Frank served as a pivotal mediator between Einstein and Mach in ways that the founder of relativity theory was unaware of at the time. Although Mach’s critical philosophical and historical works were at the radical vanguard of physics when he penned them in Prague, his return to Vienna in 1895 brought misfortune and a degree of incomprehension. In 1898, at the age of 61, Mach suffered a severe stroke that forced his early retirement in 1901. Largely incapacitated, he retired to a Vienna suburb and engaged with the world of physics through correspondence and pilgrims who came to visit. Sometimes, these pilgrims were summoned. Around the time that Einstein first wrote him, Mach became aware of the buzz around relativity theory (already four years old) and how others thought it was linked to his own concepts. He himself could not follow it at first, and in June 1910 he invited a specialist from the University of Vienna to explain it to him: Philipp Frank. (Frank would four decades later describe Mach as “a man with a gray, somewhat wild beard, who looked like a Slovak physician or lawyer.”) Frank attempted to articulate how the view of spacetime propounded by Einstein was a brilliant confirmation of Mach’s approach to mechanics.35
Mach was not entirely convinced, especially as Hermann Minkowski in Göttingen began to interpret the theory in terms of four-dimensional “world lines” and Einstein himself proclaimed the equivalence principle and sought a theory with curved spacetime—both of which sounded suspiciously metaphysical. The crucial turning point seems to have been 1911, when Berlin physicist Max Planck initiated a full philosophical assault on Mach’s antimetaphysical position; coincidentally, this was the same year that Einstein moved to Prague and began working in earnest on general relativity. Although the documentation of Mach’s thinking in these final years is not as comprehensive as one would like, it seems reasonably clear that he began to turn against relativity theory in a rearguard effort to defend what he saw as proper physical reasoning. He did not include a discussion of relativity in updated editions of his Mechanics, and his posthumous Principles of Physical Optics (1922) included a foreword dated “July 1913” that attacked Einstein’s theory as wrongheaded.36
After Mach’s death, the contingent of his admirers in Prague attempted to rescue the legacy of their now-deceased icon from what seemed like a complete repudiation of their own conviction that relativity and “Machism” were one and the same. Anton Lampa, for example, wrote a brief but hagiographic biography of Mach that took on this issue in 1918. (“Hagiographic” here is meant literally; this is how Lampa describes first meeting Mach: “It was something entirely different than what I had until then met with in outstanding minds, something entirely distinct from the great researchers, the great poets; I was standing before a saint, who has overcome the final remnants of earthly troubles and from whose eyes beamed the infallible goodness of understanding everything.”)37 With grateful acknowledgment of Frank’s assistance concerning the material related to relativity—although Lampa had brought Einstein to the German University in Prague and considered his work revolutionary, he was not especially familiar with the details—he went on to claim that “Mach is the forerunner of general relativity theory and had prepared the ground for it long before Einstein and Minkowski,” even if Mach did not himself appreciate the theory.38 This view was not dissimilar to Frank’s own admiration for the clarity of Mach’s conceptual analysis, which he continued to laud throughout his career, even as he began to diverge with the orthodoxy of Mach’s views and develop his own intellectual position.39
Einstein himself was not so generous. Already during World War I he had begun to express exasperation in his letters to Michele Besso about the Machist gloss on general relativity being propounded by their mutual friend from their school days, Friedrich Adler, whom Einstein had come to regard as “a rather sterile Talmudist, pig-headed, without a sense for the real. Ultra-selfless with strong stitch of the self-torturing, even the suicidal. A true martyr’s nature,” someone who “rides Mach’s nag to exhaustion.”40 Adler was a stubborn interlocutor, no doubt, but Einstein had also become disillusioned with Mach himself. Although he had failed to persuade Mach to relent on atomism, he thought he had made progress in other areas and wrote in 1921 that he was “amazed that Mach was not in favor of relativity theory. This course of reasoning lies precisely and entirely in his line of thought. I am curious how he comes to his standpoint of rejection.”41 (He still retained enough respect to endorse the construction of a monument to Mach in 1926.)42
With further reflection, Einstein deepened his own epistemological framework and came to see the problem as inherent to Mach’s dogmatic insistence that everything had to be tied directly to sense experience, that concepts were only valid when they served as generalizations of sense data introduced to economize on mental exertion. By 1946, he was “convinced that even much more is to be asserted: the concepts which arise in our thought and in our linguistic expressions are all—when viewed logically—the free creations of thought which can not inductively be gained from sense-experiences.”43 For Einstein, scientists made their theories independently of experience, imaginatively, and without reference to sense data; only after one had the theory in hand would it be submitted to the acid tests of observation and experimentation. Mach wanted to reduce theory to an outgrowth of experiment, and the mature Einstein considered this too limiting. He began to criticize his own past allegiances to Mach, as, for example, in his 1947 autobiographical reflections:
It was Ernst Mach who, in his History of Mechanics, shook this dogmatic faith; this book exercised a profound influence upon me in this regard while I was a student. I see Mach’s greatness in his incorruptible skepticism and independence; in my younger years, however, Mach’s epistemological position also influenced me very greatly, a position which today appears to me to be essentially untenable. For he did not place in the correct light the essentially constructive and speculative nature of thought and more especially of scientific thought; in consequence of which he condemned theory on precisely those points where its constructive-speculative character unconcealably comes to light, as for example in the kinetic atomic theory.44
In these postwar years, Einstein became increasingly vocal in arguing that Mach underestimated the power of human creativity, and he even began to rethink his own educational trajectory to elevate the influence of the eighteenth-century Scottish empiricist David Hume on his thought over and against the conceptual critique proposed by Mach.45 Mach was good for tearing down old ideas but not for building up new ones. This was the lesson that the history of relativity theory taught Einstein, who in this way also cut one of the ties connecting him to the intellectual traditions rooted in the German University.
* * *
Despite his insistence on the lack of connection between relativity theory on the one hand and Machian empiricism and its descendant logical positivism (or logical empiricism) on the other, Einstein did not control the narrative that developed around his concepts. The dominant view among philosophers for the rest of Einstein’s life was that relativity theory provided one of the greatest illustrations of the validity of logical positivism as an epistemological framework, no matter what Einstein might retrospectively offer in rejoinder. This solid connection between relativity and positivism owes its persistence to the unflagging intellectual and organizational work spearheaded by Philipp Frank.46 It was a link forged in Prague.
Frank worked tirelessly on his defense of relativity theory, seeing its triumph as a vindication of the positivist position rooted in the framework first propounded by Mach. As he told Kuhn in 1962, “originally the relativity theory was based on positivism,” and “it was Einstein who later more or less abandoned the positivistic conception of science.… But so to say in the birth, in the history of birth, the relativity [theory] has always been connected with positivism.”47 The best source for this connection, according to Frank, was Einstein himself. “It is indeed today generally known that Einstein’s general relativity and gravitational theory grew immediately out of the po
sitivist doctrine on space and motion,” he wrote in a 1917 assessment of Mach’s work that Einstein openly admired, “which Einstein himself described in detail in his eulogy for Mach.”48 The most influential Frank essay in this vein appeared in 1949, in the two-volume compilation Albert Einstein: Philosopher-Scientist, edited by Paul Arthur Schilpp, which featured other essays by positivist-affiliated thinkers that reinforced Frank’s specific reading. “Einstein speaks here almost completely in the line of the logical empiricists,” he stated, “which is not surprising, inasmuch as logical empiricism is, to a considerable extent, a formulation of the very way in which Einstein envisaged the logical structure of his later theories, e.g., the theory of gravitation.”49 The connection could not be severed: Einstein based his thinking on Mach, and the later positivists who followed Mach in turn based their thinking on Einstein. “Briefly,” Frank concluded, “I do not see in the question of the origin of the fundamental concepts of science any essential divergence between Einstein and twentieth century logical empiricism.”50
But even if Einstein had not arrived at special and general relativity by following a positivist playbook, Frank believed that the theories served as admirable illustrations of the conceptual coherence that came from positivism’s epistemological stance. Like his fellow logical positivists, Frank had modified Mach’s initial prescription—all sensible statements are based on sense perception—by adding another class of allowable utterances: analytic statements of logical relations. If one could purge from the fusty halls of science all statements that did not restrict themselves to the logical connections among sense data, then one would have a modern science cleansed of metaphysics and clotted thinking. An excellent example of this, perhaps even the best example, was general relativity:
In this theory Einstein derived his laws of motion and laws of the gravitational field from very general and abstract principles, the principles of equivalence and relativity. His principles and laws were connections between abstract symbols: the general space time coordinates and the ten potentials of the gravitational field. This theory seemed to be an excellent example of the way in which a scientific theory is built up according to the ideas of the new positivism. The symbolic or structural system is neatly developed and is sharply separated from the observational facts that are to be embraced. Then the system must be interpreted, and the prediction of facts that are observable must be made and the predictions verified by observation.51
Studying relativity not only would be a way for philosophers as well as scientists to learn the true nature of spacetime but also could offer an exemplar of rigorous thought. This was all the more important, as Frank noted in 1938, because misinformed intellectuals (including scientists) felt a need to graft all sorts of metaphysical claptrap onto relativity:
It is hardly possible to open a textbook on the theory of relativity—even if written by an otherwise competent physicist—without coming upon sentences of an entirely metaphysical character. Such sentences, wholly meaningless in physics, stand side by side with obviously physical sentences. It is therefore not amazing that great confusion occurred among young physicists and also in wider circles of educated people, and that the opinion arose that the theory of relativity is of an entirely different character from all previous physical theories: that it is constructed less logically and contains many contradictions. One cannot blame the philosophers who sought enlightenment in the writings of physicists for believing that all statements in these papers were the outcome of physical research. But in spite of their sincere desire for scientific enlightenment, they assimilated from those papers on physics a host of purely metaphysical sentences.52
(As we shall see, this is a reasonably good description of Frank’s views toward Oskar Kraus.) After Frank moved to the United States, he took this message to the American public in a work called Relativity: A Richer Truth. (Einstein wrote the foreword.) For Frank, relativity theory not only was unrelated to moral relativism, but was the antidote to precisely the kind of pernicious thinking that lay behind both the fascism of the past and the Stalinism of the present.53
Fascism, much more than Stalinism, was much on Frank’s mind during the 1930s in Prague. Before then, he dedicated himself not just to publicly advocating for Einstein’s relativity and the philosophical school of logical positivism he saw as connected with it, but also to working within the local German University and the transnational German Physical Society to make them friendlier to a progressive philosophy of science. Although many faculties at the German University greeted the advent of an independent Czechoslovakia with some apprehension—would the institution survive the creation of a Czech-dominated state, and would their rights as minorities be protected under the regime of President Tomáš Masaryk? (yes and yes)—for Frank the interwar period was in many ways the height of his career. It is true, as we will see later, that the status of the German University changed symbolically in 1920, declining such that the university become a somewhat subordinate institution in the new capital city, but the same reforms also created the new faculty of natural science, and this was a boon for Frank. Not least it meant that, while still being a physicist and teaching his usual classes, he was now free to act more forcefully as a philosopher. In the pre-independence faculty of philosophy, where he had been yoked to mainstream philosophers (like Oskar Kraus), Frank had had to worry about treading on toes. Now he was unleashed upon epistemology. He trained a number of students, including Josef Winternitz, the son of the Indologist who had been a good friend of Einstein’s during his time in Prague (and who came to pick up the physicist on the train platform in 1921). Under Frank, the younger Winternitz wrote a sophisticated dissertation on epistemology and relativity with a neo-Kantian slant—referencing, among other topics, the ongoing disagreements between Frank and Kraus—that was reviewed favorably by Einstein himself, who encouraged Frank’s explorations in this area even if he did not always agree with them.54
Frank’s pedagogical and organizational talents—he served as rector for the German University in 1925–1926 and then as prorector the following year—also attracted the attention of other leaders of the logical positivist movement, who saw Prague as a potential solution for their own underemployment or unemployment. Rumors traveled fast among this group. Moritz Schlick, later the guiding light of logical positivism, wrote to Einstein in 1920 from his post in Rostock on the Baltic littoral, angling for some insight into what was happening in Prague: “Then supposedly at the German University in Prague they have the intention of dividing the philosophical faculty and hiring a special philosopher in the natural-sciences section. They supposedly have already thought of me for it. That would be truly great! Because in its geographical situation and its intellectual life Prague has great advantages over Rostock.”55 Einstein was still tied in many of his colleagues’ minds to Prague, and they thought he would have inside tips. Schlick soon moved (via Kiel) to greener pastures in the Austrian capital, but others hoped for a haven in Prague. In 1925 philosopher Hans Reichenbach lamented his uncertain career prospects and aspired to emigrate to the United States—he would do so in 1938 to escape the Nazis—but was instead encouraged by Einstein to wait until Frank could put together something suitable in the natural sciences faculty in Prague.56 (In the end, Einstein made a similar arrangement for Reichenbach in Berlin.) Frank did eventually fill his post with none other than Rudolf Carnap in 1931, drawing on the personal support of President Masaryk (himself a former professor of philosophy at the Czech University). Carnap was still there in 1933 when the young American philosopher W. V. O. Quine came for a visit that he later claimed transformed his entire intellectual trajectory—another important chapter in the philosophy of science midwifed by Frank.57
The most prominent organizational triumph for Frank, however, was the institutionalization of logical positivism as an international movement linked to the sciences, marked by the establishment of the Vienna Circle (which was inaugurated, ironically enough, in Prague). Once again Frank was
able to take advantage of his dual identity as a physicist and a philosopher. In September 1929, the Fifth Congress of German Physicists and Mathematicians, sponsored by the German Physical Society, was set to take place in Prague; Frank served actively on the local coordinating committee. The strong presence in Czechoslovakia of this German society, founded in 1845 before there was such a country as Germany, was a response to the shock that the Central European academic community had suffered following the Triple Alliance’s loss of the Great War. A boycott of German and Austrian scientists engineered by the Belgians, British, and French (and, somewhat desultorily, by the Americans) had cut off German physicists—with the important exception of the world-famous pacifist Albert Einstein—from participation in international conferences and travel. It was therefore especially important to strengthen networks among the outcast nations, even extending them in the mid-1920s to the pariah state of the Soviet Union.
Frank had become a member of the German Physical Society on 28 June 1918 through the nomination of Peter Debye, a Dutch (and later American) physical chemist and physicist who had himself been Einstein’s successor at the University of Zurich when the latter decamped for Prague’s German University. Within a few months of obtaining this membership, Frank’s residence had shifted from his native Austria-Hungary to Czechoslovakia without him stirring from the camp bed in his office at the Physical Institute on Weinberggasse. Hoping to retain the German Physical Society’s contacts in the newly independent states while also decentralizing the organization by reducing the dominance of Berlin, Society president Arnold Sommerfeld began in 1920 to create a series of so-called Gauvereine (regional societies). The first, not surprisingly, was established in Munich, Sommerfeld’s residence, with the next appearing in Vienna. The fifth of the eventual 10 Gauvereine was founded in Prague on 2 February 1922. Frank served as its chairman until its dissolution on 7 March 1934, at which point all the members simply became out-of-town affiliates of the larger umbrella organization. At its inception, the Prague division seemed extraordinarily healthy—with 56 members in 1922, it was larger than its elder sibling in Munich—but its rolls quickly hemorrhaged physicists, and it soon became the smallest, half the size of the next largest one. By 1929, the year the Fifth Congress came to Prague, it had only 35 members.58
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