On Jun 23, 9:17 am, George Dishman wrote:
"jacob navia" wrote in message

...

What physical evidence we have that the CMB is not just
radiation coming from a diluted hydrogen cloud whose mean
temperature is 2.7K

I assume here the implied qualification: "post redshift"

and whose radius is (say) 20 billion
years?

The evidence is the observed Hubble red shift. Take
the cloud and divide it into thin spherical shells.
We see some light from each shell but more distant
shells are red shifted to a greater degree. If the
cloud is at a uniform temperature, we should see
the integral of the redshifted curves. Ned Wright
produced a similar curve based on the CMBR being
red shifted starlight to illustrate the problem:

http://www.astro.ucla.edu/~wright/Stolmar_Errors.html

And if we were in the middle of such a HUGE cloud?

Yes, we would have to be at the centre, but the
model only works if the temperature is proportional
to the radius from us so that the redshifted
temperature is 2.7K for all shells.

Absolutely. This is the crux of the matter.

The cloud has
to have a spherically symmetric temperature profile

And what is wrong with that? The same is true, in essence, within
classical BB theory, for increasing z, no matter what cosmological
parameters you choose.

with the lowest temperature of 0K at the centre,

Why?

exactly where our galaxy is situated, but the
temperature 13.7 billion light years away is 3000K.

And that would be just *one* of the explanations for the
CMB that doesn't require a big bang or a "beginning".

Why is this so hard for some people to accept?

xanthian.

Yes, why would that be so difficult to accept?

It is difficult to accept because there is no good
explanation for how a cloud could maintain such a
strange temperature profile without the gas at the
centre being warmed to equilibrium,

Expansion and accelerating expansion potentially account for that.
Otherwise you are essentially re-introducing Olber's paradox at a
lower EM frequency range.

Incidentally, what, precisely, is the z/T relationship predicted by
EFE? (I honestly don't remember)

and personally
I find the idea that the universe is centred on the
Earth even more distasteful than a beginning with a
homogenous and isotropic universe.

AHA! Back to the foundations of natural philosophy, I am pleased to
see! It has been pointed out (by prior authors) that Einstein's
general principle (also attributed {by some} to Galileo), puts the cat
amongst the pigeons in this respect. Stated pregeometrically, all
bodies of ref. are equiv. for formulating general laws of nature.
Hence coordinates centred around the observer are as good as any
other. Thus, the pre-Copernican and Copernican approaches are
equivalently valid in this relativistic respect. This is the "sting in
the tail" of GR theory, and greater authors than me have made this
point before.

On the other hand, the cooling of a dense cloud to the
point where it becomes transparent at around 3000K is
not unlike looking at the surface of the Sun where we
see the outer surface of the opaque layers.

Agreed

[snip]

George

Touchee, Chalky.