At the two four-kilometre long LIGO observatories in the US, scientists developed incredibly sensitive detectors, capable of spotting a movement 100 times smaller than the nucleus of an atom. In 2015, they spotted the ripples produced by two black holes spiralling into each other, setting spacetime quivering. This was the first time black holes had ever been directly detected, and it promises far more for the future of astronomy. Brian Clegg presents a compelling story of human technical endeavour and a powerful new path to understand the workings of the universe.