Leading critics of Hawking and Hartle’s and Vilenkin’s quantum cosmological models have noted the arbitrary nature of the constraints they impose.39 For example, Christopher Isham has noted that although quantum cosmologists do generate a wave function that includes universes such as ours, they only do so as the result of their use of restrictive mathematical approximations and their own decisions to impose many arbitrary constraints on the possible universes (in “superspace”) that they will consider.
