The Hubble constant ($H_0$) estimated from the local Cepheid-supernova distance ladder is in $3\text{−}\sigma$ tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents new physics or systematic effects is the subject of intense debate. Here, we investigate how new, independent $H_0$ estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon supernova sample yields an $H_0$ posterior near identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of $\sim 50$ binary neutron star “standard sirens” (detectable within the next decade) will be able to adjudicate between the local and CMB estimates.

• Received 21 March 2018
• Revised 6 July 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.061105