Searching for Signals of Inhomogeneity Using Multiple Probes of the Cosmic Expansion Rate H (z )

It is argued that cosmic chronometers yield estimates of the spatially averaged expansion rate even in a universe that is not well described by a global FLRW model—as long as the universe is statistically homogeneous and isotropic with a sufficiently small homogeneity scale. On the other hand, measurements of the expansion rate based on observations of redshift drift will not in general yield estimates of the spatially averaged expansion rate—but it will in the case where the universe is described well by a single FLRW model on large scales. Therefore, a disagreement between measurements of the expansion rate based on cosmic chronometers versus redshift drift is an expected signal of non-negligible cosmic backreaction.