Regarding the speed of galaxies, there is the astrophysical concept of comoving observers: https://en.wikipedia.org/wiki/Comoving_distance https://en.wikipedia.

Regarding the speed of galaxies, there is the astrophysical concept of comoving observers: https://en.wikipedia.org/wiki/Comoving_distance https://en.wikipedia.org/wiki/Comoving_distance I stumbled upon this, when I searched for the question: is there any point in talking about the age of the Universe if there is no absolute reference frame? There is a good stackexchange page about this too: https://astronomy.stackexchange.com/questions/6525/age-of-the-universe-and-time-dilation https://astronomy.stackexchange.com/questions/6525/age-of-th...