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Understanding communication via QE - is filtering the only obstacle? to FTL

  1. Jun 16, 2012 #1
    Understanding communication via QE - is filtering the only obstacle? to FTL communication

    FTL = faster than light

    In a two-photon (i.e. entangled photons) double slit or similar experiments -

    Information cannot be sent FTL because there are no patterns (mapping to which-way or no-which-way) on the screen yet.

    to get the patterns we have to filter out noise etc

    to filter out noise we have to compare/match both the photons via co-incidence counter.

    to compare both the photons we need a classical channel which will of course work at or slower than the speed of light

    Question 1:

    If Alice and Bob were sitting in a relatively noiseless (i.e free from stray photons, enough to discern an interference pattern) environment, could they, in principle, communicate FTL?

    Note: It may not be possible to have an environment that is free of stray photons. however for now let's ignore this fact.

    Question 2:

    (how) Does FTL communication, involving massless/energy-less transmission method, violate relativity?

    Note: Massless/energy-less information transfer might not be possible and this might be a fundamental, however for now we are ignoring this point.
    Last edited: Jun 16, 2012
  2. jcsd
  3. Jun 16, 2012 #2
    One of the assumptions of relativity is that there is a finite speed of causality. (which happens to be the speed of light) This assumption has it's basis in experiment.

    If faster than light communication were possible, we'd either have to raise the speed of causality to this new speed, abandon causality, or throw out the speed limit and relativity along with it.
  4. Jun 16, 2012 #3
    thanks, for the information, Reptillian.

    I guess causality is not involved here because nothing is being caused, there is no involvement of mass-energy.

    The question becomes: can information be transferred without cause and effect (i.e. without mass-energy)? I think the answer is no.
    Last edited: Jun 16, 2012
  5. Jun 17, 2012 #4
    You're right, causality is related to information transfer, not just matter or energy transfer. I could send a signal to a robot on Mars and tell it to start digging a hole. My signal has caused the robot to act. Relativity says that I can't do that instantly, that the signal has to take time to propagate across a distance.
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