t vision with other scientists," says Stan Whitcomb (BS '73), the chief scientist for the LIGO Laboratory at Caltech, who began working on the project in 1980.
Also in 1972, Weiss published a detailed analysis of his interferometers. He identified all of the major obstacles that could prevent the instruments from detecting gravitational waves, such as vibrations of the earth and of the mirrors, and he invented techniques to deal with each obstacle. At this stage, it became evident that large interferometers, several kilometers or more in size, might possibly prove successful—as, indeed, they ultimately did with LIGO and its 4-kilometer-long arms. Also evident was the fact that perfecting the interferometers would be exceedingly difficult: a passing gravitational wave would induce mirror motions 1,000 times smaller than a proton, and these infinitesimal changes would have to be measured. That's 100 million times smaller than an atom, and a trillion times smaller than the wavelength of the light being used in the measurement.
Triggered by Weiss's work, Drever's research group in Glasgow switched from bars to interferometers, as did a research group in Garching, Germany, led by Heinz Billing. By 1975, there were three prototype interferometers under development at MIT, Glasgow, and Garching.
A Fateful Hotel Room Discussion
At first Thorne was skeptical of Weiss's interferometer idea. "I even wrote, in a textbook, that it was not very promising," he says. But that changed when Thorne studied, in depth, Weiss's 1972 analysis. Thorne came to call it a "tour de force" and a "blueprint for the future."
In 1975, Weiss invited Thorne to speak at a NASA committee meeting in Washington, D.C., about cosmology and gravitation experiments in space. Hotel rooms that summer were fully booked, so the two shared a room, where they stayed up all night talking. Thorne came away so excited by the experimental prospects that he went home and proposed creating an experimental gravity group at Caltech to work on interferometers in parallel with MIT, Glasgow, and Garching. Caltech then brought Drever on board in 1979 to lead the new experimental effort, because, as Thorne says, they knew his inventiveness would prove crucial to LIGO's success. Soon thereafter, in 1980, Caltech hired a young Chicago astrophysicist, Whitcomb, to assist in the leadership.
"What a pleasure it was to have this brilliant, budding experimental group working alongside my theory group at Caltech," says Thorne. "Those were heady days."
Together, Drever and Whitcomb led the design and construction of a 40-meter interferometer at Caltech—a prototype to test and perfect the ideas of Weiss, Drever, and others, including the teams at Glasgow and Garching.
Meanwhile, Thorne and his theory students—in collaboration with the late Vladimir Braginsky of Moscow State University, a regular Caltech visitor over three decades—were analyzing various sources of noise that the big interferometers would face, especially "quantum noise," or random fluctuations of the mirrors' positions predicted by quantum theory. They were coming up with ways to deal with those fluctuations.
In 1984, all of this parallel work came together. Caltech and MIT, with encouragement from the NSF, formed a collaboration to design and build LIGO. Rochus E. (Robbie) Vogt, Caltech's R. Stanton Avery Distinguished Service Professor and Professor of Physics, Emeritus, was recruited in 1987 as LIGO's first director. Vogt led the merging of the Caltech and MIT experimental groups; the early planning for LIGO; the writing of a proposal to NSF to fund the project; and the education of Congress about this high-risk project with a potentially exceedingly high payoff. In 1992, Congress allocated the first major funding. "NSF and Congress have backed LIGO unwaveringly ever since," says Thorne.
Scaling up LIGO
Building LIGO was a tremendous challenge—logistically and technically. To meet this challenge, Caltech and MIT later recruited, as LIGO's second director, Barry Barish, who at that time had been the leader of several very 