For over two decades, one of particle physics' most intriguing puzzles seemed to hint at the existence of unknown forces hidden beyond the known laws of nature. On Wednesday, those hopes were dashed: the most precise calculation ever performed of the muon’s anomalous magnetic moment was published in the journal Nature. The results showed that the long-standing discrepancy between theory and experiment was due to an error in previous calculations rather than a crack in the Standard Model, according to Phys.org.

A Decade of Supercomputing

An international team led by University of Pennsylvania physicist Zoltán Fodor utilized lattice quantum chromodynamics—a method that models strong nuclear interactions by dividing space-time into a fine grid—on some of the world's most powerful supercomputers. The work spanned over 10 years to reach the final result. The key challenge lay in calculating the "hadronic vacuum polarization" contribution, which arises from the chaotic interactions of quarks and gluons governed by the strong force.

Instead of relying solely on an older method based on experimental data that produced the apparent discrepancy, the team combined lattice calculations at small and intermediate distances with experimental data at long distances, where measurements are already well-established. Additionally, the scientists conducted simulations on finer lattices than any previous study, significantly reducing uncertainties. The resulting calculation is nearly twice as precise as the previous world consensus, reaching an accuracy of 0.48%.

No Fifth Force, but a Triumph for Quantum Theory

When integrated into the full Standard Model prediction, the new calculation brings theory and experiment into agreement within half a standard deviation—confirming the model to 11 decimal places. The paper, titled "Hybrid 0.48% precision calculation of the hadronic vacuum polarization in the muon anomalous magnetic moment," was authored by researchers from Europe, the US, and Australia.

"We applied a new method to calculate this discrepancy and showed that it isn't there," Fodor said. "That new interaction we were hoping for simply doesn't exist. The old interactions fully explain the observed value."

This discovery comes just days after the Muon g-2 experiment—conducted at CERN, Brookhaven, and Fermilab over six decades—received the 2026 Breakthrough Prize in Fundamental Physics for its high-precision measurements. In 2025, Fermilab announced its final experimental result, determining the muon’s magnetic anomaly with a precision of 127 parts per billion.