  A common feature of reparametrization invariant theories is the difficulty
involved in identifying an appropriate evolution parameter and in constructing
a Hilbert space on states. Two well known examples of such theories are the
relativistic point particle and the canonical formulation of quantum gravity.
The strong analogy between them (specially for minisuperspace models) is
considered in order to stress the correspondence between the ``localization
problem'' and the ``problem of time,'' respectively. A possible solution for
the first problem was given by the proper time formulation of relativistic
quantum mechanics. Thus, we extrapolate the main outlines of such a formalism
to the quantum gravity framework. As a consequence, a proposal to solve the
problem of time arises.
