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Problem of superluminal communication in Non-local HVTs

  1. Aug 14, 2015 #1

    Zcs

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    Hi there.

    I have been studying on Bell Inequalities and hidden variables problem for quite some time now however my general knowledge on the problem of superluminal communication is superficial at best. I know that non of the standing interpretations (Everett, Copenhagen, Bohmian, QBist etc.) allow superluminal communication and I do know how Everett, Bohr-Copenhagen and QBists handle the formalism of it but I have no idea how Bohmians deal with it, I know that it has something to do with the guiding equation but that's all.

    My request-problem here is that there are lots of misinformation on this subject and I don't want to waste my time trying to figure out which article or book is valid and which is not (I'm just a grad student and my advisor asked a quick review on the subject). Can anyone (especially if you are a Bohmian) kindly push me towards the general direction of some useful review articles on the subject, that would be much appreciated.
     
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  3. Aug 15, 2015 #2

    bhobba

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    Last edited: Aug 15, 2015
  4. Aug 17, 2015 #3

    Demystifier

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  5. Sep 18, 2015 #4

    jfizzix

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    With quantum mechanics as we know it, there is no way we can measure a single particle and tell if it's half of an entangled pair or not.

    Because of this, there is no way to communicate faster than light via quantum entanglement even though the correlations between pairs of particles might really be nonlocal.

    I would look up the no-signalling theorem (which this notion is based on) to learn more about this.
     
  6. Sep 19, 2015 #5

    stevendaryl

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    In Wikipedia, it's called the no-communication theorem:
    https://en.wikipedia.org/wiki/No-communication_theorem
     
  7. Sep 19, 2015 #6

    stevendaryl

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    To me, there is something a little unsatisfying about a number of attempts to interpret the quantum predictions realistically (Bohm, transactional interpretation, superdeterminism, etc.) in light of the no-communication theorem. Although you can prove that it's impossible to communicate FTL using QM, in these various interpretations, this fact seems almost "accidentally" true. Bohm for instance, specifically has FTL influences, but these FTL influences happen to be impractical for communication. In the transactional interpretation (Cramer), there are influences traveling both forward and backward through time. Even though every influence propagates at the speed of light or slower, the combination of subluminal forward-in-time and backward-in-time signals can give rise to an effective FTL signal. So what's the deep reason that this doesn't happen?

    At the level of the evolution of the wave function (or quantum field), it is easy enough to see that there are no FTL influences on that evolution, but in making the connection between the quantum state and observations requires going beyond the evolution equations (except possibly in the Many-Worlds Interpretation), and it's a little mysterious to me how things conspire so that these additional elements don't permit FTL communication.
     
  8. Sep 21, 2015 #7

    Demystifier

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    There is no conspiracy, there is a simple general reason why hidden variables cannot be used for FTL communication. That's precisely because they are hidden, which implies that they cannot be controled. If we could control them, then we could choose to put them in one state or another as we wished, so we could encode some meaningful information in them. Then their FTL influence would not be merely a meaningless physical influence, but a meaningful communication.

    This is like asking whether a thunderbolt lightning can be used for communication (with the velocity of light). As long as thunderbolt lightning behaves as a natural effectively random event, you cannot use it for communication. But if you find a way to control the thunderbolt lightning (Nikola Tesla comes to my mind in that context), then yes, you can use it for communication.

    Of course, the thunderbolt lightning is not hidden. But the issue is whether it is controlable. Being not hidden is a necessary condition, but not a sufficient condition, for being controlable.
     
  9. Sep 21, 2015 #8

    stevendaryl

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    I understand that. An alternative form of the question "Why is FTL communication impossible?" is "Why must the hidden variables must remain hidden (or uncontrollable)?"
     
  10. Sep 21, 2015 #9

    Demystifier

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    They do not need to remain hidden forever. They are hidden at the current development of physics, but this may change in the future. For instance, atoms were hidden variables in 19th century (serving as a possible deeper explanation of chemistry and thermodynamics), but they are not hidden variables today.
     
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