Electromagnetic stress-energy tensor

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In physics, the electromagnetic stress-energy tensor is the portion of the stress-energy tensor due to the electromagnetic field. In free space, it is given by (in cgs units):

T^{\alpha\beta} = \frac{1}{4\pi} [ -F^{\alpha \gamma}F_{\gamma}^{\beta}+\frac{1}{4}g^{\alpha\beta}F_{\gamma\delta}F^{\gamma\delta}].

And in explicit matrix form:

T^{\alpha\beta} =\begin{bmatrix} \frac{E^2+B^2}{8\pi} & \frac{S_x}{c} & \frac{S_y}{c} & \frac{S_z}{c} \\ \frac{S_x}{c} & -\sigma_{xx} & -\sigma_{xy} & -\sigma_{xz} \\ \frac{S_y}{c} & -\sigma_{yx} & -\sigma_{yy} & -\sigma_{yz} \\ \frac{S_z}{c} & -\sigma_{zx} & -\sigma_{zy} & -\sigma_{zz} \end{bmatrix}

where

\vec{S}=\frac{c}{4\pi}\vec{E}\times\vec{H} is Poynting vector,
F_{\alpha\beta}\! is the Electromagnetic field tensor,
g_{\alpha\beta}\! is the metric tensor and
\sigma_{\alpha\beta}\! is Maxwell stress tensor

The stress-energy tensor for an electromagnetic field in a dielectric medium is less well understood and is the subject of the unresolved Abraham-Minkowski controversy.

The element, T^{\alpha\beta}\!, of the energy momentum tensor represents the flux of the αth-component of the four-momentum of the electromagnetic field, P^{\alpha}\!, going through a hyperplane xβ = constant. It represents the contribution of electromagnetism to the source of the gravitational field (curvature of space-time) in general relativity.

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