Dark matter is five times more massive than ordinary matter, yet it emits no light. Its nature remains unknown. One candidate is the ultra-light axion particle. Axions could pierce right through the planet, barely noticing atoms. But on rare occasions, an axion can give an electron a gentle nudge, like an invisible breeze deflecting a compass needle.
Physicists built a supersensitive “compass”: a tiny magnetized rod levitated in a vacuum on a magnetic cushion, its vibrations tracked by a laser beam. Over five hours of observation, the needle didn’t budge. Remarkably, the whole setup worked at room temperature — no bulky refrigerators, typical for such experiments. The lack of signal allowed them to set a record-tight limit for the first time: axions interact with ordinary matter ten million times more weakly than previously thought.
The instrument’s silence is a crucial result, narrowing the search. Now scientists plan to cool the detector and surround it with a superconducting shield, boosting sensitivity a hundredfold. The idea of dark matter was born thanks to Fritz Zwicky, and observational proof came from Vera Rubin.
Axions are named after a laundry detergent because they ‘clean up’ an annoying problem in particle physics.