Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Bell Proof Against Hidden Variables in EPR