Everyone loves the satisfying pop when a bubble bursts, but what exactly produces the sound? Adrien Bussonnière at Sorbonne University in Paris, France, and his colleagues studied audio of bubbles popping to find out – and it involves an imbalance of forces.

On a fundamental level, sound is a pressure wave. The air inside a bubble is under more pressure than the air outside it, as it is compressed by the surface tension of the bubble film – that is, until it bursts. “The forces applied by the liquid soap …