[John Larkin]

On Wed, 26 Dec 2007 23:20:18 +0000 (UTC), (Don
Klipstein) wrote:

In article , John Larkin wrote:
On Tue, 25 Dec 2007 09:34:20 -0500, "Ethan Winer" ethanw at
ethanwiner dot com wrote:

Rich,

'I see you, you see me' is pretty much a universal law.

Not if I'm in the dark, and you're in the sun. Or if I'm hiding in the
bushes and you're not. Or if I have a telescope but you don't.

I thought this refers to a principle that when a ray is traced from
origin to destination, percentage loss at each lossy point are the same in
both directions, percentage reflected by partially reflective objects
in the way is the same for both directions, and percentage making it from
origin to destination are the same in both directions.

Of course, polarizers and polarized light can complicate this, but we
can't have a situation where there is a container that light can enter but
not exit along the same path in a way that allows a thermal radiator to
heat a target in the container to a higher temperature than the thermal
radiator is at.

- Don Klipstein )

There are optical isolators, like electrical isolators, that let light
go from port A to port B, but block light from B to A. They violate no
laws of thermodynamics, because they absorb the light from B, rather
than reflecting it.

http://en.wikipedia.org/wiki/Optical_isolator


John