The cosmological theory called the big bang theory assumes that the universe began from a singular state of infinite density. This theory was implicit in the complete solution of Albert Einstein's equations, obtained by Aleksandr Friedmann in 1922. In 1927, Georges Lema”tre used these equations to devise a cosmological theory incorporating the concept that the universe is expanding from an explosive moment of creation.
The theory was further developed in the 1940s by George Gamow and R. A. Alpher. They envisaged a high-temperature state in the beginning and elaborated the concept to include a theory of element synthesis and background radiation. (The term big bang itself has been attributed to Fred Hoyle, who coined it derisively, but it was readily accepted.) In the light of the evidence currently available, including the discovery of the background radiation, the big bang theory appears to best account for the evolution of the universe. In the later 20th century the theory was further elaborated by inflationary theory (see cosmology). The steady-state theory, which postulates the continuous creation of matter and a universe with no beginning or end, still has adherents.