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I hear a lot about nonlocality and it's relationship to QM

  1. Oct 4, 2006 #1
    I hear a lot about nonlocality and it's relationship to quantum mechanics and relativity. But I don't know anything about it. Please give me a basic description.
  2. jcsd
  3. Oct 4, 2006 #2


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    The basic idea of non-locality is that sending a cause over a spacelike interval, or in other words faster than light, is non-local. If we accept relativity, this would be a no-no.

    But beyond this, especially in connection with interpetations of quantum mechanics, there are subtleties. Decades ago the late physicist Johm Bell, at CERN, devised a set of inequalities on the predictive abilities that a local theory might have concerning a set of things with spacelike separation, and this made it possible to test experimentally whether quantum mechanics obeys those inequalities, and settle a question that goes back to EInstein's challnges to QM, whether QM is local or not. A long series of experiments have been done since, and the majority consensus is that it has been shown that QM is weakly nonlocal in that the predictive limits derived by Bell for local theories are violated, But the concensus denies that the strong sense of nonlocal I started off with applies to QM; correlation is not causation.

    There are active dissent movements on these points and I'll let them speak for themselves. Possible points of dipute seem to be (1) Did the experiments really show what is claimed? and (2) Just what did Bell mean by "local" and "nonocal?"
  4. Oct 4, 2006 #3
    I would be grateful if someone could point me to a copy of John Bell's paper.
  5. Oct 4, 2006 #4


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    You can find it at this link (my site), in PDF format (along with the key EPR & Aspect papers):

    The Original References
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