In 1916, the famed theoretical physicist Albert Einstein postulated certain events in the universe would produce gravitational waves. The detection of such waves would be even more confirmation of general relativity, but Einstein suspected the waves would be too faint to be detected on Earth. Now, 100 years later, three US scientists are sharing the Nobel Prize in Physics for detecting gravitational waves.
The Nobel Committee has awarded this year’s prize in physics to Rainer Weiss, Kip Thorne, and Barry Barish. Weiss gets half of the nine million Swedish kronor ($ 1.1 million) prize, and Thorne and Barish share the other half. The first detections came in 2015 (published in early 2016), but the Nobel Committee always waits at least a year to make an award. If it had made this award last year, Scottish physicist Ron Drever would most likely have shared the award with Thorne and Weiss, with whom he worked before his death in March of this year.
All three winners have been involved with the Laser Interferometer Gravitational-Wave Observatory (LIGO) project in some way. LIGO is composed of two facilities; one in Washington state and the other in Louisiana. A European station was added just this year in Italy. Weiss was awarded half of the prize for developing the strategy used at LIGO to make the gravitational wave detection. Meanwhile, Thorne did the theoretical work that pointed LIGO in the right direction. Barish was the second director of LIGO, beginning in 1994. He’s credited with spearheading the effort at LIGO that made detection possible.
Gravitational waves were the last major prediction from general relativity that remained unconfirmed before LIGO researchers made their announcement. According to relativity, movements of mass should cause ripples in the spacetime continuum. These “waves” would propagate outward at the speed of light, but the waves themselves were extremely faint. Thus, we could only hope to detect the largest events like the collision of two black holes.
LIGO uses a technique called laser interferometry to detect gravitational waves. It bounces lasers off reflectors at the end of a 4-kilometer tube, then monitors the laser’s return for evidence of movement from gravitational waves. If there’s no alteration in the mirrors, the light returns unchanged and the beams cancel each other out. If a gravitational wave perturbs the system, the waves won’t cancel out. It can detect movements as small as a ten-thousandth the charge diameter of a proton. LIGO successfully detected waves emanating from a pair of black holes orbiting around each other as they prepared to merge. The paper was published in 2016 along with an audio recording of the wave.
This discovery has been hailed as a monumental achievement for science, one now recognized by the Nobel Committee. The work of these scientists not only confirms a 100-year-old theory–it opens up new avenues of study today and into the future.