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From: sra@oddjob.UUCP (Scott R. Anderson)
Newsgroups: net.physics
Subject: Re: Re: White Holes?
Message-ID: <951@oddjob.UUCP>
Date: Wed, 28-Aug-85 11:17:32 EDT
Article-I.D.: oddjob.951
Posted: Wed Aug 28 11:17:32 1985
Date-Received: Fri, 30-Aug-85 09:00:39 EDT
References: <3656@decwrl.UUCP> <166@prometheus.UUCP> <490@talcott.UUCP> <937@oddjob.UUCP> <171@prometheus.UUCP>
Reply-To: sra@oddjob.UUCP (Scott R. Anderson)
Organization: University of Chicago, Department of Physics
Lines: 30
Summary: 

>> So far as we know, the "fundamental" particles (quarks, leptons, etc.) ARE
>> points.  Experiments have yet to determine any finite extent for these
>> particles.  I believe that the current upper limit on the radius of the
>> electron is 10^(-18) meters or 0.001 fermi.

In article <171@prometheus.UUCP> pmk@prometheus.UUCP (Paul M Koloc) writes:
>If you had said kilometers.  Actually, electron radius is ~ e^2/(m*c^2)
>which comes to about 3 * 10^(-15) meters.  Still infinitely larger than
>a point radius. --"e" is charge; "m" is electron mass; and "c" is light 
>speed. They are represented as points, for convenience. 

This is what is known as the classical electron radius; it can be derived
in several ways based on classical electrodynamics (ref. Jackson, Classical
Electrodynamics).  However, an electron is a quantum mechanical object, and
as one might expect the above expression is only valid in certain regimes
(e.g. when the experimental probe has a wavelength much greater than the
c.e.r.).  Current experimental results make clear that the c.e.r. has
nothing to do with the true electron radius, assuming it has one.  Note
that I am not saying that the electron doesn't have a finite radius,
just that experiments have set a limit on what it can be.  And ascribing
a finite size to electrons (or muons or quarks) is an unnecessary
complication for most field theories (recall Occum's Razor!).

>I think "point" in quantum mechanics means "smudge".

If you choose to know nothing at all about a particle's momentum, "point"
means "point" in the mathematical sense.  This is the delta function.

				Scott Anderson
				ihnp4!oddjob!kaos!sra