Superluminality, Parelectricity, and Earnshaw's Theorem in Media with Inverted Populations

Population inversion leads to the phenomena of superluminality, in which wave packets can propagate dispersionlessly near dc faster than c, and parelectricity, in which the dc susceptibility is negative, implying the levitation of a charge above a parelectric medium. Also, charges placed in a cavity surrounded by a parelectric medium form stable configurations, in seeming violation of Earnshaw's theorem. Einstein causality is not violated.