(January 10, 2011) Leonard Susskind gives a lecture on the string theory and particle physics. In this lecture, he begins by describing the theory of reductionism and then goes on to tell why string theory and other modern theories spell the end of reductionism. In the last of course of this series, Leonard Susskind continues his exploration of string theory that attempts to reconcile quantum mechanics and general relativity. In particular, the course focuses on string theory with regard to important issues in contemporary physics.