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At the same time

  1. Sep 3, 2007 #1

    If we say that two particles that are entangled can pick their states simultaneously, with respect to which frame of reference are the two events considered simultaneous?
  2. jcsd
  3. Sep 3, 2007 #2
    Why would you say that?

    If you know that the socks in a pair have the same color, and you observe one being blue, when exactly the other sock becomes blue too?
  4. Sep 14, 2007 #3
    Both socks become blue when you observe the first one. It does look like you could get a relativistic paradox if the two socks are in distant galaxies. However, the question is irrelevant if you never observe the second sock. So the only interesting question is 'what happens when you observe the second sock?'

    When you observe the other sock, then both observations have clear spacetime coordinates, and so you can analyze it in any frame you want.

    Now, it can happen that in one frame you appear to observe sock 'A' first, and in another frame you observe sock 'B' first, but, as I see it, the non-causal nature of entanglement means that your experimental results never depend on which sock you observe first (unless you impose a causality through classical means). For example, in the tests of Bell's inequality, it is the difference between the polarization angles that produces the effect, and this difference does not depend on which photon was observed first.
    Last edited: Sep 14, 2007
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