Respuesta :
Doppler shift due to random motion of galaxies ,an aging of light as gravity weakens with time ,the difference in temperature and star formation in old and new galaxies
It's simply showing red-shift on a big, big stage. The Big Bang explosion was so massive that most things we can see in the universe are still moving away from us. Some things nearby -- planets or stars -- are moving closer. So, cosmological red-shift means that light stretches as space expands. This is one of the defining proofs for the The Big Bang Theory as well as that the Universe is expanding.
