A Globally Unevolving Universe

A scalar-tensor theory of gravity is formulated in which $G$ and particle masses are allowed to vary. The theory yields a globally static cosmological model with no evolutionary timescales, no cosmological coincidences, and no flatness and horizon `problems'. It can be shown that the energy densities of dark energy ($\rho_{DE}$) and non-relativistic baryons and dark matter ($\rho_{M}$) are related by $\rho_{DE}=2\rho_{M}$, in agreement with current observations, if DE is associated with the canonical kinetic and potential energy densities of the scalar fields. Under general assumptions, the model favors light fermionic dark matter candidates (e.g., sterile neutrinos). The main observed features of the CMB are naturally explained in this model, including the spectral flatness of its perturbations on the largest angular scales, and the observed adiabatic and gaussian nature of density perturbations. More generally, we show that many of the cosmological observables, normally attributed to the dynamics of expanding space, could be of kinematic origin. In gravitationally bound systems, the values of G and particle masses spontaneously freeze out by a symmetry breaking of the underlying conformal symmetry, and the theory reduces to standard general relativity (with, e.g., all solar system tests satisfied).