Physical properties of space and time

Since space and time play dynamical roles in general relativity and are measured by physical instruments, they can be expected to participate in quantum features such as fluctuations, correlations and entanglement. This talk presents several canonical methods and results that have demonstrated the possibility of non-trivial features of quantum space-time, such as signature change at large curvature and enhanced decoherence implied by physical clocks. The latter can be used to place an upper limit on a potential fundamental period of time which is several orders of magnitude better than values obtained from high-energy experiments.