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

Long-distance correlation, information, and faster-than-light interaction

  1. Jan 21, 2016 #1

    edguy99

    User Avatar
    Gold Member

    [Mentor's note: Split off from https://www.physicsforums.com/threads/an-abstract-long-distance-correlation-experiment.852684/page-6 because this subthread was discussing possible mechanisms behind the phenomenon]


    My take on these:

    1) - not weird at all - you send a photon in one direction and the other guy gets it
    2) - not weird at all - you send two photons with the same polarization (defined by its Jones Vector) in two directions and if one guy gets it, he knows what the other guy will see for polarization subject to the inherent randomness in the Jones Vector definition of photon polarization.
    3) - PRBox - not sure what this is, a google search produces a wide variety of topics ???
    4) - not weird at all - it doesn't happen

    What I think is weird:

    1) Ignoring the fact that photon polarization has inherent randomness and designing FTL or multi-world theories based on this assumption
    2) Not using the "weirdness" of the experiment in question here to develop theories of what the inherent randomness of the photon is all about and how it works (the hidden variables behind its behavior).

    What I look forward to:

    A data set of matrices based on this experiment that someone feels cannot be explained. We could then take a careful look at the definition of photon polarization (without resorting to FTL or multi-world theories) to see how to reproduce the experimental results in the animation leading to a better understanding of "weirdness".
     
    Last edited by a moderator: Jan 22, 2016
  2. jcsd
  3. Jan 21, 2016 #2
    Noone serious does this. Please read up on Bell's theorem.

    This is exactly what Bell proved impossible, assuming no FTL transmission and one real world.
     
  4. Jan 21, 2016 #3

    edguy99

    User Avatar
    Gold Member

    I have read a lot on Bell's theorem, but I feel this is a change in topic. The original post describes a specific Bell type of experiment and the weirdness that this experiment is providing. If the FTL explanation is all that works to explain this experiment, then that is pretty weird.

    Bell's theorem is true for the models it covers, check the definitions. It does not cover all possible models of the photon. In fact, Bell's theorem proves that his type of model is not a proper model of a photon since it doesn't work.
     
  5. Jan 21, 2016 #4

    Ken G

    User Avatar
    Gold Member

    By the way, there is nothing in this experiment that requires anything FTL, so we should not regard the need for FTL as the source of the weirdness. FTL only appears if you regard information as having a location other than in the intelligent brain that is analyzing that information, and I see no evidence that information does exist anywhere else. There certainly is no physics theory that requires information to exist any place else. So if we are to say the results of the experiment are "weird", we must be able to say why it is weird, without invoking anything FTL, or else it is our own belief system that is imposing the weirdness and the solution is to simply stop thinking about information as if it had a location other than in our heads.
     
  6. Jan 21, 2016 #5
    I don't follow, what's special about the brain anyway? The measurement results are correlated depending on the settings in a FTL fashion.
     
  7. Jan 21, 2016 #6

    Ken G

    User Avatar
    Gold Member

    No experiment ever requires that we assign a location to information, other than where we see it operating-- in the brain. No one would say "knowledge" has a location, so why should we imagine that "information" is any different from "knowledge"? It doesn't show up any differently. It's true that once a hand of cards is dealt, we can imagine that the "information" of what the cards are exists locally in that hand, but we never use that claim-- ever. The only information we ever use is what we know, because what could we use but what we know?
     
  8. Jan 21, 2016 #7
    Why does it have to be information? And even then, everything would be that way, all experimental results, all physical settings, including slower-than-light interactions. Why would you conclude that FTL should be ignored then?
     
  9. Jan 21, 2016 #8
    Ah sorry, there was no quote in your post. Though I don't think this reasoning is sound, because referring to gathering information in the abstracted fashion you're pointing to and claiming it eludes the FTL problem is a category mistake: "speed" is unapplicable here, either way, and your information just refers to what happened where. So the phenomena you refer to and which you have information about still have a FTL property. And I'm assuming what you're saying about information is consistent, which I doubt.
     
  10. Jan 21, 2016 #9

    Ken G

    User Avatar
    Gold Member

    I'm not sure what you are arguing, I agree that information only refers to what happened where. There is never any need for anything FTL in this experiment, that all comes from the idea that a system must in some sense itself "store" information locally, which is the idea we need to let go of. If you just put information processors everywhere, and "store" the information in them, rather than in the system, you never need the processors to communicate FTL-- their information is local, it is not FTL, and they can predict any correlations in any experiment they have access to. Go back to the example of the highly cooled white dwarf, an information processor anywhere in that white dwarf will discover it cannot alter the momentum state of the electrons it encounters. It will not require anything FTL to happen to reach that conclusion, it is a simple local experiment, but the processor will be able to conclude that it is in a Fermi sea all the same.
     
  11. Jan 21, 2016 #10
    We can let go of it, but it doesn't change the fact that a polarizer angle choice on Alice's side can influence the measurement outcome on Bob's side FTL.
     
  12. Jan 21, 2016 #11

    Ken G

    User Avatar
    Gold Member

    I agree we don't want to get caught up in this, but there is simply no reason to say that anything that happens at Alice "influences" what happens at Bob. The experiment shows there is a correlation, not an influence. Indeed, one cannot even say which event influenced the other, it just isn't the way "influences" normally work. I think the whole concept of "influence" is misplaced in entanglement experiments, but all that can be demonstrated is that the concept is never necessary to make the correct predictions. Similarly, when we find we cannot put an electron into a momentum state already occupied by another electron in a white dwarf, even though we have no idea where that other electron is (and indeed, there is no such "other electron", electrons are indistinguishable), we have no need to say that other electron "influenced" the one we are experimenting on. We simply find that the state of the system does not permit the momentum change-- that's all we actually observe, and no other concept is necessary.
     
  13. Jan 21, 2016 #12
    The shortcoming of language doesn't call for dropping the issue. The issue of FTL is still there. Sure there's a time ordering problem, but if Alice had chosen a different angle Bob's result would've been FTL different (to not say instantaneously).
     
  14. Jan 21, 2016 #13

    Ken G

    User Avatar
    Gold Member

    All we can say is the correlations observed depend on the choice of the angles, that's it. Interpreting that as an "influence" on the events is never necessary, it is unnecessarily limiting the language. The correlations depend on the state of the system, and the measurements done on the system, that's what we observe.
     
  15. Jan 21, 2016 #14
    Maybe it has to do with SR's framework where FTL is just not possible, I guess that's why Bohmian mechanics needs Lorentz's ether. This is where my little knowledge hits the wall. I hope for other users to comment further.
     
  16. Jan 22, 2016 #15
    Maybe "exactly like QM" for a single photon, but not for multiple entangled particles. It does not reproduce the Bell violations. But I am sure you already know this. Also you probably know the trivial "non-classical" hidden FTL mechanism that needs to be added to this model in order to make it reproduce QM entanglement. If I am wrong and you don't, maybe we should discuss this in a different thread, to not sidetrack this one.

    TBH I am not exactly sure what your purpose of bringing this up here is...
    I also did not quite understand your relationship to the simulation website you posted earlier, that used this model:
    http://www.animatedphysics.com/games/photon_longdistance_nonlocality.htm
    If you are the author of that simulation and you want to make it useful for the current topic, maybe you can add the FTL mechanism to it (or make it optional for bonus points?) so it matches QM and reality, and also add a way to more quickly simulate a large number of trials so the end data can finally get some statistical significance.
    And even then, I'm not sure now useful it would be for the current topic. It can certainly help people new to the subject in understanding the Bell violation that's happening in reality, and how a FTL effect helps in simulating/explaining that, but I think this thread is already targeted at people understanding this well enough.
     
  17. Jan 22, 2016 #16
    But exactly there is the tricky part. The correlations depend on the state of the system as a whole. You can not break it apart and say this measurement depends only on the state in this part of the system. You either have to stick to always looking at the whole thing only, or you can break it up into local parts but then have to admit a FTL influence between them.
     
  18. Jan 22, 2016 #17
    You are ignoring the very next sentence in their text: "In 1964 Bell showed that this is impossible." Their model is intended as an example of what doesn't work.
     
  19. Jan 22, 2016 #18
    In the latter case, how do you consider it with respect to different inertial frames? In a frame where Bob measures first, it's Bob influencing FTL and Alice's side is being influenced, and vice-versa?
     
  20. Jan 22, 2016 #19

    Ken G

    User Avatar
    Gold Member

    Exactly, if you regard it as an "influence", it's more than just FTL, it requires that the influence be able to go back in time. That defeats the whole purpose of the "influence" concept, because you have lost the concept of one-way causation. You can still have causation emerge as some kind of macroscopic limit that is one-way even though it is comprised of two-way "influences", but then we've lost the "influence" concept as it is normally formulated. If we're going to lose that concept anyway, I say just dump it from the start. Electrons in white dwarf stars do not "influence" each other, they are simply indistinguishable. Parts of an EPR experiment do not "influence" each other, they are simply entangled. A system is what it is, if we wish to imagine it is broken into pieces that "influence" each other, that's on us-- and when it doesn't work, it's on us to recognize it isn't working, and use a different picture.
     
  21. Jan 22, 2016 #20

    Ken G

    User Avatar
    Gold Member

    Yes-- so why not look at the whole thing? You never see anything FTL if you look at only part of a system, you only see it when you look at the whole thing (the correlations), but also insist on imagining it is made of pieces that "influence" each other. Why does a system have to be made of pieces that influence each other, when that is simply not what we are observing to be the case? You can observe many types of influences by intercepting the influencing signal, so when you cannot do that, as here, it is a good indication this is the wrong way to think about it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Long-distance correlation, information, and faster-than-light interaction
Loading...