Generation of gravitational waves in vacuum FRW models

A soliton solution of Einstein's equations is presented which evolves in time towards a Milne universe containing gravitational waves. These waves have cylindrical symmetry and start as gravitational radiation at initial null hypersurfaces, go through a particle-like stage at some finite time and, finally, evolve towards gravitational radiation with decreasing amplitude at future null infinity. In these final stages the solution resembles the final stages of an open Friedman-Robertson-Walker model with gravitational waves. This metric can be extended through the initial null hypersurfaces. The extended metric represents two incoming gravitational waves from past null infinity which collide without a singularity. (author)