I asked this question of a physicist and he told me to ask a philosopher. If one was to observe a closed, isolated region of space under vacuum conditions, i.e. there are no particles in this region and none may enter into it. Also there are no fields (i.e. gravitational, electromagnetic, etc.) acting or existing on or in this region. The only interaction with this system is as an outside observer. Can this observer notice the passing of time? If so, how? And does the act of observation make the observer part of the system, since the observer is technically interacting with it? Currently we measure time by the movement of quantum mechanical particles, such as the molecules in a ticking clock; the vibrations of atoms; and the decay of radioactive isotopes. But could we perhaps, in this hypothetical system, justify using properties of space itself, such as quantum foam or the expansion of space (expanding universe), and, if so, how would we observe these features?