The math behind the Big Bang only really works if you assume some particles actually weigh less than zero.
arXiv · March 16, 2026 · 2603.13208
Why it matters
Astronomers have long struggled with a discrepancy between the measured mass of neutrinos and the requirements of our standard model of the universe. By allowing for "effective negative mass" in their simulations, researchers found they could resolve these major cosmological tensions, suggesting our fundamental understanding of how mass behaves on a cosmic scale might be incomplete.
From the abstract
We investigate the impact of spatial curvature, $\Omega_k$, and dynamical dark energy on the cosmological constraints of the neutrino mass sum, $\sum m_\nu$. Using a joint analysis of the latest CMB (Planck and ACT DR6), BAO (DESI DR2) and SNe Ia (DESY5 and DES-Dovekie) datasets, we perform an exploration of the neutrino mass parameter space. To mitigate prior-driven biases near the physical boundary, we implement a symmetric extension wrapper that allows for effective negative masses. We find t