Three American physicists have won the Nobel prize in physics for the first observations of gravitational waves, ripples in the fabric of spacetime that were anticipated by Albert Einstein a century ago.
Rainer Weiss has been awarded one half of the 9m Swedish kronor (£825,000) prize, announced by the Royal Swedish Academy of Sciences in Stockholm on Tuesday. Kip Thorne and Barry Barish will share the other half of the prize.
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The 2017 physics Nobel prize was awarded for the detection of gravitational waves. But what else could be revealed now that this discovery has been made?
All three scientists have played leading roles in the Laser Interferometer Gravitational-Wave Observatory, or Ligo, experiment, which in 2015 made the first historic observation of gravitational waves triggered by the violent merger of two black holes a billion light-years away.
Prof Olga Botner, a member of the Nobel committee for physics, described this as “a discovery that shook the world”.
The Ligo detections finally confirmed Einstein’s century-old prediction that during cataclysmic events the fabric of spacetime itself can be stretched and squeezed, sending gravitational tremors out across the universe like ripples on a pond.
The direct detection of gravitational waves also opens a new vista on the “dark” side of the cosmos, to times and places from which no optical light escapes. This includes just fractions of a second after the Big Bang, 13.7 billion years ago, when scientists believe gravitational waves left a permanent imprint on the cosmos that may still be perceptible today.
The notion that space-time is malleable was first predicted by Einstein’s general theory of relativity. But Einstein himself was unsure whether this was merely a mathematical illusion, and concluded that, in any case, the signal would be so tiny that it would “never play a role in science”.
It was a significant career gamble then, when in the mid-1970s Weiss and Thorne, who is now the Feynman professor of theoretical physics at California Institute of Technology, began the decades-long quest to detect gravitational waves, which they believed could revolutionise our understanding of the universe.
Weiss designed a detector, called a laser-based interferometer, that he believed would be capable of measuring a signal so tiny that it could easily be masked by the background murmur of the ocean waves. Thorne, a theorist, began making crucial predictions of what the signal of a gravitational wave emanating from two black holes colliding would actually look like.
Independently, Ronald Drever, a Scottish physicist, also began building prototype detectors in Glasgow and after moving to Caltech, he, Weiss and Thorne formed a trio that laid the groundwork for Ligo. Drever died in March after suffering from dementia, and while the Nobel prize is not normally awarded posthumously, he is widely recognised as having made a decisive contribution.
Barry Barish, a former particle physicist at California Institute of Technology (now an Emeritus professor) came to the project at a much later stage but is often credited for making Ligo happen. When he took over as its second director in 1994, the project was at risk of being cancelled. Barish turned things around and saw it through to construction.
In the end, detection required a peerless collaboration between experimentalists, who built one of the most sophisticated detectors on Earth, and theorists, who figured out what a signal from two black holes colliding would actually look like.
Ligo’s twin detectors, two pairs of 4km-long perpendicular pipes, one in Hanford, Washington state, the other in Livingston, Louisiana, are so sensitive that they can spot a distortion of a thousandth of the diameter of an atomic nucleus across a 4km length of a laser beam.
The phenomenon detected was the collision of two giant black holes, one 35 times the mass of the sun, the other slightly smaller, 1.3 billion light-years away. At the start of the 20-millisecond “chirp” in the signal, the two objects were found to be circling each other 30 times a second. By the end, the rate had accelerated to 250 times a second before meeting in a violent collision.
Since then, three further black hole collisions have been made and rumours are afoot that the consortium may have also observed the collision of a pair of neutron stars. In the future, scientists hope to supernovae, pulsars and the insides of stars as they collapse into black holes. A network of gravitational-wave observatories could even allow us to gaze back to almost the beginning of time itself.
Last year’s prize went to three British physicists for their work on exotic states of matter that may pave the way for quantum computers and other revolutionary technologies.