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Two entangled electrons

  1. Oct 19, 2009 #1
    I'm not a physicist but here goes. What happens if you have two entangled electrons A and B. What if B goes against what is probable and collapses onto a star 10 billion light years away traveling away from its "twin" electron back on earth. Would the two electrons still be entangled, even though B's now is many many years before A's now?

    Moreover, would the B from earth hundreds (or thousands) [before being entangled with A] of years ago have some kind of non-local effecton B that "just" collapsed onto the star 10 billion years ago? What about the A from hundreds (or thousands) of years ago on earth and the B that collapsed on a receding star 10 billion light years away?

    [note that an observer on a planet 10 billion c years away from year walking away from earth at a speed of approximately 9.7mph, his/her now slice would be about 150 years before earths now slice.]
     
  2. jcsd
  3. Oct 20, 2009 #2

    DrChinese

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    There is no correct answer for this. It is somewhat interpretation dependent.
     
  4. Oct 20, 2009 #3
    You cannot have two coherent states for that long anyway. So I think this question is experimentally irrelevant.
     
  5. Oct 20, 2009 #4

    zonde

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    How would you know that the electron that collapsed onto a star 10 billion light years away is the same electron that get entangled with electron A a moment before if you can't establish causal sequence?
     
  6. Oct 20, 2009 #5
    Why are people brushing off this question? Isn't this just the EPR paradox?
     
  7. Oct 20, 2009 #6

    zonde

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    No, it isn't.
    In EPR paradox you first of all have more or less unambiguous way to identify pairs of particles and after that you analyze statistical correlations in pairs.

    But this question is more in line with discussion in this thread
    https://www.physicsforums.com/showthread.php?t=339957"
    about uncertainty "exceeding" speed of light.

    I can point to my answer in that thread:
    https://www.physicsforums.com/showthread.php?p=2363289#post2363289"
    And as well there was similar answer to texta's question in another forum:
     
    Last edited by a moderator: Apr 24, 2017
  8. Oct 20, 2009 #7
    No, that's incorrect. There is no pairwise statistical analysis in the EPR paradox. That came thirty years later when Bell proposed an experimental means for checking the result of the EPR thought experiment. The EPR paradox is essentially exactly what the OP wrote down.
     
  9. Oct 20, 2009 #8

    zonde

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    Sure :approve:
    But if I may I will hold to my position.
     
  10. Oct 20, 2009 #9
    When you put it that way, how can I disagree?
     
  11. Oct 20, 2009 #10

    DrChinese

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    Yes, that's fine.

    But the questions being asked relate to things like: would they still be entangled? Who knows when entanglement can be said to "end". That is interpretation dependent. In some: when one particle is observed, the other collapses as well simultaneously. But there are others in which this point is silent. In others, such as Relational Block World (RBW): there is no absolute time frame to which to attach the end time for either.

    The OP's other question was whether there is a non-local effect. Again, some interpretations would say yes, others no, others silent.

    So I am sorry to say that there are no concrete answers on these. But I think it would be safe to say: an entangled particle could itself avoid collapse for many years into the future IF you assume strict locality (i.e. I think MWI would work here) or don't quibble over the issue of when collapse occurs (i.e. I think RBW would work here).
     
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