Overview
- Two peer‑reviewed reanalyses published in Monthly Notices of the Royal Astronomical Society on June 10–11 reached opposite conclusions about cosmic expansion from the same Pantheon+ supernova dataset.
- The core dispute is methodological: one side applies a long‑used host‑galaxy mass correction while the other applies a newer progenitor‑age correction and those choices change inferred distances.
- Phil Wiseman and colleagues show that applying the routine host‑mass correction and correcting progenitor‑age assumptions removes the apparent age bias and leaves evidence for ongoing acceleration.
- Animesh Sah, Mohamed Rameez and Subir Sarkar report that applying a progenitor‑age correction to Pantheon+ erases an isotropic acceleration signal, infers overall deceleration, and finds an anisotropy aligned with local motion.
- Both teams say the disagreement is technical and unresolved and that the Rubin Observatory’s LSST plus independent probes such as the CMB and BAO will be needed to settle which calibration is correct and what that means for dark energy research.