Topology and Time Reversal

Abstract

In this lecture we address some topological questions connected with the existence on a general spacetime manifold of diffeomorphisms connected to the identity which reverse the time-orientation.

24 pages LaTeX, short version of an extended paper still under construction, to appear in the Proc. of the Erice School on ``String gravity and physics at the Planck scale'' (Erice, 8-19 September 1995)