SUMMARY. — The idea of complementarity may be viewed as the core of Bohr's strategy, in 1927, to save both observation and definition. To this end, Bohr sought to incorporate, within the new quantum theory, the usual concepts of space and time, as well as the invariance principles and their associated conservation laws. At the time, Bohr saw himself as following in the footsteps of Einstein, who, in 1905, used a similar strategy to resolve the apparent contradiction between the constancy of the velocity of light and galilean invariance. By clarifying Bohr's deliberately vague notions, Dirac made the search for invariance transformations the aim of quantum physics. Dirac's work thus illustrates the importance of Bohr's of 1927 for the future development of theoretical physics.
SUMMARY. — The idea of complementarity may be viewed as the core of Bohr's strategy, in 1927, to save both observation and definition. To this end, Bohr sought to incorporate, within the new quantum theory, the usual concepts of space and time, as well as the invariance principles and their associated conservation laws. At the time, Bohr saw himself as following in the footsteps of Einstein, who, in 1905, used a similar strategy to resolve the apparent contradiction between the constancy of the velocity of light and galilean invariance. By clarifying Bohr's deliberately vague notions, Dirac made the search for invariance transformations the aim of quantum physics. Dirac's work thus illustrates the importance of Bohr's of 1927 for the future development of theoretical physics.
SUMMARY. — This paper emphasizes the evolution of complementarity, in Niels Bohr's successive formulations of this idea, from 1927 to 1939, despite little, if any change in the definition of the concept with time. In the Como lecture, in 1927, Bohr introduced the idea of « complementary descriptions » in a problematic, polemical way. Against Schrödinger' s interpretation, he stressed the « irrationality » inherent in the quantum postulate. In 1935, Bohr again used complementarity polemically, in his reply to Einstein-Podolsky-Rosen. But far from intending it to convey irrationality this time, he meant to use it instead to prove that quantum mechanics is a complete theory. Finally, I will take up Bohr's attempts to apply complementarity to fundamental problems in biology, psychology, sociology, and so forth. I will argue that the introduction of complementarity outside physics was not motivated by an imperialist ambition of the Copenhagen School, but rather inspired by Bohr's own personal philosophy.
SUMMARY. — In this article, I examine Einstein's objections to quantum mechanics, with the formalism's interpretation in terms of complementarity as the historical setting. From 1924 to 1927, the period of development of a formalised quantum theory, Einstein raised certain questions that kept him from joining the throng of ardent supporters. Against the theory and its interpretation of 1927, he at first advanced arguments with the idea of eventually finding a flaw in quantum mechanics, and casting doubts upon its pretensions of completeness. Finally acknowledging, in 1931, the theory's coherence and accuracy at describing phenomena, he then tried to put forth objections to the theory's interpretation, which aimed at demonstrating the theory's incompleteness. These arguments culminated in the « Einstein-Podolsky-Rosen » article of 1935, and Einstein repeated them continually until his death. The analysis here calls, of course, for assessments of both the import of Einstein's arguments in relation to physics today, as well as to Einstein's own conceptions where theoretical physics is concerned, but these go beyond the aims of the present article.
This paper examines the transformation of Bohr's interpretation of quantum phenomena and quantum mechanics, known as complementarity, from the version presented in his famous Como lecture (1927), which introduced complementarity, to a new version that was developed by Bohr shortly thereafter, in part under the impact of his intervening exchanges with Einstein. While the existence of more than one version of Bohr's complementarity (and of still different versions of the Copenhagen interpretation by others) has been noted, Bohr's rethinking itself of complementarity has rarely been adequately addressed. Apart from refining and indeed correcting the Como argument, the transformation in question was, I argue, defined by a shift from a more philosophical to a more experimental argument. My aim is to explore both this shift and the complexity of the relationships between physics and philosophy in Bohr's thinking in order to understand better the beginnings and the ends, also in the sense of aims, of Bohr's complementarity.
Although Dirac rarely participated in the interpretational debates over quantum theory, it is traditionally assumed that his views were aligned with Heisenberg and Bohr in the so-called Copenhagen-Göttingen camp. However, an unpublished—and apparently unknown—lecture of Dirac's reveals that this view is mistaken; in the famous debate between Einstein and Bohr, Dirac sided with Einstein. Surprisingly, Dirac believed that quantum mechanics was not complete, that the uncertainty principle would not survive in the future physics, and that a deterministic description of the microworld would be recovered. In this paper I show how we can make sense of this unpublished lecture in the context of Dirac's broader philosophy of quantum mechanics, and how our present understanding of Dirac's philosophical views must be revised.
Quantum complementarity is a fundamental feature of quantum systems and has captivated the physics research community for nearly a century, with significant advancements emerging in recent decades. This review traces the historical evolution of the concept of complementarity, beginning with Bohr's original formulation. It then explores its modern quantification through complementarity relations and its profound connection to the foundational postulates of quantum theory. Furthermore, it delves into key related developments, such as the operational definition of complementarity in the context of incompatible observables, its potential links with quantum uncertainty relations and contextuality, its various applications, and other pertinent topics. This review aims to serve physicists interested in quantum resources, quantum correlations, and the foundational principles of quantum mechanics.
This book gives a clear and comprehensive exposition of Niels Bohr's philosophy of physics. Bohr's ideas are of major importance, for they are the source of the Copenhagen interpretation of quantum physics; yet they are obscure, and call for the sort of close analysis that this book provides. The book describes the historical background of the physics from which Bohr's ideas grew. The core of the book is a detailed analysis of Bohr's arguments for complementarity and of the interpretation which he put upon it. Special emphasis is placed throughout on the contrasting views of Einstein, and the great debate between Bohr and Einstein is thoroughly examined. The book traces the philosophical influences on Bohr, and unravels the realist and anti-realist strands in his thinking. Bohr's philosophy is critically assessed in the light of recent developments in the foundations of quantum physics (the work of Bell and others) and in philosophy (the realism-anti-realism debate) and it is revealed as being much more subtle and sophisticated than it is generally taken to be. While the book will be of interest to specialists, it is written in a style that will make it accessible to those who have no specialist knowledge of the relevant physics and philosophy.