Quantum mechanics is a fundamental theory in physics, describing nature at the smallest scales, such as atoms and subatomic particles. Developed in the early 20th century, key figures include Max Planck, Albert Einstein, Niels Bohr, and Erwin Schrödinger. Planck's constant (h = 6.62607015 × 10⁻³⁴ Js) is central to the framework. The theory introduces wave-particle duality, where particles like electrons exhibit both wave and particle properties