ANTONY VALENTINI is a Research Associate, Department of Phyics, at Imperial College in London. He received his PhD in Astrophysics at the International School for Advanced Studies in Trieste, Italy, under Dennis Sciama (whose former PhD students include Stephen Hawking, David Deutsch and Martin Rees). The Thesis develops the pilot-wave theory of de Broglie and Bohm into a complete, alternative approach to modern physics, with applications to quantum gravity and cosmology.