2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34500We describe how the Barrett-Crane spin foam model defines transition amplitudes for quantum gravity states and how causality can be consistently implemented in it.6 pages; uses IOP conference macros; to appear in the Proceedings of the 15th SIGRAV Conference on General Relativity and Gravitational PhysicsGeneral Relativity and Quantum Cosmologytext