On Wed, May 24, 2006 at 08:36:46AM -0400, Byron A Jeff wrote:
> 
> Not a problem. Photons have no mass. So they are not really particles in
> the true sense of the word.
> 
Not according to accepted nomenclature. Modern theories claim that
particles (field quanta) compose all matter, carry all energy, and
mediate all forces. Mass is merely one of the qualities a particle may
or may not have (such as angular momentum, various charges, etc.

A free photon is indeed massless, but as Russell noted, that is only
true upto Heisenberg's uncertainty principle, which allows photons to
acquire a small mass, as long as they put it back before anyone notices.
These massive photons (a.k.a. virtual photons) travel slower than c,
have a third polarization mode (longitudal) and among other things
mediate the electric and the magnetic fields.

Furthermore, the photon is merely one of a quadraplet of particles.
Their behaviour is quite similar, and there are processes which can be
mediated by either a photon or one of the others. Yet the other three
are some of the most massive particles known.

Yair.
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