CMB energy

[Bartosz Lew]

On Tue, 24 Feb 2004, Jarek Rzepecki wrote:

> 
> 
> On Tue, 24 Feb 2004, Bartosz Lew wrote:
> 
> > The correct answer is: Nothing happened to that energy. It's still there
> > (unless photons gets older or other crap like that), the only thing that 
> > changed is that we no longer see hot photons because, as we've been tought 
> > in high school, we're floating away from everything else according to the hubble law.
> > (So the answer is essentialy in the question ;)
> > The "doppler effect" which can easily be derived from SR transformaiton
> > formulas causes  that we see everythig red. The only difference from the
> > situation described above with observers looking at identical photons (and
> > yet seeing them in different colors) and
> > complication I see here is that it is not possible to find a recerence frame
> > in which we will see the whole CMB photons at different temperature - color
> > etc. This is of course because it's the space that expands and there is nothing
> > we can do about it, so changing reference frame won't help in understanding
> > that it is just our obserwational effect not a true energy theft by some
> > more less unidentified process. But still I belive that  this reddening can
> > be ballanced once when Universe start to collapse.
> 
> Well I think that the problem is closer to the question: Why photons 
> getting out of potential well suffer from red-shift - where their energy 
> go in that case? then to the Doppler...
> 
> 

well, your question, as I understood it, was about what's with the energy
that seems to be missing because of the redshift. 
So I disagree. The cosmological redshift
isn't caused by gravitational effects - i.e. gravitational reddening, but by 
combined effect of time dilatation and lenght change which comes from
transformation from one reference frame to another - and together we call it
"a doppler effect".
Sahs Wolfe effect is a minor one here, and fully understood in terms of GR
predisitons.

However I do realise that my explanation is a bit outstretched, because SR
do not allow space to change in time, or at least doesn't say anything about
that. But on the other hand a single photon, or any other particle (eg.
proton, neutrino) can't  (or can ? - I think not :) feel it travels trough 
space that is actually expanding. If it did, we all would grow in time, atoms would
have become greater etc. So eventually it makes no difference weather space
is expandind or observer is receeding, except the problem I said before >>



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Bartosz Lew			e-mail: blew w astri.uni.torun.pl
					blew w astro.uni.torun.pl
Centrum Astronomii UMK			
TORUN, POLAND			www: http://adjani.astro.uni.torun.pl/~blew
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