If anything fell upwards, it would rewrite physics textbooks. Amazingly fiddly experiments to test whether antimatter can do just this are kicking off

What goes up… Li Wei/Solent News/REX/Shutterstock

ON 11 November last year, a small birthday party was held in an apparently unremarkable hangar onthe outskirts of Geneva, Switzerland. Nothing too fancy, just a few people gathered around a cake. The honourees were there. Well, sort of – they were still locked in the cage where they had spent their first year. But then again, there is no other way to treat a brood of antimatter particles.

The antimatter realm is so bizarre as to be almost unbelievable: a mirror world of particles that destroy themselves and normal matter whenever the two come into contact. But it’s real enough. Cosmic rays containing antiparticles constantly bombard Earth. A banana blurts out an anti-electron every hour or so. Thunderstorms produce beams of the stuff above the planet.

Making and manipulating antimatter ourselves is a different kettle of fish. Hence that birthday party held at the particle physics centre CERN, celebrating on behalf of a quadruplet of antiprotons. There’s a lot we would like to learn from these caged beasts and their ilk, not least this: do they fall up?

Cards on the table, few physicists believe that such “antigravity” effects exist – that if you released one of those antiprotons and somehow ensured it free passage through the hostile world of matter, it would magically float up. But the recalcitrant nature of antimatter means we’ve never done the experiments, and until we do, we simply don’t know. “Progress is often made by asking the questions we think we already know the answer to,” says Daniel Kaplan of the Illinois Institute of Technology in Chicago. …