In article ,
Chalky wrote:
On Jun 28, 10:10 am, Martin Hardcastle
wrote:
In article ,

Chalky wrote:
Closer to us than the surface of last scattering, we should 'see'
successively closer shells of successively cooler gas, which should
emit thermal radiation, according to temperature.

I don't really want to get involved in this argument, since I have to
moderate it, but here's a hint: since this 'cooler gas', after the
epoch of recombination, will be neutral atomic hydrogen,

Actually, if the concordance model is correct, it is mostly dark
matter.

We're talking about the material that might radiate, or affect
radiation. That's normal baryonic matter, mostly neutral hydrogen.
Non-baryonic dark matter does not directly interact with radiation,
practically by definition.

However, if dark matter does not obey the rules of thermodynamics, by
emitting thermal radiation, the term "cold dark matter" would be an
oxymoron (given initial conditions).

There's no 'rule of thermodynamics' that says that material --
baryonic or non-baryonic -- has to radiate or interact with radiation.
`cold dark matter' vs `hot dark matter' refers to the energy of the
(putative) dark matter particles.

At what rest-frame
wavelength will the radiation appear?

What do you mean by rest frame? The possibilities are infinite.

`rest frame' is used by physicists to mean `a frame in which the body
under discussion is at rest'.

From thermodynamic and logic considerations, black body spectrum. (You
can't get any darker than black).

A black-body spectrum is produced only if radiation is in thermal
equilibrium with matter. (There's a common misconception, which can
sometimes even persist past undergraduate level, that `thermal
radiation' = `black-body radiation' but that's not so.) Since being in
thermal equilibrium with radiation requires the material to be
optically thick, it's not true of baryonic matter after the epoch of
recombination and it's essentially never true of dark matter. So,
given this, what contribution would you expect the baryonic matter
post-recombination to make to the observed background radiation?
Again, you should try to think about the process by which this matter
might radiate.

Martin
--
Martin Hardcastle
School of Physics, Astronomy and Mathematics, University of Hertfordshire, UK
Please replace the xxx.xxx.xxx in the header with herts.ac.uk to mail me