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Physicists think they've resolved the proton size puzzle
Two independent, ultra-precise hydrogen spectroscopy experiments have provided compelling evidence to resolve the long-standing 'proton radius puzzle' — a disagreement since 2010 over conflicting meas
Two independent, ultra-precise hydrogen spectroscopy experiments have provided compelling evidence to resolve the long-standing "proton radius puzzle" — a disagreement since 2010 over conflicting measurements of the proton's charge radius. Both teams used lasers to measure previously unobserved electron energy transitions in hydrogen atoms, and not only did their results match each other, but they also aligned with the landmark 2010 muonic hydrogen measurement , pointing to a proton radius of approximately 0.84 femtometers. The increased certainty of the proton's size is especially important for refining theories about new particles, and the MPQ experiment was already precise enough to test quantum electrodynamics to within 0.5 parts per million.
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Source: Ars Technica | 2026-04-14