A partial differential equation which appears in differential geometry and relativistic field theory. Its name is a wordplay on its similar form to the Klein-Gordon equation. The equation, as well as several solution techniques, were known in the 19th century, but the equation grew greatly in importance when it was realized that it led to solutions ("kink" and "antikink") with the collisional properties of solitons. The sine-Gordon equation also appears in a number of other physical applications (Barone 1971; Gibbon et al. 1979; Davydov 1985, pp. 202 and 240), including the propagation of fluxons in Josephson junctions (a junction between two superconductors), the motion of rigid pendula attached to a stretched wire, and dislocations in crystals.

Klein-Gordon equation | sinh-Gordon equation | soliton