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

Bells' Inequality Spin Violations

  1. Jul 12, 2013 #1

    morrobay

    User Avatar
    Gold Member

    When entangled photons are generated from a cascade of a Calciums' 6s level
    this inequality : n[y+z-] + n[x-y+] ≥ n[x-z-] is derived for what is equivalent to spin in photons.
    When the detectors at A and B are parallel the perfect anti correlations are due to conservation
    laws of angular momentum - a total spin of zero.
    When the inequality is dis proven with non parallel detector settings what happened to
    the conservation law ?
    Regarding Bells' inequality with electrons: When a sample is measured for 45° , 1/2 are found
    to be spin up. When a sample is measured for 90° , 1/2 are spin down. But when the sample that
    was measured for spin up at 45° is measured at 90° , only 15% are spin up.
    How can the possibility that the magnetic field in the detector alters electron spin be distinguished from QM forbidding knowledge of mutually non commuting observables when the inequality is
    dis proven ?
     
    Last edited: Jul 13, 2013
  2. jcsd
  3. Jul 14, 2013 #2

    morrobay

    User Avatar
    Gold Member

    This paper:www.arxiv.org/pdf/quant-ph/0407041 Correlation Function, Bells inequality and
    fundamental conservation laws. Bells inequality and a theory that satisfies the fundamental conservation law violates the inequality.
    Therefore - a theory of correlations satisfying Einstein locality, reality in the Einstein - Bell sense
    and the validity of the fundamental conservation laws cannot be constructed.
     
  4. Jul 20, 2013 #3
    Very interesting paper!

    If I understand you correctly, you ask why it is assumed that although the detector clearly interacts with the electron when it passes through, it can only act on (and not interact with) the electron spin. Indeed, that article (which was apparently reviewed) seems to ignore that in my eyes necessary option completely - it handles the measurement interaction as a "projection"!

    Can anyone clarify that issue?
     
    Last edited: Jul 20, 2013
  5. Jul 20, 2013 #4

    stevendaryl

    User Avatar
    Staff Emeritus
    Science Advisor

    I think you're right. One could imagine that there is angular momentum transferred between the particle and the detector. In that case, looking at the spin of the particles alone would not be sufficient to account for all the angular momentum. So there would be no reason for particle spins to add up to zero after interacting with the detector. So I agree that the correlation doesn't follow from angular momentum conservation alone.
     
  6. Jul 20, 2013 #5

    stevendaryl

    User Avatar
    Staff Emeritus
    Science Advisor

    Actually, now I'm not sure. The interaction with the detector would mean that you don't have conservation of momentum for just the particles, but maybe when you take AVERAGES, the effect of the detectors should average to zero?
     
  7. Jul 20, 2013 #6
    Maybe it should, according to classical theory. But that's I think another issue than the one that the paper addresses: Unnikrishnan claims in the summary that 'any theory of correlations of such discrete variables satisfying the fundamental conservation law of angular momentum violates the Bell’s inequalities'.
    And more clearly in the body text:
    'a physical system with discrete observable values can show correlations different from what
    is predicted by quantum mechanics only by violating a fundamental conservation law!'.


    In view of Morrobay's pertinent question, I don't see how that follows from that paper.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Bells' Inequality Spin Violations
Loading...