2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34315The null splitting theorem (proved in math.DG/9909158) is discussed. As an application, a uniqueness theorem for Minkowski space and for de Sitter space associated with the occurrence of null lines (inextendible globally achronal null geodesics) is presented.Contribution to the Proceedings of the Workshop "The conformal structure of space-times: geometry, analysis, numerics", Tuebingen April 2001. To appear in Lecture Notes in Physics, Springer Verlag, edited by J. Frauendiener and H. FriedrichGeneral Relativity and Quantum CosmologyDifferential Geometrytext