## Four-current |

In
**four-current** (technically the **four-current density**)^{
[1]} is the four-dimensional analogue of the
*four-dimensional spacetime*, rather than three-dimensional space and time separately. Mathematically it is a

Analogously, it is possible to have any form of "current density", meaning the flow of a quantity per unit time per unit area. see

This article uses the

Using the

where *c* is the
*ρ* is the
**j** the conventional
*α* labels the

This can also be expressed in terms of the
^{
[2]}^{
[3]}

where *ρ* is the
*ρ*_{0} the charge density for an observer moving at the speed *u* (the magnitude of the

Qualitatively, the change in charge density (charge per unit volume) is due to the contracted volume of charge due to

Charges (free or as a distribution) at rest will appear to remain at the same spatial position for some interval of time (as long as they're stationary). When they do move, this corresponds to changes in position, therefore the charges have velocity, and the motion of charge constitutes an electric current. This means that charge density is related to time, while current density is related to space.

The four-current unifies charge density (related to electricity) and current density (related to magnetism) in one electromagnetic entity.

Other Languages

català: Quadricorrent

español: Cuadricorriente

فارسی: چاربردار جریان

italiano: Quadricorrente

मराठी: चौधारा

Nederlands: Vierstroom

日本語: 電荷・電流密度

português: Quadricorrente

русский: 4-ток

українська: 4-струм

中文: 四維電流密度