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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.physics
Subject: Re: The Epistemological Aspect
Message-ID: <622@utastro.UUCP>
Date: Mon, 8-Oct-84 19:23:12 EDT
Article-I.D.: utastro.622
Posted: Mon Oct  8 19:23:12 1984
Date-Received: Fri, 12-Oct-84 04:42:36 EDT
References: <12668@sri-arpa.UUCP>
Organization: UTexas Astronomy Dept., Austin, Texas
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[]

Well actually, it's not just that the 'timing' of the collapse
of the wave function is not predicted.  It is predicted in the
sense that its rather peculiar properties are well defined.
Loosely stated it can be put this way:
  It is impossible for two measurements to imply inconsistent
things about the state of a system even if the system was
initially prepared as a superposition of states.

In the case of a single particle this is taken to mean that if
you measure the position of the particle then future measurements
must be consistent with that measurement i.e. must not involve
the particle moving faster then the speed of light.

In the case of a correlated system like two atoms whose spins
sum to zero this means that the measurements of the spins of
the atoms (as long as they are undisturbed) must sum to zero
regardless of whether the atoms are subsequently separated and
given separate homes (oops   wrong discussion).

This does not *necessarily* imply faster-than-light propagation
of wave function collapse.  I'm an agnostic on this subject, but
I believe that there are alternative views.  An example is the
many-worlds picture in which a superposition of states is literally
a superposition of possible future world lines you might be following.
In that case there is an objective reality to all quantities at all
times that does not entail ftl propagation of signals.  Playing these
games of alternate interpretations of quantum mechanics is frustrating
because one lacks means for distinguishing between possibilities.

                         
"I can't help it if my     Ethan Vishniac
    knee jerks"         {charm,ut-sally,ut-ngp,noao}!utastro!ethan
                           Department of Astronomy
                           University of Texas
                           Austin, Texas 78712