“For most of us, the paradigm Realist is Einstein”.1
With Einstein’s criticism of quantum mechanics in mind, both physicists and philosophers of science have long regarded Einstein as a paradigm of the realist conception of scientific theories. Of course the meaning of the term “realism”, like many others in philosophy, has distinct context and time-sensitive connotations. One result is that the notion of a realist conception of scientific theories changed considerably during the course of the 20th century, largely under pressure of philosophical dialectic with quite different and distinctive non- or anti-realist viewpoints. In this chapter, and in the next two, a case is made that Einstein is legitimately considered a realist, though not a scientific realist in the contemporary sense, largely because of constructivist and empiricist tendencies that remain anathema to scientific realism. Aspects of realism are present in Einstein’s earliest contributions to physical theory on “the molecular-kinetic theory of heat” and the 1905 account of Brownian motion. Later confrontations over quantum mechanics, and a broader disagreement with an overt positivism and instrumentalism of many quantum physicists, led to heightened emphasis on realism. It became increasingly clear just how much of a breach quantum mechanics demanded with what Einstein presumed to be a largely uncontroversial previous conception of physical theory.
As understood today, scientific realism is broadly the view that current best theories in the “mature” sciences are true, or at least “approximately true”, descriptions of both observable and unobservable aspects of a mind-independent nature. Though emphases may be differently placed, contemporary scientific realists widely subscribe to three subordinate theses. In the detailed expositions of Psillos (1999) and Chakravartty (2011),2 these are:
As with most longstanding philosophical theses, this particular packaging reflects both contemporary debate and philosophical developments. Bas van Fraassen influentially argued that scientific realism crucially involves the thesis that the aim of science is to develop theories that are true, in the above correspondence sense.3 Steven Leeds (op. cit.) on the other hand, points out that the “correspondence theory” of truth, and so thesis 2), only became a key component of scientific realism after 1970, presumably impelled by adoption of Tarski-Davidson theories of reference and truth within analytic philosophy of logic and language. Just as “realism” has distinct and changing connotations, a fortiori this is the case with expressions of realist commitments. It is all too easy to overlook the rather obvious hermeneutic warning that the significance of terms and assertions from an earlier era, with their largely implicit context, should not, at least without argument, be simply identified with word-for-word equivalents occurring in contemporary discussions.
The semantic apparatus of reference and truth characteristic of contemporary scientific realism presupposes both empirical success as well as relative stability of theory. For the two revolutionary developments of 20th-century physics, relativity theory and quantum mechanics, these conditions were clearly met in the first decades following WW II, a period coinciding with a gradual liberalization of positivist currents in philosophy of science. Cracks began to appear in the reigning hegemony of complementarity and the “Copenhagen Interpretation” of quantum mechanics; Bohm’s ontological version of quantum mechanics dates from 1952. But up through the 1960s, the furthest reaches of quantum theory in high-energy physics yielded little more than a confusing and imperfect taxonomy of elementary particles, congenial to an instrumentalist view of physical theories. In the philosophical literature, it is difficult to find an expression of the contemporary doctrine of scientific realism prior to the work of Grover Maxwell around 1960. Employing the new tool of Tarski-style semantics, Maxwell promoted a “radically realistic interpretation of theories” seeking to extend semantic notions of truth and reference to statements and terms pertaining to unobservable or theoretical entities.4 Psillos recognizes this paper as the initial expression of contemporary scientific realism. However, the first book in English in which the term scientific realism prominently appears in the title, J.J.C. Smart’s Philosophy and Scientific Realism (1963), targets not the semantic double standard of the observable/unobservable dichotomy that animated Maxwell, but a considerably wider collection of foes, inter alia the later Wittgenstein, phenomenalism, biblical literalists, anti-mechanist dualists, idealism of all varieties, and perhaps above all Kant’s “anti-Copernican counter-revolution … his metaphysics, putting (man) back in the centre again”.5 Resistance to putting “man back in the centre” appeared also in reaction to the mind-dependence or subjectivity of Thomas Kuhn’s account of mature science using the core notion of “paradigm” in Structure of Scientific Revolutions (1962). Kuhn’s account of theory-change, caricaturized by some as “mob rule”, provided further impetus to scientific realism, initiating a new round of debate between realism and antirealism that continues into the 21st century. In the light of these later developments, it is plausible that putative realists in the first half of the 20th century subscribed only to a version of thesis 1), but hardly to 2) or to 3).
Even the above cursory overview indicates that both the term “scientific realism” and the doctrine are of fairly recent vintage in the philosophical literature. What about the term “realism” itself? Its usual metaphysical sense is captured in the following Ur-intuition, recently described by Kit Fine:
One might think of the world and of the propositions by which the world is described as each having its own intrinsic structure; and a proposition will then describe how things are in themselves when its structure corresponds to the structure of the world.6
But realism’s original philosophical meaning is otherwise, standing in opposition to the doctrine of nominalism, a dispute stemming from medieval philosophy concerning the existence (or not) of abstract universals and their relation to the concrete individuals, or particulars, that instantiate them. Only in the course of the 19th century did the term “realism” come to acquire a wholly distinct meaning within a new context of discussion. One source of change was a revival of direct, or causal, theories of perception, directing attention from the quality or character of an individual’s percept or idea to the object itself, as the external cause of perception. Thomas Reid’s critique of Lockean and Humean representationalist theories of ideas was an initial counter to empiricism’s epistemological idealism (that we know or perceive objects only via our representations of them). Realism also would come to signify opposition to ontological idealism (denial of the existence of objects external to mind, as in Berkeley, Fichte, Schelling, and, in some readings, Hegel). By the 1850s, idealist metaphysics was widely regarded as an embarrassment by a burgeoning technological age accustomed to regular advances in the sciences.
One response was a disregard for professional philosophy as irrelevant to their concerns by many, if not most, scientists. Post-Hegelian German philosophy itself was in transition from idealism to various forms of naturalism or materialism, positivism, and to an emerging school (“Back to Kant”) of neo-Kantian thinkers, some urging a return to Kant’s empirical realism. Even so, as can be seen by a glance at John Dewey’s 1902 entry for “Realism” in what was then a standard reference work, Baldwin’s Dictionary of Philosophy and Psychology, the traditional anti-nominalist significance of the term within philosophy retained precedence. Noting that “the term has two important meanings in philosophy, wholly distinct from each other”, Dewey’s article is almost entirely a discussion of the realism-nominalism controversy. Dewey notwithstanding, the contemporaneous “New Realism” of the young Cambridge philosophers Bertrand Russell, G.E. Moore, and G.F. Stout, targeted equally both traditional nominalism as well as the idealism of the British Hegelians, such as F.H. Bradley and Bernard Bosanquet.
At the beginning of the 20th century, a “new theory of knowledge” (die neuere Erkenntnistheorie) had arisen “out of the soil of the natural sciences”, and so independently of traditional philosophy.7 An influential trend in this development was the purely instrumentalist conception of physical theory promoted by Gustav Kirchhoff followed by emerging realist responses to it. In 1876 Kirchhoff famously stated the task of mechanics as that of describing “the motions occurring in Nature completely and in the simplest way”.8 Kirchhoff’s descriptivism is better known to most philosophers of science today through the version advanced by Pierre Duhem, lauding Kirchhoff and Mach as “more modest and more far-sighted” physicists who
recognized that physical theory is not an explanation, but a simplified and orderly representation grouping laws according to a classification which grows more and more complete.9
Mach had expressed similar views, even “more radical” (as he put it in his Mechanik of 1883), earlier in 1872. Mach elevated Kirchhoff’s descriptivism in mechanics to a stricture on science as a whole; in an 1894 lecture in Vienna, against those who maintained that “description leaves unsatisfied the requirement of causality (Kausalitäts-bedürfnis)”, Mach expressed his hope that “the science of the future will discard the idea of cause and effect, as being formally obscure” as well as his belief that “these ideas contain a strong tincture of fetishism”.10 Causal explanations of phenomena, if not cashed out as regularities between groups of sensations, are metaphysical ballast that science doesn’t need and adopts only on pain of mischief. The legitimate task of the scientist is to provide the simplest and most economical description of phenomena, employing the language of functional dependences between sensations in place of the metaphysical notions of cause and effect.
Mach’s anti-metaphysical positivism met with resistance from many scientists who refused to surrender what might be termed a “common-sense realism” regarding a physical world familiar to the experience of all individuals but whose existence and nature is independent of all who experience (or think). Among certain theoretically inclined physicists, such a view was accompanied by a more expansive conception of physical theory than descriptivism permitted. To its most prominent turn-of-the-century advocates, Boltzmann and then Planck, the augmented common-sense realism largely took the form of defending the use of hypotheses, such as atomism, in testable and empirically confirmed theories. Hypotheses allowed theory the resources of autonomous development, and in doing so, underscored the explanatory benefits of theoretical concepts that go beyond and supplement experience. Whether, and in what sense, Boltzmann was a realist about atoms is a matter of some delicacy; he surely believed in kinetic theory and that kinetic theory presupposes atoms and molecules. However, he died in 1906, just after Einstein’s 1905 paper on Brownian motion that would play a pivotal role in atomism’s ultimate vindication. That paper derived the hypothetical mechanism producing invisible molecular motions whose consequences might even be observed; Jean Perrin’s experiments in Paris (in 1908) confirmed Einstein’s theory and the existence of physical atoms was ever afterwards taken for granted. Einstein referred to his early realist motivations much later, in 1946:
My principal aim … was to find facts that would guarantee as much as possible the existence of atoms of definite size…. The agreement of these considerations with experience together with Planck’s determination of the true molecular size from the law of radiation (for high temperatures) convinced the skeptics, who were quite numerous at that time (Ostwald, Mach), of the reality of atoms.11
Many contemporary philosophers of science view the confirmation of Einstein’s (and independently in 1906, Polish physicist Marian Smoluchowski’s) molecular hypotheses explaining the mechanism of Brownian motion as vindicating realism over positivism, and there is a sense in which this is correct. But it should be recognized that atomism’s triumph is not one of realism regarding scientific theories but of the justifiable posit of unobserved physical entities in the explanation of observations. This fallible entity realism is also the basis of Boltzmann’s atomism. It presupposes a conception of physical theory as a deductively complex structure that is capable of deriving the phenomena of observation from hypotheses regarding unobserved theoretical entities and underlying processes. This is a view Einstein also shared, as will be discussed in Chapter 9.
Planck had consistently argued against Boltzmann’s statistical interpretation of the second law and accordingly rejected the hypothesis of atomism that interpretation presupposed. But he was converted to atomism during the course of his investigations of blackbody radiation. With the zeal of a new convert, in a notable lecture in Leiden on December 9, 1908, Planck attacked the leading anti-atomist Mach and the latter’s positivist conception of physical theory. The lecture was Planck’s philosophical debut, a first intervention in ongoing discussions by physicists and others, such as Poincaré, over the nature and character of physical theory. Planck’s thesis is prominently stated in the lecture’s title “The Unity of the Physical World Image” (“Die Einheit des physicalischen Weltbild”). The issue of atomism was now peripheral and largely passé; Planck simply pronounced atoms to be “as real as the heavenly bodies”.12 Rather the lecture’s significance concerns Planck’s shift of realist focus from the existence of atoms to the definition of the task of the theoretical physicist. This was, contra Mach, the search for a unifying physical world image (Weltbild). The lecture was extensively discussed, not least because Planck reprinted it no less than four times in various collections of philosophically themed essays. In fact, the main themes of 1908 appear again and again in later essays, extending almost up to his death in 1947.
One suspects that the source of Planck’s ire was not so much directed at Mach’s philosophy as a perceived pernicious influence on the younger generation of physicists. Under the banner of positivist anti-metaphysics, Mach had urged that the task of physical theory is simply to provide the most “economical” description of empirical connections between sensations (that is, observable quantities), having no further epistemological, and certainly no metaphysical, significance. To Planck, such an emaciated conception of the role of physical theory, apparently having to do only with the ordering of sensations, was unbearably anthropomorphic. Against this, Planck proclaimed the goal of the theoretical physicist to be the construction of a de-anthropomorphized, complete, consistent, and unified physical world image (physikalischen Weltbild) of such permanency that it can be taken to be a definition of physical reality:
The constant unified Weltbild is … the fixed goal to which actual (wirkliche) natural science progressively approaches through all its changes. In physics we even may justifiably claim that our contemporary Weltbild contains certain traits that will never disappear through any revolution, either in Nature or in human thought. This constancy, independent of any human, more generally any intellectual individuality, is now plainly that which we call the real (das Reale).13
The term Weltbild merits special emphasis. The next chapter looks into the origin of the term Bild in the context of late 19th-century discussions of the constructive character and nature of physical theory. It will be sufficient here to note that an image (Bild) is distinct from what it portrays or represents; the possibility of comparing image and object, and establishing their difference, is normally presupposed. Yet this is not the case, at least regarding the Weltbild of the future, the projected unified complete representation of physical reality. Herein lies its suitability in establishing the very meaning of physical reality:
Is there any recognizable difference between (physicists’ talk of “the world” or “Nature itself”) and our “Weltbild of the future”? Certainly not. For that there is no method of proving such a difference has, through Immanuel Kant, become common property (Gemeingut) of all thinkers.14
Kant had shown that there is no way of delineating a “recognizable difference” between the noumenal metaphysically real world with its mind-independent objects, properties and structures and the physicists’ “Weltbild of the future”. The term Weltbild therefore has a precise function; it is adopted “as a precaution (Vorsicht), to exclude certain illusions from the start”; that is, to exclude the conceit of assuming that any physical theory, even an ideal future one, can ever portray with complete and faithful accuracy a mind-independent reality. Planck would make abundantly clear in subsequent essays that an “unbridgeable chasm” always remains between the phenomenal world characterized by physical theory and the metaphysically real world that is presupposed as the target of physical inquiry. Between the two there is “a constant, unbalanced tension” that gives exact science “an irrational element (it) can never shake off”.15 This can be an attenuated realism at most; physics is about an independent external world; physical theory aspires to be a complete description of such a world; yet the non-philosophically naïve physicist must continue to work in an existential state of tension, possessing the knowledge that such an aspiration can never be fully realized.
Planck allowed that even the contemporary physical Weltbild contains some permanent elements. These are universal principles, laws, and constants that always shall be elements of yet more refined and complete future world-images. His examples are the second law of thermodynamics, the principle of conservation of energy, the principle of least action (governing reversible processes), and the physical constants of universal character, independent of reference to any particular body or substance. In the course of work on blackbody radiation in 1900, Planck gave an explicit list. They are h and k, both appearing in Planck’s radiation law, the velocity of light in vacuo c and Newton’s gravitational constant G; together they allow a characterization of physical measurement transcending the conventions of particular experimenters at particular times. These “natural unit constants” provided
the possibility of establishing units of length, mass, time, and temperature, that independently of special bodies or substances, necessarily retain their significance (Bedeutung) for all times and for all cultures, even extraterrestrial and nonhuman ones.16
To this list, Planck would later append relativistic invariants such as the interval ds2 of space-time. Planck’s 1908 polemic elicited a spirited reply from Mach (his Leitgedanken) and from Mach’s followers, but Planck was adamant. His final retort to Mach fairly drips with sarcasm: “the physicist, if he wants to promote science, has to be a realist, not an economist”.17 Though we shall refer to “Planck’s realism”, this sense of “realism”, whose goal is the construction of a physical Worldbild purporting to define physical reality, is to be understood primarily in opposition to positivism. And on account of the “unbridgeable chasm” that always remains between theory-image and reality, Planck’s realism is more aptly described as a variety of neo-Kantianism. It lacks the “epistemic optimism” needed to bridge the two, a bridge required by the semantics of truth and reference of scientific realism in the contemporary sense.
Einstein will always deny the attribution “realist”. The most vivid of these denials is made in a September 25, 1918 letter to Bonn mathematician Eduard Study, responding to Study’s 1914 monograph, Die realistische Weltansicht und die Lebre vom Raume (The Realist World Outlook and the Doctrine of Space). As its title suggests, Study had written a polemic against the opponents of realism (“Idealists, Positivists, Pragmatists”) and a defense of the realist Weltbild (Das realistische Weltbild), that is, of the hypothesis of the existence of an external world independent of the knowing subject that is the topic of natural science. To Study, Einstein objected,
I do not feel comfortable and at home in any of the “isms”. It always seems to me as though such an ism were strong only so long as it nourishes itself on the weakness of its counter-ism. But if the latter is struck dead and it is alone on an open field, then it proves to be wobbly on its legs. Therefore, away with the grousing (los mit der Stänkerei)!
“The physical world is real”. That is supposed to be the basic hypothesis. What does “hypothesis” mean here? To me, a hypothesis is an expression whose truth is presupposed for the time being, but whose meaning has to be elevated above any ambiguity. However, the above statement appears to me to be meaningless in itself, as if one said “The physical world is cock-a-doodle-doo (ist kikeriki)”. It seems to me that “real” is an in-itself meaningless category (pigeon hole) whose monstrous importance only lies in this, that I can do certain things inside it and not certain other things…. I grant you that natural science concerns the “real” and yet I am not a “realist”.18
On the other hand, earlier that year in the full flush of success following the completion of the general theory of relativity, Einstein embraced Planck’s attempt to define the “real” in terms of a striven- for constant world image (Weltbild) and that the task of the theoretician is to advance such a world image through establishing the permanence of certain of its constituents, and of its most general basic laws. This occurs in the text of Einstein’s warm appreciation of Planck at the Berlin Physical Society’s celebration of Planck’s 60th birthday on April 26, 1918. Einstein did not take this responsibility lightly. When inviting Arnold Sommerfeld to attend the festivities some weeks before, he wrote, “I’ll be happy that evening if the gods grant me the gift to speak profoundly, because I am very fond of Planck, and he will certainly be pleased when he sees how much we all care for him and how highly we treasure his life’s work”.19 It cannot be a coincidence that the prominent message of Einstein’s keynote tribute is an endorsement of Planck’s signature philosophical position, the characterization of the task of theoretical physics as the search for a unifying and universal “Weltbild”.
Do the results (of the theoretical physicist) deserve the proud name “Weltbild”? … the proud name is well-deserved since the most general laws, upon which the thought-structure [Gedankengebäude] of theoretical physics is based, raise the claim of being valid for all natural occurrences … Therefore the highest task of the physicist is the search for those most general elementary laws from which the world-image (Weltbild) is to be obtained by pure deduction.20
Einstein’s audience undoubtedly understood that this embrace of Planck’s conception of “the highest task of the physicist” is a deliberate public alignment with Planck and so with the latter’s passionate polemic against Mach and positivist ideas of physical theory. The theoretical physicist is to be understood as engaged in building up a “physical world image”, much of which is an admittedly mental construction. Employing symbols for the metaphysically real, the Weltbild is not readily expressible in ordinary language, and it may posit elements that outstrip present capacities for observational test. At the same time it must yield consequences that are possible to observationally confirm, and in addition it must be flexible enough to accommodate new phenomena. Though in a sense a creation of mind, its implications purport to refer to a mind-independent real external world. As it is always incomplete, it can never be supposed in satisfactory agreement with mind-independent states of affairs, and in any case such agreement can never be directly ascertained but at most indirectly inferred. Perhaps its most important functions are to serve as a platform within which further thought may develop, as well as to suggest experiments whereby it can be transcended or amended.21 It is worth mentioning that in 1933, Einstein allowed the text of this 1918 lecture to appear as a “Prologue” to a collection of Planck’s philosophical articles in English.22
Some dozen years after 1918, Einstein again expressed fundamental philosophical agreement with Planck’s anti-positivist realism, this time with Planck’s article “Positivism and the Real External World” (“Positivismus und reale Aussenwelt”). The article is the text of Planck’s lecture on November 12, 1930 at Harnack-Haus, in the Dahlem district of Berlin. Harnack-Haus was completed in 1929 as an international guest house for the Kaiser Wilhelm Gesellschaft; since 1917 Einstein had been titular head of the Kaiser Wilhelm Institut für Physik, and in 1929 he had received the Max Planck medal of the German Physical Society from Planck himself. There are reasons to assume that Einstein was in the audience; he would leave for a second visit to Pasadena and Caltech beginning in December.
Planck’s theme is the looming dual crisis at the end of 1930, both material (between summer 1929 and early 1932, German unemployment had risen from 1.3 million to 6 million, some 24 percent of the labor force23) and “spiritual” (by which Planck certainly included “political”: since 1927 street fighting between “reds” (communists) and “browns” (Nazis) had become common in Berlin). Though physics should have claim to be a firm foundation on which to base a modern outlook on the world, Planck took the opportunity to express his disquiet at the confusion and contradiction now active among certain physicists. Mach was long dead, but quantum physicists had resuscitated positivism in physical science, fundamentally posing limits on how far and in what way the human mind is capable of attaining knowledge of the external world, and by challenging the law of causality. Again in opposition to positivism Planck articulates the Bild conception of physical theory, and the invariable tension between the presupposition of a real world in the metaphysical sense and the realization that theories are images, never to be known capable of completely grasping its nature.
Positivism always rigorously maintains that there are no other sources of knowledge except sense perceptions. Now, the two theorems (Sätze): (1) there is a real external world independent of us and (2) the real external world is not directly knowable form together the hinge point (Angelpunkt) of the whole of physical science. And yet they stand in a certain opposition to one another. In this way they at the same time disclose the purely irrational element that adheres to physics as to every other science. The result is that a science is never able to fully complete its task. We must accept that as an irrefutable fact, one that cannot be removed, as positivism tries to do, by restricting the task of science at its very start. The work of science therefore poses itself to us as an incessant struggle toward a goal that will never be reached and fundamentally is unattainable. For this goal has a metaphysical character, lying beyond any experience.24
Planck’s lecture marks not so much an intervention in, but a response to, the debate about the meaning of the Heisenberg uncertainty relations and quantum indeterminism. Whereas Planck deplores the quantum physicists’ abandonment of the “law of causality”, Einstein’s criticisms by 1930 had shifted, as seen in Chapter 4, to questioning whether the Ψ-function of wave mechanics could be considered a complete description of the states of individual systems. The quantum physicists’ resort to positivist doctrine, then under vigorous revival by philosophers particularly in Vienna and Germany, had spurred Planck into action. One of these philosophers was Moritz Schlick, Planck’s former student and now leader of the Vienna Circle. Indeed, Planck’s lecture prompted a response from Schlick retorting that statement (1) above is meaningless.25
Two documents show that Einstein was in full accord with Planck’s conception of realism while opposed to Schlick’s positivism. A handwritten draft note from 1931 in the Einstein Archives was possibly intended as the preface to the published pamphlet of Planck’s lecture that appeared on March 9, 1931. For one reason or another Einstein’s note was never published. Lauding Planck’s article, it states:
I presume I may add that both Planck’s conception of the logical state of affairs as well as his subjective expectation concerning the later development of science corresponds entirely with my own understanding.
Citing the above passage, physicist and historian Gerald Holton observes that from this time forward, “Einstein’s and Planck’s writings on these matters are often almost indistinguishable from each other”.26
Of course by 1930 it had become increasingly apparent to Einstein that many of the leading quantum physicists sought to cloak what he considered to be the theory’s shortcomings under the mantle of positivist strictures upon the meaningfulness of scientific statements. This in turn led to more and more forceful counters of a realism à la Planck. In the autumn of 1930, Schlick, in 1917 a realist supporter of relativity theory but now a leading logical empiricist, completed a lengthy essay purporting to attain “philosophical clarity” about the standing of the principle of causality in the new physics of quantum mechanics. It appeared in the German scientific weekly Die Naturwissenschaften at the beginning of 1931. Upon finishing it, sometime in November 1930, Schlick posted a typescript copy to Einstein. If Schlick had any awareness of Einstein’s objections to quantum mechanics, he knew beforehand that Einstein was not disposed to favor the essay’s conclusion, that “quantum physics teaches us … that within the bounds established by the uncertainty relations the (causality) principle is bad, useless or idle, and incapable of fulfillment”.27 But Schlick’s essay had transgressed much further, impugning the conception of physical theory guiding both Planck and Einstein. At the beginning, Schlick lampooned the “obstinacy” of the physicist’s traditional belief that the explanation of nature required comprehensible models, a rejection of the Bild conception of physical theory. At the end, he proclaimed “the human imagination is incapable of conjecturing the world structure revealed to us by patient research”.28 Einstein was quick to disagree with these two claims in particular. In a letter to Schlick of November 28, 1930, two weeks after Planck’s lecture, Einstein condemns the constraints of positivism’s conception of physical theory. Alluding to the irrational bifurcation between real world and the world of experience that Planck viewed as the hinge point of natural science, Einstein freely admitted to the metaphysical character of the theoretician’s realist impulses:
I tell you straight out: Physics is the attempt at the conceptual construction of a model of the real world and of its lawful structure. To be sure, (physics) must present exactly the empirical relations between those sense experiences to which we are open; but only in this way is it chained to them…. In short, I suffer under the (unsharp) separation of Reality of Experience and Reality of Being.
… You will be astonished by Einstein the “metaphysicist”. But every four- and two-legged animal is de facto in this sense metaphysicist”.29
Without acknowledging the scientist’s motivational realism, admitted even by descriptivists like Duhem, positivism can give only a misleading account, perhaps only a caricature, of scientific method. This will become an increasingly prominent theme in Einstein’s response to quantum mechanics.
Near the end of Chapter 4, it was seen that after WW II, two previously distinct lines of argument against quantum mechanics had coalesced into the thesis of “macrorealism”. Prior to then, Einstein wielded a two-tiered critique. First, a parade of heuristic examples of individual systems purporting to show incompleteness of quantum mechanical description without violating Heisenberg’s strictures on simultaneous measurement of exact values of canonically conjugate observables. At the same time, on a methodological/philosophical level, he repudiated complementarity’s positivist inference that since simultaneous measurements cannot reveal exact values of conjugate properties, such values cannot be said to exist and accordingly need not be described. By the late 1940s, Einstein began to emphasize that even positivists found it difficult to deny that macroscopic objects possessed “real states” independent of observation. An incompleteness argument could then be marshaled if the quantum mechanical characterization of the transition from micro- to macro-object, such as is required by allowing the mass of single particle to increase to classical scale (e.g., 1 g), hence a transition quantum mechanics was obliged to describe, did not terminate in a “real state” of the corresponding macro-object; that is, did not produce the definite kinematical and dynamical properties that classical particle mechanics takes for granted.
A first step is to throw down the gauntlet to positivism, postulating what in 1953 Einstein termed the “thesis of reality”:
“thesis of reality”: there is such a thing as the “real” state of a physical system existing independently of any measurement or observation that in principle can be described by the means of expression of physics.30
The thesis, representing clearly at least a shift in philosophical emphasis from the response to Study in 1918, is a fundamental posit of what in 1949 is termed realism as a “program”; that is, a program for complete description of “real states”:
The “real” in physics is to be taken as a type of program to which we are … not forced to cling a priori. No one is likely to give up this program within the realm of the “macroscopic” … But the “macroscopic” and the “microscopic” are so interrelated that it appears impractical (untunlich) to give up this program in the “microscopic” alone.31
Three related points will be mentioned here (see also the discussion at the end of Chapter 4 and further in Chapter 9). First, realism “as a program” is widely assumed, though perhaps only implicitly, in classical physics. Objects or states of objects are regarded as having definite values of observable properties independently of observation or measurement. Naturally the temperature of a solution may be altered by the insertion of a thermometer not at equilibrium with it. Or the value of a magnetic field at a point of a region may be changed by an encounter with a charged particle whose altered trajectory indicates the strength of the field. But the operative assumption is that the unmeasured values exist and are definite, and that refined procedures of measurement can reduce the disturbances involved to negligibly small quantities. Second, the entwined “interrelation” between microscopic and macroscopic systems gives reason to think the operative assumption above should not be restricted to the realm of the macroscopic. Third, adherence to the program is not compelled a priori; after all, the assumption of the real external world is a metaphysical assumption that may be consistently denied, as by solipsism. Such an assumption is not, after all, terribly controversial. Even quantum theoreticians adhere to it “so long as they are not discussing the foundations of quantum theory”.32
The thesis of realism is affirmed to be generally applicable, and so to apply indifferently to all physical systems. Controversy ensues only when it is claimed that there are “real states” of micro-objects that are only incompletely described by the Ψ-function. But then the quantum theoretician, as indeed Bohr broadcasts, has had to admit that the notion of “real state” is not univocal between classical and quantum, and that there is a fundamental difference in kind between the character and method of the classical physical description of objects, and the quantum mechanical description of quantum objects. This is the postulate, even the defining characteristic, of complementarity. Einstein insists on viewing this postulate as a positivist inference, and is prepared to be a labeled a “metaphysicist” for doing so:
What does not satisfy me in that theory (quantum mechanics) from the principled standpoint is its advocated (vertretene) attitude towards what appears to be the programmatic aim of all physics: the complete description of the real states of affairs possible according to the laws of nature (die vollständige Beschreibung der naturgesetzlich möglichen realen Sachverhalte). If the modern physicist of positivist persuasion hears such a formulation, his reaction is that of a pitying smile. He says to himself: “There we have the naked formulation of an empty metaphysical prejudice without content, the conquest of which has been the major epistemological achievement of physicists within the last quarter-century. Has anyone ever perceived a “real state of affairs”? Can anyone say in general what is to be understood by “real state of affairs”? How is it possible that a reasonable person could still believe today that he can refute our principal cognitions by allowing such a bloodless ghost to be conjured?” Patience! The above laconic characterization was not meant to convince anyone; it was merely to indicate the point of view around which the following elementary considerations freely group themselves.33
In place of the incoherent EPR “criterion of reality”, the “thesis of reality” is an attempt to reinstate the conception of physical theory outlined above, in which the intended meaning of the concepts <physical reality>, <external world>, and <real state of (an individual) system> characterize what it is that physical theory attempts to describe. Realism as a “program” thus pertains to the intended target of description of any physical theory, the real external world as partitioned by physics into systems and subsystems. With the advent of quantum mechanics, positivism reappeared in physical theory in the form of Bohr’s complementarity. And to the extent that complementarity enjoins a sharp conceptual separation between the respective realms of classical and quantum, it presents a vulnerable target to the “thesis of reality”. Not because the thesis merely affirms what Bohr and quantum orthodoxy deny, the existence of definite states of quantum objects at all times: this is moot and merely begs the question. Rather the intent of the thesis is to highlight that, as a matter of consistency and as a theoretical requirement of quantum mechanics, there must be a faithful quantum mechanical characterization of the transition in the limit from the domain of quantum phenomena to macroscopic physics. This quantum mechanics does not do, then or arguably now, and so the “thesis of reality” points out a glaring gap in the case that complementarity can make to be an adequate and definitive philosophical interpretation of quantum mechanics.
Einstein’s realism vis-à-vis the quantum physicists is also a dispute over the explanatory goals of physical theory. “Realism as a program” delineates categories of understanding, not necessarily of nature. Yet it supports the characterization of quantum mechanics as incomplete. Realist theories, as Einstein conceived of them, share a common world picture, i.e., they represent a cumulative understanding of nature as comprised of relativistic (in the sense of the general theory) deterministic (causal) non-quantum continuous fields in which individual systems are spatiotemporally separable and can be characterized completely by properties having determinate values independent of any act of measurement or observation. The concepts of this realist program of description are not to be assumed either a priori valid or as impossible. They are not essential to the practice of science but neither are they to be merely dismissed as excrescences of the metaphysically diseased mind. Like all other concepts they are justifiable only by experience. Occasionally rivals (e.g., “purely algebraic physics”) are mentioned.34 Characteristically, after laying out his vision, Einstein will immediately observe there is absolutely no compelling reason, conceptual or metaphysical, to regard it as correct. Justification for any choice of a physical theory and its attendant concepts and presumed ontology lies principally with the ability of such theories to implement coordination with experience (confirmation) “with advantage” (mit Vorteil).35 The latter phrase is significant, for it is an oblique indication of the requirement that a theory must provide understanding,
a conceptual model (Konstruction) for the comprehension of the interpersonal whose authority lies solely in its confirmation (Bewährung). This conceptual model refers precisely to the “real” (by definition), and every further question concerning the “nature of the real” appears empty.36
Two distinct components comprise Einstein’s realism: 1) metaphysical, affirming the existence of an external mind-independent world; and 2) a motivational or aspirational aspect, affirming the aim of fundamental physical theory to provide a model of this world. They share the common dialectical purpose of opposition to positivist conceptions of physical theory that Einstein perceived to be widely, and largely uncritically, assumed by quantum physicists under the aegis of Bohr’s complementarity. Einstein’s realism lacks the semantic apparatus of truth and reference of scientific realism. It also lacks the “epistemic optimism” encouraging the scientific realist to commit to claims of “approximate truth” for current theories. On the other hand, following Planck’s example, Einstein can endorse claims that certain elements of the current “conceptual model” (Konstruction) may well be permanent fixtures of the future “world image” that gives meaning to the term “physical reality”. Such elements are not entities or laws of particular theories but meta-level constraints on theories, values of physical constants, principles of connection (e.g., between entropy and probability) or symmetries that remove the bias of particular observers or frames of reference. With these provisos, Einstein is indeed a “paradigm realist”.
1Leeds, Steven, “Correspondence Truth and Scientific Realism”, Synthese v. 157 (2007), pp. 1–21; p. 19.
2Psillos, Stathis, Scientific Realism: How Science Tracks Truth. London and New York: Routledge, 1999; Anjan Chakravartty (2011), “Scientific Realism”, in Edward N. Zalta (ed.), The Stanford Encyclopedia of Philosophy (Fall 2015 Edition), available at http://plato.stanford.edu/archives/fall2015/entries/scientific-realism/
3Van Fraassen, Bas, The Scientific Image. New York: Oxford University Press, 1980.
4Maxwell, Grover, “On the Ontological Status of Theoretical Entities”, in Herbert Feigl and Grover Maxwell (eds.), Scientific Explanation, Space, and Time, Minnesota Studies in the Philosophy of Science, vol. 3. Minneapolis: University of Minnesota Press, 1962, pp. 3–27.
5Smart, John Jamieson Carswell, Philosophy and Scientific Realism. London: Routledge and Kegan Paul, 1963, p. 151.
6Fine, Kit, “The Question of Realism”, The Philosophers’ Imprint v. 1, no. 1 (2001), p. 25.
7Physicist-turned-epistemologist Paul Volkmann wrote of “eine auf dem Boden der Naturwissenschaften erwachsene Erkenntnistheorie” in his Erkennistheoretische Grundzüge der Naturwissenschaften, Zweite Auflage, 1910. B.G. Teubner: Leipzig, Germany & Berlin, p. 241.
8Kirchhoff, Gustav, Vorlesungen über mathematische Physik: Mechanik. Leipzig, Germany: Teubner, 1876, p. 1.
9Duhem, Pierre, The Aim and Structure of Physical Theory. Second edition (1914). As translated by P. Wiener. Princeton, NJ: Princeton University Press, 1991, p. 54.
10Mach, Ernst, “Über das Prinzip der Vergleichung in der Physik”, in Ernst Mach, Populär-Wissenschaftliche Vorlesungen. Leipzig, Germany: Johann Barth, 1896, pp. 251–74; p. 269; translation altered from “On the Principle of Comparison in Physics”, in T. J. McCormack (trans.), Ernst Mach Popular Scientific Lectures. Chicago: Open Court Co., 1898, pp. 236–58; p. 254.
11“Autobiographical Remarks”, p. 45; p. 47.
12Planck, Max, “Die Einheit des physikalischen Weltbildes”, as reprinted in Wege zur physikalischen Erkenntnis: Reden und Vorträge. Zweite Auflage. Leipzig, Germany: S. Hirzel Verlag, 1934, pp. 1–32; pp. 28–9.
13Ibid., p. 30.
14Ibid., p. 32.
15Planck, Max, “Sinn und Grenzen der exakten Wissenschaft”, Die Naturwissenschaften v. 130 (February 27, 1942), p. 130: “from the standpoint of exact science there always remains an unbridgeable chasm between the phenomenological and the metaphysically real worlds (that) engenders a constant, unbalanced tension…. In this bifurcation, which expresses itself in that we view the presupposition of a real world in the absolute sense as inevitably required but, on the other hand, we are never capable of completely grasping its nature, lies an irrational element which exact science can never shake off”.
16Planck, Max, “Über irreversible Strahlungsvorgänge”, Annalen der Physik, Vierte Folge Bd. 1 (1900), pp. 69–122.
17Planck, Max, “Zur Machschen Theorie der physikalischen Erkenntnis: Eine Erwiderung”, Physikalische Zeitschrift Bd. 11, pp. 1186–90 (1911), p. 1188, translation as “On Mach’s Theory of Physical Knowledge: A Reply” in Stephen Toulmin (ed.), Physical Reality: Philosophical Essays in Twentieth-Century Physics. New York: Harper and Row, 1970, pp. 44–52; p. 46.
18CPAE 8 (1998) Part B, Doc. 624.
19Hermann, Armin (ed.), Albert Einstein/Arnold Sommerfeld Briefwechsel. Basel/Stuttgart: Schwabe & Co. Verlag, 1969, Doc. 10, p. 48. The letter has the approximate date, “end of February, beginning of March 1918”.
20Einstein, “Motive des Forschens” (“Motives of Research”), April 26, 1918. CPAE 7 (2002), Doc. 7.
21See the insightful review by Harry T. Costello (“H.T.C.”) of Ernst Zimmer, The Revolution in Physics. New York: Harcourt, Brace and Co., 1936. The Journal of Philosophy v. 33 (1936), pp. 527–8.
22Planck, Max, Where Is Science Going? Prologue by Albert Einstein. Translated and edited by J. Murphy. New York: W.W. Norton and Co., 1933.
23Dimsdale, Nicholas H., Nicholas Horsewood, and Arthur Van Riel, “Unemployment and Real Wages in Weimar Germany”, University of Oxford, Discussion Papers in Economic and Social History, Number 56, October 2004.
24Planck, Max, “Positivismus und reale Aussenwelt” as reprinted in Wege zur physikalischen Erkenntnis: Reden und Vorträge. Zweite Auflage. Leipzig: S. Hirzel Verlag, 1934, pp. 208–32; p. 217.
25Schlick, Moritz, “Positivismus und Realismus”, Erkenntnis v. 3 (1932), pp. 1–31; English translation in Henk L. Mulder and Barbara F. B. van de Velde-Schlick (eds), Mortiz Schlick Philosophical Papers, vol. 2 (1925–1936). Dordrecht: D. Reidel, 1979, pp. 259–84.
26Physicist and historian Gerald Holton reports the note was “written on or just before April 17, 1931”. Holton, “Mach, Einstein, and the Search for Reality”, 1968, p. 262.
27Schlick, Mortiz, “Die Kausalität in der gegenwärtigen Physik”, Die Naturwissenschaften v. 19 (1931), pp. 145–62; English translation in H. Mulder et al (eds), Mortiz Schlick Philosophical Papers, vol. 2 (1925–1936). Dordrecht: D. Reidel, 1979, pp. 176–209; p. 196.
28Ibid., p. 206.
29EA 21–603.
30Einstein, “Einleitende Bemerkungen über Grundbegriffe”, in Louis de Broglie: Physicien et Penseur, collection dirigée par André George. Paris: Éditions Albin Michel, 1953, pp. 4–14; p. 6.
31“Replies to Criticisms”, p. 674.
32Einstein, “Einleitende Bemerkungen über Grundbegriffe”, pp. 4–15; p. 6.
33“Replies to Criticisms”, p. 667; German, p. 494.
34See Stachel, John, “Einstein and the Quantum: Fifty Years of Struggle”, in R. Colodny (ed.), From Quasars to Quarks: Philosophical Problems of Modern Physics. Pittsburgh: University of Pittsburgh Press, 1986, pp. 349–85.
35Einstein, “Elementare Überlegungen zur Interpretation der Grundlagen der Quanten-Mechanik”, in Scientific Papers presented to Max Born on his Retirement from the Tait Chair of Natural Philosophy in the University of Edinburgh, Edinburgh: Oliver & Boyd, 1953, pp. 33–40; p. 34.
36“Replies to Criticisms”, p. 680.
Fine, Arthur, The Shaky Game: Einstein Realism and the Quantum Theory. Second edition. Chicago: University of Chicago Press, 1996.
Howard, Don, “Einstein’s Philosophy of Science”, in Edward N. Zalta (ed.), The Stanford Encyclopedia of Philosophy. Winter 2015 edition, URL = <http://plato.stanford.edu/archives/win2015/entries/einstein-philscience/>.
Scheibe, Erhard, “The Origin of Scientific Realism: Boltzmann, Planck, Einstein”, in M. Pauri (ed.), The Reality of the Unobservable. Dordrecht: Kluwer Publishers, 1999; reprinted in B. Falkenburg (ed.), Between Rationalism and Empiricism: Selected Papers in the Philosophy of Physics. New York: Springer Verlag, 2001, pp. 142–55.