A Consistent Histories Formulation of Wheeler-DeWitt Quantum Cosmology

We summarize a fully worked-out consistent histories formulation of a quantum cosmological model, and illustrate with an example calculation of the probability that the quantum universe becomes singular. Specifically, we take a complete Wheeler-DeWitt canonical quantization of a flat Friedmann-Robertson-Walker cosmological model sourced with a free massless scalar field, and construct the decoherence functional which determines which quantum histories may be consistently assigned probabilities. As an example, we exhibit the probability that the quantum universe is singular in the sense that it assumes zero volume. The classical solutions of this model are all singular; we show that the quantum solutions are as well. We comment on the crucial role played by quantum decoherence in arriving at this conclusion.