Russian-American physicist George Gamow proposed that the universe was created in a gigantic explosion now called big bang. This theory provided a basis for understanding the earliest stages of the universe and its subsequent evolution. Extremely high density would cause the universe to expand rapidly. Hydrogen and helium would cool and condense into stars and galaxies. According to Gamow’s theory, radiation left over from the big bang would cool to about 3 K (about -270C/-454F) today. This cosmic background radiation was detected in 1965, providing what most astronomers consider to be confirmation of the big bang theory. Inflationary theory resolves difficulties in Gamow’s original theory by including recent advance in particle physics.