From: ddixon@nyx.cs.du.edu (David Dixon)
Subject: Re: Quantum reality silliness
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Date: Wed, 14 Oct 92 19:32:31 GMT

In article <1992Oct13.174345.20680@lmpsbbs.comm.mot.com> bhv@areaplg2.corp.mot.com (Bronis Vidugiris) writes:
>In article <1992Oct10.025445.14017@mnemosyne.cs.du.edu> ddixon@nyx.cs.du.edu (David Dixon) writes:
>...
>)I think a lot of the confusion about quantum mechanics occurs because we
>)have been imbued with this belief in the wave-particle duality, as if
>)sub-atomic particles somehow consisted of a "wave" which carried along a
>)tiny point-like particle with it.  Baloney.  The proper way to think of it
>)is that the wave function is a field which tells you probabilities of a
>)certain amount of energy or momentum being exchanged at a certain point
>)in space-time.  Nothing mystical about it.
>
>The issue isn't one of determinism.  Non-deterministic theories that are
>local and realistic also have the same problem.
>
>If you accept classical definitions of probability, and also believe that
>trees do make a sound when they fall in a forest even if there is no one
>to hear it :-) (and particles do have a spin direction even if they haven't
>been measured yet), you run into the problem with QM.
>
>The experimental evidence is, of course, the key issue.  If locality or
>realism had been definitely disproved, that would be one thing.   The
>current status is not quite that clear.
>
You're right.  I do tend to get my determinism and realism mixed up
(damn classical prejudices).

That said, though, I do think that the way quantum mechanics is taught
engenders a lot of confusion, because the implication is that there is
some classical ball-bearing type particle which is magically either a wave
or point-like, depending on how you try to look at it.  This bias seems
to show up in every text I've seen (not exactly a library-full, mind you)
and is probably the result of the wide acceptance of the Copenhagen
Interpretation.

As Roger Penrose pointed out, QM predicts *deterministically* the time
evolution of a system, until it gets observed, at which point there is a
discontinuity in the state vector as it gets "forced" into an eigenstate
(assuming it wasn't there to begin with.  And yes, I know I'm over-
simplifying the matter.  I'm just trying to lead you down the garden
path :-))  This separation of observer and observed (due to the CI)
seems at best arbitrary, and at worst unphysical.  It's like saying
"Look, I've made ice from liquid water.  Since ice has a lower entropy
than liquid water, the 2nd law of thermodynamics is violated."  Of course,
all you've really done in this case is isolated a subsystem from the whole
system, and then attempted to draw conclusions about it while neglecting
possible external effects.  Hence the problem with observation in QM:
if you leave out your "observation" when computing the Hamiltonian for
your experiment, obviously the time evolution of the state when observed
will show screwy, unpredictable behavior.

By the way, there are theories which attempt to incorporate the observer
as part of the system.

					Dave