By Jon Mooallem

The MIT physicist Ranier Weiss was never that interested in abstractions. Weiss, who died Aug. 25 in Cambridge, Mass., at age 92, told the podcast "The Searching Conversations" that, confronted with complex equations describing the cosmos, he would try to picture what those numbers and variables were actually signifying in physical space. He was a hands-on guy, he said; he preferred a universe he could tinker with and touch.

Everywhere Weiss went, in fact, he seemed to be assessing how the things around him worked, or obsessively endeavoring to repair the ones that didn't. His daughter, Sarah Weiss, said, "If you had a broken toaster, and he happened to be visiting you, that toaster would go home with him." (Weiss is also survived by his son, Benjamin, and wife, Rebecca.)

Weiss was born Sept. 29, 1932, in Berlin and grew up in Manhattan; his family fled Europe after his father, a Communist, was temporarily imprisoned by Nazis. As a teenager, he taught himself to hack together surplus military electronics into sophisticated hi-fi receivers and, one night, invited his father's friends to listen to a broadcast of the New York Philharmonic. "They couldn't believe their ears," Weiss recalled. The signal was clear and vibrant; the music unmuddled -- "like being in Carnegie Hall." Instantly, he had a little business going. Everyone in the living room wanted one, too.

"That's the beginning," Weiss explained on the podcast. "The whole rest of my life is based on improving the signal to noise."

In 2017, Weiss shared the Nobel Prize with two collaborators, Kip S. Thorne and Barry C. Barish of Cal Tech, for the culmination of his life's work: the first-ever detection of gravitational waves -- faint distortions in spacetime whose existence had been predicted by Einstein in 1916.

Weiss and his colleagues had accomplished this by building a mind-bogglingly sensitive, exceptionally large-scale scientific instrument called LIGO, the Laser Interferometer Gravitational-Wave Observatory, which Weiss had initially dreamed up a half-century earlier and worked on ever since.

In layman's terms, LIGO was like a giant radio, rigorously tuned to pick up signals from our universe that no one had managed to hear before.

Detecting the undetectable

Einstein's general theory of relativity reimagined gravity as an indentation that mass makes in the fabric of spacetime, like a bowling ball settling into a trampoline. Whenever that mass moves, ripples radiate outward.

These disturbances -- gravity waves -- would be so subtle, however, that Einstein presumed they'd be impossible to detect. Consequently, generations of physicists didn't try. Weiss liked to point out that, when he arrived at MIT as a student in 1950, you had to go to the math department if you wanted to study gravity; that branch of physics had stopped being about running concrete experiments and got trapped in the realm of equations instead.

Weiss initially dropped out of MIT, having recklessly abandoned his coursework to follow a young woman to Chicago, but returned to graduate in 1955 and received his Ph.D in 1962. He hit on his initial design for LIGO as a faculty member five years later, during an exercise with his students. (At the time, another physicist, Joseph Weber, was claiming to have detected gravity waves but was also in the process of being disproved.) In 1972, Weiss fleshed out his thinking in a paper for an internal MIT publication.

"That was a momentous paper," said Thorne, who along with the late Scottish physicist Ronald Drever, would become co-founders of LIGO with Weiss. And yet, Thorne added, "When I first heard about it -- I had not dug deeply into it myself -- I thought Rai had gone crazy."

Gradually, LIGO grew to comprise more than 1,500 scientists around the world and centered on two colossal observatories in Washington state and Louisiana. (Other detectors now operate in Italy and Japan.) Inside each observatory, laser light is sent traveling a set distance between mirrors. Weiss reasoned that a passing gravity wave would stretch or compact that space, causing an infinitesimal -- but hopefully discernible -- change in the amount of time it took the light to traverse it.

"It's as simple as that," he said in his Nobel lecture. "The big problem [is], you have to do it extremely well."

A faint reverberation

LIGO'S first detection was made on Sept. 14, 2015 -- the gravitational residue of two black holes slamming into each other. That collision happened 1.3 billion years ago, the experimenters determined; LIGO was picking up the very faintest reverberation of it now.

"I feel an enormous sense of relief and some joy, but mostly relief," Weiss said, after the announcement. The word he'd consistently used to describe working on LIGO was "fun." Building an experiment was fun. Discovering your experiment doesn't work the way you anticipated, then figuring out why and rebuilding it -- that was all fun, too. And yet, Thorne explained, Weiss had also been struggling with considerable guilt, having roped several generations of graduate students and more than $1 billion of taxpayer money into the project, via the National Science Foundation, without any guarantees it would ever pay off.

Detecting gravity waves for the first time wasn't just a resolution to a story -- proof, finally, that Einstein was right. It was also the start of one. Weiss and his colleagues' breakthrough has provided a new way of looking at the universe, of observing, through the charting of gravity waves emitted by moving objects, what was previously unobservable or unknown -- a milestone that is frequently compared with Galileo's invention of the telescope.

For Weiss, this was exhilarating, his daughter noted. But, having devoted his long career to opening that new scientific frontier, he also recognized that he didn't have nearly enough life left to satisfactorily explore it himself. "He was absolutely delighted," Sarah Weiss said. "And he was also disappointed that he couldn't be 40 years old again."

Write to Jon Mooallem at jon.mooallem@wsj.com

(END) Dow Jones Newswires

The first name of Rainer Weiss was misspelled as Ranier in the headline and text of "Ranier Weiss, Who Won the Nobel Prize for Proving Einstein Was Right, Dies at 92" at 10 a.m. ET.

(END) Dow Jones Newswires

September 05, 2025 12:09 ET (16:09 GMT)

Copyright (c) 2025 Dow Jones & Company, Inc.