From: carlip@physics.ucdavis.edu   
      
   On 2/1/18 11:55 PM, SEKI wrote:   
   > Consider a photon pair.   
   >   
   > (1) Each of paired photons is created simultaneously at the same   
   > point, and travels at the speed of light in a direction opposite to   
   > each other.   
   >   
   > (2) No or, at most, negligible interaction is possible between   
   > photons.   
   >   
   > (3) No restriction is imposed on superposition of quantum waves of   
   > photons, which are bosons.   
   >   
   > Then, is any correlation between paired photons earthly, other than   
   > those determined at the point of pair creation?   
      
   It depends on what you mean by correlations.   
      
   In your example, I can choose to measure the polarization   
   of each photon along any axis I choose.  Given any such   
   axis, I will measure the photon as either having a   
   polarization in the direction of the axis or in the   
   perpendicular direction.  Quantum mechanics predicts the   
   probability of each outcome, and also predicts certain   
   correlations between the results when I measure both photons.   
      
   Bell showed that if these were ordinary local, "classical"   
   correlations, they would have to satisfy a certain inequality.   
   "Classical" here means that each photon has carries some set   
   of properties -- "hidden variables" -- that determine the   
   probability of finding a given polarization along any chosen   
   axis.  In other words, if I tell you the axis along which I   
   want to measure the polarization, you can use these properties   
   to determine the probability of finding a parallel or a   
   perpendicular polarization.  "Local" means that the properties   
   of the photons might be correlated, but that any correlation   
   must have been established when they were first produced --   
   they can't communicate with each other after they have   
   separated.   
      
   Quantum mechanics predicts correlations that *violate* the   
   Bell inequalities.  Such correlations can't be explained by   
   what I've called local, classical correlations.  And when   
   the experiments are done, they agree with quantum mechanics   
   -- Bell's inequalities are, in fact, violated by nature.   
      
   If you want to argue against Bell's results, you have to   
   look at his proof and identify *specifically* which of the   
   assumptions you want to change, and how to change it.  The   
   proof itself is not hard -- there's a nice version in the   
   introductory quantum mechanics text by Griffiths, for instance.   
   But it's not enough to just say that you are certain that   
   there must be some way out.   
      
   Here are some ideas that don't work.  You can't say that when   
   the photons are produced, they already "know" the settings   
   of the detectors.  Experiments have been done in which the   
   detector settings are randomly changed after the photons   
   are already in flight.  You can't say that the experimental   
   results are misleading because not all of the photons are   
   actually detected.  This "detection loophole" was always a   
   stretch, but now it's been experimentally closed.   
      
   Steve Carlip   
      
   --- SoupGate-Win32 v1.05   
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