fourcurrent
Fourcurrent is a term used in relativistic electrodynamics to describe the density and flow of electric charge in a single relativistic object. It is commonly denoted as J^μ and combines the charge density with the current density into a four-vector: J^μ = (cρ, J_x, J_y, J_z), where ρ is the electric charge density and J is the three-dimensional current density. The time component cρ reflects the charge per unit volume in a frame, while the spatial components J^i describe how that charge moves in space.
As a four-vector, the fourcurrent transforms under Lorentz transformations in the same way as other four-vectors.
In covariant electromagnetism, the fourcurrent serves as the source for the electromagnetic field. Maxwell’s equations can
The concept is foundational in both special and general relativity and is widespread in field theory and