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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.physics
Subject: really elementary particles
Message-ID: <281@utastro.UUCP>
Date: Mon, 14-May-84 18:20:16 EDT
Article-I.D.: utastro.281
Posted: Mon May 14 18:20:16 1984
Date-Received: Wed, 16-May-84 03:35:47 EDT
Organization: UTexas Astronomy Dept., Austin, Texas
Lines: 36

[If this is the answer, what was the question?]

The question has recently arisen, in connection with the cosmology
debate, on the extent to which one can imagine that all known particles
are merely composities of some very simple structures.  There is an
article in a recent SciAm on this topic (sorry, don't remember the
month).  The essential problem is as follows.

  It is now widely believed that baryons and mesons are composite
particles made up of quarks whose interactions are mediated by
gluons.  In this picture we have 3 "generations" of particles
which for leptons are electrons, muons, and tau particles with
their accompanying neutrinos, and for quarks are three pairs
(up/down, strange/charm, top/bottom [ or truth/beauty]).  In addition,
there exist various particles (photons, W and Z bosons, gluons, and
gravitons) that mediate the forces of nature.  This may simply be
some small fraction of a larger picture.  The question has naturally
arisen: could these particles represent the rearrangement of few
basic particles (called preons or rishons or ...).  The major
difficulty is that the effective "size" of quark is very small and
the mass of a up or down quark is only a fraction of a proton mass.
In order to fit smaller particles inside a quark they must have
tremendous momentum (Heisenberg uncertainty principal del p x del x
is less than Planck's constant).  Therefore they must have a large
energy, which in turn corresponds to a mass which is much greater than
the mass of the quark into which they fit.  It is not clear how to
make this work.


                     "Just another Cosmic Cowboy"
                         
                         Ethan Vishniac
                         {ut-sally,ut-ngp,kpno}!utastro!ethan
                         Department of Astronomy
                         University of Texas
                         Austin, Texas 78712