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Portrait of Joseph Rotblat
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Nobel Peace Prize · 1995

Joseph Rotblat

A physicist who walked away from the atomic bomb project and spent 60 years working to rid the world of nuclear weapons.

The Nobel citation: “for their efforts to diminish the part played by nuclear arms in international politics and, in the longer run, to eliminate such arms”
Born
November 4, 1908, Warsaw, Russian Empire (now Poland)
Died
August 31, 2005, London, United Kingdom
Shared with
Pugwash Conferences on Science and World Affairs

Peace prize

1995

Shared with 1 other laureate.

Age that year

87years

Born in 1908.

Sources cited

23

Fact-checked September 24, 2026.

  • In late 1944 he became the only scientist known to quit the Los Alamos atomic bomb project for reasons of conscience.
  • He left Warsaw days before Germany invaded Poland in 1939. His wife, Tola, was too ill to travel and stayed behind; she was killed in the Holocaust.
  • When he asked to leave Los Alamos, security officers produced a dossier falsely claiming he planned to hand bomb secrets to the Soviets.
  • Of the 11 scientists who signed the 1955 Russell-Einstein Manifesto warning against nuclear war, he was the youngest, and he outlived all the others.
  • At 87 he accepted the 1995 Nobel Peace Prize, shared with the Pugwash Conferences he had helped organize since 1957.

The breakthrough

Leaving the bomb project, then building a bridge between rival scientists

In early 1939, working in Warsaw, Rotblat was among the first to show that when a uranium nucleus splits (fission), it throws out extra neutrons. Those neutrons can split more uranium nuclei, which release still more neutrons: a chain reaction, like one falling domino knocking over two, and each of those knocking over two more. He soon realised that if this happened fast enough, the result would be an explosion. Afraid that Hitler would build such a bomb first, he worked on the Allied bomb, first in Liverpool and then at Los Alamos in New Mexico. When it became clear in late 1944 that Germany was not close to a bomb, he asked to leave. He was the only scientist known to quit the project on grounds of conscience. His real life's work came after the war. He moved into medical physics, and in 1955 he helped show that fallout from a 1954 American hydrogen-bomb test was far worse than officials had admitted. That same year he signed the Russell-Einstein Manifesto, which warned that nuclear war could end the human race, and chaired the press conference that launched it. The manifesto led to the Pugwash Conferences, which he organised for decades: private meetings where scientists from both sides of the Iron Curtain spoke as individuals, not as government spokesmen, about how to limit and finally eliminate nuclear weapons.[2],[6],[7],[8],[10],[13],[20]

“But science, the exercise of the supreme power of the human intellect, was always linked in my mind with benefit to people.”
Joseph Rotblat, Opening of his Nobel Peace Prize acceptance and Nobel lecture, Remember Your Humanity, Oslo, December 1995.[3]

What it meant for humanity

Rotblat's main gift was a way for enemies to keep talking. During the Cold War, Pugwash meetings brought together scientists, and later officials, from the United States, the Soviet Union, Britain and many other countries. They spoke as individuals and off the record, so ideas could be tested there before governments were ready to touch them. The Norwegian Nobel Committee judged that Pugwash probably played a real part in the 1963 treaty banning nuclear tests in the atmosphere, the 1968 Non-Proliferation Treaty, and the 1972 SALT I arms-limitation agreement and Biological Weapons Convention. One example: from 1964 to 1967, Pugwash participants argued about banning anti-missile defenses until a leading Soviet scientist changed his mind; the Anti-Ballistic Missile Treaty followed in 1972. Pugwash contacts also carried messages during the Cuban missile crisis and the Vietnam War, and Mikhail Gorbachev later said Pugwash papers and conferences helped guide the policy that thawed the Cold War. The British government, which at first suspected Pugwash of being a Communist front, came to value it and honoured Rotblat. He also put nuclear physics to work for health. For 26 years he was professor of physics at St Bartholomew's Hospital Medical College in London, studying how radiation affects living things, and he edited the journal Physics in Medicine and Biology. His research on fallout fed the public pressure that ended atmospheric testing by the three nuclear powers that signed the 1963 treaty. In the 1980s he was the main author of World Health Organization reports on what nuclear war would do to health. He also urged scientists everywhere to weigh the human consequences of their work, proposing a voluntary Hippocratic oath for scientists.

  • The New York Times reported that historians see Pugwash talks as preparing the ground for five arms agreements, from the 1963 Partial Test Ban Treaty to the 1993 Chemical Weapons Convention.[5],[10]
  • Rotblat led Pugwash as secretary-general from 1957 to 1973 and as president from 1988 to 1997. Through the Cold War, its meetings were one of the few open lines between scientists of the Soviet bloc and the West.[2],[11],[12],[22]
  • Former Soviet leader Mikhail Gorbachev credited Pugwash meetings and papers with helping to shape the foreign policy behind the Cold War thaw, according to the Guardian.[9]
  • At St Bartholomew's Hospital (1950-1976) he applied nuclear physics to medicine and studied the effects of radiation on living organisms; he edited Physics in Medicine and Biology from 1960 to 1972.[2],[12]
  • From 1984 to 1990, as rapporteur for a World Health Organization group, he was mainly responsible for its reports on the effects of nuclear war on health and health services.[2]
  • He organised the Atom Train (1947-1950), described in his Nobel CV as the first large-scale effort to teach the public about peaceful and military uses of nuclear energy. It toured Britain, Europe and the Middle East.[2],[14]

Impact in numbers

Rotblat's impact is mostly about risk reduced and conversations kept open, and it resists honest counting. Pugwash, which he organised for four decades, gave scientists and officials from rival blocs a private place to test ideas, and the Nobel Committee judged it probably contributed to the 1963 test ban, the 1968 Non-Proliferation Treaty and the 1972 SALT I and biological-weapons agreements. Ending atmospheric tests reduced radioactive fallout worldwide. But no one can say how many lives these treaties saved, or how much of the credit belongs to one man among many diplomats, leaders and campaigners, so we record no benefit numbers. His medical physics and his WHO reports on nuclear war mattered too but cannot be counted. We do record one harm: a very small share (0.1%) of the deaths from the 1945 atomic bombings, because his early experiments helped show the bomb could be built, even though he left before it was finished and spent the rest of his life working against it.

PeaceHealthFundamental science

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.

  • HarmLow confidenceRippleSourced totalPeace

    Deaths within 2-4 months of the 1945 atomic bombings of Hiroshima and Nagasaki

    150–246

    deaths caused, credited share

    That is 0.1% of 150,000–246,000 deaths caused since 1945.

    How this number was built

    RERF estimates acute deaths within 2-4 months at 90,000-166,000 in Hiroshima and 60,000-80,000 in Nagasaki, so low = 150,000 and high = 246,000. Later radiation cancers and test fallout are excluded to stay conservative. Share 0.001: in 1939 Rotblat saw that a fast chain reaction would explode, and from late 1939 his Liverpool measurements on fast neutrons and uranium-235 helped show a bomb was feasible, feeding the 1941 MAUD Report that helped push the US program. At Los Alamos in 1944 he measured fission gamma rays, then left before the bombs were built; he judged his impact small. Thousands of scientists and workers built the bombs, others contributed far more, US leaders chose to use them, and others would soon have made his measurements. Result: about 150-250 deaths credited.[7],[8],[19],[21],[23]

    Sources: Radiation Effects Research Foundation (RERF); U.S. Department of Energy, Office of History and Heritage Resources (OSTI); Atomic Heritage Foundation / National Museum of Nuclear Science & History, Voices of the Manhattan Project; josephrotblat.com (archived copy, Internet Archive); josephrotblat.com (archived copy, Internet Archive)

The double edge

Rotblat's own record includes the weapon he later fought. In 1939 he was among the first to see that a fission chain reaction could cause an explosion, and his wartime experiments in Liverpool helped show that a bomb was feasible. That work fed the British report that helped push the United States to build one. He left Los Alamos before the bombs were finished and later judged his part to have been small, but he never denied that he had helped. His peace work also drew criticism. British officials at first saw Pugwash as little better than a Communist front, and a senior Reagan administration official called its leaders Communist dupes, pointing to the ABM Treaty as serving Soviet interests. Rotblat gave critics more ammunition in 1995 when he told a reporter that past Soviet atomic spying could, in some circumstances, have been a good thing if it helped balance the superpowers. And papers in his own archive do not match parts of the story he told about leaving Los Alamos.

  • Moderate

    Helped show that an atomic bomb was possible

    In 1939 he realised that a fast fission chain reaction would be explosive. From late 1939 he led Liverpool experiments on fast neutrons and uranium-235; with other British work, they became part of the basis for the 1941 MAUD Report, which helped convince the Americans to press ahead with a bomb. At Los Alamos in 1944 he measured gamma rays given off in fission before resigning.[7],[8],[21],[23]

  • Minor

    Accused of being soft on the Soviet Union

    British officials first treated Pugwash meetings as little better than Communist front gatherings, and Richard Perle, a Reagan administration official, called its leaders Communist dupes. Rotblat answered that they worked for all of civilization, not for the Russians. But in 1995 he told the New York Times that past Soviet atomic spying could, under some circumstances, have been a good thing if it helped balance the two superpowers.[10],[14]

  • Minor

    Parts of his Los Alamos story are disputed

    Rotblat gave a detailed account of why he left Los Alamos, including a 1944 remark by General Leslie Groves that the bomb's real purpose was to subdue the Soviets. The historian Barton Bernstein has questioned his memory, and a study of his archive found papers that contradict parts of his story, such as his claim that his Los Alamos papers were lost.[7],[15],[20]

Against the odds

Rotblat was born in 1908 in Russian-ruled Warsaw, into a large Jewish family that was comfortable until the First World War. The war destroyed his father's business; his Guardian obituary says a wave of antisemitism helped sweep it away. He grew up hungry, cold and sometimes abused in a starving city, and he later said this was when he decided he never wanted to see war again. His family could not pay for high school, so he worked as an electrician and studied at night until he won a place to study physics. In interwar Poland, home to 3.3 million Jews, Jews were shut out of the civil service and most state jobs, and the late 1930s brought new pogroms and boycotts. In spring 1939 he took up a research post in Liverpool. That August he went home to bring back his wife, Tola, but she was recovering from appendicitis and stayed behind. Days later Germany invaded. His efforts to get her out through Denmark, Belgium and Italy all failed. She was killed in the Holocaust, probably in 1942; his archive's catalogue says at the Majdanek camp. He learned of her death only after the war and never remarried. His mother, sister and brothers survived, some by escaping the Warsaw ghetto into hiding. At Los Alamos, his decision to leave led security officers to assemble a false dossier accusing him of spying for the Soviet Union.

  • 1914

    Poverty

    The First World War ruined his family's business, amid a wave of antisemitism. He grew up hungry and often deprived, his parents could not afford secondary school, and he worked as an electrician while studying at night.[9],[12],[13]

  • —

    Discrimination

    In interwar Poland, Jews were barred from the civil service and almost all state jobs, and the late 1930s brought a new wave of pogroms and anti-Jewish boycotts.[17]

  • 1939

    Exile

    The German invasion in September 1939 stranded him in Britain, separated from his wife and family. The stipend he received from Poland stopped, and he faced real financial hardship in Liverpool.[7],[21]

  • 1942

    Family killed

    His wife, Tola Gryn, trapped in occupied Poland, was killed in the Holocaust, probably in 1942. His archive's catalogue says she died at Majdanek, the Nazi camp near Lublin where tens of thousands of Jews were killed; other accounts differ. He learned of her death only after the war.[12],[18],[21]

  • 1943

    Persecution

    His mother, a brother, and his sister Ewa with her husband and young daughter survived the Warsaw ghetto. They got out not long before the Germans razed it in 1943: most hid in a Polish family's house outside Warsaw, while Ewa and her daughter lived openly as Poles on false papers. With his help they settled in England in 1946.[9],[16],[20]

  • 1944

    Other

    When he asked to leave Los Alamos, US security officers built a dossier accusing him of planning to pass atomic secrets to the Soviets. The charge was false, but he was allowed to leave only on condition that he tell no one why.[7],[8],[14]

Jewish background

Both parents JewishDistant from Jewish identity

Rotblat was born in Warsaw to Jewish parents, Zygmunt Rotblat and Sonia (née Krajtman), one of seven children; NobelPrize.org describes him as of Jewish descent. He grew up in a religious home, and his parents hoped he would become a rabbi. As an adult he was not religious and called himself an agnostic. He rarely spoke about his life before 1939. He kept his Polish citizenship until 1946 because he hoped to go home, and in his Nobel lecture he urged people to become world citizens. His wife, Tola Gryn, died in the Holocaust; his mother, sister and brothers survived it.[1],[3],[8],[9],[10],[11],[12],[20]

Key dates

  1. November 4, 1908

    Born in Warsaw, then part of the Russian Empire, into a Jewish family; one of seven children.[1],[10],[12]

  2. 1938

    Earns his doctorate in physics at the University of Warsaw, after an MA from the Free University of Poland in 1932.[2]

  3. 1939

    Reports in Nature that splitting uranium nuclei releases extra neutrons, and soon realises that a chain reaction could make a bomb.[6],[8]

  4. 1939

    Moves to the University of Liverpool to work with James Chadwick, the discoverer of the neutron.[2],[7]

  5. August 1939

    Leaves Warsaw days before Germany invades Poland; his wife, Tola, too ill to travel, stays behind. He never sees her again.[7],[9]

  6. 1942

    Tola is killed in the Holocaust, probably in 1942 (his archive's catalogue says at Majdanek); Rotblat learns of her death only after the war.[9],[12]

  7. February 1944

    Joins the British Mission at the Los Alamos laboratory of the Manhattan Project.[5],[7]

  8. December 1944

    Learns Germany is not close to a bomb and leaves Los Alamos on grounds of conscience in December, returning to Liverpool.[5],[7],[8]

  9. 1950

    Becomes professor of physics at St Bartholomew's Hospital Medical College, London, where he works on medical uses and effects of radiation until 1976.[2],[12]

  10. July 9, 1955

    Signs the Russell-Einstein Manifesto warning of nuclear war and chairs the press conference that launches it.[2],[14]

  11. 1957

    Helps organise the first Pugwash Conference in Nova Scotia and becomes its secretary-general, serving until 1973.[2],[10]

  12. October 13, 1995

    Awarded the Nobel Peace Prize, shared equally with the Pugwash Conferences, for efforts to diminish and eventually eliminate nuclear arms.[4]

  13. 1998

    Knighted (KCMG) for services to international understanding.[9],[11]

  14. August 31, 2005

    Dies in London, aged 96, the last surviving signer of the Russell-Einstein Manifesto.[1],[9]

Sources

  1. 1.Joseph Rotblat - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.Joseph Rotblat - Biographical (Curriculum Vitae) · NobelPrize.org (from Les Prix Nobel 1995), 1995
  3. 3.Joseph Rotblat - Nobel Lecture: Remember Your Humanity · NobelPrize.org, 1995
  4. 4.The Nobel Peace Prize 1995 - Press release · NobelPrize.org (Norwegian Nobel Committee), 1995
  5. 5.The Nobel Peace Prize 1995 - Award ceremony speech by Francis Sejersted · NobelPrize.org, 1995
  6. 6.Emission of Neutrons accompanying the Fission of Uranium Nuclei (Nature 143, 852) · Nature, 1939
  7. 7.The Manhattan Project: An Interactive History - Joseph Rotblat · U.S. Department of Energy, Office of History and Heritage Resources (OSTI)
  8. 8.Joseph Rotblat's Interview (with Martin Sherwin, 16 October 1989) · Atomic Heritage Foundation / National Museum of Nuclear Science & History, Voices of the Manhattan Project, 1989
  9. 9.Obituary: Sir Joseph Rotblat · The Guardian (GO Jones and Anthony Tucker), 2005
  10. 10.Joseph Rotblat, 96, Dies; Resisted Nuclear Weapons · The New York Times (archived copy, Internet Archive), 2005
  11. 11.Professor Sir Joseph Rotblat (obituary) · The Daily Telegraph (archived copy, Internet Archive), 2005
  12. 12.The Papers of Professor Sir Joseph Rotblat (GBR/0014/RTBT), collection description · Churchill Archives Centre, University of Cambridge
  13. 13.Dr. Rotblat: Or How I Learned to Start Worrying & Fear the Bomb · Culture.pl (Adam Mickiewicz Institute), 2017
  14. 14.The Political Rehabilitation of Joseph Rotblat (Lawrence S. Wittner) · History News Network (archived copy, Internet Archive), 2005
  15. 15.Joseph Rotblat, the bomb and anomalies from his archive (Underwood, Science and Engineering Ethics 19:487-490) · PubMed / Science and Engineering Ethics, 2013
  16. 16.Obituary: Halina Sand · The Guardian (Katherine Sand), 2009
  17. 17.Virtual Jewish World: Poland · Jewish Virtual Library
  18. 18.Lublin/Majdanek Concentration Camp: Conditions · United States Holocaust Memorial Museum, Holocaust Encyclopedia
  19. 19.Frequently Asked Questions (estimated acute deaths in Hiroshima and Nagasaki) · Radiation Effects Research Foundation (RERF)
  20. 20.Joseph Rotblat · Wikipedia
  21. 21.Joseph Rotblat: Nuclear physics (Martin Underwood) · josephrotblat.com (archived copy, Internet Archive), 2011
  22. 22.Pugwash Conferences on Science and World Affairs - Facts · NobelPrize.org
  23. 23.Rotblat: An introduction (Martin Underwood) · josephrotblat.com (archived copy, Internet Archive), 2011

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 9 corrections made. How we check

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