The Field Nature of Time in General Relativity
  The paper is devoted to the description of the reparametrization - invariant dynamics of general relativity obtained by resolving constraints and constructing equivalent unconstrained systems. The constraint-shell action reveals the "field nature" of the geometric time in general relativity. The time measured by the watch of an observer coincides with one of field variables, but not with the reparametrization-noninvariant coordinate evolution parameter.   We give new solution of such problem, as the derivation of the path integral representation of the causal Green functions in the Hamiltonian scheme of general relativity. 
Marek Pawlowski, Victor Pervushin, Denis Proskurin