Antimatter
Antimatter is the counterpart of ordinary matter, and the two destroy each other on contact. In March 2026, 92 antiprotons were driven around CERN on a truck, and none were lost.
Particles and antiparticles appeared in pairs after the Big Bang, which means the universe ought to hold as much of one as the other, and wherever the two meet they annihilate. To look for any difference, physicists trap antiprotons and compare them with protons. They are hard to come by: running flat out, CERN could make about a billionth of a gram a year, so one gram would take a billion years. Yet on 24 March 2026, 92 antiprotons rode a truck 7.5 km around CERN, and none were lost.
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