Abstract

We have known about the expanding universe for around a century, but the story of this discovery has been obscured by a number of myths. Chief among these has been the role attributed to Edwin Hubble, and far too little credit has been given to the true pioneers in this field. More than anyone, the figure of Vesto Slipher stands out. Working in isolation at the Lowell Observatory in Arizona, he was the first to prove the true nature of galaxies and demonstrate that they are in motion (including the motion of our own Milky Way), around 100 years ago. The first half of this talk presents this history, leading on to a review of the legacy in modern cosmology of the peculiar velocities that Slipher discovered. The induced “redshift-space distortions” of galaxy clustering are now a leading tool that allow us to discriminate between Einstein’s relativistic theory of gravity and competing alternatives.