In this book, Roger Penrose presents a masterly summary of those areas of physics in which he feels there are major unsolved problems. These ideas are then challenged by three distinguished experts from different backgrounds - Abner Shimony and Nancy Cartwright as Philosophers of science and Stephen Hawking as a theoretical physicist and cosmologist. Finally, Roger Penrose responds to their thought-provoking criticisms. This paperback edition has been updated to include a striking and easily accessible example of Godel's theorem, and a ground-breaking proposal for a physical experiment designed to test some of Penrose's most novel ideas about quantum mechanics. Penrose's enthusiasm, insight and good humour shine through this accessible, illuminating, and brilliant account of 21st-century theoretical physics.

'To see a scientist of Penrose's ability, stature and achievement toss large parts of modern physics into the air as though juggling balls and try to keep them aloft while marshalling them into a coherent pattern is a thing to behold. It is a wonderful illustration of a first-rate scientist doing what first-rate scientists have always done: make bold conjectures and display them for others to confirm, refute or amend.' Keith Devlin, New Scientist
'When Oxford physicist and mathematician Penrose ... has something to say about general relativity, quantum physics and artificial intelligence, we would do well to listen.' Publishers Weekly
'The book is an attractive and stimulating introduction to some fascinating issues, on some of which (such as the intelligibility of the universe) theists would certainly be able to offer some alternative insights.' John Polkinghorne, Science and Christian Belief
'... a very interesting and stimulating book.' Brian Josephson, The Times Higher Education Supplement
'... a stimulating and compact review of Penrose's own thinking.' Bernard Dixon, The Independent