In special and general relativity, the four-current is the four-dimensional analogue of the electric current density, which is used in the geometric context of four-dimensional spacetime, rather than three-dimensional space and time separately. Mathematically it is a four-vector, and is Lorentz covariant.

In special and general relativity, the four-current is the four-dimensional analogue of the electric current density, which is used in the geometric context of four-dimensional spacetime, rather than three-dimensional space and time separately. Mathematically it is a four-vector, and is Lorentz covariant.