Key points are not available for this paper at this time.
The quantum state of the universe may be described by a wave function which is a functional of the metric and matter fields of a hypersurface which divides the spacetime into two parts. If the spacetime is not simply connected, this hypersurface will in general have more than one connected component. Most physical observables depend only on a single connected component and can be calculated from a density matrix obtained by integrating over the unobserved surfaces. On the "no boundary" proposal for the quantum state of the universe, this density matrix is given by a path integral over all metrics, connected and disconnected that are bounded by two surfaces. The extension of these ideas to string theory is discussed.
S. W. Hawking (Thu,) studied this question.