Einstein (34 page)

Einstein admired the pluck and courage of a feisty female physicist who had emerged from a land where women were generally not allowed to go into that field. Nowadays, when the same issues still reverberate across a century of time, the courage that Mari
displayed by entering and competing in the male-dominated world of physics and math is what should earn her an admired spot in the annals of scientific history. This she deserves without inflating the importance of her collaboration on the special theory of relativity.
⁸⁰

Einstein had raised the curtain on his miracle year in his letter to his Olympia Academy mate Conrad Habicht, and he celebrated its climax with his one-sentence drunken postcard to him. In September, he wrote yet another letter to Habicht, this one trying to entice him to come work at the patent office. Einstein’s reputation as a lone wolf was somewhat artificial. “Perhaps it would be possible to smuggle you in among the patent slaves,” he said. “You probably would find it relatively
pleasant. Would you actually be ready and willing to come? Keep in mind that besides the eight hours of work, each day also has eight hours for fooling around, and then there’s also Sunday. I would love to have you here.”

As with his letter six months earlier, Einstein went on to reveal quite casually a momentous scientific breakthrough, one that would be expressed by the most famous equation in all of science:

One more consequence of the electrodynamics paper has also crossed my mind. Namely, the relativity principle, together with Maxwell’s equations, requires that mass be a direct measure of the energy contained in a body. Light carries mass with it. With the case of radium there should be a noticeable reduction of mass. The thought is amusing and seductive; but for all I know, the good Lord might be laughing at the whole matter and might have been leading me up the garden path.
⁸¹

Einstein developed the idea with a beautiful simplicity. The paper that the
Annalen der Physik
received from him on September 27, 1905, “Does the Inertia of a Body Depend on Its Energy Content?,” involved only three steps that filled merely three pages. Referring back to his special relativity paper, he declared, “The results of an electrodynamic investigation recently published by me in this journal lead to a very interesting conclusion, which will be derived here.”
⁸²

Once again, he was deducing a theory from principles and postulates, not trying to explain the empirical data that experimental physicists studying cathode rays had begun to gather about the relation of mass to the velocity of particles. Coupling Maxwell’s theory with the relativity theory, he began (not surprisingly) with a thought experiment. He calculated the properties of two light pulses emitted in opposite directions by a body at rest. He then calculated the properties of these light pulses when observed from a moving frame of reference. From this he came up with equations regarding the relationship between speed and mass.

The result was an elegant conclusion: mass and energy are different manifestations of the same thing. There is a fundamental interchangeability between the two. As he put it in his paper, “The mass of a body is a measure of its energy content.”

The formula he used to describe this relationship was also strikingly simple: “If a body emits the energy
L
in the form of radiation, its mass decreases by
L/V
²
.” Or, to express the same equation in a different manner:
L=mV
²
. Einstein used the letter
L
to represent energy until 1912, when he crossed it out in a manuscript and replaced it with the more common
E.
He also used
V
to represent the velocity of light, before changing to the more common
c.
So, using the letters that soon became standard, Einstein had come up with his memorable equation:

E=mc
²

Energy equals mass times the square of the speed of light. The speed of light, of course, is huge. Squared it is almost inconceivably bigger. That is why a tiny amount of matter, if converted completely into energy, has an enormous punch. A kilogram of mass would convert into approximately 25 billion kilowatt hours of electricity. More vividly: the energy in the mass of one raisin could supply most of New York City’s energy needs for a day.
⁸³

As usual, Einstein ended by proposing experimental ways to confirm the theory he had just derived. “Perhaps it will prove possible,” he wrote,“to test this theory using bodies whose energy content is variable to a high degree, e.g., salts of radium.”

Einstein’s 1905 burst of creativity was astonishing. He had devised a revolutionary quantum theory of light, helped prove the existence of atoms, explained Brownian motion, upended the concept of space and time, and produced what would become science’s best known equation. But not many people seemed to notice at first. According to his sister, Einstein had hoped that his flurry of essays in a preeminent journal would lift him from the obscurity of a third-class patent examiner and provide some academic recognition, perhaps even an academic job. “But he was bitterly disappointed,” she noted. “Icy silence followed the publication.”
¹

That was not exactly true. A small but respectable handful of physicists soon took note of Einstein’s papers, and one of these turned out to be, as good fortune would have it, the most important possible admirer he could attract: Max Planck, Europe’s revered monarch of theoretical physics, whose mysterious mathematical constant explaining black-body radiation Einstein had transformed into a radical new reality of nature. As the editorial board member of
Annalen der Physik
responsible for theoretical submissions, Planck had vetted Einstein’s papers, and the one on relativity had “immediately aroused my lively attention,” he later recalled. As soon as it was published, Planck gave a lecture on relativity at the University of Berlin.
²

Planck became the first physicist to build on Einstein’s theory. In an article published in the spring of 1906, he argued that relativity conformed to the principle of least action, a foundation of physics that holds that light or any object moving between two points should follow the easiest path.
³

Planck’s paper not only contributed to the development of relativity theory; it also helped to legitimize it among other physicists. Whatever disappointment Maja Einstein had detected in her brother dissipated. “My papers are much appreciated and are giving rise to further investigations,” he exulted to Solovine. “Professor Planck has recently written to me about that.”
⁴

The proud patent examiner was soon exchanging letters with the eminent professor. When another theorist challenged Planck’s contention that relativity theory conformed to the principle of least action, Einstein took Planck’s side and sent him a card saying so. Planck was pleased. “As long as the proponents of the principle of relativity constitute such a modest little band as is now the case,” he replied to Einstein, “it is doubly important that they agree among themselves.” He added that he hoped to visit Bern the following year and meet Einstein personally.
⁵

Planck did not end up coming to Bern, but he did send his earnest assistant, Max Laue.
*
He and Einstein had already been corresponding about Einstein’s light quanta paper, with Laue saying that he agreed with “your heuristic view that radiation can be absorbed and emitted only in specific finite quanta.”

However, Laue insisted, just as Planck had, that Einstein was wrong to assume that these quanta were a characteristic of the radiation itself. Instead, Laue contended that the quanta were merely a description of the way that radiation was emitted or absorbed by a piece of matter. “This is not a characteristic of electromagnetic processes in a vacuum but rather of the emitting or absorbing matter,” Laue wrote, “and hence radiation does not consist of light quanta as it says in section six of your first paper.”
⁶
(In that section, Einstein had said that the radiation “behaves thermodynamically as if it consisted of mutually independent energy quanta.”)

When Laue was preparing to visit in the summer of 1907, he was surprised to discover that Einstein was not at the University of Bern but was working at the patent office on the third floor of the Post and Telegraph Building. Meeting Einstein there did not lessen his wonder. “The young man who came to meet me made so unexpected an impression on me that I did not believe he could possibly be the father of the relativity theory,” Laue said, “so I let him pass.” After a while, Einstein came wandering through the reception area again, and Laue finally realized who he was.

They walked and talked for hours, with Einstein at one point offering a cigar that, Laue recalled, “was so unpleasant that I ‘accidentally’ dropped it into the river.” Einstein’s theories, on the other hand, made a pleasing impression. “During the first two hours of our conversation he overthrew the entire mechanics and electrodynamics,” Laue noted. Indeed, he was so enthralled that over the next four years he would publish eight papers on Einstein’s relativity theory and become a close friend.
⁷

Some theorists found the amazing flurry of papers from the patent office to be uncomfortably abstract. Arnold Sommerfeld, later a friend, was among the first to suggest there was something Jewish about Einstein’s theoretical approach, a theme later picked up by anti-Semites. It lacked due respect for the notion of order and absolutes, and it did not seem solidly grounded. “As remarkable as Einstein’s papers are,” he wrote Lorentz in 1907, “it still seems to me that something almost unhealthy lies in this unconstruable and impossible to visualize dogma. An Englishman would hardly have given us this theory. It might be here too, as in the case of Cohn, the abstract conceptual character of the Semite expresses itself.”
⁸

None of this interest made Einstein famous, nor did it get him any job offers. “I was surprised to read that you must sit in an office for eight hours a day,” wrote yet another young physicist who was planning to visit. “History is full of bad jokes.”
⁹
But because he had finally earned his doctorate, he had at least gotten promoted from a third-class
to a second-class technical expert at the patent office, which came with a hefty 1,000-franc raise to an annual salary of 4,500 francs.
¹⁰

His productivity was startling. In addition to working six days a week at the patent office, he continued his torrent of papers and reviews: six in 1906 and ten more in 1907. At least once a week he played in a string quartet. And he was a good father to the 3-year-old son he proudly labeled “impertinent.” As Mari
wrote to her friend Helene Savi
, “My husband often spends his free time at home just playing with the boy.”
¹¹