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Hugh Haskell wrote in an earlier post -- Photons are particles (not like
electrons or protons, but particles nevertheless)
I would like some discussion on this point as I try to clarify my thinking.
What characteristics are necessarily present in order to call something a
particle?
I have listed a few characteristics particles often seem to have and
thoughts about how each may apply to photons. Comments, clarifications,
disagreements, and instructions are hereby solicited.
1) Charge - No. Photons like neutrons and many other "particles" have no
charge.
2) Mass - No.
I guess photons are massless since they travel at the speed of
light. I don't really understand what this means however especially when
momentum and energy are considered.
3) Momentum - Yes. I understand that photons do have momentum.
Exactly what this means however is unclear to me.
It must not mean p = mv since photons have no mass.
4) Inertia - I am really baffled on this one. No mass means no inertia but
photons obey Newton's First Law. How can that be?
5) Energy - Yes, they can cause change I suppose.
I used to be more sure of
this, but that was when I thought I understood what energy was.
After considering Leigh's thoughts and those of others I'm not
so sure anymore.
6) Something that is quantized - Perhaps a particle can be considered
anything that is quantized.
All points here well taken. I was not trying to make any definitive
statement about particles, just trying to differentiate them from
maxwellian waves, without letting them get mixed up with the
"ordinary" particles of everyday life.