John Archibald Wheeler

American physicist

• Born: July 9, 1911; Jacksonville, Florida
• Died: April 13, 2008; Princeton, New Jersey

American physicist John Archibald Wheeler made important contributions to the theories of general relativity, quantum gravity, and quantum electrodynamics. He is known for his role in the development of both the atomic and the hydrogen bombs, as well as for naming one of the strangest astronomical bodies known to science: the black hole.

Primary field: Physics

Specialties: Quantum mechanics; relativity; nuclear physics

Early Life

Wheeler was born on July 9, 1911, in Jacksonville, Florida. As a child he showed an aptitude for mathematics and was always attracted to scientific topics in his reading. At the age of sixteen Wheeler enrolled at Johns Hopkins University in Baltimore, Maryland, as an engineering student but soon realized that his real passion was for the science of physics.

He graduated with a PhD in physics in 1933 and went on to become a professor of physics at the University of North Carolina. In 1938 Wheeler was invited to teach at Princeton University, where he would write, give lectures, and conduct research for nearly four decades.

Although Princeton had become his professional home, in the late 1930s Wheeler spent a year abroad working with the Danish physicist Niels Bohr at the University of Copenhagen. It was at that point that his work on nuclear physics began in earnest.

During the same period, the rumblings of the Second World War could be heard in the background. Scientists and politicians all over the world were starting to realize that nuclear fission—a complex process by which the nucleus of an atom can be split apart, creating a tremendous burst of energy—could potentially be used to create a bomb that would be more powerful than any that had been made before. They called this hypothetical weapon an atomic bomb.

Life’s Work

Wheeler and Bohr wrote a paper in 1939 explaining their theory of how nuclear fission actually takes place. The paper also suggested that if one were to build a bomb using nuclear fission, the best possible source of atoms and nuclei would be the artificial element known as uranium-235—the substance that is, in fact, the major ingredient used to make an atomic bomb.

The US government sponsored the development of the first atomic bomb through a World War II–era venture known as the Manhattan Project. In 1951, Project Matterhorn was initiated to develop the even more powerful hydrogen bomb, based on similar scientific principles. Wheeler worked on both projects and was awarded the Atomic Energy Commission’s 1968 Enrico Fermi Award for his contributions to national defense. Beginning in the 1940s, Wheeler became interested in a theory known as quantum physics, or quantum mechanics. This branch of physics emerged in the early years of the twentieth century and was still developing at the time that it caught Wheeler’s attention (his mentor, Bohr, had helped to establish the field).

In the 1950s and 1960s Wheeler became involved in an area of quantum mechanics called quantum electrodynamics. Together with Richard Feynman, a graduate student at Princeton who went on to win the Nobel Prize in Physics in 1965, Wheeler made various contributions in this field.

In addition, Wheeler had become interested in Albert Einstein’s theory of general relativity and its relationship to quantum mechanics; Wheeler is commonly credited with reviving interest in general relativity. With these two theories in mind, he started to wonder about the nature of space-time, which is the term physicists use to describe the cosmic backdrop of the universe. Space-time can be thought of as the background setting for every event that takes place, anywhere; it includes all three dimensions of space, plus time. Thinking in quantum terms, Wheeler tried to imagine space-time on an extremely small scale; specifically, he thought about the level of the Planck length. This is an unimaginably tiny unit of measurement, about 10 to the power of minus 35 meters.

The basis of Wheeler’s hypothesis is that gravity’s force works through fields, like the magnetic fields that surround a magnet. General relativity states that gravity comes about as a result of the way space-time curves. Quantum mechanics has demonstrated that fields constantly experience tiny variations, or quick random jumps in the level of their energy. Combining general relativity and quantum mechanics, Wheeler put forward the theory that, on a scale as small as the Planck length, space-time itself experiences uncountable sudden changes in its shape and structure that make it look almost like it is boiling. He called this quantum foam. No one has ever found any evidence for quantum foam, but it is an example of Wheeler’s ability to make connections between different scientific theories.

In the late-1960s Wheeler famously coined the term “black hole” for the mysterious space objects he was studying—which had until then been called frozen stars, dark stars, or collapsed stars. The notion of a black hole dated back to eighteenth-century natural philosopher John Michell, who speculated about what might happen if an object the size of the sun increased in mass so much that its “escape velocity” was greater than the speed of light. Due to gravitational pull, the more dense and massive an object is, the more powerfully it tends to tug anything around it (dust, asteroids, light) toward itself; additionally, the more dense and massive an object is, the faster other things around it have to travel away from it in order to escape the tremendous pull of its gravity. In the case of a star, any light traveling away from the object would simply be pulled back towards it. Since light could never bounce off the object and be seen by the human eye, Michell realized that the object would be invisible.

In 1939, scientists Robert Oppenheimer and Hartland Snyder guessed that such an object might be formed if a very massive star ran out of energy and all its matter collapsed into a single tiny, incredibly dense point called a singularity. Wheeler initially thought the idea of a singularity was ridiculous and did not believe that a dying star would experience this kind of gravitational collapse. Wheeler began to study cold, dead stars to prove that Oppenheimer and Snyder’s theory was wrong. The more he examined dead stars, however, the more evidence Wheeler found that a very massive star really would collapse in on itself when it died. By 1967 he had not only become an enthusiastic supporter of the singularity theory, he had also given John Michell’s hypothetical object the name “black hole.”

Impact

Throughout Wheeler’s career he made significant contributions to areas of science including nuclear and particle physics, black holes and gravitation, and information theory studies, while also changing conceptions of general relativity. He developed the concept of wormholes and formulated geometrodynamics. In his quantum mechanics research he proposed what became known as Wheeler’s delayed choice experiment, a thought experiment for detecting photons. His work with other researchers in the field of quantum mechanics also led to the development of the “many-worlds interpretation” of reality and conception of the universe.

As his career progressed, Wheeler continued to make important contributions to the development of research in many areas of physics, especially concerning the topics of black hole physics and quantum gravity. Wheeler’s 1973 book Gravitation (coauthored with Charles S. Misner and Kip S. Thorne) is a landmark text on the subject of gravitation physics, general relativity, space-time, and other subjects. In 1976 he accepted a position as professor of physics at the University of Texas at Austin, where he continued to teach and study until his retirement in 1986.

Wheeler was the recipient of the 1969 Franklin Medal, the 1970 National Medal of Science, and the 1988 Albert Einstein Medal. In 1997 he was honored with the prestigious Wolf Prize in Physics. Wheeler served as a president of the American Physical Society and as a member of organizations including the American Philosophical Society, the Royal Academy, the Accademia Nazionale dei Lincei, and the Royal Academy of Science. In the 1970s, he was appointed to the US General Advisory Committee on Arms Control and Disarmament. Wheeler died in 2008 at the age of ninety-six.

Bibliography

Ford, Kenneth W. “John Wheeler’s Work on Particles, Nuclei, and Weapons.” Physics Today 62.4 (2009): 29–33. Print. Describes the life and work of nuclear physicist John Wheeler. Discusses Wheeler’s major career achievements.

Misner, Charles, Kip Thorne, and Wojciech Zurek. “John Wheeler, Relativity, and Quantum Information.” Physics Today 62.4 (2009): 40–46. Print. Discusses Wheeler’s work on relativity and quantum theory and describes his teaching and research methods.

Wheeler, John Archibald, and Kenneth Ford. Geons, Black Holes, and Quantum Foam: A Life in Physics. New York: Norton, 1998. Print. Autobiography of John Wheeler, documenting his life and his scientific career.