Sign of the Static Electric Polarizability in Relativistic Quantum Theory

The question of the sign of the static electric polarizability ${\alpha }_E$ of an elementary system is studied within the framework of relativistic quantum theory. It is emphasized that a high-energy assumption is necessary to derive ${\alpha }_E>0\mathrm{}$. Thus, although available experimental information is consistent with this inequality, the discovery of a system for which ${\alpha }_E$ is negative does not appear to be excluded on the basis of general principles alone.