Editing Field equation (section)

=== Waves ===

Field equations underlie wave equations, because periodically changing fields generate waves. Wave equations can be thought of as field equations, in the sense they can often be derived from field equations. Alternatively, given suitable Lagrangian or Hamiltonian densities and using the principle of stationary action, the wave equations can be obtained also.

For example, Maxwell's equations can be used to derive [[inhomogeneous electromagnetic wave equation]]s, and from the Einstein field equations one can derive equations for [[gravitational wave]]s.