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Important Scientists

JOHN WHEELER

(1911 - 2008)
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John Wheeler
John Wheeler

John Wheeler was an eminent American theoretical physicist, perhaps best known for having initially coined the terms “black hole”, “wormhole” and several other colourful phrases. In the 1930s, he developed the important “S-matrix” in particle physics and worked with Niels Bohr to explain nuclear fission in terms of quantum physics. Later, he developed the equation of state for cold, dead stars, helped popularize the study of general relativity in the mainstream of theoretical physics, and to firm up the theory and evidence for black holes. He also collaborated with Albert Einstein in his search for a Grand Unified Theory of physics.

John Archibald Wheeler was born on 9 July 1911 in Jacksonville, Florida, USA, the oldest child in a family of librarians. The family moved around a lot, and over the years they lived in Florida, California, Ohio, Washington D.C., Maryland and Vermont. He attended the Baltimore City College high school, graduating in 1926, and went on to study physics under the supervision of Karl Herzfeld at Johns Hopkins University. He received his doctorate in 1933, with a dissertation on the theory of the dispersion and absorption of helium. Soon after graduating, he travelled to Copenhagen, where he worked for a time with Niels Bohr, the godfather of the quantum theory revolution. He married Janette Hegner in 1935, and they were to have two daughters (Alison Letitia) and a son (James), and were to stay together for the whole of their long lives.

He became a professor of physics at Princeton University in 1938, where he remained, with an interruption during World War II, for 38 years until 1976. During his very early years at Princeton, he introduced the scattering-matrix (or “S-matrix”), which relates the initial state and the final state for an interaction of particles, and which was to become an indispensable tool in particle physics.

Wheeler knew Einstein well, and sometimes used to hold seminars with his students in Einstein’s home. When Bohr visited the United States in 1939, with news of the achievement of nuclear fission in Germany, he and Wheeler collaborated on the development of the influential “liquid drop” model of the atom, first proposed by George Gamow, in an attempt to explain the theoretical basis of nuclear fission.

Together with many other leading physicists, Wheeler interrupted his academic career during World War II to participate in the development of the U.S. atomic bomb as part of the Manhattan Project at the Hanford Site in Washington state. Among other things, he correctly anticipated that the accumulation of "fission product poisons" (particularly an isotope of xenon) would eventually impede the ongoing nuclear chain reaction by absorbing neutrons.

After the war, he returned to Princeton to resume his academic career, and began to teach a course on Einsteinian gravity in the early 1950s, when it was still considered not quite an acceptable field of study, although for many years he resisted the idea that the laws of physics could lead to something as apparently absurd as a singularity. He also continued to do government work, however, and was integrally involved in the development of the American hydrogen bomb in the early 1950s at Los Alamos and at Princeton (where he was responsible for setting up Project Matterhorn). At one point, in 1953, he was he officially reprimanded for apparently losing a classified paper on the hydrogen bomb. His somewhat hawkish views on national defence, the Vietnam War and missile defense often ran counter to those of his more liberal colleagues.

With his government research finished, Wheeler returned to Princeton, where he collaborated with Albert Einstein in the waning years of his life on a “unified field theory” of the physical forces of nature. In 1956, he helped to determine what types of materials are located inside dead, cold stars with the “Harrison-Wheeler Equation of State for Cold, Dead Matter”, ascertaining that it would be largely iron because the efficient fusion process breaks down when the core reaches that state. In 1957, while working on extensions to general relativity, he introduced the word “wormhole” to describe hypothetical tunnels in space-time.

In the late 1950s, he formulated the theory of geometrodynamics, a program of physical and philosophical reduction of all physical phenomena (including gravitation and electromagnetism) to the geometrical properties of a curved space-time. However, he later abandoned this theory in the early 1970s, having failed to explain some important physical phenomena, such as the existence of fermions (electrons, muons, etc) and gravitational singularities.

He always gave a high priority to teaching, and continued to teach freshman and sophomore physics even after he had achieved fame, believing that the young minds were the most important. He was known for his high-energy lectures, writing rapidly on chalkboards with both hands, and twirling to make eye contact with his students. Among his graduate students were some important theoreticians of the later 20th Century, including Richard Feynman, Kip Thorne and Hugh Everett.

He worked extensively on the theory of gravitational collapse, and he is usually credited with coining the term “black hole” during a 1967 talk at the NASA Goddard Institute of Space Studies (although in fact he was prompted to it by a shout from the audience). Along with Dennis Sciama at Cambridge and Yakov Borisovich Zeldovich in Moscow, Wheeler was integral to the so-called “Golden Age of general relativity” of the 1960s and 1970s, a paradigm shift during which the study of general relativity (which had previously been regarded as something of a curiosity) entered into the mainstream of theoretical physics. Under his leadership, Princeton became the leading American centre of research into Einsteinian gravity. The comprehensive general relativity textbook “Gravitation”, which he co-wrote with Charles Misner and Kip Thorne, appeared in 1973, and it became the most influential relativity textbook for a generation.

After Einstein’s death, Wheeler continued his pursuit of the role of gravity in a Grand Unified Theory of physics, and became something of a pioneer in the field of quantum gravity. This led to his collaboration with Bryce DeWitt and the development of the Wheeler-DeWitt Equation or, as Wheeler pereferred to call it, the “wave function of the universe”. Other products of Wheeler’s colourful way with words include the phrase "black holes have no hair" (to describe how black holes should be a perfect, simply definable shape, and not have any sorts of projections out of them), “mass without mass" (to indicate the need to effectively remove any mention of mass from the basic equations of physics), “it from bit” (to describe how information is fundamental to the physics of the universe, just as it is in computing) and “quantum foam” (to describe a space-time churned into a lather of distorted geometry).

In 1976, faced with mandatory retirement at Princeton, Wheeler moved to the University of Texas at Austin, where he held the position as director of the Center for Theoretical Physics from 1976 until his retirement in 1986. It was during this time (specifically in 1978) that he proposed a variation of Thomas Young’s double-slit experiment (and Richard Feynman’s later refinement), often referred to as the "delayed choice” experient. He posited that the detection of a photon even AFTER passing through a double slit would be sufficient to change the outcome of the experiment and the behaviour of the photon. Therefore, if the experimenters know which slit it goes through, the photon will behave as a particle, rather than as a wave with its associated interference behaviour. This somewhat counter-intuitive hypothesis was finally verified in a practical experiment in 2007.

Wheeler returned to Princeton as a professor emeritus in 1986, where he remained for the next twenty years. His so-called “Everything Is Fields” phase (in which he viewed the universe and all the particles which make it up as mere manifestations of electrical, magnetic and gravitational fields and space-time itself) gave way to an "Everything Is Information" phase (when he focused on the idea that logic and information is the bedrock of physical theory). He also began to speculate that the laws of physics may be evolving in a manner analogous to evolution by natural selection in biology, and he coined the term “participatory anthropic principle” to describe his version of the anthropic principle, in which observers (i.e. us) are necessary to bring the universe into being.

Wheeler received numerous honours over the years, including the National Medal of Science, the Albert Einstein Prize, the Enrico Fermi Award, the Franklin Medal, the Niels Bohr International Gold Medal and the Wolf Foundation Prize. He was a past president of the American Physical Society, and a member of the American Philosophical Society, the Royal Academy, the Accademia Nazionale dei Lincei, the Royal Academy of Science and the Century Association. He was awarded honorary degrees from 18 institutions.

Wheeler died of pneumonia on 13 April 2008, at the grand old age of 96, in Hightstown, New Jersey.

 
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