D-Particles, D-Instantons, and A Space-Time Uncertainty Principle in String Theory

The purpose of this talk is to review some considerations by the present author on the possible role of a simple space-time uncertainty relation toward nonperturbative string theory. We first motivate the space-time uncertainty relation as a simple space-time characterization of the fundamental string theory. We then argue that the relation captures some of the important aspects of the short-distance dynamics of D-particles described by the effective super Yang-Mills matrix quantum mechanics, and also that the recently proposed type IIB matrix model can be regarded as a possible realization of the space-time uncertainty principle.