The speed of light and the color of light are related. If the speed of light has increased, would the old light from galaxies long ago and far away appear to be redshifted?
I actually sat down to do some calculations trying to figure that out assuming that light had changed speeds over history, i.e., c = c(t). I got up after my head started hurting. Ever since I went to an astronomy lecture about the red shift as a child, I have wondered whether there was another explanation for it and maybe this is it.
The speed of light and the color of light are related. If the speed of light has increased, would the old light from galaxies long ago and far away appear to be redshifted?
A darned good question that I hope someone with a good understanding of the physics of light will answer for us.
I think it would depend on how the observer is affected by the changed speed of light. Put yourself in the position of a omniscient being who is unaffected by the change. To you, the speed of light has changed and you could measure the difference in light travel time from point A to point B. But to the non-omniscient who are affected by the light speed change, their concept of distance would change with the speed of light. I think the change in distance would be proportional to the change in the speed of light: ie. no net change in measured frequency. Think of the Doppler Effect where only relative motion can be detected (to the first order).
I think a far more interesting concept is the idea of an anisotropic speed of light. Local differences could be measured.