As an astronomer observes a galaxy, which is receding, Does time dilation occur between the two comoving galaxies? If so, which (rf) is (t) longer in, as observed here on Earth (Our local Milkyway galaxy or the remote galaxy)? Thank you.
May I ask just one more question? Does expansion separate individual photons, which are massless? I'm not referring to geodesics, or curved space. I'm interested to know if expansion itself can cause two, almost parallel, photons to separate. I suspect that the answer is no.
Thanks :)
Regarding expansion, from the present to the past: Do light beams (generally) converge to a single point, in the remote past, as geometry and matter was also condensed to a single point, prior to the big bang?
Thank you.