Last Updated on May 12, 2015, by eNotes Editorial. Word Count: 2442

Niels Bohr
Niels Bohr (1885–1962) was a Danish physicist known as the first to apply quantum theory to the study of atomic and molecular particles. He is also known for proposing the liquid model of the atomic nucleus and for formulating the Bohr theory of the atom. Bohr received a doctoral degree from the University of Copenhagen in 1911. He studied under J. J. Thomson at Cambridge University in England, but, when he learned that Thomson was not interested in his work, Bohr left to work under Ernest Rutherford in Manchester, England. There, Bohr distinguished himself by formulating the Bohr atomic model. He returned to Copenhagen in 1912 and in 1921 was named director of the Institute for Theoretical Physics. Under his direction, the Institute soon gained an international reputation for research in quantum theory and atomic physics. Bohr’s principle of complementarity offered a theoretical basis for quantum physics, which became widely accepted among many scientists, although Albert Einstein continued to dispute it. Bohr’s ground-breaking ‘‘liquid drop’’ model of the atomic nucleus and his ‘‘compound nucleus’’ model of the atom led other scientists to the discovery of nuclear fission. With the outbreak of World War II, Nazi Germany invaded Denmark, as a result of which Bohr and his family fled the country for England and then the United States. He worked on the Manhattan Project in Los Alamos, New Mexico, which developed the first atomic bomb. However, Bohr expressed concern throughout his life about the threat to humanity posed by nuclear warfare.

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Sir James Chadwick
James Chadwick (1891–1974) was an English physicist credited with the discovery of the neutron, for which he received a Nobel Prize in 1935. Chadwick worked with Ernest Rutherford at the Cavendish Laboratory in Cambridge, England, in researching properties of the atomic nucleus. In 1945, he received the honor of being knighted for his accomplishments.

Arthur Compton
Arthur Compton (1892–1962) was an American physicist who shared the Nobel Prize for Physics in 1927 for his research on X rays. Compton received his doctorate from Princeton University in 1916. In 1920, he was made head of the department of physics at Washington University in St. Louis, Missouri. Compton’s research helped to make legitimate Einstein’s quantum theory, which was not yet widely accepted among scientists. In 1923, Compton became professor of physics at the University of Chicago, a post that he retained until 1945. He became the chairman of the committee of the National Academy of Sciences that in 1941 conducted research into the potential development of nuclear weapons, ultimately organizing the Manhattan Project. Compton worked on the Manhattan Project as the director of the University of Chicago Metallurgical Laboratory from 1941 to 1945.

Albert Einstein
Albert Einstein (1879–1955) was a German- Jewish physicist whose theories of relativity forever changed scientific approaches to space, time, and gravity. Einstein was awarded the Nobel Prize for physics in 1921. After Hitler came to power in 1933, Einstein fled Nazi Germany, eventually taking a post at the Institute for Advanced Study at Princeton University in New Jersey, where he remained for the rest of his life. In 1939, Niels Bohr alerted Einstein to the possibility that Germany could develop an atomic bomb. Bohr asked Einstein to write a letter to President Franklin D. Roosevelt, suggesting that the United States initiate research on an atomic bomb. Einstein, however, was not involved in the research carried out by the Manhattan Project and was not even aware of the successful development of the atomic bomb until after it was dropped on Hiroshima. In the wake of this event, Einstein became a vocal advocate for world peace and the prevention of further nuclear warfare.

Enrico Fermi
Enrico Fermi (1901–1954) was an Italian-born physicist who won the Nobel Prize for physics in 1938 for his research on nuclear fission. Fermi earned a doctoral degree at the University of Pisa for his research on X rays. In 1926, he became a professor of theoretical physics at the University of Rome, where he was instrumental in developing a community of brilliant young physicists. On the pretext of traveling to Sweden to receive his Nobel Prize, Fermi fled fascist Italy with his family and settled in the United States. In New York City, Fermi met with other nuclear physicists, eventually becoming a part of the Manhattan Project. Based at the University of Chicago, he developed the first self-sustained nuclear chain reaction, which quickly lead to the making of the first atomic bomb. He became an American citizen in 1944 and, in 1946, was named professor of Nuclear Studies at the University of Chicago.

Richard Feynman
Richard Feynman (1918–1988) was an American theoretical physicist who received the Nobel Prize for physics in 1965 for his work on the theory of quantum electrodynamics. Feynman received his doctorate from Princeton University in 1942. From 1941 to 1942, he worked on the Manhattan Project in Princeton, joining the laboratory at Los Alamos, New Mexico, in 1943. Feynman was among the youngest scientists to hold a leadership position at Los Alamos. From 1945 to 1950, he worked as an associate professor at Cornell University, and from 1950 until his retirement he worked as a professor of theoretical physics at the California Institute of Technology. Feynman is considered one of the most brilliant scientific minds of the twentieth century.

Otto Frisch
Otto Frisch (1904–1979) was an Austrian-born physicist who worked on the Manhattan Project at Los Alamos, New Mexico. Frisch earned his doctorate degree at the University of Vienna in 1926. He worked with his aunt, the physicist Lise Meitner, together discovering and naming uranium fission in 1939. After the War, Frisch became director of the nuclear physics department of the Cavendish Laboratory at Cambridge University in England.

Brigadier General Leslie R. Groves
In September 1942, Brigadier General Leslie R. Groves (1896–1970) was named head of the Manhattan Engineer District, in charge of all army activities concerned with the Manhattan Project. Groves was responsible for contracting independent building industries to construct the facilities at the various research and production sites that made up the Manhattan Project, such as a gaseous diffusion separation plant and a plutonium production facility.

Otto Hahn
Otto Hahn (1879–1968) was a German chemist who won the Nobel Prize for chemistry in 1944 for his discovery (along with Fritz Strassmann) of nuclear fission. Hahn received a doctorate degree from the University of Marburg in 1901. At the University of Berlin, he conducted research on radioactivity and in 1911 joined the Kaiser Wilhelm Institute for Chemistry. During World War I, he was instrumental in developing chemical warfare. Although his research was instrumental to the development of the atomic bomb, throughout the remainder of his life he opposed the further development of nuclear weapons.

Lise Meitner
Lise Meitner (1878–1968) was a Jewish Austrian- born physicist whose collaborative research with Otto Hahn, Fritz Strassmann, and her nephew Otto Frisch resulted in the discovery and naming of uranium fission. Meitner received her doctorate from the University of Vienna in 1906. In 1907, she began working with Hahn in Berlin on research in radioactivity. In 1938, she fled Nazi Germany for Sweden.

Robert Oppenheimer
Robert J. Oppenheimer (1904–1967) was an American theoretical physicist most widely known as the director of the Los Alamos laboratory of the Manhattan Project, which developed the first atomic bomb. Upon graduating from Harvard, Oppenheimer studied atomic physics under Lord Rutherford at the Cavendish Laboratory at Cambridge. He received his doctoral degree from Göttingen University in 1927, after which he taught physics at the University of California at Berkeley and the California Institute of Technology. His collaboration with a team of scientists on the Manhattan Project lead to the first nuclear explosion test in 1945 at Alamogordo, New Mexico. In 1947, Oppenheimer took a post as head of the Institute for Advanced Study at Princeton University. From 1947 to 1952, he was chairman of the General Advisory Committee of the Atomic Energy Commission. In 1953, during the Red Scare in which many intellectuals were accused of treason, Oppenheimer was put on trial for suspicion of having leaked military secrets, based on his earlier sympathies with communism. He was found not guilty, but his position with the Atomic Energy Commission was terminated. The Federation of American Scientists, however, supported Oppenheimer. In 1963, President Lyndon B. Johnson presented Oppenheimer with the Enrico Fermi Award of the Atomic Energy Commission, thus officially retracting all public denunciation of the scientist.

Sir Rudolf Peierls
Rudolf Peierls (1907–1995) was a Germanborn physicist whose theoretical work was instrumental in the development of the atomic bomb. Peierls worked with Otto Frisch at the University of Birmingham, in England, where they collaborated on a memo explaining the theories that suggested the possibility of creating an atomic bomb. He became a British citizen in 1940 and in 1943 joined the team of British scientists who moved to Los Alamos, New Mexico, to work on the Manhattan Project. After the war, he returned to his post as a professor at Birmingham. In 1963, he left Birmingham to become a professor at the University of Oxford. Peierls was knighted in 1968.

Max Planck
Max Planck (1858–1947) was a German theoretical physicist who was awarded the 1918 Nobel Prize for physics for his formulation of quantum theory. Planck earned his doctoral degree in 1879 from the University of Munich. In 1892, he became a professor at the University of Berlin, a position that he held throughout his life. Although it was not immediately recognized as such by the scientific community, his quantum theory eventually revolutionized theoretical physics. While Einstein was instrumental in championing Planck’s achievement, Planck was instrumental in calling attention to the significance of Einstein’s theory of relativity. Although Planck was openly opposed to Hitler’s racist policies, he remained in Germany throughout World War II to continue his research.

President Franklin Roosevelt
President Franklin Delano Roosevelt (1882– 1945) was in his third term of presidency when the United States entered World War II. In 1939, he received a letter from Einstein alerting him to the potential for developing an atomic bomb, but he failed to see the true significance of this information until the United States entered the war in 1941. Roosevelt died in office on April 12, 1945, several months before the dropping of the first atomic bombs and ending of World War II.

Sir Ernest Rutherford
Ernest Rutherford (1871–1937) was a New Zealand-born British physicist awarded the Nobel Prize for chemistry in 1908 for his research that led to the development of nuclear physics (also referred to as atomic physics). In 1895, Rutherford came to the Cavendish Laboratory at Cambridge, in England, where he studied under J. J. Thomson. In 1898, Rutherford took a post as a professor of physics at McGill University in Montreal, Canada. He moved back to England in 1907 to work at the University of Manchester. Rutherford’s most important accomplishment was his nuclear theory of atomic structure, called the Rutherford atomic model. In 1914, he was knighted for his many accomplishments. In 1919, he became head of the Cavendish Laboratory.

Major Charles Sweeney
Major Charles W. Sweeney piloted the B-29 bomber, named the Great Artiste, which dropped the atomic bomb over Nagasaki on August 9, 1945.

Leo Szilard
Leo Szilard (1898–1964) was a Hungarian physicist who was a key figure in the formation of the Manhattan Project. Szilard earned his doctoral degree from the University of Berlin in 1922. He worked as a staff member at the Institute of Theoretical Physics at the University of Berlin until 1933, when Hitler came to power, and he left Germany. Szilard worked for several years at the college of St. Bartholomew’s Hospital in England, before moving to the United States to occupy a post at Colombia University. From 1942 to 1945, Szilard worked on the Manhattan Project with Fermi’s research team at the University of Chicago. After the war, he accepted a position as professor of biophysics at the University of Chicago. Following the war, Szilard became a strong advocate of the use of atomic energy for peaceful purposes and supported limitations on the nuclear arms race.

Edward Teller
Edward Teller (1908-) was a Hungarian-born Jewish nuclear physicist who worked on the Manhattan Project. Teller worked with Enrico Fermi at the University of Chicago before joining the research team at Los Alamos, New Mexico. However, Teller was more interested in research into the development of a hydrogen bomb, which was considered a lesser priority during World War II. After the war, however, Teller became a leading proponent of United States efforts to create a hydrogen bomb, which was potentially more powerful than the atom bomb. In 1951, Teller collaborated with Stanislaw Ulam in a major breakthrough for research on the hydrogen bomb known as the Teller- Ulam configuration. Teller was thus dubbed the ‘‘father of the H-bomb.’’

Sir J. J. Thomson
J. J. Thomson (1856–1940) was an English physicist who discovered the electron in 1897. Thomson began research at the Cavendish Laboratory of Cambridge University in 1880 and in 1884 was made chair of the physics department there. For his accomplishments, Thomson was granted the Nobel Prize for physics in 1906 and was knighted in 1908. Thomson was an influential teacher at Cavendish, and many of his students, including Ernest Rutherford, were awarded Nobel Prizes.

Colonel Paul Tibbets Colonel Paul W. Tibbets, Jr. was the pilot who flew the B-29 bomber, named Enola Gay, which dropped the atomic bomb on Hiroshima, in Japan, on August 6, 1945.

President Harry Truman
Harry S. Truman (1884–1972) was the thirtythird president of the United States. He took office on April 12, 1945, the day of President Roosevelt’s death. Upon being sworn into office, Truman was apprised of the developments of the Manhattan Project, about which he had known little up to that point. While he attended the Potsdam Conference to discuss peace negotiations between the Allies and a defeated Germany, he received notice that the first atomic bomb had been successfully tested by the Manhattan Project on July 16. From Potsdam, a message was sent to Japan, threatening the use of a devastating new weapon unless they agreed to unconditional surrender.When Japan refused this offer, Truman ordered the dropping of the atomic bomb on Hiroshima on August 6, 1945, and on Nagasaki on August 9, 1945.

H. G. Wells
H. G. Wells (1866–1946) was an English writer known today primarily for his classic science fiction novels such as The Time Machine (1895), The Island of Doctor Moreau (1896), The Invisible Man (1897), and The War of the Worlds (1898). Wells’ novel The World Set Free (1914) was prophetic in essentially predicting atomic warfare.

Eugene Wigner
Eugene Wigner (1902–1995) was a Hungarianborn physicist who shared the 1963 Nobel Prize for physics for his work on nuclear physics. Wigner received his doctoral degree in 1925 from the Institute of Technology in Berlin. In 1938, he became a professor of mathematical physics at Princeton University, a position that he held until 1971, when he retired. In 1939, Wigner, with Leo Szilard, helped to convince Albert Einstein to draft a letter to President Roosevelt, alerting him of the possibility of developing an atomic bomb. Wigner worked with Enrico Fermi at the University of Chicago Metallurgical Laboratory, part of the Manhattan Project.