Interpretations of quantum mechanics

Interpretations of quantum mechanics are frameworks that explain how the theory’s mathematical states and probabilities relate to physical reality, measurement, and experimental outcomes.

Copenhagen interpretation: A family of views that treats quantum probabilities as central and measurement outcomes as definite, without assigning ordinary properties to unmeasured systems. It is the historically dominant family, though its claims about measurement and reality vary.
Quantum measurement problem: The problem of explaining how definite measurement outcomes arise from quantum theory’s evolution of superpositions. It is the central challenge that motivates competing accounts of measurement.
Niels Bohr: A Danish physicist who helped establish quantum theory and developed influential views on complementarity and measurement. His account of complementarity shaped the interpretation later associated with Copenhagen.
Bell's theorem: A theorem showing that no theory satisfying specified locality assumptions can reproduce all quantum predictions. It places rigorous limits on local accounts of quantum reality.
Quantum mechanics: A physical theory describing matter and radiation through states, observables, and probabilistic rules. Interpretations explain the physical meaning of this shared mathematical framework.
Many-worlds interpretation: An interpretation in which quantum evolution never collapses and measurement outcomes occur in distinct branches of the universal wavefunction. It removes collapse by treating every possible outcome as realized in a different branch.
Wave function collapse: A proposed change in which a quantum state becomes one of the possible states associated with a measurement outcome. Interpretations disagree over whether collapse is physical, effective, or absent.
Werner Heisenberg: A German physicist who formulated matrix mechanics and contributed to early interpretations of quantum theory. His views on measurement and potentiality helped define early debates about quantum meaning.
Bell test: An experiment that tests whether observed correlations violate a Bell inequality. Experimental violations rule out local hidden-variable explanations under stated assumptions.
Quantum field theory: A framework combining quantum principles with fields and special relativity to describe fundamental interactions. Interpretive questions persist when quantum theory is extended to relativistic fields.

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