Craig Franck wrote:
> 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 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.
If a light source emits two light pulses a certain time t apart, then,
if the light source is moving away from you, the second light pulse
will be emitted from a larger distance and hence it will take an
additional time time to reach you. When you receive the two signals,
their time separation will then be greater than t (this is essentially
the same reason why the Doppler redshift occurs in the first place).
However, even if one assumes that the redshift is not associated with a
recession of the galaxy, the apparent delay of the supernova light
curves could be caused by the light intensity getting additionally
reduced by the redshift ( see my web page