"Steve Willner" wrote in message
ps.com...
Robert Karl Stonjek wrote:
The frequency of light is like a clock in itself - if the frequency is
lower
then the clock at the source is slower as measured by an observer who
also
measures that redshift.

As you indicate, this is pretty well known. One familiar application
is that high-redshift supernovae
take longer to fade than supernovae at low redshift. This rules out
tired-light models for redshift.
There's also an extra factor of (1+z) in the equation when you
calculate a distant object's luminosity.


Amazingly, others are arguing against it. For me it was just a penny
dropping - how obvious when you think about it...

Tired light would also have to incorporate time dilation. I don't see how
one can change the frequency of an emitted source without dilating time in
some way. Tired light would necessarily have to include tired time as well.

I'm also interested to know how redshift data is effected by the concept of
a universe made up of so much dark matter. Surely dark matter contributes
to space curvature and so would have to contribute to gravitational
redshift, and with a universe made up of 90% dark matter this must
constitute an appreciable component of the redshift in the form of
gravitational redshift.

As I recall, earlier (1990s?) calculations that considered the accumulated
effect of gravitational redshift were insufficient to counter an expanding
spacetime model, but not by that much. With the large portion of dark
matter in the universe, the accumulated gravitational redshift would be more
than sufficient to account for all the observed redshift plus a bit, though
I don't have those earlier calculations to hand (doing a bit of hand waving
myself...

Thanks,
Robert