Abstract
Any Riemannian metric on a compact manifold is geodesically complete. By contrast, it is widely known that incomplete compact Lorentzian manifolds exist. In this article it will be proven that a compact manifold with a smooth Lorentz metric must be complete if the metric is flat everywhere. This question of completeness; which has significant implications for the classification of (compact) Lorentzian space forms, has remained unresolved until quite recently, when it was finally established by Carrière as a special case of an even more general result. Here, a simple, alternative proof of this special case of Carrière’s theorem is given; the proof requires minimal mathematical machinery but still involves the use of some intriguing connections between the topology and global geometry of a compact flat space‐time.

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