Following the discovery by Edwin Hubble of a linear relation between the redshifts of the galaxies and their distance in 1929, Einstein abandoned his static model of the universe and proposed expanding models such as the Friedmann–Einstein universe and the Einstein–de Sitter universe. In both cases, he set the cosmological constant to zero, declaring it "no longer necessary... and theoretically unsatisfactory". In many Einstein biographies, it is claimed that Einstein referred to the cosmological constant in later years as his "biggest blunder". The astrophysicist Mario Livio has recently cast doubt on this claim, suggesting that it may be exaggerated.