The Cosmological Constant

Abstract

The cosmological constant introduced by Einstein in 1917 was controversial, widely regarded as both promising and troubling. Early cosmologists within the new paradigm of general relativity, such as Einstein and Willem de Sitter, vaguely realized that the field equations implied a vacuum energy and pressure. The connection to the cosmological constant was only made explicit by Georges Lemaître in an address of 1933, when he suggested a vacuum energy density corresponding to about 10 - 27 g cm - 3. His suggestion was ignored for more than three decades. While Lemaître associated the cosmological constant with a vacuum energy, he did not consider its connection to quantum theory.