The Legacy of John Archibald Wheeler
One thing that has amazed John Wheeler’s students and colleagues alike over the more than 65 years that he has been practicing physics is his versatilityâ€”not just in the kinds of physics that he does, but in the way that he does physics. He has often turned the crank, churning through detailed, complex calculations; and just as often, he has stepped back from this machinery of the theoretical physicist to contemplate, wonder about, and ask the most probing questions about the machinery of the whole universe. The same John Wheeler who calculated how an excited uranium nucleus wiggles its way toward fission has also dared to ask: How come existence? To Wheeler, the fissioning nucleus and the nature of existence are parts of the same fabric of physics.
John Archibald Wheeler likes to use the full name that captures his American lineageâ€”many generations of Archibalds on his mother’s side and many generations of Wheelers on his father’s side. He was born in Jacksonville, Florida in 1911 and grew up in Glendale, California; Youngstown, Ohio; Benson, Vermont; and Baltimore, Maryland. Thanks to a teacher in Vermont who moved him through three grades in one year (in a one-room schoolhouse), he entered the Johns Hopkins University early and earned his Ph.D. there before reaching his 22nd birthday. He says it was the combined engineering-physics library at Hopkins that undid his original intent to become an engineer. When he went to the library to study engineering materials, he found himselfc aptivated by Zeitschrift fur Physik.
From the moment he chose physics as a career, Wheeler looked always for what was most fundamental, what was on the frontier. In 1933, just a year after the neutron and positron were discovered, what lay on the frontier were nuclear physics and the quantum physics of electrons, positrons, and photonsâ€”called pair theory at the time. These subjects and their offshoots, electrodynamics, muons, and weak interactions, occupied Wheeler for nearly 20 years. In that period, besides inventing the S matrix, being the first to study nuclear rotation (with Edward Teller), calculating the scattering of light by light with Gregory Breit (a phenomenon observed 60 years later), and providing a theory of nuclear fission with Niels Bohr, he worked with Richard Feynman on the action-at-a-distance formulation of electrodynamics, conceived of positrons as electrons moving backward in time, calculated the properties of bi-electrons (positronium) and tri-electrons (discovered decades later), and, with Jayme Tiomno, postulated a universal Fermi interaction.
During World War II, Wheeler was a key figure in the Manhattan Project, active in the design and operation of the plutonium-producing reactors at Hanford, Washington. In 1950 he went back to weapons work, helping to design the first hydrogen bomb. Yet throughout his work on fission and fusion weapons, he always found time for his Princeton physics. Wheeler likes to say that his career has moved through three phases, from “Everything is particles” to “Everything is fields” to “Everything is information.”
Particles gave way to fields when Wheeler became captivated by general relativity and gravitation, beginning with his offering of Princeton’s first-ever course on relativity in 1952-53. In the years that followed, it is scarcely an exaggeration to say that he single-handedly changed Einstein’s general theory of relativity from the playground for mathematicians that it had become to the vital field of physicsâ€”both theoretical and observationalâ€”that it is today. He was hardly into the field before he was probing its limits, the limit of small size and quantum fluctuations that led to his concept of quantum foam and the limit of intense gravity that led him to the idea of a geon and into the study of gravitational collapse and eventually his coinage of the term black hole. He says that he fought against the black hole as long as he could, until his last defense was breached and he had to conclude that it was more than likely real, and so deserved a name. For the reality of black holes, there is now abundant evidence. Quantum foam and geons remain to be found. So do Wheeler’s wormholes, although they have made their appearance in popular fiction (Michael Crichton’s Timeline).
In his Fields Period, Wheeler imagined a beginning and end of time, saying: “There was no ‘before’ before the Big Bang?” and “There will be no ‘after’ after the Big Crunch?” (When he said that, the Big Crunch seemed a more likely eventual fate of the universe than it does today.) He took seriously and extended Mach’s principle, the idea that the distribution of mass and energy in the universe is the seat of inertia. And he explored the idea of mutability, that the laws of physics themselves can change, that perhaps the laws we have came about by chance at the time of the Big Bang in the same way that life on Earth arose by chance.
Enter the Information Period. Wheeler, in his later years, has been asking two kinds of questions. One centers around the reality of existence out there independent of our observations. In Wheeler’s hands, this is a physics question, not a philosophical question. The concept of a participatory universe, in which we shape events by observing them, is subject to experimental test. To bring home the point, he devised the delayed choice experiment, which has indeed been carried out in the laboratory and can be imagined over billions of light years.
The other kind of question concerns the nature of physical law. “It from bit?” is Wheeler’s way of asking if the nature and the behavior of the world around us (it) is accounted for entirely by on-off gates of information (bits). Is the computer a better model for nature than the differential equations of continuous variables that has governed physics for several hundred years? Wheeler has no specific theory of it from bit. It is avision. He calls it an idea for an idea, one that he hopes will inspire the productive work of others in the 21st century.
As Wheeler has moved from particles to fields to information, he has increasingly emphasized the mystery of quantum physics. “How come the quantum?” he likes to ask. Recently he wrote, “Relativity is exciting almost beyond measure, yet there is nothing so mysterious about it. Quantum mechanics is a different storyâ€”an incredibly successful theory that has steered much of twentieth-century science yet remains, at its core, entirely mysterious.” He goes on, “Throughout my career, I have tried to look beyond the immediacies of this or that calculation to ask how it all hangs together. In my vision of the world there is a reason, a simple reason, not only for every individual phenomenon, but for every general theory. This magnificent edifice of quantum mechanics is sitting there with, so far, no clear reason for its being. I may not live to see that reason unearthed,” he adds, “but I try, in my small way, to encourage the young to pursue that vision and find the reason. It could make the twenty-first century as dramatically exciting for physicists as the twentieth has been.”