2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207057Motivated by the important work of Brown adn York on quasilocal energy, we propose definitions of quasilocal energy and momentum surface energy of a spacelike 2-surface with positive intrinsic curvature in a spacetime. We show that the quasilocal energy of the boundary of a compact spacelike hypersurface which satisfies the local energy condition is strictly positive unless the spacetime is flat along the spacelike hypersurface.4 pages; final published versionGeneral Relativity and Quantum CosmologyDifferential Geometrytext