Re: teeny atoms absorb huge EM waves

[Leigh Palmer <palmer@SFU.CA>]

At 00:02 -0700 8/3/99, William Beaty wrote:
> On Mon, 2 Aug 1999, Leigh Palmer wrote:
>
> > OK, Bill. I'll accept that challenge. Suppose I think of the potential
> > energy of an assemblage of charges as being associated entirely with
> > their geometrical relationships. I can calculate that energy entirely
> > in terms of their geometry, and Then I may think of the energy of that
> > system as being localized in the charges, or at least as being inside
> > the smallest convex polyhedron I can draw around them. You, on the
> > other hand, think of that energy as being distributed in space; and
> > potentially in all of space!
> >
> > If we can't agree on where this stuff called energy is, how can we
> > possibly ascribe reality to it?
>
> I don't quite understand.  Here's where my brain-fuzz is located:

Stick to one problem at a time. You said that you believed the energy
was located in the static electric field; I pointed out that it could
as well be considered to reside in the geometrical configuration of
the charges. Refute my claim or reject the idea that the energy can
be localized.

Energy is a quantity that can be calculated *given a physical system
and a frame of reference*. You calculate it by integrating over all
space outside the charges; I calculate *the same number* by looking
only at the geometrical relations of the charges on a small scale. We
calculate in the same frame; we get the same number. The energy can't
be localized.

> In a short pulse of laser light, energy is located in the propagating EM
> radiation, OK?

No. The energy cannot be localized. Your difficulties are associated
with pushing a metaphor too far.

> [remainder of Bill's posting deleted]

If one calculates the Poynting flux into something simple, say a
current carrying cylindrical wire of resistive conductor, one will
correctly infer the joule heat ing due to that current. There is
absolutely nothing wrong with that calculation because it gives
the correct answer. It is a perfectly satisfactory description of
the system in the real world. If you wish to view it as a flow of
energy (or, perhaps, heat) then you are free to do so, but it is
misleading in my view. I just don't like to think of this energy
as flowing in from infinity! Still the fact remains that this is
a perfectly acceptable way to calculate the rate of Joule heating.
It is no accident that it works in this case. It always works.

Leigh

Leigh