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Bell's Theorem Correlations Velocity

  1. Jan 6, 2012 #1
    The observable universe is about 92 billion light years in diameter. It would take 80 years for us just to reach the edge of our galaxy travelling at the speed of light. And there are a magnitude billions of galaxies with the space between them even more distant than within a galaxy.

    Does it make sense Bell's Theorem still work for two entangled particles at say between 92 billion light years separation between them?

    What is more logical is Bell's Theorem correlations have speed limit, such that they are near instantaneous in between say the edge to edge of a galaxy. This means the correlations need to have speed.

    Aspect experiments have not proven the correlation is instantaneous.. just that it would be at least 10 times faster than the speed of light.

    This means for separations of billions of light years. The correlations couldn't be instantaneous but needs to have speed limit. Would this be possible? What law forbid it to be even possible?
  2. jcsd
  3. Jan 6, 2012 #2
    It's not clear to me what this question is asking. But it seems that as long as you have channels that are able to transmit entangled particles, undisturbed, to detectors that are 92 billion light years apart, then Bell's theorem should still hold.

    My understanding is that Bell's theorem is about whether a local realistic hidden variable (LRHV) formalism is compatible with the formalism of standard QM. Afaik, Bell showed, definitively, that it isn't. Subsequent experiments have demonstrated (not definitively because of some remaining experimental loopholes, but convincingly enough for most) that Bell-type LRHV models/theories of quantum entanglement are not viable.

    Whether Bell's LRHV formulation should be considered the general LRHV formulation is something of an open question.

    It seems that you're assuming some sort communication/transmission/propagation between entangled particles. This isn't what Bell's theorem is about. What Bell said was that if you assume some sort of communication/transmission/propagation between entangled particles, then that communication/transmission/propagation would have to be instantaneous. But, wrt ordinary language, that's a semantic contradiction. Another way of saying it is that these effects are happening (or might be recorded by a god's view observer) as happening simultaneously.

    "Bell's theorem correlations", or, perhaps more appropriately, Bell test correlations, are statistical correlations, and there's no speed limit, afaik, on those. So, no, the correlations don't need to have a speed. But if you're assuming propagations between entangled particles, then, yes, those would be amenable to statements regarding their speed, and a limit on that speed.

    But, as noted above, that's not what Bell's theorem is about.

    Aspect et al.'s experiments haven't proven anything. They have demonstrated, ie., provided one example of, the nonviability of Bell-type LRHV models of quantum entanglement, and the viability of the standard QM formalism.

    If you want to assume some sort of communication/transmission/propagation between entangled particles, then it seems that it would have to be travelling quite a bit faster than light. But there's absolutely no physical evidence that anything like that is happening. And, as mentioned, it isn't what Bell's theorem is about.
  4. Jan 6, 2012 #3
    But even if there were no communication/transmission/propagation between the entangled particles themselves, something behind the scene communication/transmission/propagation is occuring in order to conspire to make the entangled pairs correlated. So I wonder if this behind the scene "thing" has velocity limit.. it would be a stretch to think they can handle 92 Billion Light years instantaneously hence I wonder if there is a speed limit to the correlation information sychronizer (what it is)?
  5. Jan 6, 2012 #4
    The way I've learned to think about it is in terms of a relationship between measurable properties of the entangled particles. And that wouldn't necessarily have anything to do with communications/transmissions/propagations between the separated particles. If the particles have interacted with each other, or have been emitted from the same atom, etc., then they're related -- and that relationship can be measured by global instrumental variables (such as the angular difference between crossed polarizers in optical Bell tests).

    Well, you can assume that the entangled particles are communicating in some way. That's not ruled out. Just not the most parsimonious way to approach understanding quantum entanglement, imho. And if you assume that they're communicating, then I think it's been demonstrated that that would have a lower bound. Not sure about an upper bound.

    Afaik, the "correlation information synchronizer" would refer to the coincidence circuitry and the post experimental data processing which doesn't per se, afaik, imply any sort of communication between entangled particles.

    But, as mentioned, you can assume that the particles are communicating with each other and then from any particular experimental preparation you can calculate at least a lower bound for such communications.

    If you approach quantum entanglement in terms of relationships between entangled particles, then the distance between them isn't a consideration insofar as you're able to preserve the entanglement relationship.
    Last edited: Jan 6, 2012
  6. Jan 6, 2012 #5
    You might find this paper interesting:
    The authors then conclude:
    Quantum nonlocality based on finite-speed causal influences leads to superluminal signaling
    Last edited: Jan 6, 2012
  7. Jan 6, 2012 #6


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    Staff: Mentor

    Yes, but it's also a stretch to think that they can handle 92 billion light-years in any time less than 92 billion years :-)

    And kidding aside... When you speak in terms of an influence that propagates at some finite speed, you're speaking in realistic terms. If that finite speed is greater than the speed of light, then your realistic model is incompatible with relativity and therefore not local (as the term is generally used). I don't find "faster than light but finite" to be any more digestible than "infinite".
  8. Jan 6, 2012 #7
    So, if communication between entangled particles is assumed, and if the speed of that communication is assumed to be finite (ie., not instantaneous), then superluminal signalling is possible? Is that what the paper is saying? Haven't read it yet.

    It would seem that either the paper is wrong, or the 'no signalling theorems' are wrong, or the assumption of communication between entangled particles is wrong, or maybe it's just that the technology hasn't gotten 'up to speed' yet. And I have no idea at this time which it might be because I don't assume that separated entangled particles are communicating. As I mentioned, I just think about quantum entanglement in terms of relationships between entangled particles.

    The understanding of experimental violations of Bell inequalities has an explanation in terms of how LRHV formalism relates to Bell test preparations. It doesn't inform wrt what's going on in the reality underlying instrumental behavior. At least that's my current assessment/understanding.
    Last edited: Jan 6, 2012
  9. Jan 6, 2012 #8
    Yes, that's how I interpreted it. One of the authors (Gisin) was involved in testing Bell's (although it doesn't close all loopholes):

    Experimental demonstration of quantum correlations over more than 10 km
  10. Jan 6, 2012 #9
    You misunderstood my statements above. When I mentioned behind the scene communications/transmissions/propagations, I was referring to the wave functions. So the communications is not in between the particles, but somehow the wave function has to communicate.

    Or we can put it in the following statement. It would be a stretch to think that the wave function can be maintained 92 Billion Light years instantaneously hence I wonder if there is a speed limit to the wave function speed?

    Of course this is assuming the wave function was physical.

    But supposed the wave function was not physical. The correlations on paper still has to be maintained 92 Billion light years. And again. It would be a stretch to think that the wave function on paper can be maintained 92 Billion Light years instantaneously hence I wonder if there is a speed limit to the wave function on paper. (?)
  11. Jan 7, 2012 #10
    Wavefunctions are just mathematical entities. If you want to assume that they actually describe propagating particles, then the communication you suggest is between entangled particles. Isn't it?

    Afaik, QM doesn't describe any communication between entangled particles.

    Not if the wavefunction is just a mathematical entity. As I mentioned, if you think of quantum entanglement in terms of relationships between separarated entangled particles, then the distance between those particles isn't important insofar as you're able to maintain the relationship between them.

    Wavefunctions are mathematical entities. I don't know what else to say.

    Ok. But there's no particular reason to assume that.

    Well, it isn't physical, it's mathematical. You can assume that it corresponds to the physical world, but that's just an assumption. All that's known is that it's mathematical.

    They are maintained 92 billion light years -- provided that the relationships between quantum entangled particles can be maintained for that distance/period.

    Well, I think it's a stretch also.
    And, in any case, it can't be tested. So why worry about it?

    My honest opinion is that you're thinking about this in the wrong way, based on assumptions that have no support wrt empirical science.

    Are quantum entangled particles communicating with each other? I have no idea. Is there any reason to assume that they are? Afaik, no.
  12. Jan 7, 2012 #11
    I think I heard arguments of the sort that for the entangled pairs to be compared. It has to be done conventionally. So you are saying that for Alice and Bob stationed 92 billion light years away. They can only compare the results by travelling for 92 billion years near light speed and it is only upon meeting at the common point that the past got created (hence explaining the correlations)? I'm not arguing anything but just need to know what is the conventional understanding of this.
  13. Jan 7, 2012 #12
    Ok, I don't understand your understanding of quantum entanglement correlations. There's nothing, afaik, particularly mysterious about them, but I don't know what the conventional or mainstream understanding is (except to say that the physicists that I know and have talked to about this regard entanglement as being due to relationships between entangled particles, and not due to ftl communications between entangled particles).

    Afaik, it doesn't make any sense to say that "the past got created" when Alice and Bob meet to compare results. Bell tests are like any other experiments involving global measurement parameters in that results accumulated at separated detectors have to be combined and then analysed/correlated wrt the associated global instrumental variables in order to demonstrate the correlations -- and this is all done via local transmissons.

    So, I guess that I'm really not sure what your concern is. This is not to criticize your questions (questions are always ok), because the meaning of Bell's theorem has been debated for a few decades. It's not an easy thing to explain, and it really has nothing to do with the popularizations of Bell's theorem, or with ftl communications.
  14. Jan 7, 2012 #13
    Have you seen this site?


    Do you understand all the arguments mentioned there?

    In Aspect experiment, the angles were changed in between. For example. After the photons have reached say half or 42 billion light years of the 92 billion light years distance, the angles of the polarizers of both ends were changed, and the results violated Bell's Inequality.
  15. Jan 7, 2012 #14
    I took a quick look at it. It seems to be saying that the correlation between the angular difference of the polarizers and the rate of coincidental detection must be linear if nature is local. Which is, imho, wrong.

    It doesn't matter how many times the angle is changed while the photons are in flight. Each photon of an entangled pair interacts with its polarizer being at some specific orientation, and the pair's detection attributes are associated with one and only one angular difference.

    Randomly changing the polarizer settings while the photons are in flight just removes the possibility of the photons being 'attuned' to some particular setting(s) on emission, or for them to be communicating with each other via local signals.

    So, you're left with three possibilities: 1) the separated photons are communicating with each other via ftl signals, 2) the separated photons are communicating with each other via action at a distance, or 3) the separated photons aren't communicating with each other.

    None of those possibilities has been proven or disproven, and, imho, 3) is the most reasonable assumption.
    Last edited: Jan 7, 2012
  16. Jan 7, 2012 #15
    I think you are asking about nonlocality: There are two events A and B. Event A cannot influence event B if B is outside of A's light cone. The correlations though seem to imply a faster than light signal from A that influences B.

    One explanation for nonlocality that avoids faster than light signals is backward causation:
    From event A not only a forward light cone is emitted but also a backward light cone. This reaches the source and therefore the particle measured at B. So this backward light cone tells the other particle to have the opposite spin. I wrote more about this in another thread:
    Help for a beginner....Bell's Theorem

    Other explanations are offered by interpretations of quantum mechanics (I have to mention that I don't understand them):
    1. Relational quantum mechanics:
    - Nonlocality A Backreaction blogpost on a paper by Rovelli.
    - There was a discussion on PF too

    2. Many Worlds interpretation
    - From what I understand there is no collapse in this interpretation, thus no instantaenous collapse of the entangled state.
    I read about it here:
    The Interpretation of Quantum Mechanics: Many Worlds or Many Words?
    Many lives in many worlds
    Both articles by Max Tegmark
  17. Jan 7, 2012 #16
    Sure, but what are those entities about? What are they describing/modelling? How does one explain double-slit type interference phenomena (e.g. using single photons)? Moreover, there are papers suggesting that the wave functions are more than just mathematical entities; that is, they are telling us something about the way nature is. And here, I'm not denying that our view of nature will always be somewhat veiled due to our own cognitive filters.

    The quantum state cannot be interpreted statistically (this is the original paper)
    Generalisations of the recent Pusey-Barrett-Rudolph theorem for statistical models of quantum phenomena
    Completeness of quantum theory implies that wave functions are physical properties
    Quantum theorem shakes foundations
    Can the quantum state be interpreted statistically?
    Direct Measurement of the Quantum Wavefunction
    Last edited: Jan 7, 2012
  18. Jan 7, 2012 #17
    I don't think that either the entanglement correlations or the formalism of QM implies ftl communication between A and B. It's just that QM doesn't explicitly forbid it, and the correlations themselves are in line with the way light has been observed to behave wrt crossed polarizers in both classical and quantum polariscopic setups.

    What experimental violations of Bell inequalities do indicate is that Bell-type LRHV formalizations of quantum entanglement aren't viable, and that the standard QM formalization of quantum entanglement is viable. But the QM formalization of quantum entanglement is neither explicitly local nor nonlocal.

    What quantum nonlocality has evolved to refer to (and I'm guessing that this is how most physicists think of it) is the nonseparability of the QM formalization of quantum entanglement.

    So, nonlocality (insofar as it refers to ftl propagations or action at a distance) is just an assumption based on no physical evidence other than the inability to fully account for quantum entanglement correlations via Bell-type LRHV models.

    But, while imo that sort of nonlocality is an unwarranted assumption, it isn't ruled out, and if one chooses to assume it, then one is faced with some problems (imho ... pseudo-problems) that have led to some, imo, unwarranted (and unfalsifiable) interpretations of standard QM.
  19. Jan 7, 2012 #18
    You mean wrt a reality underlying instrumental behavior? Well, there's no way to definitively ascertain that afaik. Is there?

    In terms of a qualitative comprehension/understanding of what's happening in the underlying reality? One doesn't, afaik.

    What I take from it is that there's a good possibility that the underlying reality involves wave mechanics in a hierarchy of particulate media. But afaik there's no way to determine exactly how a particular wave function corresponds to the underlying reality.

    Thanks for the links.
  20. Jan 7, 2012 #19
    I found this old thread between you and Jesse about the Helbert website.


    You mentioned: "But, according to Malus Law the number of mismatches at 60 degrees should be greater than the number of mismatches at 30 degrees + the number of mismatches at 30 degrees."

    Jesse (Science Advisor) declared:

    "No, the classical Malus' law does not predict this, not in the setup that Bell and Herbert described. The fact that you can find a completely different setup where the classical Malus' law does predict mismatches at 60 is greater than the sum of mismatches at 30 is just a strawman argument, since Bell never argued that his inequalities should apply in any experiments other than ones meeting the conditions he specified. Since classical electromagnetism is a local realist theory, it would indeed be impossible to replicate the 0.5 cos^2 (a-b) in a classical optics experiment that actually matched Bell's setup."

    Hence, you ThomasT as an amateur is refuted by the professional. That thread was written in July of 2010. You still haven't learnt after all this months and time?

  21. Jan 7, 2012 #20
    My understanding of the issues surrounding the interpretation of Bell's theorem (Bt) has improved since that thread, wherein I probably made a lot of incorrect statements.

    I don't know for sure, but my guess would be that most physicists don't think that Bt (including experimental violation of Bell inequalities) implies that nature is nonlocal. But, iirc, Jesse is one who does.

    Anyway, the analogy was intended to show that the restrictions (for the purpose of making the assumptions of locality and realism explicit) encoded in Bell-type LRHV models of quantum entanglement (applied to optical Bell tests) amount to requiring light to behave in a way contrary to the way that light has been observed to behave in other, imo similar (such as classical and quantum polariscopic), setups.

    To illustrate, consider a simple optical Bell setup with an emitter flanked by polarizers (a and b) and detectors (A and B). Like this:

    A <--------- a <------------Emitter----------> b ---------> B

    An interesting thing is that polarizer a can be placed between the emitter and polarizer b. Like this:

    A <-------------------------Emitter-----> a -----> b -----> B

    And you get the same coincidental photon flux (which, in the ideal, is .5(cos^2Theta), with Theta=a-b) as when the polarizers are in the original configuration, except that in second setup, just considering the right hand wing, it's easy to see that the rate of photon flux at B, .5(cos^2Theta), corresponds to observed polariscopic behavior of light.

    On the left side of the second setup, A is recording the maximum photon flux. While on the right side the photon flux at B is .5(cos^2Theta). So, the coincidental photon flux goes from half the maximum (with the polarizers aligned) to zero (with the polarizers perpendicular).

    This is one of the considerations that got me to thinking that requiring the number of mismatches at 60 degrees to be equal to or less than double the number of mismatches at 30 degrees might not be in line with the way light should be expected to behave in optical Bell tests (in a local universe), given the prior experimental literature on the behavior of light. And yet, this is the way that Bell-type LRHV models of entanglement require light to behave.

    There's no argument that Bell's theorem rules out Bell-type LRHV models of quantum entanglement. But there's still some dispute about whether experimental violations of Bell inequalities demonstrate nonlocality. You're free to assume that nature is nonlocal, in the sense of entangled photons communicating with each other via ftl signals (it isn't ruled out, afaik ... but it might be an unfalsifiable assumption), and then proceed to solve the problems associated with that assumption.

    Anyway, assuming that entangled particles are communicating with each other, then, afaik, there's a lower bound on the speed of such communication. As I mentioned, I don't know about an upper bound. According to the dBB interpretation it's instantaneous. Isn't it? Not sure. But if it is, then that means action at a distance. EPR showed that either there's instantaneous action at a distance, or standard QM is an incomplete description of physical reality. That the latter is the more reasonable assumption seems obvious to me. But it has to be qualified. Standard QM is complete in that it includes everything that's known that's pertinent to any particular experimental preparation.
    Last edited: Jan 8, 2012
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