I study the dynamics of gravity in situations where the short-distance structure of space-time becomes important, for example, in the early Universe. As a tool, I use string theory, which is the unique dynamical system incorporating both the existence of gravity and the uncertainty principle of quantum mechanics.

My recent work has mapped out the various different phases of string theory and the transitions the theory can make from one phase to another, in a cosmological environment. These phase transitions alter several features of the theory dramatically. For instance, the number of dimensions of the space-time can change, or the transition may restore a highly stable type of order known as supersymmetry, or else the character of the string dynamics may change altogether.

This network of connections has turned out to unify all known string theories for the first time ─ via dynamics that are intrinsically cosmological.