Fourth Course: String Gravity and Physics at the Planck Scale

Recent advances in observational cosmology are changing the way we view the nature of time. In general relativity, the freedom in choosing a time hypersurface has ham-pered the implementation of the theory. Fortunately, Hamilton-Jacobi theory enables one to describe all time hypersurfaces on an equal footing. Using an expansion in powers of the spatial curvature, one may solve for the wavefunctional in a semiclas-sical approximation. In this way, one may readily compare predictions of various in ation models with observations of microwave background anisotropies and galaxy clustering. in Proceedings of the International School of Astrophysics \D. Chalonge&quot