On Jun 5, 6:28*pm, Keith Dysart wrote:
There are indeed negative values. These occur when the energy is
flowing in the other direction, ...

Let's take a close look at the illusion that you are seeing and not
comprehending. Observe a snapshot of the instantaneous power envelope
of a traveling wave. It is a sinusoidal envelope with peak
instantaneous power levels and zero instantaneous power levels. When
it is traveling in the forward direction we consider that to be
positive power. When it is traveling in the reverse direction, we
consider that to be negative power. It is only a directional
*convention* not proof that negative power exists. The only waves that
can exist as waves on a transmission line are traveling waves.

Since the forward wave and reverse wave do not interact while Z0
remains constant, they have zero effect on each other and we can just
simply algebraically add the two instantaneous powers to obtain the
net instantaneous power. Thus, when the instantaneous power in the
forward wave is a greater magnitude than the instantaneous power in
the reverse wave, the net instantaneous power is positive. When the
instantaneous power in the forward wave is a lesser magnitude than the
instantaneous power in the reverse wave, the net instantaneous power
is negative. At the point where they are equal, the net instantaneous
power is zero. This is the illusion, based on net instantaneous power,
that you are observing. Please note that net instantaneous power is an
oxymoron. Is it net or is it instantaneous? How can it be both?

All you are observing is that sometimes the instantaneous power in the
forward traveling wave is more, less, or equal to the instantaneous
power in the reverse traveling wave which causes the net instantaneous
Poynting vector direction to alternate. But it is all a moot point
because photons cannot perform the feats of magic that you are
ascribing to them. You are simply being fooled by an illusion based on
the misguided algebraic addition of two separate and distinct
instantaneous powers that you believe are interacting but while Z0
remains constant, they are not interacting in any way and it is
impossible for the photons to change direction without a physical
cause. Your mashed-potatoes version of energy doesn't even obey
Maxwell's equations. Why do you think the concept can possibly be
meaningful?

In "Optics", Hecht says instantaneous power is "of limited utility."
You seem to have discovered that limit, stepped over it, and stepped
in it. :-)
--
73, Cecil, w5dxp.com