Mathematicians from the University of California, Davis, are proposing a radical rethink of cosmic expansion, suggesting that dark energy may not be necessary to explain the universe’s accelerating growth. In a study published in the Proceedings of the Royal Society A, they use the Einstein-Euler equations—combining general relativity and fluid dynamics—to demonstrate that Friedmann spacetimes, which underpin the standard cosmological model, are inherently unstable at both small and large scales. This instability, they argue, makes the current Lambda-cold dark matter model physically implausible.

The team, led by distinguished professor emeritus Blake Temple, compares the standard model to a pencil balanced on its tip: mathematically possible but physically unstable. Their analysis shows that even tiny perturbations cause deviations from uniform expansion, leading to observed accelerations without requiring dark energy. Instead, they propose self-similar solutions during the radiation epoch of the Big Bang as a more natural explanation within Einstein’s original framework.

The findings also challenge the Copernican principle, which assumes no special location in the universe. Both the standard model and their alternative imply a center of symmetry, raising questions about which framework better reflects reality. Funded by the UK’s EPSRC and the American Institute of Mathematics, this work could reshape how physicists interpret cosmic observations and model the universe’s evolution.