What causes the random movement of particles inside a conductor? I'm reading about currents in electricity right now, and it was mentioned that even if there's no electric field inside a conductor, charged particles inside are still undergoing random movement.
I wanted to know what forces cause this random movement to occur? Or if it's not any force which causes this mysterious movement, then what is it?
Thanks.
 A: In the quantum mechanical description of a conductor all energy levels of the conductor are filled up to some specific energy level, called the Fermi level. This is because of the Pauli exclusion principle, which says that electrons with the same spin cannot occupy the same energy level and thus causes higher energy levels to be populated. Therefore, even at zero-temperature electrons have some amount of kinetic energy. This motion is, however, random and does not contribute to a net current. To get a current an electric field must be supplied.
Some more info:
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html
A: Does your conductor have any resistivity? In that case the fluctuation-dissipation theorem applies. In the case that your conductor is a perfect superconductor, it would still couple inductively to the electromagnetic field around it, which, per 3rd law of thermodynamics must have a non-zero temperature. To remove those fluctuations, the total field volume would have to be zero, i.e. your conductor would have to have zero loop area, which is obviously unphysical. 
