THE QUANTUM GRAVITATIONAL BACK-REACTION ON INFLATION

We describe our recent calculation of two-loop corrections to the expa nsion rate of an initially inflating universe on the manifold T-3 x R. If correct, our result proves that quantum gravitational effects slow the rate of inflation by an amount which becomes non-perturbatively l arge at late times. In a preliminary discussion of basic issues we sho w that the expansion rate is a gauge invariant and that our ultraviole t regulator does not introduce spurious time dependence. We also deriv e a sharp bound on the maximum strength of higher loop effects. (C) 19 97 Academic Press