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Cliff Parker's question (was: heat is a form of energy)



Sorry, I got sick of that old Subject line.

At 07:02 -0700 9/11/99, Cliff Parker wrote:

[my statement]: I have high school teachers asking me
if photons are pure energy. How do I answer such a question?
Most of them don't know what a photon is (I'm not sure I could
tell them) and if I tell them there's no such thing as "pure
energy" they just don't seem to want to hear me.

Leigh,

You may chose not to get into this but I wish you would. I am one of those
high school teachers and I am a bit confused. Is the reason you would not
call
a photon pure energy because of the dual nature of light? If there is no such
thing as pure energy then what is a wave? I have thought that describing a
wave as pure energy was appropriate. If this is not the case I would like to
have you and or others help me to clarify my thinking.

Don't feel that this is something simple that you should, somehow,
understand much better than you do. The extended quote from Feynman
that Bob Sciamanda posted speaks directly to this point. The quantum
world is weird, indeed; it is now trite to say so. Feynman's point (and
mine) is that the macroscopic world with which we all feel so familiar
and comfortable, and to which our vocabulary and analogistic capability
seem to be so well matched, has attributes which are not exactly
describable in common language.

There are well two prescribed formulae relating the physical quantities
(electric and magnetic fields, frequency, number of quanta) associated
with electromagnetic radiation with the energy of the radiation. Either
one adds up all the bits of field energy using the first formula or one
uses the quantum energy and multiplies by the number of quanta, or
photons. Both formulae give the same result. In either case the energy
of the particular batch of photons is an abstract function of physical
quantities. The radiation still interacts with matter (or with other
radiation) in both ways, which is the real meaning of "duality"; it
doesn't care how you calculate the energy*!

Photons are not "pure energy" any more than neutrinos are. The very
idea that "pure energy" exists is contrary to fact. Energy is an
abstract invention, the product of the mind of man, with absolutely no
corporeal existence. If Man had never existed energy would not exist in
even its present ephemeral form. Feynman says this most clearly in the
parable in Chapter four of his "Lectures". This is done so well and so
clearly in common English that any physics teacher who has not read it
and understood its message should go immediately to it and do so!

Oh yes. Thanks for asking, Cliff.

Leigh

*For some reason a new misspelling has crept into my typing. I
systematically misspell "energy" as "enrgy". Please excuse my poor
proofreading if this annoyance obtrudes. I'm not trying to reform
English spelling, too!

"...there are no blocks." -R. P. Feynman