  In the last years several theoretical papers discussed if time can be an
emergent property deriving from quantum correlations. Here, to provide an
insight into how this phenomenon can occur, we present an experiment that
illustrates Page and Wootters' mechanism of "static" time, and Gambini et al.
subsequent refinements. A static, entangled state between a clock system and
the rest of the universe is perceived as evolving by internal observers that
test the correlations between the two subsystems. We implement this mechanism
using an entangled state of the polarization of two photons, one of which is
used as a clock to gauge the evolution of the second: an "internal" observer
that becomes correlated with the clock photon sees the other system evolve,
while an "external" observer that only observes global properties of the two
photons can prove it is static.
