cosmological redshift

The cosmological redshift is the redshift produced by the expansion of the universe and the reason most galaxies in the universe have redshifts. Contrary to popular belief, this is not a Doppler shift. A Doppler redshift arises when an object moves away from us. Most galaxies move away from us, but this is not the cause of their redshifts. Instead, as a light wave travels through the fabric of spacetime, the universe expands and the light wave gets stretched and therefore redshifted. This is a subtle but importance difference. The farther a galaxy, the longer its light waves have traveled through space and the more redshifted they have become.