Chapter 4: The Theory of General Relativity: Final Formulation and Confirmation
chapter 4: THE THEORY OF GENERAL RELATIVITY: FINAL FORMULATION AND CONFIRMATION
EINSTEIN’S 1905 MAY INDEED have been a “wonder year,” but his remarkable series of publications did not lead to offers of academic employment pouring in. In May 1905, Einstein submitted his doctoral thesis to the University of Zürich, titled “A New Determination of Molecular Dimensions.” In July, he learned it had been accepted. Yet no academic appointment was forthcoming. Recognition and advancement of a more modest nature, however, lay to hand. In April 1906 Einstein was promoted to technical expert, second class, at the Bern patent office. It was not what he really wanted, but the increase in salary proved welcome.
Finally, the University of Zürich opened the door to an academic career. In October 1909, Einstein was appointed as an adjunct professor in theoretical physics, allowing him to devote himself to the pursuit of science.[85] Two years later, he was appointed as full professor at the Karl-Ferdinand University in Prague, before returning to Switzerland in 1912 to take up a chair at the Eidgenössische Technische Hochschule (ETH) in Zürich. Meanwhile, his growing body of German admirers, headed by the physicist Max Planck and the physical chemist Walther Nernst, were working to bring Einstein into the heart of German-language culture and scientific research. Planck had been the associate editor of Annalen der Physik in 1905 and had been impressed by Einstein’s articles of that year. (At that time, peer review was unusual, and Einstein sent his articles directly to Planck.) Those efforts proved successful. In 1914, Einstein was appointed director of the Kaiser Wilhelm Institute for Physics and professor in the University of Berlin.
Yet all was not well. Einstein’s marriage came under stress shortly after the move to Berlin. Mileva and their two children returned to Zürich in 1914. In 1917, Einstein became ill and was cared for by his cousin, Elsa Loewenthal. In 1919, following the required five years of legal separation, Einstein divorced Mileva and married Elsa, who already had two daughters from her first marriage. The divorce agreement was unusual in that Einstein agreed to support Mileva and his two sons financially with immediate effect, as well as promising her the prize money, to be placed in trust for their two sons, if he were ever to be awarded a Nobel Prize.
In the meantime, European political tensions were rising. In July 1914, Einstein gave his first lecture to the Prussian Academy of Sciences. It was a momentous event in his personal history, marking the end of his transition from an academic outsider to a person of eminence. Yet that same month saw the Austro-Hungarian Empire issue an ultimatum to the Serbian government. The Austrians seemed willing to precipitate a general European war as a solution to their fragile international position. The outbreak of the First World War —then known as the “Great War” —in August 1914 marked the end of international intellectual and scientific collaboration.
Einstein was isolated in Germany during this period. He now had the time to try to resolve a major scientific problem that had preoccupied him since 1909: how to develop a generalization of his theory of special relativity. The scientific problem is not difficult to understand. The theory of special relativity that Einstein had set out in his landmark article of 1905 applied only to the relationship between a body at rest and a body moving at a constant velocity. The theory considered only the effects of relativity to an observer moving at constant speed. So what about bodies that were moving at changing velocities? And what about the influence of gravitational fields on space-time?
The Theory of General Relativity
Einstein was aware that Newton’s law of universal gravitation appeared to be fundamentally incompatible with his own views on relativity. Newton had assumed that the force of gravity was generated purely by mass, whereas Einstein’s equation E = mc2 showed that all forms of energy had effective mass and must therefore also be sources of gravity. The theory of the equivalence of mass and energy raised important questions about how gravity was to be understood.
As we noted earlier, Newton had proposed gravity as a force between bodies as they moved through space, understanding space as a vast empty container. He had no idea what space was made of. Newton understood it in effect as a gigantic box through which objects moved in straight lines until some force —such as gravity —caused them to be deflected and move in curves. In the nineteenth century, the British physicists Michael Faraday and James Clerk Maxwell introduced the idea of electromagnetic fields. Maxwell was able to show that light “is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.”[86] Einstein came to the view that, like electricity and magnetism, gravity was conveyed through a “gravitational field” —and, more radically, that this gravitational field is actually what Newton considered to be “space.” Bodies do not move through space but through a gravitational field. Instead of thinking of space as a container through which planets move under the influence of gravity, we need to think of space itself as a gravitational field, which is distorted locally on account of the mass of stars.
On the basis of this approach, Einstein predicted the phenomenon of the gravitational dilation of time. The closer a body is to a large mass, with its substantial gravitational pull, the slower time runs for it. It is as if gravity is exercising an influence on the passage of time itself. This phenomenon is now well known and is important for the functioning of Global Positioning Systems (GPS), which rely on signals from satellites orbiting above the Earth to establish the observer’s position. However, the atomic clocks in those satellites run 45 millionths of a second faster per day than clocks here on the surface of the Earth. Why? Because time passes at a different rate on the surface of the Earth due to the greater effect of the Earth’s gravity.
Newton had understood matter to attract other matter across empty space. Einstein developed the quite different idea that matter distorts space-time. In effect, gravity causes space-time to bend around massive objects. Newton himself never applied his theory of universal gravitation to the behavior of light. However, as we noted earlier, scientists who held that light could be thought of as a beam of particles predicted that gravity would affect its passage through space. Two predictions are of especial interest. The first is John Michell’s 1783 prediction of “dark stars” that could not be seen because light was unable to break free from the force of their gravity. The second is the 1804 prediction of Johann Georg von Soldner that a beam of light would be deflected by the gravitational field of a star, such as the sun. Soldner himself was able to calculate the extent of this deflection.
Einstein did not regard light as a beam of particles, which would be affected by gravity on account of their mass. His argument was somewhat different. Einstein’s principle of the equivalence of mass and energy meant that light, on account of its enormous velocity, had an “effective mass.” Newton thought light possessed mass; Einstein showed that it behaved as if it had mass and could therefore be attracted to other sources of mass —such as the sun and other stars. In effect, Einstein’s theory of general relativity confirmed both these predictions but placed them on a different theoretical foundation.
The Trampoline
An illustration of how an object warps space and time.
So how can we visualize this changed understanding of gravity? The analogy I find most helpful is to imagine space-time as a trampoline. If you place a heavy object on a trampoline, it stretches the elastic fabric and makes it sag or bend. So imagine a trampoline on which someone has placed a lump of iron near its middle. Unsurprisingly, the fabric sags at that point. Now imagine that you roll a small ball across the trampoline fabric. It will move towards the lump of iron. Why? Because it is drawn to the iron? Or because it naturally follows the deformation in the shape of the fabric resulting from the weight of that iron? The second explanation is correct.
General relativity asks us to think of the sun and the planets warping space-time. The planets orbiting the sun are not really being pulled by the sun; they are actually following the curved space-time deformation caused by the sun. The astrophysicist John Archibald Wheeler summed up this view rather nicely when he remarked that “matter tells space-time how to curve, and space-time tells matter how to move.”[87] Einstein thus converted gravitational physics into the geometry of space-time.
By November 1915, Einstein had worked out most of the details of how he could develop a more general theory of relativity. He had presented a draft and incomplete version of the general theory in the form of lectures the preceding summer at the University of Göttingen. In March 1916, Einstein submitted his paper, titled “The Foundation of the General Theory of Relativity,” to the German scientific journal Annalen der Physik, which had published his landmark articles of 1905. The article was not as widely read as he might have hoped, due to the wartime conditions. Nevertheless, it was clear that the paper set out a comprehensive and sophisticated general theory, which was capable of being tested against observation.
So how are we to understand the relation of these two theories of relativity —the special and the general? Einstein himself offered a neat explanation in an article titled “What Is the Theory of Relativity?” written in November 1919 in response to the massive public interest in his theories:
The theory of relativity resembles a building consisting of two separate stories, the special theory and the general theory. The special theory, on which the general theory rests, applies to all physical phenomena with the exception of gravitation; the general theory provides the law of gravitation and its relations to the other forces of nature.[88]
One of the most significant aspects of Einstein’s paper on “The Foundation of the General Theory of Relativity” was its specific predictions of what would be observed if the theory was correct. Einstein was absolutely clear that his theory had to be evaluated as a whole. As he remarked in 1919, its chief attraction lay in its logical completeness. “If a single one of the conclusions drawn from it proves wrong, it must be given up; to modify it without destroying the whole structure seems to be impossible.” There were, in Einstein’s view, three such predictions that were open to testing:
Yet one prediction is strikingly absent from this short list —the expansion of the universe. Einstein’s first cosmological solution of his field equations left him unsatisfied. Why? Because it indicated that the universe was expanding. In 1917, Einstein modified his equation, adding another term —the so-called “cosmological function” —in order to yield a static, unchanging universe. George Gamow later reported that Einstein thought this was the “biggest blunder” of his career (although the reliability of this recollection is questionable). In 1922 the Russian mathematician Alexander Friedmann used Einstein’s equations to show that such a universe cannot be static. In 1929, the research of Edwin Powell Hubble suggested that the observational evidence was best explained by an expanding universe. Einstein’s approach suggests that the universe expands not on account of the movement of galaxies but because space-time is expanding.
So why did Einstein not trust his original equations? Why introduce what his critics considered to be a “fudge factor” designed to fit the soon-to-be-abandoned model of a static and eternal universe? I have not found a convincing answer, although many suggestions have been made. Perhaps Einstein wanted his theory to fit in with physicists’ thinking at the time; or maybe, as an admirer of the Dutch Jewish philosopher Spinoza, he genuinely believed that the universe was necessarily eternal. Yet with the benefit of hindsight, a century later, Einstein’s “blunder” may actually have turned out to be an explanatory triumph. Einstein’s cosmological function plays an important role in the dominant Lambda-CDM model of the origins of the universe and is seen to be critical in helping us understand the mysterious notion of “dark energy.”[89]
If Einstein had predicted an expanding universe, his theory of relativity would have been sensationally confirmed by 1930. But let us return to the three predictions Einstein did make and consider their importance.
The first of these was more of a retrodiction than a prediction. In other words, it was something that was already known but which could not be explained by any existing theory. On November 18, 1915, Einstein presented a paper on the explanation of Mercury’s advancing perihelion on the basis of his new general theory of relativity to the Prussian Academy of Science.[90] Although Einstein’s formulation of the issue was later given added mathematical precision through the work of Karl Schwarzschild, his basic solution was perfectly adequate to show that this otherwise puzzling phenomenon could be convincingly explained in an elegant and persuasive way.
The third such prediction required significant technological advances if it was to be observed and so had to await future verification.[91] The absence of any evidence of a redshift in spectral lines was cited in British scientific circles in the next few years as a reason for having doubts about Einstein’s theory.
The second prediction, however, could be confirmed by existing instrumentation. All that was needed was a total solar eclipse so that the impact of the mass of the sun on starlight could be measured. How that happened is a story in itself.
The Confirmation of Einstein’s Theory of General Relativity
Scientific teams had already attempted to verify Einstein’s theories by observing star deflections during a solar eclipse. An American team from Lick Observatory in Mount Hamilton, California, had observed the total eclipse of June 8, 1918. Their conclusion was inconclusive, even pessimistic. However, the observatory had used low-quality equipment, and there were questions about the reliability of their results. There was clearly room for further investigation using more reliable equipment.
Einstein’s scientific work was based in Germany and Switzerland and was published in the German language. All the available evidence suggests that British and American scientists knew little, if anything, of his ideas. Those who did were not particularly sympathetic to those ideas, which seemed to be in tension with those of leading English-speaking scientists, such as Lord Kelvin and Oliver Lodge. More seriously, the First World War had created major tensions within the international scientific community, with many British and American scientists expressing open hostility towards readmitting a defeated Germany into their circle.
Yet to everyone’s surprise, Einstein found a champion in the British physicist Sir Arthur Eddington, who gained a reputation as one of the very few British scientists who was even interested in the theory of relativity, let alone understood it.[92] A story went around that Eddington was once complimented on being one of only three people in the world who understood the theory. Eddington didn’t respond to this compliment. On being asked why not, he replied that he was trying to think of who the third person was.
Sir Frank Watson Dyson, the British astronomer royal, chaired the Joint Permanent Eclipse Committee (JPEC). On hearing of Einstein’s prediction of the deflection of starlight in March 1917, Dyson decided that the eclipse on May 29, 1919, would be used to test this prediction. The star field near the eclipsed sun would be particularly rich, and the locations at which the total eclipse would last the longest were accessible to British astronomers. He recruited Eddington to lead the expedition.
As a Quaker, Eddington had been a conscientious objector during the First World War. This would normally have resulted in him being sent to a labor camp. However, in a stroke of creative genius, Dyson seems to have managed to persuade the British authorities to see the eclipse expedition as an act of military service on Eddington’s part. It was agreed that Sobral in Brazil and the island of Principe off the west coast of Africa were the best sites in terms of the totality of the eclipse, the anticipated weather, and the ease of access. Eddington himself led the Principe team. However, at the time of the eclipse, a significant degree of cloud cover caused some problems in taking good photographs. There were also some issues in the interpretation of the photographic plates.
The key question was the extent to which rays of starlight passing the sun would be deflected by the sun’s gravitational field. In a paper written in advance of the expedition, Eddington suggests that there are three possible outcomes of the solar eclipse observations and considers their implications. Given their importance for Einstein’s theory, we shall allow Eddington to set them out in his own words:
With the enormous velocity of light only the sun would be able to produce an observable effect. The light ray from a star close to the sun should be slightly displaced; that might be tested next year when the totally eclipsed sun would be in a field of bright stars. The experiment might lead to one of three results: (1) A deflection amounting to 1.75 seconds of arc at the limb of the sun would confirm Einstein, but would be twice as great as otherwise expected; (2) a deflection of 0.83 seconds would prove that light had weight, but would overthrow Einstein’s theory; (3) the absence of a deflection would show that light, though possessing mass, had no weight, and hence the Newtonian law of proportionality between mass and weight would break down in another unexpected direction.[93]
Yet not all of Eddington’s readers were persuaded that there were only three options. His critics suggested that there might be other possible explanations of any observed starlight deflections, including an uneven cooling of the Earth’s upper atmosphere during the period of the eclipse. Why hadn’t Eddington included these possibilities in his discussion?
In what many now see as a shrewd piece of media stage management, Dyson and Eddington arranged a dramatic event that they believed would decisively shape public opinion on Einstein’s theories. On November 6, 1919, Dyson and Eddington were joined by the leading astronomer A. C. D. Crommelin at a much-hyped joint London meeting of the Royal Society and the Royal Astronomical Society. Dyson and Eddington declared to the gathered representatives of the British scientific community that expeditions to Africa and Brazil to observe the eclipse had indeed confirmed Einstein’s prediction and ruled out its Newtonian counterpart.
This was presented as a stunning achievement that transformed our understanding of the universe. The Times headline, noted earlier, both captured and created a popular mood: “Revolution in Science. New Theory of the Universe. Newtonian Ideas Overthrown.” The down-market Daily Mail made much the same point with its cheeky headline “Light Caught Bending.” Other newspapers were caught up in this febrile mood. The New York Times declared that leading scientists were “More or Less Agog over Results of Eclipse Observations.” A revolution had taken place in science; Einstein’s theory was triumphant! However, the New York Times helpfully reassured its readers that there was no cause for immediate alarm; these discoveries did not “affect anything on this earth.”[94] Einstein’s brilliant theories had caught the imagination of the public through extensive media coverage, instantly propelling Einstein to international fame.
Yet scientific opinion remained divided —both about the merits of Einstein’s theory of relativity itself and about whether the 1919 eclipse observations really had confirmed it. The photographic plates resulting from these expeditions proved difficult to interpret at points. Some were so blurry that they had to be discarded.[95] This has led to suggestions —sometimes sensationalist —that Eddington and others may have discarded plates that did not fit in with their predetermined ideas, in effect fixing their results. However, a 1979 reexamination of the photographic plates shows that this suggestion does not appear to be substantiated.[96] Although many astronomers of the day, including Dyson, felt that these observations ought to be repeated at an eclipse predicted for 1922 before treating the case as closed, the 1919 plates were clear enough. Eddington’s skills as a publicist had not interfered with his integrity as a scientist.
Many British scientists, however, were rather more disturbed by sensationalist newspaper reports of a “scientific revolution” that had “overthrown” Newton. This, it seemed to them, was simplistic and shallow journalism that failed to highlight the obvious and important continuities between Newton and Einstein. In April 1921, aware of this problem, Einstein himself gave an interview with the New York Times in which he emphasized that his theories were to be seen as an evolution that consolidated Newton’s heritage rather than a revolution that discarded it:
There has been a false opinion widely spread among the general public that the theory of relativity is to be taken as differing radically from the previous developments in physics. . . . The men who have laid the foundations of physics on which I build are Galileo, Newton, Maxwell, and Lorentz.[97]
Hoping to counter the loose and lazy language of a “revolution” in science, Einstein made it clear he considered his theories to be “the natural completion” of the work of earlier physicists, so that his new approach was to be seen as representing an “orderly transition” to a better way of seeing our world.[98] Einstein consistently emphasized his continuity with the theories of his precursors, such as Newton in the seventeenth century and James Clerk Maxwell in the nineteenth. Einstein thus did not regard his special theory of relativity as revolutionary but as a systematic development of earlier approaches. Yet the conventions and agendas of popular journalism led to his being portrayed as a revolutionary thinker who had overthrown an existing scientific orthodoxy in much the same way as Russian revolutionaries had toppled the czar and established a radically different world.
Yet while British and American readers lionized Einstein as a scientific genius, others took decidedly more negative attitudes —above all, back in Germany.
German Physics: The Campaign against Einstein
In 1919, Einstein was a German citizen occupying a senior position at the prestigious University of Berlin and was director of the Kaiser Wilhelm Institute for Physics. He was at the heart of the German scientific establishment and had become —largely through the influence of Eddington —an international celebrity. Such adulation for Einstein was echoed in the Berliner Tageblatt, which proclaimed that Einstein was a genius who had uncovered “a highest truth, beyond Galileo and Newton, beyond Kant.” Finally, on December 14, 1919, the front page of the Berliner Illustrirte Zeitung was given over to an image of Einstein, proclaiming him to be “a new eminence in the history of the world.” Einstein’s research, it assured its readers, caused a “complete revolution in our understanding of Nature.” Yet, as Einstein would discover, there were some unwelcome consequences of such uncritical adulation and publicity.
The surge in populist admiration for Einstein allowed his critics in the German scientific establishment to present him as an academic lightweight who indulged in both fraud and plagiarism to promote his flaky ideas.[99] Two events that took place in Germany in 1920 help us appreciate the hostility that was building up towards Einstein in the aftermath of his publications about relativity.[100] The campaign against Einstein was launched on August 6, 1920, with an inflammatory article by the populist journalist Paul Weyland in the Tägliche Rundschau, a Berlin daily newspaper, accusing Einstein of shameless self-promotion or stealing other scientists’ ideas and presenting physics in purely theoretical terms, rather than as arising from experimental investigation.
To resist this contamination of German science, Weyland created the “Working Society of German Scientists for the Preservation of Pure Science” and organized a series of public lectures in the large auditorium of the Berlin Philharmonic Orchestra, capable of holding 1,600 people. In his opening lecture, Weyland ridiculed comparisons between Einstein and Copernicus, Kepler, or Newton. Surely Einstein should stop this shameless self-promotion in the media? After all, he seemed to know all the right people in the newspaper world.
Weyland here was hinting at something that would become increasingly significant in the 1920s: Einstein’s Jewish identity as something that was not properly German. (The newspapers that were most positive about Einstein’s scientific achievements had close connections with Berlin’s Jewish community.) The phrase “Jewish physics” began to be used, often contrasted unfavorably with “German physics.” In 1937, Einstein’s theory of relativity was criticized by Nazi sympathizers because of its alleged Jewish roots, which contaminated its scientific credentials.[101]
Tensions increased further as a result of a heated and inconclusive public debate, chaired by Max Planck, between Einstein and the distinguished physicist Philipp Lenard in September 1920. Although press reports emphasized the dispassionate and scholarly nature of this debate, it left Einstein deeply disturbed and wondering whether he had any place in the German academic world. Perhaps more worryingly, it suggested that his theory of relativity had become entangled with cultural and political agendas, above all with the question of whether there was a distinct “German physics,” which was represented by Lenard —and not by Einstein. Was Einstein becoming un-German?
Although Einstein was clearly rattled by these developments, he did not consider leaving Germany during the 1920s.[102] Yet Einstein was not, and could not be, detached from the political and social controversies of his age and was actively affected by them. To understand scientists —including Einstein —we need to place them within the context of their social and political history. Einstein’s theory of relativity was misunderstood by many in Germany during the 1920s. Some of these were genuine misunderstandings, while others seemed to be deliberate distortions aimed at discrediting Einstein in the eyes of certain social and political groups.[103]
The Nobel Prize in Physics
Einstein’s brilliant theoretical work —evident in his articles of 1905 —had clearly put him in the frame for a Nobel Prize. From 1910 to 1922, Einstein was nominated for the Nobel Prize in Physics every year except 1911 and 1915. Yet as events in Germany indicated, by 1920 Einstein had become controversial. His theory of relativity was too easily dismissed by critics as excessively theoretical. On the other hand, Einstein had become an international symbol of the explanatory and predictive power of science. Eventually, it was announced that the 1921 Nobel Prize in Physics would be awarded to Albert Einstein “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.”
So why did it take so long for Einstein to be awarded that prize? The Nobel Prize in Physics was awarded by the Royal Swedish Academy of Sciences, which based its decisions on the recommendations of the five members of the Nobel committee for physics and chemistry. In the early 1900s, this committee was dominated by a school of thought at Uppsala University that considered precise measurement the chief aim of their work. After all, theoretical developments ultimately rested on accurate measurements.
The 1907 Nobel Prize in Physics was given to the American physicist Albert Michelson for his “optical precision instruments and the spectroscopic and metrological investigations carried out with their aid.” The Nobel Committee thus thought that Michelson’s development of precise measuring instruments was more important than his theoretical developments based on those measurements!
In 1920, the Nobel Prize in Physics was awarded to the Swiss physicist Charles Édouard Guillaume for his discovery of Invar, a nickel-steel alloy that remained relatively unaffected by changes in its environment and thus allowed scientific instruments to make precision measurements with greater accuracy. Many saw it as an utterly bizarre choice. Guillaume was not an academic scientist at a prestigious university; he worked at the International Bureau of Weights and Measures. Yet understanding why Guillaume was awarded the 1920 prize helps us understand why Einstein was not.[104]
Unsurprisingly, Albert Einstein was nominated for the prize again in 1921. Allvar Gullstrand, professor of optics at Uppsala University, undertook a report on Einstein’s contributions to relativity and gravitational theory and recommended rejection of any award.[105] The committee found itself deadlocked and ended up not awarding a Nobel Prize in Physics in 1921.
A chance conversation led Carl Wilhelm Oseen, a theoretical physicist from Uppsala, to the conclusion that Gullstrand simply did not understand Einstein’s theoretical work or appreciate its significance. Yet there was nothing he could do about this; he was not a member of the committee that evaluated potential nominations. But in 1922, things changed. Oseen became a member of the nominating committee. Having himself grasped the importance of Einstein’s work, he devised a strategy to get around Gullstrand’s marked hostility towards Einstein, which was largely based on his theory of relativity —which had yet to be fully confirmed experimentally.
Why not instead award Einstein the Nobel Prize for his work on the photoelectric effect, which had been verified by experiment? In the end, this subtle compromise won the day. Einstein would receive a postdated Nobel Prize for 1921 for his explanation of the photoelectric effect, “without taking into account the value that will be accorded your relativity and gravitation theories after these are confirmed in the future.” Was the committee leaving the door open to a later award for the theory of relativity once this had been experimentally confirmed in the future?
The Nobel Prize increased still further Einstein’s reputation and international appeal. Under the terms of Einstein’s divorce agreement of 1919, his former wife, Mileva, was entitled to the financial —as opposed to reputational —benefits of the prize. As a result, she bought three apartment blocks in Zürich as an investment, living in one herself and renting out the other two. Einstein remained in Berlin, his reputation enhanced by this international recognition. However, his personal situation remained problematic, as growing anti-Semitism became an increasingly significant concern for him.
Einstein’s Move to America
Following its defeat in the First World War, Germany faced a series of political and financial crises during the early 1920s as the postwar Weimar Republic found itself saddled with a massive reparations bill. It simply could not afford to pay it. The value of the German mark plummeted, causing massive inflation. In the first half of 1921, the US dollar was worth 90 German marks; by November 1923, the US dollar was worth 4,210,500,000,000 German marks. The value of savings went into freefall.
Anti-Semitism now began to emerge as a significant force in German politics. In an article of June 1921, Einstein spoke of his growing awareness of prejudice and discrimination against Jews in Germany. Yet far from causing Einstein to downplay his Jewish identity, it encouraged him to reaffirm and reassert it:
Until seven years ago I lived in Switzerland, and as long as I lived there I was not aware of my Jewishness. . . . This changed as soon as I took up residence in Berlin. There I saw the plight of many young Jews. . . . These and similar experiences have awakened my Jewish national feelings.[106]
The Wall Street crash of October 1929 caused a worldwide slump of unprecedented severity, which proved fatal for the political stability of the Weimar Republic. The failure of a democratic government to come to grips with the crisis led to growing popular interest in authoritarian alternatives such as Communism and National Socialism (the latter being better known in its contracted form “Nazism”), which people hoped would provide firm leadership in the face of such crises. The National Socialist party leader was Adolf Hitler. Joseph Goebbels, under Hitler, translated the ideology of National Socialism into a popular movement, replete with a quasi-religious symbolism and strongly anti-Semitic mythology.
The emergence of a Nazi ideology seems to have spurred Einstein into developing his own creed —political, social, and religious. There is an interesting parallel here with the British novelist E. M. Forster, who penned A Room with a View. Writing in 1939, Forster remarked that the aggressive ideologies he saw in Nazi Germany and the Soviet Union forced him to develop his own beliefs in response. “There are so many militant creeds that, in self-defence, one has to formulate a creed of one’s own.”[107]
Einstein was rightly alarmed at the rise of Nazism. In 1930, he had taken the view that Hitler’s growing influence reflected the economic crisis of the moment. Once economic conditions started to improve, he would no longer have the same appeal. Yet by late 1932, Einstein had realized that nothing could stop Hitler’s rise to power. As a Jew, he knew that he and his family would no longer be safe in Germany. On December 12, 1932, Albert and Elsa Einstein left Berlin for the United States. Hitler was installed as the German chancellor a month later. German newspaper headlines made it clear Einstein would not be welcome if he returned: “Good News about Einstein —He Is Not Coming Back!”
Facing up to the inevitable, Einstein resigned from the Prussian Academy of Sciences and renounced his German citizenship. He eventually became an American citizen in 1940. His home would be the newly founded Institute for Advanced Study at Princeton University, where he remained for the remaining twenty-two years of his life. Yet Einstein’s period in the United States, though unquestionably comfortable, did not lead to the scientific breakthroughs that some appear to have expected. His breakthroughs were made in the 1900s and 1910s. What followed was an attempt to consolidate and expand those earlier insights and a rigorous, yet ultimately fruitless, attempt to integrate the great theoretical insights of that time.
Einstein died at Princeton Hospital on April 18, 1955, of an abdominal aortic aneurysm. Perhaps aware of the risk of becoming the center of some kind of postmortem celebrity cult, Einstein stipulated that his body was to be cremated and his ashes scattered in the Delaware River. In at least one important respect, his last wishes were disregarded. In a bizarre twist of events, Einstein’s brain was removed by Thomas Harvey, the pathologist on call that evening, and removed from the hospital without any authorization. Harvey also removed —again, without permission —Einstein’s eyeballs and gave them to Henry Abrams, Einstein’s ophthalmologist. Perhaps Harvey hoped to acquire fame and fortune through his illicit possession of Einstein’s brain. In the end, however, the brain was returned to the pathology lab at Princeton in 1997.[108]
Einstein’s Failed Quest for Theoretical Unity
Einstein’s achievements were remarkable, from his decisive 1905 contribution to the formation of quantum mechanics to his development of the theory of general relativity in 1915. Yet Einstein saw his work as incomplete. Why? Because his quest for die Einheitlichkeit —the fundamental unity of all phenomena —remained unfulfilled. Einstein’s writings of the 1910s show how he was driven by this quest. In a letter of November 1916 to the Dutch astronomer Willem de Sitter, Einstein remarked on his almost compulsive desire to find a unified view of reality: “I am driven by my yearning to generalize.”[109]
His 1918 Berlin lecture to mark the sixtieth birthday of the great German physicist Max Planck is especially revealing here. For Einstein, the quest for a single “simplified and clear image of the world” was not merely the ultimate objective of science but also corresponded to a deep human psychological need to escape from the banality of everyday life into a purer world of objective perception and thought. The scientist’s committed engagement to the study of the natural world thus required a “state of feeling” similar to that of a religious believer.
It is widely agreed that general relativity is at present the best generalized theory of gravitation and space-time structure. Yet although it can account for a remarkably wide range of phenomena, it is incomplete in that it ignores the quantum effects that govern the subatomic world. Most physicists adopt a pragmatic work-around to this problem, using general relativity to describe the large-scale phenomena of astronomy and cosmology and using quantum mechanics to account for the behavior of atoms and elementary particles. As these two realms are generally far removed from each other, this strategy works quite well in practice. But it is a theoretical fudge.
This approach is clearly unsatisfactory from a conceptual perspective. It is a work-around, not a solution. For a start, these two theoretical frameworks are quite different. General relativity has geometric precision and is deterministic; the world of quantum physics is shaped by uncertainties and is probabilistic —a feature that caused Einstein to have serious misgivings concerning its viability and that led to his famous (and often misunderstood) remark to the effect that God “does not play dice” with the universe.[110] More fundamentally, Einstein believed that there had to be a grander and more complete theory that enfolds both general relativity and quantum physics as special or limiting cases. Finding that grand theory that would embrace the “totality of empirical facts” was Einstein’s life goal.
Einstein hoped to achieve a complete and coherent account of reality —a goal that some might see as philosophical rather than scientific.[111] Yet Einstein failed in this quest. Robert Oppenheimer, director of the Institute for Advanced Study at Princeton, where Einstein spent the final two decades of his career, suggested that Einstein’s attempts to formulate such a unified theory were “a complete failure.” Einstein was just “wasting his time.”[112] Others, however, were more generous. The physicist Brian Greene believes that Einstein was simply ahead of his time. Mainstream physics of Einstein’s time was simply not ready for the grand unified theory that Einstein believed lay tantalizingly within his grasp. “More than half a century later, his dream of a unified theory has become the Holy Grail of modern physics.”[113] Einstein may have started from the wrong place, but he rightly grasped the possibility of holding together the complexities of the universe within a single grand theory.
Einstein’s pursuit of a unified view of the world remains important beyond the world of physics. One of the central themes of this volume is the need to reflect on Einstein’s belief that it was possible to hold together —if not to weave together into a coherent unity —his views on science, ethics, politics, and religion.[114] The search for a unified view of reality is not limited to physicists or cosmologists. We each, in our own way, try to weave together the threads of our beliefs and commitments in the hope of creating a coherent picture of reality —a Weltbild, to use the German term that Einstein favored.
Earlier Einstein scholars focused on the development of his scientific ideas and how they shaped and redirected scientific thinking. Yet more recent work has revealed the surprisingly large volume of material in which Einstein wrote about religious, ethical, and political issues, often reflecting on how these were to be related to each other. This growing interest in Einstein as a human being prompts two questions, both of which are explicitly addressed in this book. First, how did Einstein engage life’s big questions, and what answers did he advocate? And second, irrespective of whether we agree with Einstein’s views on science, religion, or ethics, can the way in which he tried to hold these together be of service to us as we try to develop our own view of reality, however modest and limited this might be?
We shall turn to consider these questions in the second part of this book.
[85] Technically, Einstein was appointed as “außerordentlicher Professor,” which is not easy to convert into an English-language equivalent.
[86] Maxwell, “A Dynamical Theory of the Electromagnetic Field,” 466.
[87] Wheeler, Geons, Black Holes and Quantum Foam, 235.
[88] Einstein, Ideas and Opinions, 100–105.
[89] O’Raifeartaigh et al., “One Hundred Years of the Cosmological Constant.”
[90] Einstein, “Erklärung der Perihelbewegung des Merkur aus der allgemeinen Relativitätstheorie.”
[91] See Holberg, “Sirius B and the Measurement of the Gravitational Redshift.”
[92] For an excellent study, see Almassi, “Trust in Expert Testimony.”
[93] Sponsel, “Constructing a ‘Revolution in Science,’” 448.
[94] “Lights All Askew.”
[95] See especially Waller, Einstein’s Luck, 102–3.
[96] Harvey, “Gravitational Deflection of Light.”
[97] Cited in Holton, “Einstein’s Search,” 1–15.
[98] Pais, “Subtle Is the Lord”, 30.
[99] Goenner, “The Reaction to Relativity Theory I.”
[100] These are discussed in van Dongen, “Reactionaries and Einstein’s Fame.”
[101] Thüring, “Physik und Astronomie in jüdischen Händen.”
[102] For this period of Einstein’s life, see Goenner, Einstein in Berlin 1914–1933; Hoffmann, Einstein’s Berlin.
[103] See, for example, Hentschel, Interpretationen.
[104] For what follows, see Friedman, The Politics of Excellence.
[105] Ravin, “Gullstrand, Einstein, and the Nobel Prize.”
[106] Rowe and Schulmann, Einstein on Politics, 151–52.
[107] Forster, “What I Believe,” 67.
[108] For the story, see Paterniti, Driving Mr. Albert.
[109] Letter to Willem de Sitter, in Collected Papers, vol. 8.
[110] This quote is found in a private letter from Einstein to the Hungarian physicist Cornelius Lanczos, who was then based at Princeton, dated March 12, 1942. Einstein wrote, “It seems hard to sneak a look at God’s cards. But that he plays dice and uses ‘telepathic’ methods (as the present quantum theory requires of him) is something that I cannot believe for a single moment.” This is unfortunately often simplified to “God does not play dice.” For a good discussion, see Ghirardi, Sneaking a Look at God’s Cards, 149–64.
[111] Paty, “The Nature of Einstein’s Objections to the Copenhagen Interpretation of Quantum Mechanics.”
[112] Van Dongen, Einstein’s Unification, 186.
[113] Greene, The Elegant Universe, 15.
[114] For a good discussion, see Paty, Einstein Philosophe.