Quantum mechanics is the branch of physics treating atomic and subatomic systems and their interaction based on the observation that all forms of energy are released in discrete units or bundles called " quanta ". Remarkably, quantum theory typically permits only probable or statistical calculation of the observed features of subatomic particles, understood in terms of wave functions. The Schrödinger equation plays the role in quantum mechanics that Newton's laws and conservation of energy serve in classical mechanics—i.e., it predicts the future behavior of a dynamic system —and is a wave equation that is used to solve for wavefunctions.