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On Heisenberg's key statement concerning ontology.

In PHYSICS AND PHILOSOPHY: The Revolution in Modern Science, (1) Werner Heisenberg aims, "in a not too technical language," to clarify the "change in the concept of reality manifesting itself in quantum theory."

He means to contribute to an articulation of "the ontology" (not only the "epistemology") that "underlies" quantum theory's "modified logical patterns." (2) To a highly unusual degree, Heisenberg is gripped by a sense of the responsibility of the modern quantum physicist to convey, in language immediately intelligible to the thinking public, his most serious and far-reaching reflections on the metaphysical implications of his scientific work. One may go so far as to say that there is substantial evidence, partly within Physics and Philosophy, that Heisenberg regards such reflections and their public communication as his most important task. Heisenberg is especially apt for this intensely self-conscious contribution to humanity's historical-cultural development because his stature as a principal originating architect of quantum theory at its most fundamental level is complemented by his deployment of an unusually broad and deep erudition in and a lifelong preoccupation with philosophic and artistic ontology from Anaximander through Kant and Goethe to Heidegger. No thinker has yet appeared who possesses such an authoritative combination of the decisively necessary learning in quantum physics and in the historical development of philosophic ontology. Despite a flurry of renewed scholarly interest in the development of Heisenberg's scientific work, (3) and in his complex relation to the dramatic unfolding of German cultural history in his time, (4) there has yet to be executed a sustained and philosophically critical interpretative commentary on this book that is his crucial philosophical-ontological legacy. Given the profound ontological puzzles that continue to attend quantum physics and its implications for humanity's past as well as present and future conception of reality, such a critical exegesis of this text is overdue. In what follows I try to extricate the central nerve of Heisenberg's sinuously unfolding, dialectical exposition, and in the process to elucidate its strengths but also its deep ambiguities and perplexities--which express, I believe, fundamental dilemmas that pervade contemporary ontology.


Heisenberg makes the inviolability of the principle of noncontradiction a cornerstone of his discussion. Unlike Aristotle (5) Heisenberg does not wrestle with the challenge posed by a possible denial of the principle. He understands the nonmathematical articulation of quantum theory to escape what would otherwise be devastating contradictions--most obviously the contradiction in the wave/particle character of the basic entities described by the theory--through Bohr's famous principle of "complementarity" (which Heisenberg closely associates with von Weizsacker's notion of "coexistent states"), combined with Heisenberg's own principle of "potentia," "potentiality," "potentialities." (6)


After a brief introduction, Heisenberg in his second chapter sketches the "history of quantum theory" and in the process begins to explain what he means by "potentia." In 1924 Bohr and his colleagues "tried to solve the apparent contradiction between the wave picture and the particle picture by the concept of the probability wave." The "electromagnetic waves were treated not as 'real' waves" but as "abstract" mathematical descriptions of the "probabilities," in every point in the relevant space, for "the absorption (or induced emission) of a light quantum by an atom at this point." Later this idea of the probability wave was applied more effectively to a much more abstract mathematical wave "in a many-dimensional configuration space that was discovered through the researches of Schrodinger." Heisenberg reinterprets this mathematical "probability wave" in ontological tenus, as signaling a "tendency [Tendenz]" for "a definite happening [einem bestimmten Geschehen]," thus "introducing a remarkable kind of physical reality, standing in the middle between possibility and actuality": "a quantitative version of the old concept of 'dunamis' or 'potentia' in the philosophy of Aristotle." (7)


The third chapter introduces Heisenberg's ontological explanation of the "Copenhagen Interpretation" of quantum theory, centered on Bohr's complementarity concept. (8) The objects of study in quantum physics are grasped in "two pictures" which "are of course mutually exclusive, because a certain thing cannot at the same time be a particle (that is, a substance confined to a very small volume) and a wave (that is, a field spread out over a large space)." (9) But the "two complement one another," and, as such, do not contradict each other--so long as we cling to the awareness that "particle" and "wave" are to be understood as mental pictures, in the human mind: "by playing with both pictures, by going from the one picture to the other and back again, we finally get the right impression of the remarkable kind of reality standing behind our atomic experiments." (10)

Heisenberg takes a big further step when he goes on to raise and to answer the question, entailing what he calls "a real difficulty in" the Copenhagen interpretation: How are we to understand "what happens 'really' in an atomic event? (11) The initial "probability function contains statements about possibilities or better tendencies ('potentia' in Aristotelian philosophy)." It "must be emphasized that the probability function does not itself express a course of events in time." What it "expresses is a kind of tendency to occurrences, the possibility for occurrences or our awareness of occurrences." (12) It is "the observation itself' that "changes the probability function discontinuously, selecting from all possible events the actual one that has taken place." Since "through the observation our knowledge of the system has changed discontinuously, its mathematical representation also has undergone the discontinuous change and we speak of a 'quantum jump'"--which is not to be ascribed to nature, as object of study, so much as to the human mind: when quantum theory is criticized on the grounds that "Natura non fecit saltus," then "we can reply" (says Heisenberg), "that certainly our knowledge can thus change suddenly and that this state of affairs justifies the use of the term 'quantum jump.'" "If we want to describe what happens in an atomic event, we have to realize that the word 'happens' can apply only to the observation, not to the situation between two observations." (13)

Heisenberg is evidently uneasy about a possible overly subjectivist reading of the preceding. The word "happens," he immediately adds, "here characterizes the physical, not the psychical, act of observation" (but can the psychical be disentangled from the physical in an act of observation?! (14)); the transition from the "possible" to the "actual" that has been under discussion "is not connected with the registration of the result in the mind/spirit [Geist] of the observer." "Certainly," Heisenberg expostulates, "quantum theory does not contain properly subjective features, it does not introduce the mind or the consciousness of the physicist as a part of the atomic event." (15)

That these are overstatements (16) becomes clear at the end of this same chapter, where Heisenberg "emphasizes a subjective element in the description of atomic events, since the measuring device has been constructed by the observer; and we have to remember that what we observe is not nature itself but nature as it is exposed to our mode of questioning"--articulated in "the language that we possess." As regards that language, Heisenberg has previously insisted that it is a "misunderstanding" to conclude that because "we must describe our experiments in the terms of classical physics" while knowing that "these concepts do not fit nature accurately," we "should give up the classical concepts altogether." Quantum physics can never cease to depend on "the concepts of classical physics" because those concepts "are just a refinement of the concepts of daily life, and," as such, "are an essential part of the language that provides the presuppositions for all natural science." This reliance on the classical concepts, as derived from the concepts of daily life, is "finally a consequence of the general human way of thinking": "it makes no sense to discuss what could be done if we were other beings than we actually are." In this regard "we must be clear that, as von Weizsacker has formulated it, ... 'nature is earlier than man, but man is earlier than natural science.'" Or as Heisenberg will say in a clarifying repetition a bit later: while "it has been pointed out before that in the Copenhagen interpretation of quantum theory we can describe nature without bringing into this description ourselves as individuals," still, "we cannot disregard the fact that natural science is formed by humans;" natural science "describes and explains nature not simply, as it is 'in itself;" natural science "is rather a part of the interplay between nature and ourselves." (17)

All this implies that ontologically prior to the "remarkable kind of reality" that quantum physics imperfectly articulates as "potentia" are two other, more fundamental, realms of reality. There is in the first place the reality of the human mind and its articulation in language. (18) Then there is the reality of what Heisenberg calls "nature itself' (the "nature" that von Weizsacker characterizes as "earlier than man") which is, as "earlier than man," not directly accessible by natural science (since nature as it is grasped by natural science is filtered through the "interplay with," is "pictured" by, the human mind). "Nature itself' comprises not only the "remarkable kind of reality standing behind our atomic experiments." Equally or more mysterious, "nature itself' as "earlier than man" is the source of the potentiality for mind, including experimental mind, a potentiality that has become more or less fully and stably actualized in humans. (19)


When Heisenberg proceeds in his fourth chapter to explain the historical development of atomic science in pre-Socratic philosophy, his account takes on a dramatic new dimension, whose relation to all that has preceded is puzzling. Suddenly arising at center stage is the concept of "substance" (which has appeared previously only as part of the questionable concept of particle, as "substance confined to a very small volume"). It now transpires that redeploying the pre-Socratic philosophers' concept of "substance" (Substanz), and indeed of "a fundamental substance (Grundsubstanz), a fundamental element (Grundelement), out of which all things are constituted," a "fundamental stuff [Grundstoff]" that "would be infinite, eternal and unchanging, filling the entire world" and that "would be transformed into the various substances that we know from experience," according to "a single fundamental principle [Grundprinzip], " illuminates the meaning and goal or aspiration of today's quantum physics. "Physicists today try to find a fundamental law of motion for matter from which all elementary particles and their properties can be derived mathematically;" this "fundamental equation of motion may refer either to waves of a known type," or "to waves of an fundamentally different character which have nothing to do with the waves of any of the known elementary particles." In the latter case, "all the different elementary particles could be reduced to a fundamental stuff [Grundstoff] which one may call energy or matter," and which "corresponds to the doctrine of Anaximander;" "and I myself am convinced," Heisenberg declares somewhat assertively, "that in modern physics this view is the correct one." "Energy is in fact the stuff from which all elementary particles, all atoms, and therefore all things are made, and energy is that which moves." "Energy may be viewed as the fundamental cause [Ursache] for all change in the world." (20)

Now this obviously raises some big questions about and in relation to what we have heard in the previous chapter. Is not this "fundamental substance," this primal energy, the eternal grounding source of Heisenberg's "potentia."? If or since this substance is the fundamental cause of all things and of all change, must it not be also the cause or source of the human mind? Is not this energy-substance equivalent to "nature itself," or, to borrow Spinoza's expression, natura naturans? But then, is not "nature itself' more accessible than we first were led to suppose? It would seem that in plunging back into the historical roots of science in the pre-Socratics, Heisenberg has reawakened the original desire and goal of the philosophic-scientific mind to make perspicuous the ultimate archai of the whole.

A few pages later in this fourth chapter there is a brief glimpse of Heisenberg's concept of potentiality--in a passage that makes clear how much this concept has now become eclipsed by the concept of fundamental substance. Heisenberg reiterates, now more radically, that the "elementary particles" can not be accurately conceived as fundamental, or even as having existence, strictly speaking: "if one wants to give an accurate [genau] description of the elementary particle--and here the emphasis is on the word 'accurate'--the only description that can be written down" is the probability function. "But then one recognizes that not even the quality of 'being' [Sein] (if that may be called a 'quality') belongs to the elementary particle without qualification;" the particle is only "a possibility or a tendency for being [Sein]." In contrast, on the basis of the theory of relativity's equivalence of mass and energy, "one can say that all elementary particles consist of energy;" "one can therefore consider energy as the fundamental substance, the fundamental stuff, of the world." It has "indeed the essential property belonging to the term 'substance,' that it remains conserved." The results of experimental particle collisions are "the best proof that all particles are made of the same substance: energy." (21)

Heisenberg immediately introduces a major complication, however, in the observation that "modern physics takes a definite stand against the materialism of Democritus, and decides for Plato" who in his Timaeus "combined" mathematical forms with "ideas that were near to atomism." (22) Following Plato, Heisenberg contends that equally or more primordial than energy as fundamental substance is number, as dynamic form of energy: "in today's quantum theory we can scarcely doubt that the elementary particles will finally also be mathematical forms, but of a much more complicated and abstract kind." Yet whereas Plato conceived of "static, geometric forms," "modern" natural science "has since its inception" made "the problem of motion central, including the concept of time in the foundations." "Since Newton, what is unchangeable in physics is not configurations or geometric forms, but dynamic laws." The "equation of motion holds for all times, it is in this sense eternal, whereas the geometric forms, like the planetary orbits, change." Accordingly, "the mathematical forms that express the elementary particles must in the end be solutions of some unchanging law of motion for matter." Heisenberg is aware that there is a certain playfulness in Plato's Timaeus, in its discussion of the mathematical forms, such as "when Plato says, for instance, that the smallest particles of fire are tetrahedrons;" Heisenberg insists that there is no such irony in modern physics: "the statements of modern physics are in some way meant much more seriously than the statements of Greek philosophy." (23)

If, following Heisenberg's pointer, we turn back to Aristotle and consider his mode of thinking, and specifically if we survey the overall movement of the first book of his Physics, we see that Aristotle turned away from his predecessors' worthy but unsuccessful attempts to bring to light the unchanging nature of the "first things" that are the eternal sources or roots, the archai, of all else, and instead embarked on a second sailing which consisted in articulating physical being in the threefold terms of visible forms (eidos), matter or substratum (hyle), and varieties of (particularized) "privation" (steresis) in matter. This "privation" Aristotle conceived alternatively as dynamis or potentia in "matter," (24) and this conception seems at least consanguineous with Heisenberg's notion of "potentia." But Heisenberg, in this fourth chapter, moves in the opposite direction to this Aristotelian movement.

Does this not involve him in some of the deep difficulties that seem to have rebuffed Aristotle? For how will the "final equation of motion of waves" express more than a completion, a tying together under one all-embracing law, of natural science's previous mathematical wave functions--which Heisenberg has declared to be no more and no less than results of the "interplay between nature and ourselves," that is, not "nature itself' but "nature as exposed to our method of questioning"? Is not even or precisely the concept "energy" one of the "classical concepts" that we must remain aware "do not fit nature accurately"? (25)

On the other hand: if we succeed in discovering the unvarying mathematical law according to which energy as "fundamental substance" is eternally in motion, then it would seem that we have discovered the eternal actuality that is the source of all potentiality. This eternal actuality would seem to have to be somehow transhuman, and even transmind (trans-"natural science"). The human success in discovering this mathematical form will be a major event in human history; but the "eternal law" that will thus become, in history, humanly articulated would seem to have to somehow preexist human or mental articulation. It would seem to have to preexist, in some manner, the events of "interplay" between mind-in-history and nature as substance.


Further light is shed on this puzzle as we follow Heisenberg into the next, fifth, chapter--where he critically assesses key aspects of Kant's teaching in the Critique of Pure Reason, Heisenberg focuses his amending critique on Kant's doctrine of causality. (26) Heisenberg stresses that according to Kant, the "law of causality" is a "synthetic a priori judgment"--one of the deeply embedded foundations of the human mind without which we humans cannot coherently order our experience of empirical phenomena. Heisenberg adopts this Kantian teaching, with major modifications. The replacement, by quantum physics, of strict causality with probabilistic causality, at the subatomic level, shows a major incompleteness in Kant's teaching on causality as a synthetic a priori. Heisenberg no sooner states this criticism than he qualifies it. The use of the Kantian law of strict causality is after all essential to quantum theory: "when we carry out an experiment we have to assume a causal chain of events that leads from the atomic event through our apparatus finally to the eye of the observer; ... if this causal chain was not assumed, nothing could be known about the atomic event." So: Kant is in large part vindicated, after all, by the essential practice of quantum physics. Kant's teaching is incomplete but not incorrect. Here Heisenberg returns to the point he forcefully made in the third chapter: "our actual situation in science is such that we do use and we must use the classical concepts for the description of the experiments; otherwise we could not make anything intelligible to ourselves." "The task of quantum theory consists in this: to interpret theoretically the experiments on this basis." (27)

Yet, going even further than Kant, Heisenberg insists that these essential, classical concepts, including above all strict causality, are not only such as to "have only a limited range of applicability;" "the synthetic judgments a priori" have "the character of a relative truth," a truth that is "practical" rather than "metaphysical." Prompted by the great biologist Konrad Lorentz, Heisenberg goes so far as to speculate that even such basic, a priori categories as "what Kant calls our 'pure intuition' of space and time may belong to the species 'man,' but not to the world independently of men; ... but"--Heisenberg draws back--"we are perhaps entering into too hypothetical discussions by following this biological commentary on the 'a priori.'" (28)

Does this not suggest that "substance," especially substance conceived as energy, is a concept that has "the character of a relative truth," pertaining to the human mind as "practical," not "metaphysical?" Heisenberg certainly notes that "Kant took as a priori [the] concept of substance." Heisenberg does not, however, discusses this Kantian doctrine of substance. Heisenberg does introduce Kant's notion of the "thing-in-itself," and confronts Kant's insistence that we cannot conclude anything about the thing-in-itself from the world of perception. Heisenberg demurs: "the thing-in-itself' is for the atomic physicist, if he uses this concept at all, finally a mathematical structure; but this structure is--contrary to Kant--indirectly deduced from experience." This would seem to be a somewhat bashful reassertion of the previous chapter's strong asseveration of the existence of knowable, primal, transhuman "substance." In the present chapter, however--in the presence of Kant so to speak--Heisenberg no longer speaks in terms of his own concept of "substance." (29)


The eclipse of "substance" intensifies in the next or sixth chapter, on "the relation of quantum theory to other parts of natural science." Heisenberg begins his conclusion to this chapter by "looking back to the different systems of concepts that have been formed in the past or may possibly be formed in the future with the goal of finding our way through the world by means of scientific inquiry," and sees "that they appear to be ordered by the increasing part played by the subjective element in the system of concepts." Most emphatically, "quantum theory does not allow a completely objective description of nature." "Even if complete clarity has been achieved" through a mathematical structure covering a body of knowledge, "it is not known how accurately this system of concepts fits reality." (30) And when Heisenberg proceeds to give the reason for this, he opens up a major additional dimension of his ontological reflections, taking us well beyond the Kantian critique of scientific reason.

Heisenberg now declares that mathematical physics is composed entirely of mental "idealizations," that "may be characterized as a part of the human language that has been formed by the interplay between the world and ourselves, a human response to the challenges of nature;" and "in this respect" the mathematical idealizations "may be compared to the different styles of art, say of architecture or of music." This "comparison between the different systems of concepts in natural science with different styles of art may seem outlandish if one views the styles of art as seemingly arbitrary products of the human spirit."--"But are they?" Heisenberg asks. Each artistic "style arises out of the interplay between the world and ourselves, or more specifically between the spirit of the time and the artist." The "spirit of the time is probably as objective a fact as any fact in natural science." "Therefore, the two processes in science and in art are not all so different." If natural science is fully to understand itself and its roots, natural science must give sufficient thought to the historical dimension of human mental reality, and most acutely to the historical dimension of human language as a single whole that is the integral scientific-artistic matrix of the rational human mind: "science and art form in the course of the centuries a human language in which we can speak about the more remote parts of reality;" and "the coherent systems of concepts of science, even as the different styles of art, are only different words or groups of words in this [single] language." (31)

We suddenly see disclosed here a momentous fuller development of what was implied in Heisenberg's crucial earlier statement that "the concepts of classical physics are just a refinement of the concepts of daily life," and are as such "an essential part of the language which forms the basis of all science." If or since daily life with its concepts and language is in a profound sense historical, continually reshaping itself by the ever mutating "spirit of the time," which expresses itself most vividly in art (and religion), we move in the direction of an outlook that would identify the deepest knowable level of reality with the human mind's historically evolving language, expressing mutating concepts of "daily life," as molded by and molding art and religion, as well as science. Heisenberg does qualify the implicit historicism when he adds, about "the spirit of a time," that it "brings out certain features of the world which are even independent of time," and "in this sense can be characterized as eternal." (32) Heisenberg does not here specify, however, what these "eternal" features of the world are, which are disclosed by art and religion as much as by science. Are they sufficient to prevent a slide into historical relativism or relativistic pragmatism? How are they related to the aspiration to discover the "final equation" that is the eternal form of energy? In his 1973 lecture "Tradition in Science," Heisenberg declares that the history of science shows that "we apparently have little freedom in the selection of our problems;" as scientists, "we are bound up with the historical process." This is also true of "the scientific method," which, Heisenberg insists, is historically much more mutating than usually supposed. What is more, "the influence of tradition is perhaps strongest in shaping or passing on the concepts." (33) One begins to wonder whether the science that would study the fundamental dimension of reality that is most knowable to us would not be a philosophic science of the history of the human mind--as artistic and religious, as well as scientific-philosophic. Such a philosophic science of the mind as historical would clarify the evolution of the language and concepts of daily life, and especially of art and religion, viewed as the changing source of the basic categories from which, and in revision of which, refined physics and mathematics develop (and themselves play a major shaping, as well as shaped, role in humanity's historical-linguistic evolution). Heisenberg adumbrates this science in chapter five's brief discussion of the sources, especially theological (or antitheological), of the emergence of mathematical physics. (34)


That physics is able, at any rate in our time, to have a powerful shaping effect on the concepts of daily life, or at least on the accepted scope of those concepts, becomes clear in the next or seventh chapter, sketching the ontological implications of Einstein's theory of relativity. Here Heisenberg introduces again the concept of substance. "The equivalence of mass and energy" has "raised problems concerning very old philosophical questions." This equivalence entails the falseness of the classical proposition that "substance or matter cannot be destroyed." "Does this mean that these older philosophical systems have been disproved by modern experience?" This, Heisenberg responds, "would certainly be a rash and unjustified conclusion, since the terms 'substance' and 'matter' in ancient or medieval philosophy cannot simply be identified with the term 'mass' in modern physics." One may "consider mass and energy as two different forms of the same 'substance' and thereby keep the idea of substance as indestructible." Yet no sooner do we begin to think that Heisenberg is returning to his strong conception of substance, when he disabuses us: "on the other hand, one can scarcely say that one gains much by expressing modern knowledge in an old language; ... the concepts to which the philosophers a long time ago were led through an analysis of their experiences of nature cannot fit phenomena that can only be observed by the elaborate technical tools of our time." (35)

But then this statement is almost immediately qualified in its turn. For the theory of relativity has taught the need to return to "very old philosophic questions": "is space finite or infinite? What was there before the beginning of time? What will happen at the end of time? Or is there no beginning and no end?" These questions, once seriously asked, make it necessary to consider the answers that have been given, not only by the philosophers such as Aristotle and Kant, but by the theologian Augustine--who answers that "time has been created together with the world." Heisenberg observes, "in such statements the word 'created' at once raises all the essential difficulties." For the word "creation, as it is usually understood," means "that something has come into being that has not been before, and in this sense it presupposes the concept of time;" "therefore," Heisenberg concludes, "it is impossible to define in rational terms what could be meant by the phrase 'time has been created.'" This does not by any means lead Heisenberg to dismiss the possibility of a creator God who has created time. It only reinforces Heisenberg's conviction of the limitations of all human language: it "reminds us again of the often discussed lesson that must be derived from modern physics," namely that "every word or every concept, clear as it may seem to be, has only a limited range of applicability." "In the general theory of relativity these questions about the infinity of space and time can be asked"--but only "partly answered on an empirical basis." (36) It would seem that the possibility of a radically mysterious, and even contradictory, divine creation cannot be disposed of by science. (37)

Certainly the theory of relativity does not alter "the fact," to which Kant drew attention, "that the concepts of space and time belong to our relation to nature, not to nature itself; ... these concepts are a priori in some sense"--"they are the condition for and not primarily the result of experience." What appeared "as a great surprise" through the theory of relativity was "the necessity of the change" in these a priori mental concepts, a change brought about by a radically improved experiential-theoretical "interplay" between the human mind and "nature itself." "It was the first time that the scientists learned how cautious they had to be in applying the concepts of daily life to the refined experience of modern experimental science." (38)

At the same time, we also have Heisenberg declaring that the success of the theory of relativity revealed that "the common words 'space' and 'time' refer to a structure of space and time that is actually an idealization and oversimplification of the real structure [wirklichen Struktur]." (39) Does Heisenberg here slip back into conceiving of the space and time disclosed by the theory of relativity as modes of "nature itself," modes of "fundamental substance"? Or does he employ the word "real" here as shorthand for: "the most adequate theoretical-idealized expression that history has yet produced of the interplay between nature itself and the human mind's a priori categories of space and time"?

Heisenberg does indeed seem to be suggesting that as regards the theory of relativity at any rate, the "refined," scientific conception is an improved continuation of, a deepening and broadening of--and not a radical and deeply perplexing break with, not a decline in intelligibility or "reality" from--the concepts of daily life and the derived concepts of classical physics. (40)


That the preceding is not so true, however, of the objects described in quantum theory--that the objects of quantum theory are inferior in ontological status (in "reality") to space and time as described in the theory of relativity--comes to light in the next or eighth chapter, which is devoted to defending the "Copenhagen interpretation" against leading critics, including Einstein. "All the opponents" are in agreement on one crucial point: "it would, in their view, be desirable to return to the reality concept of classical physics or, more generally speaking, to the ontology of materialism," as applicable to the atomic phenomena. In other words, "they would prefer to come back to the idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them." This, Heisenberg insists, "is impossible" or (he hesitates) "at least not entirely possible because of the nature of the atomic phenomena." Arguing against Schrodinger, Heisenberg contends that "the three dimensional matter waves or radiation waves" (of De Broglie) even though they "have a continuous density of energy and momentum, like an electromagnetic field in Maxwell's theory," nonetheless "are just as much and just as little objectively real as the particles." The "ontology of materialism rests on the illusion that the kind of existence, the direct facticity [die Art der Existenz, das unmittelbar Faktische] of the world given around us, can be extrapolated into the atomic range." But "every description of phenomena, of experiments and their results, rests upon language as the only means of communication;" and "the words of this language represent the concepts of daily life, which in the scientific language of physics may be refined to the concepts of classical physics;" these latter concepts "are the only tools for an unambiguous communication about events," including "the setting up of experiments and about their results." Humans therefore encounter an insuperable barrier to their conceiving of the atomic realm. "When therefore the atomic physicist is asked to give a description of what really happens in his experiments," the "words 'description' [Beschreibung] and 'really' [wirklich] and 'happens' [geschieht] can only refer to the concepts of daily life or of classical physics." (41)

At this point we see Heisenberg beginning to make clearer another major dimension of his unfolding ontology. It transpires that "reality, "being," "factual" existence--what "exists" in the full or fullest sense--is to be understood as the realm constituted by the interplay between "nature itself' and the human mind in its natural capacity for articulateness through language rooted in daily life or common sense. It is on this basis that Heisenberg now stresses that "the Copenhagen interpretation of quantum theory is in no way positivistic": "for, whereas positivism is based on the sensual perceptions of the observer as the elements of happening [Geschehen], the Copenhagen interpretation regards things [Dinge] and processes [Vorgange] which are describable in terms of classical concepts, that is, the factive," as "the foundation of any physical interpretation." (42)


As we learn in the next or ninth chapter, on quantum theory and the structure of matter, this does not mean that Heisenberg abandons the concept of fundamental substance. Despite all limitations on the human mind's capacity to penetrate the subatomic level, he is convinced that experimental results have already produced "the final proof for the unity of matter," showing that "all the elementary particles are made of the same substance [Substanz], of the same stuff [Stoff], which" (he adds) "we may now call energy or universal matter": Heisenberg now problematizes or qualifies his earlier use of the word "energy." Here for the first time Heisenberg brings together his contrapuntal concepts of fundamental "substance" and the retrieved Aristotelian "potentia." He explains that in speaking of "substance" he has in mind Aristotle's concept of hyle or "matter [Stoff]" as distinguished from "form." But for Aristotle, as Heisenberg understands him, matter is "essentially 'potentia,' that is, possibility [Moglichkeit];" by comparison, in "our energy concept," energy "emerges into appearance as material reality through the form [tritt als materielle Realitat durch die Form in Erscheinung]," according to "the mathematically formulated natural laws" that "determine the forms of matter, i.e., the elementary particles and their forces." (43)

Heisenberg is not daunted by the discouraging state of affairs which he immediately proceeds to confess: there are baffling mathematical contradictions between the quantum mechanical, mathematical, account of "the natural laws that determine the 'forms' of matter," and the mathematical formulas of the theory of relativity. "Any theory which tries to fulfill the requirements of both special relativity and quantum theory will lead to mathematical inconsistencies"--"arbitrarily high momenta and energies must occur with overwhelming probability." Heisenberg lives in the "hope" that future research "will someday lead to a complete understanding of the unity of matter": and this expression, "complete understanding" would mean, he explains, "that the forms of matter--in the sense something like the way Aristotle in his philosophy used the term--would appear as results, that is, as solutions, of a closed mathematical scheme representing the natural laws for matter." (44)


The next, penultimate chapter, on "language and reality in modern physics," makes clearer the limited, because prehuman, kind of reality (45) of this fundamental energy-substance that has the potentiality to appear to the human mind as mathematically formed particles and their forces. That which is most real, that which is the "actual event," the "fact," in quantum physics is the directly observed changes in the measuring apparatuses of experiment, observations perfectly articulable in everyday language--"for instance, the black spots on a photographic plate or the water droplets in a cloud chamber." (46) "It belongs to the concept 'fact' that it can be described in ordinary language." "Even for the physicist, the description in ordinary language will be a criterion of the degree of understanding that has been reached." "In the experiments" about atomic events, "we have to do with things and facts, with phenomena that are just as real as any phenomena in daily life." In contrast, "the atoms or the elementary particles are not as real;" they "form a world of tendencies or possibilities rather than one of things and facts." "Physicists have gradually become really accustomed to considering the electron orbits, and similar concepts, not as a reality but rather as a kind of 'potentia.'" Bohr's concept of complementarity has "encouraged the physicists to use an ambiguous rather then an unambiguous" language, "alternating the application of various classical concepts which would lead to contradictions if used simultaneously." To conceive of subatomic "electron orbits, matter waves and charge density, energy and momentum, etc." as "potentia" is to employ a language that "produces pictures in our thinking, but together with them the feeling, that the pictures have only an unclear connection with reality, that they represent only the tendency toward a reality." (47)


Heisenberg takes a final step in his concluding chapter, on "the role of modern physics in the present development of human thinking." His use of the word "development" (Entwicklung) signals a return to the fundamental dimension of reality that is "History": that is, human mentality as historically unfolding. What Heisenberg now spotlights is the paradoxical recognition that the concepts of daily life or common sense are less mutable than modern scientific concepts--even as, and precisely because, the concepts of daily life are integrated into a much more comprehensive framework than modern scientific concepts. "One of the most important features of the development and the analysis of modern physics" is the "experience" that "the concepts of ordinary language, vaguely defined as they are, seem to be more stable, in the expansion of knowledge" than are "the precise terms of scientific language." On reflection, "this is in fact not surprising." For scientific language is to a much greater degree than ordinary language not only "derived from an idealization," but, what is more, from an "idealization" that is based on "only limited groups of phenomena." In sharp contrast, "the concepts of natural language [as Heisenberg now calls the language of common sense] are formed by the immediate connection with the world; they express reality," in its genuine wholeness--even though, or precisely inasmuch as, they "undergo changes in the course of the centuries, just as reality itself undergoes changes." As "natural language," however, "they never lose the immediate connection with reality." To be sure, the scientific concepts are "idealizations" with "precise definitions" that make possible the connection with a "mathematical scheme;" but "through this process of idealization," the "immediate tie with reality is lost." This is the price scientific concepts must pay for their "very close" correspondence "to reality in that part of reality which had been the object of research." (48)

What Heisenberg has in mind becomes more specific and concrete when he attacks "the nineteenth century" for having "developed an extremely rigid frame for natural science" (from which frame we have been liberated, thanks in no small measure to quantum theory (49)): "this frame was so narrow and rigid that it was difficult to find a place in it for many concepts" that "belong to ... the very heart [of] our language"--"for instance, the concepts mind [Geist], the human soul, or life." "On the basis of the experience of modern physics" we recognize that "our attitude toward such general concepts as mind [Geist], the human soul, life, God must be different from that of the nineteenth century, since these concepts belong to the natural language and have therefore immediate connection with reality." "The general trend of human thinking in the nineteenth century had been toward [a] general skepticism with regard to those concepts of ordinary language--for instance, those of religion--which do not fit into the closed frame of scientific thought." "Modern physics" has admittedly "in many ways enhanced this skepticism." But "it has at the same time turned" skepticism "against the overestimation of precise scientific concepts themselves," and "against a too optimistic view on progress in general, and finally against skepticism itself." Modern physics and especially quantum theory has brought home to us that "existing scientific concepts cover always only a very limited part of reality, and the other part that has not yet been understood is infinite." We now "know" that "any understanding must rest finally upon ordinary language because it is only there that we can be certain to touch reality." (50)

Yet ordinary language and the concepts of daily life manifest profound internal conceptual problems of their own. Recognizing that his Anglo-American audience, whose mind and language have been historically shaped and prejudiced by the reigning liberal democratic culture, will resist, Heisenberg nevertheless insists that "we cannot close our eyes to the fact that the great majority of people can scarcely have any well-founded judgment concerning the correctness of certain important general ideas or doctrines" that constitute the moral and cultural foundations of every society. The word "belief' can "for this majority" not mean "perceiving the truth," but only "making this the basis for life." What is more, "in the practical decisions of life it will scarcely ever be possible to go through all the arguments in favor of or against": therefore, all the "most important decisions in life," including especially society's fundamentally constitutive civic, moral, and cultural decisions, "must always contain this inevitable element of irrationality." (51) Science in its essence, and not least the intransigently rationalist (Socratic) science that directly and critically analyzes the most accessible dimension of reality--the historically developing "concepts of daily life"--inevitably unveils the pervasive "irrationality" in those concepts, and thus dangerously shakes the spiritual foundations of its own as well as other civic cultures. This profoundly dangerous antagonism between the public practice of science and its historical matrix has led to the assertion that science must be "esoteric [esoterisch]"--the "problem of the 'twofold truth' that in the history of Christian religion in the late Middle Ages is encountered again and again." "In our time," Heisenberg avows, the "problem is still essentially the same;" for it is a "problem that has belonged to human life through all times." (52) Here again Plato proves to be a guide and indeed to provide a model of scientific life lived in keen and beleagured awareness of this problem. As Heisenberg declares elsewhere, "if we may take our cue [from] Plato's dialogues, the unavoidable limitations of our means of expression were already a central theme in the philosophy of Socrates; one might even say that his whole life was a constant battle with these limitations." (53)

University of Texas at Austin

(1) Werner Heisenberg, Physics and Philosophy: The Revolution in Modern Science, trans., A. J. Pomerans (New York: Harper, 2007); originally delivered as the Gifford lectures 1955-56 and published 1958; hereafter Physics and Philosophy. References will be to pages of this edition with corrections of the translation on the basis of the German original: Physik und Philosophie (Stuttgart: Hirzel, 1959); reproduced in Werner Heisenberg Gesammelte Werke, vol. 2, ed. Walter Blum et al. (Munich: Piper, 1984); where needed, equivalent page numbers of the latter will be indicated after an equals sign.

(2) Heisenberg, Physics and Philosophy, 2-3, 22, 158-59.

(3) Most notable among which is Kristian Camilleri, Heisenberg and the Interpretation of Quantum Mechanics (Cambridge: Cambridge University Press, 2009)--who characterizes his book as "but a first step in exploring Heisenberg's overall world view," since it does not address "the central task of Heisenberg's physics after 1950" (10; compare 13; Camilleri does not treat Heisenberg's ontological thought until the last few pages). David Cassidy's intellectual biography, Uncertainty: The Life and Science of Werner Heisenberg (New York: W. H. FYeeman, 1992) treats in astonishingly cursory fashion Heisenberg's "systematic philosophical pronouncements." See 46-47, 190, 209, 226, 255, 257 (contrast 275), 447-50, 543-44. For many years the most fertile study was Patrick Heelan's Quantum Mechanics and Objectivity: A Study of the Physical Philosophy of Werner Heisenberg (The Hague: Martinus Nijhoff, 1965). I agree with Camilleri (Heisenberg and the Interpretation, 9-10) that Heelan assesses Heisenberg too much with a view to a rather polemical articulation of Heelan's own outlook (rooted in Lonergan), and overstates Heisenberg's Kantianism (though Heelan seems to qualify this slightly in his later "Heisenberg and Radical Theoretic Change," Zeitschrift fiir allgemeine Wissenschaftstheorie 6, no. 1 [1975]: 113-36, at 125-26).

(4) Most notably Cathryn Carson, Heisenberg in the Atomic Age (Cambridge: Cambridge University Press, 2010).

(5) See Aristotle, Metaphysics, 1005b35-1009a38.

(6) Heisenberg, Physics and Philosophy, 7, 17, 23, 24, 26, 155-56, 159; on the problematic basic contradiction between wave and particle, see also Heisenberg's Physical Principles of the Quantum Theory, trans. C. Eckart and F. C. Hoyt (Chicago: University of Chicago Press, 1930), 11, 47. In the purely mathematical formulations, no contradictions appear: once Schrodinger "was able to prove that his formalism of wave mechanics was mathematically equivalent to the earlier formalism," of Heisenberg's "matrix mechanics," which treats the phenomena as discrete particles, "one finally had a mathematical formalism freed from contradiction [wiederspruchsfrein], which could be defined in two equivalent ways." "But," Heisenberg at once adds, "in what sense did the new formalism really describe the atom. The paradoxes of the dualism between wave picture and particle picture were indeed not solved; they were only hidden somehow in the mathematical scheme." Physics and Philosophy, 13-14 (=22); see also 24.

(7) Heisenberg, Physics and Philosophy, 14-15 (=23-24); see also 117 and Heisenberg, Physics and Beyond, Encounters and Conversations, trans. A. J. Pomerans (New York: Harper, 1972), 122-23: "the mathematical symbols with which we describe such observational situations represent possibilities rather than facts." Kurt Riezler, to whom Heisenberg does not refer, had previously insisted that quantum physics would remain unintelligible until it reinterpreted what was described by the probability waves in terms of (a somewhat Heideggerized) Aristotelian concept of Being as potentiality and event: Physics and Reality (New Haven: Yale University Press, 1940), esp. 44-45, 80, 100.

(8) Heelan, Quantum Mechanics: ix-x, 44, 48, 53, 134, insisted on a gulf between the outlook of the "empiricist and positivist" Bohr and "the most metaphysical," the "idealist," Heisenberg. The latter, replying directly to Heelan's later article, politely but firmly denied any such gulf: Heisenberg, "Comments to Heelan's Thesis," Zeitschrift fur allgemeine Wissenschaftstheorie 6, no. 1 (1975): 137. The insistence on a gulf has nonetheless continued, most recently by Carson and by Camilleri, the latter of whom unearths "hidden differences" that were "buried within Heisenberg's carefully worded exposition" through perhaps "deliberate obfuscation" (Heisenberg and the Interpretation, 7, 117: the notion of "deliberate obfuscation" is strongly advanced by Mara Beller, Quantum Dialogue: The Making of a Revolution (Chicago: University of Chicago Press, 1999)).

(9) Here, Heisenberg is referring not to the abstract mathematical probability waves in a multi-dimensional configuration space, but rather to the three dimensional field waves--for example, light waves (see also his response to Schrodinger, Physics and Philosophy, 117).

(10) Ibid., 23 (=32), my italics; see also Heisenberg, Physical Principles, 10 and 64-5.

(11) Heisenberg, Physics and Philosophy, 24. See also Heisenberg's autobiographical recollections of Einstein's question to Heisenberg: "but what happens during the emission of light ... and Schrodinger's insistence that "we must ask ourselves how precisely the electron behaves during the jump;" "it ought to be possible to determine in principle how" electrons behave "during the transmission from one state to the next." Physics and Beyond, 67 and 74.

(12) If we follow Heisenberg's pointer to Aristotle, we may say that the "the remarkable kind of reality standing behind our atomic experiments" manifests a passive potentiality to manifest itself as particle or as wave, a potentiality which is actualized by the active potentiality in the human being as theorizing experimenter: Aristotle, Metaphysics, 1019al5-23 and 1046al2-14; contrast Heelan, Quantum Mechanics, 152.

(13) Heisenberg, Physics and Philosophy, 20 (=29); 23 (=32); 27-28 (=36-38); prefigured in Riezler, Physics and Reality, 44.

(14) See David Bohm, "Classical and Non-classical Concepts in the Quantum Theory: An Answer to Heisenberg's Physics and Philosophy," British Journal for the Philosophy of Science 12 (1962): 265-80, at 268-69.

(15) Heisenberg, Physics and Philosophy, 28-29 (=38-39).

(16) Contrast the view taken by Henry P. Stapp, Mind, Matter, and Quantum Mechanics (New York: Springer, 2004): especially 127, 150. In his later Mindful Universe, 2nd ed. (New York: Springer, 2011) Stapp makes it clear that he is assimilating Heisenberg to Whitehead.

(17) Heisenberg, Physics and Philosophy, 30 (=39-40), 32 (=41), 55 (=66); see also Heisenberg, Physical Principles, 1-3, 11, 65, and The Physicist's Conception of Nature, trans A. J. Pomerans (London: Hutchinson, 1958), 25, 29, as well as the prefiguration in Riezler, Physics and Reality, 27-28.

(18) We soon begin to learn that Heisenberg doubts that the human mind can be adequately explained or described on the basis of physics and chemistry: Physics and Philosophy, 54-55, 78-80, 171; see also Physics and Beyond, 114; but compare Physics and Philosophy, 65.

(19) Heisenberg, Physics and Philosophy, 23 (=32), 32 (=41).

(20) Ibid., 34 (=44), 35-37 (=45-47); on substance see also Riezler, Physics and Reality, 68.

(21) Heisenberg, Physics and Philosophy, 44-45 (=55-56).

(22) See also especially "Platons Vorstellungen von den kleinsten Bausteinen der Materie und die Elementarteilchen der modemen Physik," in

Gesammelte Werke, vol. 1, 394-97; and "Natural Law and the Structure of Matter," op. cit., vol. 2, 362-68.

(23) Heisenberg, Physics and Philosophy, 41 (52), 45-46 (=55-56), 48 (=60).

(24) Aristotle, Physics, 191b27-29 and context; On Coming into Being and Passing Away, 1.3.

(25) Heisenberg, Physics and Philosophy, 30 (=39-40); and see 153 (=173): "one speaks" about "energy and momentum etc., always conscious of the fact that these concepts have only a very limited range of applicability." Consider also Heisenberg's critique of Bohm at ibid., 104.

(26) Riezler observes at Physics and Reality, 42-43, that discussions of quantum physics tend to "mix up the principium rationis [principle of sufficient reason, elaborated by Leibniz] with the law of causality [spotlighted skeptically by Hume]." The latter, as Heisenberg stresses, is violated by the experimental evidence underling quantum physics; but--as Riezler insists--the

the former, which is more fundamental and is at home in mathematics and hence mathematical physics, is not violated by quantum physics. Heisenberg moves in this "Riezler" direction in "Grundlegende Voraussetzungen in der Physik der Elementarteilchen," in Martin Heidegger zum siebsigsten Geburtstag: Festschrift (Pfullingen: Neske, 1959), 291-97, at 295.

(27) Heisenberg, Physics and Philosophy, 30 (=40), 62, 64 (=76-77); see also Physics and Beyond, 122.

(28) Heisenberg, Physics and Philosophy, 64-65 (=76-78).

(29) Ibid., 62, 65.

(30) Ibid., 23 (=32), 80-82 (=94-96); see similarly Physicist's Conception, 15 and "Grundlegende Voraussetzungen," 291.

(31) Heisenberg, Physics and Philosophy, 82-83 (=96-98).

(32) Ibid., 30, 83 (=98); see also Physics and Beyond, 124. Camilleri's stress on what he calls "the linguistic turn in Heisenberg's thought" fails to recognize adequately the implications of this "turn" for the ontological importance of History; and this failure may be due to an underestimation of the influence of Heidegger, and an overestimation of the influence of non-Heideggerian philosophy of language. Camilleri, Heisenberg and the Interpretation, ch. 8. On Heisenberg's complex relations with Heidegger, see Carson, Heisenberg in the Atomic Age, 89-91, 453-54.

(33) Heisenberg, Tradition in Science (New York: Seabury Press, 1983), 118. Consider the remarkably "perspectivalist" statement of a leading contemporary quantum physicist, Brian Greene, in his Fabric of the Cosmos (New York: Vintage, 2005), 224-25: "When you encounter a proposed law of nature, a natural question to ask is: Why this law?" The fact that it enables "predictions that have been repeatedly confirmed" is "one important answer," but "it leaves out something important": "physicists also believe these theories are on the right track because, in some hard-to-describe way, they feel right, and ideas of symmetry are essential to this feeling." It "feels right that no location in the universe is somehow special;" it "feels right that no particular constant-velocity motion is somehow special;" and "so the symmetries of nature are not merely the consequences of nature's laws"--they are "compelling;" they are, "from our modern perspective," the "foundations from which laws spring." Herbert Dingle, in his 1953 Presidential Address before

the Royal Astronomical Society acidly observed: "In every age there is a certain climate of opinion that predisposes thinkers towards a certain type of view.... Now it is the exceptional that is out of favor. By a sort of cosmic democracy we are predisposed to deny any unique characteristic to anything." Quoted in Helge Kragh, Higher Speculations: Grand Theories and Failed Revolutions in Physics and Cosmology (Oxford: Oxford University Press, 2011), 130.

(34) Heisenberg, Physics and Philosophy, 53; see also Heisenberg's "On the History of the Physical Interpretation of Nature," in Philosophic Problems of Nuclear Science, trans. F. C. Hayes (London: Faber and Faber, 1953); and Part Two of The Physicist's Conception of Nature, trans. A. J. Pomerans (London: Hutchinson, 1958).

(35) Heisenberg, Physics and Philosophy, 93 (=109-10).

(36) Ibid, 97-99 (=114-16).

(37) See also the autobiographical recollection of Niels Bohr's remarks as follows: "when we speak of divine intervention, we quite obviously do not refer to the scientific determination of an event, but to the meaningful connection between this event and others or human thought. Now this intellectual connection is as much a part of reality as scientific causality; it would be much too crude a simplification if we ascribed it to the subjective side of reality." Heisenberg, Physics and Beyond, 91; also 213, 215.

(38) Heisenberg, Physics and Philosophy, 101.

(39) Ibid., 88 (=104), my italics.

(40) Contrast, however, Heisenberg's autobiographical account of the difficulty he found in truly understanding the concept of time in relativity theory: "the mathematical framework of relativity theory caused me no difficulties, but that did not necessarily mean that I had 'understood' why a moving observer means something different by 'time' than an observer at rest. The whole thing baffled me, and struck me as being quite 'incomprehensible.'" He continues: "you might even say that I have grasped the theory with my brain, but not yet with my heart." Physics and Beyond, 29.

(41) Heisenberg, Physics and Philosophy, 103 (=120), 117-19 (=133-36).

(42) Ibid., 119.

(43) Ibid., 134 (=151); this crucial formulation leaves unexpressed the precise ontological status of what is conceived as the "field" of energy and the "waves" undulating in it. See also ibid., 20, 27, 154-55.

(44) Ibid., 134-36, 140 (=159); see also "Grundlegende Voraussetzungen," 291.

(45) The fashionable category "realism," when applied to Heisenberg (for example, Alisa Bokulich, "Heisenberg Meets Kuhn: Closed Theories and Paradigms," Philosophy of Science 73, no. 1 [2006]: 90-107), blurs subtle and essential distinctions. Camilleri's attempt to deny that Heisenberg's concept of potentia involves a "foray into metaphysics" goes together with a rather amazing silence on Heisenberg's extensive discussion of his concept "substance."

(46) Elsewhere Heisenberg stresses that the "path of an electron in a cloud chamber" is not observed as "an infinitely thin line with well-defined positions and velocities;" on close inspection what is observed is "a sequence of points which were not too well defined by the water droplets." "Development of Concepts in the History of Quantum Mechanics," in Tradition in Science, 29.

(47) Heisenberg, Physics and Philosophy, 142 (=161), 153 (=172-73), 155 (=175), 160 (=180); emphasis mine.

(48) Ibid., 171 (=191-92), 174-75 (=194-95); see also 54, 78-80.

(49) See similarly Riezler, Physics and Reality, 25.

(50) Heisenberg, Physics and Philosophy, 174-76 (=195-96).

(51) Ibid., 178-79 (=199).

(52) Ibid., 115 (=131-32); see also Physics and Beyond, 246.

(53) Heisenberg, "Natural Law and the Structure of Matter," 376 and context.

Correspondence to: Thomas L. Pangle, Dept, of Government, University of Texas 158 W. 21st St., STOP A1800, Austin TX 78712-1704.
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Title Annotation:Werner Heisenberg
Author:Pangle, Thomas L.
Publication:The Review of Metaphysics
Article Type:Essay
Date:Jun 1, 2014
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