From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: Why do physicists make preposterous predictions?
Date: 25 Sep 92 15:23:08 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <Bv458q.1E1@news.cso.uiuc.edu>, jjt@uihepa.hep.uiuc.edu writes:

> It is experimentally detectable (according to QM) only after the two observers
> exchange messages by conventional (that is, causal) means.

True enough. If you are suggesting that causality is preserved because of this,
that is a complex question and it depends on what definition of causality
you use. Either special relativity or causality as defined in classical
mechanics is violated.

> >The results that quantum mechanics predicts are only possible if information
> >about the angle of at least one polarizer is transmitted
> >instantaneously across billions of light years to the other observation and
> >influences the results there. 
> 
> This depends how you define "information."  Your use is not in accord either
> with the dictionary (where it means knowledge) or with common practice in
> physics.

I think all the standard definitions apply. In a suitable experiment you
know something instantaneously about what happened at a distant site. You
know that certain combinations of polarizer angles and detections are more
or less probable. Bell's result implys that this knowledge must have
been transmitted instantaneously in at least one direction.

> > You cannot by changing the angle of your polarizer send a signal to the
> > distant star gazer. But you can, nontheless, change which events are
> > detected instantaneously over a distance of billions of light
> > years. At least thats the story quantum mechanics tells.
> > Why would serious physicists believe this seemingly preposterous prediction?
> 
> You are using the word "change" in a nonstandard way.  No effect is seen by
> the distant observer.  "Correlation" is not "change."

If I change the settings on a dial and this produces experimental results
that are different then they would have been then it is correct to say
that I have changed what events are detected. This is what happens in
tests of Bell's inequality. The fact that this is not detectible
*at the time* by the distant observer is hardly relevant. It is detectible
eventually.

> >The theoretical principle on which this prediction is made is ... (sigh, I
> >cannot even give it a name without creating controversy). ...
> 
> They cannot agree, because they do not need to.  It does not make any 
> difference to the predictions that one makes.  That is why interpretations are
> not the same as theories.

Perhaps they cannot agree because this aspect of physics is hopelessly
muddled. That is why interpretations are needed. No one ever talks about
interpretations of special relativity.

> You may be correct in your belief that QM is wrong and the wave function is a
> physical entity, subject to the usual laws of physics.  Experimental tests of
> QM are important.  However, it is not necessary to misrepresent the
> conventional ideas to make your case.

By using conventional language clearly and correctly I seem to make
statements at odds with the way some physicists describe these things.
If you look at P. H. Eberhard, Il Nuvo Cimento 46 B, 392, (1978), a
clear discussion of these issues, I think you will find that my
lanuguage is similar to his. I think some physicists abuse language
to make these issues appear less problematic then they are. 

Paul Budnik