第4章
The Making of a Physicist
After moving to Baltimore's Mt. Washington neighborhood, Wheeler needed a scholarship to attend college despite his paper route savings. With a Maryland state scholarship secured through a local politician, he enrolled at Johns Hopkins as an engineering student at sixteen. His path changed when he discovered physics journals in the engineering library and was captivated by the excitement of quantum mechanics shared by his chemistry professor.
Wheeler had the extraordinary fortune to study physics during what many historians consider its golden age. The late 1920s and early 1930s saw the discovery of quantum mechanics, the uncertainty principle, antimatter, the neutron, the unification of quantum theory with relativity and electromagnetism, the invention of the cyclotron, and the realization that the universe is expanding.
Though cutting-edge physics hadn't fully penetrated standard courses, Wheeler's education thrived through apprenticeship. At Hopkins, each advanced student rotated monthly between professors, allowing him to learn firsthand from masters like Augustus Pfund in physical optics, Gerhard Dieke in quantum mechanics applications to atomic spectra, and Joyce Bearden in X-ray spectra. Norman Feather from Rutherford's Cavendish Laboratory introduced him to nuclear physics, teaching him the exacting work of counting alpha particle flashes on zinc sulphide screens-the same detection method used when Rutherford discovered the atomic nucleus in 1911.
Karl Herzfeld, an Austrian emigre and leading theoretical physicist at Hopkins, became Wheeler's dissertation advisor. Under Herzfeld's direction, he began researching light absorption and scattering in helium atoms using quantum-mechanical methods. This work produced his first solo paper, "Theory of the Dispersion and Absorption of Helium," where he calculated helium's refractive index within 3% of measured values-establishing approaches that would characterize his entire career: fearlessly diving into mathematical analysis and numerical calculations using only hand-cranked mechanical calculators.
After completing his doctoral work on the helium atom in 1933, Wheeler's path was clear: he wanted to do theoretical physics research and eventually pursue an academic career. With a National Research Council fellowship, he chose to work with Gregory Breit at New York University, attracted to Breit's puzzling style rather than the more charismatic but show-off personality of Robert Oppenheimer.
第5章
Exploring the Frontiers with Bohr and Breit
Wheeler's early career was shaped by two remarkable mentors-Gregory Breit and Niels Bohr-who provided inspiration without hierarchy, treating him as a colleague from the start. With Breit at NYU, Wheeler worked on understanding quantum wave functions of innermost electrons near nuclei in heavier atoms, calculating electron overlap with the nucleus in ionized lithium to learn about nuclear magnetism through its tiny effects on atomic electron energies.
Breit also taught Wheeler pair theory-the interaction of electrons, positrons, and photons. Dirac's 1928 work combining relativity with quantum mechanics had predicted three electron properties: half-quantum spin, the exclusion principle, and the existence of a positively charged sister particle (the positron). Wheeler and Breit calculated the probability of two photons colliding to create electron-positron pairs, though they doubted laboratory detection was possible-a conclusion disproven 63 years later when Stanford Linear Accelerator Center observed such pairs in 1997.
The electron's elegant Dirac theory enchanted Wheeler, sparking years of wondering: could everything be made from electrons? He tried finding ways to build all particles from electrons and positrons, though Breit preferred staying closer to laboratory measurements. These musings led Wheeler to explore physics without photons-a world of particles without fields-work he later pursued with Feynman at Princeton, discovering that in hypothetical worlds with few particles, the future would affect the past.
Encouraged by Breit, Wheeler shifted from Leipzig to Copenhagen for his second postdoctoral year. Bohr's University Institute for Theoretical Physics was a global center for physics, attracting virtually every notable physicist of the 1930s. When Wheeler arrived, Bohr was grieving his seventeen-year-old son Christian's death in a boating accident. Though subdued, he maintained his distinctive presence-constantly lighting but never keeping lit his pipe, and mumbling deeply thoughtful comments that everyone strained to hear.
Dialogue was Bohr's mode of progress, always needing someone to bounce ideas off, whether in private conversations or seminars where he might gradually take over from the original speaker. Bohr was known for his concept of complementarity-that there are mutually exclusive ways of describing quantum events, where one measurement makes another impossible.
During Wheeler's Copenhagen year, Bohr developed his compound-nucleus model, which Wheeler participated in discussing extensively. Bohr realized that a nucleus's behavior after excitation was largely disconnected from how it became excited-like a bar patron who, agitated by one person, unleashes energy randomly on others. The liquid-droplet model emerged gradually as an embodiment of this concept, proving crucial to their later work on fission.
第6章
Academic Life and the Path to Princeton
After his European fellowship, Wheeler accepted an assistant professorship at the University of North Carolina. Chapel Hill proved wonderful-he taught and researched while making good friends and starting his family, having his first two children at Duke's hospital. When Princeton offered him a position after three years, his wife Janette wept at leaving.
Returning from Copenhagen to North Carolina gave Wheeler glorious freedom as an academic scientist. He had teaching duties but could pursue research of his own choosing without specific obligations. As a new professor, he enjoyed minimal administrative burdens-few committees, little correspondence, no requests for recommendations or reviews.
Wheeler saw two promising research directions: electrodynamics (studying electrons, positrons, and photons) and nuclear forces (what held neutrons and protons together). He chose to focus primarily on nuclear forces, developing mathematical techniques for describing nuclei even when details of the force between constituent nucleons were unknown. After two years' work, he published three related papers in Physical Review totaling forty-five pages. In one, he introduced the scattering matrix (S matrix), which later proved useful for analyzing elementary-particle events.
After just a year at UNC, Wheeler spent three months at Princeton's Institute for Advanced Study, hoping to work with luminaries like Wigner, Weyl, and von Neumann. When he returned to Chapel Hill, he received a promotion to associate professor with tenure. Later, he received competing offers from Johns Hopkins and Princeton, choosing Princeton for its exciting research environment despite the less secure position.
In 1938, Wheeler and his wife moved their young family to Princeton, first renting on Murray Place before purchasing land from the Institute for Advanced Study on Battle Road and building their home. Their neighborhood became an intellectual haven with remarkable neighbors: Carl Ten Broeck of Rockefeller Institute, television pioneer Vladimir Zworykin, economist Winfield Riefler, mathematician Hermann Weyl, and art historian Erwin Panofsky.
Palmer Physical Laboratory and Fine Hall formed an extraordinarily vibrant intellectual center when Wheeler arrived in 1938. Walking to the tea room meant encounters with luminaries from both Princeton and the Institute for Advanced Study. In 1939, he met the brash, appealing twenty-one-year-old Dick Feynman when he was assigned as his teaching assistant. At their first meeting, Wheeler placed his pocket watch on the table to track his time expenditure. At their next meeting, without cracking a smile, Feynman placed his newly purchased dollar watch beside Wheeler's. They both dissolved into laughter, setting the tone for a wonderful lifelong friendship.
第7章
The Manhattan Project and Beyond
When news of fission broke in January 1939, Wheeler was teaching at Princeton. Ten days after Bohr's arrival, Leon Rosenfeld reported the discovery at Princeton's Journal Club. Though invited by Bohr to attend the Conference on Theoretical Physics at George Washington University where the official announcement would be made, Wheeler stayed in Princeton, prioritizing his teaching obligations.
In 1939, when Bohr and Wheeler collaborated on fission theory, he was twenty-seven and Bohr was fifty-three-a Nobel Laureate director of Copenhagen's renowned institute paired with a first-year untenured assistant professor. Their working style involved trading chalk back and forth at blackboards, circling hallways in continuous discussion, and moving between their offices when one seemed confining.
They discovered that the puzzling experimental results showing high fission probability at both high and low neutron energies could be explained by isotopic differences. The rare isotope U-235 (0.7% of natural uranium) undergoes fission with slow neutrons, while the abundant U-238 requires higher energy neutrons. This insight helped them predict which other isotopes might undergo fission with low-energy neutrons, including the yet-undiscovered plutonium-239, which would later become crucial for nuclear weapons.
During World War II, Wheeler worked on the Manhattan Project, first in Chicago and later at Hanford, Washington, where he helped solve critical problems with the plutonium production reactors. After identifying xenon poisoning as the cause of the B Reactor's mysterious shutdown, Wheeler determined it was the daughter product of iodine-135 with a 9.2-hour half-life. The reactor's behavior showed the poison was itself produced by a shorter-lived radioactive parent, creating a chain of at least two radioactive decays.
After the war, Wheeler returned to Princeton where he continued his research and teaching. In 1948-49, he established a cosmic-ray laboratory, becoming its first director before transferring responsibility to George Reynolds. The lab attracted international talent including W.K. Chang from China, who discovered important gamma ray patterns emitted when muons cascade through energy states.
Working with Brazilian physicist Jayme Tiomno, Wheeler studied muon decay and capture. Their groundbreaking work in 1947-49 led to the conclusion that muons are essentially "heavy electrons" with identical properties-same half-quantum spin, weak nuclear interactions, and similar decay patterns. This puzzling equivalence prompted I.I. Rabi to ask, "Who ordered that?"
第8章
From Nuclear Physics to Black Holes
On May 6, 1952, Wheeler began a new chapter in his scientific life. After a busy day at Project Matterhorn (the Princeton-based hydrogen bomb research project), he started a notebook titled "Relativity I," recording his excitement about teaching relativity the following year. Though the Mike test-the first full-scale thermonuclear explosion-was less than six months away, Wheeler was already looking beyond it, planning to create the best possible course that might eventually become a book.
Wheeler's interest in relativity actually grew from his work in nuclear physics and quantum theory. Earlier that year, he had studied Oppenheimer's classic 1939 papers on gravitational collapse, which predicted massive stars could collapse to "singularities"-geometric points of infinite density. Though Wheeler would eventually embrace gravitational collapse and help popularize the term "black hole," in 1952 he was troubled by the concept of singularities.
By the 1950s, several stunning consequences of general relativity had emerged, including an expanding, evolving universe and the prediction that matter could collapse to points of infinite density. Unlike many relativists of the 1930s-40s who focused on mathematical aspects, Wheeler believed in exploring the theory's extreme limits, where new insights awaited discovery. His philosophical conviction was that nature would utilize all possibilities offered by valid theories-if matter could collapse to infinitesimal size, then somewhere it would.
In 1955, Wheeler introduced the concept of "geons"-hypothetical entities made entirely of electromagnetic fields held together by their own gravity. Though likely unstable and unobserved in nature, geons represented an intriguing case of "mass without mass," potentially offering insight into the problematic concept of point particles in physics. His 1955 geon paper also introduced another revolutionary concept: "charge without charge." In Einstein's curved spacetime, electric field lines could seemingly begin and end without particles-by disappearing into one region of space and emerging elsewhere through what he later named "wormholes."
Wheeler's ideas about quantum foam took substantial form during eight productive months at the University of Leiden in 1956, where he held the H.A. Lorentz Visiting Professorship. Working with Charles Misner, he explored how quantum principles might govern the gravity field-spacetime itself. This vision of quantum gravity revealed a picture of turbulent spacetime that goes beyond mere bumpiness to fracture into ever-changing, multiply connected geometries at the incredibly small Planck length.
第9章
Black Holes and the Universe's Deepest Mysteries
Of all the entities Wheeler encountered in physics, none matched the black hole in fascination or cosmic importance. The black hole epitomizes general relativity's revolution, pushing its distinctive features to extremes: spacetime curvature, geometry as physics, and gravitational radiation. Near a black hole, starlight can be trapped in orbit forever, and light from disappearing atoms is infinitely stretched until it appears not to vibrate at all.
In fall 1967, while speaking at NASA's Goddard Institute about pulsars, Wheeler mentioned needing a shorter phrase than "gravitationally completely collapsed object." Someone in the audience suggested "black hole," a term he had been searching for. It felt exactly right, and he used it in his formal lecture at the New York Hilton that December, later including it in the published version in spring 1968.
In 1970, Wheeler and his student Remo Ruffini postulated that black holes are extraordinarily simple objects, influenceable only through mass, charge, and spin-"no hair." This was later proven by others. Wheeler's student Jacob Bekenstein tackled black hole entropy in 1972, demonstrating that a black hole's horizon area is its entropy. This insight revealed black holes as complex, disordered entities despite their simple exterior. Stephen Hawking's 1974 discovery of black hole radiation confirmed Bekenstein's work, proving black holes communicate with the outside world.
As Wheeler approached his sixty-fourth birthday in 1975, he wasn't ready for retirement. When George Sudarshan approached him about moving to the University of Texas in Austin, he was receptive. At Princeton, despite twenty years of advocating, he remained a "group of one" in relativity research. Wheeler and his wife moved to Austin in fall 1976, quickly resonating with the can-do spirit of Texas. Within four years, he had built a vibrant research group at the Center for Theoretical Physics.
第10章
Information, Quantum Reality, and the End of Time
After settling in Texas, Wheeler turned increasingly to quantum theory. While relativity challenges our understanding in profound ways, quantum theory stretches human credulity even further. For a deeper understanding of our world, these two great 20th century theories must be harmoniously joined.
The "delayed-choice experiment" illuminates the core of the Bohr-Einstein debate about quantum reality. Using a baseball diamond analogy, photons sent from home plate can take either of two paths, and our later decision to place or not place a second half-silvered mirror determines whether photons behaved as particles following one path or as waves following both paths simultaneously. This thought experiment became reality in 1984 when Carroll Alley demonstrated delayed choice at the University of Maryland.
Wheeler developed the concept "it from bit"-the idea that the universe and all it contains ("it") may arise from myriad yes-no choices of measurement ("bits"). Information may not just be what we learn about the world but what makes the world. When a photon is absorbed, that bit of information determines the reality of its time and place of interaction.
By 1970, Wheeler became convinced not only that black holes exist throughout the universe but that they imply the mutability of physical law itself. If time can end in a black hole, if space can be crumpled to nothingness at its center, why should we believe our physical laws are unique or special? These laws must have emerged with the Big Bang just as space and time did.
Like biological evolution, the laws of physics may represent just one possible path among many. Just as life arose from non-life and evolved through chance events on our particular planet, physical laws may be contingent rather than necessary. By whatever chance, space arose, time arose, laws of physics arose. Perhaps there were limits to what might arise, but it wasn't "only one thing goes."
At seventy-five, after a decade at the University of Texas where he explored black holes, quanta, measurement and information, Wheeler and his wife moved to Meadow Lakes retirement community near Princeton. In these later years, he dared to ask questions some colleagues considered outside science's scope: Is the universe a self-excited circuit made real by observation? Do the laws of physics emerge in the Big Bang and extinguish in the Big Crunch? Can physical laws mutate like living organisms?
Wheeler didn't apologize for such speculations. Like Spinoza, Riemann, Clifford, Mach, and Bohr before him, he believed speculation has its place alongside rigorous science. As Piet Hein wrote: "I'd like to know what this whole show is all about before it's out."
