Cosmic Inhomogeneities and the Average Cosmological Dynamics

Understand

If general relativity (GR) describes the expansion of the Universe, the observed cosmic acceleration implies the existence of a `dark energy'.

• However, while the Universe is on average homogeneous on large scales, it is inhomogeneous on smaller scales.
• While GR governs the dynamics of the \emph{in}homogeneous Universe, the averaged \emph{homogeneous} Universe obeys modified Einstein equations.
• Can such modifications alone explain the acceleration? For a simple generic model with realistic initial conditions, we show the answer to be `no'.