Even though quantum systems in energy eigenstates do not evolve in time, they
can exhibit correlations between internal degrees of freedom in such a way that
one of the internal degrees of freedom behaves like a clock variable, and
thereby defines an internal time, that parametrises the evolution of the other
degrees of freedom. This situation is of great interest in quantum cosmology
where the invariance under reparametrisation of time implies that the temporal
coordinate dissapears and is replaced by the Wheeler-DeWitt constraint. Here we
show that this paradox can be investigated experimentally using the exquisite
control now available on moderate size quantum systems. We describe in detail
how to implement such an experimental demonstration using the spin and motional
degrees of freedom of a single trapped ion.Comment: 5 page
