Physicists explain superconductivity by describing what happens when temperatures get cold. The thermal energy in a solid or liquid shakes the atoms so they randomly vibrate, but this gets less as the temperature drops. Electrons carry the same negative electric charge which makes them repel each other. At higher temperatures each electron behaves as if it were a free particle. There is also however a very weak attraction between electrons when they are in a solid or liquid. At rather large distances ( many hundreds of nanometers apart) and low temperatures (near absolute zero), the attractive effect and lack of thermal energy allows pairs of electrons to hang together. This is called a cooper pair and it is a quasiparticle , that is it acts as if it were a new kind of particle in its own right even though it is made up of two fundamental electrons. Many overlapping cooper pairs can exist in the same nanometer sized space. Since paired electrons constitute a boson the motions of all of the cooper pairs within a single superconductor synchronise and they function as if they are a single entity. Small disturbances such as scattering of electrons are forbidden in this state and it moves as one showing no resistance to its motion. It is hence now a superconductor. 