A suggestion of Bohr's to the effect that numerous situations exist among the life sciences and the social sciences which exhibit characteristics of complementarity strikingly parallel to those of quantum physics is developed further in this paper. The supposition is advanced that there may exist for biological systems inherent relations of indeterminacy between sets of observable properties of such systems analogous to the Heisenberg indeterminacy relations between canonically conjugate pairs of observables in quantum mechanics. The existence of such indeterminacies would be manifested, as it is in physical systems, in disturbances, uncontrollable in principle, produced when such systems interact with instruments and apparatus used to gain information about them. The fact that radical disturbances, whether incidental or inherent, accompany the process of observation in the life sciences is, of course, quite obvious. If a well-defined portion of such disturbances should turn out to be inherent, indeterminacy and probability would be introduced into biological phenomena as basic elements. Further progress in scientific explanation and synthesis of knowledge in these fields would then require a redefinition of the state of a biological system analogous to the necessity for using quantum ψ-functions for specifying the state of a physical system with the attendant possibility of wholly new insights, such as those in physics which ultimately depend on the symmetry properties of ψ-functions. This new, and presently unknown, scheme for specifying the state of biological systems would then presumably result in the typically complementary aspects of phenomena in these fields to which Bohr has called attention. A number of familiar examples of apparently complementary phenomena among the biological and social sciences are described, and the possibility that they may arise from inherent indeterminacies basic to the systems which exhibit these phenomena is considered. It is concluded that these considerations lead to the expectation that an approach along such lines in future investigations in the life sciences holds considerable promise, and that the physics teacher is in a unique position to assist in stimulating such an approach and in pointing out by analogy the means at each stage which are likely to prove best suited for carrying it through.
A suggestion of Bohr's to the effect that numerous situations exist among the life sciences and the social sciences which exhibit characteristics of complementarity strikingly parallel to those of quantum physics is developed further in this paper. The supposition is advanced that there may exist for biological systems inherent relations of indeterminacy between sets of observable properties of such systems analogous to the Heisenberg indeterminacy relations between canonically conjugate pairs of observables in quantum mechanics. The existence of such indeterminacies would be manifested, as it is in physical systems, in disturbances, uncontrollable in principle, produced when such systems interact with instruments and apparatus used to gain information about them. The fact that radical disturbances, whether incidental or inherent, accompany the process of observation in the life sciences is, of course, quite obvious. If a well-defined portion of such disturbances should turn out to be inherent, indeterminacy and probability would be introduced into biological phenomena as basic elements. Further progress in scientific explanation and synthesis of knowledge in these fields would then require a redefinition of the state of a biological system analogous to the necessity for using quantum ψ-functions for specifying the state of a physical system with the attendant possibility of wholly new insights, such as those in physics which ultimately depend on the symmetry properties of ψ-functions. This new, and presently unknown, scheme for specifying the state of biological systems would then presumably result in the typically complementary aspects of phenomena in these fields to which Bohr has called attention. A number of familiar examples of apparently complementary phenomena among the biological and social sciences are described, and the possibility that they may arise from inherent indeterminacies basic to the systems which exhibit these phenomena is considered. It is concluded that these considerations lead to the expectation that an approach along such lines in future investigations in the life sciences holds considerable promise, and that the physics teacher is in a unique position to assist in stimulating such an approach and in pointing out by analogy the means at each stage which are likely to prove best suited for carrying it through.
On August 15, 1932 Niels Bohr gave opening address of International Congress on Therapy held in Copenhagen. Bohr's title was Light and Life, and his purpose was to draw attention to epistemological implications for life sciences of fundamental changes that quantum theory had brought to conception of natural law (Bohr 1933). He thought that these changes, which extend to very idea of nature of scientific explanation, were important not only for a full appreciation of new situation brought to physics by quantum theory. According to Bohr, these developments had also created an entirely new background for viewing problems of biology, especially as concerns our views on position of living organisms in realm of natural science. In particular, Bohr proposed that notion of complementarity, which he had first presented 5 years earlier at International Congress of Physics in Como, relevant also for physiological and psychological aspects of life. Bohr began his address by stating what nowadays stigmatized as reductionist credo, namely that subtle character of riddle of life notwithstanding, any scientific explanation of biological phenomena necessarily must consist of reducing description of more complex phenomena to that of simpler ones. But, Bohr continued, discovery of an essential limitation of mechanical description of natural phenomena, as revealed by recent development of atomic theory, has lent new interest to old problem of how far program of reductive biological explanations can be carried. Bohr then presented a brief historical account of rise of quantum theory in connection with study of light, which he thought is perhaps least complex of all physical phenomena. Yet, it turned out that despite its lack of complexity, phenomenon of light cannot be given a coherent mechanical explanation, inasmuch as from viewpoint of classical physical theories, the quantum of action . . . must be considered as an irrational notion. The spatial continuity of light propagation, on one hand, and atomicity of light effects on other hand, must, therefore, be considered as complementary aspects of one reality, in sense that each expresses an important feature of phenomena of light. Those aspects are complementary, because, although they are conceptually irreconcilable from a mechanical point of view, they can never be shown to be in direct, or empirical, contradiction. The reason for this that any closer analysis of either wave aspect or particle aspect of light demands mutually exclusive observational arrangements.
Niels Bohr asserted both that (i) the properties of quantum systems are specifiable, in general, only in relation to mutually exclusive experimental arrangements which may be freely chosen by experimenters, and that (ii) observed physical behavior is objective. In a move that reduces the apparent tension between those two assertions, Bohr put forward an analogy between quantum complementarity (in effect, the dependence of property values on measurement apparatus configuration in quantum mechanics) and the principle of relativity (in effect, the dependence of property values on the inertial reference frame in special relativity). Here, Bohr's analogy is considered in a theoretical context. The elements of quantum mechanics and special relativity involved are set side by side, the analogous elements are identified with their roles in the analogy spelled out, and a number of dissimilarities that impact the force of the analogy are indicated-for example, quantum value determination, in general, requires an uncontrollable interaction during measurement, whereas non-quantum relativistic value determination does not. These dissimilarities point to weaknesses in the analogy, which he did not highly develop, and suggest that any stronger such analogy involving the two theories must take these differences more fully into account.
On August 15, 1932 Niels Bohr gave opening address of International Congress on Therapy held in Copenhagen. Bohr's title was Light and Life, and his purpose was to draw attention to epistemological implications for life sciences of fundamental changes that quantum theory had brought to conception of natural law (Bohr 1933). He thought that these changes, which extend to very idea of nature of scientific explanation, were important not only for a full appreciation of new situation brought to physics by quantum theory. According to Bohr, these developments had also created an entirely new background for viewing problems of biology, especially as concerns our views on position of living organisms in realm of natural science. In particular, Bohr proposed that notion of complementarity, which he had first presented 5 years earlier at International Congress of Physics in Como, relevant also for physiological and psychological aspects of life. Bohr began his address by stating what nowadays stigmatized as reductionist credo, namely that subtle character of riddle of life notwithstanding, any scientific explanation of biological phenomena necessarily must consist of reducing description of more complex phenomena to that of simpler ones. But, Bohr continued, discovery of an essential limitation of mechanical description of natural phenomena, as revealed by recent development of atomic theory, has lent new interest to old problem of how far program of reductive biological explanations can be carried. Bohr then presented a brief historical account of rise of quantum theory in connection with study of light, which he thought is perhaps least complex of all physical phenomena. Yet, it turned out that despite its lack of complexity, phenomenon of light cannot be given a coherent mechanical explanation, inasmuch as from viewpoint of classical physical theories, the quantum of action . . . must be considered as an irrational notion. The spatial continuity of light propagation, on one hand, and atomicity of light effects on other hand, must, therefore, be considered as complementary aspects of one reality, in sense that each expresses an important feature of phenomena of light. Those aspects are complementary, because, although they are conceptually irreconcilable from a mechanical point of view, they can never be shown to be in direct, or empirical, contradiction. The reason for this that any closer analysis of either wave aspect or particle aspect of light demands mutually exclusive observational arrangements.
This article explores Bohr's argument, advanced under the heading of 'complementarity,' concerning quantum phenomena and quantum mechanics, and its physical and philosophical implications.In Bohr, the term complementarity designates both a particular concept and an overall interpretation of quantum phenomena and quantum mechanics, in part grounded in this concept.While the argument of this article is primarily philosophical, it will also address, historically, the development and transformations of Bohr's thinking, under the impact of the development of quantum theory and Bohr's confrontation with Einstein, especially their exchange concerning the EPR experiment, proposed by Einstein, Podolsky and Rosen in 1935.Bohr's interpretation was progressively characterized by a more radical epistemology, in its ultimate form, which was developed in the 1930s and with which I shall be especially concerned here, defined by his new concepts of phenomenon and atomicity.According to this epistemology, quantum objects are seen as indescribable and possibly even as inconceivable, and as manifesting their existence only in the effects of their interactions with measuring instruments upon those instruments, effects that define phenomena in Bohr's sense.The absence of causality is an automatic consequence of this epistemology.I shall also consider how probability and statistics work under these epistemological conditions.
Niels Bohr developed the framework of complementarity in response to the binding of measuring device and quantum system into an irreducible whole or "individual" at the instant of measurement. On the grounds that an organism and its environment are also bound irreducibly upon interaction, Bohr extended complementarity to biology and psychology, treating mechanistic reduction of the organism and neural objectification of consciousness as mere perspectives opposed by equally valid perspectives. In contrast to Bohr's aversion to metaphysical speculation, Heisenberg suggested that the quantum-mechanical wave function represents a real entity which determines probable outcomes of measurements given the forces acting on the system. In light of Bohr's parallel between quantum and biological systems, the probability wave of the atom ought to be mirrored in the equally intangible consciousness of the organism. I propose further that life is indeed an irreducible property of the organism and that mechanistic biology mischaracterizes life. Key to my analysis is the dual nature of time.
From the preceding exposition it follows that not only physics but natural science as a whole is basically dependent on ordinary language. The complementarity of quantum physics displays the fundamental interdependence of observation and description of natural phenomena, and the very objectivity of natural science relies directly on the differentiation of experiences into external and private phenomena afforded by ordinary language. Because of the extreme smallness of the quantum of action the complementarity of physical phenomena is not experienced either in daily life or in classical physics. But the interdependence of observation and description of phenomena prevails as much in classical science as in quantum physics. The very aim of experimental investigation is to perform observations in those particular ways which make possible the communication of information sufficient for the reproduction of the observed phenomena. Concordantly the elementary physical variables, which are indispensable to any systematic analysis in natural science, are defined through reference to measuring arrangements constructed so as to be unambiguously describable in ordinary language. Thus no scientific formula, law, or result of measurement can be given objective significance independent of ordinary language. Through every hierarchy of descriptions in natural science ordinary language penetrates as the unambiguity of propositions.