Positive Energy

My term paper for the general relativity course at Berkeley was a guide through Edward Witten’s proof in 1981 of the positive energy theorem, partly for which he was awarded the Fields Medal as a physicist. The theorem asserts under appropriate assumptions that the total energy of a gravitating system is always positive and can be zero only if the geometry of spacetime is that of flat Minkowski space. It establishes Minkowski space as a stable ground state of the gravitational field. Witten’s proof had greatly simplified the original proof given to this theorem.