At a fixed point in spacetime (say, x0), gravitational phase space consists of the space of symmetric matrices {F ab} [corresponding to the canonical momentum π(x0)] and of symmetric matrices {Gab} [corresponding to the canonical metric gab(x0)], where 1 ≤ a, b ≤ n, and, crucially, the matrix {Gab} is necessarily positive definite, i.e. ∑ uGabu b > 0 whenever ∑ (ua)2 > 0. In an alternative quan...