Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Bell's Inequality: Must we ditch locality, realism or something else?

  1. Sep 18, 2011 #1
    Bell's theorem is generally thought to show that the world cannot be both local and real.

    http://en.wikipedia.org/wiki/Bell's_theorem

    In simplistic terms, Bell derives an inequality which allegedly must be satisfied if the world is both local and real. In practice, it is found in numerous experiments that Bell's inequality is actually violated - leading to the conclusion that either the locality assumption, or the reality assumption, (or both) must be rejected.

    But the following paper allegedly provides a counterexample - a hypothetical situation which involves assumptions that are most definitely both local and real, and yet the scenario described would also violate Bell-type inequalities if analysed in a manner similar to that used for Bell's theorem.

    http://rugth30.phys.rug.nl/pdf/aipqo0-KRM.pdf [Broken]

    Conclusion: Violation of Bell-type inequalities does not necessarily always imply that either locality or realism assumptions are incorrect?

    Comments?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 18, 2011 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Please provide the exact citation on where this paper was published.

    Zz.
     
  4. Sep 18, 2011 #3
    Appears to be a conference proceedings paper, http://rugth30.phys.rug.nl/dlm/Down7535load.htm [Broken], which is typically at best barely referreed - however the authors have published papers on related topics in journals. I would have to spend far too much time wading through the paper to understand it, never mind formulate an opinion, but I personally would be amazed if the authors have uncovered something profound that has not already been considered and discarded.
     
    Last edited by a moderator: May 5, 2017
  5. Sep 18, 2011 #4
    ADVANCES IN QUANTUM THEORY: Proceedings of the International Conference on Advances in Quantum Theory, edited by G. Jaeger, A. Khrennikov, M. Schlosshauer, G. Weihs, (AIP Conference Proceedings, Melville and New York, 2011), vol. 1327, p. 429 - 433

    Similar but much more detailed paper published here:

    J. Comp. Theor. Nanosci. 8, 1011 - 1039 (2011); http://arxiv.org/abs/0901.2546
     
  6. Sep 18, 2011 #5

    Ken G

    User Avatar
    Gold Member

    If anyone has time to wade through it and explain it to the rest of us, that would be great. They seem to be saying that they have a different scheme for generating Bell-type inequalities that do work for quantum mechanics, so understanding the differences between the assumptions that work and those that don't would be an interesting insight.
     
  7. Sep 18, 2011 #6
    With respect, this reminds me of the alleged Lord Kelvin statement over 100 years ago:

    "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement"
     
  8. Sep 18, 2011 #7
    Yes, but more and more precise measurements drive advances in theoretical physics - and there are a lot more physicists in the world than there were in his time, armed with sophisticated experimental and computational tools. It's simply highly unlikely that they have uncovered anything that someone else hasn't already considered and discarded, and that would explain experimental results that I am not aware of - that does not make it impossible, just highly unlikely, though I would love to see a chink in the armor of QM that might lead to something more likely to be fully correct.
     
  9. Sep 18, 2011 #8

    Ken G

    User Avatar
    Gold Member

    I don't think these authors are looking for a chink in QM with this work, I think they are looking for a better way to characterize the pedagogies that QM allows. They seem to be saying that right now all we have is a particular brand of local realism (ruled out by Bell), versus "anything else." They want to find a new version of the inequality that still holds, so they can create a third category, fully consistent with QM, that distinguishes something like "naive local realism" from "our more sophisticated version" from "what QM cannot do." If they've pulled it off, it's a valuable accomplishment, I just don't know how long, or if ever, it would take me to figure out if they did pull it off, but maybe someone can.
     
  10. Sep 18, 2011 #9
    I have studied the De Raedt et al, papers extensively. We had a big discussion of them on the sci.physics.foundations newsgroup. It appears that they have successfully invalidated the EPRB type experiments with photons. If the time coincidence window is taken out of the experiments, then the experiments do not produce the QM results. They produce Bell's results. They also have a successful computer simulation that does produce QM results when a time coincidence window is used and produces Bell's results when it is not used; it is not supposed to be possible for a computer simulation to produce QM results. IMHO, they have shown that Bell's theorem does not and can not match physical reality. Not surprising since Joy Christian has also "disproved" Bell's theorem. Disproved is in quotes because you can't really disprove a mathematical theorem but what he has disproved is that Bell's theorem doesn't match physical reality same as De Raedt et al. Basically, Bell and its variants missed that you have to match pairs up in time.

    Fred
     
    Last edited by a moderator: Sep 22, 2011
  11. Sep 18, 2011 #10

    Ken G

    User Avatar
    Gold Member

    So are you saying that there is a more sophisticated version of local realism, taking account of some sort of ambiguity in coincidence matching, that reality obeys, or that reality obeys the garden variety local realism and it was simply an error in interpretation of the experimental correlations that said local realism was violated? Also, are you saying that quantum mechanics is making incorrect predictions, or that it is making correct predictions but the entangled wave function is not breaking locally real constraints?
     
  12. Sep 18, 2011 #11
    QM makes the correct predictions and are backed up by Joy Christian's geometric algebra presentation. I am only saying that the experiments are probably flawed and Bell's theorem doesn't match physical reality since we have two classical examples (possibly more) that violate the inequalities. So local realism is still quite alive contrary to what has been said for a few decades now. :-) As far as EPRB type scenarios go.

    Fred
     
    Last edited by a moderator: Sep 22, 2011
  13. Sep 18, 2011 #12
    QM makes the correct predictions and are backed up by Joy Christian's geometric algebra presentation. I am only saying that the experiments are probably flawed and Bell's theorem doesn't match physical reality since we have two classical examples (possibly more) that violate the inequalities. So local realism is still quite alive contrary to what has been said for a few decades now. :-) As far as EPRB type scenarios go.

    Fred
     
    Last edited by a moderator: Sep 22, 2011
  14. Sep 18, 2011 #13

    Ken G

    User Avatar
    Gold Member

    OK, I'm getting that the presence of a time coincidence window is needed to get violations of Bell's inequality, and so that distinction is crucial for understanding the ability of real and computed systems to violate or not violate that inequality. What I'm not getting is how having a time coincidence window is still a version of local realism. Same with the computer codes with it-- why does such a code have to exhibit local realism? Are you saying that if we allow ourselves magical powers to match up coincidences in ways we can't actually know, then we can give ourselves the impression we have violated Bell, even when in fact we have not violated either Bell or local realism? If I have this right, does this mean QM predictions are themselves consistent with LR, or does it mean that our experiments have simply not yet probed the domain of departure?
     
  15. Sep 18, 2011 #14
  16. Sep 18, 2011 #15
    Ken G,

    Yes, a time coincidence window is necessary to get violations of Bell's inequalities for the EPRB type experiments IMHO. This is what Bell and its variants missed and why they are just mathematical theorems that have not much to do with actual physical reality. QM predictions do violate Bell; but it doesn't matter because Bell doesn't really apply physically. That is what De Raedt et al, and Joy Christian have shown.

    See the link that billschnieder provided plus there is a bunch more here on Physics Forums and at sci.physics.foundations if you search.

    Fred
     
    Last edited by a moderator: Sep 22, 2011
  17. Sep 19, 2011 #16

    Ken G

    User Avatar
    Gold Member

    Thank you for this information. The issue seems controversial, but in an interesting way.
     
  18. Sep 19, 2011 #17
    Thanks for this, Fred.

    I'm struggling to understand their work. It seems to me the time coincidence window cannot be taken out of the experiments (all work to date has relied on time coincidence to identify entangled pairs?), so their algorithms (based on local reality) can be made to match the experimental data - but I'm struggling to understand what implications their algorithms have for the kind of local reality we would have to accept. It seems their model entails a dependency on the time-separation of the measurements on entangled pairs, which seems just a little weird if its correct?
     
  19. Sep 19, 2011 #18

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    This is an extremely complex issue, and it is going to be hard to discuss here. First, it is not at all generally accepted that Bell is anything other than rock solid. That considers the attacks by de Raedt, Christian, etc. These show up quite frequently.

    Second, I have studied the de Raedt et al simulation, and in fact it does as you describe. However, it does not follow QM in that the basic Malus rule is not followed. The coincidence time window "loophole" has been closed in other experiments so I would not call this a viable model.
     
  20. Sep 19, 2011 #19
    Well, I will withhold judgement on this until it becomes widely accepted in the community. Even if I read and fully understood the cited references, chances are I would miss something, and the same is true for everyone else; hence, the value of consensus.
     
  21. Sep 19, 2011 #20

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Don't hold your breath... :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Bell's Inequality: Must we ditch locality, realism or something else?
  1. Local Realism After Bell (Replies: 24)

Loading...