In his general theory of relativity, Albert Einstein predicted the existence of gravitational waves—ripples in the fabric of space time set off by violent cosmic events in the early universe. He also assumed these waves would be nearly impossible to detect. This February, a century after Einstein changed our perception of the universe, scientists at MIT helped to prove him right—and wrong—when they detected gravitational waves arising from the collision of two black holes 1.3 billion years ago.
“The effect we’re measuring on Earth is equivalent to measuring the distance to the closest star, Alpha Centauri, to within a few microns,” says Matthew Evans, assistant professor of physics at MIT and researcher at the Laser Interferometer Gravitational-Wave Observatory (LIGO), a joint research project between MIT and CalTech. “Einstein never expected this to have been pulled off.”
The 1.3-billion-year-old waves were received at twin interferometers at LIGO facilities in Louisiana and Washington State. In each L-shaped device, a laser beam travels between mirrors spaced four kilometers apart. The distance between the mirrors changes, infinitesimally, when the gravitational wave passes between them. Once detected, the gravitational signal is converted into audio waves, enabling LIGO researchers to hear the sound of two black holes merging. “We’re actually hearing them thump in the night,” says Evans.
First proposed in the 1980s, LIGO has been funded since 1992 by the National Science Foundation. “LIGO is an example of a high-risk, high-return investment in discovery-driven science,” says Maria T. Zuber, vice president for research at MIT. “It is a triumph for federally funded research…. And while the discoveries reported here are already magnificent, they represent the tip of the iceberg of what will be learned about fundamental physics and the nature of the universe.”