RELATIVISTIC MATERIAL REFERENCE SYSTEMS

This work closes certain gaps in the literature on material reference systems in general relativity. It is shown that perfect fluids are a s pecial case of DeWitt's relativistic elastic media and that the veloci ty-potential formalism for perfect fluids can be interpreted as descri bing a perfect fluid coupled to a fleet of clocks. A Hamiltonian analy sis of the elastic media with clocks is carried out and the constraint s that arise when the system is coupled to gravity are studied. When t he Hamiltonian constraint is resolved with respect to the clock moment um, the resulting true Hamiltonian is found to be a functional only of the gravitational variables. The true Hamiltonian is explicitly displ ayed when the medium is dust, and is shown to depend on the detailed c onstruction of the clocks.