Concept

Complementarity (physics)

Overview

In physics, complementarity is a conceptual aspect of quantum mechanics that Niels Bohr regarded as an essential feature of the theory. The complementarity principle holds that certain pairs of complementary properties cannot all be observed or measured simultaneously. For example, position and momentum, frequency and lifetime, or optical phase and photon number. In contemporary terms, complementarity encompasses both the uncertainty principle and wave-particle duality.

Bohr considered one of the foundational truths of quantum mechanics to be the fact that setting up an experiment to measure one quantity of a pair, for instance the position of an electron, excludes the possibility of measuring the other, yet understanding both experiments is necessary to characterize the object under study. In Bohr's view, the behavior of atomic and subatomic objects cannot be separated from the measuring instruments that create the context in which the measured objects behave. Consequently, there is no "single picture" that unifies the results obtained in these different experimental contexts, and only the "totality of the phenomena" together can provide a completely informative description.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

Possible passages

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Broadly speaking, traditional physics has collapsed into two portions, truisms and geography. There are, however, newer portions of physics, such as the theory of quanta, which do not come under this head, but appear to give genuine knowledge of laws reached by experiment. The world which the theory of relativity presents to our imagination is not so much a world of “things” in “motion” as a world of _events_.
Bertrand Russell, The A B C of Relativity
States what Complementarity is.
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On the other hand, any two particulars of which I am aware are either simultaneous or successive, and their simultaneity or successiveness is sometimes itself a datum to me. We may therefore define the perspective to which a given particular belongs as "all particulars simultaneous with the given particular," where "simultaneous" is to be understood as a direct simple relation, not the derivative constructed…
Bertrand Russell, Mysticism and Logic and Other Essays
States what Complementarity is.
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To simplify the enunciation, suppose that the sum of the work of the external forces is null, as well as that of the quantities of heat given off to the outside. Then the signification of our principle will be: _There is a combination of these n - p relations whose first member is an exact differential_; and then this differential vanishing in virtue of our _n_ - _p_ relations, its integral is a constant and this…
Henri Poincaré, The Foundations of Science
States what Complementarity is.
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Philosophers who discussed Complementarity (physics)

Paul Feyerabend

Related ideas

Place in the tradition

Part of Interpretations of quantum mechanics.

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