  In this work we present a discussion of the existing links between the
procedures of endowing the quantum gravity with a real time and of including in
the theory a physical reference frame. More precisely, as first step, we
develop the canonical quantum dynamics, starting from the Einstein equations in
presence of a dust fluid and arrive to a Schroedinger evolution. Then, by
fixing the lapse function in the path integral of gravity, we get a
Schroedinger quantum dynamics, of which eigenvalues problem provides the
appearance of a dust fluid in the classical limit. The main issue of our
analysis is to claim that a theory, in which the time displacement invariance,
on a quantum level, is broken, is indistinguishable from a theory for which
this symmetry holds, but a real reference fluid is included.
