In 1961 he suggested that the gravitational constant varies with time (see Brans–Dicke Theory). In 1964, with the Canadian-born American physicist Phillip James Edwin Peebles (1935– ) and others, he began to develop a hot Big Bang theory, independently of G. Gamow. The theory predicted the existence of the cosmic microwave background, discovered shortly after by A. A. Penzias and R. W. Wilson. He also invented the Dicke radiometer and Dicke switch, and in 1957 set out what has become known as the weak anthropic principle.