Abstract
Many complications encountered in discussions of time can be avoided using a purely operational definition of time in terms of clocks. This circumvents issues stemming from the gauge invariance of coordinate choices in diffeomorphism invariant theories like the vanishing of the Hamiltonian. Time itself as a local coordinate is unobservable but measurements of clocks evidently are. This, however, requires a definition of what kind of system constitutes a clock without reference to the concept of time. In this essay, we attempt such a definition and argue that the possibility of defining time consistently in terms of clocks in an unambiguous way independent of the physical materialisation of the clocks reveals a deep property of nature underlying the concept of time.
Robert C Helling