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Article 6088 of comp.ai.philosophy:
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>From: holmes@opal.idbsu.edu (Randall Holmes)
Newsgroups: comp.ai.philosophy
Subject: Re: Quantum mechanics (no AI here, sorry)
Message-ID: <1992Jun4.231401.13271@guinness.idbsu.edu>
Date: 4 Jun 92 23:14:01 GMT
References: <1992Jun03.203556.4561@spss.com> <1992Jun3.225545.27925@guinness.idbsu.edu> <1992Jun04.181928.5451@spss.com>
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In article <1992Jun04.181928.5451@spss.com> markrose@spss.com (Mark Rosenfelder) writes:
>In article <1992Jun3.225545.27925@guinness.idbsu.edu> holmes@opal.idbsu.edu 
>(Randall Holmes) writes:
>>It's local properties of the _waves_ that are involved.  Such an
>>experiment is carried out by setting up a state in two widely
>>separated locations which depends on an unobserved factor in a single
>>earlier event.  One then makes observations at the widely separated
>>points, and, lo, they agree with one another.  These results make
>>perfect sense (require no explanation at all, in fact) on a hidden
>>variables interpretation, i.e., on the interpretation that there was a
>>real underlying value to the unobserved factor in the earlier event
>>which we did not in fact observe (we couldn't observe it and do the
>>experiment, in fact).  The "non-locality" has to do (on my
>>interpretation) with the fact that getting extra information about
>>event A may immediately give me extra information about event B even
>>if A and B have space-like separation (suppose that event A and event
>>B are individuals listening to television broadcast years earlier from
>>Earth, at the same distance from the Solar System in opposite
>>directions in the conventional frame of reference of the Solar System,
>>and the information that I have acquired is a copy of the TV schedule;
>>I then know that if A watched "I Love Lucy" at a certain time, so did
>>B).  [...]
>
>Perhaps we are not talking about the same thing.  Let me attempt to
>describe the problem in more detail.  I hope physicists reading this
>will gently correct any errors I make.
>
>An apparatus is set up which emits a stream of spin-correlated photon pairs 
>in opposite directions.  Observers at points A and B are using calcite 
>crystals to test the polarization of each pair of photons.  The following 
>results are noted:
>
>   Angle between orientation   Errors in their
>   of A's and B's calcite      spin observations
>           0                     0 in 4
>          30                     1 in 4
>          60                     3 in 4
>          90                     4 in 4
>
>Now, this seems to be what you are talking about: we observe a correlation
>between A's and B's observations, but we have no reason to suppose any
>superluminal (or even subluminal) connection between the photons once they 
>leave the apparatus.
>
>A local hidden-variable theory could explain the observations by supposing
>that each photon, as it leaves the apparatus, "knows" how it is going to
>react to each possible setting of the observer's calcite (perhaps by 
>having an explicit angle of polarization, rather than the binary spin
>value assumed by QM).  
>
>A photon leaves the apparatus, and A twists his calcite 30 degrees left.
>No problem: the photon knows how to respond to any angle.  Before either
>photon is measured, but after they've left the apparatus, however, B turns
>*her* calcite 30 degrees right.  If the locality assumption is true, that
>can make no difference in A's observations.  But it does: the observations
>are now correlated at the 3-errors-in-4 rate.  
>
>To know how to respond to A's observation, the photon needs to react not
>only to the orientation of A's calcite, but to that of B's too, and its
>knowledge is not limited by the speed of light.
>
>Hidden variables are not ruled out, but solely local ones are.

No, they aren't.  The particle has a whole spectrum of reactions to
the settings of the instruments, which are probabilistically
correlated with each other.  They are decided at the source.
Certainly a single angle of polarization won't work, but independent
yes-or-no answers for each angle which are correlated with one another
with probabilities depending on angles in the usual way work fine.  No
one said that the hidden variables were simple!


-- 
The opinions expressed		|     --Sincerely,
above are not the "official"	|     M. Randall Holmes
opinions of any person		|     Math. Dept., Boise State Univ.
or institution.			|     holmes@opal.idbsu.edu


