Faraday effect is the rotation of the plane of polarization of a light beam by a magnetic field. Is it absent in vacuum?
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$\begingroup$ The Faraday effect is, by definition, an effect that happens in matter. Are you asking if there is a vacuum Faraday effect? If there is, it's most likely not measurable in the lab on visible light. I don't know if there are QFT interaction terms that could be interpreted as the equivalents of a Faraday effect and what it would take to see them in high energy systems. $\endgroup$– FlatterMannCommented May 10, 2023 at 16:04
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$\begingroup$ I’m asking if the same rotation effect from magnetic field happens on light in vacuum. $\endgroup$– BipedalJoeCommented May 10, 2023 at 16:15
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$\begingroup$ Certainly not on a scale that is detectable by any imaginable means. In the low energy regime (visible photons and static fields) the self-interaction of the electromagnetic field is extremely small. There are such interactions at extremely high energies, but I can't tell you whether they could amount to something like a Faraday effect like rotation. $\endgroup$– FlatterMannCommented May 10, 2023 at 16:22
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2 Answers
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There is no Faraday effect in a vacuum. The Faraday effect results from the permeability of the medium being a skew-symmetric tensor generated by the bias field, $\mu_0$ is a scalar independent of the fields.
answered May 10, 2023 at 16:22
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The solutions of Maxwell's equations in a vacuum, where there are no sources, are amenable to linear superposition, so you can add a static magnetic field to a plane wave/wave packet with no effect. Axion production notwithstanding.
