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From: torek@umich.UUCP (Paul V. Torek )
Newsgroups: net.physics
Subject: Re: Blimey, Rimey (QM & Many-Worlds)
Message-ID: <419@umich.UUCP>
Date: Sun, 26-Jan-86 02:05:16 EST
Article-I.D.: umich.419
Posted: Sun Jan 26 02:05:16 1986
Date-Received: Sun, 26-Jan-86 20:27:33 EST
References: <408@umich.UUCP> <11524@ucbvax.berkeley.edu.BERKELEY.EDU>
Reply-To: torek@umich.UUCP (Paul V. Torek )
Distribution: net
Organization: University of Michigan, EECS Dept., Ann Arbor, MI
Lines: 61
Summary: Taking measurements seriously

rimey@ernie.UUCP (Ken Rimey) writes:
>>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. [TOREK]
>
>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.

"The deterministic nature of physical law"?  Aren't you begging a question
there?  What I find disturbing -- incoherent, even -- about the Many Worlds
Interpretation as described by you, is that it doesn't take measurements
seriously.  Now see here:  measuring devices are part of reality too, and
so are human minds.  You can try to get out of "wave packet collapse" by
saying that measuring devices exist in an "uncollapsed" state too, but when
you get to the experimenter your position breaks down.  The experimenter
thinks "aha, the result was E1" or "aha, the result was E2", but not both,
not neither, not in-between (etc.).  (Unless you start postulating multiple,
branching universes, but you said you weren't going to do that.)

Let me put it this way:  how can a deterministic theory have it that the
very same initial conditions (particle, measuring device setup, etc.) lead
in different trials to the different outcomes experimenter-thinks-"E1!"
and experimenter-thinks-"E2!"?

>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. 

Vague mumbling?  One can derive the probabilities from the math.

>all the calculations, the
>numbers, the meat, is contained in the deterministic theory.

Except that the deterministic theory can't predict what I'll be thinking
after I perform the experiment.  Again -- the point bears repeating -- my
thoughts are events in the universe too.

--------------------[different issue]-------------------------
>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.

OK, I see your point here.  But suppose instead of entropy, it's a difference
in energy between "pure states" that matters; that is, perhaps wave packets
collapse whenever the difference in energy exceeds a certain value.  (For
greater detail, see a recent article by N. Maxwell in *Philosophy of Science*
-- I'll post a more complete reference next time, I promise, plus a few
choice passages.)

The point being, one can make sense of wave packet collapse without giving
aid to "crackpots" (making "observation" a fundamental notion) and without
resorting to multiple universes or (worse) taking measurement too lightly.

--Paul V. Torek							torek@umich