I I don't believe Nature in her formulation of fundamental laws of physics uses non-beautiful pieces.' Professor Chen Ning Yang, now of the State University of New York, won the Nobel Prize for Physics in 1957 for his work on elementary particles. He talks to John Maddox about the physicists' dogma - that they are not merely chasing chaos, but a set of simple and beautiful mathematical rules which will describe the Universe. Producer GEOFF DEEHAN followed by an interlude