Slipher's redshifts as support for de Sitter's model and the discovery of the dynamic universe

Abstract

Of the first two relativistiv world models, only the one by de Sitter predicted redshifted spectra from far away astronomical objects. Slipher's redshifts therefore seemed to arbitrate against Einstein's model which made no such predictions. Both models were trying to describe a static universe. However, Lemaitre found that de Sitter's construct resulted in a spatially inhomogeneous universe. He then opted for a model that correspondes to Einstein's closed, curved universe but allowed the radius of curvature to change with time. Slipher's redshifts suggested to him that the universe is dynamic and expanding. We also discuss the respective merits of Friedman and Lemaitre in revealing the dynamic nature of the universe.

Refereed contribution to the proceedings of "Origins of the Expanding Universe: 1912-1932", M. J. Way & D. Hunter, eds., ASP Conf. Ser., Vol. 471 in press. A meeting held in September 2012 to mark the Centenary of Slipher's first measurement of the radial velocity of M31