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.