Backreaction in late-time cosmology
  We review the effect of the formation of nonlinear structures on the expansion rate, spatial curvature and light propagation in the universe, focusing on the possibility that it could explain cosmological observations without the introduction of dark energy or modified gravity. We concentrate on explaining the relevant physics and highlighting open questions. 
Thomas Buchert and Syksy Rasanen
astro-ph.CO gr-qc