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From: brooks@lll-crg.ARPA (Eugene D. Brooks III)
Newsgroups: net.physics
Subject: Re: Heisenberg Uncertainty Principle
Message-ID: <775@lll-crg.ARPA>
Date: Fri, 9-Aug-85 01:58:26 EDT
Article-I.D.: lll-crg.775
Posted: Fri Aug  9 01:58:26 1985
Date-Received: Mon, 12-Aug-85 02:13:54 EDT
References: <3506@decwrl.UUCP>
Organization: Lawrence Livermore Labs, CRG group
Lines: 19

> In over-simplified terms Heisenberg's Uncertainty Principle says that we
> cannot know the simultaneous position and momentum of an individual
> elementary particle with unlimited accuracy.  Yet, we are able to
> determine the simultaneous position and momentum of conglomerations of
> these elementary particles.  That is, I can determine the position and
> momentum of my desk to a degree of accuracy limited only by the resolution
> of the measuring equipment I use, whereas the Uncertainty Principle says
> that no matter how accurate my measuring equipment, when it comes to the
> individual particles making up the desk, it is fundamentally impossible to
> even make the observation.

You can not measure the simultaneous position and momentum of your desk to any
degree of accuracy.  QM applies to your desk as well and sets appropo limits.
There are gravity wave detectors, aluminum bars, that weigh several tons and
require QM to correctly describe them.

In the case of your desk, the limits set by QM happen to be many orders of
magnitude smaller than any measuring device available to measure its position
and momentum.