When water drains from a bathtub, a whirlpool often forms above the drain, and its narrow core can start to wobble and twist. For almost 150 years, physicists have predicted that these wobbles can become turbulent, passing energy from large ripples down to ever smaller ones. Until now, however, this “Kelvin-wave turbulence” had never been seen directly in an experiment.

In new research published in Physical Review Letters, a team led by Eric Falcon at Université Paris Cité has observed the effect using a carefully controlled whirlpool in a tank of water.