Title: "Gravitational energy as dark energy: Towards concordance cosmology without Lambda"
I present an unexpected explanation for dark energy , purely within
general relativity with matter obeying the strong energy condition.
Cosmic acceleration is explained quantitatively, as an apparent effect due
to quasilocal gravitational energy differences - and hence clock rate
variance - that arise in the decoupling of bound systems from the global
expansion of the universe. Although the universe was initially very smooth,
today it is very inhomogeneous on scales less than 200 Mpc, with clusters
of galaxies strung in filaments and bubbles surrounding huge voids.
Accounting for spatial curvature and gravitational energy gradients
between galaxies and the volume average location in voids, leads to a
recalibration of average cosmological parameters.
I present a model [1,2] of the universe based on this proposal, which
passes three key independent cosmological tests : supernova luminosity
distances, the angular scale of the sound horizon in the cosmic microwave
background (CMB) and the baryon acoustic oscillation scale in galaxy
clustering statistics. It may simultaneously resolve particular
anomalies, including primordial lithium abundances and CMB ellipticity.
The expansion age is increased allowing more time for structure formation.
Best-fit parameters and implications will be discussed. Unique predictions
include a quantifiable variance in the Hubble flow below the scale of
apparent homogeneity, consistent with the observed "Hubble bubble"
feature, which sheds new light on the decades long debate about the
value of the Hubble constant.
 D.L. Wiltshire, New J. Phys. 9 (2007) 377
 D.L. Wiltshire, Phys. Rev. Lett. 99 (2007) 251101
 B.M. Leith, S.C.C. Ng and D.L. Wiltshire, ApJ 672 (2008) L91