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From: rimey@ernie.BERKELEY.EDU (Ken &)
Newsgroups: net.physics
Subject: Re: Blimey, Rimey (QM & Many-Worlds)
Message-ID: <11524@ucbvax.berkeley.edu.BERKELEY.EDU>
Date: Fri, 24-Jan-86 04:24:59 EST
Article-I.D.: ucbvax.11524
Posted: Fri Jan 24 04:24:59 1986
Date-Received: Sat, 25-Jan-86 08:03:53 EST
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Reply-To: rimey@ernie.UUCP (Ken Rimey)
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>>What I mean is that it is unnecessary to postulate that wave functions
>>collapse during measurements.  Measurements are ordinary physical
>>interactions of matter with matter, and are adequately described by
>>ordinary equations of motion.
>
>OK, fine, except for one thing.  You speak of "a theory in which the universe
>is deterministic."  Then how come, when one performs a measurement on a
>"mathematical object that represents the state of the universe", the outcome
>is only *probable*.  That is, given two electrons (fired in sequence through
>the famous "two slits") represented by the same mathematical equation, and 
>using a single measuring device, one nevertheless can get different 
>measurements.

Nevertheless, abstractly, the theory only tells us how to calculate
one future, one that incorporates both outcomes of the experiment.
That is the only mathematical theory we have.  The values of the
probabilities we observe in the real world stare us in the face when
we calculate that deterministic future, but to interpret them as
probabilities and contradict the deterministic nature of physical law
is beyond the mathematical theory.  It would be nice to have something
more to say, but we don't.  People talk of nondeterministic collapse
of wave functions, but that is only vague mumbling unrelated to any
mathematical model of the universe.  The reason that this gap in our
understanding is not a handicap is that all the calculations, the
numbers, the meat, is contained in the deterministic theory.

>>> >Many working
>>> >physicists will, if you ask them, express doubt as to whether quantum
>>> >mechanics is really applicable to cats and such. [RIMEY]
>>> 
>>> And one interpretation of QM has it that it [QM] doesn't [crucially depend
>>> on an "observer"], because macroscopic
>>> objects like cats and such involve entropy (i.e. when the cat dies, entropy
>>> is increased, thus an irreversible process has taken place). [TOREK]
>
>>That is not an interpretation of QM.  It is simply wrong.
>
>It is?  What's your evidence?  (Or were you misinterpreting me?  What I meant
>was that one could assume that wave packets collapse whenever entropy is
>increased (or maybe it's, increased *by a sufficient amount*).  Thus, one
>can admit wave packet collapse without deifying observers and encouraging
>crackpots.)

Entropy is a statistical concept, like standard deviation.  There is much
arbitrariness in defining it, though this doesn't make any difference in
practice for macroscopic systems.  The familiar thermodynamics definition
is funny because it is history dependent and not a function of the
current state of the system.  Entropy can play no role in the fundamental
laws of the universe.  It is not a physical thing.  (Well, I challenge
anyone else to say it better.  Please.)

						Ken Rimey