Re: Cosmic Background Radiation (Not Very Speculative, Honestly)

[baez@galaxy.ucr.edu (John Baez)]

In article <387AD3FD.5BB862DC@netcom.ca>,
Jackie & Barry  <jandb@netcom.ca> wrote:

>Lets start with ancient starlight, flying around every which way, in an
>infinite, eternal but not perfectly empty space, let the space be filled
>with some rarefied dust. The kind of Universe Eddington seems to have
>had in mind. 

Okay, now we're getting closer to positing a specific mechanism for 
the starlight to come into thermal equilibrium. 

>Now let's forget the stars, we'll switch them off, since current direct
>starlight is not the issue. Let's go for lunch. We'll come back 1,000
>billion years later, just to make sure that any residual direct
>starlight is negligible. As I see it, most of the light will have
>bounced around long enough to lose evidence of its origins. As I
>understand it, it would have the form of blackbody radiation at *some*
>temperature. 

Right.  The problem with this scenario is the business of "switching
off the stars" for a trillion years and then switching them back on.  

If you really think this happened, you have to explain how.  If you
don't think it happened - and I bet you don't - you have to explain 
where the last trillion years of starlight went, and also what powered
them for the last trillion years.  That's a lot of energy!

In particular, if it takes starlight a trillion years to equilibriate 
with the "dust" you posit, there will be hundreds of billions of years of 
more recent starlight floating around that *hasn't* come into equilibrium 
yet.  This starlight will still bear some imprint of the spectral 
properties of that dust.  And there will be a *lot* of this starlight.
What does it look like, exactly?  If we don't see it, why not?  A
realistic model would need to answer these questions.

Since people have by now posted some very detailed descriptions of 
Eddington's original calculation and why it didn't actually predict
blackbody radiation, I won't keep pestering you for the details of his 
model.  My point now is just that I haven't yet seen any plausible model
for "blackbody radiation due to equilibriated starlight".