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Re: convert light into energy



At 9:31 AM -0800 2/2/00, Jim Green wrote (inter alia):

However, saying that a "wave packet" (or anything else) is converted into
"energy" is really nuts.

This _is_ clear: "energy" is a property of an "object" -- like color, mass,
and charge, etc.

While what Jim says is both true and important, many teachers refuse
to appreciate it. Slow down and think, folks! Energy is not a thing;
it is not real. It is just a number that we calculate by canon. It
has utility, indeed, but it has neither corporality nor reality, and
as such it cannot be expressed with purity either.

-> There is no such thing as "pure energy". Get over it! <-

It is unfortunate that our manner of speech has endowed an abstract
entity with a certain degree of concreteness in the popular mind. I
would like very much to retain the ability to use the colloquial
metaphor (even including "energy transport", but not, to my taste,
"heat transport") in my teaching. I must do this while vigilantly
keeping the caveat in the students' minds that energy is not real.

Jim and I have been pressing this point for years (with only slight
differences) and I'm glad that neither he nor I has felt it necessary
to give up. For those among you who feel this is a religious matter,
you are mistaken. It is a fundamental physical principle, as you will
see by an example of its application.

I've just come from my astrophysics class where I am developing the
background necessary to introducing the Saha equation. The unreality
of energy comes beautifully to the front when one shows the students
that the Boltzmann factor is the *only* possible functional form for
an energy dependent population distribution of excited states of an
atom (or anything else). One invokes the arbitrary nature of the
zero of energy and the result (the Boltzmann factor) drops out
entirely naturally. There is no way I know to derive it otherwise.

Leigh