Quantum mechanics (QM; also known as quantum physics or quantum theory), including quantum field theory, is a branch of physics which is the fundamental theory of nature at the small scales and energy levels of atoms and subatomic particles.[2] Classical physics (the physics existing before quantum mechanics) derives from quantum mechanics as an approximation valid only at large (macroscopic[3]) scales. Quantum mechanics differs from classical physics in that: energy, momentum and other quantities are often restricted to discrete values (quantization), objects have characteristics of both particles and waves (i.e. wave-particle duality), and there are limits to the precision with which quantities can be known (uncertainty principle).[note 1] Quantum mechanics gradually arose from Max Planck's solution in 1900 to the black-body radiation problem, and Albert Einstein's 1905 paper which offered a quantum-based theory to explain the photoelectric effect. Early quantum theory was profoundly re-conceived in the mid-1920s by Erwin Schrodinger, Werner Heisenberg, Max Born and others
