Every time two black holes collide somewhere in the universe, they send ripples through the fabric of spacetime itself. We call these ripples gravitational waves. The problem is detecting them since they are almost impossibly faint by the time they reach Earth. LIGO, the Laser Interferometer Gravitational-Wave Observatory, solves that problem with a 4 kilometre laser tunnel so sensitive it can measure a change in distance a thousand times smaller than a proton. But what if there was another way to measure such changes?

Researchers at Stockholm University, Nordita, and the University of Tübingen think there might be. Their new theoretical study, published in Physical Review Letters, suggests that gravitational waves leave detectable fingerprints in the light emitted by atoms and that a cloud of atoms just a few millimetres across might one day serve as a gravitational wave detector.