🚀 go-pugleaf

In article <3NOV199212473739@csa2.lbl.gov> sichase@csa2.lbl.gov (SCOTT I CHASE) writes:
>In article <1992Nov3.064405.29610@CSD-NewsHost.Stanford.EDU>, pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes...
>>Is there any difference between the 3-degree-K background radiation and
>>the light we should be seeing from all the stars according to Olber's
>>paradox?  Are they same, is one only a part ("subset") of the other, or
>>are they unrelated?
>
>Olber's paradox (READ THE FAQ!) suggests
>that the entire sky should be uniformly luminous with the brightness of our
>Sun.  The temperature of this radiation would be quite a few thousands of 
>degrees (6000K if every star were identical to the Sun).  The Universe is
>far too young for most of the available light to have reached us yet.  
>However, you can look forward to the night sky getting brighter and brighter
>over the next billions of years.  And the light from the stars is, of course,
>correlated with the positions of the stars.

Actually it was the explanation of Olber's paradox in your FAQ that
prompted my question.  You account for the paradox in terms of
redshifting starlight downwards (4) and the age of the universe (5).
So it occurred to me that if indeed the bulk of the 6000K starlight
that *has* reached us so far has been redshifted down so far as to
appear to have vanished "into obscurity," maybe it hadn't completely
vanished but had become the 3K background radiation.

Meanwhile Ben Zellner sent me email to the effect that the *shape* of
the 3K radiation was the clue.  It is the right shape for blackbody
radiation from a *fixed* temperature, and is presumed to be that
temperature at which atoms formed and the plasma became transparent
(the "big flash"?).  Black-body radiation summed over the distribution
of temperatures of stars yields a different shape from what one gets
with a fixed temperature.

I found this somewhat convincing but not completely so since it left
open the possibility of some combination of temperature and distance
distributions that could fake single-temperature radiation.  Too big a
coincidence?  Nowhere near as big a coincidence as required for the
FAQ's (3), stars lined up to hide behind each other.  With the right
plausible assumptions it could conceivably be a theorem that the
combined radiation from all sources of an expanding universe should sum
to the equivalent of one black-body source.  At least I haven't so far
seen anything detailed enough to rule out this possibility.

In addition it raised a question in my mind as to why all the radiation
from the "big flash" *was* characteristic of a single temperature, i.e.
why has it all been downshifted the same amount.  Shouldn't the parts
of the flash that appear further away from us reach us at a lower
temperature?  Or was the universe so small back then that all parts of
it would now appear equidistant to any modern observer?

Furthermore as the plasma continued to cool, presumably it continued to
radiate.  Why doesn't that contribution skew the shape away from a
single-temperature shape?  Is it because the amount of radiation
decreases with the 4th power of the temperature, and hence the skew
must be negligible?

All very puzzling to a nonphysicist.  Scott?
-- 
Vaughan Pratt				There's no truth in logic, son.