Space of events and the time observable
  Quantum mechanical time operator is introduced following the parametric formulation of classical mechanics in the extended phase space. Quantum constraint on the extended quantum system is defined in analogy to the constraint of the classical extended system, and is interpreted as the condition defining the space of physical events. It is seen that the peculiar properties of the time observable, otherwise obtained in the models of time measurement, are of the classical origin, (i.e.), due to the quantized classical constraint of the parametric Hamiltonian dynamics. 
Nikola Buri\' c and Slobodan Prvanovi\' c
quant-ph