Complementarity is a concept of epistemology for two (apparently) contradicting, mutually exclusive, non-reducible modes of description or experimental arrangements, which are, however, necessary in their mutual complement to understand a phenomenon or fact as a whole. The physicist Niels Bohr introduced this term into quantum physics as a principle of complementarity and then applied it to many areas. This is why the term became ambiguous and often only describes a basic “as well as”.
Two complementary properties belong together if they have the same reference , i.e. concern the same “ object ”, but are not causally dependent on one another. The two methods used differ fundamentally in terms of the procedure and can generally not be used simultaneously, but only one after the other.
Precursors and Related Ideas
The ethnologist Claude Lévi-Strauss recognized the basic pattern of any categorization in the human being in the formation of complementary opposites (so-called dichotomies ) such as “man↔ woman”, “old↔ young”, “small↔ large”, “cold↔ hot” etc. Think.
Forerunners of the concept of complementarity with the intention of eliminating a fundamental contradiction or characterizing a paradox can be found:
- in Chinese philosophy with the yin-yang principle, the inextricable connection of opposites to a wholeness ( Taoism );
- in theology and christology about the divine, god-like or created nature of Jesus ( First Council of Nicaea , Council of Chalcedon ), the compatibility of God's love and omnipotence with the existence of evil in the world ( theodicy ), and in determining the relationship to natural science in the question of creation and the origin of the world (see philosophy of science of theology );
- in the coincidentia oppositorum ( Nikolaus von Kues );
- in the doctrine of the two attributes of a doctrine of substance (double aspect doctrine) by Baruch de Spinoza , according to which spirit and matter are two sides of one and the same thing ( una eademque res );
- in the theory of psychophysical parallelism ( Gottfried Wilhelm Leibniz , Gustav Theodor Fechner );
- in Immanuel Kant's antinomies , for example on freedom of will and causality .
The word "complementary" can also be found long before Bohr's new term was coined:
- in logic the relationship between two classes, one of which contains all elements that are not elements of the other (see set theory , complement );
- in perception and sensory physiology as a complementary color ;
- in psychology and psychoanalysis for the separation of areas of consciousness , which then coexist and whose contents become mutually inaccessible ( William James , Sigmund Freud );
- In linguistics , the antonym (counterword) describes the complementary term;
- in social policy , technology and natural sciences .
In quantum physics , complementarity is mostly explained today using the example of the wave-particle dualism of light , which in one experimental set-up can be described as a wave and in the other as a particle (see double slit experiment ). In addition, reference is made to the facts of quantum mechanics that certain complementary measured quantities , e.g. For example, the location and the momentum of an electron , can not have a precisely defined value at the same time ( Heisenberg uncertainty principle ).
Bohr did not use the term clearly. Central is the complementary character of the quantum mechanical description of nature, which requires a new view of the relationship between space-time representation and the requirement of causality . What is essential is the epistemological insight that quantum mechanical determinations and - generalized - many scientific findings, for example in biology and psychology , depend on the experimental set-up and other test conditions and can represent mutually exclusive features of the description. In this respect, Heisenberg's uncertainty principle is only an elementary example for Bohr (see principle of complementarity ).
To what extent Bohr was inspired by the history of ideas and precursors in philosophy and theology in his choice of the expression complementarity is controversial.
Newer concepts of complementarity
Examples can be found:
- in biology, the relationship between complementary spatial molecular structures whose interaction according to the key-lock principle is a prerequisite for the fulfillment of a certain function;
- In neuropsychology , psychophysiology , psychosomatics and complementary medicine, the context and the interrelated being of personal experience (the immaterial consciousness processes) and the neural processes, the “purely psychological” and “purely physical” factors, to explain health disorders and diseases ;
- In ethnopsychiatry according to Georges Devereux , complementarity describes the mutual complementation and correction of various methods that have the same object, e.g. B. the theory of an ethnocentric imperialism against the assumption of universal psychic principles or the location awareness of an ethnopsychiatrist against the absolutization of partial aspects of a culture;
- in the communication theory by Watzlawik the interplay of two patterns in circular communication processes that complement each other and condition (such as teachers and students or tracker and persecution);
- in the economy, the interaction of two currencies in local economic cycles ( complementary currency );
- in the education according Jongebloed , a principle of the phenomenon formation to explain based on the ratio of knowledge and experience;
- In international criminal law , the principle of complementarity describes the relationship between the International Criminal Court and national courts.
Following Bohr's example, the principle of complementarity was adopted in various areas of science. Critically, it can be objected that the generalization of the original term to other opposites in the sense of a vague both-and-also provides little more than a metaphor . The expression complementarity is basically superfluous or only covers up contradictions. Not every pair of opposites, every dilemma or every duality can be called a complementary relationship.
Such transfers deviate from important defining features of the complementarity principle in quantum mechanics. As a rule, no physically formulated observation sentences from experimental test arrangements are given. The methods used are rarely precisely defined, and the questions of whether they are mutually exclusive or not to be used simultaneously remain open. Do the (two) methods used differ fundamentally and do they belong in categorically completely different reference systems ? The existing difference or contradiction is seldom formulated in a strictly mutually exclusive form, i.e. not paradoxical . It is no longer a matter of incompatible observational sentences that coexist experimentally, but rather of interpretative sentences (see principle of complementarity ) or even just simple combinations of methods or views or interactions .
Other authors claim a heuristic , relational function and methodological fruitfulness of the concept, whereby often it is not a solution of a problem that is claimed, but rather it is understood as an attempt at mediation. Therefore, it would be useful for understanding in most cases to speak at most of complementary relationships and mutual complementarity, or to prefer the less burdened terms perspective , double perspective and perspectivity , which are not complicated by definitions from quantum mechanics.
- Jochen Fahrenberg: On the theory of categories in psychology. Complementarity principle. Perspectives and change of perspective. Pabst Science Publishers, Lengerich 2013, ISBN 978-3-89967-891-8 
- David Favrholdt (Ed.): Complementarity Beyond Physics (1928–1962). Volume 10. Elsevier, Amsterdam 1999.
- Ernst-Peter Fischer: Both and. Thinking experiences of the natural sciences. Hamburg: Rasch and Röhrig, Hamburg 1987. ISBN 9783891361184 .
- Ernst-Peter Fischer, Heinz S. Herzka, Karl-Helmut Reich (eds.): Contradictory Reality. New thinking in science and everyday life. Complementarity and dialogue. Piper, Munich 1992, ISBN 3492115543 .
- Karl-Helmut Reich: Developing the horizons of the mind: Relational and contextual reasoning and the resolution of cognitive conflict. Cambridge Univ. Press, Cambridge 2002. ISBN 978-0521817950 .
- Dieter Haller (text), Bernd Rodekohr (illustrations): Dtv-Atlas Ethnologie. 2nd Edition. dtv, Munich 2010, pp. 53, 91, 247.
- Fahrenberg: On the theory of categories in psychology. Complementarity principle. Perspectives and Change of Perspectives , 2013, p. 334 ff.
- Fahrenberg: On the theory of categories in psychology. Complementarity principle. Perspectives and Change of Perspectives , 2013, pp. 318–321 pp. 357–361.