Truly Strong Coupling and Large Radius in String Theory

Abstract

String theory, if it describes nature, is probably strongly coupled. In light of recent developments in string duality, this means that the ``real world'' should correspond to a region of the classical moduli space which admits no weak coupling description. We exhibit, in the heterotic string, one such region of the moduli space, in which the coupling, $λ$, is large and the ``compactification radius'' scales as $λ^{1/3}$. We discuss some of the issues raised by the conjecture that the true vacuum lies in such a region. These include the question of coupling constant unification, and more generally the problem of what quantities one might hope to calculate and compare with experiment in such a picture.