What a trapped antimatter particle could tell us about reality

Host Flora Lichtman introduces antimatter as particles corresponding to ordinary matter—antiprotons for protons, antineutrons for neutrons, and positrons for electrons—that annihilate with matter and release energy. Gerald Gabrielse says trapping antimatter is difficult, though his team first succeeded when people told him it was impossible. He clarifies that the major advance was not merely holding a positron for months, but cooling it enough to probe its quantum structure. The researchers created what they call a one-positron quantum cyclotron.

Gabrielse explains that people, President Trump, and even garbage are all made from combinations of protons, neutrons, and electrons—an unexpectedly small ingredient list for the universe’s variety. Their antimatter counterparts have the same measured masses but opposite charges, and their magnetic directions are predicted to be opposite as well. The universe could theoretically have been made from antimatter instead of matter, so why matter dominates remains a mystery. Gabrielse says further mysteries appear when considering the universe as a whole.

The scientists’ trap acts like an artificial atom: the positron is confined inside a system cooled nearly to absolute zero, allowing Gabrielse to watch it make quantum jumps between its lowest energy levels for months. Radio or microwave signals induce transitions, and counting those jumps reveals the size of the positron’s magnetic moment. Gabrielse previously measured an electron’s magnetic moment to one part in 10 to the 13th. Having a positron in the same kind of environment should let the team make an equally precise comparison.

Flora asks whether the experiment can establish that a positron is the exact mirror image of an electron. Gabrielse says the new result makes that comparison possible; if the magnetic moments are not exactly opposite, it would be a huge theoretical and experimental shock. Researchers do not currently have convincing theories explaining how such a difference could arise, but Gabrielse insists experiments should not be limited by theorists’ imaginations: “God decides and we measure.” He predicts that a discrepancy would prompt roughly 100 explanatory papers in its first year.

The positrons come from the nuclear decay of radioactive sodium atoms. Sodium emits them at high energies and speeds, while the experiment requires coaxing them into a trap only a few feet away and cooling them to nearly absolute zero. Gabrielse identifies that conversion as the central experimental challenge. He recalls telling Science Friday in 1999 that he hoped to make cold antihydrogen the following year. The team eventually produced antihydrogen, but it took about six more years because its first apparatus was not sensitive enough to detect it and CERN’s antiproton facility later went offline for upgrades.

Flora asks about an antimatter version of herself and about science-fiction claims that antimatter could provide limitless energy or a devastating weapon. Gabrielse jokes that hugging an antimatter self would release enough annihilation energy to destroy a city, but says all the antimatter studied in history would not contain enough energy to boil a cup of tea. The research is not application-driven; its goal is understanding reality. Gabrielse says fundamental measurements can eventually produce technologies, though their applications and timescales are impossible to predict.