Part of a series of articles about
Quantum mechanics
${\displaystyle i\hslash \frac{d}{dt}|\mathrm{\Psi }⟩=\hat{H}|\mathrm{\Psi }⟩}$ Schrödinger equation
Introduction Glossary History
Background Classical mechanics Old quantum theory Bra–ket notation Hamiltonian Interference
Fundamentals Complementarity Decoherence Entanglement Energy level Measurement Nonlocality Quantum number State Superposition Symmetry Tunnelling Uncertainty Wave function Collapse
Experiments Bell's inequality CHSH inequality Davisson–Germer Double-slit Elitzur–Vaidman Franck–Hertz Leggett inequality Leggett–Garg inequality Mach–Zehnder Popper Quantum eraser Delayed-choice Schrödinger's cat Stern–Gerlach Wheeler's delayed-choice
Formulations Overview Heisenberg Interaction Matrix Phase-space Schrödinger Sum-over-histories (path integral)
Equations Dirac Klein–Gordon Pauli Rydberg Schrödinger
Interpretations Bayesian Consciousness causes collapse Consistent histories Copenhagen de Broglie–Bohm Ensemble Hidden-variable Many-worlds Objective-collapse Quantum logic Superdeterminism Relational Transactional
Advanced topics Relativistic quantum mechanics Quantum field theory Quantum information science Quantum computing Quantum chaos EPR paradox Density matrix Scattering theory Quantum statistical mechanics Quantum machine learning
Scientists Aharonov Bell Bethe Blackett Bloch Bohm Bohr Born Bose de Broglie Compton Dirac Davisson Debye Ehrenfest Einstein Everett Fock Fermi Feynman Glauber Gutzwiller Heisenberg Hilbert Jordan Kramers Lamb Landau Laue Moseley Millikan Onnes Pauli Planck Rabi Raman Rydberg Schrödinger Simmons Sommerfeld von Neumann Weyl Wien Wigner Zeeman Zeilinger
v t e

Inquantum mechanics, aHeisenberg cut, is the hypothetical interface between quantum events and anobserver's information,knowledge, orconscious awareness. Below the cut everything is governed by thewave function andSchrödinger equation; above the cut aclassical description is used.^[1] 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.^[1][2][3][4]

The cut is named afterWerner Heisenberg who first raised the idea during the 1929Como Conference, during the discussions that followedNiels Bohr's introduction of the principle ofcomplementarity.^[5]

The Heisenberg cut is associated with theCopenhagen interpretation of quantum mechanics, which requires awave function collapse.^[6] Interpretations of quantum mechanics that do not recognise wave function collapse (such asDe Broglie–Bohm ormany-worlds interpretations) do not require Heisenberg cuts.

Heisenberg stated the concept in many different ways in his work, for example, in 1952 he writes:^[7]

In this situation it follows automatically that, in a mathematical treatment of the process, a dividing line must be drawn between, on the one hand, the apparatus which we use as an aid in putting the question and thus, in a way, treat as part of ourselves, and on the other hand, the physical systems we wish to investigate. The latter we represent mathematically as a wave function. This function, according to quantum theory, consists of a differential equation which determines any future state from the present state of the function... The dividing line between the system to be observed and the measuring apparatus is immediately defined by the nature of the problem but it obviously signifies no discontinuity of the physical process. For this reason there must, within limits, exist complete freedom in choosing the position of the dividing line.

The idea that the result of measurement does not depend on the location of the cut was shown byJohn von Neumann in his 1933 bookMathematical Foundations of Quantum Mechanics.Wolfgang Pauli informed Heisenberg of this in a letter in 1933.^[5]

• Correspondence principle
• De Broglie–Bohm theory
• Mind–body dualism
• Observer effect
• Pilot wave model
• Schrödinger's cat
• Universal wavefunction

• Quantum measurement
• Interpretations of quantum mechanics
• Werner Heisenberg

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• Short description is different from Wikidata