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Portrait of Isidor Isaac Rabi
Photo: Nobel Foundation, http://nobelprize.org/nobel_prizes/physics/laureates/1944/rabi-bio.html · Public domain via Wikimedia Commons

Nobel Prize in Physics · 1944

Isidor Isaac Rabi

He tuned radio waves to the spin of atomic nuclei, the idea behind MRI scanners, NMR chemistry and the atomic clocks that time GPS.

The Nobel citation: “for his resonance method for recording the magnetic properties of atomic nuclei”
Born
July 29, 1898, Rymanow, Austria-Hungary (now Poland)
Died
January 11, 1988, New York, NY, USA
Affiliation at the time
Columbia University, USA

Physics prize

1944

Awarded alone.

Age that year

46years

Born in 1898.

Headline credited impact

9–33million people benefited

People who have benefited from MRI examinations worldwide since the early 1980s. How it was built

Sources cited

19

Fact-checked September 24, 2026.

  • At home he was Izzy; when his mother enrolled him in school, the official wrote down Isidor, and the name stuck.
  • For his bar mitzvah, the young science fan gave a speech in Yiddish on how an electric light works.
  • After his 1919 chemistry degree he got no job offers, at a time when Jews were largely shut out of chemistry jobs, and spent about three years in dull work, including bookkeeping.
  • In 1945 he suggested his resonance method could run a clock. The second is now defined by cesium atoms, and every GPS satellite carries atomic clocks.
  • In 1949 he and Enrico Fermi urged the US not to build the hydrogen bomb, warning that such a weapon endangered humanity as a whole.

The breakthrough

Tuning radio waves to atomic nuclei: the magnetic resonance method (1937-38)

The nucleus at the heart of an atom spins, and a spinning nucleus acts like a tiny bar magnet. How strong that magnet is reveals what is going on inside the nucleus, but nuclear magnetism is about two thousand times weaker than an electron's and very hard to measure. Otto Stern had shown how to fire a thin beam of atoms or molecules through a vacuum and bend it with magnets. Rabi, who had learned the method in Stern's Hamburg lab, added a clever twist in 1937 and 1938. He sent the beam through two magnets arranged to steer the particles back onto a detector. In between, he bathed them in a weak magnetic field that wobbled at a radio frequency he could tune, much like turning a radio dial. At most settings nothing happened. But when the radio frequency exactly matched the natural wobble of the nuclear magnets, the nuclei flipped to a new direction, missed the detector, and the signal dropped sharply. Think of pushing a child on a swing: small pushes only add up when they match the swing's own rhythm. Because radio frequencies can be measured very precisely, Rabi's team could read nuclear magnetism far more accurately than ever before. In 1939 the method showed that the deuteron, the nucleus of heavy hydrogen, is shaped like a football rather than a ball, which pointed to a previously unknown kind of nuclear force.[1],[3],[5],[6]

“Real peace is more than the absence of violent war.”
Isidor Isaac Rabi, From his address to the Fourth International Conference on the Peaceful Uses of Atomic Energy, as quoted by Norman Ramsey in Rabi's National Academy of Sciences biographical memoir.[5]

What it meant for humanity

Rabi's resonance method became the seed of a family of technologies. It was the basis for nuclear magnetic resonance (NMR), which Felix Bloch and Edward Purcell independently discovered in 1945-46. NMR soon became an indispensable tool for chemists and was later used to map the 3D shapes of large biological molecules. In the early 1980s the same physics reached hospitals as magnetic resonance imaging. MRI shows the brain, spinal cord, tumors and joints in fine detail without X-rays, and it has replaced several invasive and unpleasant examinations. In 2002 about 22,000 scanners performed more than 60 million examinations; later estimates put the total at more than 95 million a year on about 50,000 machines. In 1945 Rabi proposed that atomic resonance could keep time. The first atomic clocks followed within a decade, the second has been defined by cesium atoms since 1967, and atomic clocks aboard every GPS satellite now support navigation, telecommunications, power grids and finance. His Columbia laboratory produced future Nobel laureates, including Norman Ramsey and Polykarp Kusch, and its postwar measurements of hydrogen helped spark modern quantum electrodynamics. In World War II he helped lead the MIT Radiation Laboratory, whose microwave radar many physicists credited with winning the war. Afterwards he helped create Brookhaven National Laboratory, proposed at UNESCO the European laboratory that became CERN, initiated the international conferences on peaceful uses of atomic energy and persuaded President Eisenhower to set up a standing science advisory committee.

  • Norman Ramsey, his former student, wrote that Rabi's 1937 paper on atoms in a rotating magnetic field gave the theory behind every later magnetic resonance experiment.[5],[6]
  • In 2002 MRI scanners worldwide performed more than 60 million examinations, especially valuable for the brain and spinal cord; later estimates exceed 95 million a year.[4],[17]
  • His 1945 proposal of an atomic clock was followed by working atomic clocks between 1949 and 1955; since 1967 the second itself has been defined by cesium atoms.[5],[12]
  • The MIT Radiation Laboratory, where he led research, helped put some 20,000 three-centimeter radar systems into service by the end of World War II.[6],[7]
  • He helped found Brookhaven National Laboratory in 1947 and, at a 1950 UNESCO meeting in Florence, proposed the European laboratory that became CERN.[5],[6]

Impact in numbers

Rabi's lasting gift is a method: tuning radio waves to the natural wobble of atomic nuclei to measure them precisely. That idea runs through NMR spectroscopy in chemistry, MRI scanners in hospitals, and the atomic clocks that define the second and time GPS signals. We record two small, conservative shares of those large outcomes: 3% of the people who have benefited from MRI scans, and 1% of the US economic benefits of GPS, which depends on atomic clocks. Both shares reflect how many later scientists and engineers were essential. We also record a small share of the deaths at Hiroshima and Nagasaki, reflecting his role as a senior consultant to Los Alamos. Much of his influence cannot be counted: the Columbia school of physicists he built, wartime radar, his opposition to the hydrogen bomb, and the laboratories he helped found, Brookhaven and CERN.

Fundamental scienceHealthTechnologyEconomyPeace

Each number is the laureate’s credited share of a real-world outcome, cumulative to 2025. The whole outcome, the share of credit, and the reasoning are shown so you can check the arithmetic. Outcomes shared with other laureates are counted once on the impact page.

  • Low confidenceRippleModeledHealth

    People who have benefited from MRI examinations worldwide since the early 1980s

    9–33

    million people benefited, credited share

    That is 3% of 300 million–1.1 billion people benefited since 1981.

    How this number was built

    Nobel Assembly: clinical MRI began in the early 1980s; in 2002 about 22,000 units did over 60M exams. GE HealthCare (citing OECD 2017 data): about 50,000 units, over 95M scans a year. Low exams: linear rise from 0 (1981) to 60M (2002) = 0.66B; 60M to 95M over 2003-17 = 1.18B; 95M a year for 2018-25 = 0.76B; total 2.6B. High assumes the 95M figure is a floor: a rise to 110M by 2017 and 130M by 2025, total 2.9B. An OECD-data study cites estimates that 20-50% of imaging is low-value, so count 50-80% as beneficial, and assume 4 (low) or 2 (high) scans per person: 2.6B x 0.5 / 4 = 0.33B, rounded to 0.3B; 2.9B x 0.8 / 2 = 1.17B, rounded to 1.1B. Share 0.03: his 1937-38 resonance theory and method underlie all magnetic resonance, but Bloch and Purcell's NMR, Lauterbur and Mansfield's imaging, Ernst's methods and magnet and computer engineering were also essential.[4],[5],[6],[17],[18]

    Sources: NobelPrize.org (Nobel Assembly at Karolinska Institutet); National Academy of Sciences, Biographical Memoirs vol. 62; Encyclopedia.com (Charles Scribner's Sons / Gale); GE HealthCare; Healthcare (MDPI), via PubMed Central

  • Low confidenceRippleModeledTechnology

    Economic benefits of GPS to US private industry, which depends on atomic clocks

    $32–64

    billion in economic value, credited share

    That is 1% of $3.2–6.4 trillion in economic value since 1984.

    How this number was built

    Same whole-outcome range as the Einstein profile. RTI International's 2019 study for NIST puts US private-sector GPS benefits for 1984-2017 at about $1.4 trillion, range $903 billion-$1.8 trillion (2017 dollars). Its Figure ES-1 shows about $300 billion of benefit in 2017 alone; scaling by the study's own range gives $200B-$400B a year. For 2018-2025 we hold that rate flat, with no further growth: 8 x $200B = $1.6T (low) and 8 x $400B = $3.2T (high). Totals $2.50T-$5.00T in 2017 dollars; BLS CPI-U (313.689 / 245.120 = 1.28) gives about $3.2T-$6.4T in 2024 dollars. Other countries excluded. Share 0.01: RTI calls the atomic clock perhaps the most critical part of satellite navigation. Rabi proposed it in 1945 from his resonance method, but clock builders, Ramsey, satellites, signal design and relativity corrections were all essential.[5],[12],[13],[14]

    Sources: National Academy of Sciences, Biographical Memoirs vol. 62; National Institute of Standards and Technology (NIST); National Institute of Standards and Technology (NIST); US Bureau of Labor Statistics

  • HarmLow confidenceRippleSourced totalPeace

    Deaths from the atomic bombings of Hiroshima and Nagasaki within two to four months

    300–492

    deaths caused, credited share

    That is 0.2% of 150,000–246,000 deaths caused since 1945.

    How this number was built

    The Radiation Effects Research Foundation estimates acute deaths within two to four months at 90,000-166,000 in Hiroshima and 60,000-80,000 in Nagasaki, so 150,000-246,000 in total (the same range as the Bohr, Einstein and Rotblat profiles; later cancer deaths excluded). Share 0.002: Rabi declined Oppenheimer's offer to be associate director at Los Alamos but from 1944 was a senior consultant to him, advised on broad policy, visited the lab and watched the Trinity test. The Nobel Foundation says he took part in the bomb's development, but our sources document no design work by him, he doubted it could be finished in time to affect the war, and the thousands who built the bombs and the leaders who chose to use them carry nearly all the responsibility. Result: roughly 300-490 deaths credited.[1],[6],[7],[11],[16]

    Sources: NobelPrize.org (Nobel Prize Outreach); Encyclopedia.com (Charles Scribner's Sons / Gale); Columbia Magazine, Columbia University; Atomic Heritage Foundation, National Museum of Nuclear Science & History; Radiation Effects Research Foundation (RERF)

The double edge

Rabi's resonance method carried no built-in harm, but his war work did. At MIT's Radiation Laboratory he helped develop the microwave radar that equipped Allied fighters, warships and bombers. From 1944 he was a senior consultant to J. Robert Oppenheimer at Los Alamos, and he watched the first atomic test in July 1945; weeks later the bombs dropped on Hiroshima and Nagasaki killed an estimated 150,000 to 246,000 people within two to four months. In 1987 he said he had not opposed building the bomb during the war, when, in his words, the country faced an emergency and was trying to save civilization. After the war he pushed back: in 1949 he and Enrico Fermi condemned the hydrogen bomb on ethical grounds, and in 1954 he forcefully defended Oppenheimer. Yet the same 1949 advisory report also urged more work on battlefield atomic weapons. According to his biographer, he also never took a woman as a doctoral student and generally opposed women as faculty candidates.

  • Moderate

    Senior consultant to the atomic bomb project

    Rabi turned down Oppenheimer's offer to be associate director at Los Alamos but became a senior consultant to him in 1944, advised on broad policy, visited the lab and witnessed the Trinity test. The Hiroshima and Nagasaki bombs killed an estimated 150,000 to 246,000 people within two to four months. In 1987 he said he had not opposed building the bomb during the war, calling it an emergency.[6],[7],[8],[11],[16]

  • Moderate

    Radar built for war

    As associate director of MIT's Radiation Laboratory, Rabi pushed radar to shorter wavelengths, making sets small enough for fighter planes and ships. The 3-centimeter work his groups started fed into airborne bombing radars such as H2X. The same technology helped defeat Nazi Germany.[5],[6],[19]

  • Minor

    A mixed record on nuclear arms

    In October 1949 Rabi and Fermi argued that no ethical principle could justify using a hydrogen bomb, and President Truman ignored the advisers. But the main report of the committee on which both served also recommended studying larger production of bomb material and intensifying work on atomic weapons for battlefield use.[6],[15]

  • Minor

    Closed to women physicists

    His biographer John Rigden reports, as summarized on Wikipedia, that Rabi did not believe women could be physicists, never had a woman as a doctoral or postdoctoral student, and generally opposed women as candidates for faculty posts.[19]

Against the odds

Rabi's parents were poor Orthodox Jews from Galicia. Columbia's magazine says they came to America hoping for a better life away from prejudice and the danger of persecution. In New York his father made women's clothes in a sweatshop by day and ran a failing grocery at night, and the family lived in a poor Jewish enclave on Manhattan's Lower East Side before moving to Brownsville, Brooklyn. Rabi won a scholarship to Cornell, but after he graduated in chemistry in 1919 he received no job offers, at a time when Jewish chemists were largely shut out of industry and universities. Chemistry also bored him, and he spent about three years in uninspiring jobs, including bookkeeping. Even after his doctorate and two years with Europe's leading physicists, he did not expect a university post, because Jewish scholars then struggled to get one; a recommendation from Werner Heisenberg brought Columbia's offer in 1929. Rabi later said he felt shut out of parts of American society because he was Jewish, though inside academia he did not really meet antisemitism. In 1933 Nazi rule drove his Jewish mentor Otto Stern from his Hamburg post, and many members of Rabi's family died in the Holocaust. In 1940 he left his laboratory for five years of war work aimed at defeating Nazi Germany.

  • 1899

    Poverty

    The family was poor. His father worked in a sweatshop by day and ran a small, unsuccessful grocery at night, and his parents never learned to read or write English.[5],[6]

  • 1919

    Discrimination

    After earning his chemistry degree at Cornell he received no job offers, at a time when Jews were largely excluded from jobs in the chemical industry and academia; he spent about three years in jobs outside his field, including as a bookkeeper.[2],[5],[10],[19]

  • 1929

    Discrimination

    Jewish scholars had great difficulty winning university posts in 1929, and Rabi did not expect one; Heisenberg's personal recommendation led Columbia to offer him a lectureship.[6],[7]

  • —

    Discrimination

    In 1987 Rabi said he felt he would have been admitted to many parts of society if he were not Jewish, although once in academia he did not really meet antisemitism, and he always made his Jewishness clear.[8],[9]

  • —

    Family killed

    The Jewish Telegraphic Agency reported that many members of Rabi's Orthodox Jewish family perished in the Holocaust.[8]

Jewish background

Both parents JewishIdentified as Jewish, secular

Rabi was born in Galicia to Orthodox Jewish parents, David Rabi and Janet (Sheindel) Teig, and grew up speaking Yiddish at home in the Jewish immigrant neighborhoods of Manhattan's Lower East Side and Brownsville, Brooklyn. He started Hebrew school at three, but reading about Copernicus as a boy led him to question God. In 1987 he said he did not practice Jewish rituals or go to synagogue on Yom Kippur. He credited his religious upbringing with his taste for fundamental questions, told a Jewish news agency that year that he was glad to be Jewish and part of a great history, joined the board of governors of Israel's Weizmann Institute in 1959 and advised Bar-Ilan University.[2],[5],[6],[8],[9]

Key dates

  1. July 29, 1898

    Born Israel Isaac Rabi in Rymanow, Galicia, in the Austro-Hungarian Empire (now Poland), to Orthodox Jewish parents.[1],[5]

  2. 1899

    Brought to New York as a baby; the family settles among Jewish immigrants on Manhattan's Lower East Side, moving to Brownsville, Brooklyn, when he is nine.[2],[5],[6]

  3. 1919

    Graduates in chemistry from Cornell; spends about three years in jobs outside science, including bookkeeping, before returning to graduate study.[2],[5],[19]

  4. 1927

    Earns his PhD at Columbia for work on magnetic crystals, then spends two years in Europe with Sommerfeld, Bohr, Pauli, Stern and Heisenberg.[2],[6]

  5. 1929

    On Heisenberg's recommendation, becomes a lecturer in theoretical physics at Columbia, where he spends the rest of his career.[2],[6],[7]

  6. 1938

    With Millman, Kusch and Zacharias, carries out the first molecular-beam magnetic resonance experiment, measuring the magnetism of lithium nuclei.[1],[5]

  7. 1940

    Takes leave from Columbia to become a leader, later associate director, of the MIT Radiation Laboratory developing microwave radar.[2],[5],[6]

  8. 1944

    Awarded the Nobel Prize in Physics, unshared, for his resonance method for recording the magnetic properties of atomic nuclei.[1]

  9. 1945

    In his Richtmyer lecture, proposes using atomic beam magnetic resonance to run a clock; the New York Times report is the first published account of atomic clocks.[5],[12]

  10. July 16, 1945

    Witnesses the Trinity test, the first atomic explosion, as a consultant to the Manhattan Project.[7],[11]

  11. 1947

    Brookhaven National Laboratory, which he and Norman Ramsey first proposed, is established on Long Island.[5],[6]

  12. 1949

    With Enrico Fermi, writes an annex to the Atomic Energy Commission advisers' report opposing the hydrogen bomb on ethical grounds.[15]

  13. 1950

    As US delegate to UNESCO in Florence, wins a resolution for a shared European accelerator laboratory, which leads to CERN.[6]

  14. January 11, 1988

    Dies of cancer in New York City, aged 89.[1],[5]

Sources

  1. 1.Isidor Isaac Rabi - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.Isidor Isaac Rabi - Biographical · NobelPrize.org (from Nobel Lectures, Physics 1942-1962, Elsevier, 1964), 1964
  3. 3.The Nobel Prize in Physics 1944 - Award ceremony speech (broadcast lecture by E. Hulthen, 10 December 1944) · NobelPrize.org, 1944
  4. 4.Press release: The Nobel Prize in Physiology or Medicine 2003 (magnetic resonance imaging) · NobelPrize.org (Nobel Assembly at Karolinska Institutet), 2003
  5. 5.I. I. Rabi 1898-1988: A Biographical Memoir, by Norman F. Ramsey · National Academy of Sciences, Biographical Memoirs vol. 62, 1993
  6. 6.Rabi, Isidor Isaac (Complete Dictionary of Scientific Biography entry by John S. Rigden) · Encyclopedia.com (Charles Scribner's Sons / Gale), 2008
  7. 7.I.I. Rabi: Physics and Science at Columbia, in America, and Worldwide, by Samuel Devons · Columbia Magazine, Columbia University, 2001
  8. 8.Special Interview: A Nobel Laureate's Lament · Jewish Telegraphic Agency, 1987
  9. 9.Nobel Laureate Physicist Isidor Isaac Rabi Dead at 89 · Jewish Telegraphic Agency, 1988
  10. 10.Scientist of the Day: Isidor Isaac Rabi, by William B. Ashworth Jr. · Linda Hall Library, 2021
  11. 11.Isidor I. Rabi (profile) · Atomic Heritage Foundation, National Museum of Nuclear Science & History
  12. 12.A Brief History of Atomic Clocks at NIST · National Institute of Standards and Technology (NIST)
  13. 13.Economic Benefits of the Global Positioning System (GPS), final report by RTI International · National Institute of Standards and Technology (NIST), 2019
  14. 14.Consumer Price Index for All Urban Consumers (CPI-U), series CUUR0000SA0 · US Bureau of Labor Statistics
  15. 15.General Advisory Committee's Majority and Minority Reports on Building the H-Bomb (October 1949) · AtomicArchive.com, 1949
  16. 16.Frequently Asked Questions: How many people died as a result of the atomic bombings? · Radiation Effects Research Foundation (RERF)
  17. 17.Committing to sustainability in MRI · GE HealthCare
  18. 18.Diagnostic Technology: Trends of Use and Availability in a 10-Year Period (2011-2020) among Sixteen OECD Countries · Healthcare (MDPI), via PubMed Central, 2023
  19. 19.Isidor Rabi · Wikipedia

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 13 corrections made. How we check

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