Measurement problem information

In quantum mechanics, the measurement problem is the problem of definite outcomes: quantum systems have superpositions but quantum measurements only give one definite result.^[1]^[2]

The wave function in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states. However, actual measurements always find the physical system in a definite state. Any future evolution of the wave function is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the system that is not obviously a consequence of Schrödinger evolution. The measurement problem is describing what that "something" is, how a superposition of many possible values becomes a single measured value.

To express matters differently (paraphrasing Steven Weinberg),^[3]^[4] the Schrödinger equation determines the wave function at any later time. If observers and their measuring apparatus are themselves described by a deterministic wave function, why can we not predict precise results for measurements, but only probabilities? As a general question: How can one establish a correspondence between quantum reality and classical reality?^[5]

^ Schlosshauer, Maximilian (2005-02-23). "Decoherence, the measurement problem, and interpretations of quantum mechanics". Reviews of Modern Physics. 76 (4): 1267–1305. arXiv:quant-ph/0312059. doi:10.1103/RevModPhys.76.1267. ISSN 0034-6861.
^ Leggett, A. J. (2005-02-11). "The Quantum Measurement Problem". Science. 307 (5711): 871–872. doi:10.1126/science.1109541. ISSN 0036-8075.
^ Weinberg, Steven (1998). "The Great Reduction: Physics in the Twentieth Century". In Michael Howard & William Roger Louis (eds.). The Oxford History of the Twentieth Century. Oxford University Press. p. 26. ISBN 0-19-820428-0.
^ Weinberg, Steven (November 2005). "Einstein's Mistakes". Physics Today. 58 (11): 31–35. Bibcode:2005PhT....58k..31W. doi:10.1063/1.2155755. S2CID 120594692.
^ Zurek, Wojciech Hubert (22 May 2003). "Decoherence, einselection, and the quantum origins of the classical". Reviews of Modern Physics. 75 (3): 715–775. arXiv:quant-ph/0105127. Bibcode:2003RvMP...75..715Z. doi:10.1103/RevModPhys.75.715. S2CID 14759237.

[1] Schlosshauer, Maximilian (2005-02-23). "Decoherence, the measurement problem, and interpretations of quantum mechanics". Reviews of Modern Physics. 76 (4): 1267–1305. arXiv:quant-ph/0312059. doi:10.1103/RevModPhys.76.1267. ISSN 0034-6861.

[2] Leggett, A. J. (2005-02-11). "The Quantum Measurement Problem". Science. 307 (5711): 871–872. doi:10.1126/science.1109541. ISSN 0036-8075.

[Weinberg-3] Weinberg, Steven (1998). "The Great Reduction: Physics in the Twentieth Century". In Michael Howard & William Roger Louis (eds.). The Oxford History of the Twentieth Century. Oxford University Press. p. 26. ISBN 0-19-820428-0.

[Weinberg2-4] Weinberg, Steven (November 2005). "Einstein's Mistakes". Physics Today. 58 (11): 31–35. Bibcode:2005PhT....58k..31W. doi:10.1063/1.2155755. S2CID 120594692.

[Zurek-5] Zurek, Wojciech Hubert (22 May 2003). "Decoherence, einselection, and the quantum origins of the classical". Reviews of Modern Physics. 75 (3): 715–775. arXiv:quant-ph/0105127. Bibcode:2003RvMP...75..715Z. doi:10.1103/RevModPhys.75.715. S2CID 14759237.

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