In paperback for the first time, this compact volume presents quantum mechanics for the general reader. It offers a lucid description of the intellectual challenges and disagreements in the study of the behavior of atomic and sub-atomic particles--a field that has completely changed our view of the physical world, but that is still the subject of unresolved debate about its own fundamental interpretation. The work is accessible to those with no background in higher mathematics, but will also interest readers who have a more specialized knowledge of scientific topics. The author has spent most of his working life as a theoretical elementary particle physicist and from 1968 to 1979 was Professor of Mathematical Physics at the University of Cambridge. In 1979 he resigned to train for the ministry of the Church of England, and he is now an ordained priest. Here he describes a theory that has been spectacularly successful in predicting the behavior of objects the size of atoms and smaller but that has aroused conflicting views about the nature of reality and the degree of independence between the world around us and ourselves as observers.