collapse theory

The "collapse theory" in quantum mechanics refers to the abrupt and discontinuous change in a system's wave function during a measurement. While the Schrödinger equation describes the determinate evolution of a wave function between measurements, the act of measurement itself causes this "collapse" or "reduction" to a single state, which is unpredictable.1

This phenomenon raises questions about how the microscopic quantum world interacts with the macroscopic classical world of measuring instruments. Various interpretations exist, including the role of a conscious observer, the pragmatic Copenhagen interpretation, and the idea that irreversibility is key. Alternative theories, like the many-worlds interpretation, propose that the universe branches into multiple universes with each possible outcome. The Ghirardi, Rimini, and Weber (GRW) theory suggests that wave functions spontaneously "jump" or collapse randomly, though these jumps are too rare to observe for microscopic systems. The measurement problem remains a significant challenge in quantum mechanics, as the distinction between "measurement" and "ordinary physical processes" is not clearly defined.123