In the mid-1980s Bernard Schutz came up with a new solution to one of astronomy’s oldest problems: how to measure the distance from Earth to other objects in the cosmos. For generations, researchers have relied on an object’s brightness as a rough gauge of its distance. But this approach carries endless complications. Dim, nearby stars, for example, can masquerade as bright ones that are farther away. Schutz, a physicist at Cardiff University in Wales, realized that gravitational waves could provide the answer. If detectors could measure these ripples in spacetime emanating from interacting pairs of distant objects, scientists would have all the information needed to calculate how strong the signal was to start with—and thus how far the waves must have traveled to reach Earth. Therefore, he predicted, gravitational waves could be unambiguous markers of how quickly the universe is expanding.