  We explore the consequences of requiring that quantum theories of gravity be
unitary, mostly focusing on simple cosmological models to illustrate the main
points. We show that unitarity for a clock that encounters a classical
singularity at finite time implies quantum singularity resolution, but for a
clock that encounters future infinity at finite time leads to a quantum
recollapse. We then find that our starting point - assuming the general
covariance of general relativity - is actually incompatible with general
quantum unitarity: singularity resolution in quantum gravity can always be
engineered by choosing the right clock, or avoided by using a different one.
