Einstein's War

by Matthew Stanley

  Hilbert was interested in whether it would be possible to derive entire sciences just from these logical structures, without any physical references. His project was enormously ambitious and he had tremendous optimism: “There is the problem. Seek its solution. You can find it by pure reason, for in mathematics there is no ignorabimus.” That last bit of Latin—ignorabimus—meant something like “we can never know,” a famous declaration of the limits of science. Hilbert rejected this flatly. He had great confidence in the power of pure reason and also thought that scientists should challenge themselves by tackling vast problems. He was fine with science having “loose foundations” as long as everyone was exploring boldly.

  He thought that the electromagnetic theory of matter (ETM for short) was an excellent candidate for “axiomization”—that is, that he could figure out the basic properties of matter from purely logical and mathematical principles. This was how he encountered Einstein’s work in 1912 or so. Einstein’s efforts to ground relativity in a handful of elegant principles looked very promising to Hilbert. Predicted phenomena such as light deflection suggested there was some connection between matter (via gravity) and electromagnetic energy (the essence of light), which might help crack open his ETM ideas. He decided to include some of Einstein’s work in his physics seminar, which only deepened his interest. He then teamed up with his mathematics colleague Felix Klein to invite Einstein to Göttingen to deliver the Wolfskehl Lectures from June 28 to July 5.

  Göttingen, both university and town, were ancient and elegant. The university was the most visited school in Europe, drawing international students from around the world. It produced not just top-class mathematicians but also the Brothers Grimm and Otto von Bismarck. Cutting-edge research blended with antique traditions—doctoral graduates were drawn across town in handcarts to kiss the statue of the goose girl.

  Einstein gave six two-hour lectures on relativity (specifically, the state of the Entwurf) during his week there. Presumably his unimpressive delivery did not compare well to Hilbert’s famously clear teaching. Nonetheless, Einstein and Hilbert developed an immediate rapport. Einstein said he found himself “enchanted.” He called Hilbert a “great man!” and “a man of astonishing energy and independence in all things.” He was impressed not just with Hilbert’s mathematical virtuosity—he was one of the few people of the time who actually understood the project of general relativity—but also his political leanings. Hilbert had refused to sign the Manifesto of 93 and was public about his opposition to the war. This combination of scientific and political comradeship deeply affected Einstein. He found himself appreciating Hilbert as someone who, as he put it, could rise above the fray. The respite from being surrounded by imperialism was remarkable: “Berlin is no match for Göttingen, as far as the liveliness of academic interest is concerned.”

  He found that his conversations with Hilbert had “clarified very much” the state of relativity. Klein, who was present at most of these, had a slightly different take: he reported that Einstein and Hilbert were often talking past each other and not paying that much attention to what the other was actually saying. With a verbal shrug, Klein said this was fairly common for mathematicians. And there is an important sense in which he was right—Hilbert was interested in the ETM, Einstein was interested in the nature of time and space. They were looking at the same sets of equations but for different reasons.

  Nonetheless, both Hilbert and Einstein came away from their debates stimulated and, though they probably did not know it at the time, armed with everything they would need for their battle plans against the problem of relativity. They both began working on a better, more complete version of the Entwurf. As the two parted, on good terms and as good friends, the stage was set for one of the great scientific races of all time. They both had the keys to general relativity; the question was, who would realize it first?

  * * *

  THE TRIP TO Göttingen got Einstein thinking about how much the war had isolated him. He had used to travel quite a bit to see scientific collaborators, but it was much harder now. He commented that his “truly profound colleagues”—meaning Planck and Hilbert—still wanted to maintain connections with scientists in other countries. “Hilbert now regrets doubly, as he told me, having neglected to maintain international relations better. Planck is doing everything to bridle the chauvinistic majority at the [Prussian Academy].”

  A planning meeting at the BNV seems to have prompted Einstein to contact Lorentz with a new plan. In a moment of big-tent ecumenism, he contended that academics were innocent of the war (quite a change from his earlier reactions to the Manifesto) and that solidarity among scientists was more important than assigning blame. If he didn’t live in Berlin, he wrote, he would be contacting like-minded scientists in Britain and France to gather in a neutral country and nurture personal connections. But he did live in Berlin under the blockade. Worse, he had few contacts of his own. Worst of all, Einstein admitted, he just wasn’t very good at talking to people. He hoped Lorentz could take on this project of gathering international supporters. Surely there must be other scientists battling “nationalistic blindness” in other countries?

  Lorentz declined to take up the project, apparently because he thought the mood of British and French scientists was already too far gone to make a real difference. Einstein was disappointed, though not particularly surprised. He tried to explain the political tenor of Berlin, saying that the scientists were generally level-headed—it was the historians and philologists that were “chauvinistic hotheads.” He defended Planck by saying that the elder man had signed the Manifesto of 93 without reading the text. In the end, though, Einstein said he had realized that apparently advanced societies were really just disguised oligarchies. The powerful would forever be able to make the people hate one another.

  Einstein’s pessimistic mood may have been shaped by his reading material at the time—Tolstoy’s Christianity and Patriotism. He saw little opportunity to convince the masses not to fight for their masters. Sourly, he wrote, “no education and intellectual cultivation seems to be able to protect against this wretched madness.” He confessed that he had recently shared a train car with soldiers and “relished their stupidity and crudeness.”

  Einstein probably encountered those soldiers on his journey to or from Göttingen. He had also hoped to take another trip that summer. Relations with his oldest son, Hans Albert, had become strained since Mileva took the boys back to Zurich. They had recently exchanged emotionally charged letters in which Hans Albert declared that he had no interest in seeing his father. Einstein took that at face value, canceled his trip, and took Elsa and her daughters on a vacation to the Baltic.

  They were all delighted to be out of Berlin, even for a short time. The effects of the British blockade were growing rapidly, and were generally magnified in the imperial capital. Rationing had begun in February 1915. Each Berliner received one half pound of bread per day. Meat, eggs, and fat were distributed by ration card. Potatoes were soon rationed as well, leading to the violent protests known as the Kartoffel-Krawalle (the potato riots). By the fall, the government was enforcing meatless and fatless Tuesdays and Fridays (extended to Sundays for bars and restaurants). Elsa had been cooking lunch regularly for a group of poor women, trying to spread her family’s better-than-most resources.

  At the universities, paper, ink, and coal were all heavily restricted. Library orders were canceled as finances entered a crisis. Government support had been severely cut, and the precipitous drop in enrollment (75 percent fewer students by summer 1915) came with a proportional decline in student fees. The German High Command at one point considered simply closing all the universities.

  Patriotism was widely encouraged and often enforced. Foreign movies were banned and replaced with nationalistic films. A replica of a front-line trench was set up in a park, a common sight in the combatant capitals. The rising toll of the war—in lives and money—was becoming increasing
ly clear, and there were quiet conversations about the goals and eventual outcome of the war. Was it still possible to emerge from the conflict as an imperial power the equivalent of Great Britain? The great political split was between those who called for a German victory that resulted in territorial gains and those who called for a German victory without any annexation. Einstein hoped that Germany would lose the war but signed a petition for the latter anyway (as did Planck and Hilbert). A return to prewar conditions would at least be better than a revitalized Germany dominating Europe. The petition garnered 141 signatures, one-tenth of the signatures attached to a pro-annexation petition.

  But there were widespread doubts about the conduct of the war that had emerged after the first year of fighting. The staggering death toll and virtually nonexistent gains in the west made optimism difficult. Even the nationalists in Einstein’s circle had begun to moderate their enthusiasm. Both of Nernst’s sons had been killed. One of Planck’s sons had been killed; one was a prisoner of war.

  * * *

  EINSTEIN MANAGED TO reconnect with his own sons in September. He decided to make a trip to Zurich regardless of the earlier tensions. International travel was far from easy, even to a neutral country. This was aggravated by Einstein’s habit of forgetting (perhaps intentionally) to register his absence from Berlin with the police, as was required.

  The train to the Swiss border took a couple of days. During a stopover in Heilbronn he wrote to Elsa to excitedly report on how much better the food was there than in Berlin: “Milk and honey may not be flowing anymore, but there is still a decent trickle. You cannot get any fruit here, but there are vegetables.” To pass the time on the journey he read Spinoza’s Ethics.

  Once in Zurich he hiked with Hans Albert, much to both of their delight. Albert’s unflagging friend Besso helped mediate between Einstein and Mileva, setting up schedules where the estranged parents did not have to speak to each other. In addition to his family visits, though, Einstein had another job. The BNV had been very interested in allying with Romain Rolland, the Nobel Prize–winning French pacifist writer who had taken up residence in Switzerland. Rolland was influential among antiwar thinkers across Europe but had refused to join any organizations. Einstein had written to Rolland earlier and met him in person after discharging his family responsibilities.

  They had a vigorous conversation about the war. Rolland described Einstein as both “very vivacious and serene; he cannot help giving the most serious thoughts a jocular form.” He asked whether Einstein voiced his criticisms of Germany to his friends in Berlin. Einstein replied that he did not, and instead asked many Socratic questions in order to upset their peace of mind. “People don’t like that very much.”

  After the meeting, while he was still in Switzerland (and thus free from the German censors), Einstein wrote Rolland a passionate letter. He described the dire straits in which the BNV found itself: “It is being harassed by the inspection authorities and being condemned (on the whole) by the press. . . . In many cases intellectuals have completely lost their composure.” The “war of words” had started among Berlin writers. Einstein luxuriated in these few days of unfettered conversation.

  On his way back to Germany, Einstein crossed at Konstanz. The German border authorities turned him back. He had failed to file the proper paperwork for his passport while he was in Zurich. Humiliatingly, a soldier escorted him back to Kreuzlingen in Switzerland, where he had to wait for a few days until the bureaucracy was sorted out. Strangely, he found himself trapped in a place he loved and where he was free to talk, seeking permission to return to the patriotic bustle he hated.

  He finally made it home on September 22 after twenty hours on the train. His travel weariness was wiped away when he saw on his desk a new scientific paper from Lorentz. He read it eagerly. The paper involved applying what is known as Hamilton’s principle in gravitational and electromagnetic fields. The principle, named after the formidable Irish mathematician Sir William Rowan Hamilton (1805–1865), was a powerful alternative tool used for analyzing the motions of bodies. In classical Newtonian mechanics one can take a given object, figure out the forces acting on it and how those forces change, and then calculate the path it will take. This can quickly get tedious. Instead, Hamilton’s principle ignores the specific forces at work and analyzes the energy the object has, including how that energy changes back and forth between kinetic (energy of movement, easily seen) and potential (hidden energy, ready to be unleashed when conditions allowed). The principle basically says that objects will move in the way that requires the least expenditure of energy over the least amount of time—as one famous physicist put it, “Nature always uses the simplest means to accomplish its effects.” “Simple” here means something like “thrifty”—minimal effort, done quickly.

  So to use Hamilton’s principle, you take an object in a particular environment and set up your equations to express this thriftiness. Out will pop the trajectory—the path—that your object takes. This makes many problems much, much easier, at the cost of a high level of abstraction. You can no longer talk about a specific force pushing your object, only a general sense of energy shifting around. Lorentz’s paper applied this method in a new way to objects subject to gravitational and electromagnetic forces. This was similar to some of the methods, called Lagrangians, that Einstein had been using to understand the conservation laws in his Entwurf theory. He immediately sat down to see if Lorentz’s methods could help, firing off a letter to Lorentz describing how “delighted” he was.

  This was a new wrench that Einstein was checking against old bolts. He was already happy with how the Entwurf handled conservation laws, but a new wrench was a new wrench—he couldn’t not try it out. It seems that while he was checking out the conservation laws he decided to take a look at some other old bolts too. Specifically, rotation. The problems of how rotation worked with the equivalence principle and covariance were some of the initial steps in his attempts to generalize relativity, so he expected no problems. But in retracing those original steps, he found something extraordinary. He found a mistake.

  It actually wasn’t a new mistake. Back in 1913 when he and Grossmann had been putting the Entwurf together, Grossmann had pointed out that the equations were not covariant for certain kinds of rotation. That was when Einstein formed his “hole argument” explaining why that was not really a problem. But now that he studied the initial problem with two years of perspective, something looked different. He wasn’t sure exactly what, though. Was the Entwurf wrong? On one hand, despair was creeping up on him—had he been on the wrong path this whole time?—on the other he said that the possibility of something new “electrifies me enormously.”

  After a few days of intense thought, he wrote to Freundlich, someone physically close by who was familiar with relativity’s foundations. The rotation problem wasn’t really one of mathematics. The calculation involved was extremely simple, just a few lines. And he had seen it all before, there was nothing new. Einstein realized he just needed to think about it in a different way. He also realized that he couldn’t do it. He told Freundlich that he was stuck “in the same old rut.” He had been staring at it too long to shift his perception. “I must depend on a fellow human being with unspoiled brain matter to find the error. If you have time, do not fail to study the topic.”

  We do not know if Freundlich offered anything useful. Einstein threw himself into the problem, though. In early October he decided to try to re-derive the entire Entwurf theory to try to find the source of the difficulty. He and Grossmann originally crafted the Entwurf from a mix of mathematical and physical reasoning. This time he decided to try a purely mathematical approach, perhaps using the new Hamiltonian tools.

  This was the beginning of what Einstein would later call the most intense and stressful period of scientific work of his entire life. Nonetheless, on two occasions in October he put relativity to the side. The first was when the Central Organization for a Durab
le Peace, a pacifist group based in The Hague, contacted him. They were setting up a Large International Council and invited Einstein to serve. He agreed to do so, and sent a postcard to that effect.

  The second was a letter from the Berlin Goethe League, a well-known cultural organization. The League wanted to publish a patriotic album consisting of essays by intellectuals that would help reassure the public of the war’s righteousness. Inexplicably, they asked Einstein for a contribution. Presumably they expected a conventionally professorial statement of nationalism. Instead they got a three-page screed mocking the very notion of patriotism and rejecting any kind of war. He decried nationalism as a tool for encouraging “animal hatred and mass murder.” He called for a new political order in Europe that would prevent all future conflict. The League was, to say the least, surprised.

  EINSTEIN SOMEHOW WROTE this essay, “My Opinion of the War,” while furiously reworking the foundations of general relativity. His problem was essentially this: he had rediscovered a problem in his theory (the lack of general covariance). But he had already come up with a neat explanation for why that wasn’t really a problem (the hole argument, which said you shouldn’t expect general covariance). So he had to figure out why the hole argument was wrong, and come up with a better way to solve the initial problem.