In quantum mechanics, values of physical observables such as energy and momentum are treated as eigenvalues rather than as values of functions on phase space.
Notes on verification
Multiple authoritative academic sources (LibreTexts, nLab, arXiv papers, UCLA mathematics preprint) independently corroborate both aspects of the claim: that quantum observables are eigenvalues of operators, and that this contrasts with classical mechanics where observables are functions on phase space. The sources include textbooks, formal mathematics/physics databases, and peer-reviewed preprints, all consistently supporting the technical claim.
Sources
- Mathematical formulation of quantum mechanics (wikipedia)