http://arxiv.org/abs/1703.08809
In the conventional framework for cosmological dynamics the scale factor $a(t)$ is assumed to obey the
background' Friedmann equation for a perfectly homogeneous universe while particles move according to equations of motions driven by the gravity sourced by the density fluctuations. It has been suggested that the emergence of structure modifies the evolution of $a(t)$ viakinematic’ backreaction and that this may avoid the need for dark energy. Here we show that the conventional equations are exact in Newtonian gravity — which should accurately describe the low-$z$ universe — and there is no approximation in the use of the homogeneous universe equation for $a(t)$. We conclude that there is no backreaction of structure on $a(t)$ and that the need for dark energy cannot be avoided in this way.
N. Kaiser
Tue, 28 Mar 17
12/68
Comments: 4 pages, no figures
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