Backreaction of inhomogeneities can mimic dark energy

In the standard approach to cosmology, the evolution and observations associated with an inhomogeneous universe with density are modeled by employing a homogeneous cosmological model of density , where ⟨⋅⋅⋅⟩ refers to some sort of spatial average. While there is broad agreement that since general relativity is a nonlinear theory, this procedure cannot strictly be correct, there is less agreement that the effect of backreactions can be significant. Some have proposed that effects usually attributed to dark energy may be due to the backreactions of inhomogeneities, and there is no dark energy and the universe is not accelerating (at least, not in the usual sense). Here, I present a critical analysis of the standard dark-energy approach and discuss the proposal that the backreaction of inhomogeneities on scales much less than the Hubble radius mimics dark energy.