Frank responded soberly in Lotos, dismantling the idea that motion cannot be understood as relative. The problem with Kraus’s reading was that he did not understand the difference between a stated and an unstated comparison: “If the predicate of a judgment is a relative concept and the object of comparison or relation is not named, the judgment remains incomplete and all the consequences about incompatibility, indeterminacy, and absurdity are invalid.”90 Irate, Kraus repeated his earlier charges essentially unmodified, adding that the classical relativity principle and the principle of the constancy of light—the relationship between which Einstein himself had come to modify during his time in Prague, unbeknownst to Kraus—were incompatible.91 Frank left the matter there, while Kraus picked a fight with Hans Reichenbach in the Berlin periodical Umschau in 1921, assuming that the latter had been implicitly ridiculing him in a previously published piece, and the philosopher Benno Urbach reignited the dispute in Lotos in 1922.92 That last exchange ended with a calm but final note from the editors: “With the preceding article we close the discussion about this contentious matter in our magazine. The form in which it has been published here in its personalizing acerbity departs from our usual practice, the responsibility for which is the author’s alone.”93
Kraus continued to actively defend his view, earning support from the most militant and bigoted opponents of Einstein. Kraus provided them needed cover: they could not be anti-Semitic if Kraus joined them, and they could not be philosophical ignoramuses if someone with Kraus’s reputation argued alongside them. Kraus’s debut as a prominent antirelativity critic outside of Prague came with an invitation from Hans Vaihinger, the important neo-Kantian philosopher, for Kraus to come to the German city of Halle in late May 1920 and contest not so much relativity as the positivist Machian reading of it. “Professor Kraus from Prague will … give a lecture here in Halle against Einstein’s doctrine of relativity. He explicitly wanted to express the wish that you,” Vaihinger wrote to the ultra-Machian defender of relativity, Josef Petzoldt, “be invited to this lecture.… You would be welcomed by all, and we would be especially pleased by your participation in a debate about Kraus’s lecture.”94 Petzoldt was willing to come and represent special relativity and positivism.
Einstein was unwilling to represent either. The previous year, he had refused to give Vaihinger an article on the interpretation of relativity for his prominent journal Kantstudien, but that did not stop the organizers of the Halle meeting from inviting Einstein and putting his expected attendance on the program.95 The psychologist Max Wertheimer, himself born in Prague and a graduate of the German University, wrote to Einstein in outrage:
In April, in Prague, I heard about the “imminent important congress about Einstein, where Prof. Kraus (!) has been granted the chief role, which will now (finally) in public reveal the elementary absurdities of the Einsteinian theories before a philosophical tribunal, so that it will become clear, how—.”
Here I find an invitation from the Kant Society: Mr. Einstein will also be in Halle! …
Heavens alive, what kind of publicity racket have you gotten yourself into?! Would physicists of comparable caliber risk something like this?! For the most part feeble-minded, sluggishly cud-chewing, squabbling mediocrities and some like Kraus: insolent; and obsessed with publicity—yes, my Lord, if one could at least think that it made any sense at all: that something could be honestly advanced in the “conference” or even just treated seriously—but you, my good man, don’t you know what these people are like and what they want—?!96
Wertheimer was not the only one who pressured Einstein to stay away, especially given the outburst of right-wing protests against relativity at other similar meetings. “I believe that I’ll turn Halle down,” Einstein wrote to his wife Elsa a few days later, “because the jabbering will sit poorly with me.”97 A good thing, too. Petzoldt would later report that the whole affair had been a shambles, and that the “philosophers there were not at all even clear on the experimental foundations of the theory.”98
Kraus was in full flower at the event, elaborating again on the fictive status of relativity: “Fiction: a representational image which corresponds to reality in nothing, proving its worth as an auxiliary for calculation and research, as a trick for thinking. This is also, in my view, the case with Einstein’s so-called relativity theory,” he wrote in the article expanding on his speech, “but these fictions are not always recognized as such—including by their author—they are treated not as though they were auxiliary assumptions in the sense of conceptual constructions without a value in reality or merely analogical symbols, but rather as though these imagined things existed. So fiction becomes reality and vice versa reality a fiction.”99 The relativity of simultaneity was a case in point, because it was a patent absurdity that something could be at once both simultaneous and not simultaneous. Rather, Kraus contended that one should take these ideas as if they were true, adapting his host Vaihinger’s conception of an “As-If” (Als-ob) philosophy, a notion that he claimed Einstein’s former colleague, the mathematician Gerhard Kowalewski, had introduced him to.100
As it happens, Einstein had already refuted this argument in a charming 1918 dialogue he composed between a relativist and an imagined opponent, eerily foreshadowing these controversies: “Thus still none of the magnitudes dependent on choice of coordinates correspond, for example, to the components of the gravitational field at a spacetime point; so nothing ‘physically real’ corresponds to the gravitational field at one place, let alone to that gravitational field in combination with other data. One can thus neither say that the gravitational field at a point is something ‘real,’ nor that it is something ‘merely fictive.’ ”101 Kraus either never became aware of this piece or chose to ignore it.
Soldiering on, Kraus became a highly sought-after member at antirelativity gatherings, though he was careful to avoid association with the more disreputable segments of the scene. When writing a diatribe against relativity at the invitation of a Viennese newspaper, he insisted that he wanted no part of the xenophobic and racist demagoguery that had characterized the attacks on Einstein and general relativity at Bad Nauheim in 1920.102 For example, he withdrew from a proposed lecture series at the Berlin Philharmonic scheduled for 2 September of that same year when he learned that it was going to be a largely anti-Semitic event, despite already appearing on the program. The organizers, hoping to cover up Kraus’s real reasons and at the same time stoke the resentment of the conspiracy-minded, claimed he had been denied a visa by the German government, which was seeking to protect the tender feelings of their prized physicist.103
Kraus was never one of the most prominent voices in the chorus of Einstein’s attackers—those roles were played by Gehrcke and Nobel laureates Philipp Lenard and Johannes Stark—but he continued to promote his views in a variety of venues that treated him as a more respectable face of what was becoming an increasingly unhinged movement. Although he continued to publish articles developing the same limited set of arguments in local newspapers and occasionally academic journals—when they would entertain the increasingly polemical tone of his writing—his main intervention that decade was the release in 1925 of a short book entitled Open Letters to Albert Einstein and Max von Laue.104 (Kraus included von Laue because the latter had once rejected one of his pieces for a physics journal, an act of professional gatekeeping that Kraus saw as aggressive censorship.) The book makes for unusual reading: the text is studded with boldfaced terms, italics, and exclamation points, and the tone veers occasionally well beyond the threshold of politeness. “The edifice of special relativity theory is nothing other than [the] structure of all mathematical deductions that can be drawn out from the—in itself absurd—postulate of the invariance of the speed of light,” he proclaimed to his principal adversary. “From your invariance postulate, whose correctness is assumed from the outset, is deduced an unforeseeable abundance of consequences and even if the entire system based on this statement were subsequently
completely ‘free of contradiction,’ then it would not achieve the slightest thing for our knowledge of the physical world; it is and remains a deduction from impossible premises, a mathematical concept-fiction.”105 To forestall rebukes (such as Frank had made, quite accurately) that his physics knowledge was too meager and his understanding of relativity theory based on popularizations, Kraus announced that Lenard and Gehrcke had proofed his text to make sure the physics was correct. Very reassuring.
Needless to say, neither Einstein nor von Laue registered a response to these charges. There was little need. The consensus on the validity and utility of special relativity had been almost unanimous among the physics community by the time Einstein had arrived in Prague in 1911, and by the late 1920s even the last reputable naysayers within the mainstream physics community had given general relativity their stamp of approval in the face of astronomical findings reported from London and California. The anti-Einstein group continued to write, but both the changed intellectual environment and the intensifying ugliness of the movement’s right-wing affiliations all but discredited it. In a last-ditch salvo, a group of authors produced a polemical booklet, One Hundred Authors Against Einstein, consisting mostly of quotations from Einstein’s more and less legitimate critics over the years, typically out of context. Oskar Kraus’s name was featured prominently on the title page, and he penned some new paragraphs to reiterate his old points. The Prague philosopher continued to provide cover, as did the lead editor Hans Israel (and two other Jews among the 28 contributors), for the thinly veiled anti-Semitism of the chief actors.106
This focused examination of Kraus’s antirelativity polemics could give one the impression that he was single-mindedly focused on this one issue, and that he had come to be broadly recognized as a crank. Yet Kraus did not live by relativity alone, and he continued a broad range of activities across the Prague intellectual spectrum. At the same time he was writing his Open Letters, for example, he produced a sensitive assessment of Albert Schweitzer’s theology that bordered on the hagiographic.107 (In December 1928, he arranged for the famous physician and humanitarian to receive an honorary degree from the German University.) He also concentrated on more philosophical work. He was active in the famed Prague Linguistic Circle, the polyglot collection of scholars who were transforming the science of language in midcentury Europe. Although he objected to some presentations delivered to the Circle, such as that of Rudolf Carnap on 20 May 1935, he gave his own lecture to the group a few months later and entertained an active exchange of ideas on a wide range of conceptual issues (all from a Brentanist perspective, of course).108 It is possible that Kraus was mellowing as he neared retirement. Einstein’s long-time correspondent and Bertha Fanta’s son-in-law, the philosopher and Zionist Hugo Bergmann, ran into Kraus on a visit to his hometown from Palestine in late September 1935. “On the final evening I also visited Oskar Kraus and the Brentano Archive,” he noted in his diary. “Kraus was actually very touching when he paused in the middle of the conversation and with closed eyes demonstrated Brentano’s reduction to the act on a certain occasion, and when he conceded that it was Husserl’s achievement that he articulated that an a priori psychology existed.”109 Next to Einstein, Husserl was one of Kraus’s nemeses, so this praise stood out.
Even Einstein, as it turned out, benefited from Kraus’s late style. In 1938, Kraus published a piece, “On the Misinterpretations of Relativity Theory,” in an edited volume commemorating the centenary of his master Franz Brentano. A reader who had been following Kraus’s decades of publication attacking the relativity of simultaneity would have noticed a sharp change in both tone and content. “This concept of psychological simultaneity is the inevitable assumption of the concept of any physical measurement,” Kraus wrote. “Against Einstein one can say that his ‘heaven-storming titanic work’ is not pernicious only because the immediate views about space and time remain untouched in the unattainable heights of a priori necessities of thought.”110 By introducing the notion of psychological simultaneity, Kraus was able to come to terms with Einstein: relativity of simultaneity cannot hold psychologically for any observer, Kraus believed, but it might actually be a physical truth. For several years, Kraus had been having conversations with Reinhold Fürth, one of Philipp Frank’s students who had been appointed to the natural sciences faculty of the German University. Fürth had patiently succeeded where Frank had failed in explaining to Kraus that his understanding of relativity theory was inaccurate.111
Kraus felt he needed to make amends to those he had maligned. As his widow recalled in an undated note preserved in his archives in the Austrian city of Graz: “Many years after” the 1921 public debate at the Prague Urania, “Kraus realized that he had been wrong on a certain point. He summoned together all the students of Charles University and all the professors of the various faculties. He demonstrated before the assembled auditorium with a colleague from the natural sciences faculty the aforementioned problem. Then he stepped before the platform and said very plainly: ‘I made a mistake.’ ”112 He even wrote a private letter to a party he had only previously addressed publicly. “In recent years it became clear to me that it is possible to interpret the sp. theory of relativity in such a way that it does not contradict any self-evident truth,” he wrote (in English) to Albert Einstein in July 1940. “I should be glad if you, after perusal of my Essay, could agree that my interpretation is possible.”113 He included a copy of the 1938 article. Einstein never responded.
* * *
Kraus’s apologia came rather late, for him and for Prague. He had retired from teaching at the German University in December 1938, a citizen of the amputated state of Czecho-Slovakia. For reasons known only to him, he remained in Prague until March 1939, when Nazi forces rolled into the city. He was arrested and held by the Gestapo for six weeks. Granted an entry visa to Great Britain, he fled first to Scotland and then to Oxford, where he died of cancer on 26 September 1942. Kraus’s dogged philosophical defense of strict adherence to the views of Brentano had already contributed to his eclipse among mainstream philosophers, who had gravitated toward the phenomenology of his rival Edmund Husserl and the latter’s student Martin Heidegger. Philosophers of science ignored him as well due to his association with the reviled anti-Einstein cohorts. His works on the topic of relativity, including his recantation, were no longer read, though a cryptic aside from Philipp Frank in 1962 attacking readings of relativistic theories as “fictions” indicates that even decades later the sting of his barbs had not entirely faded.114
Frank had left Prague with his wife in fall 1938, at first intending only to engage in a limited lecture tour in the United States but eventually permanently settling in Cambridge, Massachusetts.115 It was a difficult time for the couple. The Great Depression meant that jobs were scarce, and the earlier wave of refugees from Central Europe—admitted reluctantly and placed with difficulty—had taken the few academic positions available. Frank’s world had crumbled around him. Two years earlier, the dictatorship in Vienna had shuttered the Vienna Circle in the wake of the assassination of Moritz Schlick by a former student. Otto Neurath, one of the original members of the discussion circle with Frank and Hans Hahn, had been in exile since 1934 in the United Kingdom. (He died in 1945 in Oxford, three years after Oskar Kraus.) Rudolf Carnap had also fled, first to Chicago and then to the University of California at Los Angeles, assuming the mantle of leadership of the logical positivist movement there along with Hans Reichenbach. The center of gravity had moved to the West Coast and the Midwest of the United States. Frank now stood on the sidelines and had to fend for himself.116
He had some help from friends who specifically valued him for his philosophy of science more than for his achievements in physics. At the tail end of his lecture tour of 20 colleges from October to December, he ended up at Harvard, where he gave a talk on “Philosophical Interpretations and Misinterpretations of Quantum Theory.” None of his supporters wanted to send a Jewish scholar back to Prague, where it w
as only a matter of time before Hitler’s vise clamped shut. Astronomer Harlow Shapley raised $2,000 and managed to parlay that into a one-year position lecturing on philosophy and physics at Harvard. Frank grew very active in philosophical communities in the United States, becoming the first elected president of the Philosophy of Science Association in 1946 and establishing in 1949 the Institute for the Unity of Science—an American cousin to Neurath’s intellectual program. After his temporary position at Harvard ended in 1953, the Institute became his only affiliation until his death on 21 July 1966. He continued to publish widely on the philosophy of science, especially relativity, and kept body and soul together through soft money scrounged up here and there.
Einstein, now similarly a Germanophone one-time resident of Prague marooned on the eastern seaboard of the United States (though with an infinitely more secure perch at the Institute for Advanced Study at Princeton), proved vital in rescuing the fortunes of his former successor as professor of theoretical physics at the German University. Frank needed to earn money, and he turned to Einstein with a plan. “I conceived the idea of taking advantage of this physical proximity to prepare an account of his life and work,” he wrote in the preface to his 1947 biography of his predecessor. “When I told Einstein about this plan he said: ‘How strange that you are following in my footsteps a second time!’ ”117 The advance on the biography from the Knopf publishing house largely financed Frank’s post at Harvard.118 The book was composed in German but was first published in a slightly abridged form in English. The German text explains a bit more about the composition: Frank began writing it in 1939 in New York, continued it in Chicago the following year, and then concluded the first draft in Boston in 1941. The only part that was composed originally in English and had to be rendered into German concerned Einstein’s relationship to the atomic bomb, a section that Frank added to his manuscript after the public revelation of that device in 1945.119
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