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C.V. Vishveshwara's Revolutionary Black Hole Research Turns 50

Dec 29, 2020
Originally published on December 29, 2020 10:44 pm

For a scientist, few things are sweeter than data from an experiment that confirms a theoretical prediction.

Frequently, however, scientists don't live long enough to savor that reward. Take Albert Einstein's prediction about gravitational waves. Einstein postulated their existence in 1916, but they weren't detected until a hundred years later, long after the great physicist had died.

C.V. Vishveshwara was one of the lucky ones. He got to enjoy what Einstein had missed, and the detection of gravitational waves verified a theoretical prediction that Vishveshwara himself had made nearly half a century earlier.

In 1970, Vishveshwara, known to his friends as Vishu, was a physics graduate student at the University of Maryland.

His thesis adviser had given him a problem to solve: Figure out what would happen if two black holes collided.

"Study the whole process, computing all the characteristics of the emitted gravitational wave" is how he described the assignment in a memoir. Vishu's daughter Smitha Vishveshwara, herself a physicist, says her father realized the problem was too complex to solve in one go.

"What he did was to break it up into parts," she says.

As he worked on the parts, Vishu had what turned out to be a fundamental insight. He found that black holes had a kind of structure. If you were able to bang on a black hole, it would vibrate, much like a bell does when you hit it with a mallet. He wrote a paper about his insight, and it was published in Nature.

"This is the very first time that we realized that black holes could be dynamical objects that could vibrate or ring like a bell," says Kip Thorne. Thorne was a young theoretical physicist on the faculty of the California Institute of Technology when Vishu made his discovery.

Thorne says the paper was one of those aha moments. Vishu had found a characteristic of black holes that others had missed up to that point.

"It became obvious after we saw Vishu's simulations," says Thorne.

At the time, there was no way to prove Vishu correct. You can't bang on a black hole with a mallet to see what will happen. But Thorne and others realized that if a gravitational wave happened to bang into a black hole, a wave would be emitted from the black hole that would vibrate like the sound of a bell.

Thorne ultimately embarked on a quest to build a device that could confirm Vishu's prediction and prove Einstein's prediction about the existence of gravitational waves correct.

That instrument was LIGO, an enormous detector that physicists hoped would be sensitive enough to measure the tiny perturbations of matter that would occur when a gravitational wave passed by. In 2016, LIGO did just that, a stunning feat that won Thorne and two colleagues the Nobel Prize in physics just one year later.

The first gravitational wave that LIGO recorded came from the collision of two black holes. And sure enough, when they looked carefully at the wave they recorded, they saw the signature of that ringing bell, what Vishu had predicted nearly 50 years earlier.

Vishu did live to see it happen. The LIGO discovery made him a celebrity in his native India, and just this month he was honored by the Indian Association for General Relativity and Gravitation. The International Centre for Theoretical Sciences, based in India, also runs a lecture series in his name.

In the days after the gravitational wave detection was announced, he was swamped with requests to speak about his work.

In one talk, Vishu's delight at the LIGO discovery, and his dry wit, are evident.

"There's a story of a physicist: He had a nightmare that he was giving a talk and woke up and found that he was," he said. The audience chucked appreciatively.

Vishu died in 2017.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

MARY LOUISE KELLY, HOST:

The history of science is littered with researchers who made absolutely critical contributions to understanding the fundamental forces of the universe. Many of their names are largely unknown or forgotten. Today NPR science correspondent Joe Palca brings us the story of an Indian scientist whose calculations helped lay the groundwork for the most important discovery in physics this century.

JOE PALCA, BYLINE: Fifty years ago, C.V. Vishveshwara was a physics graduate student at the University of Maryland known to his friends as Vishu. His thesis advisor had given him a problem to solve. Figure out what would happen if two black holes collided.

SMITHA VISHVESHWARA: Study the whole process, computing all the characteristics of the emitted gravitational radiation.

PALCA: That's Smitha Vishveshwara, Vishu's daughter, who is herself a physicist. Albert Einstein predicted gravitational waves, but he thought they might be too faint to ever detect. So at the time, Vishu was trying to solve a completely theoretical problem with no way to know if he was right. Vishveshwara says her father realized the problem was too complex to solve in one go.

S VISHVESHWARA: What he did was to break it up into parts.

PALCA: As he worked on the parts, Vishu made a fundamental insight. Black holes had a kind of structure, and if you were able to bang on a black hole, it would vibrate like a bell when you hit it with a mallet. He wrote a paper about his discovery that appeared in Nature, a top scientific journal.

KIP THORNE: This is the very first time that we realized that black holes could be dynamical objects that could vibrate or ring like a bell.

PALCA: That's Kip Thorne, a theoretical physicist at Caltech. He knew Vishu back then. He says the paper was one of those aha moments, a characteristic of black holes everyone had missed up to that point.

THORNE: It became obvious after we saw Vishu's simulation.

PALCA: But this was just a theoretical prediction. You can't bang on a black hole with a mallet. But if a gravitational wave happened to bang into one, a wave would be emitted from the black hole that would show a vibration like the sound of a bell. And then in 2016, Vishu's prediction went from theoretical to proven.

S VISHVESHWARA: It's been nearly a 50-year wait, and it happened. It happened.

PALCA: A team led by Kip Thorne made what has to be one of the most significant discoveries of the century. Using an instrument called LIGO, Thorne and his colleagues were able to make the world's first recording of a gravitational wave. Thorne and two colleagues won the Nobel Prize just one year later. And sure enough, when they looked carefully at the wave they recorded, they saw the signature of that ringing bell in the wave, what Vishu predicted you would see nearly 50 years earlier. And Vishu lived to see it happen.

He was a bit of a celebrity in his native India. In the days after the LIGO discovery was announced, he was swamped with requests to speak about his work. Here he is at one of those talks, displaying the dry wit he was known for.

(SOUNDBITE OF ARCHIVED RECORDING)

CV VISHVESHWARA: There's a story of a physicist who had a nightmare that he was giving a talk and woke up and found that he was. So I'm in that situation because of all the excitement in the last three days. I have not been able to sleep.

PALCA: Vishu died in 2017. On the 50th anniversary of his 1970 paper in Nature, it seems like an appropriate time to remember his contribution.

Joe Palca, NPR News.

(SOUNDBITE OF RAMIN DJAWADI'S "BLACK HOLE SUN") Transcript provided by NPR, Copyright NPR.