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EPR and Lorentz transformation

  1. Nov 2, 2011 #1
    Hello

    I have been thinking at EPR experiment during some time. It is very suggestive for me that the entanglement effects travel faster than ligth between the positions of 'Alice' and 'Bob'. I understand this is not contradictory with special relativity, due there is a not real exchange of information travelling between the 2 positions.

    However, if we apply a Lorentz transformation, for some observer the entanglement must travel in the time direction.

    I have some questions about that:
    1. Is this correct?
    2. What are the implications, if any?

    Thanks
     
  2. jcsd
  3. Nov 3, 2011 #2

    DrChinese

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    In QM, the ordering of the observations is not a factor in the results. So regardless of reference frame, you see no difference at all - even when relativistic effects are added.
     
  4. Nov 14, 2011 #3
    Ummm... good answer.

    I have seen an experimental paper (http://arxiv.org/abs/quant-ph/0007009) where the "tension" between EPR experiment and relativity is explored playing with the concept of time ordering: They prepared 2 moving detectors in such a way that each one, in its own framework, believes it triggered the EPR wave function collapse.

    The results are coherent with QM. But for me it opens some questions regarding the nature of the decoherence process and the concept of causality in some areas of QM

    Thanks for your answer
     
  5. Nov 14, 2011 #4
    I take the minority view that information is exchanged. To human beings it is not useful information, but for the photon it is useful information.

    This is not contradictory to relativity because relativity is all about masses: energy and matter. If transfer of information doesn't involve any transfer of energy or matter, then there is no reason it's speed should be constrained.

    How the info is transferred without energy or matter no one yet knows, as far as I know.
     
  6. Nov 15, 2011 #5

    Demystifier

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    Maybe it is a minority view, but you are not alone. I think the same way about it.
     
  7. Nov 15, 2011 #6

    Matterwave

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    It's interesting to think whether information is exchanged or not. Being that the two detection events are space-like separated (if they were time-like separated, obviously nothing super-luminal is happening), one can always transform into a Lorentz frame where Alice measured the particle before Bob, and similarly a frame where Bob measured the particle before Alice. In which direction would the information go? From Alice to Bob, or from Bob to Alice?
     
  8. Nov 15, 2011 #7

    Demystifier

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    I agree with these words, but in a different way. If the sign of mass squared is not constrained, then the speed is also not constrained. See e.g.
    http://xxx.lanl.gov/abs/1006.1986
     
  9. Nov 15, 2011 #8

    Demystifier

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    This question cannot be answered without referring to a particular model of information exchange. For example, in the relativistic-covariant version of Bohmian mechanics
    http://xxx.lanl.gov/abs/1002.3226 [Int. J. Quantum Inf. 9 (2011) 367-377]
    sometimes information goes in one direction and sometimes in another, depending on the initial conditions of hidden variables.
     
  10. Nov 15, 2011 #9
    I'm curious why you take this view, since in the view that entanglement is a consequence of relationships between entangled entities no such information transfer is necessary, which is the more parsimoneous view. And isn't the more parsimoneous view to be preferred?

    What sort of 'information transfer' doesn't involve any transfer of energy or matter? As you note, nobody knows, which makes this 'concept' more or less meaningless, doesn't it?
     
    Last edited: Nov 15, 2011
  11. Nov 15, 2011 #10
    My understanding -- always a shaky standpoint -- is that the Bell result shows us that the state of each of the entangled particles is undefined until measured. So my thinking is, how does the one entity "know" what the other one did? Since it can't be hidden local variables, some sort of information transfer must have occurred. If this naive view can be upgraded I'd appreciate the help.
     
  12. Nov 15, 2011 #11
    I take the position that information is exchanged, but does not involve a superluminal communication. Yakir Aharonov's time symmetric interpretation of quantum mechanics provides the explanation.

    Please visualize two particles that are quantum entangled moving apart in opposite directions. At some distance from their common origin, Alice measures the spin of one of the particles and finds that the spin is in the up direction. In traveling from the point of origin to Alice, we may understand the particle's wave function to have, in a probabilistic sense, taken all possible paths and to possess all possible states consistent with the initial boundary condition of the system at the origin. With TSQM we must now visualize a time-reversed wave function which proceeds backwards in time from the occurrence of Alice's experiment to the time and point of origin for Alice's particle. This backward in time wave function would also, in a probabilistic sense, take all possible paths and possess all possible states consistent with three constraints: (i) the time evolution of the wave function is backward in time; (ii) the time-reversed wave function is bounded by the initial state of the system at the origin and (iii) the time-reversed wave function is also bounded by the particle location and spin information arising from Alice's experiment. It should be noted at this point that due to conservation of momentum the direction of spin manifest in Alice's time-reversed wave function will be opposite to the spin direction that Alice measured; and identical to the spin Bob will find when his measurement later occurs. In any event, Alice's time-reversed wave function may be understood to carry the spin information arising from Alice's experiment to the time and location of origin for the entangled particles. Here, the information contained in Alice's time reversed wave function may be understood to "bounce" forward in time in a state that is entangled with Bob's particle. Please note that weak measurements of Bob's and Alice's particles immediately prior to the occurrence of their respective ideal measurements will show that each particle has remained entangled with the other.

    My conclusion from the foregoing is that TSQM reintroduces a classic-like causality, and locality, to quantum mechanics that I believe has very broad implications. This interpretation based on time reversal is far from original. As early as in 1983 Costa de Beauregard gave a formulation of the EPR setting that allowed a time-reversed EPR.

    J. W. Moffat in his paper “Quantum Measurements, Nonlocality and the Arrow of Time” (See: http://arxiv.org/pdf/gr-qc/9710019) proposes an absorber wave function reduction process to resolve the EPR paradox that is based on the retarded (forward-in-time) and advanced (backward-in-time) waves that John Cramer proposed in his transactional interpretation of QM.

    The TSQM approach, which I favor, is presented in a paper by Yakir Aharonov and Jeff Tollaksen titled New Insights on Time-Symmetry in Quantum Mechanics (see http://arxiv.org/PS_cache/arxiv/pdf/0706/0706.1232v1.pdf

    Additionally, Dr. Henry Stapp in a private communication I catalyzed has stated:
    “If one considers an EPR-Bohm-Bell correlation experiment, then during some interval in Process Time the initial (singlet) state of the two particles will be created.

    Over an interval in Process Time this singlet state will grow out in an expanding V-shaped region of spacetime, toward the two far-apart detection regions. At some Process Time a detection will occur. At that moment in Process Time the state of the universe in the space-time past of the associated space-like surface will suddenly change, relative to what it was at the earlier moments in Process Time. In the V-shaped region of spacetime the state will suddenly jump from a singlet state of the two diverging particles to a state in which, for example, one particle is polarized in one specific direction, specified by the orientation of the device in one of the two regions, and the particle traveling along the other wing of the V is polarized in the opposite direction. The correlation between the parts in the two wings will be fixed instantly (in Process Time) over the entire V-shaped region in spacetime. The effective transfer of information about the choice of polarization direction, which choice was seemingly made by the agent/observer in one region, is made via the V-shaped region that extends backward in time: the [apparent] faster-than-light transfer of information is made by an effective transfer first backward in time to the region where the two particle interacted (or originated), and then forward along the other wing of the V.”
     
  13. Nov 16, 2011 #12

    DrChinese

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    Thanks for the post, very fine explanation!
     
  14. Nov 16, 2011 #13

    DevilsAvocado

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    Thanks currojimenez for bringing this up, I think it’s very interesting.


    1) I would like to add that there are 'premises' for this to be a 'problem', i.e. it’s in solutions containing non-locality + realism you get this tension between SR and QM. However, if you accept the Many-worlds interpretation (MWI), this tension is gone completely.

    2) People can’t agree if there are 'implications' or not. :smile:
     
  15. Nov 16, 2011 #14

    DevilsAvocado

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    What happens if one would use a PDC crystal Type I for correlated photon pairs?
     
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