Leó Spitz of Budapest
Leo Szilard was born Leó Spitz in Budapest on February 11, 1898, the eldest child of Lajos Spitz, a civil engineer, and Tekla Vidor, a middle-class Jewish couple who raised him, his brother Béla and his sister Rózsi on the Városligeti Fasor in Pest. In 1900 the family exchanged the German name Spitz for the Hungarian Szilárd, meaning “solid.” Though raised in a religious household, Leo became an agnostic.
He showed early gifts in physics and mathematics and in 1916 won the Eötvös Prize, Hungary’s national mathematics award. He began engineering studies in Budapest but was drafted into the Austro-Hungarian army. In September 1918, before his unit was sent to the front, he caught Spanish influenza and was sent home; he later learned that his regiment had been nearly annihilated in battle.
Driven out of Hungary
In the turmoil after the war, Szilard and his brother formed a small socialist student group. When the short-lived Communist regime of Béla Kun collapsed in 1919, the brothers formally changed their religion from “Israelite” to Calvinist, but when they tried to re-enrol at the Budapest technical university, nationalist students barred them because they were Jews. Convinced he had no future in Hungary, Szilard left for Berlin on Christmas Day 1919.
In Berlin he abandoned engineering for physics and attended lectures by Albert Einstein, Max Planck, Walther Nernst and Max von Laue, and befriended fellow Hungarians Eugene Wigner, John von Neumann and Dennis Gabor. His doctoral thesis, praised by Einstein, tackled the old puzzle of Maxwell’s demon and showed a deep link between thermodynamics and information; a follow-up paper introduced the thought experiment now called the Szilard engine and became a founding text of information theory. As a lecturer in Berlin he filed early patent applications for the linear accelerator, the cyclotron and the electron microscope, and between 1926 and 1930 worked with Einstein on a refrigerator with no moving parts.
London, 1933: the crossing
When Hitler became chancellor in January 1933, Szilard urged his family and friends to leave Europe while they could, and himself moved to England. There he helped found the Academic Assistance Council, which found places for refugee scholars; by 1939 it had helped more than 2,500 of them.
On September 12, 1933, Szilard read a report in The Times of a speech in which Ernest Rutherford dismissed the idea of extracting power from atoms as “moonshine.” Irritated, he went walking. By his own later account, as he waited for a traffic light to change on Southampton Row in Bloomsbury, and then stepped off the curb, the idea came to him: if an element could be found that, struck by one neutron, released two, a self-sustaining chain reaction could liberate enormous energy. Nuclear fission had not yet been discovered, but he grasped the principle at once. He had read H. G. Wells’s novel The World Set Free, which imagined “atomic bombs” and he understood the danger as well as the promise. In 1934 he filed a patent on the neutron chain reaction and, to keep it secret, assigned it to the British Admiralty.
In London he also did practical science. Working at St Bartholomew’s Hospital in 1934 with a young physicist, Thomas Chalmers, he discovered a way to separate radioactive isotopes produced by neutron bombardment. The Szilard–Chalmers effect became widely used to prepare isotopes for medicine. From 1935 to 1937 he worked at Oxford’s Clarendon Laboratory, still searching, without success, for an element that would sustain a chain reaction.
The letter to Roosevelt
Foreseeing another European war, Szilard sailed for New York, arriving on January 2, 1938. When news of fission reached America a year later, he immediately suspected that uranium could sustain a chain reaction. Working without a formal post at Columbia University, on borrowed money, he and Walter Zinn showed early in 1939 that fissioning uranium released more neutrons than it absorbed. That night, he said later, he knew the world was headed for grief.
Fearing that Nazi Germany would build a bomb first, Szilard drafted a letter to President Franklin Roosevelt warning of the danger and urging an American research programme. In August 1939, with Wigner and Edward Teller, he persuaded his old friend Einstein to sign it. The Einstein–Szilard letter led to the government’s first uranium research and, ultimately, to the Manhattan Project.
The first reactor
Szilard proposed using graphite to slow neutrons and, crucially, discovered that commercial graphite was contaminated with boron, a neutron absorber; he arranged for boron-free graphite to be produced. German researchers who did not catch the impurity concluded graphite was unusable. As chief physicist at the Metallurgical Laboratory in Chicago he worked on reactor design, and on December 2, 1942, he was present when Enrico Fermi’s Chicago Pile-1 achieved the first self-sustaining nuclear chain reaction, and shook Fermi’s hand. Wigner remarked that if the uranium project could have run on ideas alone, no one but Szilard would have been needed.
He was also its gadfly. Alvin Weinberg recalled him asking all the embarrassing questions, and during one heated dispute over reactor design Arthur Compton and General Leslie Groves moved to dismiss him; the Secretary of War, Henry Stimson, refused. Szilard became an American citizen in 1943. Before he formally joined the project, the Army offered him $25,000 for his inventions, and he refused. He later sold his share in the reactor patent, held jointly with Fermi, to the government for reimbursement of his expenses, about $15,400, plus the standard one-dollar fee. He is also credited with coining the term “breeder reactor.”
Conscience
As Germany’s defeat neared, Szilard’s fear turned from a Nazi bomb to an American one. In July 1945 he drafted a petition, signed by dozens of Manhattan Project scientists, urging President Truman not to use the bomb against Japan without warning and the chance to surrender; it was held back from reaching the president. He predicted that its use would start an arms race with the Soviet Union. After the war he lobbied successfully for civilian rather than military control of atomic energy.
In 1950 he warned on radio that a large thermonuclear bomb rigged with cobalt could, in principle, destroy humanity. In 1960 he met the Soviet leader Nikita Khrushchev in New York and proposed a direct communication link between Moscow and Washington, an idea realised after the Cuban Missile Crisis as the hotline. In 1962 he founded the Council for a Livable World to bring “the sweet voice of reason” about nuclear weapons to Congress and the public.
He also wrote fiction to make his arguments. In the 1949 story “My Trial as a War Criminal” he imagined himself in the dock after a lost war with the Soviet Union, and in a 1960 interview he argued that had Germany dropped atomic bombs on American cities and then lost the war, the United States would have called it a war crime. His campaigning earned him the Atoms for Peace Award in 1959 and the Humanist of the Year award in 1960.
A second career in biology
Szilard had been interested in biology even in 1933, and after the war he turned to it in earnest at the University of Chicago with the chemist Aaron Novick. Together they invented the chemostat, a device for growing microorganisms at controlled rates, and discovered feedback inhibition, the mechanism by which the product of a biochemical pathway switches off its own production. He gave essential advice to Theodore Puck and Philip Marcus in their first cloning of a human cell in 1955. His 1961 book of stories, The Voice of the Dolphins, imagined an international biology laboratory in Europe; when the European Molecular Biology Laboratory was founded, its library was named for him.
Szilard lived for years in hotel rooms and was known for scattering ideas for others to develop. In 1951 he quietly married Gertrud “Trude” Weiss, a physician he had known since 1929.
Last years and legacy
Diagnosed with bladder cancer in 1960, Szilard designed his own course of cobalt-60 radiation therapy at Memorial Sloan-Kettering, and the cancer did not return. He helped Jonas Salk create the Salk Institute for Biological Studies in La Jolla, California, and became a resident fellow there in April 1964. He died in his sleep of a heart attack on May 30, 1964, aged sixty-six.
Szilard never won a Nobel Prize; others built the devices he had patented, and he gave away ideas faster than he could claim them. Yet few people shaped the twentieth century more directly. A Jewish refugee twice over, first from Hungary and then from Germany, he saw sooner than almost anyone both the power locked in the atom and the danger of letting tyrants reach it first, and then spent his last two decades trying to make sure that power would never be used again. Nuclear reactors, molecular biology and the arms-control movement all carry his mark.
Recognition came mostly after his death. A crater on the far side of the Moon was named after him in 1970, the American Physical Society established the Leo Szilard Lectureship Award in 1974, and William Lanouette’s 1992 biography, Genius in the Shadows, brought his life to a wider audience. In Christopher Nolan’s 2023 film Oppenheimer he appears as the restless conscience of the bomb project, the role he had played in life.
Sources & further reading
Leo Szilard, Wikipedia · Leo Szilard, Atomic Heritage Foundation / National Museum of Nuclear Science & History · Leo Szilard, Wikiquote · 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.