  The Bohm-de Broglie interpretation of quantum mechanics is applied to
canonical quantum cosmology. It is shown that, irrespective of any
regularization or choice of factor ordering of the Wheeler-DeWitt equation, the
unique relevant quantum effect which does not break spacetime is the change of
its signature from lorentzian to euclidean. The other quantum effects are
either trivial or break the four-geometry of spacetime. A Bohm-de Broglie
picture of a quantum geometrodynamics is constructed, which allows the
investigation of these latter structures. For instance, it is shown that any
real solution of the Wheeler-De Witt equation yields a generate four-geometry
compatible with the strong gravity limit of General Relativity and the Carroll
group. Due to the more detailed description of quantum geometrodynamics given
by the Bohm-de Broglie interpretation, some new boundary conditions on
solutions of the Wheeler-DeWitt equation must be imposed in order to preserve
consistency of this finer view.

General Relativity and Quantum Cosmology