Antimatter has always been full of surprises. The first was that it existed. The second was that it didn’t.
First things first. In the 1920s, British physicist Paul Dirac managed to marry quantum theory with Einstein’s special relativity to explain how tiny, fast-moving fundamental particles such as electrons work. But his austerely beautiful unifying equation, honoured with a plaque in London’s Westminster Abbey, had an unwanted consequence. For every matter particle like an electron, it predicted the existence of a second particle that was the same, but opposite in things like electric charge.
Dirac initially brushed this under the carpet – out of “pure cowardice” he later said – but three years on, the antimatter version of the electron, the positron, was discovered in cosmic rays. Since then, as the standard model of particle physics was built on the foundation that Dirac and others laid, a very different problem has emerged. Antimatter shouldn’t just exist, it should be abundant: every time a matter particle is made, an antimatter particle should also be conjured from the void. “We should have a universe half full of antimatter,” says Michael Capell, an astroparticle physicist at the Massachusetts Institute of Technology. So where are these particles?
They can’t be near us because matter and antimatter mutually “annihilate” whenever they meet, and we would notice the flash of X-ray energy produced when they do. Various small-scale particle behaviours