Maxwell’s theory was quite powerful. One of its great benefits was its ability to explain what is perhaps the single most important physical phenomenon for our modern civilization: induction. When you move a magnetic field over a conductor like a piece of wire (or alternatively, move the wire through the magnetic field), an electrical current appears in the wire. This is the principle by which virtually all electricity is generated today. Unless you are in a solar-powered home or outdoors, the light by which you are reading this almost certainly relies on electromagnetic induction. Every electrical generator—coal, gas, nuclear—and electrical motor comes down to a magnet moving past a wire or vice versa. Maxwell was able to not only make sense of induction but also predict a strange new phenomenon from it. His theory said that electrical charges and magnets themselves were not so important; it was actually the electrical and magnetic fields (that were thought, remember, to be particular states of the ether) that made induction work. When a magnetic field in a particular spot changed—by moving a magnet close to the spot, say—it generated an electric field. When an electric field changed—by hooking up a battery, say—it generated a magnetic field. So in certain circumstances, the electric and magnetic fields could be separated from their sources and simply generate each other, in a microscopic dance of energy shifting back and forth between electrical and magnetic fields. Maxwell showed mathematically that this shuffling packet of energy would move through the ether in the form of a wave traveling at an astounding 186,292 miles per second.
Maxwell noticed that this was exactly the speed of light, and decided this could not be a coincidence. He concluded that light was nothing but an electromagnetic wave. What we saw with our eyes was merely a special sort of vibration in the ether. There could be many other sorts of vibrations—what we now call radio waves were found in the laboratory by the German physicist Heinrich Hertz in 1888.
So what it meant to do physics around 1900 was to walk in the footsteps of Maxwell. A good theoretical physicist closely examined Maxwell’s equations and thought about the physical behavior of the ether in some particular circumstance (say, inside a radio transmitter). Specific equations would be developed for that situation, and then those would be analyzed for a possible consequence that could be seen in the laboratory or on the engineering bench.
This is what filled the science books that the adolescent Einstein pored over while lying on his parents’ couch. He thought deeply about the behavior of the ether and wondered about its properties. When he was about sixteen, a particular puzzle occurred to him during these speculations. What would happen if, he pondered, he ran alongside an electromagnetic wave at the speed of light? If you ran at ten miles per hour alongside a train going the same speed, it would essentially appear as though the train was not moving. This was Galileo’s great insight (though he used ships instead of trains) and was often called the principle of relativity. It essentially argued that motion was relative—someone sitting on the train appeared to be moving to someone standing on the platform, but the train passenger was perfectly justified in claiming that they were sitting still and the person on the platform was moving.
Einstein wondered how this could apply to waves moving through the ether. Maxwell’s equations described a wave of alternating electrical and magnetic fields moving through this universal substance at the speed of light. So if Einstein ran alongside that wave—at the speed of light compared to a stationary ether—the wave should not appear to be moving. Like the person running alongside the train, that very fast runner will see the wave frozen in place. This was what Galileo’s thought experiment would seem to suggest anyway. But Einstein realized that such a frozen wave made no sense in Maxwell’s theory. There was no equation to represent electromagnetic waves sitting still. It was the very nature of those shifting fields that they must move. Galileo’s claim—that motion was always relative, that no one observer could declare that they were “really” moving and someone else was not—was not easily applied to the world of electromagnetism. The ether seemed to provide an absolute reference. Someone moving against the background of the ether could tell they were really moving because of how electromagnetic waves zoomed around them. Einstein realized there was something wrong with how physics was thinking about motion in the ether.
Einstein certainly wasn’t alone in this realization, and many of the great minds of physics were occupied with attempted solutions to these problems. Einstein most admired the work of Hendrik Antoon Lorentz, a Dutch physicist who had constructed a masterful theoretical extension of Maxwell’s physics, combining those equations with the recently discovered electron. Einstein and his circle of friends eagerly discussed the work of Lorentz and others, carefully studying papers that appeared in journals such as the prestigious Annalen der Physik coming out of Germany.
Journals such as the Annalen were the lifeblood of science. Whether someone had carried out a new experiment or found a new theoretical explanation, it hardly mattered unless they told someone about it. Sometimes this could be done in person at conferences or similar events. The scientific groups that organized these were often nationally oriented, such as the German Physical Society, the French Academy of Sciences, or the Royal Society in Great Britain. But it was not always possible to attend, and who wanted to wait a year until the next meeting? So those scientific groups often published journals in which scientists reported their latest work. Thus students like Einstein, or someone far removed from the centers of scientific work, could still keep up to date with the latest developments through the mail. The scientific community was defined, in a large sense, by where these journals could travel. A French scientist could feel as though they were participating in German research, reacting to developments and contributing their own ideas.
The papers in these journals provided Einstein the opportunity to argue with Mileva and Michele over equations of electromagnetic optics, the validity of mathematical transformations, and the proper interpretation of experiments with giant electric coils. Many of the papers were incremental additions and adaptations of ether theory. Very few scientists had the virtuosity seen in Lorentz’s attempts to overhaul the whole system and grasp the most fundamental principles at work. Ether theory accumulated a number of strange puzzles, though no one truly doubted it. It was the hypothesis that led to the greatest triumphs of physics, from electrification to radio—how could it be wrong? Even Lorentz became frustrated on occasion, though. He wrote down a series of equations—now called the Lorentz transformations—that made some of the puzzles go away if one adopted the ridiculous hypothesis that measurements of time and space could change as one moved through the ether. He reassured his readers that this idea was merely a mathematical convenience to make calculations work out correctly, and should not be taken seriously.
This was the kind of work on which Einstein wanted to spend his days. Einstein even came up with an experiment to measure the Earth’s movement through the ether (the so-called ether drift). But in order to do that kind of cutting-edge physics, the young scientist needed to appease certain bourgeois conventions: he had to finish his degree. He and Mileva studied together intently. Einstein was constantly apologizing for wandering off with her physics texts without asking, and his habit of forgetting his apartment keys often complicated getting them back. Come the graduation exams, Einstein received an average of 4.91 out of 6—the lowest grade among those who passed. Mileva received a 4 and was denied her diploma. Discouraged but not defeated, she went back to studying as Albert spent the spring of 1901 trying to figure out what to do with his life.
He had hoped to be able to get a job as an assistant in a physics laboratory. Most graduates of the ETH could. Einstein could not. The chief requirement for getting such a position was a letter of recommendation from the applicant’s college professors, usually praising their work ethic and responsibility. Einstein’s teachers had vivid recollections of the lazy dog skipping their classes, though, and declined to support his applications. As hi
s mailbox filled with rejection letters, Einstein began to wonder if his chief recommender, Weber, was actively sabotaging his attempts to find employment.
Beyond the inherent anxiety of a new college graduate looking for work, Einstein had some additional pressures. Mileva was pregnant and they were not married. Einstein’s mother was deeply traumatized at the thought of him marrying this Serbian—especially while unemployed—and made her feelings known sharply. As Einstein tried to calm his family, Mileva went home to Novi Sad to deliver their baby, a daughter referred to as Lieserl. Einstein sent a steady stream of letters to them, remarking that he had forgotten his nightshirt, toothbrush, comb, and hairbrush while traveling.
Einstein never met the baby. We do not know her fate. She suffered an attack of scarlet fever at one point, and may have died or been given up for adoption or taken in by a family member. Mileva returned to Switzerland alone. She and Albert married in a civil ceremony on January 6, 1903. Returning to their apartment after the wedding that night, he realized he had forgotten his keys. They had to wake the landlord.
Fortunately Einstein had found a way to support his new bride despite his total failure to secure a job in physics. Thanks to his friend Grossmann’s father, Einstein began work as a Technical Expert III Class at the Swiss patent office in Bern. The head of the office was somewhat skeptical that this fuzzy-headed theorist could handle the day-to-day practicalities of invention and industry. But Einstein had grown up surrounded by electricity meters and dynamos. He was quite comfortable with machines. He liked standing at his desk and distilling a complicated patent application to its simplest essence: was the machine based on a fundamental principle that would work? Years later he recalled fondly his time at the patent office, remarking that it helped shape his distinctive approach to scientific problems: “It enforced many-sided thinking and also provided important stimuli to physical thought.”
Einstein’s entry into the federal bureaucracy was just one part of a wider embrace of his new home. He had already taken on Swiss citizenship. And—in an amazing move considering his disgust at the kaiser’s army—reported for a physical for military service. The health examination recorded his varicose veins and flat, sweaty feet. He was marked unfit for service and was required to pay a small fee to compensate, which he dutifully sent in for the rest of his life.
He found Bern charming. In a letter to Mileva he sang its praises: “An ancient, exquisitely cozy city, in which one can live exactly as in Zurich. Very old arcades stretch along both sides of the streets, so that one can go from one end of the city to the other in the worst rain without getting noticeably wet. The homes are uncommonly clean.” In the summer of 1903 they moved into an apartment at Kramgasse 49, a beautiful old street. The next year their first son, Hans Albert, was born there.
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EDDINGTON’S FAMILY WAS perturbed that marriage and children did not seem to be anywhere in his future. After some tense conversations when he apparently declined to marry one Emmeline Yates (her brother Rex was a friendly swimming partner), he focused again on his science. His impressive placement on the Tripos exam led to an invitation from William H. M. Christie, the eighth Astronomer Royal, to become chief assistant at the Royal Greenwich Observatory.
The observatory was the literal heart of the British Empire—it defined the meridian on the globe from which all distances and times were measured. Precision measurements of the motions of the stars made there were the foundation of the navigational tables on which British ships relied. It was the most visible and important site of astronomy anywhere. The importance of astronomy for commercial, political, and military power was undoubted.
The chief assistant position was traditionally filled with one of the top wranglers from Cambridge, in order to put their mathematical skills to work for the nation. Strangely, few of those Cambridge men would have had much experience with observational astronomy—that is, actually looking through sophisticated telescopes and making precise measurements of stars and planets. Instead, their education usually focused on mathematical astronomy and physics—using the laws of nature to calculate the forces acting on those stars and planets, and predicting their movements.
Those sorts of calculations were, at root, based on the work of Cambridge’s own Sir Isaac Newton. In the late seventeenth century Newton revolutionized physics and astronomy with an entirely new set of concepts and methods. The core of the Newtonian world view was his laws of motion and his theory of gravity. The laws of motion gave the basic interactions of forces and matter—objects tend to continue moving in their current way unless acted upon by a force (inertia); larger forces produce greater acceleration; and every force has an equal and opposite reaction. The law of gravity was fairly simple conceptually but rich in consequences: every piece of matter in the universe exerts a force of attraction on every other piece of matter, increasing with the size of the masses and decreasing rapidly with the square of the distance between the masses (that is, doubling the distance quarters the force). Newton also provided new mathematical tools to combine with these ideas, and he was able to explain and predict both the motions of the heavens and Eddington’s more terrestrial golf balls. He bound together the universe through gravity.
A basic application of this idea is the planetary orbits. A planet like Earth tries to move in a straight line through space, but the gravity of the sun pulls that line around in a curve, making an ellipse over which the planet travels year by year. High school physics is enough to show why the Earth moves as it does. The calculations become much more complicated once you take into account all the other bodies in the solar system, though. For a solid prediction of the Earth’s motion you need to calculate not just the force of the sun, but also that of the moon, Venus, Mercury, Mars, Jupiter, Saturn, and so on, all of which are themselves in motion and also subject to those same forces. These equations are ferociously difficult and require the highest skill. An exact solution to the equations is actually impossible; the best that could be done was increasingly precise approximation.
Newton’s own mathematics proved to be largely inadequate for this, and it was more common that the tools of the French astronomer Pierre-Simon Laplace were used for day-to-day work. This detail was often ignored as English scientists proudly claimed ownership of the physics underlying the cosmos. Newton’s theory was the most successful of all time and Eddington’s new job required an absolute mastery of it. He rose to the challenge and set to applying the equations of gravity to an entirely new realm: the movements of the Milky Way as a whole. He tried to analyze the motions of what he called “star streams”—vast currents of billions of stars spinning through space, held together only by Newton’s gravity.
Perhaps Eddington focused on distant oceans of stars to separate himself from developments on the seas closer to home. The Royal Observatory was closely tied to the Royal Navy, which was increasingly worried about a new competitor. As part of Germany’s push for imperial status, in 1898 Adm. Alfred von Tirpitz proposed to build a fleet that could challenge the British. It had been British policy for decades to maintain unquestioned naval superiority—without control of the seas, the empire would wither and die. So the German shipbuilding program was seen as a direct existential threat. British industry stepped up not just quantity but quality. The First Sea Lord Sir John Fisher introduced new, powerful designs such as the dreadnought and the battlecruiser. Both Germany and Britain poured resources into an arms race for larger, faster, better-armed ships. Other powers around the globe began to follow suit.
Germany was preparing its military on land as well as sea. Their army was very well equipped and extremely well trained. And despite their size, they expected to be outnumbered in any European conflict. If Russia and France honored their mutual defense treaties, Germany would find itself fighting on two fronts. And even worse, Russia was gradually modernizing its army and within a generation would be a genuine threat. The German High Command decided that it
could not win an extended war and instead gambled on their operational superiority to knock their likely opponents out early in any fighting. In 1905, Gen. Alfred von Schlieffen finalized his invasion plan. This called for a lightning-fast mobilization (made possible by the efficient German railway system) supporting a vast flanking movement through Belgium into northern France. Once the French were outmaneuvered and defeated, forces would then be shifted eastward to confront the slower-mobilizing Russians. This depended on precise timing and a carefully orchestrated logistical plan. A formidable task, but intricate offensive plans were how the Germans won in 1871, and they had only been improving since then.
Having escaped the kaiser’s armies himself, Einstein spent little time thinking about these arms races. The diplomatic neutrality of the Swiss meant he could focus on his physics. Some of his attention was spent on what is called statistical mechanics, the analysis of the movement of atoms and molecules on a microscopic level. The hypothesis of molecular motions (it was still not universally accepted that ordinary objects were made up of tiny particles) had been immensely fruitful for understanding the behavior of heat. Einstein found he had some talent at the statistical methods needed for these investigations, and worked steadily at polishing up a paper on molecular motions that would be sufficient for a doctoral thesis.
His scientific passions remained focused on the mysteries of electromagnetism, however. One particular formulation stuck in his head. It was again based on induction, that phenomenon underlying so much of Einstein’s world. Imagine the coil of wire and magnet at the heart of every electric dynamo. Place the wire at rest against the unseen ether. Now move the magnet past it. The magnetic field in the ether around the wire will increase as the magnet gets closer. By Maxwell’s equations this changing magnetic field creates an electric field that then pushes a current through the wire. But if the magnet is at rest in the ether and the wire is moved past it, Maxwell’s equations predict a current without any electrical field. Einstein was frustrated that there was an asymmetry here. The same observable situation—moving wires and magnets past each other—was given a different physical explanation: electric versus magnetic fields. The “what” was the same in both cases, but the “why” was different.
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