N:dlzc D:aol T:com (dlzc) wrote:

Dear Tom Roberts:

"Tom Roberts" wrote in message

. ..
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?

Not at all. At Z~1000 the 3000K background glow was isotropic and the
distance to the surface of last scattering correspondingly shorter. The
distance to the surface of last scattering for H-alpha and other
wavelengths where neutral hydrogen can absorb (and re-emit) will be
different and second order effects may make for a slight change in the
BB radiation intensity at those wavelengths, but to first order every
neutral hydrogen atom is surrounded by an isotropic black body emitter
at 3000K.

Each hydrogen atom that absorbs an H-alpha photon will enventually
re-emit it in some other direction. The radiation field stays isotropic
- to first order all the neutral hydrogen in that era does is to make
the universe more opaque at certain resonant frequencies.

Because hydrogen is transparent to most of the CMBR
radiation. The CMBR was emitted as a continuous blackbody
spectrum ~3000 K; hydrogen can only absorb discrete lines
from it, and the large redshift and Doppler shifting of the
hydrogen in the early universe smeared out the bands so much
they are not prominent (or perhaps not apparent at all,
I don't know).

Not detectable at all.

Beyond experimental limits. I think your problem is that you are not
imagining the situation correctly. The universe is bathed in an
isotropic radiation field from the big bang. It is now a tiny 3K
background but at Z~1000 it was 3000K (and still isotropic).

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). So let me ask this question about the Universe that
contains ours... It would be certainly opaque, since we cannot
see beyond the Big Bang, but would the container Universe appear
isothermal? Rather than the CMBRM being some intermediate matter
state on *this* side of the Big Bang, could it simply be
infalling light?

The observable horizon is moving away from us at the speed of light. The
challenge for cosmology is to explain why our patch of universe is so
isotropic. Alan Guth's inflation is one possible solution:

http://nedwww.ipac.caltech.edu/level..._contents.html

You need to think more carefully about how absorbtion lines arise in a
continuum spectrum. Energy is always conserved.

Regards,
Martin Brown