Why did a US$3-million-winning result leave one physicist feeling like <i>Peanut</i>’s character Charlie Brown, scuppered from kicking the football at the last second by his friend Lucy?
I recently wrote a story for Nature (https://www.nature.com/articles/d41586-026-01014-9) about this year’s Breakthrough Prizes, including the several hundred recipients of the Fundamental Physics prize which has been awarded to somewhere between 300 and 400 physicists who worked on the Muon g-2 experiment series, that took place first at CERN, near Geneva, Switzerland, then at the Brookhaven National Laboratory in Long Island, New York, and finally at Fermilab, in Batavia, Illinois. The experiments endeavoured to pin down the value of the muon’s magnetic moment, its internal quantum property that makes it behave like a little bar magnet, when placed in a magnetic field, precessing or wobbling due to quantum effects, like the axis of child’s spinning top. There had long been intriguing hints that this value deviated from the Standard Model’s predictions, potentially pointing to new physics, so particle physicists had been keen to keep upping the precision of experiments to check.
I had a lovely chat with David Hertzog of the University of Washington in Seattle, who worked on the experiment at Brookhaven and then later led follow-up measurements at Fermilab. He noted that when Fermilab reported the final results in 2025—to a precision of 127 parts in a billion—most news outlets reported that the experiment confirmed the Standard Model’s predictions, end of story. He slightly frustrated because things are not quite that simple. See QSpace News for more.
