Although he made his discoveries more than three centuries ago, all roads in modern physics lead back to Sir Isaac Newton. This book begins with a lucid summary of Newton's laws. These fundamental theories changed contemporary concepts about space, time and motion. The author then moves on to explain six of the most important theoretical developments since Newton and to show how they have changed our understanding of how science has developed. These developments include wave theory, field theory, statistical probability, special relativity theory, quantum theory and general relativity theory.