Gary Harnagel wrote:
I'm having trouble picturing why we should see the CMBR at all. Since it's
traveling at the speed of light but we're moving somewhat slower, shouldn't
it have passed us long ago? I know, the FLWR metric must have something to
do with it, but ...

I replied with an analogy:
# Imagine an infinite static Euclidean universe (i.e., flat spacetime,
# no gravity involved) filled with (stationary) fog which both emits and
# scatters (visible) light, and consider a (stationary) observer in that
# fog. [[...]]

Gary Harnagel replied:
I like your fog analogy; however, let's consider the case where the fog
consists of photons which begin in some finite volume of space.

Stop here.

In my analogy the fog consisted of matter (water) + a bunch of photons,
not just photons. And the matter+photons are everywhere in space, not
restricted to "some finite volume of space". The case that you're now
describing (photons only, restricted to a finite spatial volume) is not
a good analogy to the hot-big-bang-model CMBR formation.

In the hot-big-bang model, the "fog" consists of matter (mostly a plasma
of protons, alpha particles, and electrons) in radiative equilibrium
with am ambient field of (approximately black-body) photons. These
matter and photons are everywhere in space, not restricted to a finite
spatial volume.

In the hot-big-bang model the occurence analogous to my analogy's
"fog condensing" is (was) the temperature dropping low enough so that
the ambient matter could "condense" and form (mostly) hydrogen & helium
atoms. This happened roughly 0.5e6 years after the big bang.

ciao,
--
-- "Jonathan Thornburg [remove -animal to reply]"
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
currently visiting Max-Plack-Institute fuer Gravitationsphysik
(Albert-Einstein-Institut), Potsdam-Golm, Germany
"There was of course no way of knowing whether you were being watched
at any given moment. How often, or on what system, the Thought Police
plugged in on any individual wire was guesswork. It was even conceivable
that they watched everybody all the time." -- George Orwell, "1984"

----- End forwarded message -----