Non-perturbative, background independent canonical quantum gravity in Fock representations

Abstract

It is commonly believed that a quantum field theory of General Relativity requires a non-perturbative formulation. In addition, the background independence of classical General Relativity supplies a physical selection criterion for suitable Hilbert space representations of the corresponding quantum field theory. In this contribution we show that there exist background independent representations of Fock type within the manifestly non-perturbative, canonical approach to quantum gravity. Mandatory for their existence is the presence of suitable matter fields next to the geometry field. In particular, the excitations of the corresponding Fock vacuum necessarily entangles matter and geometry. In this article we use the constraint quantisation method. We compare the resulting Fock incarnation of background independent, non-perturbative canonical quantum gravity with the well known Loop quantum gravity incarnation. One of the most important differences is that the Fock quantum gravity (FQG) Hilbert space, in contrast to the Loop quantum gravity (LQG) Hilbert space, is separable. This has many advantages when attempting to implement the Hamiltonian constraint, also known as Wheeler-DeWitt constraint, as a densely defined quadratic form.