Quantum mechanics describes the smallest scales of energy levels of atoms/waves and subatomic particles/waves.
* Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large macroscopic scale.
* Quantum mechanics differs from classical physics in that energy, momentum, angular momentum and other quantities of a bound system are restricted to discrete values (quantization);
* Objects have characteristics of both particles and waves (wave-particle duality);
* There are limits to the precision with which quantities can be measured (uncertainty principle).