Re: Just what is a particle?

[William Beaty <billb@ESKIMO.COM>]

On Thu, 17 Feb 2000, Cliff Parker wrote:

> 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.

I think that photons have zero rest mass, meaning that all of their mass
is caused by their motion.   If we converted Jupiter into a narrow beam of
light, would we feel its gravity as the light-pulse raced by?  Do pulses
of light emit gravity waves when they bounce off a mirror?




> 6) Something that is quantized - Perhaps a particle can be considered anything
> that is quantized.


I think #6 is the big one.  Early on in the history of QM there was
resistance to the idea that quanta were particles.  If I recall my history
readings correctly, when Stoney coined the term "electron", it was in
reference to the quantization steps of electric charge, and he briefly
fought against the idea that "particles of electricity" had real
existence.

If light is emitted as quanta and detected as quanta, but it acts like
waves as long as nobody touches it, maybe particles of light do not exist.
Maybe the physics of atoms requires that EM waves always be emitted with
quantized energy and absorbed the same, but only the waves are real.  (If
so, then how are those single-quantum, light-years-wide light wavefronts
from individual atoms in distant stars collapsed instantly so they only
strike one dye molecule in the retina of our eyes?)




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