  The transition from a static to a dynamic universe opens up the  possibility of a disorderly universe where galaxies could collide,  that is, their world lines might intersect. Roughly speaking, Weyl’s  Postulate states that the actual universe is an orderly universe. It  says that the world lines of the galaxies form a 3-sheaf of   non-intersecting[82]  geodesics orthogonal to layers of spacelike hypersurfaces.