Einstein

by Philipp Frank

  Since the beginning of the twentieth century more and more emphasis has been placed on the conflict between the above view that science can only describe and systematize the results of observations and the view that it can and must investigate the real world. This controversy became particularly acute among the physicists in central Europe. Max Planck was the spokesman for the latter view, which he called the “metaphysical” view, and he directed his sharpest polemics against those who seemed to him to be the most radical representatives of the opposite side. In particular he attacked Mach’s positivistic conception of science, which agrees with Bohr’s view.

  About this time a reformulation of positivism started in Vienna and Prague. The new movement was closely related to “Mach’s requirement.” The core of the movement was the Wiener Kreis (Vienna Circle), Moritz Schlick, R. Carnap, O. Neurath, and others. In this country it was described as logical positivism and established contact with related established tendencies such as pragmatism and operationism. In England a similar movement is headed by Bertrand Russell.

  5. Einstein’s Philosophy of Science

  Since the positivistic conception of physics had been stimulated strongly by Einstein’s pioneer work in the theory of relativity and in atomic physics, many persons regarded Einstein as a kind of patron saint of positivism. To the positivists he seemed to bring the blessing of science, and to their opponents he was the evil spirit. Actually his attitude to positivism and metaphysics was by no means so simple. The contradictions in his personality that we have observed in his conduct as a teacher and in his attitude to political questions also manifested themselves in his philosophy.

  Einstein recognized wholeheartedly the great success of Bohr’s theory in explaining the many phenomena of atomic physics, but from a more philosophical standpoint he was not ready to admit that one must abandon the goal of describing physical reality and remain content only with the combination of observations. He was aware that it was not possible, as Newton had thought, to predict all future motions of all particles from the initial conditions and the laws of motion. But perhaps, thought Einstein, physical events could be described in terms of a new theory as yet unknown. It would consist in a system of field equations so general that they would contain the laws of motion of particles and of photons as special cases.

  I must admit that over a long time I myself believed that Einstein was an adherent of the positivistic interpretation of Bohr’s theory. In 1929, at a congress of German physicists in Prague, I delivered an address in which I attacked the metaphysical position of the German physicists and defended the positivistic ideas of Mach. After my address a well-known German physicist with whose philosophical views I was not acquainted rose and said: “I hold to the views of the man who for me is not only the greatest physicist of our time, but also the greatest philosopher: namely, Albert Einstein.” Thereupon I felt a sense of relief and expected the speaker to support me against my opponents, but I was mistaken. The speaker declared that Einstein rejected the positivistic theories of Mach and his supporters and that he regarded physical laws as being more than combinations of observations. He added that Einstein was entirely in accord with Planck’s view that physical laws describe a reality in space and time that is independent of ourselves.

  At that time this presentation of Einstein’s views took me very much by surprise. It was oversimplified, indeed, but I soon realized that Einstein’s partly antagonistic attitude toward the positivistic position was connected with his attitude toward Bohr’s conception of atomic physics. Shortly afterward I saw a paper by Lanczos, one of Einstein’s closest collaborators, in which he contrasted the theory of relativity with Bohr’s theory in the following manner: Einstein’s general theory of relativity is the physics corresponding to the metaphysical conception of science; Bohr’s theory, on the other hand, is in accord with the radical positivistic conception. I was quite astonished to find the theory of relativity characterized in this manner, since I had been accustomed to regarding it as a realization of Mach’s program.

  Not long afterward — I believe it was in 1932 — I was visiting Einstein in Berlin. It had been a long time since we had conversed personally, and consequently I knew little of his stand on questions about which he had not published anything. We discussed the new physics of Bohr and his school, and Einstein said, partly as a joke, something like this: “A new fashion has now arisen in physics. By means of ingeniously formulated theoretical experiments it is proved that certain physical magnitudes cannot be measured, or, to put it more precisely, that according to accepted natural laws the investigated bodies behave in such a way as to baffle all attempts at measurement. From this the conclusion is drawn that it is completely meaningless to retain these magnitudes in the language of physics. To speak about them is pure metaphysics.” In this statement, among other things, he apparently referred to magnitudes such as the “position” and “momentum” of an atomic particle.

  Hearing Einstein talk in this way reminded me of many other discussions to which his theory of relativity had given rise. Repeatedly the objection had been raised: if magnitudes such as the “absolute temporal interval between two events” cannot be measured, one should not conclude that consequently it is completely meaningless to speak of this interval and that “absolute simultaneity” is simply a meaningless conglomeration of words. Einstein’s reply to this argument had always been that physics can speak only about magnitudes capable of being measured by experimental methods. Furthermore, Professor P. W. Bridgman regarded Einstein’s theory of simultaneity as the best illustration of the fruitfulness of his “positivistic” requirement that only magnitudes having an “operational definition” should be introduced into physics. Consequently I said to Einstein: “But the fashion you speak of was invented by you in 1905?” At first he replied humorously: “A good joke should not be repeated too often.” Then in a more serious vein he explained to me that he did not see any description of a metaphysical reality in the theory of relativity, but that he did regard an electromagnetic or gravitational field as a physical reality, in the same sense that matter had formerly been considered so. The theory of relativity teaches us the connection between different descriptions of one and the same reality.

  Actually Einstein has been a positivist and empiricist since he has never been willing to accept any perennial framework for physics. In the name of progress in physics he claims the right to create any system of formulations and laws that would be in agreement with new observations. For the older positivism the general laws of physics were summaries of individual observations. For Einstein the basic theoretical laws are a free creation of the imagination, the product of the activity of an inventor who is restricted in his speculation by two principles: an empirical one, that the conclusions drawn from the theory must be confirmed by experience, and a half-logical, half æsthetic principle, that the fundamental laws should be, as few in number as possible and logically compatible. This conception hardly differs from that of “logical positivism,” according to which the general laws are statements from which our observations can be logically derived.

  In the twentieth century, when Einstein created his special theory of relativity, and even more so when he produced his general theory, it became evident that physical theories were to an ever increasing degree no longer simple summaries of observational results, and that the path between the basic principles of the theory and the observational consequences was more involved than had formerly been thought. The development of physics from the eighteenth century to Einstein was accompanied by a correspondent development of philosophy. The conception of general laws as summaries of observations gave way more and more to the conception that laws are creations of the imagination, which are to be tested by observation. Mach’s Positivism was replaced by Logical Positivism.

  In the Herbert Spencer Lecture which he gave at Oxford in the summer of 1933 shortly before he left Europe forever, Einstein presented the finest formulation of his views on the nature of
a physical theory. He spoke first about the physics of the eighteenth and nineteenth centuries — that is, the period of mechanistic physics:

  “The scientists of those times were for the most part convinced that the basic concepts and laws of physics were not in a logical sense free inventions of the human mind, but rather they were derivable by abstraction — that is, by a logical process from experiment. It was the general theory of relativity that showed in a convincing manner the incorrectness of this view.”

  After Einstein had emphasized that the fundamental physical concepts were products of invention or fictions, he continued:

  “The conception here outlined of the purely fictitious character of the basic principles of physical theory was in the eighteenth and nineteenth centuries far from being the prevailing one. But it continues to gain more and more ground because of the ever widening gap between the basic concepts and laws on the one side and the consequences to be correlated with our experience on the other — a gap which widens progressively with the developing unification of the logical structure — that is, with the reduction of the number of the logically independent conceptual elements required for the basis of the whole system.”

  As in so many aspects of his life and thought, we also note a certain internal conflict in Einstein’s attitude toward the positivistic conception of science. On the one hand, he felt an urge to achieve a logical clarity in physics such as had not previously been attained, an urge to carry through the consequences of an assumption with extreme radicalism, and was unwilling to accept any laws that could not be tested by observation. On the other hand, however, he felt that even Logical Positivism did not give sufficient credit to the role of imagination in science and did not account for the feeling that the “definitive theory” was hidden somewhere and that all one had to do was to look for it with sufficient intensity. As a result Einstein’s philosophy of science often made a “metaphysical” impression on persons who are unacquainted with Einstein’s positivistic requirement that the only “confirmation” of a theory is its agreement with observable facts.

  6. Unified Field Theory

  In his general theory of relativity Einstein had treated the force of gravity as due to a gravitational field. Matter gave rise to a gravitational field, which in turn acted on other material bodies to cause forces to act. Einstein had taken this force into account by means of curvature in space. A similar situation existed for electrically charged particles. Forces act between them, and they could be taken into account by considering the electric charges to give rise to an electromagnetic field, which in turn produced forces on other charged particles. Thus matter and gravitational field were exactly analogous to electric charge and electromagnetic field. Consequently Einstein sought to build a theory of “unified field” which would be a generalization of his gravitational theory and would include all electromagnetic phenomena. He also thought that in this way he might be able to obtain a more satisfactory theory of light quanta (photons) than Bohr’s, and derive laws about “physical reality” instead of only laws about observational results.

  The great success of the geometrical method in the general theory of relativity naturally suggested to him the idea of developing the new theory in the structure of four-dimensional space. In this case it must have still other characteristics besides the curvature which takes care of gravitational effects.

  The news that Einstein was working on a unified field theory became particularly widespread in 1929, the year of Einstein’s fiftieth birthday. To the public at large it seemed to be an especially attractive idea that on the very day on which he attained fifty years, a man should also find the magic formula by which all the puzzles of nature would finally be solved. Einstein received telegrams from newspapers and publishers in all parts of the world requesting that he acquaint them in a few words with the contents of his new theory. Hundreds of reporters beseiged his house. When some reporters were finally able to get hold of him, Einstein said with astonishment: “I really don’t need any publicity.” But everyone expected some new sensation that would surpass the wonder produced by his previous theories. They learned that a communication dealing with the new theory would be published in the transactions of the Prussian Academy of Science, and efforts were made by newspapers to secure galley proofs from the printer, but without success. There was nothing to do but to await the publication of the article, and in order not to be too late, an American newspaper arranged to have it sent immediately by phototelegraphy.

  The article was only a few pages long, but it consisted for the most part of mathematical formulæ that were completely unintelligible to the public. The emotion with which it was received by the layman may be compared to that experienced at the sight of an Assyrian cuneiform inscription. For an understanding of the paper a considerable capacity for abstract geometrical thinking was required. To those who possessed this quality it revealed that general laws for a unified field could be derived from a certain hypothesis regarding the structure of four-dimensional space. It could also be shown that these laws included the known laws of the electromagnetic field as well as Einstein’s law of gravitation as special cases. Nevertheless, as yet no result capable of experimental verification could be derived from them. Thus for the public at large the new theory was even more incomprehensible than the previous theories. For the expert it was an accomplishment of great logical and æsthetic perfection.

  X

  POLITICAL TURMOIL IN GERMANY

  1. Einstein’s Fiftieth Birthday

  As the month of March in 1929 approached, Einstein and his family began to fear that the sensationalism of the newspapers would be so great on the date of his fiftieth birthday that it would only be disagreeable for Einstein. Many newspapers had undertaken to secure Einstein’s own remarks on more or less personal matters and to publish them. Moreover, the visits and congratulations of his true admirers and friends threatened to assume such proportions that Einstein decided to avoid everything and to leave his apartment for several days. Immediately all sorts of rumors appeared: Einstein has gone to France, to Holland, to England, or even to America. But it was all greatly exaggerated. He spent the day peacefully near Berlin at the country estate of a shoe-polish manufacturer, who sometimes put at Einstein’s disposal a pavilion in his garden, situated very close to a beautiful lake. Here he was able to play the organ or to sail on the lake.

  From their apartment in Berlin Mrs. Einstein had brought along the dinner that had been prepared. Einstein’s immediate family — that is, his wife, her two daughters, and their husbands were present. Einstein was very comfortable and unceremonious, dressed in the garb he usually wore in the country, or even in the city when no strangers were present. This consisted of a pair of old trousers and a sweater, but no jacket, and very often also without shoes or stockings. From their city apartment Mrs. Einstein also brought along some of the congratulatory letters and presents that had arrived in large numbers.

  Einstein was connected with many different activities, so that he received letters and gifts from all sorts of people; naturally, from physicists and philosophers, but also from pacifists and Zionists. There were even some from very simple people who were admirers of great discoveries and wanted to express this admiration. Among these was a gift from an unemployed man, consisting of a small package of pipe tobacco. It had become generally known that Einstein was rarely to be found without a pipe. Alluding to the relativity theory and the field theory, the man wrote: “There is relatively little tobacco, but it is from a good field.”

  Several of his friends had combined to present him with a new and very modern sailboat. Einstein loved to sail the beautiful lakes and rivers around Berlin, and to daydream while the boat flew before the wind. The handling of the sails was a pleasant activity. It was a very simple application of the rules of mechanics, and it gave him a great deal of pleasure to apply the physical laws that are closest to direct experience instead of those that are most abstract. He also wrote a popular article in
which he explained to the lay public the physical laws that enable one to travel in a certain direction by placing the sails in a certain position and to reach a particular goal by means of a zigzag motion — that is, by successive tacks.

  A group of Zionists in America bought a plot of land in Palestine and planted it with trees on his birthday. They made provision that for all time to come the woods that grew there were to be known as the Einstein Grove.

  The most beautiful and interesting present, however, was to come from the municipal administration of the city of Berlin, where Einstein had lived since 1913, and which, to mention only a very trivial matter, he had helped to make a center of attraction for all foreigners. Since it was generally known that Einstein was fond of sailing on the Havel River and on the many lakes into which this remarkable stream expands, the municipal council of Berlin decided to present Einstein with a small country house situated on the bank of the Havel close to the point where it enters the Wannsee. The house was located on a plot belonging to the city of Berlin. This resolution on the part of the municipal council was well received by the entire population — a sentiment arising from a combination of love of science, respect for an illustrious fellow citizen, and a fondness for aquatic sports and sailing. In all the illustrated magazines appeared pictures of the idyllic “Einstein house.”

  When Mrs. Einstein wanted to see the house, she noticed to her amazement that people were living in it. The latter, in turn, were astonished to find someone wanting to take possession of their home, even though it was the famous Einstein. It turned out that when the city of Berlin had acquired this property, it had guaranteed to the inhabitants of the house the right to keep on living there. The municipal council seemed to have forgotten this when it gave its birthday present to Einstein. How can one explain such an occurrence in Berlin, the capital of Prussia, famous for its orderliness?