Overview
- This week, two papers published in Monthly Notices of the Royal Astronomical Society used the Pantheon+ catalog and arrived at directly opposing cosmological conclusions.
- A team led by Animesh Sah, Mohamed Rameez and Subir Sarkar applied a progenitor‑age correction and reported that the Pantheon+ data indicate overall deceleration and an anisotropic signal aligned with our local motion.
- A separate reanalysis led by Phil Wiseman applied the long‑used host‑galaxy mass correction, used simulations to model progenitor ages, found the evidence for acceleration remains robust, and identified methodological errors in the 2025 weakening claim.
- The technical heart of the dispute is how Type Ia supernovae are standardized for distance: the routine mass correction shifts measured brightness consistently across redshift while the newer progenitor‑age correction is sparsely measured at high distance and can change inferred expansion rates.
- Both teams and other cosmologists say the disagreement cannot be settled with current samples and that Rubin Observatory’s LSST and other upcoming surveys will provide the far larger supernova datasets needed to arbitrate calibration choices and the reality of changing dark energy.