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From: doug@netcom.com (Doug Merritt)
Subject: Re: Heisenberg's Uncertainty Principle
Message-ID: <dougD577wK.DwJ@netcom.com>
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
References: <smryanD470Ax.DuE@netcom.com> <3iatdb$e91@news.globalx.net> <jon-2202951316470001@hfmac323.uio.no>
Date: Fri, 10 Mar 1995 00:26:44 GMT
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In article <jon-2202951316470001@hfmac323.uio.no> jon@babel.ifl.uib.no (Jon Hareide Aarbakke) writes:
>> In article <smryanD470Ax.DuE@netcom.com>, smryan@netcom.com (Artie
>Choke) says:
>> >Broadly stated, the Uncertainity Principle in physics means that
>> >attempt to observe a system perturbs it so the observer and the
>> >system are one.
>
>Apparently this is a common mis-stating of the Principle. 

I wouldn't call it a misstatement, even though any such loose interpretation
can be misleading. During an interaction, the wave functions of the
observer and observed can become nonlinearly tangled, such that
the only accurate representation is a wave function containing both
observer and observed as a single system.

This is not the usual popularized way of thinking about the uncertainty
principle, because the above represents a measurement of a quantum entity
*by* a quantum entity, whereas the popular notion involves measurement of
a quantum entity by a *macroscopic* (classically-approximated) system.
The latter never gets represented by a wave function in practice because
it's far too complex, for one thing.

>It is not that we mess it up when trying to observe, which would be a
>_classical_ physical problem,

Actually, the uncertainty principle *does* arise in classical physics,
although it wasn't originally noticed nor formulated there, because it
falls out of the Generalized Uncertainty Principle of Linear Algebra,
a purely mathematical result that does not depend on postulates nor
observations from quantum physics, and that applies to classical systems.

It is in fact *precisely* that we mess it up when observing. And this
is undoubtedly what Artie was getting at, quite aside from physics...
the question of whether observables in linguistics are messed up in
the process of attempting to observe them. Phrased this way, the answer
is obviously yes, in some sense.

It's all but impossible to observe people without risking interfering
with the phenomenon...as is well known in linguistics, anthropology,
psychology, etc.

>but rather that there is a fundamental sense
>in which there is a limit to how accurately we may determine the value of
>certain parameters. In so-called observational pairs, the more accurately
>we measure the value of one parameter, the more variation we will find in
>the value of the other. This applies if the two parameters are so-called
>incompatible observables. In that case, you can't have your cake and eat
>it. 

That's a reasonable restatement, too, that emphasizes different things.

>As for linguistics, it has very little to do with physics at all (at least
>in methodology). Some people just think it does. Or should do.

Many disciplines suffer from what is called "physics envy". :-) This
seems unrelated to the original question, though.

There *is* a linguistic equivalent to loose intuitive statements of
the uncertainty principle. Whether that equivalent can be made rigorous,
on the other hand, is doubtful, given state of the art.

As usual on the net, the moral would seem to be: avoid nitpicking,
and try to answer someone's intention.
	Doug
-- 
Doug Merritt				doug@netcom.com
Professional Wild-eyed Visionary	Member, Crusaders for a Better Tomorrow

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