Can a magnetic field in a vacuum bend the path of light?
No. As far as I know, magnetic fields can:
1 - affect the motion of free charged particles (photons don't carry charge and are unaffected by B-fields)
2 - cause matter to become magnetized (a net alignment of the dipoles, which are throughout matter)
3 - changing magnetic fields can induce an electric field (see Faraday's law)
These statements are not the most general, but I think they are among the most common points one can make about magnetic fields.
Gravitational field can, as it alters spacetime by introducing curvature. Outside gravitational fields spacetime is flat and thus light follows a straight line path. Fair enough?
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