John Archibald Wheeler
John Archibald Wheeler was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr to explain the basic principles of nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for popularizing the term "black hole" for objects with gravitational collapse already predicted during the early 20th century, for inventing the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Stephen Hawking called Wheeler the "hero of the black hole story".
At 21, Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld. He studied under Breit and Bohr on a National Research Council fellowship. In 1939 he collaborated with Bohr on a series of papers using the liquid drop model to explain the mechanism of fission. During World War II, he worked with the Manhattan Project's Metallurgical Laboratory in Chicago, where he helped design nuclear reactors, and then at the Hanford Site in Richland, Washington, where he helped DuPont build them. He returned to Princeton after the war but returned to government service to help design and build the hydrogen bomb in the early 1950s. He and Edward Teller were the main civilian proponents of thermonuclear weapons.
For most of his career, Wheeler was a professor of physics at Princeton University, which he joined in 1938, remaining until 1976. At Princeton he supervised 46 PhD students, more than any other physics professor.
Wheeler left Princeton at the age of 65. He was appointed director of the Center for Theoretical Physics at the University of Texas at Austin in 1976 and remained in the position until 1986, when he retired and became a professor emeritus.
Early life and education
Wheeler was born in Jacksonville, Florida, on July 9, 1911, to librarians Joseph L. Wheeler and Mabel Archibald Wheeler. He was the oldest of four children. His brother Joseph earned a PhD from Brown University and a Master of Library Science from Columbia University. His brother Robert earned a PhD in geology from Harvard University and worked as a geologist for oil companies and several colleges. His sister Mary studied library science at the University of Denver and became a librarian. They grew up in Youngstown, Ohio, but spent a year in 1921 to 1922 on a farm in Benson, Vermont, where Wheeler attended a one-room school. When they returned to Youngstown he attended Rayen High School.After graduating from Baltimore City College high school in 1926, Wheeler entered Johns Hopkins University with a scholarship from the state of Maryland. He published his first scientific paper in 1930, as part of a summer job at the National Bureau of Standards. He earned his doctorate in 1933. His dissertation research work, carried out under the supervision of Karl Herzfeld, was on the "Theory of the Dispersion and Absorption of Helium". He received a National Research Council fellowship, which he used to study under Gregory Breit at New York University in 1933 and 1934, and then in Copenhagen under Niels Bohr in 1934 and 1935. In a 1934 paper, Breit and Wheeler introduced the Breit–Wheeler process, a mechanism by which photons can be potentially transformed into matter in the form of electron–positron pairs.
Early career
The University of North Carolina at Chapel Hill made Wheeler an associate professor in 1937, but he wanted to be able to work more closely with experts in particle physics. He turned down an offer in 1938 of an associate professorship at Johns Hopkins University in favor of an assistant professorship at Princeton University. Although it was a lesser position, he felt that Princeton, which was building up its physics department, was a better career choice. He remained a member of its faculty until 1976.In his 1937 paper "On the Mathematical Description of Light Nuclei by the Method of Resonating Group Structure", Wheeler introduced the S-matrix—short for scattering matrix—"a unitary matrix of coefficients connecting the asymptotic behavior of an arbitrary particular solution with that of solutions of a standard form". Wheeler did not pursue this idea, but in the 1940s Werner Heisenberg developed the idea of the S-matrix into an important tool in elementary particle physics.
In 1938 Wheeler joined Edward Teller in examining Bohr's liquid drop model of the atomic nucleus; they presented their results at a meeting of the American Physical Society in New York. Wheeler's Chapel Hill graduate student Katharine Way also presented a paper, which she followed up in a subsequent article, detailing how the liquid drop model was unstable under certain conditions. Due to a limitation of the liquid drop model, they all missed the opportunity to predict nuclear fission. In 1939, Bohr brought the news of Lise Meitner's and Otto Frisch's discovery of fission to America. Bohr told Leon Rosenfeld, who informed Wheeler.
Bohr and Wheeler set to work applying the liquid drop model to explain the mechanism of nuclear fission. As the experimental physicists studied fission, they uncovered puzzling results. George Placzek asked Bohr why uranium seemed to fission with both very fast and very slow neutrons. Walking to a meeting with Wheeler, Bohr had an insight that fission at low energies was due to the uranium-235 isotope, while at high energies it was mainly due to the far more abundant uranium-238 isotope. They co-wrote two more papers on fission. Their first paper appeared in Physical Review on September 1, 1939, the day Germany invaded Poland, starting World War II.
Considering the notion that positrons were electrons traveling backward in time, in 1940 Wheeler conceived his one-electron universe postulate: that there was in fact only one electron, bouncing back and forth in time. His graduate student Richard Feynman found this hard to believe, but the idea that positrons were electrons traveling backward in time intrigued him, and Feynman incorporated the notion of the reversibility of time in his Feynman diagrams.
Nuclear weapons
Manhattan Project
Soon after the Japanese bombing of Pearl Harbor brought the U.S. into World War II, Wheeler accepted a request from Arthur Compton to join the Manhattan Project's Metallurgical Laboratory at the University of Chicago. He moved there in January 1942, joining Eugene Wigner's group, which was studying nuclear reactor design. He co-wrote a paper with Robert F. Christy on "Chain Reaction of Pure Fissionable Materials in Solution", which was important in the plutonium purification process. It was declassified in December 1955. He gave the neutron moderator its name, replacing Enrico Fermi's term, "slower downer".After the United States Army Corps of Engineers took over the Manhattan Project, it gave DuPont responsibility for the detailed design and construction of the reactors. Wheeler became part of DuPont's design staff. He worked closely with its engineers, commuting between Chicago and Wilmington, Delaware, where DuPont had its headquarters. He moved his family to Wilmington in March 1943. DuPont's task was to build not just nuclear reactors, but an entire plutonium production complex at the Hanford Site in Washington. As work progressed, Wheeler relocated his family again in July 1944, to Richland, Washington, where he worked in the scientific buildings known as the 300 area.
Even before the Hanford Site started up the B Reactor, the first of its three reactors, on September 15, 1944, Wheeler had been concerned that some nuclear fission products might be nuclear poisons, the accumulation of which would impede the ongoing nuclear chain reaction by absorbing many of the thermal neutrons needed to continue a chain reaction. In an April 1942 report, he predicted that this would reduce the reactivity by less than one percent so long as no fission product had a neutron capture cross section of more than 100,000 barns. After the reactor unexpectedly shut down, and then just as unexpectedly restarted about 15 hours later, he suspected iodine-135, with a half-life of 6.6 hours, and its daughter product, xenon-135, which has a half-life of 9.2 hours. Xenon-135 turned out to have a neutron capture cross-section of well over two million barns. The problem was corrected by adding additional fuel slugs to burn out the poison.
Wheeler had a personal reason for working on the Manhattan Project. His brother Joe, fighting in Italy, sent him a postcard with a simple message: "Hurry up". It was already too late: Joe was killed in October 1944. "Here we were", Wheeler later wrote, "so close to creating a nuclear weapon to end the war. I couldn't stop thinking then, and haven't stopped thinking since, that the war could have been over in October 1944." Joe left a widow and baby daughter, Mary Jo, who later married physicist James Hartle.
Hydrogen bomb
In August 1945 Wheeler and his family returned to Princeton, where he resumed his academic career. Working with Feynman, he explored the possibility of physics with particles, but not fields, and carried out theoretical studies of the muon with Jayme Tiomno, resulting in a series of papers on the topic, including a 1949 paper in which Tiomno and Wheeler introduced the "Tiomno Triangle", which related different forms of radioactive decay. He also suggested the use of muons as a nuclear probe. This paper, written and privately circulated in 1949 but not published until 1953, resulted in a series of measurements of the Chang radiation emitted by muons. Muons are a component of cosmic rays, and Wheeler became the founder and first director of Princeton's Cosmic Rays Laboratory, which received a grant of $375,000 from the Office of Naval Research in 1948. Wheeler received a Guggenheim Fellowship in 1946, which allowed him to spend the 1949–50 academic year in Paris.File:Ivy Mike Sausage device.jpg|thumb|left|The "Sausage" device of Ivy Mike nuclear test on Enewetak Atoll. The Sausage was the first true hydrogen bomb ever tested.
The 1949 detonation of Joe-1 by the Soviet Union prompted an all-out effort by the United States, led by Teller, to develop the more powerful hydrogen bomb in response. Henry D. Smyth, Wheeler's department head at Princeton, asked him to join the effort. Most physicists were, like Wheeler, trying to reestablish careers interrupted by the war and reluctant to face more disruption. Others had moral objections. Those who agreed to participate included Emil Konopinski, Marshall Rosenbluth, Lothar Nordheim, and Charles Critchfield, but there was also now a body of experienced weapons physicists at the Los Alamos Laboratory, led by Norris Bradbury. Wheeler agreed to go to Los Alamos after a conversation with Bohr. Two of his graduate students from Princeton, Ken Ford and John Toll, joined him there.
At Los Alamos, Wheeler and his family moved into the house on "Bathtub Row" that Robert Oppenheimer and his family had occupied during the war. In 1950 there was no practical design for a hydrogen bomb. Calculations by Stanisław Ulam and others showed that Teller's "Classical Super" would not work. Teller and Wheeler created a new design known as "Alarm Clock", but it was not a true thermonuclear weapon. Not until January 1951 did Ulam come up with a workable design.
In 1951 Wheeler obtained Bradbury's permission to set up a branch office of the Los Alamos laboratory at Princeton, known as Project Matterhorn, which had two parts. Matterhorn S, under Lyman Spitzer, investigated nuclear fusion as a power source. Matterhorn B, under Wheeler, did nuclear weapons research. Senior scientists remained uninterested and aloof from the project, so he staffed it with young graduate and postdoctoral students. Matterhorn B's efforts were crowned by the success of the Ivy Mike nuclear test at Enewetak Atoll in the Pacific, on November 1, 1952, which Wheeler witnessed. The yield of the Ivy Mike "Sausage" device was reckoned at, about 30 percent higher than Matterhorn B had estimated.
In January 1953 Wheeler was involved in a security breach when he lost a highly classified paper on lithium-6 and the hydrogen bomb design during an overnight train trip. This resulted in an official reprimand.
Matterhorn B was discontinued, but Matterhorn S endures as the Princeton Plasma Physics Laboratory.