On September 14, 2015, physicists made history by detecting gravitational waves—ripples in space-time—marking one of the most groundbreaking achievements in physics. The concept traces back to Albert Einstein’s theory of general relativity, published in 1915. Einstein predicted that massive objects bend the fabric of space-time, and when such objects accelerate—such as during the collision of two black holes—they generate waves that travel across the cosmos. Although Einstein formulated this idea, he doubted these waves could ever be observed, since the distortions they create are far smaller than an atom.Decades later, in the 1970s, MIT physicist Rainer Weiss—who passed away in August—proposed a way to measure these minute signals. His design centered on an interferometer: a device that splits a beam of laser light into two perpendicular paths. The light beams bounce off suspended mirrors before recombining at a detector. Under normal conditions, if the paths are identical in length, the beams return perfectly in sync. But if a gravitational wave sweeps through, it subtly stretches one path while compressing the other. This minuscule difference causes the beams to arrive slightly out of phase, producing a detectable signal.Weiss, together with Caltech physicist Kip Thorne, argued that the detector’s arms had to be several kilometers long to capture such faint ripples. They also insisted on building at least two detectors, separated by great distances. This would ensure that the signals were truly cosmic, ruling out local disturbances like earthquakes or traffic vibrations, while also allowing scientists to triangulate the origins of the waves.Their vision eventually led to the Laser Interferometer Gravitational-Wave Observatory (LIGO), which confirmed Einstein’s century-old prediction. That first detection opened a new era of astronomy, allowing humanity to listen to the universe through gravitational waves.
Science history: Gravitational waves detected, proving Einstein right — Sept. 14, 2015
