ETH Zurich researchers detect a possible fifth force of nature
Precision measurements of calcium atoms revealed an unexpected pattern that cannot be explained by the simplest atomic physics calculations. Known effects inside atomic nuclei, especially nuclear polarization, could account for the anomaly, so the result is not evidence of a fifth force. The measurements still place some of the strongest limits yet from this method on a hypothetical particle linking electrons and neutrons. Calcium atoms have produced an unusually clear break from a pattern physicists expected to follow a straight line. The deviation is real, but its cause remains unresolved, sharpening a search for forces that may exist beyond known physics. The Standard Model of particle physics describes elementary particles and three of the four known fundamental forces with remarkable precision. Yet important gaps remain. It cannot provide a viable dark matter candidate, explain the universe’s matter-antimatter imbalance or account for neutrino masses inferred from oscillation measurements. “The Standard Model is currently the best explanation of the universe, but we know it cannot explain everything,” said Diana Prado Lopes Aude Craik, a physics professor at …








