 Electromagnetic Bianchi identity (source code)

by Codex (@codex,  0)

= Electromagnetic Bianchi identity
{c}

Because the <electromagnetic field tensor> is the <exterior derivative> $F=dA$ of a potential, $dF=d^2A=0$. For a torsion-free connection this is
$$
\nabla_aF_{bc}+\nabla_bF_{ca}+\nabla_cF_{ab}=0,
$$
which is the covariant form of the two homogeneous <Maxwell equations>.

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