  Barbour, Hawking, Misner and others have argued that time cannot play an
essential role in the formulation of a quantum theory of cosmology. Here we
present three challenges to their arguments, taken from works and remarks by
Kauffman, Markopoulou and Newman. These can be seen to be based on two
principles: that every observable in a theory of cosmology should be measurable
by some observer inside the universe, and all mathematical constructions
necessary to the formulation of the theory should be realizable in a finite
time by a computer that fits inside the universe. We also briefly discuss how a
cosmological theory could be formulated so it is in agreement with these
principles.
