Re: point particles

[John Denker <jsd@AV8N.COM>]

Quoting cliff parker <cparker@CHARTER.NET>:

> Why are electrons, quarks, etc presumed to be point particles in the
> standard model?  Are we just trying to force them to be fundamental
> particles since nothing can be imagined smaller than a point.

There are perhaps two or three possible answers, depending
on what one reads into the question.

 -- First of all, it depends on what "etc." means.  The bosons
(photons, pions, ...) are not pointlike.  Protons and neutrons
are not pointlike.

 -- At the most superficial level, it's a tautology.  If you make
a model that assumes certain things are pointlike, then it's
circular to ask why they are assumed to be pointlike.

 -- The non-circular version is to ask why anybody would pay
attention to a model that assumes e.g. electrons are pointlike.
The answer is that people have looked (really, really looked)
and not seen any internal structure in electrons.

On the other hand, I don't know anybody who would bet very
much on the long-term viability of any such theory.  A the
very least, a truly pointlike electron would have problems
with its electrostatic self-energy.

So the way I would express it goes like this:  there must be
something going on, but we don't know what, and whatever it
is doesn't affect the outcome of the experiments we know how
to do.  So those who wish to disregard the internal structure
can do so (for now) without penalty.

Those who do wish to pursue the structure issue have lots of
company.  Check out e.g. the annual "strings" conferences.