In gravitational-wave detectors like LIGO, an interferometer does the work: a laser beam races between mirrors in arms kilometers long, catching shifts as tiny as a thousandth of a proton. But when the power climbs to megawatts, the mirrors start to 'howl'—the reflected light shakes them even more, exactly like a microphone pointed at a speaker. This roar drowns out the faint whisper of gravitational waves from merging black holes or neutron stars.

Engineers tamed the shudder with an additional beam: they tuned it so its crest meets the main beam's trough, and the waves cancel each other, just like noise-canceling headphones, only for light. Computer simulations and an experiment on the working LIGO in Livingston showed: the vibration buildup crashed nearly a hundredfold. This method, developed by Rainer Weiss, Kip Thorne, and Barry Barish, paves the way for next-generation telescopes like Cosmic Explorer and the Einstein Telescope. They'll catch waves from events at the edge of the universe and test how spacetime curves in extreme collisions.