What led to relativity is the thought experiment where two people are attached, one to a coil and one to a magnet. It is described at the end of this page . http://www.physics.ucla.edu/demoweb...cs/special_relativity/special_relativity.html My question is in the case of the magnet moving toward the loop the magnetic field must move with the magnet. But how "stiff" is this magnetic field. Does it track the magnet perfectly, or does it lag the magnet. If it tracks the field perfectly then something must move faster than light to tell the outer perimeter to keep up with the magnet. This cannot happen. It must lag the magnetic field and in this case is it this lag that is responsible for the electric field.