(which comes from the non-linearity of Einstein field equations) and the dynamical evolution of spatial slices of space-time. As of 2017, the role of backreaction in possibly leading to an alternative to dark energy is an open question of debate among cosmologists. The existence of a homogeneity length scale can be considered to be that at which the calculations with and without backreaction give the same results. As of 2017, the existence of such a scale needs experimental confirmation.