Four-current | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-10-02

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Four-current


00:00:48 1 Definition
00:01:57 1.1 Motion of charges in spacetime
00:03:11 1.2 Physical interpretation
00:03:54 2 Continuity equation
00:05:15 3 Maxwell's equations
00:06:26 4 General relativity
00:07:40 5 Quantum field theory
00:08:07 6 See also



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SUMMARY
=======
In special and general relativity, the four-current (technically the four-current density) is the four-dimensional analogue of the electric current density. Also known as vector current, it 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.
Analogously, it is possible to have any form of "current density", meaning the flow of a quantity per unit time per unit area. see current density for more on this quantity.
This article uses the summation convention for indices. See covariance and contravariance of vectors for background on raised and lowered indices, and raising and lowering indices on how to switch between them.