Pioneering Physicist John Wheeler Dies at 96: Scientific American

April 14, 2008
Pioneering Physicist John Wheeler Dies at 96
ManhattanProject veteran came up with the term "black hole" and co-authoredstandard text on Einstein‘s general theory of relativity
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Editor‘sNote: Yesterday morning, renowned physicist John Archibald Wheeler diedof pneumonia. He was an iconic figure: a veteran of the ManhattanProject, a pioneer of the search for a quantum theory of gravity, andan originator of such evocative terms as "black hole." Most physicsstudents know him as co-author of the standard textbook on Einstein‘sgeneral theory of relativity—a tome that defies almost every stereotypeof a textbook, much as Wheeler‘s own career defied almost everygeneralization. He was rigorous yet playful, and he always had a pithy,Zen-like phrase for profound ideas and questions: "it from bit," "masswithout mass" and "Why the quantum?".An out-of-the-box thinker who wasn‘t afraid to speculate, he alwayscarefully identified speculation as such. In so doing, he opened upspace for his colleagues to push the boundaries. Here is a profile by John Horgan, published by Scientific American in 1991:
Questioning the "It from Bit"
It‘s hard keeping up with John Archibald Wheeler. When we leave histhird-floor office at Princeton University to get some lunch, he spurnsthe elevator—"Elevators are hazardous to your health," he declares andcharges down the stairs. He hooks an arm inside the banister and pivotsat each landing, letting centrifugal force whirl him around the hairpinand down the next flight. "We have contests to see who can take thestairs fastest," he says over a shoulder.
Outside, Wheeler marches rather than walks, swinging his fists smartlyin rhythm with his stride. He pauses only when he reaches a door.Invariably, he gets there first and yanks it open for me. After passingthrough, I wait a moment in reflexive deference—after all, the man willbe 80 years old in July—but a moment later he‘s past me, barrelingtoward the next doorway.
The metaphor seems so obvious I almost suspect it is intentional.Wheeler, a professor emeritus of physics at Princeton and theUniversity of Texas at Austin, where he holds a joint appointment andspends a few weeks each year, has made a career of racing ahead ofother scientists and throwing open doors for them. He has helped gainacceptance—or at least attention—for some of the most outlandish ideasof modern physics, from black holes to multiple-universe theories. "Hehas this great ability to see what is important before anyone else andpersuade others that this is so," says David Deutsch, a physicist atthe University of Oxford.
Wheeler is also renowned for his coinages, analogies and aphorisms,both self-made and co-opted. Among the one-liners he bestows on me are,"If I can‘t picture it, I can‘t understand it" (Einstein);"Unitarianism [Wheeler’s official religion] is a featherbed to catchfalling Christians" (Darwin); "Never run after a bus or woman orcosmological theory, because there‘ll always be another one in a fewminutes" (a professor of French history at Yale); and "If you haven’tfound something strange during the day, it hasn‘t been much of a day"(Wheeler). Lately Wheeler has been drawing his colleagues‘ attention tosomething strange indeed. It is a worldview uniting information theory,which seeks to maximize the efficiency of data communications andprocessing, with quantum mechanics. As usual, Wheeler has packaged theconcept in a catchy phrase: "it from bit." And as usual, he delights inbeing ahead of—or at least apart from—the pack. "I hope you don‘t thinkI‘m too much like Daniel Boone," he says slyly. "Anytime someone movedto within a mile of him, he moved on."
Wheeler might have been dismissed as fun but flaky long ago if he didnot have such unassailable credentials. The son of two librarians "whowere interested in ideas, interested in the world, interested inadventures" (and who obviously endowed him with an omnivorous appetitefor reading), he entered Johns Hopkins University at the age of 16 andemerged with a PhD in physics six years later.
He subsequently journeyed to Copenhagen to study with Niels Bohr, thegreat Danish physicist, "because he sees further ahead than any manalive," Wheeler wrote on his application for the fellowship. In 1939Bohr and Wheeler published the first paper successfully explainingnuclear fission in terms of quantum physics. Wheeler‘s expertise innuclear physics led to his involvement in the construction of theatomic bomb during World War II and, during the Cold War‘s early years,the hydrogen bomb.
I had heard that beneath Wheeler‘s puckish demeanor lay a core ofsteel. That is apparent when I ask if he has any second thoughts abouthelping to create nuclear weapons. His eyes narrowing, he acknowledgesthat "a lot of my friends have gone around giving what I call‘scare-the-dope speeches‘" deploring such weapons. But he has noregrets. Nuclear weapons, he insists, saved lives by ending World WarII quickly and by deterring Soviet aggression thereafter.
When his involvement in the H-bomb project ended, Wheeler immersedhimself in studying relativity and gravity—which he calls his "lifelonglove"—at Princeton. In 1966 he proposed that a brilliant cloud of gasknown as the Crab nebula was illuminated from within by a whirlingsphere of solid neutrons created by the implosion of a star.Astronomers later detected such spinning neutron stars, or pulsars,both in the Crab nebula and elsewhere in the Milky Way.
Wheeler also speculated that matter could collapse even beyond thesolid­neutron state, becoming so dense that nothing—not evenlight—could escape its gravitational clutches. Such an object was firstproposed by J. Robert Oppenheimer and Hartland S. Snyder in 1939, butit had been dismissed as a theoretical curiosity and not something thatmight actually exist.
Wheeler recalls discussing such "completely collapsed gravitationalobjects" at a conference in 1967, when someone in the audience casuallydropped the phrase "black hole." Wheeler immediately adopted the phrasefor its brevity and "advertising value," and it caught on. Largelybecause of Wheeler‘s proselytizing, black holes now play a crucial rolein astrophysics and cosmology.
In the 1950s Wheeler grew increasingly intrigued by the philosophicalimplications of quantum physics. According to quantum theory, aparticle such as an electron occupies numerous positions in space untilwe observe it, when it abruptly "collapses" into a single position.Wheeler was one of the first prominent physicists seriously to proposethat reality might not be a wholly physical phenomenon. In some sense,Wheeler suggested, reality grows out of the act of observation, andthus consciousness itself; it is "participatory."
These ruminations helped to inspire two of the odder notions of modernphysics. In 1957 Hugh Everett III of Princeton, in a Ph.D. thesissupervised by Wheeler, proposed the many worlds theory: Although we canobserve a particle in only a single position, it actually occupies allthe positions allowed it by quantum theory—in different universes. Fouryears later another Princeton physicist, Robert H. Dicke, introducedthe anthropic principle. It asserts that the universe is the way it isbecause if it were not, we would not be here to observe it. Althoughmany physicists recoiled from such ideas as untestable and thereforeunscientific, Wheeler urged that they be taken seriously.
At the same time, Wheeler began to draw his colleagues‘ attention tosome intriguing analogies between physics and information theory, whichwas first proposed by Claude E. Shannon of Bell Laboratories in 1948.Just as physics builds on an elementary, indivisible entity thatdepends on the act of observation—namely, the quantum—so doesinformation theory. Its "quantum" is the binary unit, or bit, which isa message representing one of two choices: heads or tails, yes or no, 0or 1.
In addition, information theory provided a new way of viewing entropy,one of the most important, and confusing, concepts in physics. Entropyis defined as the disorder, or randomness, or "shuffledness," as onephysicist has put it, of a system. Shannon had proposed that theinformation in a given system—the sum total of all its possiblemessages—is a function of its entropy; as one increases, so does theother. Wheeler pointed out that entropy, like a quantum event, is thustied to the state of mind of the observer. The potential information ofa system is proportional to one‘s ignorance, and so, therefore, is theentropy of the system.
Wheeler was not the only scientist to recognize these links, "but hewas probably the first to recognize the potential implications forfundamental physics," says physicist Wojciech H. Zurek of Los AlamosNational Laboratory. In the early 1970s Wheeler‘s speculation bore sometangible fruit when yet another of his graduate students, JacobBekenstein, described a black hole in terms of information theory. Thesurface area of a black hole‘s "event horizon," Bekenstein showed, isequal to its thermodynamic entropy, which in turn is equal to theinformation that the black hole has consumed.
Spurred by this and other findings, an ever larger group ofresearchers—including computer scientists, astronomers, mathematiciansand biologists as well as physicists—has passed through the doors flungopen by Wheeler. In the spring of 1989 a number of them gathered at theSanta Fe Institute in New Mexico to update one another on theirprogress. The proceedings of the meeting were published in 1990 asComplexity, Entropy and the Physics of Information.
The lead chapter of the book is based on Wheeler‘s address to themeeting, and it is vintage Wheeler. Over the course of 16 pages, hecites 175 sources, including the Greek poet Parmenides, Shakespeare,Leibniz, Einstein and graffiti in the men‘s room of the Pecan StreetCafe in Austin, Tex., which states: "Time is nature‘s way to keepeverything from happening all at once." Wheeler also spends some timeestablishing what reality is not: It is not a "giant machine, ruled byany preestablished continuum physical law"; at its most fundamentallevel, it even lacks dimension, such as space or time.
What is reality, then? Wheeler answers his own question with thekoanlike phrase "it from bit." Wheeler explains the phrase as follows:"Every ‘it‘—every particle, every field of force, even the spacetimecontinuum itself—derives its function, its meaning, its very existenceentirely—even if in some contexts indirectly—from theapparatus-elicited answers to yes-or-no questions, binary choices,bits."
Elaborating on this idea, Wheeler evokes what he calls the "surprise"version of the old game of 20 questions. In the normal version of thegame, person A thinks of an object—animal, vegetable or mineral—andperson B tries to guess it with a series of yes-or-no questions. Insurprise 20 questions, A only decides what the object is after B asksthe first question. A can then keep choosing a new object, as long asit is compatible with his previous answers. In the same way, Wheelersuggests, reality is defined by the questions we put to it.
How do other scientists react to such propositions? Zurek, whoorganized the Santa Fe meeting and edited the proceedings, callsWheeler‘s style "prophetic, leading the way rather than relating what‘salready been done."
Wheeler acknowledges that the ideas of the entire field are still raw,not yet ready for rigorous testing. He and his fellow explorers arestill "trying to get the lay of the land" and learning how to conversein the language of information theory. Wheeler says the effort may leadto a powerful new vision of "the whole show" or to a dead end. "I likethat phrase of Bohr‘s: ‘You must be prepared for a surprise, a verygreat surprise.‘"
Another favorite Wheelerism is "one can only learn by teaching."Wheeler has been the supervisor for some 50 PhDs in physics during hiscareer, an "enormous number," according to Jeremy Bernstein, aphysicist and science writer. Wheeler‘s most famous student was thelate Richard P. Feynman, who received a Nobel Prize in 1965 for hiswork in quantum electrodynamics. Technically, Wheeler can teach nolonger. "If you know of a school that lets its professors teach afterthey reach 70," he says, "let me know."
But of course, Wheeler can neither stop teaching nor stop learning.During my visit, we run into a young physicist who briefs us on his newcosmological theory, which posits that the universe is riddled withknotlike spatial "defects." "I can‘t believe space is that crummy,"Wheeler declares. Noting the physicist‘s somewhat crestfallenexpression, Wheeler touches his arm and says: "To hate is to study, tostudy is to understand, to understand is to appreciate, to appreciateis to love. So maybe I‘ll end up loving your theory." The smile returnsto the young man‘s face, and Wheeler marches off.

100 Years of Quantum Mysteries
The Many Worlds of Hugh Everett ($)