Radial gravitational collapse causes timelike incompleteness

We show that a globally hyperbolic spacetime containing a trapped surface and satisfying the strong energy condition and a condition on certain radial tidal forces must be timelike geodesically incomplete. This constitutes a “timelike” version of Penrose’s celebrated singularity theorem. Recall that the latter concludes that certain spacetimes are null incomplete, providing the first theoretical evidence that black holes actually exist in our Universe. By concluding timelike instead of null incompleteness, we obtain, at the expense of stronger assumptions, a clearer physical interpretation and the existence of an event horizon.