In his 1902 book Science and Hypothesis, the French mathematician and physicist Henri Poincaré surveyed the landscape of modern physics and found three fundamental conundrums bedeviling his field: the chaotic zigzagging of small particles suspended in liquid, known as Brownian motion; the curious fact that metals emit electrons when exposed to ultraviolet light, known as the photoelectric effect; and science's failure to detect the ether, the invisible medium through which light waves were thought to propagate. In 1904 a 25-year-old Bern patent clerk named Albert Einstein read Poincaré's book. Nothing the young physicist had done with his life until that point foreshadowed the cerebral explosion he was about to unleash. A year later, he had solved all three of Poincaré's problems.
"A storm broke loose in my mind," Einstein would later say of 1905, the annus mirabilis, which John S. Rigden calls "the most productive six months any scientist ever enjoyed." Between March and September, he published five seminal papers, each of which transformed physics. Three were Nobel Prize material; another, his thesis dissertation, remains one of the most cited scientific papers ever; and the fifth, a three-page afterthought, derived the only mathematical equation you're likely to find on a pair of boxer shorts, E = mc2.
Rigden's short book Einstein 1905 is a tour through each of those landmark papers, beginning with the only one that Einstein was willing to call "revolutionary." That first paper, which would earn him the Nobel Prize sixteen years later, was titled "On a Heuristic Point of View About the Creation and Conversion of Light." It could just as easily have been called "Why Everything You Think You Know About Light Is Wrong."
In 1905 most scientists were certain that light traveled in waves, just like sound. Though it troubled few others, Einstein was deeply perturbed by the notion that energy could flow in continuous waves whereas matter was made up of discrete particles. To paraphrase Bertrand Russell, why should one aspect of the universe be molasses when the other part is sand? When Einstein tried to imagine a universe in which everything, including light, was made up of particles, he realized the simple conceptual shift could explain a lot, including the mysterious photoelectric effect. This was typical of how Einstein thought, argues Rigden. He saw fundamental contradictions in the generalizations that others had made before him and then followed the trail of logic to unexpected conclusions. In some cases it took years before his ideas could be experimentally verified. His theory of light wasn't widely accepted for two decades.
The second paper of the year, completed in April, is the least well remembered, even though its many practical applications have made it one of Einstein's most cited works. In that paper, Einstein suggested a way of calculating the size of molecules in a liquid based on measurements of how the liquid behaves. The paper relied on more mathematical brute force and was less graceful than the other four of the year, but it was important nonetheless. Because it showed how to measure the size of otherwise unobservable atoms, it helped nail the coffin shut on the few lingering skeptics, like Ernst Mach, who still did not buy into the atomic theory of matter.
Even more damning for those atomic skeptics was Einstein's May paper on Brownian motion, which explained the unpredictable dance of pollen grains in water. The reason for the pollen's erratic behavior, Einstein demonstrated, is that it is being constantly bombarded by water molecules. Most of the time, that bombardment occurs equally from all angles, so the net effect on a grain of pollen is zero. But sometimes, statistical fluctuations conspire so that more molecules are pushing in one direction than another, causing a grain to zip through the water. Even though atoms are invisible, Einstein had figured out a way to see them at work. "A few scientific papers, not many, seem like magic," Rigden writes. "Einstein's May paper is magic."
Having dispatched two of Poincaré's conundrums, Einstein next turned his attention to the undetected ether; his June paper ended up being the most earth-shattering of the bunch. It demolished two pillars of Newtonian physics, the notions of absolute space and absolute time. In their place, Einstein constructed the special theory of relativity, which held that time appears to stretch and space appears to shrink at velocities approaching the speed of light. The paper had no citations, as if Einstein owed a debt to no one. In fact, that wasn't the case. "Much of his source material was 'in the air' among scientists in 1905," notes Rigden, "and some of these ideas had been published." Physics was on the verge of something big at the turn of the century. It took an Einstein to pull it all together, to ask the big question in the right way.
The final paper, published in September, might as well have been an addendum to the June paper. The profoundly simple equation he derived in three pages, E = mc2, was a logical consequence of the special theory of relativity. Equating energy and mass, it explained why the sun shines and why Hiroshima was leveled. More than anything else Einstein produced, it has come to symbolize his genius.
A half century after his miracle year, in the final sentence of his final letter to his friend and intellectual sparring partner, the physicist Max Born, a dying Albert Einstein wrote, "In the present circumstances, the only profession I would choose would be one where earning a living had nothing to do with the search for knowledge." And so the man whose thought experiments revolutionized science concluded his life posing a thought experiment about himself: Where would we be if Einstein had become a "plumber or peddler," jobs he once rhetorically suggested he'd prefer, instead of a physicist?
One place to look to start answering that question is the science itself, which is where Rigden's book begins. Another is the man himself, whose personality is abundantly on display in the letters he exchanged with Born between 1916 and 1955. Those letters, which first appeared in German in 1969 and in English two years later, have now been republished along with Born's commentary, Werner Heisenberg's original introduction and a useful new preface by Diana Buchwald and Kip Thorne. The Einstein that comes through in the letters is self-aware, philosophical, politically conscious (if sometimes naïve), modest, generous, an aesthete and--in his exchanges with Born's wife, Hedi--an occasional flirt. From these epistolary glimpses of Einstein the person it's possible to see how his science, which "seems to be so far removed from all things human," is nonetheless, as Heisenberg writes in his introduction, "fundamentally determined by philosophical and human attitudes."
By the time Einstein began corresponding with Born in 1916, his best work was behind him, and he was already an international celebrity. Their letters document the final chapter of Einstein's career, the forty years during which he was an outsider to the quantum physics revolution and alone in his pursuit of a single unified theory capable of explaining all of physics. Ironically, it was at the height of his fame that Einstein was furthest from the scientific mainstream. The aging revolutionary never ceased to be a radical.
Like Einstein, Born was an assimilated German Jew who fled the country's rising anti-Semitism in the early 1930s. Many of their letters from that period concern the deteriorating political situation in Europe and attempts to arrange teaching posts for exiled German scientists. But unlike Einstein, who perceived an inveterate savagery at the heart of German culture and never again set foot on German soil, Born was more forgiving. After sojourning in Edinburgh during World War II, he returned to Göttingen in 1953. They also differed on their shared Jewish heritage. While Einstein was a moderate Zionist, Born saw no difference between Jewish nationalism and all other embodiments of nationalism that he despised. Their political differences, though, were nowhere near as deep as their scientific disagreements.
Einstein considered Born and himself "Antipodean in our scientific expectations." Born was a leading proponent of quantum theory and was awarded the 1954 Nobel Prize for his work establishing the theory's mathematical basis. Einstein was quantum theory's foremost critic. Even though his 1905 paper on the photoelectric effect helped create the field of quantum mechanics, Einstein could never reconcile himself to its nondeterministic implications. He was adamant that the theory provided only a superficial explanation of the universe, and that a deeper theory would someday be found. This conviction was based almost entirely in aesthetic instincts about what the laws of physics ought to look like.
"Quantum mechanics is certainly imposing," he famously told Born. "But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the 'old one.' I, at any rate, am convinced that He is not playing at dice." Einstein believed that there had to be an "objective reality" at the heart of the universe. If quantum mechanics proved correct, he wrote, again teasing with one of his occupational counterfactuals, "I would rather be a cobbler, or even an employee in a gaming-house, than a physicist."
Their quarrel over quantum theory dragged out for more than three decades, but the content of their arguments changed little from the first letters they exchanged on the subject in 1919 right up until Einstein's death. In a 1953 letter Born declares, "I hope to be able to convince you at last that quantum mechanics is complete and as realistic as the facts permit." His attempt to persuade his friend after all those years seems almost comic. He goes on to call Einstein's stubbornness on the subject "quite unbearable."
Einstein's letters tend to be half as long as Born's and twice as pithy, and are almost always prefaced with an apology for having not written back sooner. Though Born and Einstein only met in person once, they grew to address each other in the tone of lifelong friends. There's no shortage of tough honesty in the letters. There's even the occasional spat. Several correspondences are consumed by discussion over whether Einstein should grant a journalist permission to publish a book called Conversations With Einstein. Born and his wife were concerned that the author would depict Einstein unflatteringly. "Your own jokes will be smilingly thrown back at you," Hedi Born warns. "This book will constitute your moral death sentence for all but four or five of your friends." Her husband pleads with Einstein, "You do not understand this, in these matters you are a little child."
Einstein replied, "The whole affair is a matter of indifference to me, as is all the commotion, and the opinion of each and every human being." Nonetheless, Einstein tried and failed to stop the publication of the book, which even Born later admitted wasn't nearly as bad as he had feared. Einstein's detachment is a persistent theme throughout the letters. He tells Born, "I hibernate like a bear in its cave," and in the same letter he off-handedly informs Born of his wife's death, which he describes as just one more thing accentuating his bearish feeling. Einstein's seeming indifference to worldly things leads Born to comment that "for all his kindness, sociability and love of humanity, he was nevertheless totally detached from his environment and the human beings included in it."
Ironically, the vague constellation of traits that, according to Rigden, stimulated Einstein's early discoveries may also help explain why he spent the second half of his career as an outsider to the quantum revolution. The same aesthetic instincts that led him to recognize the inelegance of the old theories about light and space may have blinded him to the decidedly unbeautiful reality of quantum mechanics. The same "stubbornness of a mule" that kept him on the trail of the general theory of relativity for a decade may also have kept him on less fruitful paths later in his career. And the same self-confidence that gave the 26-year-old patent clerk the audacity to challenge the central precepts of classical physics may have prevented him from recognizing his own failure of imagination with regard to quantum mechanics.
Heisenberg writes in his introduction, "In the course of scientific progress it can happen that a new range of empirical data can be completely understood only when the enormous effort is made to...change the very structure of the thought processes. In the case of quantum mechanics, Einstein was apparently no longer willing to take this step, or perhaps no longer able to do so."
But another explanation is possible. Einstein always held that posterity would value his ideas more than his peers did. He was right. Again and again, work that was at first deemed loopy has been vindicated. The quest for a unified theory, once an emblem of Einstein's isolation, has become contemporary physics' Holy Grail. It's possible that Einstein's greatest intellectual gamble, his repudiation of quantum theory, may yet prove as prescient. Indeed, though they are a minority, many highly regarded scientists still harbor the deep discomfort that Einstein felt about quantum theory. In a 1944 letter to Born on the subject, Einstein wrote, "No doubt the day will come when we will see whose instinctive attitude was the correct one." That day may yet be some time off.