What does cosmological redshift do to light?
The cosmological redshift is a consequence of the expansion of space. The expansion of space stretches the wavelengths of the light that is traveling through it. Since red light has longer wavelengths than blue light, we call the stretching a redshift. A source of light that is moving away from us through space would also cause a redshift—in this case, it is from the Doppler effect. However, cosmological redshift is not the same as a Doppler redshift because Doppler redshift is from motion through space, while cosmological redshift is from the expansion of space itself.