Classically, the effect of the electromagnetic field on particles is often said to be given by the Lorentz force law:
$$ \vec{F} = q\vec{E} + q\vec{v}\times\vec{B}. $$
However, I'm really starting to doubt this is entirely the true equation. We know there are neutral particles such as the neutrino that have a nonzero dipole magnetic moment. If we take the above equation at face value (perhaps naively), then the fact that a neutron has $q=0$ must mean the neutron has $\vec{F} = 0$ force.
Something here is clearly wrong, because a non-uniform magnetic field imposes a force on a particle with nonzero dipole moment.
Now one can reply by saying that we can imagine the magnetic dipole as the limit of two monopoles stuck together or as a loop of electric current. I agree this works as a trick, but the issue is that a neutrino is not composed of magnetic monopoles and it does not have any electric current, so how could the Lorentz force possibly apply?
