Rainer Weiss ( WYSSE, German: [vaɪs]; September 29, 1932 – August 25, 2025) was a German-American physicist, known for his contributions in gravitational physics and astrophysics. He was a professor of physics at the Massachusetts Institute of Technology and an adjunct professor at Louisiana State University. He is best known for inventing the laser interferometric technique which is the basic operation of LIGO. He was Chair of the COBE Science Working Group. In 2017, Weiss was awarded the Nobel Prize in Physics, along with Kip Thorne and Barry Barish, "for decisive contributions to the LIGO detector and the observation of gravitational waves". Weiss helped realize a number of challenging experimental tests of fundamental physics. He was a member of the Fermilab Holometer experiment, which uses a 40m laser interferometer to measure properties of space and time at quantum scale and provide Planck-precision tests of quantum holographic fluctuation.
Early life and education Rainer Weiss was born in Berlin, Brandenburg, Prussia, Germany, on September 29, 1932, the son of Gertrude Loesner and Frederick A. Weiss. His father, a physician, neurologist, and psychoanalyst, was forced out of Germany by Nazis because he was Jewish and an active member of the Communist Party. His mother, an actress, was Christian. His aunt was the sociologist Hilda Weiss. His younger sister is playwright Sybille Pearson. The family fled first to Prague, but Germany's occupation of Czechoslovakia after the 1938 Munich Agreement caused them to flee again; the philanthropic Stix family of St. Louis helped them obtain visas to enter the United States. Weiss spent his youth in New York City, where he attended Columbia Grammar School. He studied at MIT, dropping out at the beginning of his junior year with the excuse that he had abandoned his coursework to pursue a romantic relationship with a music student from Chicago. While this affair was a contributing factor, Weiss's concurrent vacillation between MIT's engineering and physics tracks may also have played a significant role. Jerrold Zacharias, then an influential physicist and MIT professor, intervened, and Weiss, after working as a technician in Zacharias's lab, eventually returned to receive his S.B. degree in 1955. He would complete his PhD in 1962, still with Zacharias as advisor/mentor.
Career Weiss taught at Tufts University from 1960 to 1962, was a postdoctoral scholar at Princeton University from 1962 to 1964, and then joined the faculty at MIT in 1964 starting a new research group in the Research Laboratory of Electronics dedicated to research in cosmology and gravitation. For Weiss's initial work at MIT, he started a group studying cosmology and gravitation. Needing to develop new technology, particularly in regards to the stabilization of equipment set to measure minute fluctuations, his lab included machine and electronics shop, with a hands-on expectation of his students for fabrication and design. By 1966, Weiss's tenure at MIT was at risk because of the failure of his group to produce publications. On advice from Bernard Burke, then head of the division on astrophysics in the Physics Department, Weiss recalibrated his standards for submitting articles for publication, eventually finding grounds for publication that he believed met his personal standards as scientifically worthy and publishable. He was then able to qualify for tenure and remain at MIT. That same year Joseph Weber claimed to have invented a way to detect gravitational waves. When Weiss's students asked him about Weber's work, he was unable to explain it to them, as it seemed to contradict his understanding of general relativity. In 1967, to illustrate the principle of gravitational wave detection in a simpler way, Weiss devised a thought experiment involving time of flight measurements of light between free masses in space, which in principle required "impossibly precise clocks". About a year later, as Weber's claims remained unconfirmed, Weiss started to realize that maybe Weber was wrong. He eventually revisited his idea and replaced the clocks with laser interferometry and concluded that such an approach could realistically detect gravitational waves, at sensitivities beyond what Weber's resonant bars could achieve.
Vietnam Era cuts to science grants In 1973, Weiss was forced to pivot with his work as the US military cut funding for any science that was not determined to be "directly relevant to its core mission." Weiss wrote a proposal to the NSF that described "a new way to measure gravitational waves." This was the work that would eventually lead to his 2017 Nobel Prize, though it was many years before the interferometers Weiss and his students built were sensitive enough to actually detect gravitational waves, making for numerous unpleasant doctoral thesis defenses where Weiss's graduate students were unable to present positive (in layman's terms: any) results.
MIT/Caltech collaboration Weiss proposed the concept of LIGO to Kip Thorne in 1972, but it took three years before Thorne was convinced it could work. After the study of prototypes at MIT, Caltech, Garching, and Glasgow, and Weiss's estimates what it would take to build a full scale interferometer, Caltech and MIT signed an agreement about the design and construction of LIGO in 1984, with joint leadership by Ronald Drever, Weiss, and Thorne. In a 2022 interview given to Federal University of Pará in Brazil, Weiss talks about his life and career, the memories of his childhood and youth, his undergraduate and graduate studies at MIT, and the future of gravitational waves astronomy.
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