On this day in 2015, the universe’s gravitational waves, predicted by Albert Einstein a century before, were observed for the first time by ultra-sensitive detectors stationed in various places in the United States. The observation led to a new way to study our universe and the 2017 Nobel Prize in Physics for Rainer Weiss, Barry Barish and Kip Thorne. Below is the story of this remarkable discovery.
The LIGO Story
We think of space as a silent place. But Janna Levin, a professor of physics and astronomy at Barnard College of Columbia University says the universe has a soundtrack, a sonic composition that records dramatic events in outer space. One such event is the sound made by black holes make when they collide.
Black holes are massive stars that have collapsed under the weight of gravity so intense that not even light can escape its grasp. Coalescing black holes release so much energy that they make a sound when that energy courses through spacetime as waves, which are known as “gravitational waves.”
Despite the cataclysmic scale of the event, we can’t hear it because it is too far away. But with ingenuity, scientists have built special detectors that can pick up this song of the universe. On September 14, 2015, this song was heard by two detectors, one in Washington State and the other in Louisiana. These ultra-sensitive sonic detectors are named LIGO, shorthand for Laser Interferometer Gravitational-Wave Observatory.
It took thousands of scientists nearly 50 years to bring this dream machine into fruition. Three of the pioneer scientists – Rainer Weiss (born 1932) from the Massachusetts Institute of Technology, Kip Thorne (born 1940) from the California Institute of Technology, and Barry Barish (born 1936), from the University of California, Berkeley, were awarded the 2017 Nobel Prize in Physics for their work in gravitational wave detection .
The 2015 LIGO discovery wasn’t just a triumph of experimental physics and engineering; it was a celebration of the power of the human imagination, in particular, that of Albert Einstein. In a 1916 paper written one year after his General Theory of Relativity, Einstein predicted that distortions in space-time caused by massive objects would produce ripples or gravitational waves moving outward from those objects at the speed of light.
For many years after the paper was published, many physicists, including Einstein himself, wasn’t certain whether the predicted waves were real or simply artefacts of the new mathematics that Einstein employed in the paper. The LIGO discovery positively settled that debated and was another glorious confirmation of the “unreasonable effectiveness” of mathematics in describing the workings of nature. The discovery, coming just a few months short of 2016, was also a fitting centennial tribute to the remarkable physicist that was Albert Einstein.
Janna Levin, physicist and author, tells the extraordinary story of the LIGO discovery.
 For an entertaining read on the heady world of scientists straining over decades to detect gravitational waves, see Janna Levin, Black Holes Blues, Alfred A. Knof, New York, 2016.