The 2017 Nobel Prize in physics was awarded today to Rainer Weiss, Barry Barish, and Kip Thorne. Their work helped prove Albert Einstein right—yet again.
The winners, who all work for LIGO (the Laser Interferometer Gravitational-wave Observatory), were given the prize for “decisive contributions” to a detector that helps detect gravitational waves. These waves are created when two massive objects, like black holes, merge or are ripped apart. Detecting them is a “direct testimony” to disruptions in space-time, said the Nobel committee.
More than 100 years ago, Einstein proposed the theory of general relativity and made a number of predictions. He proposed that the universe is like a fabric made of space and time. And the fabric will bend because of massive objects, such as stars and planets.
This was proven correct when researchers found that the sun was able to bend the light coming from stars, such that observers from Earth were able to “look through” the sun to the stars behind it.
So if space-time defines our universe, Einstein predicted that when two massive objects interact, they would create a ripple in space-time. These ripples, called gravitational waves, should in theory be detectable if we were ever able to build instruments sensitive enough.
Such an instrument remained a dream until the 1970s. That’s when Rainer Weiss of the California Institute of Technology proposed a design that he thought would be able to detect gravitational waves. His ideas were then translated, through a series of researchers, including Kip Thorne, Ronald Drever, and Barry Barish, into what would become LIGO.
Today, LIGO consists of two observatories—one in Hanford, Washington and another in Livingston, Louisiana. The design of these observatories is simple, but their measurements are extremely precise. As Quartz explained previously:
Each detector consisted of two 4-km long tunnels at right angles. Each tunnel is emptied of all air. A laser beam is split in two, and each beam is sent down one tunnel and reflected back, where they are recombined. Gravitational waves stretch and then contract spacetime as they pass, just as ripples on a pond move the surface up and then down. As they passed through the LIGO team’s lasers, they changed, ever so slightly, the times it took each laser to travel those four kilometers. The distortion would only be as wide as a fraction of the width of a single atom. But that was enough to change the pattern of the laser light where the two beams were recombined.
The two detectors are thousands of miles apart for a reason. The distance allows each detector to ensure that if they record an interference it’s not because of something local but gravitational waves. Without having a second detector, there would have been many false positives from things like moving trucks and crashing waves, which would render the detection of gravitational waves impossible.
Since the first detection in 2015, LIGO has detected gravitational waves three more times. Each of the four detections has been the result of the merger of black holes, but scientists expect to soon capture waves emanating from supernovae (exploding stars) and the merger of neutron stars.
More importantly, as Quartz explained previously:
For most of history, astronomers peered into the sky with telescopes looking at signs of visible light. Over the last century, however, technological advances have allowed them to capture new types of signals which previously weren’t detectable, from radio waves to infrared radiation.
With more confirmed gravitational waves detections, scientists now have another new tool to detect celestial events. And crucially, the events that can be understood with gravitational waves—such as black hole mergers—are those that cannot be seen through common means of detection, such as light.
Apart from LIGO, the only other gravitational-wave detector that comes close to being as sensitive is in Europe, called the Virgo interferometer. LIGO’s results have renewed interest in building such observatories in other places. India is proposing to build one by 2023, and its location is expected to help LIGO and Virgo to observe gravitational waves coming from skies in the southern hemisphere more precisely. Even more ambitiously, European and Japanese scientists have proposed to build gravitational-wave observatories in space.
Nobel Prizes are often given to researchers many years after their discoveries, but the gravitational-wave detection breakthrough was just over two years ago. This shows that the prize committee is confident that this work is going to transform astronomy and our understanding of the universe.