Professor Kip S. Thorne, a newly minted Nobel laureate, will never forget his feelings when he learned the observatory that was the focus of his career had registered a disturbance caused by two black holes merging 1.3 billion light-years away.
The detection was by the miles-long instruments making up the Laser Interferometer Gravitational-wave Observatory, which are in Hanford, Washington, and Livingston, Louisiana. By the time they reached Earth, the brief jiggles in the fabric of space were no larger than 1/1,000th of the diameter of a proton. Gravitational waves, predicted by Albert Einstein in 1915, had physically moved the detectors.
"It was a sense of profound satisfaction" that filled him upon that first success, Thorne said in a telephone interview on Oct. 10.
The first detection happened on Sept. 14, 2015, shortly after the advanced LIGO detectors were switched on. Since then, three additional black hole mergers have been verified, one potential merger was noted and, earlier this month, a crash of neutron stars was announced.
A little more than two years after the first discovery, on Oct. 3, the Royal Swedish Academy of Sciences announced its 2017 Nobel Prize for physics. The prize is the scientific world’s greatest recognition, given only for the most important advances. Half of the approximately $1.1 million prize money went to Rainer Weiss of the Massachusetts Institute of Technology, while the rest was divided between Thorne and Barry C. Barish of the California Institute of Technology in Pasadena; all three are physics professors emeritus.
The Academy cited the scientists' "decisive contributions to the LIGO detector and the observation of gravitational waves."
Thorne was born in Logan 77 years ago and raised there through high school. Both his parents were employed by Utah State University in Logan, and he has filled an adjunct professorship of physics at the University of Utah. His online biography lists some of his many accomplishments: bachelor’s degree in physics from the California Institute of Technology in 1962, doctorate from Princeton University in 1965, associate professor of theoretical physics at Caltech in 1967, full professor in 1970, Feynman professor in 2009.
"In the late 1960s, Thorne initiated theoretical studies that would underpin LIGO," says the biography. "He set up a research group at Caltech to improve the theory of gravitational waves and estimate the details and strengths of the waves that would be produced by objects in our universe such as black holes, neutron stars and supernovas."
In the mid-1970s, he decided to pursue the detection of gravitation waves "and do everything I could as a theorist to help the experimenters achieve it," he said. He and Weiss began discussions with Ronald W.P. Drever of Caltech (now deceased) that led to the construction of LIGO, adds the biography. The three are LIGO’s co-founders.
Continuing to work on the project, he helped devise techniques to dampen out nonastronomical fluctuations that otherwise would destroy gravitational-wave signals before they could be seen, the document adds.
Thorne's satisfaction derived from knowing "that I had chosen a primary direction of research for my career that had worked out really well, and that at various points along my career I had identified the optimal directions to go," he said. He and colleagues had concluded early on that "the most likely thing we would see would be what we did see: merging heavy black holes."
According to Einstein’s General Theory of Relativity, when supermassive objects orbit one another, they emit gravitational waves. These waves become strongest when they merge. The waves are distortions in the fabric of space itself.
"One way to think about it (a gravitational wave) is that it is — well, we say heuristically, it’s a ripple in the shape of space, like ripples on the surface of a pond," Thorne said. But he quickly added that it differs from those ordinary ripples.
"Instead of going up and down, it stretches and squeezes space, as you remarked — stretches in one direction, squeezes in the opposite direction, all this going on in the plane perpendicular to the direction the waves are propagating." The stretching and compression of the LIGO tubes, as tiny as these motions must be, are recorded by the detectors.
In the early years of the century, Thorne grew concerned that computer simulations of colliding black holes were "in bad shape." The simulations are "essential to being able to extract the information the waves carry.
"And so I actually left day-to-day involvement with LIGO in the early 2000s to start an effort in such simulations at Caltech, basically joining in with and helping out my colleague Saul Teukolsky at Cornell, who had been working on this for many years.”
Did Thorne ever seriously doubt that LIGO would detect these infinitesimally small motions?
"No, from the outset in the mid-'70s when I decided to pursue this, I was confident at sort of a 90, 95 percent level that we would pull it off. Basically, we knew it was extremely difficult, but I also knew how extremely good the LIGO team was that we assembled, the team of experimenters, so I had great confidence in them."
Asked if other types of violent events might be detected through gravitational waves, Thorne said, "Oh, yes, I’m confident they will be. There are a variety of other sources of gravitational waves that we’re targeting." (The interview was conducted before the announcement of a collision of neutron stars.)
The National Science Foundation’s LIGO has opened what he called "the gravitational-wave window unto the universe."
"But it’s quite similar to what Galileo did 400 years ago when he built a small optical telescope and pointed it at the sky and discovered the four moons of Jupiter: He created modern electromagnetic astronomy," Thorne said. "And according to the laws of physics, there are only two kinds of waves that can propagate across the universe bringing us information — electromagnetic waves and gravitational waves — and that’s it. What LIGO has done is the analog of what Galileo did. And just as Galileo’s discovery began an era in which enormous numbers of other things were discovered, similarly with gravitational waves."