A precise proton measurement helps put a core theory of physics to the test Skip to content Subscribe today Every print subscription comes with full digital access Subscribe Now Menu All Topics Health Humans Anthropology Health & Medicine Archaeology Psychology View All Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes View All Earth Agriculture Climate Oceans Environment View All Physics Materials Science Quantum Physics Particle Physics View All Space Astronomy Planetary Science Cosmology View All Magazine Menu All Stories Multimedia Reviews Puzzles Collections Educator Portal Century of Science Unsung characters Coronavirus Outbreak Newsletters Investors Lab About SN Explores Our Store SIGN IN Donate Home INDEPENDENT JOURNALISM SINCE 1921 SIGN IN Search Open search Close search Home INDEPENDENT JOURNALISM SINCE 1921 All Topics Earth Agriculture Climate Oceans Environment Humans Anthropology Health & Medicine Archaeology Psychology Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes Physics Materials Science Quantum Physics Particle Physics Space Astronomy Planetary Science Cosmology Tech Computing Artificial Intelligence Chemistry Math Science & Society All Topics Health Humans Humans Anthropology Health & Medicine Archaeology Psychology Recent posts in Humans Health & Medicine A simple shift in schedule could make cancer immunotherapy work better By Elie DolginFebruary 12, 2026 Health & Medicine This baby sling turns sunlight into treatment for newborn jaundice By Elie DolginFebruary 12, 2026 Health & Medicine Antibiotics can treat appendicitis for many patients, no surgery needed By Laura DattaroFebruary 10, 2026 Life Life Animals Plants Ecosystems Paleontology Neuroscience Genetics Microbes Recent posts in Life Ecosystems Food chains in Caribbean coral reefs are getting shorter By Erin Garcia de JesúsFebruary 11, 2026 Paleontology Fossilized vomit reveals 290-million-year-old predator’s diet By Jay BennettFebruary 11, 2026 Health & Medicine Tell Me Where It Hurts sets the record straight on pain — and how to treat it By Laura SandersFebruary 10, 2026 Earth Earth Agriculture Climate Oceans Environment Recent posts in Earth Earth Earth’s core may hide dozens of oceans of hydrogen By Nikk OgasaFebruary 10, 2026 Animals Some dung beetles dig deep to keep their eggs cool By Elizabeth PennisiFebruary 4, 2026 Climate Polar bears in the Barents Sea are staying fat despite rapid sea ice loss By Rebecca DzombakJanuary 29, 2026 Physics Physics Materials Science Quantum Physics Particle Physics Recent posts in Physics Physics A precise proton measurement helps put a core theory of physics to the test By Emily ConoverFebruary 11, 2026 Physics The only U.S. particle collider shuts down – so a new one may rise By Emily ConoverFebruary 6, 2026 Physics A Greek star catalog from the dawn of astronomy, revealed By Adam MannJanuary 30, 2026 Space Space Astronomy Planetary Science Cosmology Recent posts in Space Astronomy This inside-out planetary system has astronomers scratching their heads By Adam Mann17 hours ago Space Artemis II is returning humans to the moon with science riding shotgun By Lisa GrossmanFebruary 4, 2026 Physics A Greek star catalog from the dawn of astronomy, revealed By Adam MannJanuary 30, 2026 News Physics A precise proton measurement helps put a core theory of physics to the test The standard model of particle physics is confirmed to a tenth of a billionth of a percent An estimate of the proton’s radius based on measurements of hydrogen atoms has allowed scientists to test the standard model of particle physics. Shaumiaa Vector/Getty Images By Emily Conover February 11, 2026 at 11:00 am Share this:Share Share via email (Opens in new window) Email Click to share on Facebook (Opens in new window) Facebook Click to share on Reddit (Opens in new window) Reddit Click to share on X (Opens in new window) X Click to print (Opens in new window) Print For over a decade, confusion over the size of the proton has held scientists back. Disagreeing measurements of the subatomic particle’s radius meant that scientists couldn’t test one of their key theories with the extreme precision they aimed for. A new measurement pegs the radius of the proton precisely enough to enable a test of the standard model of particle physics, which describes subatomic particles and their interactions. The theory agreed with the experiment to better than a tenth of a billionth of a percent, physicist Lothar Maisenbacher and colleagues report February 11 in Nature. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday. The researchers studied hydrogen atoms, measuring the frequency of the radiation needed to make the atom jump between two different energy levels. That information, combined with other measurements, revealed the proton’s radius was about 0.84 trillionths of a millimeter. That figure agrees with a host of measurements that suggest the proton’s size is smaller than once thought, and the measurement is precise enough to rule out the approximately 4 percent larger radius found by some earlier experiments. That confirmation that the proton’s radius is small allowed the researchers to use their data to test the standard model. The standard model can predict the frequency of the radiation needed to make the atom jump between the energy levels in their experiment. But an independent measurement of the proton radius is needed. Now that the researchers had differentiated between the large and small values, they were free to use another measurement of the proton’s radius that favors the smaller size, made with an exotic type of hydrogen called muonic hydrogen. This is a proton bound to a heavy cousin of the electron, called a muon. The standard model prediction matched the experiment, vindicating the theory. Specifically, it verified a pillar of the theory called quantum electrodynamics, which describes the interactions of electrically charged particles and light. Scientists eventually expect to find a test that the standard model fails, says Maisenbacher, who performed the work at the Max Planck Institute of Quantum Optics in Garching, Germany. The theory doesn’t explain phenomena such as dark matter, the invisible substance that helps bind galaxies together. “These tests are important because we know that our understanding of the world is not complete.” Questions or comments on this article? E-mail us at feedback@sciencenews.org | Reprints FAQ Citations L. Maisenbacher et al. Sub-part-per-trillion test of the Standard Model with atomic hydrogen. Nature. Published online Feb 11, 2026. doi: 10.1038/s41586-026-10124-3. About Emily Conover E-mail X Senior physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award and a winner of th
A precise proton measurement helps put a core theory of physics to the test
