When I heard from a friend about John Wheeler's death this morning, I grimaced and actually loudly let out an exclamation of pain and sadness. That's because not only was Wheeler one of the most distinguished physicists of the century but with his demise, the golden era of physics- that which gave us relativity, quantum theory and the atomic age- finally passes into history. The one consolation is that he lived a long and satisfying life, passing away at the ripe age of 96. It was just a few weeks ago that I asked a cousin of mine who did his PhD. at the University of Texas at Austin whether he ever ran into Wheeler there. My cousin who himself is in his fifties said that Wheeler arrived just as he was finishing- after retirement from Princeton university.
Wheeler was the last survivor of that heroic age that changed the world and he worked with some true prima donnas. He was an unusually imaginative physicist who made excursions into exotic realms; particles traveling backwards in time, black holes, time travel. A list of his collaborators and friends includes the scientific superstars of the century- Niels Bohr, Albert Einstein, Enrico Fermi, Edward Teller and Richard Feynman to name a few. To the interested lay public, he would be best known as Richard Feynman's PhD. advisor at Princeton.
Wheeler is famous for many things- mentor to brilliant students, originator of outrageous ideas, coiner of the phrase "black hole", outstanding teacher and writer. My most enduring memory about him is from John Gribbin's biography of Feynman. Gribbin recounts how Wheeler in his pinstriped suits used to look like a conservative banker, a look that belied one of the most creative scientific minds of his time. The fond incident is about the playful rogue Feynman being summoned into Wheeler's office for the first time. In order to underscore the importance of his time, Wheeler laid out an expensive pocket watch in front of Feynman. Feynman who had a congenital aversion to perceived or real pomposity took note of this and during their next meeting, laid out a dirt-cheap watch on the table. After a moment of stunned silence, both professor and student burst into loud laughter, laughter that almost always accentuated their discussions on physics and life thereafter. Feynman and Wheeler together derived a novel approach to quantum mechanics that involved particles radiating backwards in time. Wheeler also initiated the discussion of the notorious sprinkler problem described by Feynman in Surely you're joking Mr. Feynman
John Wheeler was born in Florida to strong-willed and working class parents. After obtaining his PhD. from Johns Hopkins at the age of 21, he joined Princeton in 1938 where he remained all his working life. Princeton in 1938 was a mecca of physics, largely because of the Institute for Advanced Study nearby which housed luminaries like Einstein, John von Neumann and Kurt Godel. Wheeler knew Einstein well and later sometimes used to hold seminars with his students in Einstein's home. As was customary for many during those times, Wheeler also studied with Niels Bohr at his famous institute in Copenhagen. In 1939 Bohr and Wheeler made a lasting contribution to physics- the liquid drop model of nuclear fission. According to this, the nucleus of especially heavy atoms behaves like a liquid drop, with opposing electrostatic repulsive forces and attractive surface tension and strong forces. Shoot an appropriately energetic neutron into an unstable uranium nucleus and it wobbles sufficiently for the repulsive forces to become dominant, causing it to split. The liquid drop model explained fission discovered earlier. The mathematics was surprisingly simple yet remarkably accurate. Bohr was one of Wheeler's most important mentors; in his biography he describes how he used to have marathon sessions with Bohr, with the great man often insisting on walking around the department, tossing choice tidbits to Wheeler ambling at his side. Caught up in the recent heated debate about the philosophical implications of quantum theory, Wheeler argued the nature of reality with both Einstein and Bohr.
When World War 2 began, Wheeler like many physicists was recruited into the Manhattan Project. Because of his wide-ranging intellect and versatility, he was put in charge as scientific consultant to Du Pont, who was building plutonium producing reactors at Hanford in Washington state. There Wheeler tackled and solved an unexpected and very serious problem. As the reactors were transforming uranium 238 into the precious plutonium, the process suddenly shut down. After some time it started up again. Nobody knew what was happening. Wheeler who was the resident expert worked out the strange phenomenon in an all-night session. What was happening was that some of the fission products produced had a big appetite for neutrons and were therefore "poisoning" the chain reaction. After some time when these products had decayed to sufficiently low levels, they would stop eating up the neutrons and the reactor would start again. This was one of the most valuable pieces of information gained during plutonium production. Ironically, the omission of this information in a second edition of a government history of atomic energy released just after the war alerted the Soviets to its importance. Working on the Manhattan Project was also a poignantly personal experience for Wheeler; the bomb could not save his brother Joe who was killed in action in Italy in 1944. Wheeler later also worked with Edward Teller on the hydrogen bomb, a decision about which he was fairly neutral because he thought it was necessary at the time to stand up to the Soviets.
After the war Wheeler embarked on a lifelong quest in a completely different field and became a pioneer in it- general relativity. He took up where Robert Oppenheimer had left off in 1939. Oppenheimer had made a key contribution to twentieth century physics by first describing what we now know as black holes. Strangely and somewhat characteristically, he lost all interest in the field after the war. But Wheeler took it up and reinitiated a bona fide revolution in the application of general relativity to astrophysics. As his most enduring mark, he coined the word "black hole" in the 1960s. Wheeler became the scientific godfather of a host of other physicists who became pioneers in exploring exotic phenomena- black holes, wormholes, time travel, multiple universes. His most successful student in this regard has been Kip Thorne whose wonderful book expounds on the golden age of relativity. Hugh Everett, the tragic genius who invented multiple universes and the Lagrange multipliers method for optimization problems before plunging into paranoia and depression, left behind choice fodder not just for science but for science fiction; parallel universes have been a staple of our collective imagination ever since then. In retrospect, Wheeler followed his mentor and did for astrophysics what Bohr had done for quantum theory- he served as friend, philosopher and guide for a brilliant new generation of physicists.
Wheeler also was known as an outstanding teacher. His mentoring of Feynman is well-known, and he devoted a lot of time and care to teaching and writing. Along with his students Kip Thorne and Charles Misner, Wheeler produced what is surely the bible of general relativity, Gravitation, a mammoth book running more than a thousand pages whose only discouraging feature may be its length. The book has served as advanced introduction to Einstein and beyond for generations of students. Wheeler also co-authored Spacetime Physics, an introduction to special relativity which even I have timidly managed to savor a little during my college days. His own autobiography, Geons, Black Holes and Quantum Foam: A Life in Physics is worth reading for its evocation of a unique time of the last century, as well as for fond anecdotes about great physicists.
But many people will remember Wheeler as a magician. Sitting in his office in his pinstriped suits, Wheeler's mind roamed across the universe straddling everything from the smallest to the largest, exploring far-flung concepts and realms of the unknown. He grappled with the interpretation of quantum mechanics and was an early proponent of the anthropic principle- in John L Casti's magnificent book Paradigms Lost, Casti quotes Wheeler analogizing observer-created reality with the game in which a group of people asks someone else to guess an object they have in mind by asking questions, except that in the modified version of this game, they let the object be created during the process of questioning. With his mentor Bohr's enduring principle of complementarity as a guide, Wheeler produced esoteric ideas that nonetheless questioned the bedrock of reality. Wheeler was entirely at home with such bizarre yet profound concepts that still tug at the heartstrings of physicist-philosophers. Only Wheeler could have introduced paradoxical and yet meaningful phrases like "mass without mass". In celebration of his sixtieth birthday, physicists produced a volume dedicated to him with a title that appropriately captured the essence of his thinking- "magic without magic".
John Wheeler was indeed a magician. He made great contributions to physics, served as its guide for half a century and motivated and taught new generations to wonder at the universe's complexities as much as he did. He was the last torch-bearer of a remarkable age when mankind transformed the most esoteric and revolutionary investigations into the universe into forces that changed the world. He will be sorely missed.