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Using Quantum Entanglement to know the future?

  1. Dec 5, 2013 #1
    Hi there,

    Is it possible to accelerate one of a pair of photons (while under quantum entanglement) close to the speed of light, and communicate information from the future?

    For example, two pairs of entangled photons with pre-determined states (using projection measurement) have one of their members accelerated at close to the speed of light, then returned - into the relative future. In that future, a coin is flipped, and we change one or both of the photons based on the result of the coin flip. In the present, would we then derive which of the two pairs were changed and therefore know if the coin flip that is yet to happen, will be heads or tails?

    Please excuse the dumb question.

  2. jcsd
  3. Dec 5, 2013 #2


    Staff: Mentor


    Sending information into the past poses severe difficulties for causality.

  4. Dec 5, 2013 #3

    You can't accelerate one of a pair and not break entanglement. Any interaction with the environment breaks entanglement. Anyway, photons don't accelerate....they always move at 'c'.
  5. Dec 5, 2013 #4
    Ah I see. Got a 'no' as well from a professor I emailed, but just trying to wrap my brain around why. What laws of physics are being broken?
  6. Dec 5, 2013 #5
    Oh wow I forgot about that, thanks for addressing my dumb question :)
  7. Dec 5, 2013 #6


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    Welcome to PhysicsForums, Donny!

    If a pair of photons has a predetermined state, they will NOT be entangled on that basis. A pair of photons can be entangled on one basis (say momentum) but not on another (say polarization).
  8. Dec 5, 2013 #7
    Welcome to the forum kinkarso

    In addition to what's mentioned in the posts above:

    We cannot have a predetermined state either.

    Also you cannot force a change (towards a particular result) in one or both the photons.
  9. Dec 5, 2013 #8


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    Not to nitpick, but intending to clarify for readers not familiar with the point :smile: :

    It is not always clear what kinds of interactions break entanglement. For example, a photon traveling through fiber cable generally does not decohere. Similarly, a photon passing through a wave plate does not cease to be entangled. If both output paths of a beamsplitter are suitably re-combined, a input photon will remain polarization entangled with its partner.

    In some ways, it comes back to the definition of "interaction".
  10. Dec 5, 2013 #9
    Did not even supect that....what's the reasoning for what I presume is an observed phenomena??
  11. Dec 5, 2013 #10


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    I am not even sure you can make a good definition without it being circular, such as: "An interaction in which no state reduction occurs."

    But I know it when I see it. :biggrin:
  12. Dec 7, 2013 #11


  13. Apr 9, 2015 #12
    Of-course we can achieve FLT condition to get a signal back in time via quantum entanglement
  14. Apr 10, 2015 #13


    Staff: Mentor

    I don't know why you raised such an old thread - but entanglement doesn't allow a signal to be sent FTL or back in time. If you could it would violate causality and cause all sorts of problems.

  15. Apr 10, 2015 #14
    Last edited: Apr 10, 2015
  16. Apr 10, 2015 #15
    Isn't this the same as the EPRG paradox? You can't even tell IF the other entangled particle has already been measured, otherwise that would be the binary system of FTL communication instead of spin values.
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