Quantum-wave equation and Heisenberg inequalities of covariant quantum gravity

Key aspects of the manifestly-covariant theory of quantum gravity (Cremaschini and Tessarotto 2015-2017) are investigated. These refer, first, to the establishment of the 4-scalar, manifestly-covariant evolution quantum wave equation, denoted as covariant quantum gravity (CQG) wave equation, which advances the quantum state $\psi$ associated with a prescribed background space-time. In this paper, the CQG-wave equation is proved to follow at once by means of a Hamilton-Jacobi quantization of the classical variational tensor field $g\equiv \left\{ g_{\mu \nu }\right\}$ and its conjugate momentum, referred to as (canonical) $g-$quantization. The same equation is also shown to be variational and to follow from a synchronous variational principle identified here with the quantum Hamilton variational principle. The corresponding quantum hydrodynamic equations are then obtained upon introducing the Madelung representation for $\psi$, which provide an equivalent statistical interpretation of the CQG-wave equation. Finally, the quantum state $\psi$ is proved to fulfill generalized Heisenberg inequalities, relating the statistical measurement errors of quantum observables. These are shown to be represented in terms of the standard deviations of the matric tensor $g\equiv \left\{ g_{\mu \nu }\right\}$ and its quantum conjugate momentum operator.