RUI: Parallel-Plate Torsion Pendulum for Investigations of Short-range Gravitational Physics

Cal Poly Humboldt Sponsored Programs Foundation, Arcata CA

Investigators

Abstract

The goal of this project is to test the Weak Equivalence Principle (WEP) of General Relativity and the gravitational inverse-square law (ISL) at unprecedented levels. The WEP will be tested at the millimeter scale and the ISL will be probed over sub-millimeter distances with unprecedented sensitivity. Both tests will use a novel parallel-plate torsion pendulum design. Since 1999, experimental limits have improved dramatically so that the ISL has proven valid over distances down to approximately 55 micrometers. A dedicated test of the WEP, however, has not been performed below the millimeter scale. The initial work under this award will probe the WEP at the millimeter scale and below. This measurement will be accomplished with a novel parallel-plate torsion pendulum design that will provide an essentially null experiment and use multiple composition dipole combinations. Subsequently, a more difficult test of the gravitational ISL will be pursued by decreasing the pendulum/attractor mass separation to 100 micrometers. This configuration will probe the ISL down to distances of approximately 20 micrometers. In recent years the study of the gravitational interaction at short (sub-millimeter) distance scales has gained much attention due in a large part to unification scenarios arising in string or M-theory that require more than three spatial dimensions, some of which could be macroscopic. Short-range tests of gravity and the WEP also investigate possible proposed mechanisms that endeavor to explain the accelerated expansion of the universe, generally attributed to Dark Energy. Finally, such tests present the possibility to search for hypothetical new interactions due to exotic particles or other phenomena. Many scenarios concerning these effects predict a violation of the WEP or gravitational ISL at short distances. The project will be performed in the Gravitational Physics Laboratory at Humboldt State University, the only arena in which undergraduate physics students at Humboldt State University may obtain hands-on research experience. This award provides continued support for the laboratory, undergraduate stipends, equipment improvements, and support for dissemination of results including student presentations. Collaboration with the University of Washington Eöt-Wash group will expedite machining projects as well as allow one undergraduate per year from Humboldt State to gain valuable experience working with the group as an undergraduate research assistant during the summer months. In addition, software tools developed for data acquisition and analysis will be transferrable to educational opportunities in the upper division classroom.