Cosmological backreaction

During the epoch of galaxy formation, the Universe switched from nearly homogeneous to very inhomogeneous, so a more accurate metric is needed, according to which mass density is allowed to curve space. With more accurate modelling, “dark energy” is not needed, and instead seems to be a misinterpretation of the epoch of structure formation if inhomogeneous curvature is ignored in interpreting observations. The corresponding inhomogeneous metric can be measured using the shift in the baryonic acoustic oscillation (BAO) peak location recently discovered by TCfA cosmologists together with international colleagues.

http://cosmo.astro.umk.pl/foswiki/bin/view/Cosmo/CosmologicalBackreaction