> Zwicky's tired light theory proposes that the redshift of light from distant galaxies is due to the gradual loss of energy by photons over vast cosmic distances. However, it was seen to conflict with observations. Yet Gupta found that "by allowing this theory to coexist with the expanding universe, it becomes possible to reinterpret the redshift as a hybrid phenomenon, rather than purely due to expansion."
Aww, the light needs a little nap. No wonder we ( potentially ) got it wrong...!
Where's the energy going, supposedly? I'd assumed "the light's losing energy" had been firmly ruled out long ago—it was a potential explanation that occurred to me the very first time I heard about the observed red shift of distant galaxies, so I figured it must be very and obviously wrong if I'd never heard an actual physicist even mention the possibility of that as a notable factor.
[EDIT] Wikipedia "Tired Light" article:
> The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones.
Oh, so, what I might have guessed, "it hits stuff sometimes".
Article goes on to make it seem like there's a lot working against the notion, including that distant images ought to be a lot fuzzier if light's interacting with other stuff along the way.
Aww, the light needs a little nap. No wonder we ( potentially ) got it wrong...!