Brian Greene (born February 9, 1963) is an American theoretical physicist and one of the best-known string theorists. He has been a professor at Columbia University since 1996. Greene has worked on mirror symmetry, relating two different Calabi-Yau manifolds(concretely, relating the conifold to one of its orbifolds). He also described the flop transition, a mild form of topology change, showing that topology in string theory can change at the conifold point. He has become known to a wider audience through his books for the general public, The Elegant Universe, Icarus at the Edge of Time and The Fabric of the Cosmos, and a related PBS television special.