Bohr’s Idea of Complementarity

Pandora Hadzidaki

Mara Beller

Makoto Katsumori

This book explores the modern physicist Niels Bohr’s philosophical thought, specifically his pivotal idea of complementarity, with a focus on the relation between the roles of what he metaphorically calls “spectators” and “actors.” It seeks to spell out the structural and historical complexity of the idea of complementarity in terms of different modes of the ‘spectator-actor’ relation, showing, in particular, that the reorganization of Bohr’s thought starting from his 1935 debate with Einstein and his collaborators is characterized by an extension of the dynamic conception of complementarity from non-physical contexts to the very field of quantum theory. Further, linked with this analysis, the book situates Bohr’s complementarity in contemporary philosophical context by examining its intersections with post-Heideggerian hermeneutics as well as Derridean deconstruction. Specifically, it points to both the close affinities and the differences between Bohr’s idea of the ‘actor-spectator’ relation and the hermeneutic notion of the relation between “belonging” and “distanciation.”

Alberto De Gregorio

Anja Skaar Jacobsen

The Belgian physicist Leeon (1904––1974) has been called clarifier of Niels Bohr's ideas in quantum mechanics. He had a unique connection to Bohr as his close collaborator from 1930 until Bohr died in 1962. However, although he is considered Bohr's spokesman, he had his own characteristic way of articulating Bohr's views. In particular, added a dialectical-materialist layer to Bohr's ideas in certain contexts. Despite Rosenfeld's open profession of Marxism, the literature has generally avoided discussing its relevance for his work and activities. This paper suggests some reasons why and investigates Rosenfeld's combination of Marxism and complementarity, which his colleague and friend Wolfgang Pauli metaphorically denoted by the equation Rosenfeld = √√Trotsky ×× Bohr. Rosenfeld's particular views appear anomalous to the frequently expressed stereotypes of both Marxism and complementarity. The paper concentrates on the role Marxist philosophy played in Rosenfeld's fierce defense of complementarity from the late 1940s through the 1950s and the reception his campaign was accorded at the Niels Bohr Institute in Copenhagen and elsewhere.

Bernadette Bensaude‐Vincent

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.