Any Space-Time has a Plane Wave as a Limit

Abstract

It is a great pleasure for me to honour André Lichnerowicz on his 60th birthday. And since he has done so much to make relativity respectable as a branch of mathematics, I feel it is appropriate here to point out a simple, yet perhaps surprising, general mathematical property of hyperbolic normal pseudo-Riemannian manifolds which is motivated from knowledge of certain well-known exact solutions in general relativity.