A Whole Cosmology View of the Hubble Constant

Abstract

The Hubble constant $H_0$ is the value of the cosmic expansion rate at one time (the present), and cannot be adjusted successfully without taking into account the entire expansion history and cosmology. We outline some conditions, that if not quite ``no go'' are ``no thanks'', showing that changing the expansion history, e.g. employing dynamical dark energy, cannot reconcile disparate deductions of $H_0$ without upsetting some other cosmological measurement.