  Global time is a gauge or relational choice of time variable in canonical
gravity. Local time is the time used in a flat patch of spacetime. We compare
the dynamics of a scalar field with respect to choices of global time and
Minkowski patch time in an expanding cosmology. Our main results are that
evolutions starting from the same initial conditions are similar on the time
scales of terrestrial experiments, and that global time leads to a mechanism
for evolving coupling constants.
