INTRODUCTION

The organisers have asked us to review the progress of some aspect of general relativity and cosmology in which they have a particular interest and to introduce their remarks by describing its relation to their interaction with Dennis Sciama. It is a great pleasure for me to do so and also to pay tribute to the inspiration that he, and his style of doing physics, has been to me over the years. In particular I have tried to follow his example by asking simple physical questions and trying to answer them with the simplest appropriate tools available. For that reason in what follows I shall not give extensive mathematical details but refer the reader to the references. Moreover because of the personal nature of the review I have made no attempt to include in those references every paper on the subject, especially where the story is widely known and can be read up in standard textbooks. For the same reason I have perhaps erred in including too many papers of my own.

I became a Research student of Dennis Sciama in October 1969 after being enthralled by his marvelously lucid and exciting Part III lectures on General Relativity. When Dennis left for Oxford a year later I transferred to Stephen Hawking, himself a former student of Dennis.