>Are you assuming that the "aging of light" is gradual, or that it occurs in sudden jumps?
>
>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.

Well, light does go "slower" when passing through matter (but not is a vacuum,yes).

Could it be that the slowing of light in space could be a way of detecting "dark" matter??