RUI: Continuation of Support for Short-range Tests of Gravity at Humboldt State University

Cal Poly Humboldt Sponsored Programs Foundation, Arcata CA

Investigators

Abstract

Humboldt State University (HSU) is a federally-recognized Hispanic Serving Institution in a predominantly rural area of Northern California, and the Gravitational Physics Laboratory (GPL) is the only dedicated hands-on physics research laboratory in the Department of Physics and Astronomy. This award supports research in gravitation at very small ranges of the scale of the width of a human hair. Tests on the Inverse-Square Law (ISL) are conducted with tabletop experiments, looking for deviations that may indicate new physics. This award ensures the continuation of physics research at HSU and that its undergraduates, many of whom are first-generation college students and members of underrepresented groups in STEM fields, gain valuable research skills necessary for the pursuit of graduate studies or careers in industry. Undergraduates will also be sent to perform research at the University of Washington through a collaboration formed with a gravity research group there. Finally, tests of gravity are of great interest to research in diverse fields ranging from astrophysics and cosmology to particle physics and precision measurement science. This award supports high-precision experiments that will test the Weak Equivalence Principle (WEP) of General Relativity and the gravitational ISL at unprecedented levels. The WEP will be tested at the millimeter scale and the ISL will be probed over sub-millimeter distances with unmatched sensitivity down to approximately 25 microns. Both tests use a novel parallel-plate torsion pendulum and attractor mass design. 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 attempt 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 and/or ISL at short distances. Since 1999, experimental limits have improved dramatically so that the ISL has proven valid over distances down to approximately 55 microns. A dedicated test of the WEP, however, has not been performed below the millimeter scale. The funding of this project will allow the completion of the ongoing initial tests of the WEP and ISL with test mass separations at the sub-millimeter scale (with test mass separation approaching 100 microns for the ISL test). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.