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Bell Proof Against Hidden Variables in EPR

  1. May 8, 2013 #1
    I have a question regarding the paper by John Bell (www.drchinese.com/David/Bell_Compact.pdf‎ [Broken]) in which he shows that a certain hidden variable approach cannot reproduce the expectation values predicted by QM for a pair of particles in the singlet state.

    After eqn 15 on page 4, I don't understand the logic. Why can't ##P(b,c)## be stationary at the point ##b=c##? Seems like ##P## could have a minimum at ##b=c## and hence be a stationary point. How does ##P(b,c)## being the order of ##|b-c|## around ##b=c## prevent that? I guess I'm missing something big here.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. May 31, 2013 #2
    Hi Actually saying Bell's theorem rules out local hidden variables is today's take. Bell viewed the violation of his inequalities as a failure of local causality of Special Relativity.

    To me your question is just this: as b and c get close, then the difference b-c will take all sorts of small values and in Bell's words is not stationary.

    I think this is a mathematical point: apply two colinear fields at b=c and the correlation will also be non stationary.

    This point was addressed, if I recall, by CHSH who derived their inequalities to remove this point. However please note that this case (b=c) is very rare and the violation of the CHSH requires b and c to be orgononal, not colinear. Hence their magnitude is |b-c| = root(2)--look familiar.

    hope this helps
     
    Last edited by a moderator: May 31, 2013
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