Posted: Mar 24, 2017 3:53 pm
by jamest
I watched a BBC documentary this week about the expansion of the universe. It stated (I think) that the expansion of spacetime accounts for the expansion of the universe between galaxies and that light which has travelled immense distances has had its wavelength 'stretched' [by the expanding spacetime] so that old light is red-shifted, enabling us to date distant galaxies.

... So basically, I'm puzzled by why/how the wavelength of the light is red-shifted. Can somebody explain that to me because at the moment it reads [to me] as though light and spacetime are essentially the same thing? :scratch:

... Also, given that the universe hasn't expanded at a constant rate and given (I assume?) that we don't even know the rate at which the universe is expanding right now, how is it possible to accurately measure the age of distant galaxies? I may have asked this particular question before, I can't remember. :think:

Thanks in advance for enlightening me.