  An overview is presented of a recently proposed "radically conservative"
solution to the problem of dark energy in cosmology. The proposal yields a
model universe which appears to be quantitatively viable, in terms of its fit
to supernovae luminosity distances, the angular scale of the sound horizon in
the cosmic microwave background (CMB) anisotropy spectrum, and the baryon
acoustic oscillation scale. It may simultaneously resolve key anomalies
relating to primordial lithium abundances, CMB ellipticity, the expansion age
of the universe and the Hubble bubble feature. The model uses only general
relativity, and matter obeying the strong energy condition, but revisits
operational issues in interpreting average measurements in our presently
inhomogeneous universe, from first principles. The present overview examines
both the foundational issues concerning the definition of gravitational energy
in a dynamically expanding space, the quantitative predictions of the new model
and its best-fit cosmological parameters, and the prospects for an era of new
observational tests in cosmology.
