Born into danger
Rainer Weiss was born in Berlin on September 29, 1932, months before Hitler came to power. His father, Frederick Weiss, came from a well-off German Jewish family and was a neurologist and an idealistic communist who worked at a workers’ hospital. His mother, Gertrude Loesner, came from a Protestant family of civil servants and lawyers in the Rhineland and had moved to Berlin hoping to become an actress. The couple were not yet married when he was born.
Frederick Weiss had already been seized by a Nazi gang at his hospital. His wife’s family used their connections to have him released and sent to Prague, and mother and baby followed. In September 1938, on holiday in Slovakia, the family heard on the radio that Britain had given the Sudetenland to Hitler. They joined the crowds in Prague trying to get visas to anywhere that would accept Jews. They were rescued by the Stix family of St. Louis, who had guaranteed entry to the United States for thousands of Jewish professionals, and arrived in New York in January 1939.
A refugee boy and his radios
In New York the family struggled. While his father spent four years requalifying as a doctor, working meanwhile as a medical aide in a tuberculosis hospital, his mother worked behind department store counters. Rainer attended public school, then won a scholarship through a refugee relief organisation to the private Columbia Grammar School, where he stayed until he graduated in 1950. His sister, Sybille Pearson, became a playwright.
After the war, surplus military electronics were being sold for pennies on Manhattan’s Cortlandt Street, and the teenage Weiss bought vacuum tubes, transformers and old radar receivers and taught himself to build radios and amplifiers. He fixed neighbours’ radios for pocket money and built high-fidelity sound systems so good that immigrant family friends listening to the New York Philharmonic said it was like being in Carnegie Hall. Soon he had a small business, and a problem he could not solve: the hiss of needles on old shellac records. Wanting to understand filters properly, he went to the Massachusetts Institute of Technology in 1950.
Dropout, technician, physicist
At MIT Weiss switched from electrical engineering to physics. Then, heartbroken after a failed romance with a young woman he met on a cycling trip to Nantucket, he failed all his courses and had to leave. In 1953 he took a job as a technician, with a union card and a time clock, in the atomic beam laboratory of the physicist Jerrold Zacharias. There he learned machining, welding and the art of improvised experiments, and helped Zacharias develop a cesium atomic clock. Commercialised by the National Company, it became the time standard for the National Bureau of Standards, today’s NIST, and the United States Navy.
With Zacharias’s encouragement he finished his bachelor’s degree in 1955 and his PhD in 1962. He taught at Tufts University, then spent two formative years at Princeton in the gravity group of Robert Dicke, a master at designing experiments that reach the fundamental limits of measurement. In 1964 he returned to MIT as a faculty member and started a laboratory for cosmology and gravitation. He married Rebecca, a plant physiologist and later a children’s librarian; they had a daughter, Sarah, and a son, Benjamin.
Measuring the Big Bang’s afterglow
In 1965 radio astronomers had detected a faint microwave glow across the sky, interpreted as the leftover heat of the Big Bang. Weiss and his student Dirk Muehlner set out to test whether it really had the spectrum of thermal radiation. From 1967 to 1982 his group flew around twenty high-altitude balloon experiments, building new detectors and cryogenic instruments, first to measure the spectrum and then how the radiation varied across the sky.
The work convinced him that the definitive measurements needed a satellite. When the young astronomer John Mather proposed the Cosmic Background Explorer, COBE, Weiss joined the team and chaired its science working group. Launched by NASA in 1989, COBE showed that the radiation matches a perfect thermal spectrum with extraordinary precision and found tiny variations in it, the seeds of the galaxies. Mather and George Smoot received the 2006 Nobel Prize for those results.
A classroom exercise
Einstein’s general theory of relativity predicted that moving masses send out gravitational waves, ripples in space-time itself, but they were expected to be so weak that Einstein doubted they could ever be detected. In 1966 Weiss was asked to teach a graduate course on general relativity. When students asked him about claims by Joseph Weber to have detected gravitational waves with large metal bars, he could not explain the claims to himself, let alone to them.
So he worked out the simplest way he could think of to show how a gravitational wave might be detected: send light between floating masses and measure tiny changes in the time it takes. He then replaced the impossibly precise clocks with laser interferometry, splitting a laser beam down two long arms at right angles and recombining it, so that a passing wave, which stretches one arm while squeezing the other, would change the pattern of light. In a 1972 report he analysed every source of noise that might drown the signal and concluded that a detector with arms kilometres long could succeed. That report became the blueprint for LIGO.
Building LIGO
Weiss built a prototype in the 1970s and in 1976 began working with Kip Thorne of Caltech, who set up a gravitational wave group there; the Scottish physicist Ronald Drever joined in 1979. The three became LIGO’s co-founders. The path was long and uncertain. In 1973, when the military cut its support for research not directly tied to its mission, Weiss turned to the National Science Foundation with a proposal for a new way to measure gravitational waves. For years his prototypes were far too insensitive to detect anything, and his graduate students had to defend theses that contained no detections at all, only better and better instruments. In 1984 Caltech and MIT agreed to build it together, and with funding from the National Science Foundation construction began in the 1990s at two sites 3,000 kilometres apart, in Hanford, Washington, and Livingston, Louisiana. Barry Barish of Caltech led the project to completion. The detectors had to sense a change in arm length thousands of times smaller than the nucleus of an atom.
On September 14, 2015, both detectors recorded the same signal: the gravitational waves from two black holes that had collided about 1.3 billion years ago. The discovery was announced in February 2016 and confirmed a century-old prediction of Einstein. In 2017 Weiss received half of the Nobel Prize in Physics, with Barish and Thorne sharing the other half. Weiss insisted that the prize symbolised the work of hundreds of colleagues, and he used his prize money to found the Barish-Weiss Fellowship for physics students at MIT.
A new window on the universe
For all of history, astronomers had studied the universe through light and other radiation. LIGO gave humanity a new sense with which to observe it. Since 2015, LIGO and its partner observatories, Virgo in Italy and KAGRA in Japan, have recorded many collisions of black holes and neutron stars, events invisible to telescopes. In 2017 a neutron-star collision was observed both in gravitational waves and by telescopes around the world, helping to show where some of the universe’s heavy elements are made. Scientists compare the breakthrough to Galileo turning a telescope to the sky.
Weiss also helped create two scientific fields and trained many of the people who now lead them. His students and postdocs, among them Nergis Mavalvala, later dean of science at MIT, went on to guide both cosmic microwave background research and gravitational wave astronomy, carrying his rigour and decency with them, as a former department head put it.
Refugee, scientist, mentor
Weiss’s life was shaped by being a Jewish refugee child. His father, a Jew and a communist, was driven out by the Nazis; the family survived because an American Jewish family put up bonds for strangers; and a refugee relief scholarship paid for his schooling. In his Nobel autobiography he recalled how few places in the world would take Jews in 1938, and wrote simply that his family had been extremely lucky.
Colleagues described him as gruff, plain-spoken and hands-on, but deeply loyal to his students and devoted to putting people first. He insisted his students learn to build their own equipment, and late in life he still showed up at colleagues’ doors with ideas for a next-generation observatory.
Last years and legacy
Weiss remained at MIT for seven decades, from freshman in 1950 to professor emeritus. Besides the Nobel he received the Gruber Prize in Cosmology, the Einstein Prize of the American Physical Society, the Shaw Prize, the Kavli Prize and a Special Breakthrough Prize. He died on August 25, 2025, aged 92.
His legacy is a new way of knowing the universe. Every gravitational wave detected, from merging black holes to colliding neutron stars, travels through instruments that began as his answer to a student’s question. Along the way he helped pin down the afterglow of the Big Bang and, as a young technician, helped build the atomic clocks that kept America’s official time. Kip Thorne called him, by a large margin, the most influential person his field has seen.
Sources & further reading
Rainer Weiss, Biographical, NobelPrize.org · Press release: The Nobel Prize in Physics 2017, NobelPrize.org · Professor Emeritus Rainer Weiss, influential physicist who forged new paths to understanding the universe, dies at 92, MIT News · Rainer Weiss, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.