This course is an introduction to the currently accepted theory of gravity, Einstein's general theory of relativity. We begin with a review of special relativity in terms of spacetime vectors and tensors, and we introduce the stress-energy tensor, which is the source of gravity. We study the mathematical description of curved spacetime and develop an intuitive justification for Einstein's equation, relating the stress-energy tensor (matter) to the curvature of spacetime (gravity). Finally we study in some detail two solutions of Einstein's equation: the Schwarzschild solution, which applies to a spherically symmetric star, and the Friedmann model of an expanding universe. Format: lecture, three hours per week. Evaluation will be based on weekly problem sets, a midterm and a final exam, all of which have a substantial quantitative component. Prerequisites: Physics 301 or Physics 405 or Physics 411 (students with strong math backgrounds are invited to consult with the instructor about a possible waiving of the prerequisites). No enrollment limit (expected: 19).