  In this paper we consider features of graviton scattering in Matrix theory
compactified on a 2-torus. The features which interest us can only be
determined by nonperturbative effects in the corresponding 2+1 dimensional
super Yang Mills theory. We show that the superconformal symmetry of strongly
coupled Super Yang Mills Theory in 2+1 dimensions almost determines low energy,
large impact parameter ten dimensional graviton scattering at zero longitudinal
momentum in the Matrix model of IIB string theory. We then show that amplitudes
involving arbitrary transverse momentum transfer are governed by instanton
processes similar to the Polchinski Pouliot process. Finally we consider the
influence of instantons on a conjectured nonrenormalization theorem. This
theorem is violated by instanton processes. Far from being a problem, this fact
is seen to be crucial to the consistency of the IIB interpretation. We suggest
that the SO(8) invariance of strongly coupled SYM theory may lead to a proof of
eleven dimensional Lorentz invariance.
