What is the Hubble Tension and is it Significant?

One of the central open questions in cosmology today is whether our current standard model of cosmology, known as ΛCDM (Lambda Cold Dark Matter), fully describes the evolution of the universe, or whether new physics is required. A critical test of this model comes from measurements of the Hubble constant (H₀), the present-day expansion rate of the universe. Currently, some direct measurements of H₀ using nearby stars and supernovae yield values that differ significantly, with claims of up to 6 standard deviations, from those inferred from observations of the cosmic microwave background (CMB), the cosmic background radiation from the early universe. If this discrepancy,  known as the ‘Hubble tension,’  is real, it could be indicating new physics; for example,  “early dark energy” that would briefly accelerate the early universe. In this talk, I will present the latest results from the Chicago–Carnegie Hubble Program (CCHP), which aims to measure H₀ with unprecedented accuracy. Using data from the James Webb Space Telescope (JWST) near-infrared camera (NIRCam) that offers four times the resolution and ten times the sensitivity of the Hubble Space Telescope, we have new and improved distance measurements to a number of nearby galaxies. These distances are based on three independent astrophysical methods: Cepheid variable stars, the Tip of the Red Giant Branch (TRGB), and a new technique using J-Region Asymptotic Giant Branch (JAGB) stars, all three of which provide a calibration of the more distant Type Ia supernovae. These data are bringing us closer to resolving one of recent cosmology’s most persistent questions: is the Hubble tension a measurement issue, or a window into new physics?