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.