Abstract
It is well known that the inversion of populations in the ammonia maser leads to stimulated emission, and hence amplification, of microwaves. However, it is not well known that an inverted medium also leads to the superluminal propagation of off-resonance, finite-band-width wave packets, whose phase, group, energy, and “signal” velocities, as defined by Sommerfeld and Brillouin, all exceed the vacuum speed of lightc. Einstein causality is not violated, since the front velocity isc. The inversion of populations also implies a parelectric medium with negative electric susceptibility. (Parelectric media should not be confused withparaelectric media, which are ferroelectrics just above their Curie points.) The existence of a parelectric medium implies the possibility of the levitation of an electrical charge in the vacuum above this medium, as well as stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium. The apparent violation of Earn-shaw's theorem will be discussed. Numerical estimates for a proposed experiment to observe parelectricity will be given.
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Dedicated to Walther on the ocassion of his 60 birthday