Heelan argues that the philosophy of complementarity, although successful in providing physicists with a common language with which to describe quantum phenomena, also contains a theory about scientific method and about human knowing which is open to criticism. Heelan here criticises the following points arising out of the philosophy of complementarity: psycho-physical parallelism; the view that quantum mechanical properties are to be defined classically; and the perturbation theory of measurement. In the course of the criticism, he elaborates the distinction between two types of concepts with different logical structures; viz., operational or observational concepts which state a similarity between things judged on the basis of appearance or utility to us, and explanatory concepts which state a similarity between things judged on the basis of a self-defining set of different relations between things. Heelan thus shows how a physical concept is definable by any appropriate measuring-process. The description of the measuringprocess and, hence, the definition of the physical property involve the two classes of concepts described above, but in different ways. Thus one may regard the Indeterminacy Relations, not as stating limitations of our knowledge, but as describing more exactly the behaviour of individual systems.
Heelan argues that the philosophy of complementarity, although successful in providing physicists with a common language with which to describe quantum phenomena, also contains a theory about scientific method and about human knowing which is open to criticism. Heelan here criticises the following points arising out of the philosophy of complementarity: psycho-physical parallelism; the view that quantum mechanical properties are to be defined classically; and the perturbation theory of measurement. In the course of the criticism, he elaborates the distinction between two types of concepts with different logical structures; viz., operational or observational concepts which state a similarity between things judged on the basis of appearance or utility to us, and explanatory concepts which state a similarity between things judged on the basis of a self-defining set of different relations between things. Heelan thus shows how a physical concept is definable by any appropriate measuring-process. The description of the measuringprocess and, hence, the definition of the physical property involve the two classes of concepts described above, but in different ways. Thus one may regard the Indeterminacy Relations, not as stating limitations of our knowledge, but as describing more exactly the behaviour of individual systems.
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.
ENERAL philosophy claims to be the critical subject which lays down for all of us what we may be allowed to think, and yet it has played no part whatever in the great revolutions of human thought of the present century-those connected with relativity and the quantum theory. It might have been expected that the scientists would have been constantly consulting the philosophers as to the legitimacy of their various speculations, but nothing of the kind has happened. Since no one can dispense with some sort of metaphysic, each scientist has made one for himself, and no doubt they contain many crudities, but it would seem that a deep interest in metaphysic is a disadvantage rather than an advantage to the physicist-at least I have the impression that those of my friends who are most inclined to speculate on the ultimate things appear to be the ones whose scientific work is most hampered by doing so. Now I propose to risk a similar indiscretion. I want to embody in it the practical philosophy of a physicist, and I do not mean it as an attack on the pure philosophers, who are very reasonable people, only chargeable with the minor offence of not having made me want to read their books! I had better begin by stating shortly the ideas I intend to discuss. There is a notable contrast between the way we think about things and the way we think we ought to think about them.
From the preceding exposition it follows that the quantum statistical representation of an individual atomic system does not imply any renunciation regarding further knowledge about the system. On the contrary the statistical character of quantum physics directly reflects the fundamental non-causal appearance of quantal recordings, and through the discovery of the complementarity of quantal phenomena a complete but necessarily statistical description of the atom has been accomplished. Furthermore quantum physics has afforded a statistical description of macroscopic bodies through their representation as assemblies of huge numbers of identical atomic systems, and, apart from accounting in a more fundamental way for the properties already described in classical physics(the correspondence principle, p. 36), quantum statistics explains several macroscopic phenomena which cannot be understood within the conceptual frame of classical physics only. It must be maintained, however, that when observing the properties of individual atomic objects the macroscopic observational apparatus cannot be represented in terms of atomic constituents because this would destroy the unambiguity of the description. The observational apparatus fulfils its basic function of being the spacetime frame of reference for the quantal recordings precisely through its description in classical physics alone. However, when refraining from the analysis of individual quantal processes it is possible to apply quantum statistics to macroscopic phenomena, that is, the causality of classical physical phenomena can be interpreted in the quantum formalism as the statistical result of the interplay of enormous numbers of atomic processes. It is possible, then, to talk of statistical causality as a fundamental aspect of physical reality.
A short exposition is given of the foundation of the causal description in classical physics and the failure of the principle of causality in coping with atomic phenomena. It is emphasized that the individuality of the quantum processes excludes a separation between a behaviour of the atomic objects and their interaction with the measuring instruments denning the conditions under which the phenomena appear. This circumstance forces us to recognize a novel relationship, conveniently termed complementarity, between empirical evidence obtained under different experimental conditions. An appropriate tool for a complementary mode of description is provided by the quantum-mechanical formalism which allows us to account for regularities of definite or statistical character beyond the grasp of classical physical explanation. – N. B.
Niels Bohr, as is well known, introduced the notion of complementarity into physics, as a fundamental principle of quantum mechanics. It holds that objects have complementary properties that cannot be measured accurately at the same time. For example, the particle and wave aspects of physical objects are such complementary phenomena. Both concepts are borrowed from classical mechanics, where it is impossible to be both, a particle and a wave at the same time. Particle and Wave represent the complementarity of the Discrete and the Continuous. Humans reason by means of concepts (meanings) and language, as well as, by means of logical or arithmetic symbolism. Meanings are continua, whereas logic and arithmetic are based on relations of identity and difference.
AbstractQuantum physics has overturned the classical view of the world by introducing probability, indeterminacy and the participation of the observer. It is not merely a scientific revolution, it reshapes causality, reality and knowledge, opening the way to an epistemology of relation. From Bohr to Rovelli, from Heisenberg to Morin, contemporary thought recognizes that reality no longer appears as an independent structure, but as a network of interactions. This relational conception of the world crosses the boundary between science and philosophy and invites us to rethink human responsibility in the production of knowledge. Knowledge thus becomes an act of co-creation, articulating scientific rigor, reflexivity and awareness of interconnectedness : a new humanism grounded in complexity and relation. Keywordsquantum mechanics, indeterminacy, causality, reality, observer, relation, epistemology, complexity, complementarity, entanglement, Bohr, Heisenberg, Rovelli, Morin, humanism, responsibility, knowledge, interaction, philosophy of science, ethics of knowledge