## Cosmic clocks, cosmic variance and cosmic averages

Cosmic acceleration is explained quantitatively, purely in general relativity with matter obeying the strong energy condition, as an apparent effect due to quasilocal gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. ‘Dark energy’ is recognized as a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localized. Matter is modelled as an inhomogeneous distribution of clusters of galaxies in bubble walls surrounding voids, as we observe. Gravitational energy differences between observers in bound systems, such as galaxies, and volume-averaged comoving locations in freely expanding space can be so large that the time dilation between the two significantly affects the parameters of any effective homogeneous isotropic model one fits to the universe. A new approach to cosmological averaging is presented, which implicitly solves the Sandage–de Vaucouleurs paradox. Comoving test particles in freely expanding space, which observe an isotropic cosmic microwave background (CMB), possess a quasilocal ‘rest’ energy E =(γ(τ, x))mc² on the spatial hypersurfaces of homogeneity. Here 1 ≤ γ < ³/₂: the lower bound refers to fiducial reference observers at ‘finite infinity’, which is defined technically in relation to the demarcation scale between bound systems and expanding space. Within voids >1, representing the quasilocal gravitational energy of expansion and spatial curvature variations. Since all our cosmological measurements apart from the CMB involve photons exchanged between objects in bound systems, and since clocks in bound systems are largely unaffected, this is entirely consistent with observation. When combined with a non-linear scheme for cosmological evolution with back-reaction via the Buchert equations, a new observationally viable model of the universe is obtained, without ‘dark energy’. A quantitative scheme is presented for the recalibration of average cosmological parameters. It uses boundary conditions at the time of last scattering consistent with primordial inflation. The expansion age is increased, allowing more time for structure formation. The baryon density fraction obtained from primordial nucleosynthesis bounds can be significantly larger, yet consistent with primordial lithium abundance measurements. The angular scale of the first Doppler peak in the CMB anisotropy spectrum fits the new model despite an average negative spatial curvature at late epochs, resolving the anomaly associated with ellipticity in the CMB anisotropies. Non-baryonic dark matter to baryonic matter ratios of about 3:1 are typically favoured by observational tests. A number of other testable consequences are discussed, with the potential to profoundly change the whole of theoretical and observational cosmology.