Scientific significance of STEP

Abstract

The equivalence principle is fundamental to any theory of gravitation. In its weakest and thus most general form, called the weak equivalence principle, the principle states that in a gravitational field all test bodies fall at the same speed, i.e. the ratios of their inertial and passive gravitational masses are the same, regardless of the composition of the bodies. This very fundamental principle is the premise of the two more precise forms of the equivalence principle, namely the Einsteinian and the strong; the latter leading almost directly to Einstein's general relativity theory. The Satellite Test of the Equivalence Principle (STEP) experiment is being proposed to test the weak equivalence principle in the Earth's orbit at the 10 −17 level. Several co-experiments deepen and enrich the project: the Short-Range Equivalence Principle, the Constant of Gravity G, the Geodesy and the Aeronomy Co-Experiment.