Hartle-Hawking state
In theoretical physics, the Hartle-Hawking state, named after James Hartle and Stephen Hawking, is the wave function of the Universe - a notion meant to figure out how the Universe started - that is calculated from Feynman's path integral.
More precisely, it is a hypothetical vector in the Hilbert space of a theory of quantum gravity that describes this wave functional.
It 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.
References
- Hawking, Hertog, and Reall, "Brane New World", Phys. Rev. D62 (2000) 043501.
- J. Hartle and S. W. Hawking, "Wave function of the universe", Phys. Rev. D28, 2960 (1983).
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