Heisenberg cut
In quantum mechanics, a Heisenberg cut, is the hypothetical interface between quantum events and an observer's information, knowledge, or conscious awareness. Below the cut everything is governed by the wave function and Schrödinger equation; above the cut a classical description is used. The Heisenberg cut is a theoretical construct; it is not known whether actual Heisenberg cuts exist, where they might be found, or how they could be detected experimentally. However, the concept is useful for analysis.
The cut is named after Werner Heisenberg who first raised the idea during the 1929 Como Conference, during the discussions that followed Niels Bohr's introduction of the principle of complementarity.
The Heisenberg cut is associated with the Copenhagen interpretation of quantum mechanics, which requires a wave function collapse. Interpretations of quantum mechanics that do not recognise wave function collapse do not require Heisenberg cuts.
Description
Heisenberg stated the concept in many different ways in his work, for example, in 1952 he writes:The idea that the result of measurement does not depend on the location of the cut was shown by John von Neumann in his 1933 book Mathematical Foundations of Quantum Mechanics. Wolfgang Pauli informed Heisenberg of this in a letter in 1933.