The Physics of Negative Energy Densities

Abstract

I review some recent results showing that the physics of negative energy densities, as predicted by relativistic quantum field theories, is more complicated than has generally been appreciated. On the one hand, in external potentials where there is a time--dependence, however slight, the Hamiltonians are unbounded below. On the other, there are limitations of quantum measurement in detecting or utilizing these negative energies.

10 pages, latex, uses sprocl, talk given at the Quantum Fields in External Potentials Workshop, Leipzig, 1998