SOURCE: "Einstein's Image of Himself as a Philosopher of Science," in Transformation and Tradition in the Sciences: Essays in Honor of I Bernard Cohen, edited by Everett Mendelsohn, Cambridge University Press, 1984, pp. 175-90.

[In the following essay, Hiebert explores Einstein's position as a philosopher of science—as opposed to merely being a scientist—and his own views of himself as such.]

Since antiquity, natural philosophers and scientists have expressed the conviction that the observational and experimental study of nature brings with it a good measure of intellectual and aesthetic satisfaction. Indeed, scientists on the whole claim to derive considerable personal pleasure from their work. I believe these claims are true. Now it seems plausible to assert that the machinery of human perception and cognition is both biologically structured and socially motivated to accentuate certain characteristic benchmarks of excellence in human performance. These distinctive characteristics are by no means the property of scientists. They certainly are seen to be prominent as well in the arts and humanities. Still, they are glaringly visible in the work of scientists.

To be more specific, we might mention in this context a number of criteria of excellence: structure, order, and symmetry; the power of metaphor and analogical reasoning; comprehensiveness; simplicity—or a move in the direction of efficiency and economy of thought and expression; prediction into the unknown; logical rigor and internal consistency; and elegance of conception and formulation. All of these criteria obviously occupy a position of high priority among scientists, but, of course, as already intimated, scientists by no means have a corner on them.

In view of the fact that the sciences have been conspicuously successful, from the standpoint of the criteria just mentioned, it comes as no surprise to discover that scientists and their accomplishments and methods have provided the subject matter for perennial analysis by philosophers, historians, psychologists, anthropologists, theologians, and sociologists. In spite of all the commendable analyses, dissections, and reconstructions that scientists and their methods have been subjected to, we may find it shocking to see how inadequately they deem themselves to have been analyzed by others external to their intellectual and professional framework. Indeed, scientists frequently are at a loss even to identify themselves in the analyses of outsiders who purport to be examining what goes on in their own special disciplines. Although this may be a commonly encountered phenomenon, viz., the questioning or rejection by insiders of the analyses of outsiders, perhaps it tells us that the insiders are (or think they are) playing quite a different game. At minimum they are analyzing that game in another way. In any case, we have here a number of competing perspectives.

Let me express this observation in another way. At least since the middle of the nineteenth century, scientists have become increasingly more confident that professional, working scientists, on their own, can provide the most meaningful philosophy of science that is feasible. Whether this is true or not, historians of science are increasingly anxious to understand what kind of game scientists believe they are playing. Thus, this essay focuses almost exclusively on the question of the scientist's self-image.

If, in fact, there is widespread consensus among scientists that they do not really recognize themselves in treatises devoted to analyzing their methods and their work and behavior as scientists, then it is appropriate to suggest that there may be some positive merit in studying and evaluating their own self-reflections, namely, those in which they attempt to tell us what they do and how and why. Conceivably, some of the most pertinent questions to be explored in the philosophy of science touch on these aspects of the scientific enterprise that characterize the distinctive ways in which scientists see and understand themselves and their work.

Quite simply, what do scientists claim to be doing when they allege that they are engaged in scientific activity? What are the motivations, what methods (if any) are consciously cultivated; and what constitutes evidence to buttress an argument or support an explanatory hypothesis? Such questions have dimensions that can be explored profitably for the perspectives of history, psychology, the logic of science, conceptual frameworks, and various environmental contexts. But no n-dimensional analysis will help us here. We must adopt a more modest objective.

Against a specific conception of intention and outlook, viz., one that attempts to look at the scientist in the role of philosopher of science, I have undertaken a study of the self-image analysis of a number of scientists in hopes that some intrinsic pattern will emerge, if not for scientists in general, perhaps for scientists within a given discipline; and, at least within the more specialized domain of a particular science.

What I propose to do here is to examine one particular scientist's attempt to play the role of philosopher of science, namely, Albert Einstein. The rationale for this choice is that we recently celebrated Einstein's 100th birthday. Birthdays aside, the case for Einstein, his own self-image, and his view of himself as a philosopher of science provides a splendid example of the genre of questions this study purports to illuminate.

First let us mention a few landmarks in Einstein's career. In 1902, after completion of his studies at the Polytechnic in Zurich, Einstein became a Swiss citizen and worked for six years in the patent office in Bern. It was there between 1905 and 1906, when he was in his mid-twenties, that Einstein published four papers that contributed conspicuously to establishing the direction of twentieth-century theoretical physics. As is well known, these papers are models of originality, clarity, and elegance. They deal with totally diverse topics: the light quantum hypothesis, a theory of Brownian motion, an analysis of the electrodynamics of moving bodies that incorporates new views on the structure of space and time into a special theory of relativity, and a paper on the relation of the inertia and energy, or the general equivalence of the mass and energy, of a body. In one way or another, this early work of Einstein—each paper a landmark in its own right—sets the stage not only for much of his subsequent scientific work, but also for the direction of his philosophical reflections.

In 1913, after short intervals at the University of Zurich, the University of Prague, and the Polytechnic in Zurich, Einstein moved to Berlin. There, three years later, in 1916, he essentially completed his first enunciation of the general theory of relativity. The theory received its first confirmation in 1919 with the observation of the deflection of light in a gravitational field. Einstein certainly regarded his general theory of relativity as his true lifework. He said of his other contributions that they were Gelegenheitsarbeit, that is, performed as the occasion arose. But Max Born wrote that Einstein "would be one of the greatest physicists of all times even if he had not written a single line on relativity." In fact, Einstein received the Nobel Prize for 1921 for such Gelegenheitsarbeit, namely, the theory of the photoelectric effect.

In his later years Einstein turned his attention more and more to the object, methods, and limits of science. In exercising these rights, namely to pursue the philosophy of science as a scientist, Einstein was completely in step with the trends that had been set by late nineteenth-century investigators and that were being perpetuated with vigor, if not always with logical rigor, by the scientists who belonged to his generation. In his 1936 essay on physics and reality, Einstein tells us why it is not right for the physicist to let the philosopher take over the philosophy of science, especially at a time when the very foundations of science are problematic. He says: "The physicist cannot simply surrender to the philosopher the critical contemplation of the theoretical foundations: For he himself knows best, and feels more surely, where the shoe pinches." For Einstein, the philosophy of science definitely called for an in-depth knowledge of science.

On the other hand, Einstein by no means assumed that the narrow scientific specialist was qualified as a philosopher of science:

The whole of science is nothing more than a refinement of everyday thinking. It is for this reason that the critical thinking of the physicist cannot possibly be restricted to the examination of the concepts of his own field. He cannot proceed without considering critically a much more difficult problem, the problem of analyzing the nature of everyday thinking.

Certainly here is a viewpoint that mirrors one of the central themes of Mach and the nineteenth-century critical positivists.

As already stated, our main objective is to search out such self-reflective aspects of Einstein's career as may shed light on the conception he had of himself as a philosopher of science. Before doing so, however, I would like to offer an explanation for approaching the subject in the way here indicated. It is advisable to be open and honest about one's methodology and specifically to mention at this point that the self-image study this approach entails has its own intrinsic complexities. We cannot take the time to outline them here. Suffice it to say that not the least vexatious of the difficulties encountered is that scientists, including Einstein, in analyzing their own motivations and methodological directives, are apt to construct self-images that conform to what their scientific communities expect of them. Thus, in an attempt to become philosophical and sophisticated about these matters, scientists are prone to fulfill the prophecy of philosophical climates of opinion. These may relate to such factors as a hierarchy within the sciences vis-a-vis theory and experiment, master-pupil relationships, schools of thought, centers of research activity, and so on.

So we might as well acknowledge explicitly and candidly that there are some severe limitations imposed upon the investigator who chooses this approach, namely, to focus on what scientists say they are doing when they claim to be engaged in science, rather than analyzing more single-mindedly their published scientific contributions in order to discover what they do when they claim to be engaged in science. In relation to this issue, Einstein once said:

If you want to find out anything from the theoretical physicists about the methods they use, I advise you to stick closely to one principle: don't listen to their words, fix your attention on their deeds. To him who is a discoverer in this field, the products of his imagination appear so necessary and natural that he regards them, and would like to have them regarded by others, not as creations of thought but as given realities.

If Einstein has suggested here that one should not listen to what scientists say they do, but rather look at their works in order to learn what they do, he also confessed in his autobiography (or in his obituary as he called it): "The essential in the being of a man of my type lies precisely in what he thinks, not in what he does or suffers." We discover that over the years, Einstein, as so many other scientists, surrendered to the temptation to reify his own methodological preferences into a credo that guided him in all of his work—at least that is what he seems to want to tell us. But it is not that simple.

The point that needs to be stressed in advance, with these remarks, is that what a scientist really does, if we may speak that way, is not revealed to the historian of science unambiguously, either by an analysis of the scientist's reflective and retrospective account of what is going on, or by an examination of the finished, formal, published, product. In my opinion, anything that contributes to the clarification of the methodological question about how science advances, or retrogresses, is fair game for the historian.

Suffice it to say that one way to search out the self-image of Einstein as a philosopher of science, and to discover the way in which he conceives of his own work and thought within the context of the scientific currents of his times, is to listen seriously to what he has to say as he reflects on these matters in so many of his essays and lectures. Besides, the historian can take advantage of Einstein, so to speak, by invading his more unbuttoned, private, and internal life, to examine the uninhibited outpourings of his soul as revealed in the correspondence and informal interchanges with his most intimate friends and invisible opponents. Although this invasion may not be quite fair to a man like Einstein, since he undoubtedly never intended to add these documents to the historical record, they in fact substantially help to answer the questions that have been posed here.

I want to assert that Einstein had two self-images of himself and his work. The self-image that dominated his early career may be characterized by an attraction to critical positivism and the empirical status of theories advocated by Ernst Mach. The other more mature, more consciously worked out self-image of Einstein, and the one I want to talk about here, was one in which Mach's sensationalism and pluralism were abandoned and replaced by a realistic, unitary, and deterministic world view that lays claim to the intuitive recognition, or near-recognition, of rock-bottom truths about nature. Concerning his mature position Einstein wrote: "My epistemological credo… actually evolved only much later (in life), and very slowly, and does not correspond with the point of view I held in younger years."

We might mention here, parenthetically, that Einstein's dualistic image confronts us with a paradox: Virtually all of his most creative and lasting achievements were made while he was under the influence of a philosophy that he later categorically rejected. Or had he not thought through the consequences of his philosophy for his science? In fact, why does Einstein not struggle with the question of the influence of his own philosophy of science on his scientific work?

To analyze with psychological insight and historical credibility the many reflective accounts of Einstein that reveal something substantive about his self-image as a philosopher of science is an undertaking that would be far too ambitious on this occasion. Therefore we are confronted with the more modest objective of examining the way in which Einstein was prodded into explaining his philosophical position by two of his closest colleagues and critics, namely, Arnold Sommerfeld and Max Born. In both cases we have at our disposal a substantial portion of correspondence and intellectual interchange that covers a period of almost forty years.

Sommerfeld and Einstein both were enthusiastically committed to the technical mastery and critical evaluation of everything that transpired in the intellectual realm of relativity and quantum mechanics during the revolutionary era of physics from 1900 to 1930. However no two persons could have followed the shifting scientific scenario from more diverse perspectives. We learn that Einstein, the philosopher, with cool detachment, was attracted to general overarching unitary principles and through the years became increasingly impatient with, and even hostile toward, quantum mechanics with all of its outlandish baggage of indeterminacy, statistical and probability functions, and discontinuity: He simply felt that the future of physics lay more in geometry, and therefore in continuum theory, than in particles. Intellectually independent, he continued for decades to puzzle deeply about scientific questions that most physicists had accepted as self-evident. Despite his tremendous scientific contributions, he had no school or pupils or close disciples.

By contrast, Sommerfeld, the unphilosophically disposed master of broad domains in theoretical physics, ten years older than Einstein, surrounded by an energetic and productive school of disciples in Munich, became a staunch supporter of the revolutionary quantum trends. He managed, with his unique mathematical dexterity, and his facility with intuitively clever mechanical models, to squeeze out and exploit subtle implications hidden beneath the basic principles that had been laid down by other investigators. We may add, that in the process, he formulated new problems eminently worthy of being explored on their own merits. Sommerfeld was an early enthusiast for both relativity and quantum theory. We shall concentrate on the Sommerfeld-Einstein discussions about quantum theory, because they demonstrate most convincingly the distinctive philosophy that Einstein generated over the years. Einstein became increasingly confident that the failure to provide a unitary continuum field theory that would encompass both macro and microphenomena provided proof positive that the quantum theorists were on the wrong track. All this, in spite of his own tremendous contributions to early quantum theory.

It was one of Einstein's early papers, the revolutionary 1905 hypotheses on light quanta, that brought him in contact with Sommerfield. They first met in Salzburg in 1909 at the Society for Natural Scientists and Physicians, where Einstein lectured on the new quantum ideas. The next year Sommerfeld traveled to Zurich to spend a week in discussions with Einstein. At the first Solvay conference in 1911, Sommerfeld explored the theoretically exciting idea that the existence of the molecule was to be taken as a function and result of the elementary quantum of action h, and not vice versa, as had been argued.

Sommerfeld early on was stirred to action by Einstein's deduction from quantum principles about vanishing heat capacities at the absolute zero of temperature. He also was encouraged by the experimental support for the quantum theory being provided by the low-temperature heat capacity measurements conducted by Nernst and his colleagues in Berlin. Sommerfeld did his best to get into the act in 1912 by requesting from Einstein an in-principle clarification of quantum ideas. Unfortunately for Sommerfeld, Einstein was largely preoccupied with gravitational theory, in spite of the fact that he did not manage to attract much attention to this work from his colleagues. It was not Einstein's views on relativity, but rather quantum mechanics, that was the topic of lusty debates.

In 1916, Einstein wrote to Sommerfeld;

You must not be angry with me that I have not answered your interesting and friendly letter until now. During the last month I have experienced one of the most exciting and trying, and certainly one of the most successful times of my life.

What follows in the letter is a discussion of some of the germinal ideas and consequences of Einstein's general theory of relativity. Somewhat late, in 1916, while commenting favorably on Sommerfeld's spectral investigations and successful extension of Bohr's theory of the atom, Einstein remarked: "If only I could know which little screws the Lord God is using here." This remark I interpret to mean something like this: It is rather inconceivable that the real world is like that, namely, that atoms are quantized; but if it should turn out that the world is so constructed, then I must ask, is it not a bit undignified for God to have to use little screws to run the world that way?

Neither disturbed by Einstein's cavalier disregard of what was going on among quantum theorists, nor overly sensitive about the fundamental theoretical or philosophical rationale behind it all, Sommerfeld continued courageously to work out the mathematical formalism of the modified Bohr theory with great finesse and virtuosity. Obviously impressed, Einstein responded in 1918: "If only it were possible to clarify the principles about quanta! But my hope in being able to experience that is steadily diminishing." What Einstein had been trying to show, but unsuccessfully, was that particles can be treated as stable regions of high concentration of the field.

Dubious about the direction in which quantum theory was moving, Einstein believed, by 1918, that general relativity, by contrast, was an accomplished theory. Thus he wrote:

Behind general relativity henceforth there is nothing new to be found. In principle all has been said: Identity of inertia and mass; the metrical proportion of matter (geometry and kinematics) determined by the mutual action of bodies: and the nonexistence of independent properties of space. In principle, thereby, all has been said.

In this domain, Einstein was very certain that he had uncovered real physical truth about nature. In a letter to Sommerfeld in 1921, concerning a small supplementary addition to relativity theory that he and Hermann Weyl had published, he wrote: "I have my doubts about whether this thing has any physical worth. God makes it as he wills, and does not allow something to be put over on him." When asked to lecture on relativity, Einstein remarked that he had nothing new to say, and added: "The old stuff already is whistled by all the younger sparrows from the roof tops better than I can do it."

In 1920 Sommerfeld succeeded in explaining the multiplicity of many of the spectral lines by introducing an inner quantum number that had no physical meaning for him. "I can only further the technique of quanta," he wrote to Einstein, "you must construct their philosophy." Beginning with the work of Sommerfeld's pupil Heisenberg, in the summer of 1925, and promoted by the dramatic and ingenious contributions of Born, Jordan, Dirac, Schrodinger, Bohr, and Pauli, the elaboration of quantum theory was approached from quite different directions. It was given a formalism and mathematical structure that represents one of the most magnificent theoretical and practical accomplishments in the history of science. Much has been written about this subject and I only will mention here that in the outcome two opposing camps were created that divorced the enthusiasts for the Heisenberg-Born matrix mechanics—Born, Jordan, Dirac, Hund, and Pauli—from the supporters of the Schrodinger wave mechanics, for example, de Broglie, Planck, and Einstein. We have here the physics of the discrete versus the physics of continua.

Actually, Einstein essentially alienated himself from the direction in which quantum mechanics was headed, but felt moved now and then to take an occasional pot shot at the whole enterprise. Sommerfeld, typically engrossed in anything that would result in a practically useful and theoretically sound outcome, and philosophically uncommitted, stood outside the debate, but continued to elicit reactions from Einstein that at times revealed more about his (Einstein's) native intuitions and deep convictions that can be learned from studying his scientific papers.

In 1926 Einstein wrote to Sommerfeld:

I have worried a great deal about searching out the relationship between gravitation and electromagnetism, but now am convinced that everything that has been done in this direction by me and others has been sterile … The theories of Heisenberg and Dirac, in fact, force me to admiration, but they do not smell of reality.

Or again, in another letter:

The results of Schrodinger's theory make a great impression, and yet I do not know whether it deals with anything more than the old quantum rule, i.e., about something with an aspect of real phenomena.

Concerning Sommerfeld's monograph of 1930 on wave mechanics, Einstein said, in the same vein, that it was very nice, but that in spite of tremendous successes accomplished, the whole development and the prevailing trends did not satisfy him.

After 1930, as we well know, scientific investigations and communications suffered miserably in Germany. Research and discussion groups were splintered so severely that Sommerfeld in a reminiscent mood in 1937, wrote to Einstein (by then in Princeton) that he was consoling himself for having been able to experience personally the golden age of physics from 1905 to 1930. A decade later Sommerfeld was curious to know whether Einstein had changed his views about quantum theory.

Perhaps you will tell me what you now think about continua and discontinua. Or do you take the situation to be hopeless?

Einstein replied:

I still believe in all earnesty that the clarification of the basis of physics will come forth from the continuum [i.e., not quantum mechanics] because the discontinuum provides no possibility for a relativistic representation of action at a distance.

It is a fact that physicists more and more came to be preoccupied with the problems of quantum theory. It promised a better immediate yield. This did not deter Einstein (and others like Weyl and Eddington) from regarding reality as a continuous singularity-free manifold and from exploring a unified field theory on the model of general relativity. It was to include the laws of electromagnetism as well as those of gravitational fields.

In 1949 Einstein was seventy years old. In that year he believed that he had found the solution for which he strove for thirty years. The work was published by Princeton University Press as a new edition of The Meaning of Relativity.

In a tribute for Einstein's seventieth birthday, Sommerfeld, commenting about Einstein's outstanding contributions to the field of atomic theory, remarked:

In spite of all this, in the old question "continuum versus discontinuity" Einstein has taken his position most decisively on the side of the continuum. Everything of the nature of quanta—to which, in the final analysis, the material atoms and the elementary particles belong also—he would like to derive from the continuum physics by means of methods which relate to his general theory of relativity.…

His unceasing efforts, since he resides in America have been directed toward this end. Until now, however, they have led to no tangible success.… By far the most of today's physicists consider Einstein's aims as unachievable, and consequently aim to get along with the dualism: wave-corpuscle, which he himself first clearly uncovered.

In December of 1951 Einstein wrote to his lifelong friend, Michele Besso:

All these fifty years of conscious brooding have brought me no nearer to the question: What are light quanta? Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken.

I feel that one of the most significant aspects of Einstein's attempts to formulate a unified field theory was the ease with which he rejected his own theories that did not work out. When that happened he blithely took up another approach. He did this until he died in 1955.

In 1951 Sommerfeld died at the age of eighty-three, thus terminating the discussions between the philosopher-physicist Einstein and the no-nonsense master of physics, Sommerfeld, who claimed no expertise at all in the philosophy of science but who had been anxious to exchange ideas with a colleague whose philosophy he respected.

In contrast to the picture we have sketched of Sommerfeld in Munich, as the philosophically neutral correspondent of Einstein, we have at our disposal the long-standing scientific interchange of ideas between Einstein and another physicist who was himself passionately inclined to philosophize about relativity theory and quantum mechanics at the slightest provocation. This was Max Born, in Gottingen, the physicist whose completion of Einstein's statistical interpretation of quantum theory earned him the Nobel Prize twenty-eight years after it was presented. So here in Born and Einstein we have two would-be philosophers of science wrestling intellectually with one another.

The philosophical views of Einstein and Born invariably were 180 degrees out of phase on the subject of quantum mechanics. Accordingly, an examination of their intellectual debates is all the more important because of Born's relentless efforts to entice Einstein, the independent and relatively isolated thinker, to explain and defend his position as he moved around the world and took up new positions in Prague, Zurich, Berlin, and Princeton.

Leopold Infeld tells us how Max Born first learned about Einstein's revolutionary paper—the early one on special relativity—a thirty-page work that bore the modest title, "On the Electrodynamics of Moving Bodies."

When Professor Loria met Professor Max Born at a physics meeting in 1908, he told him about Einstein and asked Born if he had read the paper. It turned out that neither Born nor anyone else there had heard about Einstein. They went to the library, took from the bookshelves the seventeenth volume of Annalen der Physik and started to read Einstein's article. Immediately Max Born recognized its greatness and also the necessity for formal generalizations. Later, Born's own work on relativity theory became one of the most important early contributions to this field of science. Thus it was not before 1908 or 1909 that the attention of great numbers of scientists were drawn to Einstein's results.

As in the case of Sommerfeld, Born first met Einstein in Salzburg in 1909. Born characterizes the young Einstein, up through the early 1920s, as an empiricist and enthusiast for the philosophy of Hume, Mach, and Schlick. But, already in 1919, when Einstein was first ruminating about a unitary field theory that would bring gravitation and electromagnetic theory together, he was expressing a degree of discomfort about the developments in quantum mechanics. The theorists operate, he wrote, as though "the one hand is not allowed to know what the other does."

Basically at odds with the upsurge of the idea of discontinuity in physics, Einstein wrote to Born in 1920: "I do not believe that the quantum can be detached from the continuum. By analogy one could have supposed that general relativity should be forced to abandon its co-ordinate system." Einstein also was unhappy about what seemed to him the failure of the strict law of causality in quantum mechanics and the simultaneous encroachment of statistical and probability arguments. There is no doubt that by 1920, Einstein sought to hold tenaciously to continuum theory, in hopes that quantum phenomena would be absorbed somehow into the differential equations of a unified field theory.

In the 1920s and 1930s, Einstein was preoccupied mostly with general relativity. He was clarifying and perfecting its theoretical exposition and pursuing its practical consequences with great determination. But he wrote to Born that in his spare time he was "brooding … over the quantum problem from the point of view of relativity" because, as he said "I do not believe that (quantum) theory will be able to dispense with the continuum."

In February of 1929 in newspapers all over the world it was announced that Einstein had formulated his unified field theory in which the phenomena of electricity and magnetism were combined in a single set of equations. These ideas were reformulated and refined for twenty-five years. But during all of those years, until the last major attempt in 1949, Einstein was compelled, periodically, to admit that he was getting nowhere with his Lieblingsidee (viz.; the continuum) despite all attempts to analyze the issues. Now and again over the years, he felt, and announced, that he had achieved at least the glimpse of a reconciliation between relativity and quantum theory under the umbrella of continuum ideas, but these hopes were shattered one after another either by himself or others. In his letters to Born we come to see how often and how deeply Einstein was distressed about the conception of a wave-particle duality for radiation—a view he could not embrace except as a temporary crutch devoid of physical reality. In 1924 Einstein confided to Born:

My attempts to give the quantum a tangible form … have been wrecked time and again, but I am nowhere close to giving up hope. And if nothing works, there still remains the consolation that the failure is my fault.

In truth, the state of quantum theory in the early 1920s was one of considerable confusion. For example, there were the negative correlations with the Bohr-Sommerfeld rules. Attempts to connect quantum theory with classical mechanics were not successful. Qualitatively things worked out tolerably well, but the quantitative predictions were not impressive. Max Born certainly recognized very clearly that many technical difficulties simply escaped resolution. He referred to this state of affairs as das Quatenrdtzel and in 1921 wrote to Einstein: "The quanta are a hopeless Schweinerei"—as he expressed himself. As already mentioned, from 1925 to 1930 we witness a series of dramatic and bold moves that reveal that the negative results of current quantum theory pushed investigators in the direction of making a sharper break with classical mechanics. This simultaneously provided a new quantum mechanics, much to the consternation of Einstein.

After 1925, Einstein and Born carried on a running commentary characterized by hard arguments in which neither could convince the other to change perspectives. Commenting about this interchange some forty years later, Born wrote:

Einstein was fairly convinced that physics provides knowledge about the objective existence of the external world. But I, along with many other physicists gradually was converted, by experience in the domain of atomic quantum, to realize that it is not so—but rather that at every point in time we have no more than a rough approximate knowledge of the external world and that from this, according to specified rules of the probability laws of quantum mechanics, we can draw some conclusions about the unknown world.

In response to singular achievements in quantum mechanics by Born's Gottingen group (Heisenberg, Jordan, and Hund) Einstein could only respond: "Your quantum mechanics commands much attention, but an inner voice tells me that it is not yet the true Jacob. The theory offers much, but it brings us no closer to the secrets of the old one [der Alte]. In any case, I am convinced that he does not play dice." As Einstein said it: "Gott wiirfelt nicht." When Einstein spelled out some of the details of his attempt to establish a quantum field theory [i.e., continuum theory], Born wrote back politely that it was very interesting but not convincing. This was tit for tat.

In a letter of 1944 to Born we have a compelling illustration of Einstein's mature image of his own philosophy of science. It demonstrates convincingly how two talented scientists can be worlds apart in their interpretations of the same cognitive subject matter. Einstein writes:

In our scientific expectations you and I have reached antipodal positions. You believe in a God who throws dice, and I believe in complete lawfulness, viz, in a world of something that exists objectively and that I have attempted to snatch in a wild speculative way. I believe firmly, but I hope that a more realistic way, and especially that a more tangible evidence will be found than I was able to discover. The great initial success of the quantum theory cannot bring me to believe in the fundamental nature of a dice-throwing God, even if I know that my younger colleagues interpret this position of mine as the result of calcification. Someday it will be known which instinctive conception was the right one.

Born responded by saying that Einstein's expression about a dice-throwing God was totally inadequate:

In your determined world, you must throw dice too—that is not the difference … First of all, you underestimate the empirical basis of quantum theory… and second, you have a philosophy that somehow brings the automaton of dead things in accord with the existence of responsibility and conscience.

Einstein at this point could do no better than say (1947) that he was sorry to discover that "I just cannot manage to express my position so that you will find it to be intelligible"; and then he adds the comment that the mathematical difficulties involved in trying to reach his objectives of a comprehensive unitary theory are so severe that,

I will bite the dust before I get there … But concerning this I am convinced—that eventually we shall land a theory in which law-like things will not be probabilities for facts—facts such as formerly were just taken for granted. But to prove this conclusion I have no logical reasons.

And so the debate wore on and on. Einstein called Born a positivist. Born said that that was the last thing he wanted to be called by anyone. Einstein to Born: Don't you believe in the reality of the external world? Born to Einstein: Don't dodge the real issue: Do you really maintain the quantum mechanics is a fraudulent affair? Einstein to Born: You talk about the philosophy of quantum mechanics, but your remarks in essence are not philosophy at all but the manipulation under the cloak of indeterminacy to a hidden machinery of reasoning. Born to Einstein: Your position is one of metaphysics and not philosophy. That was the tone of the intellectual interchange.

We see that Einstein had formulated his own image of what the philosophy of science should be and what it should accomplish, and so had Born. Nevertheless, neither Einstein nor Born felt that they were being successful in communicating what that image was. Or were they just stubborn? At one point Wolfgang Pauli entered the debate and managed to convince Born that they had not so much disagreed, as argued from basically different premises. But it is clear to me that Pauli, in fact, also had constructed his own image of the philosophical positions that Einstein and Born represented.

I want to suggest that when Einstein died in 1955, he was holding in firm grasp essentially the world view that he had formulated in the 1920s and 1930s. What was this world view? In his lecture on the theory of relativity at King's College, London, in 1921, Einstein said:

The theory of relativity may indeed be said to have put a sort of finishing touch to the mighty intellectual edifice of Maxwell and Lorentz, inasmuch as it seems to extend field physics to all phenomena, gravitation included … I am anxious to draw attention to the fact that… (the theory of relativity) is not speculative in origin; it owes its invention entirely to the desire to make physical theory fit observed fact as well as possible. We have here no revolutionary act but the natural continuation of a line that can be traced through centuries. The abandonment of certain notions connected with space, time, and motion hitherto treated as fundamentals, must not be regarded as arbitrary, but only as conditioned by observed facts.

Here is a plug for the theoretical soundness and fertility of the great accomplishments of the nineteenth century.

A decade later, in an essay on the problems of space, ether, and fields, Einstein wrote:

The theory of relativity is a fine example of the fundamental character of the modern development of theoretical science. The initial hypothesis becomes steadily more abstract and more remote from experience. On the other hand, it gets nearer to the grand aim of science, which is to cover the greatest possible number of empirical facts by logical deduction from the smallest number of hypotheses or axioms. Meanwhile, the train of thought leading from the axioms to the empirical facts or verifiable consequences gets steadily longer and more subtle.

According to Einstein the theoretical scientist is compelled in an increasing degree to be guided by purely mathematical, formal considerations in the search for a theory, because the physical experience of the experimenter cannot lead him up to the regions of highest abstraction. This is the line of thought, he says, that led from the special to the general theory of relativity and hence to its latest offshoot, the unified field theory. That unified theory, however, never came within Einstein's grasp, as he freely admitted toward the end of his life.

In the early 1930s, in an essay on the methods of theoretical physics, Einstein raised the question whether we can ever hope to find the right way—seeing as he believed that the axiomatic basis of theoretical physics cannot be extracted from experience but must be freely invented. In other words, has this right way any existence outside our illusions? Einstein's position is unequivocal:

I answer without hesitation that there is in my opinion, a right way, and that we are capable of finding it. Our experience hitherto justifies us in believing that nature is the realization of the simplest conceivable mathematical ideas. I am convinced that we can discover by means of purely mathematical constructions the concepts and the laws connecting them with each other, which furnish the key to the understanding of natural phenomena. Experience may suggest the appropriate mathematical concepts, but they most certainly cannot be deduced from it. Experience remains, of course, the sole criterion of the physical utility of a mathematical construction. But the creative principle resides in mathematics. In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.

I believe it fair to say that Einstein's native epistemological credo comes through with remarkable consistency over the period of his last thirty to thirty-five years. I would mention first his characterization of God as a mathematician; or since Einstein did not believe in a personal God, we might better express his position by saying that natural phenomena can only be understood in depth, and natural laws can only be formulated successfully in the language of mathematics. Perhaps it is appropriate to mention in this context that Einstein's attitude changed considerably as he became increasingly preoccupied with relativity theory. Early in his career he displayed a far more skeptical attitude toward the role of mathematics in physics. Like Mach, who influenced him at that time, he must have felt that the abstract formalisms of mathematics were too closely allied with metaphysics and thus might disguise the deep physical significance of natural phenomena. He left such views behind when he came to recognize that his goal of achieving a more general and unitary representation of the world necessarily rested far more on sophisticated formal mathematical models than on physical terms and intuition.

Second, we see that Einstein had placed himself firmly on the side of those investigators of the classical period of physics who had expressed an unshaken faith in the ultimate conceptual unity of the physical world. In fact, in this regard he was exploring an old theme expressed cogently by d'Alembert in 1715 when he wrote: "To someone who can grasp the universe from one unified viewpoint, the entire creation would appear as a unique fact and a great truth." According to Einstein, a correct or right unitary theory of natural phenomena was conceivable and feasible, and scientists, he believed, were making steady progress in achieving that right unitary theory. Imbedded in this conception of a right theory is the belief that unambiguous progress had been achieved in moving toward the goal of constructing (discovering) a real picture, or physical representation of phenomena, that corresponds with the way things really are in nature. The right theory was equated with existence. Implied, of course, was also the conviction that the right theory is unique and not merely one of a plurality of alternative theories that might be constructed to do the job equally well.

For Einstein there was not only a right, correct, unique theory to explain the cosmos, but this theory was seen to be within our grasp. He said: "The Lord God is subtle but he is not malicious or vicious." ("Raffiniert ist der Herr Gott aber boshaft ist er nicht.") His God was a cosmic God, the God of Spinoza on a sublimated plane.

It was not a personal God, who makes notes on whether a person behaves or misbehaves, but a cosmic God, who represents the all pervading intellect which manifests itself so marvelously in the Creation.

It was man's special mission to lay bare the marvels of that Creation.

A third point. The right unitary theory upon which Einstein placed all of his stakes, is seen to rest on a mathematical foundation that deals with fields (continua), and not quanta, that is, not discontinua. He felt, as he once put it,

so long as no one has new concepts, which have sufficient constructive power, mere doubt remains; this is unfortunately my own position. Adhering to the continuum originates with me not as a prejudice, but arises out of the fact that I have been unable to think up anything organic to take its place. How is one to conserve four-dimensionality in essence (or in near approximation) and [at the same time] surrender the continuum?

For the same reasons that Einstein rejected quanta, he also put aside statistical or probabilistic arguments—because he believed that strict determinism was not to be sacrificed or even weakened.

In Einstein's fifty-year-long battle over the interpretation of quantum mechanics, one theme recurred again and again: his instinctive dislike of the idea of a probabilistic universe in which the behavior of individual atoms depends on chance. Was it likely that God would have created a probabilistic universe? Einstein felt that the answer must be no. If God was capable of creating a universe in which scientists could discern scientific laws, then God was capable of creating a universe wholly governed by such laws. He would not have created a universe in which he had to make chance-like decisions at every moment regarding the behavior of every individual particle. This was not something that Einstein could prove. It was a matter of faith and feeling and intuition. Perhaps it seems naive. But it was deep-rooted, and Einstein's physical intuition, though not infallible, had certainly stood him in good stead.

So Einstein's overall aim was a field theory that would encompass macro and micromechanics, or gravitation, electromagnetism, radiation, and atomistics including all aspects of science that pertain to the ultimate constituents of matter and their interactions at all levels. This grandiose, ambitious, and all-encompassing Weltbild was not one that Einstein was able to achieve despite more than twenty years of writing on the subject. Louis de Broglie summarized the position that most theoretical physicists took toward the end of Einstein's life when he commented that there exists

a fundamental difference between gravitational and electromagnetic fields which does not allow an extension to the latter of the geometrical interpretation which succeeded in respect to the former.… Moreover, the nature of the electromagnetic field is so intimately bound to the existence of quantum phenomena that any nonquantum unified theory is necessarily incomplete. These are problems of formidable complexity whose solution is still in the lap of the gods.

Finally, Einstein believed, that however abstract and remote from experience the mathematical formalism of theory turned out to be, the investigator nevertheless could use experience to suggest appropriate concepts. Although the concepts themselves could not be deduced from experience, experience was still acknowledged as the sole criterion of the physical utility of the theory. That is, in the end, it was absolutely crucial that the physical theory fit the empirical facts.

To these four landmarks of Einstein's image of what he considered to be a correct philosophy of science, namely, his own, I suppose we might want to add that he obviously held in high regard the importance of philosophizing about the foundational analysis, critique, and reformation of the basic concepts that lie at the heart of a right and realistic scientific world view. How closely Einstein's image of his own views about physics borders on philosophy may be seen in the way that philosophers of science have continued to discuss his philosophy perhaps even more than physicists. I therefore would not hesitate for one moment to assert that Einstein, in a special sense, was a truly important modern philosopher and that his highly individualistic philosophical ideas and self-image have exerted an influence that, as Professor Dirac has emphasized, has changed the course of history.

We have done no more here than sketch some facets of Einstein's self-image and his conception of himself as a philosopher of science. I suggest that a parallel examination of, say, Niels Bohr or Boltzmann would land us in an entirely different ballpark. But then, there should be no doubt that Niels Bohr's views and approach to physics as well as Boltzmann's changed the course of history.

Einstein was neither systematic philosopher nor analytical philosopher. He was not given over to concerns about symbolic logic or the syntax of language or the construction of a metalanguage. He was a scientist's philosopher in the tradition of Helmholtz, Mach, Duhem, Planck, Poincare, and Boltzmann. In spite of being worthy of being called the most revolutionary physicist of the twentieth century, he was at heart very much at home with the great scientific systems of the nineteenth century. He was, in fact, the natural philosopher par excellence. His revolutionary ideas are deeply imbedded in the three magnificent theoretical monuments of classic nineteenth-century thought, namely, mechanics, thermodynamics, and electromagnetic theory.

I do not believe that we know today whether nature is fundamentally simple and governed deep down by overarching simple general laws. Personally, philosophically, intuitively, I doubt it. That is, I doubt that scientists will ever reach rock bottom in such a way that no deeper digging is possible. To me, simplicity seems a myth and the lure of completeness deceptive. But having said this, I would want to add that whether nature is fundamentally simple or not, it probably is wise for investigators (if they want to get on with their work) to act as if it is. It is in this sense that I see Einstein's work as a guide and stimulus to scientific productivity and inventiveness.

Let me conclude with a quote from an article that Einstein wrote in 1918 for Planck's sixtieth birthday. It rather captures the spirit of Einstein's philosophy of science.

The supreme task of the physicist is to arrive at those universal elementary laws from which the cosmos can be built up by pure deduction. There is no logical path to these laws; only intuition, resting on sympathetic understanding can lead to them … The state of mind that enables a man to do work of this kind is akin to that of the religious worshiper or the lover; the daily effort comes from no deliberate intention or program, but straight from the heart.