ALMOST IDEAL CLOCKS IN QUANTUM COSMOLOGY - A BRIEF DERIVATION OF TIME

A formalism for quantizing time reparametrization invariant dynamics is considered and applied to systems which contain an 'almost ideal clock'. Previously, this formalism was successfully applied to the Bianchi models and, while it contains no fundamental notion of 'time' or 'evolution', the approach does contain a notion of correlations. Using correlations with the almost ideal clock to introduce a notion of time, we derive the complete formalism of external time quantum mechanics. The explicit relation between the physical Hilbert space and the usual Hilbert space for a system with an external time is also derived and the limit of an ideal clock is found to be closely associated with the Klein-Gordon inner product and the Newton-Wigner formalism.