Professional physicists, especially quantum physicists, were not much interested in the rumored coming of Einstein’s new field theory. They had made a decisive turn shortly after the Solvay Conference. On January 2, 1928, Paul Dirac submitted a paper to the Royal Society which, in the words of a Danish historian of science, “marked the end of the pioneering and heroic era of quantum mechanics.” Dirac’s paper managed what Schrödinger had failed to do two years earlier, link special relativity and quantum waves.
When Schrödinger first tried to include Einstein’s relativistic mechanics in his wave equation, he did not know about electron spin. Although the spinning electron still had never been physically observed, its effects had been measured. A spinning electric charge produces a magnetic field. Electrons carry a charge and generate a magnetic field; hence, electrons must be spinning. Using this extra knowledge, Dirac had created a miraculously exact rule for calculating the electrodynamics of the atom.
The Dirac equation (actually a set of four equations compressed into one complex expression) can be used to compute the magnetism of electrons. The answer it gives is precisely the one that experimentalists find in the lab. This discovery was the quantum theory’s equivalent of Einstein’s success at computing Mercury’s orbit. Classical
notions had failed to predict the observed ratio between the electron’s spin rate and its magnetic strength, so when Dirac’s equation calculated perfectly the experimentally observed values, physicists had no choice but to nod respectfully.
Dirac’s equation could also give the correct values in situations where Schrödinger’s equation did work. The Bose-Einstein statistics, too, were folded into the Dirac equation, along with Planck’s original quantum equation and Einstein’s E = hυ. Even Einstein’s most famous baby, E = mc2, was built into the Dirac equation. No wonder Dirac boasted that his theory described “most of physics and all of chemistry.”
But talk of Dirac’s theory can be misleading to people who take a theory to include some explanation of what is going on. Dirac was not an explainer, neither in physics nor in everyday life. As a lecturer, when asked to explain an idea he would often merely repeat word for word what he had already said. His equation was his theory. Of the Einstein-Bohr debate at Solvay 1927, Dirac said, “I was not very much interested. I was more interested in getting the correct equations. It seemed to me that the foundation of the work of a mathematical physicist is to get the correct equations, that the interpretation of these equations was only of secondary importance.” Neither Bohr nor Einstein agreed with Dirac on this point. Perhaps the tip-off is that Dirac called himself a “mathematical physicist” while Bohr and Einstein called themselves theoretical physicists.
The biggest interpretive puzzle was over what Dirac’s equation described. It had taken over the Ψ of Schrödinger’s equation, but what was that squiggle all about? Dirac accepted straight away Max Born’s interpretation of it as a statement of probability. Thus, for all Dirac’s brilliance in grasping the previous three decades of struggle with the quantum, his equation did not resolve the matters that troubled Einstein. Twenty-three years earlier Einstein had shown that Ludwig Boltzmann’s statistical abstraction could be used to measure the real actions of real atoms. He still wanted some real meaning for Schrödinger’s and Dirac’s mysterious psi. Einstein granted that the equation was “the most logically perfect presentation” of quantum mechanics yet found, but not that it got us any closer to the “secret of the Old One.” It neither described the real world phenomena that
Einstein wanted to understand nor proposed new concepts that would make the real world accessible to understanding. Furthermore, Dirac’s unification of quantum mechanics with special relativity left out Einstein’s later success with general relativity and the gravitational field. (That omission was why the equation covered only “most” of physics.) So Einstein continued pursuing his interest in unifying gravity with electromagnetism.
Berlin’s reporters were yammering excitedly about Einstein’s anticipated breakthrough, yet they had completely missed the news about how physics had taken a decisive turn. The close of the quantum revolution’s “pioneering and heroic era” brought with it a great changing of the guard in physics leadership. The world of commerce has found that it commonly takes one kind of person to found a great enterprise and another kind to direct it in day-to-day competition. In physics, the people who had invented quantum’s rules turned out not to be those who were best at using them. Einstein’s resistance to post-revolutionary quantum physics is the most famous example, but it was typical of the scientists in this history that they moved in directions away from quantum mechanics. In the summer of 1928, Dirac gave a lecture in Germany that went badly because it predicted negative energy and that seemed a plain impossibility. In this confused state, Heisenberg told Pauli, “the saddest chapter in modern physics is and remains the Dirac theory.” Pauli despaired as well and announced that he was abandoning quantum physics. Four years earlier he had moaned he should quite physics and become a film comedian. This time he really did stop doing quantum work and turned to writing a utopian novel. Heisenberg did not retreat so far, but he told Pauli he was forgetting “the more important problems” and returning to pre-Dirac quantum mechanics “in order not to frustrate myself continuously.”
Unified physics, too, is often portrayed as Einstein’s lonely, futile dream, but others also saw its appeal in one form or another. In early 1928, before turning to his novel, Pauli told Dirac that only a unified field theory would end all the confusion and he urged Dirac to try his hand at finding one. Many years later, Heisenberg, too, began looking for his own unified theory.
The press corps understood very little of this dispute and much of
its noise over an idea that even Einstein soon abandoned seems absurd. There were, to be sure, mechanical forces behind this newspaper farce that had nothing to do with Einstein, or science, or the public’s eagerness to know. Although by then fame had been industrialized, the supply sources remained preindustrial. There was not yet a cooperating industry for stamping out people eager to be famous. Hollywood was only just beginning to organize itself into the symbiotic relationship that now exists between a media desperate for celebrities and entertainers desperate for shelf space. Without that industrialized supply, the newspapers of 1929 had to cling to the relatively few accidental celebrities and squeeze them for all their juice. At the same time that the papers were besieging Einstein, they were also chasing after Charles Lindbergh and Lawrence of Arabia.
“My name is Mr. Smith,” the legendary Lawrence told waiting newsmen when his train pulled into London’s Paddington Station. He jumped into a cab, and even though the World War was now 10 years gone, the reporters hopped into other taxis and sped after the old war hero in pursuit of a paragraph.
Undoubtedly, there was much of that sort of nonsense in the roar over Einstein’s new work, but Einstein’s fame had not been created by the money-craving forces that made, say, Greta Garbo famous. When a group of reporters finally chased him to ground, Einstein pleaded, “I really don’t need any publicity.” True, but beside the point. The reporters were not trying to do their prey any service. Einstein had stayed famous because the public responded with continuing interest to the story that there was a genius out there for whom the world made sense—more, for whom the universe made sense. In this reaction, the trauma of the World War cannot be overstated. It had revealed that a world seemingly based on reason had actually rested on bloody madness. As one popular German antirationalist put it, because of the war “one has had to accept so much that was unimagined, bear such gross things patiently that even now the indignation that one strives to summon up lacks the fitting energy.” But there was Einstein, smarter than anybody, and he had found that the world still makes sense. Quantum mechanics, which the press ignored, was what people feared the world had become: arbitrary, technical, and random.
The clue to the hubbub’s underlying concern lay in the way the reporters and readers wanted to know what this new theory meant. There was none of today’s curiosity about Einstein’s personal life. Did he wear boxers or briefs? Who was the lucky woman married to him? There was so little of that side of the story that whenever a report did mention Elsa it smudged her into the background as “Frau Einstein,” with no first name given. Instead the justification for the fuss was cited as “the riddle of the universe.” Einstein was said to have solved it. When he was in a mood to be generous Einstein recognized a good side to this commotion. He once told a Dutch reporter, “The contrast between the popular estimate of my powers and achievements and the reality is simply grotesque. The awareness of this strange state of affairs would be unbearable but for one pleasing consolation: it … proves that knowledge and justice are ranked above wealth and power by a large section of the human race.”
Physicists had grown used to seeing a fantastic clamor over Einstein, but this new uproar looked especially scandalous. Bohr especially believed that Einstein was scouting an empty trail, for Einstein was building on general relativity rather than on quantum mechanics. In the British journal Nature, when Bohr finally published his notion of complementarity, he wrote, “general relativity has not fulfilled expectations. A satisfactory solution … would seem to be possible only by means of a rational quantum-theoretical transcription of the general field theory, in which the ultimate quantum of electricity has found its natural position as an expression of the feature of individuality characterising the quantum theory.”
Whenever a quotation from Bohr runs beyond a clause, it demands a second reading. “Were you never taught in school,” Dirac once asked him, “that before you begin a sentence you should have some plan as to how you are going to finish it?” Bohr’s general drift, however, was decipherable. It order to “fulfill expectations” general relativity needs a “transcription” into “quantum-theoretical” terms that would unite “the ultimate quantum of electricity” with “an expression” that would identify the ultimate quantum’s “natural position.” Put more bluntly still: Instead of toying around with the Riemannian geometry that underlies general relativity, Einstein should look squarely to quantum mechanics.
On January 10, 1929, the fame engine moved into even higher gear when Einstein again dispatched Max Planck to the Prussian Academy to present another paper. Publicly the reason for Planck’s going in Einstein’s stead was Einstein’s health, but his health had recovered enough for him to have done the thinking behind the paper. He was, however, not up to fencing with the press, which was in ultrahowl. They were not silenced by Planck’s presentation. The paper was short—five pages—but its ideas and mathematics were far beyond the understanding of the unschooled reporters, and they pressed their demand to know what the document meant.
Einstein lay low, but the following day he issued a short statement, “A few days ago [sic] I submitted to the Academy of Sciences a work that treats with a novel development of the theory of relativity. The purpose of this work is to unite the laws of the field of gravitation and electromagnetism under a uniform viewpoint.” The press dutifully published the paragraph and padded it out as best it could, but two sentences no more satisfied the fame machine than two licks of an ice-cream cone satisfies an unhappy child. Their appetite was only sharpened. A week later the New York Times still had nothing to report, so it reported that ignorance—“Amazed At Stir Over New Work, Einstein Holds 100 Journalists At Bay For Week.” Meanwhile it kept looking for something to say.
At the end of January, the Prussian Academy published its Proceedings containing the papers read that month before the assembly. Normally this journal went straight into obscure libraries. There had been no clamor to see the Proceedings back in November 1915 when Einstein announced his general theory of relativity, but in 1929, all the press wanted copies of the January issue. The normal printing of 1,000 copies sold out at once (unheard of!) and 2,000 more were promptly published and seized. Reporters cabled the article. The New York Herald Tribune published a translation, along with the equations, the next day. Arthur Eddington wrote Einstein in early February that a London department store had posted the field theory paper in its window and he had seen a mob of ordinary people pushing close to study the thing.
The press was not yet satisfied and still demanded: What does it
mean? The New York Times and the London Times managed together to persuade Einstein to write an explanation of his theory in “simplified” terms. Before turning it over to a reporter for cabling to New York, Einstein had Elsa read it back to him. When she finished Einstein said, “The article has permanent value and I shall use it in a book later.” He never did because he soon abandoned the “distant parallelism” that underlay the theory’s mathematics. It is too bad that the article was not reprinted and curious readers are still forced to suffer through scratched microfilm to find it. The article provides more than a discussion of field theory. Most of it presents an excellent summary by Einstein himself of the Newtonian view he overturned and how he did it. Even the article’s latter part spent as much space explaining what Einstein was trying to do as it did going into details about what he had done.
“The characteristics which especially distinguish the general theory of relativity and even more the new third stage of the theory, the unitary field theory, from other physical theories are,” Einstein reported bluntly, “the degree of formal speculation, the slender empirical basis, the boldness in theoretical construction and, finally, the fundamental reliance on the uniformity of the secrets of natural law and their accessibility to the speculative intellect.” Einstein summed himself up there about as well as it can be done. The difference between relativity and other physical laws was not in its notions of time, space, light, or geometry. It was speculation, boldness, and a reliance on the uniformity and accessibility of natural law. And it was that faith in accessible, natural law that made all the noise over Einstein fundamentally unlike the crowds swooning over one more pop personality. People wanted to believe that boldness, brilliance, and natural law still worked.
Einstein went on to mention that there were physicists who disliked his approach although he did not mention Mach, Bohr, or anybody else by name. Instead, he cited a philosopher he did agree with: Emile Meyerson, whose 1908 book, Identity and Reality, argued that scientific knowledge tries to get beyond mere description and predictive laws to an understanding of the reality beyond the appearances.
And once it got that explanation the press calmed down. Einstein
slipped off to Berlin’s Wannsee suburb for an undisturbed rest. The pity and foolishness of the commotion is that in chasing Einstein down and getting him to spell out what he was up to, it missed the bigger story. The press took for granted that law both underlies and guides one to reality, and it ignored the ongoing quarrel between Einstein and Bohr.
A closer comparison of their comments on what a unified theory must do gets at the heart of the difference between them. In his newspaper article Einstein, like Bohr in his complementarity essay, said he was looking for a “mathematical expression.” Bohr, however, wanted an expression “characterizing the quantum theory” while Einstein wanted “the mathematical expression of the physical fields.” The difference? Bohr’s math characterized theory while Einstein’s looked to physical reality.
This subtle divide was behind the Einstein-Bohr quarrels from the beginning. Untangling its depths can lead to arcane distinctions, but these slippery differences had led to a decade of dispute. In practice, it had come down to where, when you must, you allow your ambiguities and contradictions. In the end, of course, both wanted a coherent, unambiguous physics, but while the search persisted, Bohr preferred an ambiguous reality to a contradictory theory. He was like a novelist who tells a coherent story by finding a symbol that captures the ambiguity of an experience. He had fiercely resisted the way Einstein’s photon proposal confused the distinction between waves and particles. Meanwhile, Einstein saw contradictions between ideas as the key to finding an unambiguous, coherent reality. Of course he balked at the way quantum mechanics used formal symbols instead of the names of real things.