Dirac was a man who concentrated on the difficult problems of his time. He was principally interested in the basis of quantum mechanics and the elementary particles. However, on one occasion, around 1938, he did write a paper which went to the opposite extreme and discussed the size of the cosmos and the age of the universe in terms of very simple dimensional analysis; such data is still alive and well and still food for thought.

As the centuries have gone by, physicists have of course tended always to move in those directions where great problems remain, and I think if one looks at the progress in physics until, shall we say, the 1940s, they have definitely concentrated on very small things – atoms and small molecules. In the period, in the fifties, then the sixties, it was realised that the methods of physics could be applied to other regions which lay above the atomic scale of, shall we say, everyday life – and by that I mean below the scale of what one normally thinks of as hydrodynamic phenomena. There was a mesoscopic physcs, an inter mediate scale where the ideas and the methods of physics could work and make progress. One of the leading workers in this area, one of the prophets, is Pierre Gilles de Gennes. In the last few decades he has produced an enormous number of ideas which have been directly applicable to the experimental world, and which indeed have come to dominate our study of that world. It will be one of these areas that he will talk about here.