(January 5, 2024 at 1:59 pm)neil Wrote: When you mentioned that "gravitational redshift isn't a thing", earlier, would that include photons from very distance sources that pass near large sequences of galaxies on their route to us?
No. A photon does not change energy by the gravity it encounters on its trip. Gravity is a conservative field. Any energy gained from falling into a gravity well is lost by the same amount when coming out.
Gravitational redshift only occurs by the photon "originating" in a gravity well, and being observed in flatter space. In that case, it is the time dilation within the gravity well (where the photon is created) compared to where it is observed that causes the shift.
