Fluid Entropy as Time-Variable in Canonical Quantum Gravity

(eng) The Brown-Kucha\v{r} 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. Comment: 5 pages, Proceedings of The 3rd Stueckelberg Workshop on Relativistic Field Theories