Re: point particles

[John Denker <jsd@AV8N.COM>]

Quoting cliff parker <cparker@CHARTER.NET>:

> What do you mean by internal structure?  I imagine a marble or BB as an
> object with no internal structure.  Meaning homogeneous material through and
> through.  All marble and nothing else.

The way particle jockeys use the term, especially in this
context, "structured" is the antonym of "pointlike".
Internal structure means about the same as structure.

In this context, a marble or a BB clearly has structure,
the sort of structure you'd see in a scattering experiment.
In the vicinity of a marble, there is trivial (i.e. vacuum)
dielectric constant outside a certain radius R, and a
conspicuously non-trivial dielectric constant inside that
radius.  If you probe it with something having a wavelength
on the order of R, you are definitely going to notice that
it's not pointlike.

An electron, in contrast, appears to be pointlike according
to all experiments to date.  It's smaller than a radio wave.
It's smaller than a microwave.  It's smaller than a light wave.
It's smaller than a gamma. .... You get the idea.

Maybe somebody will see the structure of the electron
tomorrow. Maybe it's a string.  I dunno.  But I wouldn't
wager a lot on its being absolutely totally pointlike.

> Are
> you talking about things like charge distribution appearing to originate
> from one point.  No tiny "tide" effects, that sort of thing?  Therefore no
> implied size?

Tides and internal "mechanical" resonances are a more advanced
subject.  You can hypothesize a marble that is "all marble and
nothing else" but a real marble will have phonons and other
excitations running around inside it.  Almost anything you can
imagine that has nonzero size will have an "inside" and then
somebody is going to ask "what's inside".

A "particle" consisting of a void in an otherwise perfect
piece of clear glass may not have "internal" structure in
the strictest sense, but it will still have an easily
detectable size and (if you look closer) will be subject
to mechanical distortions, so it will act like a particle
with all kinds of structure.