Shing-Tung Yau, chair of Harvard's Mathematics department, and science journalist Steve Nadis discuss their new explication of string theory, *The Shape of Inner Space: String Theory and the Geometry of the Universes Hidden Dimensions*. String theory says we live in a 10-dimensional universe, but that only four are accessible to our everyday senses. According to theorists, the missing six are curled up in bizarre structures known as Calabi-Yau manifolds. In *The Shape of Inner Space*, Shing-Tung Yau, the man who mathematically proved that these manifolds exist, argues that not only is geometry fundamental to string theory, it is also fundamental to the very nature of our universe. Time and again, where Yau has gone, physics has followed. Now for the first time, readers will follow Yau's thinking on where we've been, and where mathematics will take us next.