Overview
- Researchers report their findings in Astronomy and Astrophysics, providing one of the most precise independent checks of the cosmic expansion rate to date.
- Time‑delay cosmography of gravitationally lensed quasars was used to derive absolute distances from the arrival‑time differences of multiple images.
- Critical mass measurements of the lensing galaxies came from stellar‑motion spectroscopy with the Keck Cosmic Web Imager, complemented by Keck, JWST, and VLT data.
- The established discrepancy persists, with early‑Universe inferences near 67 km/s/Mpc and late‑Universe measurements around 73 km/s/Mpc.
- Team members say unresolved systematics would need to be identified to close the gap, and they note that new physics such as early dark energy or unknown particles could be required if no measurement error emerges, with comments from Tommaso Treu, Simon Birrer, Anowar Shajib, and John O’Meara.