The new proton radius value aligns with muonic hydrogen and a 2019 Science paper, suggesting the older textbook standard was incorrect and validating the experimental approach.

Two independent experiments using hydrogen and muonic hydrogen measured a proton radius of 0.8406 femtometers, resolving the long-standing puzzle and overturning the previous standard.

Two high-precision studies led by Lothar Maisenbacher and Dylan Yost converge on the same result, greatly reducing the chance of instrument-specific bias.

The measurement used precision laser spectroscopy of hydrogen energy transitions with unprecedented accuracy and careful control of environment and error sources to isolate the proton size effect.

Published in Nature in 2026, the finding reinforces the Standard Model at extreme precision and sets tighter constraints on possible new forces or particles through hydrogen spectroscopy.

With the proton radius settled, tabletop hydrogen experiments can be leveraged to probe new physics and very light particles, complementing large-scale colliders like the LHC.

Back in 2010, a muon-based hydrogen experiment reported a proton radius about 4 percent smaller than the accepted value, igniting a 15-year debate and investigation.