Recent progress in string theory is starting to provide the tools to address basic questions about the nature of space-time, the fundamental degrees of freedom, and their interactions. This is in large part due to the discovery of dualities, which allow one to compute interesting things even in the absence of a small expansion parameter.

My main interest is in string theory as a theory of quantum gravity. There are many indications, for example from black hole quantum mechanics and the smallness of the cosmological constant, that our naive notions of space-time are inadequate. An alternative picture has arisen out of string theory in the past few years from the discovery of dualities between gravity and gauge theories (known as Matrix Theory and the AdS/CFT correspondence).

A better understanding of the degrees of freedom in string theory has recently come from studying unstable D-branes, which decay by "tachyon condensation". This has allowed a construction of various nonperturbative objects as solitons, and hints at a new connection between open and closed strings. I have been active in this area, particularly in applying techniques from noncommutative geometry to simplify the analysis.