[Sprocklem]

IIRC, this was one of the explanations proposed when the existence of a red shift was first noted: that the light is somehow slowly losing its energy over very long distances, becoming “redder” as it did so. It ultimately lost out to the dark energy / space-time expansion theory, although I do not recall why. Presumably there was some observation that precluded “degrading” light from being the sole explanation.

[semi-extrinsic]

There are several challenges for "tired light", or indeed any theory that's an alternative to expansion of the universe.

The theory has to explain why the light gets redshifted, but does not get blurred, and the spectral lines do not get broadened. This severely restricts the type of interactions possible. Also the theory has to explain the consistency between redshifts within our own galaxy, to that of far-away galaxies.

[thehappypm]

Tired light is tricky to be possible because light doesn’t experience time or distance since it travels at c. Light itself from its frame of reference is emitted and received simultaneously. That’s not to say other perspectives can have different views though!

[pigpang]

My theory is that redshifting caused by gravitational background noise. I did calculation somewhere on HN or Youtube few months ago and numbers are of same magnitude.

[hnfong]

https://en.wikipedia.org/wiki/Tired_light