think that there's an LRHV formulation of quantum entanglement that agrees with qm.

This is what I'm not clear about. Are you advocating an LRHV model that's compatible with qm, or are you saying something else?

Let me take a guess. There's an unnacceptable disparity between individual detection efficiency and coincidental detection efficiency. What you're saying is that as these converge, then qm and LRHV correlation ranges will converge, and the correlation curves will become more approximately congruent. Is that what you're saying?
I am not sure what do you mean with "unnacceptable disparity between individual detection efficiency and coincidental detection efficiency".

So let me say that I am advocating QM interpretation that is compatible with local realism.

QM is rather flexible about it's predictions. For example if we take double slit experiment. Let's say we perform double slit experiment and do not observe any interference pattern. We can say that light was not coherent (basically that means absence of interference) or that two photon paths were distinguishable (another term that means absence of interference).
So QM still holds even if we do not observe any interference.

In similar fashion we can claim (if we want) that QM still holds even if quantum entanglement correlations are reduced to classical correlations in case of efficient detection. Here with classical correlations I mean product of probabilities not Bell's model.

If by "statistical ensemble of single photon events" you're referring to either an accumulation of individual results or single individual results taken by themselves, then Bell has already shown that qm and local realism are compatible wrt this.

But you said in post #65 that if local realism holds for quantum entanglement "it would mean that QM predictions are incorrect for the limit of single photon." And you seem to be saying in post #66 that you agree with the idea that qm doesn't apply to single particles.

I don't know what that means. Don't we already know that neither qm nor LRHV models can predict the occurance of single photon detections in optical Bell tests (except when the angular difference of the polarizers is either 0 or 90 degrees and the result at one end is known)? For all other settings, the probability of individual detection is always 1/2 at both ends, ie., the results accumulate randomly.
I am saying that there is difference between statistical "sum" of 1000 experiments with single photon and single experiment with 1000 photons. If first case you can't get interference but in second case you can.

[DevilsAvocado]

So let me say that I am advocating QM interpretation that is compatible with local realism.

Wow! :surprised This is getting better and better!!

Pleeease, what is the name of this "QM interpretation" that refutes the predictions of QM!? :bugeye:

QM is rather flexible about it's predictions.

Really?? :eek: That’s not what I’ve heard... I have always gotten the impression that QM is one of the most accurate physical theories constructed thus far?? Quod Erat Demonstrandum... within ten parts in a billion (10−8).

I am saying that there is difference between statistical "sum" of 1000 experiments with single photon and single experiment with 1000 photons. If first case you can't get interference but in second case you can.

This must be the gem of everything you’ve claimed this far! I’m stunned!! :yuck:

I think you’re in for a Noble (sur)Prize if you can show that throwing ONE DICE 1000 times gives a different outcome compared to throwing 1000 dices ONE TIME!!! http://planetsmilies.net/confused-smiley-17512.gif:surprisedhttp://planetsmilies.net/confused-smiley-17512.gif

[ThomasT]

I am not sure what do you mean with "unnacceptable disparity between individual detection efficiency and coincidental detection efficiency".
In post #59 you quoted from Ultra-bright source of polarization-entangled photons (http://arxiv.org/abs/quant-ph/9810003) this,
After passing through adjustable irises, the light was collected using 35mm-focal length doublet lenses, and directed onto single-photon detectors — silicon avalanche photodiodes (EG&G #SPCM’s), with efficiencies of ~ 65% and dark count rates of order 100s−1
and this,
The collection irises for this data were both only 1.76 mm in diameter – the resulting collection efficiency (the probability of collecting one photon conditioned on collecting the other) is then ~ 10%.
and then said,
So while detector efficiency is around 65% coincidence rate was only around 10%. And it is this coincidence rate that is important if we want to speak about closing detection loophole..
I supposed that you're saying that the gap between detector efficiency and coincidence rate is due to the efficiency of the coincidence mechanism of the experimental setup, and that as the efficiency of coincidence counting increases, and therefore as detector efficiency and coincidence rate converge, then the predicted (and recorded) qm and LRHV correlation ranges will converge -- thus making the qm and LRHV correlation curves more approximately congruent.

Which would be in line with your statement that,
... let me say that I am advocating QM interpretation that is compatible with local realism.

... we can claim (if we want) that QM still holds even if quantum entanglement correlations are reduced to classical correlations in case of efficient detection. Here with classical correlations I mean product of probabilities not Bell's model.Ok, so it seems that what you're saying is that given maximally efficient detection (both wrt individual and coincidental counts), then quantum entanglement correlations will be the same as classical correlations. Is that what you're saying?

If so, then can't one just assume maximally efficient detection and calculate whether qm and classical models of entanglement give the same correlation coefficient?

I am saying that there is difference between statistical "sum" of 1000 experiments with single photon and single experiment with 1000 photons.I don't understand exactly what you mean by this, and how it pertains to what seems to be your contention that quantum entanglement should "reduce to" classical correlations given maximal coincidental detection efficiency. So if you could elaborate, then that would help.

Is this paper, Quantum entanglement and interference from classical statistics (http://arxiv.org/abs/0809.2671) relevant to what you're saying? (The author, C. Wetterich, also has other papers at arxiv.org that might pertain.)

And now I'm actually going to read your paper. I just wanted to hash out what you're saying in a minimally technical way first, because I would think that you would want to be able to eventually clearly explain your position to minimally educated, but interested/fascinated laypersons such as myself. :smile:

[zonde]

I supposed that you're saying that the gap between detector efficiency and coincidence rate is due to the efficiency of the coincidence mechanism of the experimental setup, and that as the efficiency of coincidence counting increases, and therefore as detector efficiency and coincidence rate converge, then the predicted (and recorded) qm and LRHV correlation ranges will converge -- thus making the qm and LRHV correlation curves more approximately congruent.
I am certainly not saying that gap between detector efficiency and coincidence rate is due to the efficiency of the coincidence mechanism.
Actually I was not saying anything about the reasons for that difference. What I said is that we need high coincidence rate relative to single photon detections to avoid the need for fair sampling assumption (to close detection loophole).

The reason for that gap roughly is that a lot of photons hitting two detectors are not paired up. So we have photon losses that are not symmetrical and if they happen after polarization analyzer they are subject to fair sampling assumption. And judging by scheme of experiment this is exactly the case for Kwiat experiment. There apertures and interference filters are placed after polarization analyzer.


Ok, so it seems that what you're saying is that given maximally efficient detection (both wrt individual and coincidental counts), then quantum entanglement correlations will be the same as classical correlations. Is that what you're saying?

If so, then can't one just assume maximally efficient detection and calculate whether qm and classical models of entanglement give the same correlation coefficient?
I say that in case of efficient detection correlations of polarization entangled photons approach this rule:
P=\frac{1}{2}(cos^2(a)cos^2(b)+sin^2(a)sin^2(b))
and it is classical.

I don't understand exactly what you mean by this, and how it pertains to what seems to be your contention that quantum entanglement should "reduce to" classical correlations given maximal coincidental detection efficiency. So if you could elaborate, then that would help.
By this I mean that you can observe photon interference only if you observe many photons. You detect some photons and effect of interference is that you detect more photons on average when there is constructive interference (many photons of ensemble interact with experimental equipment in a way that makes more photons detectable) and less photons when there is destructive interference.
Connection with quantum entanglement is that measurement basis of polarization entangled photons determines if you are measuring photon polarization (H/V basis) or you are measuring interference between photons of different polarizations (+45/-45 basis) i.e. mechanism behind correlations changes as you rotate polarization analyzer.
If interference disappears (efficient detection) then correlations are maximal in H/V basis and are zero in +45/-45 basis.

Is this paper, Quantum entanglement and interference from classical statistics (http://arxiv.org/abs/0809.2671) relevant to what you're saying? (The author, C. Wetterich, also has other papers at arxiv.org that might pertain.)
I do not see that it is relevant. My judgment is simple - you can speak about viable classical model for quantum entanglement only if you make use of unfair sampling. I didn't see anything like that in this paper so I say it should be faulty.