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Re: Red shift question

Subject: Re: Red shift question
From: "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:>
Date: Mon, 13 Mar 2006 17:17:25 -0700
Newsgroups: sci.astro
Dear Craig Franck:

"Craig Franck" <[email protected]> wrote in message 
news:[email protected]
> Since most red shift is produced by space expanding
> rather than the speed of a galaxy at the time a photon
> was emitted, how does the relativistic effect of
> supernova periods slowing down get introduced?

If something is moving away from you via:
- kinetic velocity, or
- Universal expansion, ...
 all time-based phenonmenon are red-shifted.  As far as the 
"stretching" of the duration of a supernova, you can think of a 
series of trains heading for Earth, representing the arriving 
photons.  As the distance gets greater, it takes longer for the 
"train load" of photons to arrive for each successive time 

It doesn't *matter* what causes the increase in distance.

> If light is getting stretched it seems the information in
> a pencil of light would take longer to get here (silly
> puddy effect), but that explanation seems a bit off for
> some reason.

Agreed.  "Stretching of light" implies a mechanism that can 
affect individual photons other than the handfull of mechanisms 
we know.  We can lose all of the energy of a photon (to gain it 
back in some other way), but we can't remove just a little of it 
and still stay specular.

Individual photons do appear redshifted by Universal expansion. 
But it is "stretching" of the succession/procession of photons 
that explains the stretching of supernova light curves.

David A. Smith 

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