Albert Einstein (1879-1955), pacifist and humanitarian, has been universally acclaimed the greatest theoretical physicist who ever lived. Adapting the old laws of physics to Einstein's space-time resulted in "relativistic" physics. He, more than anyone else, realized that every physical theory is largely an invention of the mind, a mathematical model used to "mimic" a certain domain of experimental facts. Einstein's work on relativity is indeed the greatest contribution to the philosophy of science. It has long been thought that only a handful of scientists could comprehend Einstein's theory of relativity. But in this book the inventor himself explains both the special and the general theories in terms that the layman can understand.