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Speed of transmission in quantum entanglement

  1. Nov 16, 2011 #1
    speed of "transmission" in quantum entanglement

    when we "collapse the wave-function" via observing one of the entangled photons:

    is the transfer of the collapse information instantaneous (to the twin photon) or a few/many orders of magnitude of speed of light?

    lets say we observe one of the entangled photons (A) to be spin up.

    we know that the other photon (B) will be spin down. let's say both the photons are (time-space) separated by 10 light years.

    how long does it take for photon B to be spin down (collapse into a definite state) once photon A has been observed to be spin up?

    is the "transmission of the wave function collapse from one photon to its twin photon" instantaneous
    so fast that it appears to be instantaneous?

    in other words how fast does the collapse of the wave function travel in a "bi-photon"?
    Last edited: Nov 16, 2011
  2. jcsd
  3. Nov 16, 2011 #2


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    Re: speed of "transmission" in quantum entanglement

    This is beginning to verge on a being a bunch of noise. What is it that you are asking here?

    And what does the Morley-Michaelson experiment has anything to do with light being "instantaneous"? Even before Relativity, classical E&M never claimed that "speed of light is instantaneous"!

  4. Nov 16, 2011 #3
    Re: speed of "transmission" in quantum entanglement

    The way I understand it, the results in spin-correlation experiments are always correlated, regardless of space-like separation between measurements, and regardless of taking into account questions of simultaneity. All that remains when measurements are compared is that their spins are correlated.

    Like I said, this is how I know it to be, but if it is otherwise I would like to hear about it.
  5. Nov 16, 2011 #4
    Re: speed of "transmission" in quantum entanglement

    I don't believe information can actually be extracted from the system so such a question is irrelevant. As jfy4 said, only their spins are correlated.
  6. Nov 16, 2011 #5
    Re: speed of "transmission" in quantum entanglement

    You seem to be assuming that "collapse of the wave function" refers to some physical event at the level of quantum phenomena. There's no particular reason to assume this.

    Some people do assume it, but, my guess is that most don't. "Collapse of the wave function", for most I think, just refers to the registration of a detection, at which point you might or might not be able to say something about the probability of detection of an entangled particle, depending on the settings of the filters.

    So, bottom line, you're making a mistake that most of us are cautioned to avoid at the beginning of our qm educations. You're assuming that quantum states correspond to real, physical states. And nobody has any way of knowing how the mathematical formalism of quantum states corresponds to real, physical states.
  7. Nov 17, 2011 #6


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    Re: speed of "transmission" in quantum entanglement

    San K, I’ve taken the liberty to edit you OP where it goes 'wrong':
    • First, no usable information is exchanged in EPR-Bell experiments.

    • Second, the notions on wavefunction collapse depend on QM interpretation.

    • Third, only in cases where we have so-called 'perfect correlations' could the spin of B be exactly predicted (if A is measured first).

    • Fourth, we don’t know the exact speed of QM influences between A & B, and this builds on the assumption that non-locality is an established fact, which is not finally settled (it could be non-realism instead). However, here’s a paper which sets a lower bound for the speed of the influence to 10,000 x speed of light.
    Last edited by a moderator: May 5, 2017
  8. Nov 17, 2011 #7


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    Re: speed of "transmission" in quantum entanglement

    If you define one of the major and maybe most 'irritating' phenomena in QM as "All that remains", it’s okay by me! :wink:
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