  We consider implications of the microscopic dynamics of spacetime for the
evolution of cosmological models. We argue that quantum geometry effects may
lead to stochastic fluctuations of the gravitational constant, which is thus
considered as a macroscopic effective dynamical quantity. Consistency with
Riemannian geometry entails the presence of a time-dependent dark energy term
in the modified field equations, which can be expressed in terms of the
dynamical gravitational constant. We suggest that the late-time accelerated
expansion of the Universe may be ascribed to quantum fluctuations in the
geometry of spacetime rather than the vacuum energy from the matter sector.

General Relativity and Quantum Cosmology