He postulated what is called 'The Cosmological Constant' which represents a repulsive force he first suggested keeps gravity from drawing the galaxies together in a finite static universe. Science magazine considers the biggest science story of 1998 to be the discovery that Einstein's greatest blunder may have been his greatest coup. Saul Perlmutter and his Supernova group at Lawrence Berkeley lab has shown that Einstein's repulsive force may be necessary to explain the expansion of the universe. This indicates that gravity is not the dominating force in the universe. It is this energy which is causing space to expand in an accelerating fashion.
Space is comparable to a compressed sponge.
This idea also provides a good deal of the missing 'mass' or 'dark matter' needed to explain deviations from Newton's Laws in galaxies and galactic clusters. Large aggregates of matter compress the 'sponge' of space and that increases the self gravitation. Cosmic Repulsion presents a revolutionary new view of the universe and its origins, which also explains how Quantum Theory seems to violate conservation of energy, but only temporarily borrows energy from the vacuum.