Quantum mechanics is a branch of quantum theory that simply determines the probability of an event happening, although the mathematical calculations to prove such things are very rigorous and not simple. In fact, quantum mechanics is often called the “final mathematical formulation of the quantum theory.” Developed during the 1920s, it accounts for matter at the atomic level, and is considered an extension of statistical mechanics, but based on quantum theory.

Physicist Max Planck was the first to propose the idea that energy existed in bundles called “quanta.” His theories later led to the development of quantum mechanics and modern physics.