Michio Kaku – Physics of the Future (2011)
Magnetic lines of force cannot penetrate a superconductor. This is the Meissner effect. (When a magnetic field is applied to a superconductor, a small electric current forms on the surface and cancels it, so the magnetic field is expelled from the superconductor.) When you place the magnet on top of the ceramic, its field lines bunch up since they cannot pass through the ceramic. This creates a “cushion” of magnetic field lines, which are all squeezed together, thereby pushing the magnet away from the ceramic, making it float.