Some believe this exaggerated impression of general relativity’s difficulty kept people away and contributed to the field’s stagnation. General relativity nearly withered on the vine. After a flurry of scientific publications in the early 1920s, after the theory’s well-publicized verification in 1919, interest plummeted. For some three decades afterward, less than 1 percent of physics journal articles involved relativity. It was once said at a conference that you could count the number of general relativists in the world “on the fingers of one hand.” Oppenheimer’s startling new contribution hardly made a difference in the ongoing diminution of the field. Oppenheimer himself, after he became head of the Institute for Advanced Study in Princeton, New Jersey, in 1947 advised the up-and-coming physicists there to avoid pursuing general relativity, believing it a dead end. Einstein, then in his waning years, worked in an office just down the hall from Oppenheimer.
Ultimately, physicists want a theory to connect with the world. You could argue that quantum mechanics was just as weird—what with particles acting as waves, waves as particles. Why was it so readily accepted and general relativity snubbed? It’s primarily because quantum theorists worked hand in hand with experimentalists. There was a deep pool of experimental data to support quantum mechanics’ predictions on the nature and behavior of matter (weird as it was) on very small scales. In the late 1920s Paul Dirac, for example, posited the existence of antimatter, and by 1932 an experimentalist found evidence for this new type of particle, bizarre as it sounded, in a cosmic-ray bubble chamber. General relativity, on the other hand, had merely a wobble in Mercury’s orbit and some bending of starlight skirting past the Sun to back up its tenets. The noted physicist Richard Feynman wasn’t a fan of general relativity for that very reason. “Because there are no experiments this field is not an active one, so few of the best men are doing work in it … ,” he wrote his wife from a world conference on gravity. “The good men are occupied elsewhere.”
After the brief but seminal flurry of work coming out of Oppenheimer’s group at Berkeley, the subject of total gravitational collapse didn’t just get placed onto the backburner; it got shoved into a closet. World War II only accelerated the process. It sidetracked many physicists into the more vital concerns of the moment: radar, nuclear physics, military technology. “We who worked in this field,” said Leopold Infeld, who collaborated with Einstein, “were looked upon rather askance by other physicists. Einstein himself often remarked to me: ‘In Princeton they regard me as an old fool.’ This situation remained almost unchanged up to Einstein’s death.”
7
I Could Not Have Picked a More Exciting Time in Which to Become a Physicist
It was not until the mid-1950s that interest in general relativity and its applications was at last revived after its decades-long lull. It was in the nick of time. The field had gotten so moribund that the Dutch American physicist Samuel Goudsmit, codiscoverer of electron spin and then editor-in-chief of the Physical Review, was about to lay down an edict that papers on general relativity would no longer be accepted by the journal. But by that point a renaissance for general relativity was beginning to bloom in the Soviet Union, Europe, and the United States. This happened for a variety of reasons. For one, the start of the space race and the Cold War led to more funding, especially in the United States; given their experience in the war, the US military branches had learned of the great advantages in sponsoring basic research in all types of fields. The worldwide celebration of special relativity’s fiftieth anniversary in 1955 also brought many physicists together, allowing them to recognize that gravitational research had been unfairly neglected and was due for more attention. Barely alive within the journals of physics through the Depression and the war, the topic slowly gained more and more significance. “Within a few years, understanding of gravitational collapse progressed from its inchoate beginnings to a sophisticated discipline,” said theorist Werner Israel.
One of the more unusual reasons for gravitation’s reawakening can be traced to an eccentric American financier. Born in Gloucester, Massachusetts, in 1875, Roger Babson graduated from the Massachusetts Institute of Technology with an engineering degree but was lured into the stock market during its glory days in the 1920s, where he applied his statistical training at the brokerage firm he established. Such a mathematical approach on Wall Street was fairly novel at the time, but the MIT graduate had a physics mind-set. “Babson was fascinated with Newton’s three laws of motion, and sought to apply them directly to his own studies of business trends. Most important was Newton’s third law,” science historian David Kaiser has written. That law states that for every action there is an equal and opposite reaction, which to Babson meant that the high-flying stocks then in play would surely plummet someday. Shortly before the market’s dramatic fall in 1929, he sent out a forecast to his clients of the imminent collapse and placed his money in safe havens, allowing him to sail “through the Great Depression as one of America’s wealthiest citizens,” noted Kaiser.
Convinced that Newton saved him from financial ruin, Babson and his wife began to gather a vast collection of Newton’s original publications, as well as books that the great Sir Isaac owned. The couple went so far as buying the entire front parlor of Newton’s London home (including its walls) and setting it up in a special room at the institution he founded, Babson College in the suburbs of Boston, where it remains today.
These enthusiasms for all things Newton eventually led Babson to set up and completely fund the Gravity Research Foundation in 1948. He had come to believe that gravitation was a specialty that deserved more attention among physicists, and the foundation began generously subsidizing conferences on gravity and establishing lucrative annual awards for the best essays written on gravity. Although his largesse provided a real boost to gravity researchers, Babson’s true goal was to find a way to conquer gravity. He hoped that his funds would lead to the development of “antigravity,” a means to counteract the attractive force. It was an obsession for Babson ever since his oldest sister drowned when he was young; he blamed gravity for pulling her to the water’s bottom. Special insulators and shields stop magnetism, why not search for comparable insulators that could vanquish gravity, thought Babson. When the Tufts University physics department received a hefty grant from Babson’s foundation in 1961, it became the owner of a large stone monument in honor of this pursuit. Carved into the rock are these words: “It is to remind students of the blessings forthcoming when a semi-insulator is discovered in order to harness gravity as a free power and reduce airplane accidents.” (Similar stones, about a dozen in all, were donated by Babson to other colleges situated in New England, the South, and the Midwest.) “[Tufts] legend has it that from time to time, groups of fraternity brothers band together to move the 2,000-pound monument to a different location during the night, working like anti-gravity’s little elves,” said Kaiser.
The foundation’s essay prize was at first looked upon as a joke, due to its initial focus on antigravity, leading some to label those working on gravitation as “mad men and quacks.” But the tide turned when a young relativist named Bryce DeWitt, in need of a down payment for a house, submitted a paper that brazenly argued how searches for gravity reflectors or insulators were “a waste of time.” DeWitt laid out more reasoned arguments to study gravitation and won the prize. As a result, the contest eventually attracted entries from talented physicists in gravitational research, and the submissions duly shifted to broader concerns in relativistic theory. (The contest continues, with the era’s most noted theorists, among them Stephen Hawking and Roger Penrose, winning its essay awards.)
The stone placed by the Gravity Research Foundation on the campus of Tufts University in 1961. (Daderot, courtesy of Wikimedia Commons)
In the 1950s the foundation’s president convinced another rich industrialist, Agnew Bahnson, to support a new institute for gravitational studies at the University of North Carolina, to be headed by DeWitt, a pioneer in the quest to jo
in quantum mechanics with general relativity. To separate themselves from the “mad men” and make sure the physics community deemed them legitimate, institute physicists openly declared in their literature that they had “no connection with so-called ‘anti-gravity research’ of whatever kind and for whatever purposes.” Within months of its founding, the new institute in early 1957 held a conference on the role of gravitation in physics, a meeting now deemed a “landmark” in the rebirth of gravitational studies.
“By organizing conferences, sponsoring the annual essay contests, and making money and enthusiasm widely available for people interested in gravity, the eccentric Gravity Research Foundation may claim at least some small amount of the credit for helping stimulate the postwar resurgence of interest in gravitation and general relativity,” says Kaiser.
In the United States the epicenter of this revival was situated at Princeton University, where physicist John Archibald Wheeler had decided to ponder the fate of collapsed stars, taking up where Oppenheimer left off. It was Wheeler, furiously working behind the scenes, who got Goudsmit to reverse his proposed ban on general-relativity articles in Physical Review. Wheeler spent most of his academic life at Princeton, where he set a record in the number of graduate and undergraduate students he supervised—nearly a hundred, including Richard Feynman. As a young man, Wheeler did groundbreaking work in nuclear physics but later made his greatest contribution in science by almost single-handedly taking general relativity, a field that had been stagnating for decades, and applying it to the universe at large.
Under Wheeler’s expert guidance, the subject was reborn, as he inspired his small army of students and post-docs to seek ingenious solutions that could be meaningful in understanding the cosmos. As Wheeler put it, he wanted to usurp the “’one-legged men’—men who knew nothing but relativity!” He desired to take the theory out of its ivory tower and couple it to real-world observations—to allow his students to stand on two legs. When someone mentioned the word relativist to him, Wheeler replied, “There is no such thing; they are physicists.”
Wheeler’s forays into general relativity over the succeeding years led to many research papers that, combined with the notes from his teaching, were turned into a series of noted books on relativity, many in collaboration with his former students. He became America’s dean of general relativity. As Freeman Dyson noted on Wheeler’s death in 2008, “Before anyone else, he understood that black holes are not merely an odd theoretical consequence of Einstein’s theory of gravitation, but must actually exist and play a vital role in the evolution of the universe.”
Born in Florida in 1911, Wheeler grew up around the country as his father, a librarian, served at various posts. From childhood, he displayed a knack for mathematics, teaching himself calculus in high school. He also loved machinery, electronics, and explosives, almost losing a finger one day playing with dynamite caps on the family’s vacation farm in Vermont.
Admitted to Johns Hopkins in 1927 at the age of sixteen on scholarship, Wheeler first chose to major in engineering. I was “bent on making my own way in the world,” he reminisced years later: “Saying ‘physics’ would have been like saying ‘pottery making.’” But the intellectual lure of the new physics then emerging—quantum mechanics, atomic physics, nuclear physics—was too big for him to ignore. “It is no exaggeration to call that period a watershed,” he wrote. “Classical ideas about solidity, certainty, stability, and permanence were being abandoned. They were being replaced by quantum ideas of uncertainty and granularity and the duality of waves and particles; by relativistic ideas of spacetime as cosmic actor, not merely cosmic stage; and by astronomical ideas (backed up by relativity) of a universe that is expanding, not static, and of finite age, not eternal. I could not have picked a more exciting time in which to become a physicist.”
Wheeler flew through college, not even pausing for a baccalaureate or master’s degree. “It was a non stop flight,” he liked to say. He went directly from freshman to PhD in six years, completing a dissertation in 1933 at the age of twenty-one on the absorption and scattering of light by the helium atom. Garnering a postdoctoral fellowship, Wheeler then spent time in Copenhagen, known lightheartedly as the “Vatican of physics.” There he had the opportunity to meet nearly all the greats in physics, who traveled like disciples to Niels Bohr’s institute in the Danish capital to work on nuclear physics with the master. Wheeler’s first big splash in the physics community was publishing a paper with Bohr in 1939 on a liquid-drop model of an atomic nucleus, which was crucial to the understanding of nuclear fission and played an important role in the development of the atomic bomb. They had predicted that both uranium-235 and plutonium-239 would be particularly useful in sustaining a chain reaction. Not surprisingly, given this expertise, Wheeler later worked on both the Manhattan Project and the development of the hydrogen bomb. It wasn’t until later that general relativity became the love of his life. And when that happened, he said, “I finally had a calling.”
He remembered the exact moment when relativity arrived at his door. It was 6 May 1952, at Princeton University, where he had been a faculty member since 1938. The time was 5:55 p.m. That’s when he grabbed a new research notebook, bound in black with red leather edging, and wrote down on page 1 both the time and his immediate thoughts in blue flowing ink. (All his professional life, he preferred a fountain pen over a pencil.) Just half an hour earlier, Wheeler noted in his journal, he had learned from the department chairman that he was going to teach relativity, the first time the physics department had offered such a course. He labeled this notebook “Relativity I” and followed up with many others over the years. “I wanted to teach relativity for the simple reason that I wanted to learn the subject,” Wheeler later explained. After the war, the fields of nuclear and particle physics were in flux. To Wheeler, they appeared “headed toward a complex thicket of pions and countless other particles, and I began to sense that there might be more gold in the general-relativity mine than had yet been unearthed.” For one, he had been pondering whether curved space, on the tiniest of levels, might serve as the building material for the elementary particles he had long been studying.
John Archibald Wheeler (American Institute of Physics Emilio Segrè Visual Archives, Wheeler Collection)
It was a daring yet worthwhile move. Wheeler, as a newcomer to relativity, was able to look at the theory’s decades-long problems with unjaded eyes and fresh enthusiasm. He wasn’t burdened by the judgments of the past, although he did have some initial prejudices. He had recently come across the classic 1939 papers by Oppenheimer and his students and was terribly bothered by the singularity. Could that really be the fate of a massive star? “I was looking for a way out,” said Wheeler. “Something new should happen at the tiniest dimensions, I felt, that would prevent the total collapse. … I was convinced that nature abhorred a singularity.” It was repugnant to him. His wary attitude toward Oppenheimer may have also played a role: “He seemed to enjoy putting his own brilliance on display—showing off, to put it bluntly. He did not convey humility or a sense of wonder or of puzzlement. … I always felt that I had to have my guard up.”
Wheeler was not just being stubborn in trying to get rid of the singularity. He sensed that new physics might emerge by tackling this mystery. No one yet understood how gravity acted on the very small scale, at the level of an atom, and here was a means of examining that arena. At the end of its life, a star’s core gets squeezed smaller and smaller. What could be learned from this event? Does the matter just disappear, possibly entering another space, another time? Or does it get transformed into a new minuscule state, not yet conceived by our current laws of physics?
Given his background in nuclear physics, Wheeler thought of the proton. From outside the particle, it appears that the proton’s electric field is emanating from a point. But in reality the proton has a finite size. Maybe the entire mass of a star was collapsing to a very, very small size, into a state of matter as yet unknown. Or mayb
e the compacted star fiercely radiates away its mass and energy as it shrinks inward, “until it becomes a cinder too puny for further collapse,” mused Wheeler.
That had been the popular escape mechanism for decades. A star, at the end of its life, somehow undergoes a grand fireworks show, ejecting just enough mass to prevent it from ever plummeting to a singular point in the event of a complete gravitational collapse. But to some astrophysicists this belief was “no more than a superstition,” a way to avoid confronting the unthinkable.
By teaching a course on general relativity, Wheeler hoped to get better acquainted with the enemy and find the proper means to avoid the ultimate stellar Armageddon. There was good reason for Wheeler’s hope: Oppenheimer and Snyder had set up the simplest case possible. In order to be able to handle their calculations, the star in their computations did not rotate; moreover, there were no pressures or shock waves in play. Simply put, it was an ideal star—not a real one at all. What if some force, not yet considered, stepped in to stop a singularity from forming?
Wheeler thought of all the possible escape routes and began testing them out, one by one, mathematically. In one way he was very much like Oppenheimer; he liked to work in close collaboration with his students. He adopted the research style he had learned under Bohr: “free-wheeling talk sessions with colleagues, with more questions than answers flying back and forth, [trying] always to emphasize the positive in my junior colleagues’ work, [giving] them all credit that is due,” as he put it. And he was highly generous with that credit. Even if he had made the major contribution to a paper in collaboration with a student, the authors were always placed in alphabetical order. That was Wheeler’s edict. With his name beginning with “W,” that meant his student was highly likely to be listed as “first author,” the most honored position in the scientific literature.
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