Every object in a vacuum falls with the same acceleration — that's the foundation of Einstein's gravity Einstein. But so far, this rule has only been tested on particles of ordinary matter. Now muonium enters the game: an exotic atom where the nucleus is an antimuon and the shell is an ordinary electron. This hybrid lives for two microseconds; trapping it into a dense beam seemed like science fiction.
The solution lies in superfluid helium. Its thin film, free of friction, acts like a catapult factory. Muons piercing through it strip off electrons, and these fly out as a single 'plug'. The swarm's speed is about 2180 m/s, and all particles race nearly identically, like a gunshot.
The main goal is to measure their acceleration of fall for the first time with percent-level precision. A deviation would mean a crack in physics. And along the way, the cold beam will allow more precise weighing of the muon and testing theory with spectroscopy.
Superfluid helium flows through pores without friction, pulling out the short-lived muonium into a neat beam — like a quantum illusionist.