In 1938, H. A. Bethe had proposed the proton–proton reaction as a source of energy in stars. Fowler demonstrated theoretically that the process was indeed possible. In the 1950s, he collaborated with G. R. and E. M. Burbidge and F. Hoyle on a theory of energy generation and nucleosynthesis in stars (known as the B²FH theory). Further theoretical work with Hoyle in the late 1960s showed that a hot Big Bang would produce the observed amount of helium in the Universe. He and S. Chandrasekhar shared the 1983 Nobel Prize in Physics.