Gravitational waves snare the Nobel prize

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Rainer Weiss (left) and Kip Thorne at the announcement of the first detection of gravitational waves in February 2016.
Credit: SAUL LOEB / AFP / Getty Images

This year’s Nobel Prize in Physics has gone to Rainer Weiss, Barry Barrish and Kip Thorne, three scientists behind the technology which detected gravitational waves in September 2015.

Gravitational waves had been the last great prediction of Albert Einstein’s theory of general relativity, the framework which describes how matter warps space and time.

In 1916 his equations told him that the movement of matter through space causes tiny vibrations in the spacetime fabric, spreading out like ripples on a pond – but at the speed of light.

Einstein himself thought the waves would be too tiny to ever be detected, but after decades of work, the three prizewinners – aided by huge teams of collaborators – managed to prove him wrong.

To do it, they had to figure out how to measure the stretching and squeezing of spacetime by impossibly tiny amounts – much smaller than a single atom.

In 1972, Weiss, a physicist at the Massachusetts Institute of Technology (MIT) developed the original idea to do it using laser interferometry – an instrument that can measure minute changes in length using a beam of light.

He realised that the two arms of an interferometer, placed at right angles to one another to make an ‘L’ shape, would be perfect for detecting a passing gravitational wave since the warping would squeeze one arm and stretch the other. The relative change in length of each arm would then show up as a signal.

In 1975, Weiss teamed up with Kip Thorne (the rockstar physicist who developed the ideas behind the movie Interstellar) to try to realise his idea.

Thorne, a theoretical physicist at the California Institute of Technology (Caltech), had already been using Einstein’s theory to work out how extreme events, such as colliding black holes or neutron stars, would generate gravitational waves.

Thorne worked out what the signals would look like on Weiss’s interferometer. It was this work that told physicists how to calculate the masses of two colliding black holes, once the Laser Interferometer Gravitational-wave Observatory, or LIGO, eventually detected a collision.

Over the decades the LIGO project grew. It was a group of around 40 researchers in 1994 when Barry Barish, the third recipient of this year’s prize, began leading the project. He helped it grow further and develop into the massive international collaboration, with more than 1000 researchers, that finally succeeded in detecting the waves in 2015.

The pioneers of gravitational-wave astronomy had their work cut out for them, as most of the physics community didn’t think the idea could work, explains Yuri Levin, a physicist at Monash University in Melbourne, Australia who works on the LIGO.

“These guys are amazing. They started out, 40 or 50 years ago, thinking about this, and it took all this time to convince people,” he says.

“They showed incredible scientific class, incredible charisma and incredible vision.”

Levin was supervised by Thorne during his PhD at Caltech and knows him as a very modest person, always quick to share his accolades with the LIGO team.

Besides, the real gratification is the discovery itself – one that opens up a new window on the cosmos, and will propel the field of astrophysics well into the 21st century.

“As nice as a Nobel prize will be, this this result is way beyond the Nobel prize – it’s much more important,” he says.

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