49

p The terms ’Copenhagen school’ and ’Copenhagen interpretation’ are usually employed to denote a certain community of physical and philosophical views typical for that trend in modern physics represented by Niels Bohr, Werner Heisenberg, and other scientists. This school advanced new fundamental ideas relating to quantum theory that arose from discovery of the corpuscular properties of fields and the wave properties of matter, discoveries that classical physics could not explain.

p The philosophical views of the physicists of the Copenhagen school used to coincide on the whole with the line of positivism, but it would now be wrong to characterise them in that way. The influence of positivism among the Western scientists has diminished considerably in recent years. As we have already mentioned, Bohr, Heisenberg, and Born have spoken out against positivist trends in science. 50 Probably only P. Jordan, among the distinguished members of the Copenhagen school, now clings to positivist dogmas.

p The Western physicists who have opposed positivist philosophy in their latest works hold essentially different ideological points of view, though this difference is not too clear on a number of matters and rather resembles a trend. Niels Bohr, for instance, made a definite advance towards a materialist approach to quantum mechanics. Heisenberg, on the contrary, inclined in his objections to positivism towards views close to Plato’s objective idealism. Max Born has spoken out particularly sharply against positivism.

p In this section we shall discuss the evolution of the philosophical views of quantum theory shared by the leaders of the Copenhagen school, Niels Bohr and Werner Heisenberg. The facts given below witness to the bitter philosophical struggle in modern science and oncej more demonstrate that materialist dialectics is at the centre of the philosophical issues of modern physics. Without in any way giving a full picture of the evolution of the Copenhagen school’s philosophical ideas we shall touch simply on how Bohr and Heisenberg treat the problem of reality in quantum theory.

p As we have seen, the Copenhagen school essentially faced the problem of giving meaning to, i.e. expressing in physical concepts, the objective dialectics of atomic processes.

p Were they successful in doing so? History indicates that this problem was frequently resolved by physicists in spite of their personal philosophical inclinations. Because of certain circumstances, above all social factors, many physicists of the Copenhagen school either ignored dialectical materialism or directly opposed it.

p The ambivalence of the Copenhagen interpretation was already there in embryo in Heisenberg’s formulation of the task of quantum theory. ’ Our actual situation in science is such,’ he said, ’that we do use the classical concepts for the description of the experiments, and it was the problem of quantum theory to find theoretical interpretation of the experiments on this basis.’^^44^^

p This problem was resolved by adherents of the Copenhagen interpretation by introducing the idea of the uncontrollability in principle which can be formulated as follows: in order to employ classical concepts without 51 contradictions in the description of atomic experiments, the interaction between the atomic object and the measuring instrument was regarded as uncontrollable in principle.

p The term ’uncontrollable interaction’, taken in its literal sense, is wrong: all phenomena of nature are cognisable and hence controllable in principle. This philosophically erroneous term expresses the truth that modern physics has discovered new forms of matter and motion (for which the notions of classical physics about matter and motion proved to be narrow); that the objectively real connections are much more diverse than it was admitted by classical theories; that the laws of microphenomena cannot be reduced to those of classical mechanics, i.e. the latter are not absolute. This truth could not be philosophically comprehended by physicists who were not conscious adherents of materialist dialectics, and contemporary positivism played up the term ’uncontrollable interaction’ in the spirit of subjectivism.

p The idea of uncontrollability in principle led to idealist and metaphysical philosophical conclusions that were supposedly confirmed by quantum mechanics but in reality had nothing in common with its scientific content.

p A philosophically erroneous thought was associated with this idea, to the effect that one could only employ the concept of objective reality in classical physics in the sense that nature existed independently of the human mind; in quantum theory, however, the situation was such that the atomic object allegedly had a different ’degree of reality’ than the macroscopic instrument.

p The idea of uncontrollability in principle replaced the problem of the dual particle-wave nature of atomic objects by that of whether the experimenter could decide which properties were manifested and which eliminated during observation, by selecting one method of observation or another.

p The idea of the uncontrollability in principle did not, in fact, break with the notion of an atomic object as a particle in the classical sense. An atomic object was represented as possessing both classical position and classical momentum, which could not be cognised simultaneously because of the uncertainty relation. This relation was in fact converted into a kind of agnostic enigma, and the problem of qualitatively new quantum concepts (compared with 52 classical ones) was completely excluded from atomic physics.

p The materialist criticism of the Copenhagen interpretation was directed mainly against the idea of uncontrollability in principle, which was counterposed to the idea of unity of the opposite corpuscular and wave properties of matter and fields. Among the papers devoted to this issue we would cite that of V. A. Fock, A Critique of Bohr’s Views on Quantum Mechanics,*^^6^^ in which he justly drew attention to the fact that there cannot in general be any fundamentally uncontrollable interaction. When speaking about uncontrollability in principle, Bohr essentially considered the question not of the impossibility of full analysis of the interaction between object and measuring instrument but of this interaction being expressed in the admitteily incomplete language of classical mechanics. From the v ry beginning he formulated an unresolvable problem: to iollow the simultaneous changes of the position and momentum of an atomic object while remaining faithful to classical mechanics. When, however, it proved that this was impossible, the result was ascribed not to the wave properties of matter but to the presence of supposedly uncontrollable interaction between the object and the instrument. Fock said this approach to the problems of quantum theory was an echo, perhaps, of the long abandoned view that position and momentum were always ’in reality’allegedly characterised by certain values, but because of some whim of nature would not be observed simultaneously.

p Bohr needed the concept of uncontrollability in principle in order to hide the logical inconsistency resulting from the concepts of classical mechanics being used outside their field of applicability. The introduction of this idea into quantum theory once more confirmed the profound correctness of Lenin’s words: ’It is mainly because the physicists did not know dialectics that the new physics strayed into idealism.’^^46^^

p The development of the physics of the microworld and the discovery of the contradictory and yet united opposite aspects of the micro-objects coincided with a very heightened wavering of some scientists between idealism and dialectical materialism. The discovery of the wave properties of matter and corpuscular properties of a field, i.e. discovery of the fact that matter and field have a dual particle-wave 53 nature, stimulated scientists’ recognition of dialectical contradictions in natural phenomena. Many physicists, including those whose philosophical views diverged from Marxism, began to talk about dialectics. But, through ignoring materialist dialectics they were unable to explain the contradictory nature of micro-particles or to understand the objective character of the contradictions. In that lay the source of their idealist errors.

p Wolfgang Pauli, for instance, agrees to apply ‘dialectical’ to the joint play (Zusammenspiel, his expression) of the typical aspects of the Copenhagen interpretation of quantum mechanics^^47^^; his interpretation of the dialectic nature of atomic phenomena in accordance with the idea of the fundamentally uncontrollable interaction between the instrument and the observed system is, however, subjectivist.

p When Heisenberg discusses the relations between various philosophical systems, on the one hand, and quantum theory, on the other, he finds that ’the theory of knowledge analysis of quantum; theory, moreover, especially in the form Bohr gave it, contains many features that resemble the methods of Hegelian philosophy’.^^48^^

p All modern physics and its theoretical foundations are riddled with dialectical contradictions. The opponents of dialectical materialism, however, try to draw the unjustified conclusion from their existence that there can allegedly be no objective meaning independent of the human mind in physics’ concepts and statements, as if truth were something conditional, determined simply by the point of view of one researcher or another, and erroneously state that the concept of objective reality should be revised in the light of the new discoveries in physics. This is the main line of reasoning of all contemporary positivism and ‘physical’ idealism, whatever ‘scientific’ terminology their spokesmen hide behind.

p The very essence of modern positivism and idealism excludes recognition that there are contradictions inherent in every object and phenomenon in the material world, that the concepts reflecting matter, which develops through contradictions, must necessarily be flexible, mobile, and relative, united in their opposites, and that dialectical logic with its mobile categories is incomparably more definite, consistent, and convincing than formal logic with its invariable categories.

54

To cognise all nature’s phenomena as they are, without subjectivist and other idealist additions, means to cognise them as a unity of opposites. This also applies to the problem of reality in quantum theory. Physicists approach this problem in exactly such a dialectical way, although many of them gropingly, spontaneously, inclining towards idealist and metaphysical views. This is obvious, in particular, from the facts of the evolution of the Copenhagen interpretation.

p Let us consider Bohr’s essay Quantum Physics and Philosophy again, in which, as we know, he presents the conception of complementarity without the idea of ’ uncontrollable interaction’. In this exposition complementary concepts (particle and wave, position and momentum) are juxtaposed in the form of an antinomy which is then resolved. Such a juxtaposition always played a decisive role in Bohr’s conception. Let us dwell on the antinomy of complementarity in greater detail.

p We introduce this expression here in order to stress the definite similarity between Kant’s antinomies and the concept of complementarity.

p An antinomy asserts two mutually exclusive, opposite judgments about the same object, each of them (thesis and antithesis) being stated with the same necessity. As we have remarked more than once, employment of the corpuscular and wave concepts of classical physics to describe atomic objects created contradictions in physical theory; those contradictions could be given the form of antinomies. Bohr demonstrates this convincingly when discussing numerous concrete examples in his work. Let us take one of them.

p ’If,’he writes, ’a semi-reflecting mirror is placed in the way of a photon, leaving two possibilities for its direction of propagation, the photon may either be recorded on one, and only one, of two photographic plates situated at great distances in the two directions in question, or else we may, by replacing the plates by mirrors, obser", e effects exhibiting] an interference between the two reflected wave-trains. In any attempt of a pictorial representation^ of a behaviour of the photon we would, thus, meet with the difficulty: to be obliged to say, on the one hand, that the photon always chooses one of the two ways and, on the other hand, 55 that it behaves as if it had passed both ways. ’^^49^^ Bohr sees the way out of this difficulty in the conception of complementarity. One should not, in his view, isolate the behaviour of the photon in itself from the conditions in which the phenomenon takes place: in some experimental conditions it will behave as a particle, in others as a wave.

p If we consider the application of the concept of complementarity, or rather the arguments about it employed in individual cases as they are presented in the literature, we can see quite clearly that both the conclusion and the premises contain mutually exclusive statements about one and the same thing which are formulated with the identical necessity. For example, the conclusion obtained in the imaginary experiment with a microscope for gamma-rays (a description of this imaginary experiment can be found in many publications on quantum mechanics), namely, that the greater the accuracy of the determination of the electron’s position the lower is the accuracy of the determination of its momentum, means essentially that the electron possesses both the property of a particle and the opposite property of a wave. But this latter is also confirmed by the fact that in[the^rcorresponding reasoning the essence of quantum mechanics is expressed by the formula p = hk/2n, where p is the momentum of the micro-object, h is Planck’s constant, and k is the wave vector. This formula demonstrates that both particle and wave quantities apply to the same micro-object, since p characterises a point particle, and k a spatially infinite sinusoidal wave. Each of these mutually exclusive statements about the micro-object corresponds to the experiment.

p The same must be said about complementarity as such, regardless of the individual forms in which the idea of it is employed. When it is said that the study of so-called complementary phenomena requires mutually exclusive experimental conditions and that only the whole totality of these phenomena can provide complete knowledge of an atomic object, this means, as a matter of fact, that from the standpoint of complementarity we can express two mutually exclusive opposing opinions about one and the same atomic object which would be equally correct.

p Thus, when the contradiction between the particle and wave concepts as applied to atomic objects is resolved, the complementarity principle emphasises the cognoscibility 56 of the atomic world and not Kant’s point of view, who, in ‘resolving’ his antinomies in his own way, introduced the unknowable ‘thing-in-itself’.  [56•* 

p And yet Bohr’s complementarity principle does not finally resolve the problem of particle-wave dualism. According to his ideas, the contradiction between the particle and wave properties of atomic objects is supposedly frozen in the form of an opposition of two classes of mutually exclusive experimental situations with which the ’complementary phenomena’ are associated. The true solution of the ’ antinomy of complementarity’, however, consists in considering the particle and wave properties of an atomic object as a unity of opposites. That is why quantum theory concepts reflecting the dual nature of atomic objects must differ qualitatively from classical ones.

p The drawback of the complementarity principle in Bohr’s exposition of it, namely that it concentrates attention mainly on going into the limitations of the old classical concepts instead of on philosophical comprehension of the new concepts introduced by quantum mechanics, stems from the weakness noted above. This was very clearly demonstrated by V. A. Fock: ’Bohr does not say what these new primary concepts are (physical, visualisable, pictorial and not simply symbolic) that should replace the classical ones, and does not emphasise the unlimited possibilities of making the description of atomic objects more precise by means of new concepts. For not only do the limitations proper to the description of phenomena ’in themselves’ in isolation from the means of observation (‘complementarity’) have philosophical significance but also the constructive part of quantum mechanics and the new primary concepts associated with it.’^B0

p Complementarity is undoubtedly a form of dialectical contradiction and, as Bohr, his supporters and followers who 57 developed his ideas have pointed out, the logic of this dialectical contradiction is also the logic of the development of atomic physics.

p From the angle of the questions discussed above Heisenberg’s Physics and Philosophy also presents great interest. Like Bohr’s work, it contains certain new elements relating to philosophical views on quantum theory.

p Unlike Bohr, Heisenberg actively opposed the principles of materialism. When speaking of ’materialistic ontology’, however, he essentially had metaphysical, mechanistic materialism in mind. He did not reveal in his book that he was very familiar with dialectical materialism although one can find attacks on Marxist philosophy in places in the book that are hardly of serious philosophical significance. Heisenberg stressed that the Copenhagen interpretation of quantum theory was ’in no way positivistic’. Positivism, he said, was ’based on the sensual perceptions of the observer as the elements of reality’, while ’the Copenhagen interpretation regards things and processes which are describable in terms of classical concepts, i.e. the actual, as the foundation of any physical interpretation’. It was thus recognised, he continued, that ’the statistical nature of the laws of microscopic physics cannot be avoided, since any knowledge of the “actual” is—because of the quantum- theoretical laws—by its very nature an incomplete knowledge’.⁵¹ The Copenhagen interpretation is also not materialist, as Heisenberg has more than once pointed out. In this case he counterposed the Copenhagen interpretation to materialism. But as regards philosophy, the point is not what Heisenberg personally thought of this interpretation but how he dealt with the basic problem of philosophy. In his own words, ’the ontology of materialism rested upon the illusion that the kind of existence, the direct “actuality” of the world around us, can be extrapolated into the atomic range. This extrapolation is impossible, however’.^^62^^

p According to Heisenberg physics is not so much concerned with nature itself, reflecting it in its concepts and theories, as it is concerned^ with the ‘actual’, i.e. nature transmitted as it were- through man’s perception, and which has already been subjected to certain methods of research.⁶⁸ In classical physics study of the ‘actual’ does not lead to difficulties of any kind, but in quantum theory, he says, these difficulties are unavoidable since the uncertainty 58 relation limits the applicability of classical concepts to nature.

p The need for a dialectical approach to atomic physics, evident in connection with the discovery of the unity of the particle and wave properties of atomic objects, is thus considered by Heisenberg as a need to revise the concept of objective reality in physics. One cannot, of course, disagree with Heisenberg when he says that expressing the achievements of modern physics in the concepts of the old philosophy can hardly yield any advantages, but he contradicts himself when he ‘pours’ the young wine of quantum physics into the old bottles of metaphysical and idealist philosophical systems.

p In Heisenberg observed phenomena, things, and the actual are described by means of classical concepts: atomic and other micro-particles are characterised in terms of mathematical abstractions; both these aspects are in a mutually exclusive but complementary relationship which is the quintessence of the philosophy on which he bases quantum theory. In this respect he gives epistemological significance to ‘complementarity’, trying to resolve the problem of reality in physics in an allegedly new way. (It must be noted that the meaning of the term ‘complementarity’ in Bohr’s essay Quantum Physics and Philosophy, as we have seen, is quite different.) Heisenberg’s standpoint on reality is expressed particularly plainly in his polemic with opponents of the Copenhagen interpretation, including those scientists who defend the position of dialectical materialism in physics.

p In Heisenberg’s view the merit of the Copenhagen interpretation was that it ’led the physicists far away from the simple materialistic views that prevailed in the natural science of the nineteenth century’.^^54^^ He disapproved of those who tried ’to return to the reality concept of classical physics or, to use a more general philosophic term, to the ontology of materialism. 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’.^^65^^

p Heisenberg thus identified, in fact unjustifiably, the philosophical concept of matter with classical physics’ notion about it, and also failed in essence to notice the difference between ’objective reality’ and the ‘actual’ or ‘real’. Dialectical materialism, on the other hand, discriminates between 59 them: e.g. the category of possibility, which plays an important role in philosophical questions of quantum theory, has (like the category of reality), an objective character from the standpoint of dialectical materialism. On this point dialectical materialism differs fundamentally from metaphysical, mechanical materialism, but Heisenberg did not notice this very essential difference.

p Heisenberg perpetuated the language of classical concepts in physics and retained it to describe instrument readings, the actual, and the world of phenomena. As regards the essence of these phenomena, they appear, according to him, as peculiar Kantian ‘things-in-themselves’—the mathematical abstractions of quantum theory are precisely such in his conception. It is not fortuitous that he believed the classical concepts to be somehow a priori with regard to the domains of the theory of relativity and quantum theory in which they were applied with the appropriate restrictions.

p We noted above that the problems of quantum mechanics cannot be reduced to explaining the limited nature of classical concepts. Heisenberg’s argument about the a priori character of the classical concepts ignored the dialectics of concepts, which reflects the dialectics of objective reality. The idea of the variability and evolution of concepts had already been current in science for a long time (although not all the scientists drew the appropriate philosophical conclusions from it). The development of non-classical physics has thus been accompanied with a change in the original meaning of concepts like mass and energy; they still have something in common with the original concepts but at the same time have acquired a deeper content.

p The radical revision of classical concepts made by quantum mechanics indicates that our knowledge of objective reality, nature, and matter has become deeper. Fock, in reproaching the Copenhagen interpretation of this theory for its onesidedness, justly noted the importance of the ’new primary concepts’, which in his view were relativity in respect to the means of observation, the distinction between the potentially possible and the realised, and the concept of probability as a numerical measure of the potentially possible.^^56^^

p Quantum theory confirms dialectical materialism and differs with metaphysical materialism. As for mechanical 60 materialism, Heisenberg was right in a certain sense when he criticised ’materialist ontology’. His criticism, however, had nothing to do with dialectical materialism. It is impossible to take his words seriously that, since dialectical materialism was created in the nineteenth century, its ’concepts of matter and reality could not possibly be adapted to the results of the refined experimental technique of our days’.^^57^^ (1) The very essence of dialectical materialism excludes dogmas of all kinds and inevitably alters its form with every fundamental discovery in science—both Engels and Lenin spoke directly about this very important feature of Marxist philosophy, drawing the appropriate conclusions in their philosophical works. (2) Heisenberg never analysed the dialectical materialist conception of matter and reality, which differs sharply from those of the old materialism. His statement that the concepts of Marxist philosophy ’could not possibly be adapted’ to the results of modern pure and applied science is not supported by any arguments.

p Heisenberg wrongly presented the objective dialectics of the particle-wave properties of atomic objects, which is demonstrated in the well-known experiments, as ’ complementarity’ of the mathematical symbolics relating to these objects and of the description of the atomic experiments in classical concepts. That is why the transition of physics from cognition of macro-phenomena to cognition of atomic, and in general microscopic, events is treated by Heisenberg not as a deepening of the human knowledge of matter and objective reality but as dissolution of the ’objectively real’ world ’in the transparent clarity of a mathematics whose laws govern the possible and not the actual’.^^68^^

p We must also mention, however, Heisenberg’s wobbling between idealism and dialectical materialism. His reasoning about the ‘complementarity’ of particle and wave, the possible and the real, and the mathematical apparatus as form, and about the physical content of scientific theories certainly shows signs of his coming near to an understanding of the significance of the unity of opposites that is the nucleus of dialectics. The same needs be said about his ideas about the relativity of physical theories and matter.

p In this connection Heisenberg’s statements about the unity of matter deserve mention. Having presented the experimental data on elementary particles, and the 61 discovery of the many forms of these particles, etc., Heisenberg concluded: ’These results seem at first sight to lead away from the idea of the unity of matter, since the number of fundamental units of matter seems to have again increased to values comparable to the number of different chemical elements. But this would not be a proper interpretation. The experiments have at the same time shown that the particles can be created from other particles or simply from the kinetic energy of such particles, and they can again disintegrate into other particles. Actually the experiments have shown the complete mutability of matter. All the elementary particles can, at sufficiently high energies, be trar minuted into other particles, or they can simply be created from kinetic energy and can be annihilated into energy, for instance, into radiation. Therefore, we have here actually the final proof for the unity of matter. All the elementary particles are made of the same substance, which we may call energy or universal matter; they are just different forms in which matter can appear.’^^59^^

p If we bear the philosophical aspect in mind and ignore certain inaccuracies in terminology, this statement undoubtedly expresses a materialist point of view.

p Heisenberg, however, followed it up with: ’If we compare this situation with the Aristotelian concepts of matter and form, we can say that the matter of Aristotle, which is mere “potentia”, should be compared to our concept of energy, which gets into “actuality” by means of the form, when the elementary particle is created’.^^60^^

p In this regard, we may recall Heisenberg’s words about the young wine of science and the old philosophical bottles. He does not see the new philosophy—dialectical materfalism, which fully corresponds to the new physics.

p The philosophical evolution of the Copenhagen interpretation still continues. The dialectical and materialistic elements in it have been strengthened in struggle with the metaphysical and, in particular, mechanistic ideas in atomic physics; the ’uncontrollability in principle’ appears less and less frequently in the reasoning and arguments of the Copenhagen school. That this is how matters stand can be seen from the discussion on quantum theory between Alfred Lande, on the one hand, and Max Born, Walter Biem, and Werner Heisenberg, on the other hand, in 1969.⁶¹ Lande opposed Bohr’s ideas and denied the 62 interpretation of quantum theory by Born and Biem who, according to him, regarded matter and field as having equally a particle and a wave nature. He considered the Copenhagen interpretation to be positivist (introducing a new term ’dialectical positivism’). In Lande’s view there is every reason to regard matter as simply a discontinuous formation and field as simply a continuous one.

p In summarising the discussion Heisenberg disagreed with Lande, suggesting that it had not been about the physical content of quantum theory itself but had been dealing with the language that should be used to describe quantumtheory phenomena. He noted, in particular, that Lande’s criticism of ‘sloppy’ formulations in the earlier literature on quantum theory was correct.

p How can the problem of the language of quantum theory be solved? Neither the experimental facts nor logical considerations] provide a criterion for answering this question. In that case, Heisenberg says, it is necessary to resort to historical arguments. A language has become established among physicists that had taken shape during the development of quantum theory. The concepts ‘particle’ and ‘wave’ borrowed from classical physics and the natural language had been equally employed to describe atomic phenomena regardless of whether formations with a non-zero rest mass (electrons, nucleons, mesons) were being described, or ones with zero rest mass (photons, neutrinos, phonons). The physicist, Heisenberg stressed, did not consider a quantummechanical description as dualistic. He had become accustomed to the fact that when this monistic description was translated into natural language various additional pictures might appear; the question, which picture was correct—the corpuscular or the wave—then had no meaning.

p Heisenberg also concluded that the interpretation of quantum theory employed by Born and Biem was the historical product of physicists’ forty-year experience with atomic phenomena that were explicable by quantum theory, rather than the result of dogmatic statements or agreement of some kind.

In our view, Heisenberg’s argument essentially emphasises the dialectics of concepts in physics that was left out by Lande in trying to interpret quantum theory in the language of the concepts of classical physics.