
A gravitational blueprint
The detection was an especially long-awaited payoff for Weiss, who came up with the initial design for LIGO some 50 years ago. He has since been instrumental in shaping and championing the idea as it developed from a desktop prototype to LIGO’s final, observatory-scale form.
In 1967, Weiss, then an assistant professor of physics at MIT, was asked by his department to teach an introductory course in general relativity — a subject he knew little about. A few years earlier, the American physicist Joseph Weber had claimed to have made the first detection of gravitational waves, using resonant bars — long, aluminum cylinders that should ring at a certain frequency in response to a gravitational wave. When his students asked him to explain how these Weber bars worked, Weiss found that he couldn't.
No one in the scientific community had been able to replicate Weber’s results. Weiss had a very different idea for how to do it, and assigned the problem to his students, instructing them to design the simplest experiment they could to detect a gravitational wave. Weiss himself came up with a design: Build an L-shaped interferometer and shine a light down the length of each arm, at the end of which hangs a free-floating mirror. The lasers should bounce off the mirrors and head back along each arm, arriving where they started at the exact same time. If a gravitational wave passes through, it should “stretch” or displace the mirrors ever so slightly, and thus change the lasers’ arrival times.
Weiss refined the idea over a summer in MIT’s historic Building 20, a wooden structure built during World War II to develop radar technology. The building, meant to be temporary and known to many as the “Plywood Palace,” lived on to germinate and support innovative, high-risk projects. During that time, Weiss came to the conclusion that his design could indeed detect gravitational waves, if built to large enough dimensions. His design would serve as the essential blueprint for LIGO.
An observatory takes shape
To test his idea, Weiss initially built a 1.5-meter prototype. But to truly detect a gravitational wave, the instrument would have to be several thousand times longer: The longer the interferometer’s arms, the more sensitive its optics are to minute displacements.
To realize this audacious design, Weiss teamed up in 1976 with noted physicist Kip Thorne, who, based in part on conversations with Weiss, soon started a gravitational wave experiment group at Caltech. The two formed a collaboration between MIT and Caltech, and in 1979, Scottish physicist Ronald Drever, then of Glasgow University, joined the effort at Caltech. The three scientists — who became the co-founders of LIGO — worked to refine the dimensions and scientific requirements for an instrument sensitive enough to detect a gravitational wave.
Barry Barish soon joined the team as first a principal investigator, then director of the project, and was instrumental in securing funding for the audacious project, and bringing the detectors to completion.
After years of fits and starts in research and funding, the project finally received significant and enthusiastic backing from the National Science Foundation, and in the mid-1990s, LIGO broke ground, erecting its first interferometer in Hanford, Washington, and its second in Livingston, Louisiana.
Prior to making their seminal detection two years ago, LIGO’s detectors required years of fine-tuning to improve their sensitivity. During this time, Weiss not only advised on scientific quandaries but also stepped in to root out problems in the detectors themselves. Weiss is among the few to have walked the length of the interferometers’ tunnels in the space between LIGO’s laser beam tube and its encasement. Inspecting the detectors in this way, Weiss would often discover minute cracks, tiny shards of glass, and even infestations of wasps, mice, and black widow spiders, which he would promptly deal with.
A cosmic path
Weiss was born in 1932 in tumultuous Berlin. When his mother, Gertrude Loesner, was pregnant with We