Page "Quantum mechanics" Paragraph 42

Predictions of quantum mechanics have been verified experimentally to an extremely high degree of accuracy.

According to the correspondence principle between classical and quantum mechanics, all objects obey the laws of quantum mechanics, and classical mechanics is just an approximation for large systems of objects ( or a statistical quantum mechanics of a large collection of particles ).

The laws of classical mechanics thus follow from the laws of quantum mechanics as a statistical average at the limit of large systems or large quantum numbers.

However, chaotic systems do not have good quantum numbers, and quantum chaos studies the relationship between classical and quantum descriptions in these systems.