These are nearly the considerations which drove me to still think about the perturbation of light rays, which as far as I know was not studied by anyone… Hopefully no one finds it problematic that I treat a light ray almost as a ponderable body.”
—Johann Georg von Soldner, “On the Deflection of a Light Ray from Its Rectilinear Motion,” 1804
THE CONCEPT OF dwarfs standing on the shoulders of giants—nanos gigantum humeris insidentes—is first ascribed to the twelfth-century philosopher and scholar Bernard of Chartres. It was made famous in English by Sir Isaac Newton and later invoked by Einstein when he was referring to his own advances in physics. But Einstein didn’t just improve and cultivate the accomplishments of his predecessors; he created dazzlingly new concepts. His manner of thinking appeared to be opposite that of his peers. He perfected the approach of considering experiments in the realm of pure thought. He was not bound to mere observation of an experiment. As a result, his work would produce a mind-wrenching shift in how humanity viewed its place in the universe. He might have needed those gigantic shoulders of Newton and nineteenth-century mathematical physicist James Clerk Maxwell, as well as the broad shoulders of his colleagues Max Planck, Hendrik Lorentz, Ludwig Boltzmann, and others, so that he could see farther. But he also needed the visual acuity of a prophet.
In 1895, when he was sixteen years old, Einstein began using a plan of conceptualization that would later rescue him from what he had believed would be a lackluster academic career. While the world around him was still comfortable with Victorian railways, ocean liners, hansom cabs, and steamer trunks, he imagined himself chasing a beam of light as it sped through the blackness of space, traveling faster than 186,000 miles per second. Within that early idea conceived by a teenager lay a seed that would later blossom into his first major scientific breakthrough.
Einstein certainly wasn’t the first thinker to use this process, called a thought experiment, a method of exploring complex ideas within the mind, especially if physical experiments are impossible. Over the ages, this device of intellectual pondering has been used in many fields, from law to philosophy. It predates Socrates. But in physics and related sciences, thought experiments can be traced back to the early 1600s and Galileo’s ship, an imagined vessel set sail to challenge the belief that the earth was stationary in the heavens. It was Hans Christian Øersted, a Danish physicist and chemist, who more adequately described thought experiments, in around 1812. Øersted also gave the method a name, using the mixed Latin-German term gedankenexperiment. The thought experiment would become the kind of speculative device that seemed custom designed for Einstein.
After Einstein’s youthful thought experiment in 1895, more such experiments would follow, involving trains and flashes of lightning, clock towers, speeding automobiles, falling workers, and plummeting elevators. But first, real life, outside the confines of his mind, was also happening. If we consider a young Einstein less than ten years before his first major accomplishment, the special theory of relativity, we could not imagine him becoming a world figure. In 1896, at the age of seventeen, he enrolled in the Swiss Polytechnic Institute, in Zurich. When asked by a professor why he didn’t go into a field like medicine or perhaps even law, Einstein was self-critical. “Because I have even less talent for those subjects,” he replied. “Why shouldn’t I at least try my luck with physics?”
In the autumn of that same year, he met his future wife, Mileva Marić, a fellow student and the only woman at the institute. An ethnic Serb from a wealthy family whose large acreage lay on the banks of the Danube River, she was almost four years Albert’s senior. Petite and humbly attractive, she walked with a limp, having been born with a dislocated hip joint. She had been sent to Switzerland and the institute by her family because women were still not allowed to attend university in the Austro-Hungarian Empire at that time. A year later, Albert had fallen passionately in love with the woman he would refer to as his “Dollie.”
If his future academic life seemed shaky, his courtship and forthcoming marriage would be even shakier. For the next few years, Albert penned passionate love letters to Mileva while weathering the wrath that his parents and sister rained down against his future bride. Miss Marić did not live up to the image of the woman they envisioned marrying their Albert. For one thing, overlooking her intelligence, she was plain in her appearance. For another she had the physical disability. And adding to the strikes already against her, Mileva was certainly not German. “My parents weep for me almost as if I had died,” Albert wrote to Mileva. “Mama threw herself on the bed, buried her head in the pillow, and wept like a child.”
In the summer of 1900, Einstein graduated from the institute with a diploma to teach science. But even with his father’s help, he had no luck in procuring a university job. Marcel Grossman, a family friend, suggested he apply to the patent office in Bern, Switzerland. As Einstein awaited word, he accepted a temporary job teaching math in Winterthur, Switzerland. His family’s aversion to his relationship with Mileva Marić did not lessen his ardor for her; nor did it help. He was already burdened with the possibility of not being offered the patent office job. With his family bearing down on him about his love life, he became disagreeable with Mileva. In a conciliatory letter written at the end of 1901, he admitted to being short and temperamental. To make it up to her, he decided they should meet at Lake Como.
Situated on the border of Switzerland and Italy, the lake had been immortalized in literature. The hapless lovers in The Betrothed, published in 1827 and the most widely read novel in the Italian language, hailed from a village on Lake Como. The poets Percy Shelley and William Wordsworth had fallen in love with the beauty of the region. After a 1790 walking tour, Wordsworth wrote the poem “Lake of Como,” in which he refers to it as “a treasure whom the earth keeps to herself,” The musical superstar Franz Liszt would often escape there with his mistress. Albert had selected a most romantic setting. Accepting his apology, Mileva went to meet him, arriving by train as Albert waited at the station. They spent the night together in a cozy inn. The next day, a horse and sleigh pulled them through falling snowflakes as they snuggled beneath coats and shawls. This lovers’ rendezvous would change Mileva Marić’s life forever.
Albert went back to his job teaching math as a substitute teacher. Since the scientific community of the day supported the idea that everything worth discovering in physics had already been discovered, he decided that mathematics would be a good career path, as it had been for Planck, and for the same reason. During this time, Mileva informed him that she was pregnant. Having once planned to earn her doctorate and become a physicist—a rare vocation for any woman then—she realized that becoming a mother would change all those plans. Albert wrote to her that he was working on the “electrodynamics of moving bodies.” He mentioned that he would like to have Mileva with him, “in spite of your ‘funny figure,’” referring to her pregnancy. Apparently curious about her appearance, he suggested that she “Draw it for me!” It’s possible that his mother, Pauline Einstein, had also learned of the pregnancy. Mrs. Einstein would not be interested in any artwork that celebrated it. She wrote to a friend, “That miss Maric gives me the bitterest hours of my life, if it were in my power I would do all I could to ban her from our horizon.”
Before their first child arrived, Albert had managed to find a steady job that might support his young family should he and Mileva finally wed. In December, he received word from the patent office in Bern. Offered the job as a third-level junior clerk, he eagerly accepted it. The patent office wasn’t the most inspiring work. Among the patents that would cross his desk for evaluation were those for an electromechanical typewriter and a gravel sorter. But the job paid well enough, and he needed an income. “I am an honorable federal ink pisser with a steady salary,” he would write to a friend. The hiring was also timely since a baby girl, Lieserl, was born in January 1902.1
That Einstein was much more enigmatic than anyone realized is a detail that almost escaped the world’s notice. He kept a universe of personal secrets inside his head, along with all that brilliance. Most amazing about Mileva’s premarriage pregnancy or Lieserl’s birth is that almost no one knew about them until thirty years after Einstein died. Remarkably, a good deal of his life as a lover and an eventual husband to Mileva Marić was disclosed only when their granddaughter found a shoebox filled with old letters. The packet had been bound with a worn ribbon. It appears that for almost fifty years, Mileva had saved the letters Albert had written to her.2
Given the many turbulent years in Einstein’s personal life as he conceptualized ideas that would change the world of physics, it’s astonishing that he accomplished anything at all. But other scientists before and after Einstein also utilized emotional turmoil to fuel their productivity. And Einstein had it in spades. Whatever happened to Lieserl has been a subject of speculation for years. The letters back and forth between her parents, at least those that still exist, do not say whether the child died or was adopted. They only speak of the birth at her maternal grandparents’ home in Novi Sad, Serbia; of Mileva’s difficulty in delivering the baby; and the child’s illness from scarlet fever. Albert showed concern for his daughter, at least in his letters. “I love her so much and I don’t even know her yet! Couldn’t she be photographed once you are totally healthy again? Will she soon be able to turn her eyes toward something?” He enjoyed writing about Lieserl, but visiting her seemed less attractive. It’s as if she were another thought experiment, better to imagine in his mind.
The most thorough research indicates that Lieserl was born with intellectual and physical disabilities and likely died of scarlet fever at twenty-one months. From his and Mileva’s letters, Albert apparently never saw his daughter in person, and her condition may have been the reason. He and Mileva married in January 1903, a year after Lieserl’s birth. Mileva moved to Bern to join her husband, but without the baby. Perhaps Albert had his own reasons for this. His extraordinary career was soon to be launched. He was existing on a meager salary at the patent office as it was. And then, what would his family say about his and Mileva’s imperfect child had they been told of her existence? The baby seems to have vanished after Albert’s last mention of her, in September 1903, when Mileva hurried home to Novi Sad after receiving word that Lieserl had come down with scarlet fever. In that letter, he remarked on his daughter’s illness. “I am very sorry about what has happened to Lieserl. Scarlet fever often leaves some lasting trace behind.” He then assured Mileva that she would get “a new Lieserl.”
Years before Albert Einstein began thinking of eclipses, there would be one that would add a footnote to his personal history, although he would never know it. A total solar eclipse occurred on September 21, 1903, the same month he last mentioned their daughter in a letter to Mileva. The moon’s shadow began in water, halfway between Africa and Antarctica, where the cold waves of the Atlantic meet the warmer waves of the Indian Ocean. This eclipse was mostly ignored by science for its unreachability. Its path of totality traveled down into the icy Southern Ocean and cut across Antarctica, ending very near Ross Island in a world of subfreezing temperatures and summers of constant daylight and winters of complete darkness. Probably the only witnesses to near totality, except for seals and penguins, was Captain Robert Falcon Scott and his crew, whose ship, the Discovery, was anchored in the waters of McMurdo Sound and frozen for two years into the sea ice. Even if Einstein had been interested in solar eclipses as early as 1903—and he wasn’t—this one would be too insignificant for his attention. But it is likely that it occurred the same day Lieserl died.3
Albert would keep that promise to his wife. Nine months after she returned from Novi Sad and her last visit with Lieserl, she gave birth to Hans Albert, their first son.
Although Albert Einstein was not promoted at the patent office, because he had “not fully mastered machine technology,” at least his job was made permanent. By 1905, he and Mileva, with their young son, had settled into married life in Bern. They rented a third-floor apartment in the Kramgasse (“grocer’s alley”) in the urban center of the city and a close walk to his work. In a way, the patent office was a place free of classrooms and laboratories, where he could think unimpeded. Nor did he have to worry about the curse of funding as he went about his thought experiments, since he was salaried there.
That summer, Einstein published two groundbreaking papers in Berlin’s highly respected physics journal Annalen der Physik. The first paper was on the photoelectric effect, in which he showed that electrons, knocked out of metals when light was shone on a metallic surface, carry the same discrete amount of energy that particles of light, or photons, deliver to the electrons.4 His second paper, on Brownian motion, marked the first time a human being had ever understood the size of atoms.5 This man, still twenty-six years old, was not the wild-haired scientist in the baggy sweaters we later came to expect. He was a young husband and the father of a toddler. In photographs, he is dapper and well-groomed, even handsome, a hopeful scientist with a love for the violin. Nonetheless, he was mired in a mundane job at the patent office, possibly for life, he thought, while he yearned for a university post. But a night in May of that same year—1905 would become known as his annus mirabilis, or miracle year—would change the course of that lackluster career to which Einstein felt doomed.
Michele Besso, several years older, had attended the Swiss Polytechnic Institute when Einstein did and now was a coworker at the patent office in Bern. A friend and colleague, he was also a trusted confidant. While Besso was quite brilliant and intuitive, he unfortunately lacked ambition and focus. He was a good influence on Einstein, however. He had already introduced the younger man to the works of Ernst Mach, who would greatly influence Albert’s approach to physics. Einstein would later call Besso “the best sounding board in Europe.” On that spring evening, he went to Besso’s home to discuss a problem that had plagued his thoughts for a decade: the two mainstays of physics—Newtonian mechanics and James Clerk Maxwell’s equations—were discordant. In Newton’s worldview, all velocities, including those of light, could be added or subtracted. But according to Maxwell, in a view backed up by his equations, the velocity of light is always constant. If one theory were proven to be correct over the other, then the result would mean that all of physics would need to be restructured.
After hours of discussion, frustrated and discouraged, Einstein gave up. He told Besso good night and left for home. What happened next is the most famous streetcar ride in history. As the story is often told, Albert Einstein caught a streetcar home to Kramgasse No. 49, the trolley rumbling eastward over a cobblestoned street toward the apartment he shared with his wife and son. It was a short ride—the entire street is only a thousand feet long—and yet the trip would change the foundation of modern physics. As he stared back at the centuries-old clock tower that stood in the heart of the city, an extraordinary thought experiment occurred to him. He remembered his youthful fantasy of chasing a beam of light through space. What if the streetcar he was riding on should suddenly race away from the clock tower at the speed of light?
Whether Einstein actually caught the streetcar home or walked the entire distance, here is what we do know happened that night. He says it best himself: “A storm broke loose in my mind.” After his discussion with Besso, this mental storm stirred up the ghost that had plagued him since his teenage years. And it freed him to put on paper the conceptual framework he had discussed in a letter to Mileva four years earlier. He titled it “On the Electrodynamics of Moving Bodies,” but the world would come to know it as the special theory of relativity. Tagged onto the end of the paper’s original pages would be a thank you to Besso: “In conclusion I wish to say that in working at the problem here dealt with I have had the loyal assistance of my friend and colleague M. Besso, and that I am indebted to him for several valuable suggestions.”
That paper would lead him, three months later, to publish another paper, this one on the equivalence of mass and energy: “Does the Inertia of a Body Depend Upon its Energy Content?” Those slim pages of the latter document would become science’s greatest afterthought, a brilliant and elegant footnote that would contain E =mc2, the most famous equation on the planet. The magnum opus of Einstein’s miracle year, that equation would link three dissimilar parts of nature: energy, mass, and the speed of light. This mathematical result in physics is perhaps as widely recognized as the first four notes of Beethoven’s Fifth Symphony.
The special theory of relativity hypothesized that the speed of light is constant and absolute, and nothing that conveys information can go faster. When objects travel at speeds that approach the speed of light, strange things occur. They will be measured by observers at rest to get shorter in the direction of travel, their mass will increase, and time will pass more slowly for all events on the moving object. Up until this time, and thanks to Newton’s laws of physics, it was believed that space had three dimensions and that time had only one. But more importantly in Newtonian physics, the rate at which time passes is universal, a trait called absolute time. Einstein put space and time together in a four-dimensional system where they can’t be separated or observed independently. Thus, energy and mass are the same, which is the fundamental idea of E = mc2. Energy equals mass times the speed of light squared. Therefore, a minuscule amount of matter as small as an atom could produce a tremendous amount of energy. And until a patent office clerk envisioned it, no one understood or even noticed the existence of this accessible energy.6
Given his annus mirabilis of 1905, academia finally took notice of the twenty-six-year-old who had once considered physics a hobby. If Einstein had published nothing more in his lifetime than the special theory of relativity, it would have been amazing enough in the career of any physicist. But he was not yet done. In 1907, he began challenging the classical physics of Sir Isaac Newton. In Opticks, his monumental book published in 1704, Newton had predicted that if a ray of light from a distant star grazes the edge of a huge object, the light should bend, depending on the object’s mass and, therefore, its gravitational field. “Do not bodies act upon light at a distance, and by their action bend its rays; and is not this action… strongest at the least distance?” The bigger the object, the bigger the pull. Calculations based on Newton’s prediction had determined that light would bend by 0.87 arc seconds. Given his place in time, Newton would have been unable to carry out any tests.7
Newton and Einstein were not the only ones to speculate on the gravitational bending of light. Johann Georg von Soldner, a German physicist, mathematician, and astronomer, also addressed Newton’s question. The son of a farmer and primarily self-taught, Soldner wondered if the bending of light rays might require an adjustment of certain astronomical observations. His calculations, which were published in a paper in 1804, predicted that light would bend by 0.84 arc seconds, incredibly close to Newton’s own numbers a hundred years earlier. But as there was still no practical way to make an observation that could either confirm or deny the calculations, Soldner’s paper roused even less attention from his peers than Einstein’s did when it initially was released.8
In 1909, Einstein was finally able to leave the patent office behind for an academic post at the University of Zurich. He barely had time to settle his family into a new home when a better offer arrived in March 1910. He was asked to consider a full professorship at the University of Prague. It was definitely a step up the academic ladder, even though Mileva, then five months pregnant, was not anxious to move to Prague. In late July, the couple welcomed Eduard, their second son, on the heels of two comets, the unexpected Great January Comet in January, and the highly anticipated Halley’s Comet in April. Mileva again had a difficult delivery and was ill for weeks after the baby was born.
The next spring, accepting the new position at the university, Einstein moved his family to Prague. While neither he nor Mileva were thrilled with the shabbiness of the city, they nonetheless enjoyed electric lighting for the first time and could afford to hire a housekeeper. Einstein settled into his new office and went to work. Unaware of Soldner’s calculations, he returned to the light deflection problem. He had supposed that the effect would be too small to be observed or measured. In this recent calculation, he repeated the problem based on Newtonian theory. Using his own equation E = mc2, he calculated the bending of light and came up with a value. Light grazing the sun’s outer edge would bend 0.83 arc seconds. This calculation was close to the great master’s thoughts two hundred years earlier.
But it was still just a calculation. How might one measure the effects of gravity on straight beams of light? What source would be large enough to do this? The answer was the sun, since it has 300,000 times more mass than the earth has. One way this theory could be proven would be to observe the positions of stars. Since the sun is our closest source of a strong gravitational field, starlight traveling through space and passing its field would be bent. Therefore, if one could observe a certain star or stars during the day, they should be in a different place than observing them at night, when the light emanating from them to our eyes would not be traveling past the sun. The only way to see stars in the daytime would be during a total solar eclipse.
In June 1911, Einstein completed his paper “On the Influence of Gravity on the Propagation of Light” and again submitted it to the Annalen der Physik. Even at this respected journal, which had been in business since 1799, publication rules were still relaxed in the early twentieth century. There was no peer-review process. By 1911, the journal’s submissions were overseen by two editors and an associate editor. Planck’s position as associate editor since 1895 meant that Einstein could submit papers to his good friend, who published them in the next available issue. Thus, Einstein’s eleven-page paper on light deflection was received by the journal on June 21, 1911. It would appear in volume 35, on the first day of September. Since the journal published its papers in German only, the paper would have a limited reading audience in the scientific community. As the ink was drying on his latest calculations, Einstein needed two things: a total believer, and a total eclipse of the sun.