Wave function
A wave function is the mathematical object that encodes the complete state of a quantum system, usually written as the Greek letter psi. It assigns a complex number, called an amplitude, to each possible configuration of the system. The Born rule states that the squared magnitude of the amplitude gives the probability of finding the system in that configuration when it is measured.
Role in quantum mechanics
The wave function evolves smoothly and deterministically in time according to the Schrodinger equation, but measurement introduces probability: the same prepared state can yield different outcomes, and only the statistics are predictable. Max Born introduced this probabilistic reading in 1926, receiving the 1954 Nobel Prize in Physics for it. How and whether the wave function physically collapses when a measurement occurs is the subject of the measurement problem, one of the central open questions of quantum mechanics.
Sources
- The Nobel Prize in Physics 1954 (Max Born) (The Nobel Foundation, 1954)
- Quantum Mechanics (Stanford Encyclopedia of Philosophy) (Stanford Encyclopedia of Philosophy, 2021)
Cite this entry
"Wave function." postquantum.wiki. Updated July 11, 2026. https://postquantum.wiki/wave-function@misc{pqwiki-wave-function,
title = {Wave function},
howpublished = {\url{https://postquantum.wiki/wave-function}},
year = {2026},
note = {postquantum.wiki, updated 2026-07-11}
}