Brian Randolph Greene (born February 9, 1963) is an American physicist known for his research on string theory. He is a professor of physics and mathematics at Columbia University, director of its center for theoretical physics, and the chairman of the World Science Festival, which he co-founded in 2008. Greene co-discovered mirror symmetry, relating two different Calabi–Yau manifolds. He also described the flop transition, a mild form of topology change, and the conifold transition, a more severe transformation of space, showing that topology can smoothly change in string theory. His books *The Elegant Universe* (1999, finalist for the Pulitzer Prize), *The Fabric of the Cosmos* (2004), *The Hidden Reality* (2011), and *Until the End of Time* (2020) were all top 10 *New York Times* bestsellers.