Nearly five decades passed before someone set about building an instrument to detect gravitational waves. The first person to try was an engineering professor at the University of Maryland, College Park, named Joe Weber. He called his device the resonant bar antenna. Weber believed that an aluminum cylinder could be made to work like a bell, amplifying the feeble strike of a gravitational wave. When a wave hit the cylinder, it would vibrate very slightly, and sensors around its circumference would translate the ringing into an electrical signal. To make sure he wasn’t detecting the vibrations of passing trucks or minor earthquakes, Weber developed several safeguards: he suspended his bars in a vacuum, and he ran two of them at a time, in separate locations—one on the campus of the University of Maryland, and one at Argonne National Laboratory, near Chicago. If both bars rang in the same way within a fraction of a second of each other, he concluded, the cause might be a gravitational wave.

In June of 1969, Weber announced that his bars had registered something. Physicists and the media were thrilled; the Times reported that “a new chapter in man’s observation of the universe has been opened.” Soon, Weber started reporting signals on a daily basis. But doubt spread as other laboratories built bars that failed to match his results. By 1974, many had concluded that Weber was mistaken. (He continued to claim new detections until his death, in 2000.)

Weber’s legacy shaped the field that he established. It created a poisonous perception that gravitational-wave hunters, as Weiss put it, are “all liars and not careful, and God knows what.” That perception was reinforced in 2014, when scientists at BICEP2, a telescope near the South Pole, detected what seemed to be gravitational radiation left over from the Big Bang; the signal was real, but it turned out to be a product of cosmic dust. Weber also left behind a group of researchers who were motivated by their inability to reproduce his results. Weiss, frustrated by the difficulty of teaching Weber’s work to his undergraduates at the Massachusetts Institute of Technology, began designing what would become LIGO. “I couldn’t understand what Weber was up to,” he said in an oral history conducted by Caltech in 2000. “I didn’t think it was right. So I decided I would go at it myself.”

In the search for gravitational waves, “most of the action takes place on the phone,” Fred Raab, the head of LIGO’s Hanford site, told me. There are weekly meetings to discuss data and fortnightly meetings to discuss coördination between the two detectors, with collaborators in Australia, India, Germany, the United Kingdom, and elsewhere. “When these people wake up in the middle of the night dreaming, they’re dreaming about the detector,” Raab said. “That’s how intimate they have to be with it,” he explained, to be able to make the fantastically complex instrument that Weiss conceived actually work.

Weiss’s detection method was altogether different from Weber’s. His first insight was to make the observatory “L”-shaped. Picture two people lying on the floor, their heads touching, their bodies forming a right angle. When a gravitational wave passes through them, one person will grow taller while the other shrinks; a moment later, the opposite will happen. As the wave expands space-time in one direction, it necessarily compresses it in the other. Weiss’s instrument would gauge the difference between these two fluctuating lengths, and it would do so on a gigantic scale, using miles of steel tubing. “I wasn’t going to be detecting anything on my tabletop,” he said.

To achieve the necessary precision of measurement, Weiss suggested using light as a ruler. He imagined putting a laser in the crook of the “L.” It would send a beam down the length of each tube, which a mirror at the other end would reflect back. The speed of light in a vacuum is constant, so as long as the tubes were cleared of air and other particles the beams would recombine at the crook in synchrony—unless a gravitational wave happened to pass through. In that case, the distance between the mirrors and the laser would change slightly. Since one beam would now be covering a shorter distance than its twin, they would no longer be in lockstep by the time they got back. The greater the mismatch, the stronger the wave. Such an instrument would need to be thousands of times more sensitive than any previous device, and it would require delicate tuning in order to extract a signal of vanishing weakness from the planet’s omnipresent din.

Weiss wrote up his design in the spring of 1972, as part of his laboratory’s quarterly progress report. The article never appeared in a scientific journal—it was an idea, not an experiment—but according to Kip Thorne, an emeritus professor at Caltech who is perhaps best known for his work on the movie “Interstellar,” “it is one of the greatest papers ever written.” Thorne doesn’t recall reading Weiss’s report until later. “If I had read it, I had certainly not understood it,” he said. Indeed, Thorne’s landmark textbook on gravitational theory, co-authored with Charles Misner and John Wheeler and first published in 1973, contained a student exercise designed to demonstrate the impracticability of measuring gravitational waves with lasers. “I turned around on that pretty quickly,” he told me.

Thorne’s conversion occurred in a hotel room in Washington, D.C., in 1975. Weiss had invited him to speak to a panel of NASA scientists. The evening before the meeting, the two men got to talking. “I don’t remember how it happened, but we shared the hotel room that night,” Weiss said. They sat at a tiny table, filling sheet after sheet of paper with sketches and equations. Thorne, who was raised Mormon, drank Dr Pepper; Weiss smoked a corncob pipe stuffed with Three Nuns tobacco. “There are not that many people in the world that you can talk to like that, where both of you have been thinking about the same thing for years,” Weiss said. By the time Thorne got back to his own room, the sky was turning pink.

At M.I.T., Weiss had begun assembling a small prototype detector with five-foot arms. But he had trouble getting support from departmental administrators, and many of his colleagues were also skeptical. One of them, an influential astrophysicist and relativity expert named Phillip Morrison, was firmly of the opinion that black holes did not exist—a viewpoint that many of his contemporaries shared, given the paucity of observational data. Since black holes were some of the only cosmic phenomena that could theoretically emit gravitational waves of significant size, Morrison believed that Weiss’s instrument had nothing to find. Thorne had more success: by 1981, there was a prototype under way at Caltech, with arms a hundred and thirty-one feet long. A Scottish physicist named Ronald Drever oversaw its construction, improving on Weiss’s design in the process.

In 1990, after years of studies, reports, presentations, and committee meetings, Weiss, Thorne, and Drever persuaded the National Science Foundation to fund the construction of LIGO. The project would cost two hundred and seventy-two million dollars, more than any N.S.F.-backed experiment before or since. “That started a huge fight,” Weiss said. “The astronomers were dead-set against it, because they thought it was going to be the biggest waste of money that ever happened.” Many scientists were concerned that LIGO would sap money from other research. Rich Isaacson, a program officer at the N.S.F. at the time, was instrumental in getting the observatory off the ground. “He and the National Science Foundation stuck with us and took this enormous risk,” Weiss said.