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Leo Szilard (1898-1964) was a Hungarian-American physicist and inventor.


Leo Szilard was born Leo Spitz on February 11, 1898 in Budapest, Hungary. He developed an interest in physics at age thirteen and attended public school prior to being drafted into the Austro-Hungarian Army in 1917, where attended officer’s training school. However, influenza prevented him from an active duty assignment. After World War I ended, he left Hungary for Berlin in 1919.

In Berlin, Szilard studied Engineering at the Institute of Technology (Technische Hochscule). In 1921 he enrolled at the University of Berlin to study Physics under Max von Laue. Szilard earned his Ph.D. in August of 1922 and completed his postdoctoral work at the Kaiser Wilhelm Institute in Berlin. During his stay at the Institute he became close friends with Albert Einstein.

When Hitler rose to power in 1933, Szilard moved to England. He developed the idea of the nuclear chain reaction in 1933. While in England, Szilard also collaborated with many individuals and worked as a research physicist at the Clarendon Laboratory between 1935 and 1937. During this time, he visited the United States several times and by 1938 became a visiting lecturer there.


In 1940 Szilard became an American citizen and moved to New York. He began working at Columbia University (Pupin Laboratories) where he collaborated with Enrico Fermi, Walter Zinn, and Herbert Anderson. At Columbia Szilard submitted his nuclear break-through manuscript titled: “Divergent Chain Reactions in a System Composed of Uranium and Carbon” in February of 1940.

When World War II started, Szilard became intensely concerned about the possible nuclear weapons development programs that could be initiated. As a result of these concerns, his work on atomic energy intensified. He led an effort to have all nuclear-related research data withheld from publication, to help prevent Germany from obtaining any information, or possibly creating an atomic bomb.

These concerns also prompted him, with the assistance of Eugene Wigner and Edward Teller, to contact Albert Einstein. After sharing his fears with Einstein and obtaining his consent, Szilard drafted a letter that Einstein signed. The now-famous Einstein Letter was subsequently delivered by Alexander Sachs to President Franklin D. Roosevelt in October of 1939. This letter outlined the possibility of achieving a nuclear chain reaction and its implications for the development of nuclear weapons for national defense. It also requested government support to conduct a large-scale experiment to prove whether or not a sustained nuclear chain reaction was possible.

President Roosevelt approved the funding and the project. Szilard began procuring suitable quality graphite and uranium, the necessary materials for constructing a large-scale chain reaction experiment. This experiment was successfully demonstrated on December 2, 1942 at the University of Chicago. This successful demonstration was partially the result of Szilard’s atomic theories, his uranium lattice design, and the identification and mitigation of a key graphite impurity (boron) through a joint collaboration with graphite suppliers.

Szilard was the chief physicist at the Chicago Metallurgical Laboratory from February 1942 to July 1946. He worked for Arthur H. Compton, the head of the Met Lab. Szilard helped build Chicago Pile-1, the first neutronic reactor to achieve a self-sustaining nuclear chain reaction. Szilard patented creating a neutron-based chain reaction in 1934 – although, as historian Alex Wellerstein explains, his ideas in the patent had some problems scientifically and would prove to be wrong in parts.

Szilard was very uneasy about the military’s dominant role in managing the Manhattan Project, complicated government administration, and flawed security regulations. He was very vocal about these issues as well as documenting them through his prolific letter writing.

Szilard viewed the development and eventual production of the atomic bomb as a necessary evil or counter-measure to the possibility of a German atomic bomb. After Germany surrendered and the war ended in Europe, he organized his colleagues to collectively voice the need to adopt limitations regarding the use of an atomic bomb. He drafted a letter and circulated it to the various Manhattan Project locations. The letter urged President Roosevelt to practice restraint in using the atomic bomb, but the letter was never forwarded to the President’s attention. Szilard realizing this, scheduled a meeting with Eleanor Roosevelt requesting that she personally pass the letter to the president. President Roosevelt died before the meeting with Eleanor could take place.

In June of 1945 the Franck Report was released. The Franck Report committee was appointed by Arthur Compton with James Franck as its head. Most of its contents was written by Eugene Rabinowitch, and signed by James Franck, Donald J. Hughes, J.J. Nickson, Eugene Rabinowitch, Glenn T. Seaborg, J.C. Steans, and Leo Szilard. This report outlined the possibilities and dangers of initiating or engaging in a nuclear arms race. In addition, the report also advocated for having a non-combat demonstration of the atomic bomb instead of first-use on a Japanese city.

On June 21, 1945 the report was presented to the interim committee appointed by President Harry Truman to advise him on the use of the bomb. The recommendation for a demonstration was rejected. Szilard followed by circulating another petition in July 1945 urging President Truman not to drop the atomic bomb on Hiroshima. The final version of this petition was signed by sixty-eight scientists assigned to the Met Lab. The petition was strongly opposed by General Leslie Groves. As a result, it never reached the president.

In September of 1942, President Truman advocated for the passage of the May-Johnson Bill, designed to place atomic energy in the ownership of the military. Szilard worked to help defeat this bill along with many Met Lab and Oak Ridge Lab scientists.


On June 1, 1946, Leo Szilard resigned from the Met Laboratory, to focus on molecular biology. He helped to found the Salk Institute for Biological Studies. Between 1946 and 1954, he served as a part-time professor at the Institute of Radiology and Biophysics (University of Chicago), a part-time advisor at the Office of Inquiry into the Social Aspects of Atomic Energy (University of Chicago), and a visiting professor of biophysics at Brandeis University.

In June of 1956, he became a professor of biophysics at the recently formed Enrico Fermi Institute for Nuclear Studies at the University of Chicago. Throughout the 1950s and early 1960s Szilard continued to focus on biological research that resulted in numerous scientific papers and articles. His theory on aging became a major subset of his research and was a reoccurring interest in his later years.

He applied for many patents, including one for the linear accelerator and cyclotron, and came up with many important scientific concepts, including the nuclear chain reaction and key ideas in thermodynamics. In 1955, Szilard and Enrico Fermi jointly received the patent for a neutronic reactor.

He continued his political activism, calling for international arms control, peaceful uses of nuclear energy, and improved U. S.-Soviet relations. In 1947, The Bulletin of the Atomic Scientists published a “Letter to Stalin” written by Leo Szilard. In the letter, he appealed to all world leaders to begin an open dialogue with the intent to exchange ideas to halt the rapidly escalating Cold War. In 1962, he founded the Council for a Livable World, warning of the threat of nuclear war.

Szilard’s political activities even inspired Albert Einstein and Bertrand Russell. As a result, the International Conference of Concerned Scientists was formed. The first conference took place in 1957 at Pugwash, Nova Scotia. The “Pugwash” conferences have continued to the present day. Between October 1959 and 1960, he conducted a series of interactions with Soviet Premier Nikita Khrushchev, culminating in New York with a two hour interview. During this interview, Szilard proposed the creation of a “Hot Line” between Moscow and Washington. The purpose was to foster and speed up communication between the Soviet Union and the United States. The “Hot Line” was implemented after the 1962 Cuban Missile Crisis and remains in use today.

In addition to Szilard’s research, and his dedication to nuclear, social, and political issues, he still found time to write. He wrote “The Voice of the Dolphins “in 1960. This book provides a futuristic, fictionalized, account where dolphins inherit the earth as a result of human civilization’s failure to be suitable caregivers of the planet. He also created an extensive series of historical tape recordings that archives his involvement in the Manhattan Project and other portions of his life.

Always a visionary, Szilard, sacrificing many years of his career and having no permanent post for himself, worked tirelessly to find suitable positions for many of the other scientists fleeing Germany. Often working by himself, at the detriment of his own safety and career, Szilard was responsible for numerous colleagues being offered positions. He organized several groups and worked with the Academic Assistance Council, a London-based group headed by Ernest Rutherford that helped refugee scientists and scholars.

Szilard continued his advocacy for global cooperation for the remainder of his life. In 1961 he completed a lecture tour to eight college campuses. On May 30, 1964, Leo Szilard died of a heart attack just three months after moving to La Jolla, California where he intended to continue his biological research as a Resident Fellow of the Sauk Institute.

For more information about Szilard, check out William Lanouette’s biography Genius in the Shadows: A Biography of Leo Szilard, the Man Behind the Bomb” or watch an interview with Lanouette on “Voices of the Manhattan Project.”

Much of the information for this profile was provided by David Wargowski. In 2019, Wargowski and Dr. Henry Frisch created a Leo Szilard Exhibit located at the Albert A. Michelson Center for Physics Building of the University of Chicago.

Leo Szilard's Timeline
1898 Feb 11th Born in Budapest, Austria-Hungary.
1923 Received his Ph.D. from the Humboldt University of Berlin.
1929 Applied for a patent for a cyclotron.
1933 Left Germany because of rising anti-Semitism and moved to England.
1933 Sep 12th While crossing the street in London, Szilard has an epiphany that leads him to develop the idea of the nuclear chain reaction.
1938 Began work at Columbia University.
1939 Wrote the letter signed by Albert Einstein urging President Roosevelt to explore creating a nuclear weapons program.
1942 Worked with Enrico Fermi on Chicago Pile-1.
19431945 Worked on the Manhattan Project at the Metallurgical Laboratory at the University of Chicago.
1945 Drafted a letter signed by dozens of Manhattan Project scientists urging President Truman to provide a demonstration of the bomb for the Japanese before using it on a city.
1947 Began working on molecular biology.
1957 Helped found the Salk Institute for Biological Studies.
1962 Founded the Council for a Livable World.
1964 May 30th Died in La Jolla, California.

Leo Szilard. Photo courtesy of Argonne National Laboratory

Leo Szilard. Photo courtesy of Argonne National Laboratory

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