I read that force due to electric field on some particle in one reference frame can exhibit itself as force due to magnetic field in some other reference frame and that electric and magnetic fields are two aspects of same underlying electromagnetic field.
My question is what is the mechanism which can explain how an electric field becomes/creates magnetic field in some other reference frame. Is there any such explanation available in relativity theory? I am not looking for mathematics but a physical explanation.
Wikipedia article http://en.wikipedia.org/wiki/Relativistic_electromagnetism explains something about origin of magnetic forces in a wire as a consequence of lorentz contraction and motion of electrons in the wire
Calculation of the magnitude of the force exerted by a current-carrying wire on a moving charge is equivalent to calculating the magnetic field produced by the wire. Consider again the situation shown in figures. The latter figure, showing the situation in the reference frame of the test charge, is reproduced in the figure. The positive charges in the wire, each with charge q, are at rest in this frame, while the negative charges, each with charge −q, are moving to the left with speed v. The average distance between the negative charges in this frame is length-contracted to: where is the distance between them in the lab frame. Similarly, the distance between the positive charges is not length-contracted: Both of these effects give the wire a net negative charge in the test charge frame, so that it exerts an attractive force on the test charge.
But this still does not explain origin of magnetic field in case when there are no positive charges.