Tests of the gravitational inverse square law and equivalence principle, and cryogenic torsion pendulum development

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A program of laboratory tests of fundamental gravitational physics laws is to be extended, in parallel with development of the cryogenic torsion pendulum as a general tool for research in gravitational physics. Included in the research program are: 1) a test of the inverse square distance dependence of the gravitational force for mass separation on the order of 15 centimeters, 2) tests of the weak equivalence principle over various ranges, for gravitational field sources which include laboratory masses, a nearby mountain, and the sun, and 3) completion of a measurement of the gravitational constant G. These projects are conducted in a remote underground laboratory (Battelle Gravitational Physics Laboratory, BGPL) which has been prepared with support from the Pacific Northwest National Laboratory in a former Nike missile bunker on an isolated environmental preserve near Richland, Washington. Most of this work is done in collaboration with the gravitational physics group of Paul Boynton at the University of Washington.A discovery of deviation of the apparent gravitational force from the inverse square distance dependence of Newton's law of gravity could signal the existence of new fundamental forces in Nature, with profound implications for the laws of physics. Similarly, discovery of a violation of the weak equivalence principle which asserts that all objects fall with the same acceleration in a gravitational field, would have profound implications. This principle, which is a foundation stone of Einstein's theory of General Relativity, is predicted by many modern theories of gravitation to fail at some level. The measurement of the gravitational constant G will help resolve significant discrepancies among a number of measurements of this fundamental constants made in the last two decades. Technological development of the cryogenic torsion pendulum used in this work will be of potential benefit to a wide range of experimental research in which it is important to measure small macroscopic forces with extreme sensitivity.