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Then in 2010, a lab in Germany swapped the electron in a hydrogen atom for a heavier particle and came back with a proton nearly four percent smaller. <\/p>\n
That result sparked 15 years of disagreement nobody could fully resolve.<\/p>\n
Where the puzzle began<\/p>\n
The team conducting the 2010 experiment built a special hydrogen atom by replacing its usual electron with a much heavier particle called a muon. <\/p>\n
The measurement<\/a> gave a proton radius about 4 percent smaller than the established value \u2013 a gap large enough to shake confidence in some of the most precise work in physics.<\/p>\n It opened what became known as the proton radius puzzle, sending researchers hunting for either a hidden experimental error or signs of unknown forces or particles.<\/p>\n Dr. Lothar Maisenbacher, who is now at the University of California, Berkeley (UC Berkeley<\/a>), led one of the latest efforts to solve the puzzle. <\/p>\n He and colleagues at the Max Planck Institute of Quantum Optics (MPQ<\/a>) in Garching, Germany, built a setup precise enough to distinguish between the two competing values.<\/p>\n Reading a tiny atom<\/p>\n Hydrogen is the simplest atom in existence \u2013 one proton, one electron, locked together by their opposite charges. <\/p>\n The two particles pull on each other electrically, and the proton\u2019s size appears to shift the energies available to the electron. <\/p>\n Precisely how large that shift is depends on the proton\u2019s actual dimensions.<\/p>\n That connection is the lever physicists pull on. By measuring how electrons jump between energy levels inside hydrogen<\/a>, they can work backward to the proton\u2019s size. <\/p>\n Each new measurement has to be cleaner than the last.<\/p>\n Dr. Maisenbacher\u2019s group used finely tuned lasers to nudge electrons between two energy states never measured at this precision before. <\/p>\n The transitions had been observed in earlier experiments, but never sharply enough to settle the puzzle.<\/p>\n The textbook number was wrong<\/p>\n After three measurement runs and months of cataloguing every possible source of error, the team arrived at a proton radius of 0.8406 femtometers \u2013 less than one millionth of a billionth of a meter.<\/p>\n The result is 2.5 times more precise than any previous atomic hydrogen measurement. <\/p>\n It matches the smaller value from muonic hydrogen almost exactly and confirms what a 2019 paper<\/a> had already suggested \u2013 the old textbook number was wrong.<\/p>\n Dylan Yost, a physicist at Colorado State University (CSU<\/a>), led a second team that ran a complementary experiment and landed on the same answer. <\/p>\n The identical results from two independent experiments make an instrument-specific error highly unlikely.<\/p>\n The challenge of studying hydrogen<\/p>\n These experiments look modest from the outside \u2013 a vacuum chamber, lasers, a small cloud of hydrogen atoms chilled to near absolute zero. Behind that simplicity is brutal difficulty.<\/p>\n Hydrogen atoms need a near-perfect vacuum, and the lasers require calibration so exacting that minor environmental shifts can corrupt the data. <\/p>\n Collecting raw numbers might take a few weeks. Cataloguing every possible source of error can take years.<\/p>\n Each lab\u2019s setup is unique enough that tracing divergences between results to a specific cause is difficult. <\/p>\n That difficulty becomes a strength when the results agree. Any quirk specific to one instrument would not survive two independent setups.<\/p>\n Testing the rulebook<\/p>\n With the proton\u2019s size locked in, the team pushed further. <\/p>\n The experts compared their measurement against the Standard Model \u2013 physics\u2019 master set of equations for how particles<\/a> and forces behave. Agreement to 0.7 parts per trillion.<\/p>\n One match in roughly a trillion. That kind of precision is usually reserved for atomic clocks \u2013 one of the sharpest checks ever run on how light and matter interact at the fundamental level.<\/p>\n Everything matched. There was no hint of unknown forces, no exotic particles betraying themselves through the electron\u2019s behavior. <\/p>\n The current rulebook held up under unusually heavy scrutiny.<\/p>\n A new search begins<\/p>\n The result may sound like a closed door, but Yost sees it differently. <\/p>\n Knowing the proton\u2019s size with confidence lets researchers use the same hydrogen experiments to set tighter limits on what new physics might still be hiding.<\/p>\n Giant accelerators like the Large Hadron Collider in Switzerland are built to smash particles together and create heavy new ones. <\/p>\n Tabletop hydrogen experiments are sensitive to a different breed \u2013 extremely light particles that giant colliders cannot easily see.<\/p>\n With the proton question settled, those tabletop setups become a viable tool for particle physics<\/a> searches. <\/p>\n The hardware was already there. What was missing was certainty about the background.<\/p>\n Broader implications of the study <\/p>\n For the first time, physicists have a proton radius they can stake their reputations on. <\/p>\n The atomic hydrogen number and the muonic hydrogen number finally agree, precisely enough that the 15-year disagreement is no longer scientifically alive.<\/p>\n That settles a long-standing question. Researchers can now use the same techniques to search for particles or forces beyond the Standard Model, with hydrogen serving as a sensitive detector instead of a source of uncertainty.<\/p>\n Other groups working on deuterium and similar transitions stand to gain from the methods this team developed. <\/p>\n Within a few years, the field could move from one resolved puzzle to fresh questions about physics beyond the known.<\/p>\n The study is published in the journal Nature<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Physics textbooks gave the proton a radius. Independent labs around the world kept arriving at the same number,…\n","protected":false},"author":2,"featured_media":463013,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[85,46,370,141],"class_list":["post-463012","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-il","tag-israel","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/463012","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=463012"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/463012\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/463013"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=463012"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=463012"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=463012"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}