Editing Energy (section)

=== Quantum mechanics ===
{{Main|Energy operator}}
In [[quantum mechanics]], energy is defined in terms of the [[Hamiltonian (quantum mechanics)|energy operator]]
(Hamiltonian) as a time derivative of the [[wave function]]. The [[Schrödinger equation]] equates the energy operator to the full energy of a particle or a system. Its results can be considered as a definition of measurement of energy in quantum mechanics. The Schrödinger equation describes the space- and time-dependence of a slowly changing (non-relativistic) [[wave function]] of quantum systems. The solution of this equation for a bound system is discrete (a set of permitted states, each characterized by an [[energy level]]) which results in the concept of [[quantum|quanta]]. In the solution of the Schrödinger equation for any oscillator (vibrator) and for electromagnetic waves in a vacuum, the resulting energy states are related to the frequency by [[Planck's relation]]: <math>E = h\nu</math> (where <math>h</math> is the [[Planck constant]] and <math>\nu</math> the frequency). In the case of an electromagnetic wave these energy states are called quanta of light or [[photon]]s.