 Einstein’s general theory of relativity shows that the structure of spacetime is itself a dynamical variable, subject to causal influence by the material constituents of the universe. Indeed, Einstein immediately saw the potential to apply general relativity to large-scale cosmological questions. The first cosmological model of Einstein (1917) described a static universe, i.e. one whose spatial geometry is constant over time. However, Einstein’s static universe was empirically inadequate: it could not account for the redshift data gathered by Edwin Hubble and others in the 1920s. The redshift data indicated that distant stars are moving away from us, and moving faster in direct proportion to their distance. Thus, the data indicated an expanding universe.