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.