Copenhagen interpretation

Principles

1. A system is completely described by a wave function ψ, representing an observer’s subjective knowledge of the system. (Heisenberg)^{[citation needed]}
2. The description of nature is essentially probabilistic, with the probability of an event related to the square of the amplitude of the wave function related to it. (The Born rule, after Max Born)
3. It is not possible to know the value of all the properties of the system at the same time; those properties that are not known with precision must be described by probabilities. (Heisenberg’s uncertainty principle)
4. Matter exhibits a wave–particle duality. An experiment can show the particle-like properties of matter, or the wave-like properties; in some experiments both of these complementary viewpoints must be invoked to explain the results, according to the complementarity principle of Niels Bohr.
5. Measuring devices are essentially classical devices, and measure only classical properties such as position and momentum.
6. The quantum mechanical description of large systems will closely approximate the classical description. (The correspondence principle of Bohr and Heisenberg.)

Photo:

Description: Niels Bohr and Werner Heisinberg at a Bohr Institute conference, Copenhagen.
Date: 1934 or 1936
Credit: Photograph by Paul Ehrenfest, Jr., courtesy AIP Emilio Segre Visual Archives, Weisskopf Collection
Names: Bohr, Niels Henrik David; Heisenberg, Werner