2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/178576Causal structure of the brane universe with respect to null geodesics in the bulk spacetime is studied. It is pointed out that apparent causality violation is possible for the brane universe which contains matter energy. It is also shown that there is no 'horizon problem' in the Friedmann-Robertson-Walker brane universe.LaTeX, 9 pages, 4 EPS figures to appear in Phys. Rev. LettGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext