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

by akhmeteli
Tags: entanglement, local, photon, realism, ruled
P: 3,179
 Quote by bohm2 Lecture from lead author JD Bancal from Perimeter Institute: "[...] we exclude any possible explanation of quantum correlations in term of finite-speed influences" http://pirsa.org/displayFlash.php?id=11110145
That reminds me of De Raedt et al who more than agreed with that.
As a reminder:
 A violation of the Extended Boole-Bell inequalities cannot be attributed to influences at a distance
P: 576
 Quote by ZapperZ The point here is that this thread appears to indicate that even IF all the loopholes are closed (and I will make MY prediction here that in the near future, say within 3 years, ALL the loopholes will be closed in one single experiment), the intrinsic nature of the theory will STILL not falsify local realism.
Three years have passed. As far as I know, all the loopholes have not been closed in one single experiment. For example, reporting some further progress in a recent article http://arxiv.org/abs/1212.0533 , Zeilinger e.a. still admit that “The realization of an experiment that is free of all three assumptions – a so-called loophole-free Bell test – remains an important outstanding goal for the physics community”.

I am writing this without any Schadenfreude. I do appreciate that a loophole-free experiment can be performed any moment now. It looks like the race to conduct the first experiment of this kind is really fierce. E.g., the following quote is interesting (SCIENCE, VOL 331, P. 1380 (2011)): “Zukowski thinks the race to close all the loopholes simultaneously will soon be over. “Conservatively, it could take another 5 years to complete, but it could also be done tomorrow,” he says. “We’re at the stage where everyone is scared to read their competitors’ papers, in case they find they have been beaten. The only real question is: Who will win?””

I also had this impression of a fierce race listening to talks on quantum foundations experiments at several conferences last year. On the other hand, some experimentalists admitted (typically, not in their official talks:-) ) that they encounter some formidable challenges.

So I am just trying to say that these three years since the start of this thread have demonstrated again that it is extremely difficult to demonstrate violations of the genuine Bell inequalities. Will they be demonstrated by the fiftieth anniversary of the Bell’s article next year? Or ever? My prediction is “no”. But I may be mistaken.
P: 141
 Quote by Gordon Watson The point is that particles in a singlet state have, both theoretically and experimentally, a higher correlation than you seem to allow (or expect) in your work.
I guess you're just bashing your response out, so this is not intended to be a substantive criticism, but it's not a correlation that's higher, it's a sum of absolute values of a sum and a difference between four different correlations $|A-B|+|C+D|$ (at least, that's what it is in the CHSH formulation, in no case is the difficulty for local realism that a correlation coefficient simpliciter is too high).
P: 576
 Quote by Gordon Watson The point is that particles in a singlet state deliver, both theoretically and experimentally, a higher expectation value* than you seem to allow (or expect) in your work.
Dear Gordon Watson,

I tried to explain in my post 753 in this thread why I cannot agree with you.
P: 576
 Quote by Gordon Watson OK; disagreeing with me is no big deal. BUT I'm NOT aware of any rational quantum physicist that agrees with you: "... that there are some reasons to believe Bell inequalities cannot be violated either in experiments or in quantum theory." [Cited above.]
So Santos, Marshall, nightlight are not rational quantum physicists, in your book. They are in mine. Let me add that I gave those "reasons" and properly published them (although I just repeated other people's arguments, as far as those "reasons" are concerned).

Another thing: "the foundations of quantum mechanics ... remain hotly debated in the scientific community, and no consensus on essential questions has been reached." (Schlosshauer, Kofler, Zeilinger, http://arxiv.org/abs/1301.1069 ). So disagreement is a "new normal" for quantum foundations.
P: 79
 Quote by Gordon Watson Using your terms to conclude re my position (vis-a-vis yours), I am satisfied that: 1. Bell inequalities are repeatedly violated by experiment. 2. Bell inequalities are certainly violated by quantum theory. 3. Except for their motivation toward better experiments, the remaining loopholes are of no consequence. ..
Agree. 1 and 2 are facts, and 3 seems to me to be a much more reasonable position than that taken by the loophole people.
P: 576
 Quote by Gordon Watson Using your terms to conclude re my position (vis-a-vis yours), I am satisfied that:
You are satisfied, I'm not.

 Quote by Gordon Watson 1. Bell inequalities are repeatedly violated by experiment.
Not unless you ignore the loopholes.

 Quote by Gordon Watson 2. Bell inequalities are certainly violated by quantum theory.
Not unless you use as assumptions mutually contradictory postulates of standard quantum theory, such as unitary evolution and the projection postulate. However, if you use mutually contradictory assumptions, you can get any conclusion, however absurd.

 Quote by Gordon Watson 3. Except for their motivation toward better experiments, the remaining loopholes are of no consequence.
This is an opinion, not a fact.
P: 3,179
 Quote by nanosiborg [..] position [..] taken by the loophole people.
Who are such "loophole people"? It is suggestive of people who stick to an opinion against all odds, and I would be surprised if anyone here identifies with such a position - in which case it's just a strawman (it's a derogative term, used to indicate a means of escape or evasion).
P: 79
 Quote by harrylin Who are such "loophole people"?
People who think that a loophole-free test will change the current situation, which is that qm predictions are in line with results and violate BI, and lhv predictions are not in line with results.
P: 576
 Quote by nanosiborg People who think that a loophole-free test will change the current situation, which is that qm predictions are in line with results and violate BI, and lhv predictions are not in line with results.
Whether I am one of those "loophole people" or not, I respectfully disagree with your assessment of the current situation, e.g., with the following phrase: "lhv predictions are not in line with results." As long as there are loopholes in experiments (and there have been no loophole-free experiments so far), the results of the experiments cannot rule out all lhv theories, so at least some lhv theories' predictions are in line with the results.
P: 79
 Quote by akhmeteli As long as there are loopholes in experiments (and there have been no loophole-free experiments so far), the results of the experiments cannot rule out all lhv theories ...
Strictly speaking, this is correct. But I think the evidence is overwhelming that if a loophole-free test were done, then qm would correctly predict the results and lhv would not.

 Quote by akhmeteli ... so at least some lhv theories' predictions are in line with the results.
Assumptions are required because of the inability to close all loopholes in the same test. So far, given the (reasonable, imo) assumptions used by the testers, qm agrees with experiment and lhv doesn't.

The incompatibility between qm and lhv has been mathematically proven. They necessarily predict a different correlation between θ and rate of coincidental detection. So, if qm is correct, then (Bell) lhv models of quantum entanglement are ruled out.

I'm betting that qm will continue to be confirmed, even in a loophole-free test.
P: 576
 Quote by nanosiborg Strictly speaking, this is correct. But I think the evidence is overwhelming that if a loophole-free test were done, then qm would correctly predict the results and lhv would not.
This is an opinion, not a fact. Somebody believes the evidence is overwhelming, somebody believes there is no evidence, as there have been no loophole-free experiments. How do you like the following "overwhelming evidence" that planar Euclidean geometry (PEG) is wrong (I already offered it in this thread)? PEG predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with high confidence that the sum of angles of a quadrangle and the sum of angles of a triangle on a sphere are not equal to 180 degrees. The obvious "loopholes" will certainly be closed simultaneously in future experiments:-)

 Quote by nanosiborg Assumptions are required because of the inability to close all loopholes in the same test. So far, given the (reasonable, imo) assumptions used by the testers, qm agrees with experiment and lhv doesn't.
My question is: what assumption is more reasonable: local realism or, say, fair sampling? Apparently, you'd vote for the latter one, I would vote for the former one. So who's right? I believe so far this is just a matter of opinion.

 Quote by nanosiborg The incompatibility between qm and lhv has been mathematically proven. They necessarily predict a different correlation between θ and rate of coincidental detection. So, if qm is correct, then (Bell) lhv models of quantum entanglement are ruled out.
I agree, the Bell theorem proves incompatibility between standard quantum theory and local realism. I argue though that this is not a problem for local realism, as, strictly speaking, standard quantum theory is incompatible with itself (I have in mind the notorious problem of measurements in quantum theory), so, strictly speaking, it cannot be completely correct. To prove incompatibility of standard quantum theory and local realism, you need to prove that the Bell inequalities can be violated in quantum theory. To this end, you need to use two mutually contradictory postulates of standard quantum theory: unitary evolution and, say, the projection postulate.

 Quote by nanosiborg I'm betting that qm will continue to be confirmed, even in a loophole-free test.
Strictly speaking, this phrase just attests to the strength of your opinion, not to its correctness. I don't believe local realism will be ruled out in loophole-free experiments, but again, this is just my opinion, not a fact. Maybe we should just wait and see.
P: 576
 Quote by Gordon Watson Andy, While we're waiting, please, would you mind spelling out what you mean by "local realism"? Accepting that by "local" you mean "Einstein-local", maybe we could just focus on what "realism" means to you, please?
Locality, in my book, means that no effect can have its cause anywhere beyond its past light-cone. I guess this is what you call "Einstein-local".

Realism, in my book, is not the realism of the EPR article, i.e. I don't believe that, say, a particle has definite values of coordinates, momentum, spin projections, etc., whether the relevant observables are measured or not. You may say that I do not seek noncontextual hidden variables. The version of realism that I accept is contextual: any state can be described by some set of parameters that uniquely define the state's evolution. I would not call those parameters "hidden variables", as, say, in the models of my articles, they are not exactly hidden: they are the potentials of the electromagnetic fields and their derivatives. This version is "contextual" as the set of parameters must describe the relevant instruments as well.
P: 79
 Quote by akhmeteli My question is: what assumption is more reasonable: local realism or, say, fair sampling? Apparently, you'd vote for the latter one, I would vote for the former one. So who's right? I believe so far this is just a matter of opinion.
Yes, I'd vote for the latter one. We could argue about the merits of our apparently different processing of certain articles, but I prefer to just wait for a loophole-free test.

What do you think is the likelihood of a loophole-free test in the foreseeable future?

 Quote by akhmeteli I agree, the Bell theorem proves incompatibility between standard quantum theory and local realism. I argue though that this is not a problem for local realism, as, strictly speaking, standard quantum theory is incompatible with itself (I have in mind the notorious problem of measurements in quantum theory), so, strictly speaking, it cannot be completely correct. To prove incompatibility of standard quantum theory and local realism, you need to prove that the Bell inequalities can be violated in quantum theory. To this end, you need to use two mutually contradictory postulates of standard quantum theory: unitary evolution and, say, the projection postulate.
There's no measurement problem of the sort you mention (ie., qm being incompatible with itself due to contradictory dynamical laws or postulates) with a minimalist statistical interpretation. So, in the minimalist view, if a loophole-free test affirms qm, then local realism (at least in the form of Bell lhv models) will be definitively ruled out.
P: 3,179
 Quote by nanosiborg Strictly speaking, this is correct. But I think the evidence is overwhelming that if a loophole-free test were done, then qm would correctly predict the results and lhv would not.[..] [..] What do you think is the likelihood of a loophole-free test in the foreseeable future?
I wonder if such a conclusive test will be possible; the failure to accomplish that feat in the course of decades suggests to me that it may be a law of nature that such a test is not possible (similar to the relativity and uncertainty principles).
P: 576
 Quote by nanosiborg What do you think is the likelihood of a loophole-free test in the foreseeable future?
I don't know. Just don't have enough information. Some knowledgeable people believe such a test is imminent, they say something like "in a year or two". I won't be surprised though if such a test will take much, much more time. Whenever it happens though, I don't expect any violations in a loophole-free test.

 Quote by nanosiborg There's no measurement problem of the sort you mention (ie., qm being incompatible with itself due to contradictory dynamical laws or postulates) with a minimalist statistical interpretation.
I did not consider the minimalist statistical interpretation, just standard quantum theory. However, based on the discussion of some other interpretations (such as Bohmian one) in this thread, I tend to think that if there are no contradictions in an interpretation, it is either impossible to prove that the Bell inequalities can be violated, or predictions of the interpretation differ from those of standard quantum theory, making dubious the experimental status of the interpretation.

 Quote by nanosiborg So, in the minimalist view, if a loophole-free test affirms qm, then local realism (at least in the form of Bell lhv models) will be definitively ruled out.
Irrespective of any interpretation, I agree that loophole-free experimental demonstration of violations would make a local realist's life much more difficult, although "definitively" would be a strong word even then - e.g., there would still be a possibility of superdeterminism.
P: 79
 Quote by akhmeteli I don't know. Just don't have enough information. Some knowledgeable people believe such a test is imminent, they say something like "in a year or two". I won't be surprised though if such a test will take much, much more time. Whenever it happens though, I don't expect any violations in a loophole-free test.
Whatever the results it will be exciting when (if) it happens.

 Quote by akhmeteli I did not consider the minimalist statistical interpretation, just standard quantum theory.
I was thinking of the minimalist statistical interpretation as being standard quantum theory.

 Quote by akhmeteli Irrespective of any interpretation, I agree that loophole-free experimental demonstration of violations would make a local realist's life much more difficult, although "definitively" would be a strong word even then - e.g., there would still be a possibility of superdeterminism.
I consider superdeterminism (a metaphysical conspiracy theory) to be an unacceptable stretch anyway. Given a loophole-free test that confirms qm and falsifies lhv I don't see superdeterminism being taken seriously by anybody. I mean, local realists will have to admit, if that happens, that their program has been definitively refuted and Bell lhv models of quantum entanglement are definitively ruled out.
P: 576
 Quote by nanosiborg I was thinking of the minimalist statistical interpretation as being standard quantum theory.
If this interpretation adopts both unitary evolution (UE) and the projection postulate (PP) of standard quantum theory, it also adopts its contradictions. If you believe you have a solution to the problem of measurements in standard quantum theory... Well, congratulations... Good luck "selling" your solution to physics community... If, however, this interpretation does not adopt UE and PP, it's not standard quantum theory. Moreover, it would be difficult, if not impossible, to prove that there can be violations in this interpretation.

 Quote by nanosiborg I consider superdeterminism (a metaphysical conspiracy theory) to be an unacceptable stretch anyway. Given a loophole-free test that confirms qm and falsifies lhv I don't see superdeterminism being taken seriously by anybody. I mean, local realists will have to admit, if that happens, that their program has been definitively refuted and Bell lhv models of quantum entanglement are definitively ruled out.
I agree that superdeterminism does not look good. However, I don't know how to refute 't Hooft's reasoning in favor of superdeterminism (by the way, 't Hooft is not "anybody"): "if you believe in determinism, you have to believe it all the way." (http://arxiv.org/abs/1112.1811)

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