Quantum mechanics, often referred to as quantum physics or quantum theory, is a fundamental branch of physics that revolutionized our understanding of the behavior of matter and energy at the smallest scales. It provides a description of the physical world that is fundamentally different from classical mechanics, which governs the behavior of macroscopic objects. Quantum mechanics is a cornerstone of modern physics and underlies our understanding of atoms, molecules, subatomic particles, and the very nature of reality itself.
At its core, quantum mechanics is a theory that explores the behavior of particles, such as electrons and photons, as well as the interactions between these particles and the forces that govern their behavior. The transition from classical to quantum mechanics was marked by a departure from deterministic, continuous models to a probabilistic, discrete framework.
The chapter below from Quantum Mechanical Foundations of Molecular Spectroscopy, First Edition. Max Diem gives a glimpse into how the theories of Quantum Mechanics have been derived from the principles of Classical Mechanics.