>>>>You're talking about observing a phenomenon that is already observed, Hubble Redshift.
>>>>
>>>>Any detection is a time delay, and would be observed as a loss in the frequency of the light, frequency = 1 / time.
>>>
>>>Well, that's exactly the point. A change in frequency can be caused by several phenomena: the Doppler effect (i.e., a relative speed), a gravitational potential as proposed by the General Theory of Relativity, and your hypothetical aging of light. In case anybody takes the "aging of light" theory seriously enough to invest in fancy experiments, any measurements done would have to take into consideration the other causes for the same effect - a change in frequency.
>>>
>>>>We don't observe the Hubble redshift or the expanding Universe around here, we observe out there in deeper space.
>>>
>>>Are you assuming that the "aging of light" would occur in sudden steps every such-and-such time, and that nothing could be observed if less than a 100,000 years or so passes?
>>
>>
>>Observations of supernova light curves in deep space have showing a very non-linear Hubble relationship.
>>
>>And remember that the "expansion" the Universe is faster now than it was in the past.
>>
>>That effect can be caused by the velocity of light slowing incrementally.
>>
>>
>>>Because otherwise, if you assume a gradual aging, the effect should exist even from the Moon to here - on a small scale, of course. The only question is if we can do measurements that are accurate enough for such a short distance.
>>
>>You need to look outside the local cluster before you observe the effects of expansion, so the same will be true for deceleration.
>
>Are you assuming that the "aging of light" is gradual, or that it occurs in sudden jumps?


I'm assuming that whichever model fits the body of astronomical data best is the best way to do it.



>Also: If you assume the light actually gets slower - a preposterous assumption, by most standards - but if you assume that as part of your theory, you would have yet another way to test the theory. It should be possible to at least get an estimate of the speed of light from far-away sources. I guess we are not talking about a few ppm here, but about a significant slowdown, if you consider the light from distant quasars.

The issue is that if a photon slows down in its, I suspect that when it is absorbed and re-emitted that it is a "fresh" photon, with the same energy as the old one, but now moving at c.

That means when old light enters a lens, and interacts with the electrons in the lens, it is absorbed and re-emitted and thus becomes new light again.