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Portrait of James Franck
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Nobel Prize in Physics · 1925

James Franck

He helped show that atoms take in energy in fixed packets, quit his post over Nazi racial laws and warned against a surprise atomic attack.

The Nobel citation: “for their discovery of the laws governing the impact of an electron upon an atom”
Born
August 26, 1882, Hamburg, Germany
Died
May 21, 1964, Göttingen, West Germany (now Germany)
Shared with
Gustav Hertz
Affiliation at the time
Goettingen University, Germany

Physics prize

1925

Shared with 1 other laureate.

Age that year

43years

Born in 1882.

Headline credited impact

$28.4–32billion in economic value

Cumulative world semiconductor sales, a proxy for the quantum-based electronics economy. How it was built

Sources cited

23

Fact-checked September 24, 2026.

  • At 13 he went alone to Hamburg's physics laboratory to have his broken arm X-rayed; he later recalled it as the first diagnostic X-ray taken in the city.
  • He and Gustav Hertz at first misread their famous 4.9-volt result and never mentioned Bohr's atomic theory in their paper; Franck later called that oversight incomprehensible.
  • In April 1933 he became the first German academic to resign in protest against the new Nazi law purging Jews from the civil service, though his war service exempted him.
  • In 1940 George de Hevesy dissolved Franck's Nobel medal in acid in Copenhagen to hide it from the Nazis; the gold was recovered and recast after the war.
  • The 1945 Franck Report, from a committee he chaired, urged the US to demonstrate the atomic bomb on an uninhabited area instead of using it on Japan without warning.

The breakthrough

The Franck-Hertz experiment: proof that atoms take energy in fixed packets (1914)

In 1914 in Berlin, Franck and his friend Gustav Hertz fired electrons through a glass tube filled with thin mercury vapor. They slowly raised the voltage that sped the electrons up and measured how many reached a collector at the far end. The current climbed, then suddenly dropped when the electrons carried 4.9 electronvolts of energy, then climbed and dropped again at each further multiple of 4.9 volts. Slower electrons bounced off the heavy mercury atoms almost without losing energy, like a rubber ball off a wall, an image Franck used in his Nobel lecture. But an electron with 4.9 volts could hand exactly that much energy to an atom, never a little more or less. The atoms then glowed with ultraviolet light of one wavelength, about 254 nanometers, whose energy matched the 4.9 volts. Think of a vending machine that accepts only one exact coin: the atom took in energy only in fixed packets. This was the first direct experimental evidence that atoms have separate internal energy levels, the key idea of Niels Bohr's 1913 atomic model. Franck and Hertz at first mistook 4.9 volts for the energy needed to tear an electron out of the atom, and Bohr and others supplied the correct reading. In 1925 Franck added a second insight: electrons in a molecule jump so fast that the heavy nuclei have no time to move. Edward Condon put this in mathematical form, and it became the Franck-Condon principle.[1],[2],[4],[5],[7],[8]

“We Germans of Jewish descent are being treated as aliens and enemies of the fatherland.”
James Franck, From Franck's public statement explaining his resignation from the University of Göttingen in April 1933, in the English translation published in Physics Today.[8]

What it meant for humanity

Franck's experiments with Gustav Hertz gave the first direct evidence that atoms hold energy only in fixed amounts. At the 1926 prize ceremony, the Nobel committee's C. W. Oseen said their work had turned Bohr's basic hypotheses about atomic energy levels into experimentally proven facts, which survived even as the rest of Bohr's model gave way to quantum mechanics. Their method laid the foundation of electron impact spectroscopy, the study of atoms and molecules by colliding electrons with them. Quantum science, which experiments like theirs helped establish, underpins lasers, transistors and the electronics of daily life. His second big idea, the Franck-Condon principle, has been a cornerstone of molecular spectroscopy since the 1920s. In 1949 he extended it to electron transfer between ions in solution, groundwork that Willard Libby and Rudolph Marcus built on, and it remains central to photochemistry in both chemistry and biology. At Chicago he asked how plants move captured light energy to the reaction centers where photosynthesis begins, a question researchers still study with ultrafast lasers. He shaped people as well as ideas. His circle of students and collaborators at Göttingen included Patrick Blackett, Gerhard Herzberg, Edward Condon, Robert Oppenheimer, Eugene Rabinowitch and Hertha Sponer. After 1933 he worked to find posts abroad for Jewish researchers driven out of German universities, and after 1945 he answered appeals for food and money from Germany, sending CARE packages to his old teacher Max Planck. His 1933 resignation and the 1945 Franck Report made him a lasting example of a scientist who weighs the moral consequences of his work. The University of Chicago named its James Franck Institute after him.

  • Lise Meitner recalled that after Franck lectured in Berlin on exciting mercury's ultraviolet line by electron impact, Einstein told her the result was so lovely it could make you cry.[7]
  • The Franck-Condon principle, which Franck proposed in the mid-1920s and Edward Condon put in quantum-mechanical form in 1926, has been a cornerstone of molecular spectroscopy ever since.[2],[7],[8]
  • From 1920 to 1933, with Franck and Max Born side by side, Göttingen ranked among the world's top centers of quantum physics; students celebrated his Nobel Prize with a torchlight procession.[2],[7],[8]
  • In 1919 his group at Haber's institute detected a long-lived excited state of helium and introduced the term 'metastable' for such atomic states.[8],[9]
  • From 1933 he used his international contacts to help Jewish researchers and students from his institute, and other scholars expelled by the Nazis, find positions abroad.[7],[8],[9]
  • The June 1945 Franck Report warned that a surprise nuclear attack would set off an arms race, and it became a symbol of scientists' responsibility for the uses of their work.[7],[9],[14]

Impact in numbers

Franck's main legacy is foundational. The Franck-Hertz experiment gave quantum theory its first direct experimental footing in the atom, and the Franck-Condon principle still governs how scientists read molecular spectra, photochemistry and electron transfer. We record one ripple benefit claim, a 0.2% share of cumulative world semiconductor sales, the proxy used for other quantum pioneers, because an experiment that confirmed Bohr's theory is one input among many. His moral legacy cannot be priced: the first resignation by a German academic in protest against the Nazi law purging Jews from the civil service, help for expelled Jewish scientists, and the Franck Report's early warning of a nuclear arms race. The harms are real too. He served in Germany's gas-warfare regiment in the First World War and ran the chemistry division of the Manhattan Project's Chicago laboratory for a year, so we record small harm shares of World War I gas deaths and of the atomic bombings' deaths.

Fundamental scienceTechnologyEconomyPeace

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 confidenceRippleModeledEconomy

    Cumulative world semiconductor sales, a proxy for the quantum-based electronics economy

    $28.4–32

    billion in economic value, credited share

    That is 0.2% of $14.2–16 trillion in economic value since 1955.

    How this number was built

    Same whole-outcome range as the Bohr, Born, Einstein and Bloch profiles. WSTS worldwide semiconductor billings for 1986-2025 sum to about $10.28 trillion nominal, about $14.2 trillion in 2024 dollars using the Minneapolis Fed CPI table (low). High ($16T): $14.2T + rough, unsourced allowances of ~$0.5T for pre-1986 chip sales and ~$1T for lasers and other quantum devices outside WSTS = ~$15.7T, rounded up. Sales are only a proxy for value; NIST notes that quantum science underpins lasers and transistors. Share 0.002: the Franck-Hertz experiment was the first direct proof of discrete atomic energy levels, but it confirmed Bohr's theory rather than founding quantum mechanics. Hertz merits an equal share (together 0.004, below Bohr's 0.01), and chips also needed the rest of quantum theory, band theory and decades of engineering.[4],[7],[21],[22],[23]

    Sources: World Semiconductor Trade Statistics (WSTS); Federal Reserve Bank of Minneapolis; National Institute of Standards and Technology (Taking Measure blog); National Academy of Sciences; NobelPrize.org

  • HarmMedium confidenceDirectSourced totalPeace

    Deaths within two to four months of the 1945 atomic bombings of Hiroshima and Nagasaki

    300–492

    deaths caused, credited share

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

    How this number was built

    RERF 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 range used in other profiles (later cancer deaths excluded). Share 0.002, as for Rabi: from December 1942 to December 1943 Franck directed the Met Lab Chemistry Division, whose Section C-I under Seaborg developed the plutonium extraction used at Hanford; Nagasaki was hit with a plutonium bomb. Physics Today says his job was mostly managerial and Seaborg's team did the work; per the UChicago finding aid he was only a consultant from May 1944. Designers, builders and the US decision to use the bombs carry nearly all responsibility. Only the Nagasaki bomb drew on his division's work, so 0.002 of both cities' deaths equals about 0.5-0.6% of Nagasaki's acute deaths. Credited: about 300-490 deaths.[8],[9],[15],[16],[17],[18],[19]

    Sources: Radiation Effects Research Foundation (RERF); U.S. Department of Energy, Office of Scientific and Technical Information; Hanna Holborn Gray Special Collections Research Center, University of Chicago Library; Physics Today (American Institute of Physics); U.S. Department of Energy, Office of Scientific and Technical Information; U.S. Department of Energy, OSTI.GOV; Atomic Heritage Foundation, National Museum of Nuclear Science & History

  • HarmLow confidenceDirectSourced totalPeace

    Soldiers killed by chemical weapons in World War I

    90–100

    deaths caused, credited share

    That is 0.1% of 90,000–100,000 deaths caused since 1915.

    How this number was built

    The OPCW states that more than 90,000 soldiers died from chemical agents in World War I (low); high allows about 10% for undercounting, the same range as the Fritz Haber profile. Share 0.001: Franck was an officer in Pioneer Regiment 35-36, the unit that carried out Germany's chlorine-cloud attacks from 1915, acted as Haber's trusted aide at the front and later tested gas masks. He was one of many officers and scientists in a program led by Haber (share 0.35) and German commanders, and the Allies soon built their own gas arsenals, so his personal share is small. One history places him at Ypres in 1915; NAS and Physics Today do not. Credited: about 90-100 deaths. Injuries (close to a million, per the OPCW) are not claimed separately.[7],[8],[13],[20]

    Sources: Organisation for the Prohibition of Chemical Weapons (OPCW); Springer (in One Hundred Years of Chemical Warfare; open-access copy at Max Planck Society PuRe); National Academy of Sciences; Physics Today (American Institute of Physics)

The double edge

Franck took part in two of the century's weapons programs. In the First World War he served as an officer in Germany's gas-warfare regiment, working for Fritz Haber in the unit that carried out Germany's first chlorine-cloud attacks in 1915, and later tested gas masks at Haber's Berlin institute. By the war's end chemical weapons had killed more than 90,000 soldiers. In the Second World War, fearing that Germany would build an atomic bomb first, he directed the chemistry division of the Manhattan Project's Chicago laboratory for about a year. Glenn Seaborg's section there developed the plutonium chemistry used at Hanford, and the bomb that destroyed Nagasaki was a plutonium bomb. Franck's role was mainly managerial, and from May 1944 he was only a consultant. He also tried to limit the harm: he took the job on condition that he could give his views on the bomb's use to top policymakers, and in June 1945 his committee urged a demonstration instead of a surprise attack. The recommendation was rejected. We record small harm shares for both programs.

  • Moderate

    Officer in Germany's first gas-warfare unit

    From 1915 Franck served in Pioneer Regiment 35-36, the special unit whose gas brigades carried out Germany's chlorine-cloud attacks; one history lists him among the gas-brigade men of the 1915 Ypres attack. As Haber's trusted aide he reported on how attacks had gone, serving in the West and in Russia until illness sent him home. Later he tested gas masks at Haber's Berlin institute, exposing himself to agents such as phosgene.[7],[8],[13],[20]

  • Moderate

    Chemistry chief of the plutonium bomb project

    From December 1942 to December 1943 he directed the Chemistry Division of the Metallurgical Laboratory in Chicago. Its Section C-I, led by Glenn Seaborg, worked out how to extract and purify plutonium; the bismuth phosphate process developed there was used at Hanford, and Nagasaki was destroyed by a plutonium bomb. Franck's job was mostly managerial.[8],[9],[15],[16],[17],[18]

Against the odds

Franck's father was a banker in Hamburg, where the family's Sephardic Jewish forebears had lived for more than two centuries. In the First World War his Jewish origin did not stop him becoming an army officer. After Germany's defeat, nationalists blamed the Jews for a supposed stab in the back, and by 1927 Nazi students had organized a cell at Göttingen. On 7 April 1933 the new Nazi government passed a law purging Jews from the civil service, including university posts. Front-line veterans like Franck were at first exempt, but staying on would have meant taking part in dismissing his Jewish assistants and students. On 17 April he resigned in protest, the first German academic to do so. His hope that colleagues would follow him was disappointed. Instead, 42 Göttingen lecturers publicly called his resignation sabotage, and the Göttingen Academy of Sciences expelled him. After months of searching for work in Germany that would not require political compromise, he left in late 1933. He worked in Baltimore and Copenhagen, taught at Johns Hopkins from 1935 and moved to Chicago in 1938. To help his mother, aunt and sister emigrate to the United States, he pledged his life insurance as a guarantee that they would not become a public burden. He later wrote that becoming an American citizen in 1941 freed him from enforced statelessness.

  • 1933

    Persecution

    The Nazi civil service law of 7 April 1933 pushed Jewish scholars out of German universities. Franck was exempt as a front-line veteran, but as director he would have had to help dismiss Jewish assistants and students, so on 17 April he resigned his Göttingen chair in protest.[7],[9],[10],[12]

  • 1933

    Discrimination

    On 24 April 1933, 42 Göttingen lecturers published a declaration in the pro-Nazi local press calling his resignation an act of sabotage; the Jewish Telegraphic Agency reported that it also demanded faster expulsion of the Jews.[8],[10],[11]

  • 1933

    Discrimination

    Under Nazi pressure, the Göttingen Academy of Sciences expelled him in 1933. He rejoined it only after the war.[9]

  • 1933

    Exile

    Unable to find work in Germany without political compromise, he left in late 1933, working at Johns Hopkins and in Copenhagen before settling at the University of Chicago in 1938.[2],[7],[9]

  • 1940

    War

    When Germany occupied Denmark in April 1940, George de Hevesy dissolved Franck's Nobel medal, which he had deposited at Bohr's institute, in acid so that the invaders would not find it. The Nobel Foundation recast it from the recovered gold, and Franck received it in 1952.[6],[9]

  • —

    Other

    To get his mother, aunt and sister out of Germany, he put up his life insurance as a guarantee that they would not become a public burden in the United States. He later described his US citizenship, gained in 1941, as freeing him from enforced statelessness.[8],[9]

Jewish background

Both parents JewishIdentified as Jewish, secular

Franck was born into a Jewish family in Hamburg, where his Sephardic forebears had lived for over two centuries. His father, the banker Jacob Franck, was deeply religious, and his mother, Rebecka Nachum-Drucker, came from a family of rabbis. Unlike his father, Franck was not orthodox, and later said science was his god and nature his religion, but he was proud of his Jewish heritage and married in a traditional Jewish wedding. In 1933 he resigned publicly as a German of Jewish descent. Not a Zionist, he still showed strong interest when Chaim Weizmann invited him to work in Palestine in 1934, and the Technion gave him an honorary doctorate in 1954.[7],[8],[9]

Key dates

  1. August 26, 1882

    Born in Hamburg, Germany, to the banker Jacob Franck and Rebecka Nachum-Drucker.[1],[2],[7]

  2. 1906

    Earns his doctorate at the University of Berlin under Emil Warburg, for research on how ions move through gases.[2],[7]

  3. 1914

    With Gustav Hertz, finds that electrons give energy to mercury atoms only in fixed 4.9-volt steps: the Franck-Hertz experiment.[1],[5],[8]

  4. 1915

    Serves as an officer in Germany's gas-warfare regiment, working for Fritz Haber in the West and in Russia; later tests gas masks at Haber's institute.[7],[8],[13]

  5. 1920

    Becomes professor of experimental physics and director of the Second Physics Institute at Göttingen, alongside his friend Max Born.[2],[8]

  6. 1925

    Proposes that electron jumps in molecules are too fast for the nuclei to move, the idea Condon formalized as the Franck-Condon principle.[2],[7]

  7. December 10, 1926

    Receives the 1925 Nobel Prize in Physics, shared with Gustav Hertz; the prize had been held over for a year.[1],[3],[4]

  8. April 17, 1933

    Resigns his Göttingen chair in protest against the Nazi purge of Jewish civil servants, despite his exemption as a war veteran.[7],[9],[10]

  9. 1933

    Leaves Germany late in the year for Johns Hopkins, then Bohr's institute in Copenhagen, where he turns to photosynthesis.[2],[8],[9]

  10. 1938

    Becomes professor of physical chemistry at the University of Chicago, with a laboratory for photosynthesis research.[2],[9]

  11. July 1941

    Becomes a US citizen.[9]

  12. December 1, 1942

    Joins the Manhattan Project as director of the Chemistry Division of the Metallurgical Laboratory in Chicago.[7],[9]

  13. June 11, 1945

    His committee's report urges a demonstration of the atomic bomb on an uninhabited area rather than a surprise attack on Japan; it is rejected.[7],[14]

  14. May 21, 1964

    Dies of a heart attack while visiting Göttingen.[1],[8]

Sources

  1. 1.James Franck - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.James Franck - Biographical · NobelPrize.org (from Nobel Lectures, Physics 1922-1941, Elsevier, 1965), 1965
  3. 3.The Nobel Prize in Physics 1925 - Summary · NobelPrize.org (Nobel Prize Outreach)
  4. 4.The Nobel Prize in Physics 1925 - Presentation Speech by Professor C.W. Oseen (10 December 1926) · NobelPrize.org, 1926
  5. 5.Transformations of kinetic energy of free electrons into excitation energy of atoms by impacts (Nobel Lecture, 11 December 1926) · NobelPrize.org, 1926
  6. 6.A unique gold medal (The Nobel medals and the medal for the Prize in Economic Sciences) · NobelPrize.org
  7. 7.James Franck, 1882-1964: A Biographical Memoir, by Stuart A. Rice and Joshua Jortner · National Academy of Sciences, 2010
  8. 8.James Franck: Science and conscience, by Frank von Hippel (Physics Today 63, no. 6) · Physics Today (American Institute of Physics), 2010
  9. 9.Guide to the James Franck Papers 1882-1966 (biographical note) · Hanna Holborn Gray Special Collections Research Center, University of Chicago Library, 2006
  10. 10.Protest against the Removal of Jewish Researchers (James Franck; page text in German) · Georg-August-Universität Göttingen
  11. 11.Gottingen Professors Score Franck Resignation, Demand Expulsion of All Jews · Jewish Telegraphic Agency (archive), 1933
  12. 12.Law for the Restoration of the Professional Civil Service · United States Holocaust Memorial Museum, Holocaust Encyclopedia
  13. 13.From Berlin-Dahlem to the Fronts of World War I: The Role of Fritz Haber and His Kaiser Wilhelm Institute in German Chemical Warfare, by Bretislav Friedrich and Jeremiah James · Springer (in One Hundred Years of Chemical Warfare; open-access copy at Max Planck Society PuRe), 2017
  14. 14.The Franck Report (Report of the Committee on Political and Social Problems, 11 June 1945) · Atomic Heritage Foundation, National Museum of Nuclear Science & History, 1945
  15. 15.Manhattan Project: Seaborg and Plutonium Chemistry, Met Lab, 1942-1944 · U.S. Department of Energy, Office of Scientific and Technical Information
  16. 16.History of Met Lab Section C-I, May 1943 to April 1944, by G. T. Seaborg (report record) · U.S. Department of Energy, OSTI.GOV, 1978
  17. 17.Stanley G. Thompson (profile) · Atomic Heritage Foundation, National Museum of Nuclear Science & History
  18. 18.Manhattan Project: The Atomic Bombing of Nagasaki, August 9, 1945 · U.S. Department of Energy, Office of Scientific and Technical Information
  19. 19.Frequently Asked Questions: How many people died as a result of the atomic bombings? · Radiation Effects Research Foundation (RERF)
  20. 20.History · Organisation for the Prohibition of Chemical Weapons (OPCW)
  21. 21.Historical Billings Report (WSTS Blue Book monthly data, 1986 to date) · World Semiconductor Trade Statistics (WSTS), 2026
  22. 22.Consumer Price Index, 1913- · Federal Reserve Bank of Minneapolis
  23. 23.A Quantum Leap Forward: How Tiny Particles Can Bring Us Exciting New Tech, by Corey Stambaugh · National Institute of Standards and Technology (Taking Measure blog), 2025

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 7 corrections made. How we check

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