In theoretical physics, the Hartle-Hawking state, named after James Hartle and Stephen Hawking, is a hypothetical vector in the Hilbert space of a theory of quantum gravity that describes the wave function of the Universe.
The wave function (or more precisely the wave functional) is a functional of the metric tensor defined at a (D-1)-dimensional compact surface, the Universe, where D is the spacetime dimension. The precise form of the Hartle-Hawking state is the path integral over all D-dimensional geometries that have the required induced metric on their boundary.
Such a wave function of the Universe can be shown to satisfy the Wheeler-deWitt equation.
