Walter Isaacson - Einstein - His Life and Universe

Einstein’s approach to general relativity again showed how his mind tended to work:

• He was disquieted when there were two seemingly unrelated theories for the same observable phenomenon. That had been the case with the moving coil or moving magnet producing the same observable electric current, which he resolved with the special theory of relativity. Now it was the case with the differing definitions of inertial mass and gravitational mass, which he began to resolve by building on the equivalence principle.

• He was likewise uncomfortable when a theory made distinctions

that could not be observed in nature. That had been the case with observers in uniform motion: there was no way of determining who was at rest and who was in motion. Now it was also, apparently, the case for observers in accelerated motion: there was no way of telling who was accelerating and who was in a gravitational field.

• He was eager to generalize theories rather than settling for having them restricted to a special case. There should not, he felt, be one set of principles for the special case of constant-velocity motion and a different set for all other types of motion. His life was a constant quest for unifying theories.

In November 1907, working against the deadline imposed by the Yearbook of Radioactivity and Electronics, Einstein tacked on a fifth section to his article on relativity that sketched out his new ideas. “So far we have applied the principle of relativity ...only to nonaccelerated reference systems,” he began. “Is it conceivable that the principle of relativity applies to systems that are accelerated relative to each other?”

Imagine two environments, he said, one being accelerated and the other resting in a gravitational field. 24There is no physical experiment you can do that would tell these situations apart. “In the discussion that follows, we shall therefore assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.”

Using various mathematical calculations that can be made about an accelerated system, Einstein proceeded to show that, if his notions were correct, clocks would run more slowly in a more intense gravitational field. He also came up with many predictions that could be tested, including that light should be bent by gravity and that the wavelength of light emitted from a source with a large mass, such as the sun, should increase slightly in what has become known as the gravitational redshift. “On the basis of some ruminating, which, though daring, does have something going for it, I have arrived at the view that the gravitational difference might be the cause of the shift to the red end of the spectrum,” he explained to a colleague. “A bending of light rays by gravity also follows from these arguments.” 25

It would take Einstein another eight years, until November 1915, to work out the fundamentals of this theory and find the math to express it. Then it would take another four years before the most vivid of his predictions, the extent to which gravity would bend light, was verified by dramatic observations. But at least Einstein now had a vision, one that started him on the road toward one of the most elegant and impressive achievements in the history of physics: the general theory of relativity.

Winning a Professorship

By the beginning of 1908, even as such academic stars as Max Planck and Wilhelm Wien were writing to ask for his insights, Einstein had tempered his aspirations to be a university professor. Instead, he had begun, believe it or not, to seek work as a high school teacher. “This craving,” he told Marcel Grossmann, who had helped him get the patent-office job, “comes only from my ardent wish to be able to continue my private scientific work under easier conditions.”

He was even eager to go back to the Technical School in Winter-hur, where he had briefly been a substitute teacher. “How does one go about this?” he asked Grossmann. “Could I possibly call on somebody and talk him into the great worth of my admirable person as a teacher and a citizen? Wouldn’t I make a bad impression on him (no Swiss-German dialect, my Semitic appearance, etc.)?” He had written papers that were transforming physics, but he did not know if that would help. “Would there be any point in my stressing my scientific papers on that occasion?” 26

He also responded to an advertisement for a “teacher of mathematics and descriptive geometry” at a high school in Zurich, noting in his application “that I would be ready to teach physics as well.” He ended up deciding to enclose all of the papers he had written thus far, including the special theory of relativity. There were twenty-one applicants. Einstein did not even make the list of three finalists. 27

So Einstein finally overcame his pride and decided to write a thesis in order to become a privatdozent at Bern. As he explained to the patron there who had supported him, “The conversation I had with you in the city library, as well as the advice of several friends, has induced me to change my decision for the second time and to try my luck with a habilitation at the University of Bern after all.” 28

The paper he submitted, an extension of his revolutionary work on light quanta, was promptly accepted, and at the end of February 1908, he was made a privatdozent. He had finally scaled the walls, or at least the outer wall, of academe. But his post neither paid enough nor was important enough for him to give up his job at the patent office. His lectures at the University of Bern thus became simply one more thing for him to do.

His topic for the summer of 1908 was the theory of heat, held on Tuesday and Saturday at 7 a.m., and he initially attracted only three attendees: Michele Besso and two other colleagues who worked at the postal building. In the winter session he switched to the theory of radiation, and his three coworkers were joined by an actual student named Max Stern. By the summer of 1909, Stern was the only attendee, and Einstein canceled his lecturing. He had, in the meantime, begun to adopt his professorial look: both his hair and clothing became a victim of nature’s tendency toward randomness. 29

Alfred Kleiner, the University of Zurich physics professor who helped Einstein get his doctorate, had encouraged him to pursue the privatdozent position. 30He also had waged a long effort, which succeeded in 1908, to convince the Zurich authorities to increase the university’s stature by creating a new position in theoretical physics. It was not a full professorship; instead, it was an associate professorship under Kleiner.

It was the obvious post for Einstein, but there was one obstacle. Kleiner had another candidate in mind: his assistant Friedrich Adler, a pale and passionate political activist who had become friends with Einstein when they were both at the Polytechnic. Adler, whose father was the leader of the Social Democratic Party in Austria, was more disposed to political philosophy than theoretical physics. So he went to see Kleiner one morning in June 1908, and the two of them concluded that Adler was not right for the job and Einstein was.

In a letter to his father, Adler recounted the conversation and said that Einstein “had no understanding how to relate to people” and had been “treated by the professors at the Polytechnic with outright contempt.” But Adler said he deserved the job because of his genius and was likely to get it. “They have a bad conscience over how they treated him earlier. The scandal is being felt not only here but in Germany that such a man would have to sit in the patent office.” 31

Adler made sure that the Zurich authorities, and for that matter everyone else, knew that he was officially stepping aside for his friend. “If it is possible to get a man like Einstein for our university, it would be absurd to appoint me,” he wrote. That resolved the political issue for the councilor in charge of education, who was a partisan Social Democrat. “Ernst would have liked Adler, since he was a fellow party member,” Einstein explained to Michele Besso. “But Adler’s statements about himself and me made it impossible.” 32