Redshift

When light spectra from distant sources are examined, they are found to be shifted toward the red end of the spectrum. What explains the redshift observations? There are two main theories, the Doppler and Gravitational theories, that seek to explain why observed redshifts occur, as discovered and illustrated in a graph called Hubble's Law. Doppler theory claims redshift may occur if the source recedes at speed v. Thus, if galaxies recede the universe expands. Gravitational theory claims tha...