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In other words, alpha particles produced naturally by radium and polonium had exhausted their usefulness as probes of the nucleus. They simply weren’t powerful enough. Some way had to be found to impart greater energies to the projectiles: man’s cunning had to augment nature’s gifts to create a new kind of nuclear probe. Rutherford had drawn a road map for the future of nuclear physics. Off in the distant horizon lay the reality that the task of reaching the necessary energies would overmatch the elegant bench science of Rutherford’s generation.
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Rutherford’s discoveries launched a surge of ingenuity in physics. J. Robert Oppenheimer would later describe this as “a heroic time,” not merely because of the intellectual energy focused on the challenge Rutherford posed but because the work took place in an atmosphere of intellectual crisis. Physicists were forced to confront astonishing paradoxes roiling their conception of the natural world. Through much of the 1920s, they were wracked with doubt that they would be able to resolve them at all.
The words of eminent physicists of the era bristle with intellectual despair. The German physicist Max Born, one of the earliest disciples of the new theory of quantum mechanics, wrote in 1923 that its multiplying contradictions could mean only that “the whole system of concepts of physics must be reconstructed from the ground up.” The Viennese theorist Wolfgang Pauli, who combined rigorous intellectual integrity with an acerbic tongue—his famous critique of a sloppily argued paper was that it was “not even wrong”—lamented in 1925 that physics had become so “decidedly confused” that “I wish I . . . had never heard of it.” Even the level-headed James Chadwick recalled experiments at the Cavendish “so desperate, so far-fetched as to belong to the days of alchemy.”
Despite the complexity of their quest—or perhaps because of it—their work enthralled the public. For laypersons in the twenties, physics was invested with an aura of drama, even romance. The postwar decade had begun with Sir Arthur Eddington’s spectacular confirmation of Einstein’s theory of relativity at a joint meeting of the Royal Society and Royal Astronomical Society in November 1919. “Revolution in Science / New Theory of the Universe / Newtonian Ideas Overthrown” declared the Times of London in a historic headline. Eddington’s painstaking publicity campaign launched the theory of relativity into popular culture and its father, Albert Einstein, into a life of international renown. But that only whetted the public’s appetite for news about the search for the fundamental truths of nature, while fostering the image of modern physicists as intrepid individuals given to collect their data by trekking to the ends of the earth—as Eddington had journeyed to the far-off African island of Príncipe to witness a relativity-confirming eclipse.
Newspaper editors evinced a voracious appetite for news of the latest breakthroughs. Scientists became celebrities. In 1921 a six-week tour of the United States by Marie Curie and her two daughters, Eve and Irène, inspired outbursts of public admiration. The visit was the brainchild of Mrs. Marie Mattingly Meloney, a New York socialite and magazine entrepreneur who had been shocked to learn that Madame Curie’s research was hobbled by a meager supply of radium. Meloney conceived the idea of raising $100,000 to acquire a gram of the precious mineral—about as much as would fit in a thimble—and bringing Curie to America by steamship to accept the gift. “Mme. Curie Plans to End All Cancers,” declared the front page of the New York Times on the morning after her arrival (a bald assertion that the newspaper quietly retracted the following day). The climax of Madame Curie’s visit was a glittering reception at the White House attended by Meloney and the cream of Washington society, including Theodore Roosevelt’s socialite daughter Alice Roosevelt Longworth. There Marie Curie received the beribboned vial of radium directly from the hands of President Warren Harding, after which she expressed her gratitude (the New York Times reported) “in broken English.” Such were the demands of fund-raising even in the era of small science.
The public came to imagine that physics held the key to all phenomena of the natural world, including the chemical and the biological. Wrote Rutherford’s biographer, Arthur S. Eve, physicists were “endeavoring, with some initial success, to explain all physical and chemical processes in terms of positive electrons, negative electrons, and of the effects produced by these in the ether.” If they were right, he observed, “such phenomena as heredity and memory and intelligence, and our ideas of morality and religion . . . are explainable in terms of positive and negative electrons and ether.”
Not all the physicists were quite so confident. As the decade wore on and they delved more deeply into the intricacies of atomic structure, their picture of the natural world grew only murkier. Their perplexity stemmed from two related and equally perplexing phenomena. One was the so-called wave-particle duality of nature at the infinitesimal scale: experiments sometimes showed light and electrons behaving like particles, and other times as waves.
Einstein’s earlier pathbreaking work on the photoelectric effect suggested strongly that light was composed of a stream of “light quanta,” or particles. But he acknowledged that manifestations such as diffraction, interference, and scattering were inescapably wavelike. Instead of reconciling these contradictory observations, he had laid the issue before his colleagues. “It is my opinion,” he declared at a scientific convocation in Salzburg, Germany, in 1909, “that the next phase of the development of theoretical physics will bring us a theory of light that can be interpreted as a kind of fusion of the wave and mission [that is, particle] theories.”
Physicists grappled with the mysteries of subatomic behavior into the mid-1920s, hoping that the steady accretion of observed results would lead them to the truth. But the opposite was the case: the more data they acquired, the less they seemed to know for certain. “The very strange situation was that by coming nearer and nearer to the solution,” reflected the promising young German theoretical physicist Werner Heisenberg, “the paradoxes became worse and worse.” The only answer seemed to be the one proposed as a joke by the British physicist Sir William Bragg: “God runs electromagnetics on Monday, Wednesday, and Friday by the wave theory; and the devil runs them by quantum theory on Tuesday, Thursday, and Saturday.”
It would be Heisenberg and his mentor, the soft-spoken but rigorously logical Dane Niels Bohr, who finally divined the solution, in a process Heisenberg likened to watching an object emerge from a thick fog. Their conclusion was that anything one could know about an event taking place at a quantum scale was limited to what one could observe—and this knowledge depended on the means of observation. In other words, if one used equipment designed to examine electrons as particles, they would appear to behave as particles; if one used equipment best suited for detecting waves, they appeared as waves. Electrons as particles and electrons as waves were equally valid manifestations of the same thing; there was no contradiction, but rather, in Bohr’s term, “complementarity.”
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Theoretical breakthrough that it was, complementarity did nothing to resolve the paradoxical results emanating from the atomic nucleus. Its structure was the second great mystery vexing physicists in the twenties.
Ernest Rutherford depicted the atom as a miniature solar system, with negatively charged electrons surrounding a tiny yet massive nucleus consisting of positively charged protons and negatively charged electrons. The alluring simplicity of this model helped it become received truth, especially after Niels Bohr augmented it in 1913 with the premise that the electrons could orbit only at certain distances from the nucleus associated with specific energy levels; this seemed to reconcile the classical mechanics governing orbital motion with quantum mechanics, which dictated the energy levels and thus the orbital “shells” that electrons could occupy. The atom as a whole carried a neutral charge: the negative charges of its orbital electrons balanced the positive charge of the nucleus, the latter created by an excess of protons over electrons. By Rutherford’s reckoning, therefore, the helium atom had two orbital electrons and a nucle
us comprising four protons and two electrons; radium had 138 electrons and a nucleus of 226 protons and 88 electrons.
It soon became obvious that this model created more problems than it solved—and the heavier the atom, the greater the problems. By 1923, the tenth anniversary of Bohr’s atomic model, physicists were questioning its general applicability. Bohr’s model corresponded to experimental observation only for the very simplest atom, hydrogen, which had only one proton and one electron. At the next-heaviest atom, helium, the model began to break down, creating the anomalies that drew from Max Born his expression of despair.
The troublemakers were those nuclear electrons. No one could explain how such massive particles could fit in the nucleus; or how, once wedged there, the devilishly energetic particles could be made to stay put. Bohr himself was driven to concede that his treasured quantum mechanics might not apply to the nucleus after all, or that some even more novel and confounding mechanics might have to be developed to explain the proliferating experimental anomalies.
The ready solution came from Rutherford. The grand old man of the Cavendish had been mulling over the riddle since the beginning of the decade, when he theorized that electrons became “much deformed” under the intense forces within the nucleus, so that they took on a very different character from orbital electrons. He was thinking that under such circumstances an electron might combine with a proton to form an uncharged, hitherto undetected compound particle he dubbed the neutron.
Rutherford dragooned the ever-faithful Chadwick into the search for the elusive neutron. “He expounded to me at length . . . on the difficulty in seeing how complex nuclei could possibly build up if the only elementary particles available were the proton and the electron, and the need therefore to invoke the aid of the neutron,” Chadwick related years later. “He freely admitted that much of this was pure speculation . . . and seldom mentioned these matters except in private discussion.” But “he had completely converted me.”
As the search proceeded, it became more obvious that solving the mystery of nuclear structure required probes of higher energies than nature provides. Rutherford was not reluctant to state the implications of this rule publicly. Radium emitted alpha particles at a meager 7.6 million electron volts and beta rays—that is, electrons—at only 3 million volts. “What we require,” Rutherford declared, “is an apparatus to give us a potential of the order of 10 million volts which can be safely accommodated in a reasonably sized room and operated by a few kilowatts of power . . . I recommend this interesting problem to the attention of my technical friends.”
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But generating the voltage that Rutherford specified was only part of the problem, and the easiest part at that: nature could meet that specification, as the voltage of a single lightning bolt ran to hundreds of millions of volts. These enormous, fleeting voltages made for pretty spectacles but not much else, however. The problem was harnessing the power, sustaining it, and manipulating it for an assault on the nucleus. “There appears to be no obvious limit to the voltages obtainable” by arrangements common in the power industry such as transformers connected in series, Rutherford declared, adding that a power plant could produce “a torrent of sparks several yards in length and resembling a rapid succession of lightning flashes on a small scale.” But this technology was still not capable of “approaching, much less surpassing, the success of the radioactive elements, in providing us with high-speed electrons and high-speed atoms.”
Scientists who tried managing energies of the necessary magnitude often ended up with equipment blown to smithereens and laboratories littered with glass shards. Some chose to brave nature’s fury: three men from the University of Berlin strung a pair of seven-hundred-yard steel cables between two Alpine peaks and waited for a thunderstorm. When it arrived, they measured the electrical potential at 15 million volts—but an errant lightning strike blasted one of them off the mountain to his death.
American universities, already beginning to enjoy the fruits of collaboration with big business, duly put this relationship to work. The California Institute of Technology received from Southern California Edison Co. the gift of a million-volt transformer so Caltech might develop high-voltage technologies Edison could exploit to transmit electricity to Los Angeles from a proposed dam on the Colorado River, three hundred miles away. (This would be Hoover Dam.) Caltech physicists used the machine to generate X-rays, but it was nowhere near as compact as Rutherford had specified; rather than fitting into “a reasonably sized room,” it filled a three-story, nine-thousand-square-foot building, and had to be anchored in an excavated pit to fit under the roof. And still it was not a serviceable producer of high-energy particle beams. In the end, the unit became best known for the spectacular displays it put on during Caltech’s annual community “exhibit day,” when it could be made to produce a “long sinuous snarling arc” of electricity accompanied by a thunderous report.
One of the foremost figures in the quest was physicist Merle Tuve, who was determined to put a million volts in a vacuum tube at a time when that much energy would blow existing vacuum tubes to bits. “All of us youngsters were, I believe, extremists,” he explained later. “We always wanted to go to extreme of temperature, extreme of pressure, extreme of voltage, extreme of vacuum, extreme of something or other.” His chosen instrument was the Tesla coil, a high-voltage transformer invented by the visionary physicist Nikola Tesla in the 1890s. Tuve’s version was made from copper and wire wound about a hollow three-foot glass tube submerged in a pressurized vat of oil to suppress sparking. He and his colleagues at the Carnegie Institution of Washington managed to produce 1.5 million volts and even to demonstrate the production of beta rays and the occasional accelerated proton, but the device was quirky, erratic, and uncontrollable, and before long, Tuve abandoned it as unsuitable for nuclear research and cursed it as an “albatross.”
Tuve moved on to an electrostatic generator invented by a Princeton University engineer named Robert Van de Graaff. This apparatus consisted of a large hollow metal sphere situated atop a tower through which a continuous belt turned, picking up an electrical charge at the bottom and spraying it out at the top, so that the sphere eventually acquired a suitable voltage. The Van De Graaff produced copious volts and sparks, which would turn it into a staple of many a Hollywood mad-scientist set, but did no better than any of the previous efforts at producing Rutherford’s “copious supply” of high-energy bullets. Tuve and Van de Graaff struggled to make it work with the vacuum tubes and other apparatus necessary to produce a focused beam of charged, energetic particles. Eventually they succeeded, but by the time they did, Van de Graaff’s technology had been outrun by something entirely new.
Its developer was Ernest Lawrence, who had shared his boyhood fascination with electric gadgetry with Merle Tuve, his schoolmate and friend from across the street in a compact South Dakota town named Canton. It was Ernest’s destiny to begin his career at a moment when physics had hit a brick wall in its understanding of the atomic nucleus. The obstacle was galling; physicists could peer over the wall at a murky landscape on the far side, shrouded seductively in mist. Lawrence would breach that wall and clear away the mist, marking at that same moment the transition to Big Science from small science. He did so by inventing a serviceable method for artificially driving subatomic particles into the nucleus with enough energy to give physicists a clear picture of what it was made of. To their colleagues, Rutherford and Lawrence would be known as “the two Ernests,” and their work would bookend an epochal quest for knowledge of the natural world.
Chapter Two
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South Dakota Boy
Turn of the century Canton, South Dakota, was a thriving agricultural town of two thousand residents located near the southwestern wedge of the state, where it met Iowa and Nebraska at the confluence of the Missouri and the Big Sioux Rivers. There Ernie Lawrence and Merle Tuve grew up together in tidy houses facing each other across the street, Merle the elder by
a scant six weeks. Both their families occupied prominent social positions in the town: the Tuves by virtue of Dr. Anthony Tuve’s post as president of Augustana Academy, the local prep school, and the Lawrences from Carl Lawrence’s position as the county superintendent of schools.
As the children of families that valued scholarly pursuits, Ernest and Merle both were inculcated with the virtues of study and knowledge from an early age. This was by no means an eccentric upbringing in the American Upper Midwest of the era. A tradition of academic learning had been brought to the region by its Northern European and Scandinavian immigrants; years later, Ernest’s own expanding laboratory would be staffed with accomplished young researchers who had been introduced to the natural sciences in the rural school systems of Minnesota, Montana, or the Dakotas, and who continued their training at the ambitious land grant colleges of the same states. Their education complemented their uniquely American facility with machines and technology, for they had spent their boyhoods surrounded by mechanical gadgetry: farm machines, radios, and cars. “Most of us were radio hams and had taken apart Model T Fords,” recalled Stanley Livingston, another Midwesterner (Wisconsin) who would play a crucial role in helping Ernest Lawrence to launch his career. So it was less of a coincidence than it might seem that two of the nation’s most eminent physicists would emerge from the same little prairie town or that they would spend the rest of their lives as friends, colleagues, rivals, and adversaries in parallel quests to divine the laws of nature.