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Electromagnetic waves in tensor notation

Physics Asked by occd2000 on April 2, 2021

I’m trying to derive the wave equations for the electric and magnetic fields in covariant (tensor) formulation.
Starting with Gauss-Ampere law,
$$
partial_alpha F^{alphabeta}=frac{4pi}{c}J^beta
$$

and Gauss–Faraday law
$$
partial_{alpha}(tfrac{1}{2}epsilon^{alphabetagammadelta}F_{gammadelta}) = 0
$$

I would like to derive the values of $square vec{E}$ and $squarevec{B}$, or in general get to $partial^{nu} partial_{nu} F^{alphabeta}$. Is there an elegant way to do this? I did try using summation in each of the equations, but got quite confused with all the indices.

One Answer

In the Lorentz gauge your first equation becomes the wave equation for the potential $$ partial_alpha partial^alpha A^beta = frac{4pi}{c}J^beta ~. $$ By deriving left and right hand side you obtain $$ partial_alpha partial^alpha F^{gammabeta} = frac{4pi}{c} left(partial^gamma J^beta - partial^beta J^gamma right) ~, $$ which is the required wave equation.

Correct answer by my2cts on April 2, 2021

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