Speaker
Description
The Hubble constant (H0) is crucial to the understanding of the Universe and its evolution. Hence, one would expect agreement on its value in an era of precision cosmology. However, improvements to direct H0 measurements have resulted in a growing discord with the cosmology-dependent predictions of H0 based on the Cosmic Microwave Background observed by the ESA Planck mission. Importantly, strong agreement between direct H0 measurements susceptible to different systematics has been established. Yet, correlations and interdependencies between these measurements have precluded simple averaging of partially complementary constraints.
Here, I present the Distance Network, jointly developed by 36 experts across all relevant disciplines in the context of a hands-on workshop at the International Space Science Institute (ISSI) in Bern in March 2025. The Distance Network generalizes the idea of the well-known Distance Ladder to jointly consider constraints on H0 provided by different methods in pursuit of the best consensus measurement of the local expansion rate of the Universe. The presentation will describe the philosophy underlying the Distance Network and the process by which scientific consensus was reached. The resulting Consensus Report on the Hubble constant features the most accurate direct H0 measurement today, assessment of systematics by variants, and recommendations for next steps required for further improvements. Implications for the Hubble tension will be highlighted.
