Quantum mechanics uses two important concepts we usually are not aware of in daily life: the principle of least action (as classical mechanics does) and wave functions with amplitudes, which leads to a probability density according to Born's rule. There is a third concept evolving from those: Feynman's path integral method mimics Fermat's principle.
Something Strange Happens When You Trust Quantum Mechanics
Veritasium
Mar 5, 2025
WP: Fermat's principle
WP: Action principles
WP: Path integral formulation
WP: Wave function
WP: Probability amplitude
WP: Born rule