Einstein and the Quantum (32 page)

The meeting, which the mathematician Alfred North Whitehead likened to “
a Greek drama
” in which the “laws of physics are the decrees of fate,” placed Einstein on the same level as Sir Isaac Newton in the British scientific pantheon, leading to J. J. Thomson's famous pronouncement that Einstein's new framework was “
one of the highest achievements
of human thought.”
¹
Something about this new worldview, arcane but not encased in a protective layer of technical jargon, captured the general public's imagination as the “spectral lines” and “quanta” of atomic theory could never do. Space was curved; light was subject to gravity; all motion was relative. It was mind-bending stuff, but not incomprehensible techno-speak. One could conjure with it. And one did.

The
New York Times
captured the zeitgeist with one of its most whimsical headlines ever: “
Lights All Askew
in the Heavens: Men of Science More or Less Agog Over Results of Eclipse Expeditions. Einstein Theory Triumphs; Stars Not Where They Seemed or Were Calculated to be, but Nobody Need Worry. A Book for 12 Wise Men; No More in All the World Could Comprehend It.”

By September 1920 relativity mania had swept the globe, leading Einstein to exclaim, “
At present every coachman
and every waiter argues about whether or not the relativity theory is correct.” Einstein's first biographer described the ethos thus: “
from the intellectual work of a quiet scholar
a message of salvation had emerged…. No name was uttered as much during that time as that of this man…. Here was a man who had reached out to the stars, a man in whose theory one had to penetrate to forget one's earthly troubles.” To have a transnational, apolitical figure to admire in the aftermath of the decade of senseless destruction satisfied a deep, if unanticipated, social need. And so Einstein became a symbol of man's better nature, a potential political force, an ethnic beacon to the Jews, an inspiration for revolutionary art, and a challenge to philosophers. His public lectures were sensational events; his opinions on all things were sought; he should write this or that commentary, give this or that speech, join this or that committee, for this or that worthy cause. All of which detracted from his true life's mission, to think deeply about nature and, more specifically, to finally get to the bottom of the conundrums of atomic theory. He wrote to his old friend Zangger in January 1921, “
the fragmentation of one's intentions
by the motley array of duties is crippling, especially for a person made more for concentration than for conformance.”

FIGURE 23.1.
Cover of
Berliner Illustrirte Zeitung
of December 14, 1919, proclaiming Einstein as a new genius on the world stage.

While Einstein was soaring to unprecedented celebrity for a scientist, Germany was struggling to maintain a stable political order after its defeat in the Great War. The Weimar Republic, with its liberal constitution, was established in the summer of 1919 and for the next four years suffered repeated challenges from reactionary forces, led by the right-wing
Freikorps
. These forces fed the surge of anti-Semitism that followed the German surrender and signing of the Treaty of Versailles. Einstein, due to his newfound prominence, was a natural target to attack. A fringe group of scientists and engineers, led by an obscure engineer named Paul Weyland, attacked relativity theory as fallacious and undermining of the purity of German Science. Einstein, rather naively, thought that paying attention to this claque and refuting their
claims with a combination of logical argument and sarcasm would be worthwhile. After a public meeting of the antirelativists in August of 1920, which Einstein himself attended, he attacked his critics in a newspaper article that he rapidly came to regret. “
Everyone must, from time to time
, make a sacrifice on the altar of stupidity … and I did so thoroughly with my article.”

Indeed, in addition to drawing attention to this movement, which would otherwise have been insignificant, he also angered a respectable physicist, Philipp Lenard. Lenard was a Nobel laureate whose seminal experiments on the photoelectric effect had partly inspired Einstein's breakthrough work on quanta of light. Lenard had doubted the validity of relativity theory, writing an article critical of it in 1918, but at this point had never attacked Einstein personally. Lenard's stated problem with relativity theory was one that many could identify with: it violated “
sound common sense
.” Lenard was not a theorist, and Einstein's colleagues would surely have realized that his criticisms were simply the result of an inability to grasp the theory's challenging abstractions. However, Weyland had appropriated Lenard's name for his group's use. and Einstein had assumed, perhaps with some justification, that Lenard shared their nonscientific motivations to attack him. Thus he wrote of Lenard by name: “
[he] has so far achieved nothing
in theoretical physics, and his objections to the general theory of relativity are of such superficiality that until now I had thought it unnecessary to answer them in detail.”

Lenard naturally took offense at the insulting tone of Einstein's comments, prompting Sommerfeld to implore Einstein to make some conciliatory gesture, a request to which Einstein never acceded. In fact this first flurry of German attacks on Einstein's science, with its strong overtones of anti-Semitism, was never a major movement and was widely rejected by the German physics establishment of the time. Einstein himself felt at the time that his critics were no more than an annoyance, commenting famously, “
I feel like a man lying
in a good bed, but plagued by bedbugs.” A decade later, however, the bugs would turn poisonous. Lenard would never forgive Einstein and henceforth opposed him at all turns. Eventually he would join the Nazi Party and
lead its successful effort to oust Jewish scientists, including Einstein, from the Prussian academy, and eradicate “Jewish physics” from the textbooks.

Although in 1921, at the time of these early attacks, Einstein's scientific colleagues felt that it was unwise of him to engage with this rabble at all, they uniformly defended him. Most striking was a statement by von Laue, Nernst, and Rubens: “
It cannot be our task
to discuss in detail the unparalleled profound intellectual work which led Einstein to his theory of relativity…. What we do want to emphasize, and what was not touched upon in a single work yesterday [at the antirelativity meeting], is that
quite apart from Einstein's relativistic research, his other work already assures him of an immortal place in the history of science
” (italics added). So while the public either swooned or fumed over relativity theory, his Berlin colleagues had not lost sight of the fact that Einstein was the conceptual leader of the new atomic physics. And they had not abandoned the hope that he would yet come up with a true and complete quantum theory.

Einstein himself, however, seemed for the first time in his life easily distracted from his scientific research. Although he did not feel truly threatened by the anti-Semitic mood of the right wing in 1920, it did appear to rekindle a sense of ethnic identification with his Jewish brethren. In April 1920 he addressed a Jewish group as follows: “
there is in me nothing
which can be described as ‘Jewish faith.' But I am happy to belong to the Jewish people.” Not that he had any sympathy for religious observances, as he made clear to a rabbi with whom he had debated: “
The [religious Jewish] community
is an organization for the exercise of ritualistic forms that are remote from my opinions. I must take it for what it is today and not for what one might perhaps wish to see it transformed into. When I want to drive into town, I do not lay myself down in bed in the hope that it will grow wheels and become an automobile…. [However] I gladly vow … all kinds of efforts in the interest of individual Jews and Jewish communities.”

In keeping with this pronouncement, less than a year later, despite his professed desire to focus on science, he immediately agreed to an
invitation from Chaim Weizmann, the president of the World Zionist Organization, to accompany him to the United States to solicit funding for the planned Hebrew University in Jerusalem. Never mind that the trip's schedule would require his withdrawal from the first of the revived Solvay Congresses, on “atoms and electrons,” and that among his many talents and interests fund-raising had never previously figured. To Haber (who greatly opposed his participation), he confessed: “
I am not needed for my abilities
, of course, but only for my name. Its promotional power is anticipated to bring considerable success thanks to our rich fellow clansmen of Dollaria (Einstein's nickname for the USA).” However, he regarded his participation as a moral duty: “Despite my declared international mentality, I do still always feel obliged to speak up for my persecuted and morally oppressed fellow clansmen, as far as it is within my powers…. The prospect of establishing a Jewish university delights me especially, after recently seeing from countless examples how perfidiously and unkindly fine young Jews are being treated here in the attempt to deprive them of educational opportunities.” In fact, while Einstein created a sensation everywhere he went in America, adding to his legend, the trip was only modestly successful in its monetary goals.

This trip seemed to spark a wanderlust in Einstein that he had not previously demonstrated. During the next two years, in addition to the trip to the United States, mainly by his own choice, he would visit Holland, Austria, Czechoslovakia, England, France, Italy, Switzerland, Japan, Hong Kong, Singapore, Palestine, Spain, Sweden, and Denmark, not a program conducive to deep contemplation. However, in the summer of 1921, after returning from the United States, Einstein briefly turned his thoughts to the problem of light quanta once again.

While Einstein had by this time developed his notion of “ghost fields” to explain how particles of light could exhibit the interference effects associated with waves, he did not think that the net result for observations would be exactly as predicted by the classical theory of electromagnetic waves. Thus he sought an experimental test that would directly distinguish his theory, in which all energy was carried by individual light quanta, from the predictions of classical optics. In August of 1921 he thought he had found one, a “
very interesting and quite simple
experiment about the nature of light emission…. I hope I can carry it out soon.”
²

FIGURE 23.2.
Einstein and his second wife, Elsa Einstein, photographed on their trip to the USA in 1921. Library of Congress, courtesy AIP Emilio Segrè Visual Archives.

The idea was indeed quite simple, but flawed. Einstein assumed that light quanta would not show the Doppler effect when emitted from a moving atom (i.e., its frequency would not be shifted depending on the
angle between its motion and the line of sight to the detector), whereas classical radiation was known to show such an effect. Thus he suggested imaging the light from moving atoms through a telescope lens with an inserted prismlike element, to differentially deflect the light of different frequencies. He calculated that the classical theory would give a deflected image and his quantum theory would not. He did not have to do the experiment himself, finding the seasoned professionals Walter Bothe and Hans Geiger quite happy to do these relatively easy measurements. They were completed in December of 1921; no deflection of the image was detected.

Einstein, again ecstatic, as he had been after his work on quanta in 1916, told Born the latest news. “
Thanks to the excellent collaboration
of Geiger and Bothe, the experiment on light emission is finished. Result: The emission of light by the moving [atom] is strictly monochromatic, whereas according to the undulatory theory, the color of the elementary emission ought to be different in different directions. Thus it is surely proven that the undulatory field has no real existence…. It is my most powerful scientific experience in years.” However Einstein's exultation was short-lived. Independently, Ehrenfest and Max von Laue pointed out that Einstein had got the classical prediction wrong; both the classical and the quantum theory predicted no effect. Einstein redid the calculations himself and presented the amended conclusion a couple of months later: “in light of this theoretical result, deeper conclusions cannot be derived from the experiment concerning the nature of the emission process.” He wrote again to Born, with characteristic self-deprecation, “
I … committed a monumental blunder
(experiment about the emission of light …). But one shouldn't take it too seriously. Death alone can save one from making blunders.” He was clearly getting frustrated, once again, with the unyielding quantum: “
I suppose it is a good thing
that I have so much to distract me, else the quantum problem would have long got me into a lunatic asylum…. How miserable the theoretical physicist is in the face of nature.”