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Improved test of the Equivalence Principle as a probe of quantum gravity

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Current approaches to the problems of dark energy and unification generically predict the existence of new fields (quintessence dilatons etc.) that will in principle couple with different strengths to different standard-model fields. These different coupling strengths will cause test materials of different compositions to fall at different rates in the same gravitational field violating the Equivalence Principle the foundation of General Relativity. A sufficiently sensitive measurement of the relative accelerations of different test bodies in orbit around the earth could detect or rule out these new fields complementing existing or proposed experiments in high-energy physics (colliders) and observational cosmology (space telescopes). To do this convincingly such an experiment needs at least three test materials spanning the largest possible volume in the space of atomic and molecular properties and a sensitivity to EP violations of as little as a part in $10^{18}$ (attainable only in space and at low temperatures). I discuss one such experiment the Satellite Test of the Equivalence Principle which has reached an advanced stage of prototype development and is currently awaiting a path toward a flight program.