"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:tfUHe.236624$Qo.33184@fed1read01...
Dear Tom Roberts:

"Tom Roberts" wrote in message
. ..
N:dlzc D:aol T:com (dlzc) wrote:
....
Tom, I am given to understand that the CMBR was
produced by an opaque "medium" (CMBRM).

Yes. In the early universe no atom could remain an atom
very long because the high temperature gave other particles
enough kinetic energy so a simple collision often/usually
would ionize the atom. So between a few seconds and
~300k years after the big bang the universe was filled with a charged
plasma consisting primarily of electrons
and protons. When the temperature had been reduced
enough so most collisions did not have enough K.E. to
ionize the atoms the electromagnetic attraction between
protons and electrons quickly caused them to form
hydrogen atoms. The charged plasma was essentially
opaque to all types of EM radiation (hence it was black),
but the hydrogen is transparent to most EM radiation.
So in a short time the radiation emitted by the plasma could suddenly
propagate over large distances. It is
remnants of this radiation we see as the CMBR.

But the CMBR is free of the absorption bands of "cooler" hydrogen. Let's
pretend a timeline, with "CMBRM stops glowing" at 300,000 pBB (post-Big
Bang). What about this Universe filling, formerly opticaly dense,
hydrogen at 301,000 pBB? Does this mean that it all coalesced to
"structures" in next-to-no-time?

No, it was still hot, though slightly cooler, and
still ubiquitous and pretty much homogenous but
instead of being a hot dense opaque plasma, it
was a hot dense transparent non-ionised gas. To
get a picture in your mind, watch this video of
the Landolt reaction and imagine it happening in
reverse:

http://video.uni-regensburg.de:8080/...lt_Reaction.rm

At some point the CMBR had redshifted enough so it could
not be absorbed at all by hydrogen, and since then the
universe has been transparent to it (except for isolated
objects we call stars).

Let me ask a related question. The CMBRM has been described as opaque and
isothermal. Presumably "opaque" could be defined as no emissions
detectable from beyond a certain place (watch my terms).

"a certain place" may give the wrong impression
although obviously we are "here". It is perhaps
better to consider opaque in this case in terms
of the mean free path of a photon being greater
than the time from emission to the time of
complete transparency multiplied by the speed of
light regardless of where the photon is emitted
since the CMBRM was almost homogenous throughout
the universe.

So let me ask this question about the Universe that contains ours...

There is no "Universe that contains ours" in the
Big Bang model so it is not meaningful to ask the
question.

George