Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb

Professor Leo Szilard
Testifying before joint military affairs and commerce subcommittee, Professor Leo Szilard, of the University of Chicago, criticized the War Department and Major General Leslie Groves, chief of the atomic bomb project, for making public a report on the development of atomic energy. Bettmann Archive / Getty Images

Leo Szilard (1898-1964) was a Hungarian-born American physicist and inventor who played a key role in the development of the atomic bomb. Though he vocally opposed using the bomb in war, Szilard felt it was important to perfect the super-weapon before Nazi Germany.

In 1933, Szilard developed the idea of the nuclear chain reaction, and in 1934, he joined with Enrico Fermi in patenting the world’s first working nuclear reactor. He also wrote the letter signed by Albert Einstein in 1939 that convinced U.S. President Franklin Roosevelt of the need for the Manhattan Project to build the atomic bomb.

After the bomb had been successfully tested, on July 16, 1945, he signed a petition asking President Harry Truman not to use it on Japan. Truman, however, never received it.

Fast Facts: Leo Szilard

  • Full Name: Leo Szilard (born as Leo Spitz)
  • Known For: Groundbreaking nuclear physicist
  • Born: February 11, 1898, in Budapest, Hungary
  • Died: May 30, 1964, in La Jolla, California
  • Parents: Louis Spitz and Tekla Vidor
  • Spouse: Dr. Gertrud (Trude) Weiss (m. 1951)
  • Education: Budapest Technical University, Technical University of Berlin, Humboldt University of Berlin
  • Key Accomplishments: Nuclear chain reaction. Manhattan Project atomic bomb scientist.
  • Awards: Atoms for Peace Award (1959). Albert Einstein Award (1960). Humanist of the Year (1960).

Early Life

Leo Szilard was born Leo Spitz on February 11, 1898, in Budapest, Hungary. A year later, his Jewish parents, civil engineer Louis Spitz and Tekla Vidor, changed the family’s surname from the German “Spitz” to the Hungarian “Szilard.”

Even during high school, Szilard showed an aptitude for physics and mathematics, winning a national prize for mathematics in 1916, the year he graduated. In September 1916, he attended Palatine Joseph Technical University in Budapest as an engineering student, but joined the Austro-Hungarian Army in 1917 at the height of World War I.

Leo Szilard
Portrait of Professor of Biophysics, Institute of Radiobiology and Biophysics, at the University of Chicago Dr Leo Szilard (1898 - 1964), Chicago, Illinois, 1957. PhotoQuest / Getty Images

Education and Early Research

Forced to return to Budapest to recover from the dreaded Spanish Influenza of 1918, Szilard never saw battle. After the war, he briefly returned to school in Budapest, but transferred to the Technische Hochschule in Charlottenburg, Germany, in 1920. He soon changed schools and majors, studying physics at the Humboldt University of Berlin, where he attended the lectures of no less than Albert Einstein, Max Planck, and Max von Laue.

After earning his Ph.D. in physics from the University of Berlin in 1922, Szilard worked as von Laue’s research assistant at the Institute for Theoretical Physics, where he collaborated with Einstein on a home refrigerator based on their revolutionary Einstein-Szilard pump. In 1927, Szilard was hired as an instructor at the University of Berlin. It was there that he published his paper “On the Decrease of Entropy in a Thermodynamic System by the Intervention of Intelligent Beings,” which would become the basis for his later work on the second law of thermodynamics.

The Nuclear Chain Reaction

Faced with the threat of the Nazi Party’s anti-Semitic policy and harsh treatment of Jewish academics, Szilard left Germany in 1933. After living briefly in Vienna, he arrived in London in 1934. While experimenting with chain reactions at London’s St. Bartholomew's Hospital, he discovered a method of separating the radioactive isotopes of iodine. This research led to Szilard being granted the first patent for a method of creating a nuclear chain reaction in 1936. As war with Germany grew more likely, his patent was entrusted to the British Admiralty to ensure its secrecy.

Szilard continued his research at Oxford University, where he intensified his efforts to warn Enrico Fermi of the dangers to humanity of using nuclear chain reactions to create weapons of war rather than to generate energy.

The Manhattan Project 

In January 1938, with the impending war in Europe threatening his work, if not his very life, Szilard immigrated to the United States, where he continued his research in nuclear chain reactions while teaching at New York’s Columbia University.

When news reached America in 1939 that German physicists Otto Hahn and Fritz Strassmann had discovered nuclear fission—the trigger of an atomic explosion—Szilard and several of his fellow physicists convinced Albert Einstein to sign a letter to President Roosevelt explaining the devastating destructive force of an atomic bomb. With Nazi Germany now on the verge of taking over Europe, Szilard, Fermi, and their associates feared what could happen to America if Germany built a working bomb first.

Convinced by the Einstein–Szilard letter, Roosevelt ordered the creation of the Manhattan Project, a famed collaboration of outstanding U.S., British, and Canadian scientists dedicated to harnessing nuclear energy for military uses.

As a member of the Manhattan Project from 1942 to 1945, Szilard worked as the chief physicist alongside Fermi at the University of Chicago, where they built the world’s first working nuclear reactor. This breakthrough led to the first successful test of an atomic bomb on July 16, 1945, at White Sands, New Mexico.

Shaken by the destructive force of the weapon he had helped to create, Szilard decided to dedicate the rest of his life to nuclear safety, arms control, and the prevention of further development of nuclear energy for military purposes.

After World War II, Szilard became fascinated by molecular biology and the groundbreaking research being done by Jonas Salk in developing the polio vaccine, eventually helping found the Salk Institute for Biological Studies. During the Cold War, he continued to call for international atomic arms control, the advancement of peaceful uses of nuclear energy, and better U.S. relations with the Soviet Union.

Szilard received the Atoms for Peace Award in 1959, and was named Humanist of the Year by the American Humanist Association, and given the Albert Einstein Award in 1960. In 1962, he founded the Council for a Livable World, an organization dedicated to delivering “the sweet voice of reason” about nuclear weapons to Congress, the White House, and the American public.

The Voice of the Dolphins

In 1961, Szilard published a collection of his own short stories, “The Voice of the Dolphins,” in which he predicts moral and political issues to be triggered by the proliferation of atomic weapons in the year 1985. The title refers to a group of Russian and American scientists who in translating the language of dolphins found that their intelligence and wisdom exceeded that of humans.

In another story, “My Trial as a War Criminal,” Szilard presents a revealing, though fantasized, view of himself standing trial for war crimes against humanity after the United States had unconditionally surrendered to the Soviet Union, after losing a war in which the U.S.S.R. had unleashed a devastating germ warfare program.

Personal Life

Szilard married physician Dr. Gertrud (Trude) Weiss on October 13, 1951, in New York City. The couple had no known surviving children. Before his marriage to Dr. Weiss, Szilard had been an unmarried life partner of Berlin opera singer Gerda Philipsborn during the 1920s and 1930s.

Cancer and Death

After being diagnosed with bladder cancer in 1960, Szilard underwent radiation therapy at New York’s Memorial Sloan-Kettering Hospital, using a cobalt 60 treatment regimen Szilard himself had designed. After a second round of treatment in 1962, Szilard was declared cancer-free. The Szilard-designed cobalt therapy is still used for the treatment of many inoperable cancers.

During his final years, Szilard served as a fellow at the Salk Institute for Biological Studies in La Jolla, California, which he had helped to found in 1963.

In April 1964, Szilard and Dr. Weiss moved to a La Jolla hotel bungalow, where he died of heart attack in his sleep on May 30, 1964, at age 66. Today, a portion of his ashes is buried in Lakeview Cemetery, Ithaca, New York, alongside those of his wife.

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Longley, Robert. "Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb." ThoughtCo, Dec. 6, 2021, thoughtco.com/leo-szilard-4178216. Longley, Robert. (2021, December 6). Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb. Retrieved from https://www.thoughtco.com/leo-szilard-4178216 Longley, Robert. "Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb." ThoughtCo. https://www.thoughtco.com/leo-szilard-4178216 (accessed May 28, 2023).