2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/225888The Brown-Kuchař mechanism is applied in the case of General Relativity coupled with the Schutz' model for a perfect fluid. Using the canonical formalism and manipulating the set of modified constraints one is able to recover the definition of a time evolution operator, i.e. a physical Hamiltonian, expressed as a functional of gravitational variables and the entropy.5 pages, Proceedings of The 3rd Stueckelberg Workshop on Relativistic Field TheoriesGeneral Relativity and Quantum Cosmologytext