Physicists win Nobel Prize for spotting ripples in fabric of space-time

The 2017 Nobel Prize in physics has been awarded to three researchers crucial to the first detection of ripples in the fabric of space-time – gravitational waves.

Half the prize went to MIT physicist Rainer Weiss and the other half to California Institute of Technology physicists Barry Barish and Kip Thorne. They're all members of the Laser Interferometer Gravitational-Wave Observatory (LIGO)/VIRGO collaboration.

Albert Einstein predicted gravitational waves in 1915. It wasn't until a hundred years later, on September 14, 2015, that LIGO picked up the signal of two black holes colliding and merging, producing gravitational waves. The researchers published their work in Physical Review Letters in February 2016.

Valerio Boschi, an experimental physicist at the European Gravitational Observatory in Pisa, Italy, who works on Virgo's gravitational wave detector told The Register the detection of gravitational waves "opens a new window into the universe".

The Nobel Committee recognised Weiss, Thorne and Barish for their "decisive contributions to the LIGO detector and the observation of gravitational waves".

Back in the 1970s, Weiss designed a sensitive device, called a laser-based interferometer, which LIGO used for their detection. A laser beam is split and sent down a pair of perpendicular tubes, each precisely the same length. The beams bounce off mirrors and recombine at the base. The light waves come back in such a way that they cancel each other out and no light reaches the detector. But a gravity wave distorts space and changes the distance between mirrors, which also changes the alignments of the light waves so they no longer cancel each other out. Light reaches the detector – measuring the intensity of that light is how you measure a gravitational wave.

Weiss also characterised some of the possible sources of noise that could disguise the gravitational wave signal, such as changes in beam power.

LIGO used two independent detectors spaced about 3200 km apart that both picked up the gravitational wave signal in September 2015, a change "thousands of times smaller than an atomic nucleus".

Andreas Freise, an experimental physicist at the University of Birmingham and a member of the LIGO collaboration, told The Reg that Weiss and Thorne "were really the driving force" behind the project and "without their vision and energy" it wouldn't be where it is today.

Besides his original work, Weiss was deeply involved in checking electronics and mechanics as the project went on, Freise said. And Thorne, a theorist, wrote extensively about gravity.

Freise added that Barish "rescued" the project by assuming leadership in the 1990s when Caltech scientists were struggling to manage such a large collaboration. Because of their inexperience, the scientists had had difficulties making decisions. Today LIGO's scientific collaboration has 1,167 members.

Sheila Rowan, an experimental physicist at Glasgow University who also works on the LIGO side of the collaboration, told El Reg: "I am absolutely delighted to see this. My colleagues who have been honoured are most deserving and what a fantastic way to recognise a landmark discovery."

Boschi said he and colleagues had watched the announcement from inside a meeting room, adding that he was surprised the project didn't win in 2016 when it was pipped to the post by a British trio studying exotic states of matter. "Last year, we were a little bit disappointed," he said.

He thought the Nobel Committee might have wanted to see other confirmations of gravitational waves. The LIGO-VIRGO collaboration detected more gravitational waves just last week.