Science Forums 2

[CraigD]

Originally Posted by GAHD

Light *IS* affected by magnetic feilds: they cause polarization of the waves. Faraday noted this effect and it is used quite extensively in solid state polorization controllers.

minor semantics, but there IS interaction between the two.

Just the sort of semantic we’re here to discuss!

As far as I know – and I could well know wrongly - the Faraday effect can only occur when light passes through a non-vacuum medium – that is, a volume with non-zero rest mass particles in it. I don’t believe a beam of polarized light has its polarization rotated if it passes through a magnetic field in vacuum.

So it’s not an example photons interacting with other photons – which I understand is forbidden – but magnetic interaction photons interacting with fermions (usually electrons), which interact with EM radiation photons. In practical terms, true vacuums don’t exist enough to worry about – interstellar space, for example, has at least 2000 electrons/m, so magneto-optical effects like the Faraday effect happen effectively everywhere - but for understanding fundamental interactions, the distinction is, I think, critical.

I don’t know how to describe light polarization effects – Faraday or others – in terms of photon-fermion interactions. If someone can, I’d greatly appreciate it – it’s puzzled me for a long time.