Searching for Extra Dimensions and New String-Inspired Forces in the Casimir Regime

The appearance of new fundamental forces and extra-dimensional modifications to gravity in extensions of the Standard Model has motivated considerable interest in testing Newtonian gravity at short distances (<10^-3 m). Presently a number of new gravity experiments are searching for non-Newtonian effects in the ranges 10^-4 m -- 10^-3 m. However, as challenging as these experiments are, formidable new obstacles await the next generation of experiments which will probe gravity at distances <10^-4 m where Casimir/van der Waals forces become dominant. Here we will review the motivation for conducting such very short distance gravity experiments, and discuss some of the new problems that may arise in future experiments. Finally, we suggest schematic designs for null experiments which would address some of these problems using the ``iso-electronic'' and ``finite-size'' effects.