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'Toy' universe complying with Bell experiments

  1. Oct 10, 2012 #1
    After reading a bit about Bell's theorem and various hidden variable theories, I thought a little about the detection loophole, and how it gets around Bell's theorem while still allowing a pretty much 'local' Universe. The main argument against this, as I understand it (correct me if I'm wrong) is that it requires some sort of conspiracy and is unfalsifiable.

    It occurred to me that it should be possible to 'test' this, in a way, by constructing a simple toy Universe that is totally deterministic yet non-conspiratory but still complies with any Bell test experiment (Stern-Gerlach, for example, or photon polarization).

    If it turns out that such a Universe is impossible to construct, then locality would be unquestionably refuted. If it is not impossible, then it still remains open as a possible explanation of reality.

    Has anyone ever attempted the construction of a model of such a toy Universe?
     
    Last edited: Oct 10, 2012
  2. jcsd
  3. Oct 10, 2012 #2
    I have absolutely no idea what you are trying to say in this post, could you rephrase it?
     
  4. Oct 10, 2012 #3
    Tell me what parts of the question you find confusing and I'll do my best to elaborate.
     
  5. Oct 10, 2012 #4

    ZapperZ

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    Don't you think that your toy model has no.....MODEL? It has nothing to test. You have presented nothing that can be quantitatively tested. This is not a model.

    Zz.
     
  6. Oct 10, 2012 #5
    I'm not presenting a model.

    I'm simply asking if someone has attempted to construct a toy Universe that is deterministic, local, and yet appears to produce 'nonlocal' effects like those that are seen in the Bell experiments. One's knee-jerk reaction might be 'but this is impossible!' Actually it's not. As DrChinese pointed out in another thread, one way is to posit the existence of some 'grand conspiracy' that always makes the results of the experiments match up with what is known from the Bell experiments. I'm asking if someone has constructed a toy Universe where this conspiracy either does not exist or can be reduced to the simple rules of the model (just like the 'conspiracy' of the second law of thermodynamics, for example, can be fundamentally attributed to the laws of statistics and probability).
     
  7. Oct 10, 2012 #6

    ZapperZ

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    Note that you stated this:

    Unless you are dealing with some philosophical arguments, what you have said means nothing when it doesn't have any underlying mathematical description. When tHooft argues that QM is deterministic, he showed mathematical formulation on why that is so.

    I'm not asking you to produce a model. I'm asking for you to show the mathematical criteria that this model must have or satisfy. Without that, this is philosophy, not physics.

    Zz.
     
  8. Oct 11, 2012 #7

    martinbn

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    I agree that saying "can someone make a model such that... " or "can it be proven that.." does not qualify as an idea that can be used to test anything.

    On the other hand if the (hypothetical, since you haven't presented one) toy universe is deterministic, how can it be non-conspiratory? The initial state will determine the choices of angles for measurement and the outcomes, no?
     
  9. Oct 11, 2012 #8
    Hi IttyBittyBit,

    For what its worth... I have attempted to construct a deterministic 'Toy' Universe which does not contain quantum mechanical principles. It offers an alternative explanation for such experiments as the two slit experiment; the amount of light reflected from a glass surface being dependent on the thickness of glass; etc without invoking quantum mechanics. Although these experiments aren't specifically Bell experiments, I guess they are related in that they are currently only explained using quantum mechanics.
     
  10. Oct 11, 2012 #9

    DrChinese

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    There have been many many many such attempts, and some are located at arxiv.org. Check out the following link, these are papers with the word "toy" in the title.

    http://arxiv.org/find/all/1/ti:+toy/0/1/0/all/0/1

    These all feature specific properties which attempt to "bypass" Bell by locating some potential (hidden) assumption and manipulating that. As ZapperZ correctly points out, you end up quickly running afoul of one of several traps: a) you don't really provide a model which reproduces the general predictions of QM; b) it does not actually make any predictions different than QM; and/or c) the differences really amount to definitional or semantic interpretation and there is no real change.

    The general point being that Bell provides a strict set of guidelines, and these are no simple restrictions. So to speculate that you could arrive at such is tantamount to asking to be awarded a 100% on test you are sure you could pass, but didn't actually take. Believe me, such models are not really welcome here anyway as this is not a spot for original research to be debated. The quantum physics forum is intended for discussion of mainstream physics.
     
  11. Oct 11, 2012 #10
    DrChinese: Thank you!

    Are you sure that's the right link, though? Most of those papers seem to have little, if anything, to do with Bell.

    Yes I've come to realize this myself; it is very hard to produce an exact definition for 'conspiracy'; I wasn't sure if this was due to my ignorance or it's just an ill-defined concept in general.

    I don't see this rule mentioned anywhere in the forum guidelines.
     
  12. Oct 11, 2012 #11

    micromass

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    You haven't looked for hard, I think (bolding mine):

     
  13. Oct 11, 2012 #12
    gerard` t hooft.
     
  14. Oct 11, 2012 #13

    DrChinese

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    I was trying to demonstrate that you can search on those yourself. I might suggest the keywords: bell entanglement or epr, If you look deeper, you will discover that almost all such are unpublished. And again, this is really the wrong place to come to because, by definition, toy theories are not generally accepted physics. So I was trying to point a direction for your further study.

    As to the forum guidelines, micromass answered that already. While it may seem at first glance that we are not interested in discussing, that is not really so. But you will need to do some preparation of your questions, and you will need to respect the boundaries implied by the guidelines. Remember, in this regard the burden will be on you to keep it relevant.

    For example: Gerard 't Hooft (as pointed out by audioloop) has published work on so-called conspiracy theories, usually labelled as "superdeterminism". His work on that is generally given the benefit of the doubt for inclusion here because he is a Nobel laureate. But you will find that he is given no benefit when it comes to discussing the actual merits. That is because many scientists, myself included, think that superdeterminism is not science but more metaphysics (and I am being kind - sorry Gerard) or at best, philosophy. There are already threads on the subject, if you are interested in learning more you can use the PF search to locate.
     
  15. Oct 11, 2012 #14
    Brief comment: of course 't Hoofts status in the history of physics is important, but his work has not recieved a lot of attention. The little attention his work has got has been due to him putting out several papers on it.
     
  16. Oct 11, 2012 #15
    DrChinese, again thanks for the wonderful explanation.

    I came here looking for a rigorous mathematical model of a 'superdeterministic' Universe. However, if I understood the discussion correctly, such a model either cannot be made or winds up being mathematically identical to the 'mainstream' interpretation, with the only differences being matters of interpretation. Correct me if I'm wrong here.
     
  17. Oct 12, 2012 #16

    DrChinese

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    I think that is fair to say. You can't really say "I have a model like QM but that is superdeterministic" without telling us HOW it accomplishes this feat.

    For example: if everything is a conspiracy, and Bell test results reflect that locally, then there must be some kind of DNA in every particle that tells it precisely WHEN to deviate from the normal laws and comply with Bell (i.e. it violates a Bell Inequality only during Bell tests). Where is that DNA? And it must have a complete history of the entire universe, past and present, because it is the starting conditions that predetermined everything. Whoa, that's quite a bit of info to pack into the DNA of every single particle. You end up adding rule after rule and it never ends. Which is why we never see any specifics.

    Further, why limit superdeterminism to Bell? Why not say that the gravitational constant is H but due to superdeterminism it appears to be G when measured?

    And finally, at the end of the day, we end up with sQM anyway as our map for making predictions.
     
  18. Oct 12, 2012 #17

    mfb

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    There is an interpretation of quantum mechanics which is both deterministic and local and consistent with experiments: Many worlds.
    Your toy universe is possible, assuming "totally deterministic" refers to the state of the universe.
     
  19. Oct 12, 2012 #18

    DrChinese

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    Might be stretching the word "deterministic". Each universe does not lead to a single inevitable new universe in any meaningful sense, since every outcome is realized. In other words, if you knew the state of the universe (or some system), you could still never predict with certainty any future state after an observation. It would be a random outcome, depending on the branch you fell into.
     
  20. Oct 12, 2012 #19

    mfb

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    If you know the state of the universe, you can predict the future state of the universe - that is "deterministic".

    Of course you can. You can predict "there will be some 'me' which sees X, they have a measure of p. And there will be some 'me' which see not X, they have a measure of q".
    The future branches of "you" will see different things, so what?

    In all branches, of course.
     
  21. Oct 12, 2012 #20

    DrChinese

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    So every measurement answer "proves" your definition correct. I have a term* for that idea, and it is much the same as my opinion of superdeterminism. Note that my opinion is not about MWI itself, it is simply an opinion about your description of it. I have heard it said that MWI is local and realistic (which I would dispute), but I don't believe most physicists would share your viewpoint that MWI is also deterministic.

    And, to be clear: You cannot, in principle, predict the outcome of a quantum measurement on any prepared system unless you are simply measuring an observable, the value of which you already knew. Otherwise, you would violate the Uncertainty Principle.

    *However, it is not complimentary.
     
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