Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Just what is a particle?



My guess, only a guess, is that the term received its current
meaning after it became clear that atoms have parts. Electrons,
protons and neutrons are permanent parts of atoms. Then
the terms was generalized to cover other tiny, and often
short-lived, entities, such as pions, muons, etc. etc.
Ludwik Kowalski

Jack Uretsky wrote:

Thank you for picking up on this. I have asked the same question a number
of times, usually when people talk about wave-particle duality. I have no
idea what "paricle" means in this context. And please dont tell me that
particle beams don't show interference pattern. All beams show
interference patterns to the extent that one can make the beams coherent.
Regards,
Jack

Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
Mark Twain, <Extract from Eve's Autobiography>

On Thu, 17 Feb 2000, Cliff Parker wrote:

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.

7) Others ----


Cliff Parker