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Entanglement and relativity

  1. Aug 24, 2012 #1
    Let's say there's a ship that's traveling at a sufficient velocity from the earth, such that the time is dilated for the ship by an arbitrary factor 10,000. If the ship has an entangled particle connected to another entangled particle on earth, and the entanglement is broken by observation, is entanglement still broken at the same instant in Earth's reference frame, or would there be time dilation "lag" by a factor of 10,000 that occurs on the ship? Or would this be impossible to determine? Basically im asking whether or not relativistic effects like time dilation can affect the quantum realm.
     
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  3. Aug 25, 2012 #2
    This is a good question that hasn't been fully resolved yet. It comes down to the fact that in quantum mechanics, the quantum state of the entangled particles collapses instantly over all of space, but in the context of relativity, that "instant" is ambiguous because simultaneity differs between reference frames. There haven't been any experiments performed yet that attack this problem, but there has been theoretical research into different possible resolutions. For example, you might assume that one of the reference frames is "preferred" in that the quantum state collapses simultaneously in a given reference frame: for example, the reference frame of the one doing the measurement, the reference frame of the other entangled particle, or the reference frame of the particles' source. There are a few other ways that have been suggested to resolve this question. For a good summary of this research, check out the book "Quantum Non-Locality and Relativity" by Tim Maudlin.
     
  4. Aug 25, 2012 #3
    Thanks for your response and the book reference. If you assume a preferred reference frame as the earth, the smallest unit of time measurement possible without uncertainty is the planck time 10^-43, the time dilation factor is significant enough, and you assume the quantum state collapses simultaneously, then on the ship it would appear that the entanglement breaks in a period less than the planck time. Doesn't this mean that either the quantum state cannot collapse simultaneously in a relativistic reference frame, or that the smallest unit of time possible is not 10^-43 seconds?
     
    Last edited: Aug 25, 2012
  5. Aug 25, 2012 #4
    I second that book reference. A "preferred" frame (a misnomer, what is meant is an "absolute frame") may be pictured as an inertial frame somewhat like* Newton's absolute space or Lorentz's ether. As the outcomes in question are the result of a comparison at, maximally, the speed of light, it would be impossible to determine an absolute sequence of collapse. In other words, such a frame remains "hidden" or non-preferred for observation, so that entanglement can't break the relativity principle**.

    * That is what Bell primarily suggested; Maudlin discusses several ad hoc frame possibilities with similar conclusion.
    ** While I (and Bell) refer to the relativity principles of Poincare and Einstein, Maudlin refers to a stronger one with metaphysical pretension (what he calls a "relativistic world view").
     
    Last edited: Aug 25, 2012
  6. Aug 25, 2012 #5
    I'm willing to accept that the frame is hidden, but the universe most likely has an actual logical sequence of collapse events, and understanding that sequence would probably help unify quantum mechanics with relativity. As with a lot of science today, it probably couldn't be directly observed, but it could be inferred from data generated from an experiment. The experiment could be done in such a way: by counting the number of pulses from a pulsar, and somehow recording when the entanglement breaks in terms of number of pulses. If the ship's entanglement broke after more pulses than earth's reference frame, then it can be inferred that time dilation does indeed cause a delay. However, if entanglement breaks at the same number of pulses, entanglement happens instantly across all reference frames. The pulsar is basically just a central reference point.
     
  7. Aug 25, 2012 #6
    Sorry, I don't understand what you mean with entanglement breaking in terms of number of pulses - but for sure there is no such thing! No scenario of that kind can break the PoR. Perhaps you misunderstand entanglement in QM, so that that book will be very useful for you.
     
  8. Aug 25, 2012 #7
    I think what you're suggesting is basically a Bell inequality test (like the experiments of Alain Aspect) in which one of the detectors of the entangled particles is moving at some relativistic speed relative to the other detector. As harrylin stated, experiments of this kind do not violate the principle of relativity (one cannot transmit information faster than the speed of light), but the two data sets might have some correlation that violates Bell's inequality (showing some quantum non-locality) that could be observed in retrospect. If we could do these experiments, then it might shed some light on whether there is some "preferred" frame--and honestly I doubt that such a simplistic idea could possibly be right. The problem is that it's already hard enough to do experiments on any relativistic phenomena, and it's also quite hard to set up a loophole-free Bell experiment, so setting up a relativistic Bell experiment is purely science fiction, at least for the foreseeable future.
     
  9. Aug 27, 2012 #8

    Demystifier

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    Entanglement does not need absolute simultaneity. This is best seen in the many-time formulation of QM.
     
  10. Aug 27, 2012 #9

    DrChinese

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    To add a bit: Entanglement is state which does not have a specific begin point nor a specific end point. It has no specific cause. This is part and parcel of the idea that we do not understand the "mechanism" of entanglement beyond the mathematical description.

    To demonstrate this: we know that collapse occurs at least 10^4 times c (i.e. lower bound). It could be instantaneous. But really, the entire concept of time sequencing of entanglement is more or less impossible to make sense of. You can entangle particles after they are detected. This has been done. Conceptually, you can entangle particles that have never existed at the same time. In these cases, how does the sequence of collapse make sense?

    In none of these cases does relativity appear to be a factor at all.
     
  11. Aug 27, 2012 #10
    Interesting post Dr. Chinese.

    perhaps:

    the entanglement state is held between intermediaries/third-parties and later "transmitted/shared" with the new particle that comes into existence?
     
  12. Aug 27, 2012 #11
    yes it can,
    relativistics effects on quantum:

    http://arxiv.org/pdf/0809.1907.pdf
    Physical Review A 79, 022121

    ...for entangled states in curved space-times differences can arise. To illustrate this we have studied the effect on optical entanglement of evolution through varying gravitational fields using both formalisms.The new formalism predicts a decorrelation effect that could be observable under experimentally achievable conditions...


    http://arxiv.org/pdf/1206.0965v1.pdf

    ...We consider a single photon travelling in superposition along two paths in an interferometer with each arm at a different height in a homogeneous gravitational field. If the time dilation is comparable with the photon’s coherence time the visibility of the quantum interference is predicted to drop, while for shorter time dilations the effect of gravity will result in a relative phase shift between the two arms...

    ...The gravitational time dilation between the two paths will cause the lower part of the superposition to be delayed as compared to the upper one, leading to a loss ofinterference...

    ...predict a difference in the time evolution of entangled states on a curved background as compared to predictions of standard quantum filed theory on the same space-time...
     
    Last edited: Aug 27, 2012
  13. Aug 27, 2012 #12

    DrChinese

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    If gravity were a quantum field, and you somehow *knew* an entangled photon had absorbed or emitted a graviton, you might assume that there was a way to deduce information about the photon. If there were, decoherence might occur, which you could detect by noting changes in correlation rates (as compared to pairs not experiencing acceleration).
     
  14. Aug 27, 2012 #13
    DrChinese:
    yes. Entangling particles after they are detected [observed] implies a future influence changes the past;So it would appear that a Planck interval of 10-43 seconds
    is not much of an obstacle. [see my quotes below:]
     
  15. Aug 28, 2012 #14
    Interesting! There have been discussions about similar claims (e.g. physicsforums.com/showthread.php?t=402497 ), and there was by far no consensus that such magic is required.
    If you think that this is too different, then please do start a new topic about it. :smile:
     
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