Physicists now believe that a few constants - the mass of the electron and the strength of gravity, for example - determine the behaviour of the entire material world. But why do the fundamental constants have their particular values, and why do these values seem somehow to be tied up with the existence of life on earth?
Martin Rees , Professor of Astronomy at Cambridge University, examines current thinking about the relationship between the constants of nature and theories of the universe. Producer DEBORAH COHEN