  Holding a Morris-Thorne wormhole open requires a violation of the null energy
condition, calling for the need for so-called exotic matter near the throat.
Many researchers consider exotic matter to be completely unphysical in
classical general relativity. It has been shown, however, that the existence of
an extra macroscopic dimension can resolve this issue: the throat could be
lined with ordinary matter, while the extra dimension is then responsible for
the unavoidable energy violation. The purpose of this paper is to show that the
extra dimension can be microscopic, a result that is consistent with string
theory.
