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Do we know if light is red-shifted by traveling through space? If it isn't, how do we know? I guess my pondering has lead me to wonder if the observed accelerating space-expansion is a misinterpretation. If light is red-shifted by traveling through space, we may be able to re-interpret Hubble's equation (I know, that might be heresy) as

$redshift = SomeConstant*d$ which would imply that distant objects aren't necessarily accelerating, the light we view is increasingly redshifted for more distance objects, independent of them moving away from us. Then, maybe we don't need dark energy anymore.?.

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marked as duplicate by knzhou, ZeroTheHero, Kyle Kanos, Jon Custer, user191954 Feb 28 at 13:36

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This is essentially the tired light theory. It does not, for instance, explain the apparent brightness change with distance of similar objects: if tired light is true it should remain constant, while if objects further away are receding from us it will be lower, which in fact it is.

It's horridly incompatible with GR. There are other tests it also fails.

There are undoubtedly people who still think this model is the right one, but not many, I think.

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  • $\begingroup$ When I googled "tired light" it described photon energy loss do to scattering. Is the tired light theory claiming that the speed of photons slows down(less than 300,000 kps) or that their frequency slows down? There is a difference because one involves scattering and the other does not. $\endgroup$ – Bill Alsept Feb 22 '16 at 23:02
  • $\begingroup$ @BillAlsept I think there are various proposed mechanisms: scattering I think fails as it would cause distant objects to be blurred, which they aren't in fact. If $E=h\nu$ is correct then there must be a big question about where the energy goes, which is very easily answered by recession, and it's hard to see what the tired light story about that would be. $\endgroup$ – tfb Feb 23 '16 at 9:20
  • $\begingroup$ I am not trying to make an argument for tired light. I am trying to understand what it is. All the description I have seen are related to scattering and blurring as you said. In what way does that make the light tired? Are they saying the speed slows down? Or are they saying the frequency slows down? If the second could you direct me to where it is described that way? Thanks $\endgroup$ – Bill Alsept Feb 23 '16 at 9:28
  • $\begingroup$ @BillAlsept Sorry, I didn't mean to make it sound like I thought you were defending it. I'm very much not an expert on it, but I can't believe they thought light traveled at less than c: I think the idea must have been absorption and emission of lower-energy photons or something. I think that basically it just doesn't work at all without some unexplained mechanism. $\endgroup$ – tfb Feb 23 '16 at 9:58
  • $\begingroup$ Now I'm curious, can the frequency of a photon slow down the longer it has existed? This would not lead to scattering or blurring and if possible would cause red shift. Can anyone point to an article or paper addressing this type of red shift? $\endgroup$ – Bill Alsept Feb 23 '16 at 10:09

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