Link to the paper.
Of course, without experimental verification, Page and Wooter's ideas are little more than a philosophical curiosity. And since it is never possible to have an observer outside the universe, there seemed little chance of ever testing the idea.
Until now. Today, Ekaterina Moreva at the Istituto Nazionale di Ricerca Metrologica (INRIM) in Turin, Italy, and a few pals have performed the first experimental test of Page\Wooters ideas. And they confirm that time is indeed an emergent phenomenon for 'internal' observers but absent for external ones.
In the last years several theoretical papers discussed if time can be an emergent propertiy 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 renements. 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.