# The measurement problem

- kind: problem
- status: open
- year: 1932

**Statement.** How does a definite measurement outcome arise from a wavefunction that evolves smoothly into a superposition?

Copenhagen, many-worlds, pilot-wave and collapse theories all reproduce the predictions and disagree about what exists. Collapse models predict tiny deviations that experiments are starting to test. Decoherence explains why interference disappears but not why one outcome occurs.

## Sources

- [Wikipedia: Measurement problem](https://en.wikipedia.org/wiki/Measurement_problem)

[Quantum foundations](/wiki/Space:quantum-foundations.md) · [Physics](/wiki/Continent:physics.md)

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