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

  1. Jan 13, 2010 #1
    Thank you for the suggestion. I should say this is the first thread I am starting since I joined physics forums four years ago.

    So this thread has branched from another one -"Photon entanglement and fair sampling assumption". I noted there that, on the one hand, so far no experiments demonstrating violations of the Bell inequalities have been free from some significant loopholes, such as the detection loophole and the locality loophole, on the other hand, the proof of the Bell theorem uses two mutually contradictory results/assumptions of quantum theory: unitary evolution and the projection postulate. Therefore, I argued, the Bell theorem is on a shaky ground both on the theoretical and on the experimental level. I was not taking sides with or against local realism, but pointed out that it has not been ruled out, however prevalent the opposite point of view can be.

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

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


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

    I'll try to reply to other DrC's remarks later.
     
    Last edited by a moderator: Apr 24, 2017
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  3. Jan 13, 2010 #2

    ZapperZ

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    I had just posted this reference in another thread, but maybe you should read it to if you're not aware of it.

    M.D. Reid et al. Rev. Mod. Phys. v.81, p.1727 (2009).

    If you think that none of the violation of EPR/Bell, GHZ, CHSH, Leggett, etc. inequalities constitutes a violation of local realism, then you ARE proposing something that is not already established. This means that you need to back this up with a published work to support that you are not proposing your own personal theory.

    Zz.
     
  4. Jan 13, 2010 #3

    DrChinese

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    There may be a measurement problem, but I doubt it is the problem you think it is. It is kind of like the problem of why there is more matter in the universe than anti-matter. Something it would be nice to understand, but not something that is actually in contradiction to theory.

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

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

    So this is a direct statement that the idea left by EPR - that a local realistic explanation could mimic QM - was untenable. If you advance a local realistic theory, it WILL make predictions different than QM.
     
  5. Jan 13, 2010 #4
    Dear ZapperZ,

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

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

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

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

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

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

    So there is a consensus among experts that existing experiments do not rule out local realism (and I suspect you know that). If you state the opposite (although I am almost sure you know better than that), then you are proposing your own personal theory. But you're a mentor, so that must be OK anyway:-)
     
  6. Jan 13, 2010 #5

    DrChinese

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    You are misreading the quotes to your own position, there is NO SUCH CONSENSUS. Do you think there are any loophole free experiments for gravity? Or the speed of light in a vacuum? These are subjects that are in fact debated. However, the consensus is that a) we have a good theory for gravity; b) we know the speed of light in a vacuum; and c) Bell's Theorem is valid.

    Read Genovese's statement again (which by the way is 5 years old), he uses 3 adjectives (conclusive, absolutely, uncontroversial) because there are some people - perhaps you are one - who cannot accept evidence that contradicts your world view. You are actually presenting NOTHING in support of your position.

    In probably 500+ papers in the past year alone, there are references to Bell's Theorem and EPR. These are accepted. The work on the so-called loopholes is more in analogy to finding the 5th decimal place to a number we already know to 4 decimal places. There are only a handful of working physicists still working on local realistic theories today, and that is precisely because of the convincing nature of the evidence.

    A better reference from you would show a specific case in which a quantum mechanical prediction for an entangled system was wrong, and the local realistic counterpart was right.
     
  7. Jan 14, 2010 #6
    DrChinese, let us try to sort it out. First, let me emphasize that my statement on the contradiction between unitary evolution (UE) and the projection postulate (PP) is not new, furthermore, it was published in peer-reviewed journals. Therefore, it’s not some independent research and thus does not break the forum’s rules. To prove this, I don’t need to prove that QM is generally considered self-contradictory, I just need to give a reference: L.E. Ballentine, Found. Phys., vol. 20, p. 1329 (1990). Of course, that does not necessarily mean Ballentine is correct. However, you don’t seem to challenge the statement that UE and PP are mutually contradictory (if you do, please advise). My reasoning was that PP introduces irreversibility, whereas UE cannot produce irreversibility.

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

    I’ll try to reply to your other remarks later.
     
  8. Jan 14, 2010 #7

    ZapperZ

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    This is utterly confusing.

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

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

    I've already address the latter in a previous post when I complaint that people like you can't seem to accept that both the locality loophole and the detection loophole have been closed separately, and that the SHEER VOLUME OF EVIDENCE alone from each one of them make for a very compelling indication for ruling out local realism.

    As for the former, each time an argument is presented on the logical deduction of Bell theorem as not being able to test local realism, it has been shot down. The most recent one, from a month ago, appeared in AJP. A paper by Guy Blaylock argued that both the EPR paradox and Bell's inequality fall short in testing the issue of locality[1]. This was summarily shot down in the SAME issue[2].

    THIS is what I wanted you to do, i.e. publish your argument regarding your stand that all of these quantitative tests of local realism doesn't actually test local realism or rule them out. All of the EPR-type test papers have argued for that, and yet, you haven't written either a rebuttal or any papers to counter that. The fact that such an argument still may qualify as a paper, even if it is in AJP, implies that this is a new and not generally accepted argument, and thus, should NOT be done in PF until your proposition has been published.

    Zz.

    [1] G. Blaylock, Am. J. Phys. v.78, p.111 (2010).
    [2] T. Maudlin, Am. J., Phys. v.78 p.121 (2010).
     
  9. Jan 14, 2010 #8

    zonde

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

    From G.Weihs et al paper:
    "While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."
     
  10. Jan 14, 2010 #9

    ZapperZ

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

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

    Zz.
     
  11. Jan 14, 2010 #10

    zonde

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    Basically you are saying that the problem is not in theory but rater that we have not yet done what should be possible do based on what theory says, right?
     
  12. Jan 14, 2010 #11

    ZapperZ

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

    Zz.
     
  13. Jan 14, 2010 #12

    DrChinese

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

    Please note the words he uses: "however unlikely". That pretty much sums it up. A lot of things are unlikely but possible. The sun could burn out tomorrow. That does not mean that scientists are unsure whether the sun will shine tomorrow. So, let's use language fairly. Bell is accepted, and so are Bell test results.
     
  14. Jan 14, 2010 #13

    why the glue ?

    LOCAL REALISM ruled out?

    "which concept, locality or realism, is the problem?"
     
  15. Jan 14, 2010 #14
    none.
    they are just inconsistent
    local non-realistic theory or non-local realistic theory (or local realistic theory with backward causality - TI)
     
  16. Jan 14, 2010 #15

    DrChinese

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    Welcome to PhysicsForums, yoda jedi!

    It is not clear whether it is realism, locality, or both which are ruled out. We simply know from Bell's Theorem and others, coupled with experimental verification, that at least one does not hold.
     
  17. Jan 14, 2010 #16
    The http://arxiv.org/abs/0908.3408" [Broken] won't be ruled out anytime soon.
     
    Last edited by a moderator: May 4, 2017
  18. Jan 14, 2010 #17

    Matterwave

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    It could also be that induction fails. But if we do that, we would hafta get rid of almost all of science, so let's not.
     
  19. Jan 15, 2010 #18
    Dear ZapperZ,
    I am afraid you may have misunderstood me. That means I was not clear enough. My reasoning was quite different. I concede that the Bell theorem (BT) per se rules out local realism (LR) (assuming that all predictions of standard QT are correct, and with the standard caveat on superdeterminism). I also concede that no LR theory can reproduce ALL results of standard quantum theory (QT). However, I argued that this does not mean LR is ruled out as 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP). Indeed, you cannot reasonably argue that the failure to absorb contradictions rules out LR. I argue that it’s good for LR that it cannot absorb them, and it’s bad for standard QT that it can. Further, as we cannot have both UE and PP as precise results, I expressed my opinion that PP cannot be precise, while it looks like UE is indeed precise.
    Again, this is an unfortunate misunderstanding. Looks like I was not clear enough again. In fact, I concede that if BT ruled out LR, then loophole free experiments would indeed rule out LR (I won’t repeat the caveat on determinism in the future), because I concede that the Bell inequalities cannot be violated in any LR theory.

    Let me summarize. I think you’ll agree that to rule out LR you necessarily need two things together: 1) mathematical proof that some results predicted by QT cannot be reproduced by any LR; 2) experimental proof that one of such predictions is indeed correct. I argue that, on the one hand, there is no such mathematical proof, as a proper mathematical proof cannot use two mutually contradictory assumptions, and there is no such experiment. Therefore, I argue, LR has not been ruled out so far. Furthermore (and here I speculate), I suspect that loophole free experiments would have ruled out UE, so I suspect our points of view are much closer than it looks, as it seems we both swear by unitary evolution.
    ZapperZ, I further concede that the loopholes have been closed separately. This is enough for you (although I gave my reasons to believe you’re not quite happy with that), but that is not quite enough for Shimony, Zeilinger and other experts, and it’s definitely not enough for me. Recently I offered you (okay, here I am cutting some corners) to indicate the difference between your reasoning and the following one: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sum of angles of a quadrangle and a triangle on a sphere are not equal to 180 degrees. I may have missed something, but I don’t think I’ve heard from you about that. It’s a theorem, for crying out loud! The same is true for BT: you have not even started to test it until you have made sure ALL its assumptions are fulfilled, and fulfilled simultaneously!
    As I concede that the Bell inequalities cannot be violated in LR theories, the papers you quote do not seem relevant.
    When you say such things, I feel somewhat confused. I had no intention to break the forum’s rules. Furthermore, to be on the safe side, I obtained a mentor’s permission to start this thread. If, however, you tell me, in your capacity of mentor, that my posts are inappropriate, I’ll certainly obey and stop discussing this topic. If, however, you, as a mentor, believe that my posts are appropriate, then the reference to the forum rules seems somewhat irrelevant.
    On the other hand, I believe everything or almost everything I am saying was previously published by others in peer-reviewed journals, so I honestly don’t know what I could publish (even if I wanted to forget that I am mostly following nightlight’s reasoning).
     
  20. Jan 15, 2010 #19

    ZapperZ

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

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

    Zz.
     
    Last edited: Jan 15, 2010
  21. Jan 15, 2010 #20

    DrChinese

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

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

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

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

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

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