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From: debray@sbcs.UUCP (Saumya Debray)
Newsgroups: net.physics
Subject: Re: Heisenberg Uncertainty Principle
Message-ID: <415@sbcs.UUCP>
Date: Fri, 9-Aug-85 20:33:26 EDT
Article-I.D.: sbcs.415
Posted: Fri Aug  9 20:33:26 1985
Date-Received: Mon, 12-Aug-85 05:16:57 EDT
References: <3506@decwrl.UUCP>
Organization: Computer Science Dept, SUNY@Stony Brook
Lines: 31

> 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.

Not really.  Heisenberg's principle states (more or less) that for quantities
related in a certain manner ("canonically conjugate"), the product of the
uncertainties in their measured values is of the order of Planck's constant.
The x-momentum (momentum along the x axis) and x-position of a particle are
canonically conjugate quantities, so cannot be simultaneously measured with
unlimited accuracy; however, the y-momentum and x-position are not canonically
conjugate, so they can be measured simultaneously without any problem.

If you could find sufficiently accurate measuring instruments, I suspect
you'd find the uncertainty in the x-momentum and x-position of your desk to
be, in fact, be of the order of Planck's constant.  The magnitude of this is
so small, however, that for "all practical purposes", your knowledge of the
position and momentum of your desk is accurate.
-- 
Saumya Debray
SUNY at Stony Brook

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