The discoveries of twentieth century physics have played a decisive influence in the thinking of modern man. With the exploration of the atom has come a staggering vision of the complexity of the physical world. At the same time, the pursuit of such still puzzling factors as the elusive electron, the mysterious muon, and the strange multiplicity of baryons has given us but a hint of how much is yet to be known. In the concluding volume of his celebrated UNDERSTANDING PHYSICS, Isaac Asimov brilliantly conveys this vast new knowledge and awesome sense of challenge. Treating the most advanced ideas with superb clarity, his book is the perfect supplement to the student’s formal textbook, as well as offering invaluable illumination to the general reader.