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From: brooks@lll-crg.ARPA (Eugene D. Brooks III)
Newsgroups: net.physics
Subject: Re: Re: Re: Faster than Light
Message-ID: <686@lll-crg.ARPA>
Date: Sun, 7-Jul-85 17:55:19 EDT
Article-I.D.: lll-crg.686
Posted: Sun Jul  7 17:55:19 1985
Date-Received: Fri, 12-Jul-85 05:02:47 EDT
References: <353@sri-arpa.ARPA> <681@lll-crg.ARPA> <11387@brl-tgr.ARPA>
Organization: Lawrence Livermore Labs, CRG group
Lines: 43

> > is not however real physical entity like for instance an electric field.
> 
> (followed by a discussion about how the wave function isn't real)
> 
> Everything you say about the QM wave function could also be said about
> the electric field.  What makes the electric field any more real than
> the QM wave function?

The wave function and the electric field have one fundamental difference.

The electric field is observable in a single experiment. The wave function is
not.  When an electric field collapses the stored energy density has to
go somewhere and there are measureable physical consequences.  The electric
field certainly did have its beginnings as a computational device.  And I
think that this is the root of your your comment.  I in fact won't argue
with anyone about whether or not it is real.  It is likely that you can have
it both ways.

The wave function is a different sort of animal.  It is used to describe the
probabilistic results of a large number of identical experiments.  It can be
measured only by repeating the identical experiment.  When it "collapses"
there are no measureable consequences of the "motion".  The "collapase" is
only there to explain the fact that when the particle is detected at one place
it is not going to be detected elsewhere.  The wave function (squared) gives
the probability of one of several choices.  It is inherently not measureable
in the context of a single experiment.

Reality, like beauty, is in the eye of the beholder.  I will not further
harass anyone who wants to think of the wavefunction as a real thing that
is distributed in space and moving around.

When using the Schrodinger picture (See QM by Messiah for discussion on this)
I tend to think of the wave function as a 'real' field that is distributed over
space and is moving around.  Consider, however, the Heisenberg picture where the
wavefunction is a constant vector and its the operators that move around.  You
can of course have if anywhere in between.  A case in point is the Interaction
picture.

When someone wants want to worry about the wavefunction's "instantaneous
collapse" as being in potential violation of relativity or unasthetic he/she
is thinking that the wavefunction is a bit more real than it really is.
This is something that is not in the eye of the beholder and can clearly
labeled as a misinterpretation of the facts.