Abstract Bohr took it as the key fact of QT that neither of the models for describing the behaviour of systems offered by classical physics— neither the ‘particle picture’ nor the ‘wave picture’—fitted q-systems in all aspects of their behaviour. More particularly he took these two pictures to be ‘complementary’—when one fitted the other one did not. This failure of fit was seen by Bohr as usually only partial however, as a degree of’imprecision of fit’ rather than a total failure of fit; and it is in terms of this notion that Bohr was then able to give expression to his principle of complementarity, viz. that the degrees of imprecision of fit of the wave and particle pictures are reciprocally related: to the extent that one of the pictures fits well, the other fits badly. In this chapter I shall discuss these notions in the context of a more general discussion of Bohr’s philosophy of Quantum Theory.
Abstract Bohr took it as the key fact of QT that neither of the models for describing the behaviour of systems offered by classical physics— neither the ‘particle picture’ nor the ‘wave picture’—fitted q-systems in all aspects of their behaviour. More particularly he took these two pictures to be ‘complementary’—when one fitted the other one did not. This failure of fit was seen by Bohr as usually only partial however, as a degree of’imprecision of fit’ rather than a total failure of fit; and it is in terms of this notion that Bohr was then able to give expression to his principle of complementarity, viz. that the degrees of imprecision of fit of the wave and particle pictures are reciprocally related: to the extent that one of the pictures fits well, the other fits badly. In this chapter I shall discuss these notions in the context of a more general discussion of Bohr’s philosophy of Quantum Theory.
The analogical extensions of Niels Bohr's principle of complementarity to the disciplines of biology, psychology, and theology are ineffective. It has been argued, moreover, that the principle of complementarity is ineffective within quantum theory itself. Bohr supported the claim that complementary pictorial-level interpretations are necessary for the explanation of quantum phenomena by invoking a correspondence argument. Henry Margenau criticized Bohr for recommending that physicists accept an irreconcilable dilemma, the horns of which are complementary "descriptions" in terms of classical observables and causal accounts in terms of abstract states. In his various publications, Margenau created a number of diagrams to represent the confirmation process. He agreed with P. W. Bridgman that operational definitions provide important links between constructs and the results of instrumental procedures. Despite Margenau's protest, many scientists in the 1930s were receptive to the idea that pictures of classical particles and waves are needed to complete the interpretation of quantum phenomena.
In this last chapter I shall attempt a very brief assessment of the Bohr–Einstein debate. Who won it in the view of the audience? Who actually had the better case? I will also ask two rather more specific questions. The first is ‘Have the contributions of John Bell favoured the position of either of the protagonists?’ The second is ‘Has the dramatic arrival and progress of quantum information theory anything to tell us about the Bohr–Einstein debate?’ To help to answer these questions, let me first re-assemble a few points, putting together in turn an argument for each of the protagonists against a rather hostile critic. First Bohr, and I take as his critic John Bell himself. Bell was prepared, in fact, to give Bohr great credit for what Bell called the pragmatic approach to quantum theory, which I discussed earlier. This approach says that the world must be divided into ‘classical’ and ‘quantum’ parts, with an arbitrarily placed cut between them; that the macroscopic measuring device must be described in classical terms, but that we should not expect to picture the ‘quantum’ system in physical terms, and should be content just to possess rules of calculation that work well. But Bell regarded Bohr's philosophy of what lay behind pragmatism, complementarity , as ill-defined, unsatisfactory and bizarre.
This chapter is devoted to the Bohr complementarity principle.This is one of the basic quantum principles. We dissolve it into separate subprincipleson contextuality, incompatibility, complementary-completeness,and individuality. We emphasize the role of the contexuatlity component. It is not highlighted in the foundational discussions. ByBohr, the outputs of measurements are resulted from the complexinteraction between a system and measurement context, the values ofquantum observables cannot be treated as objective properties of systems.Such Bohr contextuality is more general than joint measurement contextuality(JMC) considered in the discussions on the Bellinequality. JMC is a very special form of the Bohr contextuality. The incompatibility component is always emphasized and often referred as the wave-particle duality. The principle ofinformation complementary-completeness represents Bohr’s claim on completenessof quantum theory. The individuality principle is basic for thenotion of phenomenon used by Bohr to emphasize the individuality and discreteness of outputs of measurements. Individuality plays the crucial role in distinguishing quantum and classical optics entanglements.
To resolve the challenges (paradoxes) attending the genesis of quantum theory, Niels Bohr in 1927 proposed a generalization of the conceptual framework of classical physics, termed complementarity, which posited pairs of classical concepts that could be manifested only in mutually exclusive experimental arrangements with both needed to embrace the full range of physical experience. In this context particle–wave complementarity has encountered two major obstacles; (1) No formulation of it has commanded a general consensus; and (2) empirical evidence abounds that contradicts the claim of mutual exclusivity of particle and wave properties of quantum objects in a single experiment. These problems are rooted in the unrestricted scope of this claim. It is shown that a restricted version of particle–wave complementarity, here called “which value–interference” complementarity, is consistent with observations, is naturally contained in the mathematical formalism of quantum theory and, in fact, holds in any representation of quantum theory defined by the eigenvectors of a complete set of commuting observables, such as the configuration space position (kinematic) variables or the complementary linear momentum (dynamic) variables. Thus, the which value–interference form of particle–wave complementarity exists within kinematic–dynamic complementarity, a “layered” complementarity, so to speak. It is hoped that a consistent and valid exposition of particle–wave complementarity will be helpful to those who find the framework of complementarity useful and appropriate for some purpose.
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.
Abstract Complementarity is the idea that mutually exclusive pictures are needed for a complete description of quantummechanical reality. The paradigm example is the complementarity between particle and wave (or ‘spacetime’ and ‘causal’) pictures, which Bohr took to be reflected in the uncertainty relation LixLip 2: h. Bohr saw this relation as defining the latitude of applicability of the concepts of position and momentum to a single system, not just as putting a limit on our ability to predict the values of both position and momentum within an ensemble of identically prepared systems. Furthermore, right at the start of his celebrated reply to the EinsteinPodolsky Rosen (EPR) argument against the completeness of quantum the