Award Announcement - RUI: Search for Non-Newtonian Gravity Using a High-Sensitivity Torsion Balance at Seattle University

Document Type

Award Materials

Publication Date



Gravity represents one of the four fundamental interactions in nature. But unlike the other three interactions (electromagnetism, weak, and strong forces), its theoretical descriptions based on Newton's universal gravitation, later expanded by Einstein's General Relativity, are incompatible with the Standard Model, a quantum-mechanical framework that unifies all of the other three interactions. Faced with this dichotomy, some modern proposals in theoretical physics have suggested a possible breakdown of the inverse-square law (ISL) at experimentally-accessible sub-millimeter separations, thereby providing a tantalizing prospect for unifying gravity with quantum theory. The proposed research will utilize one of the most sensitive table-top instruments, a torsional balance, to directly probe the ISL below 100 micrometers. Specific results obtained from this research, in collaboration with undergraduate students and the Eot-Wash group of the University of Washington, will thus increase basic knowledge in fundamental research and have profound impacts across broad areas of physics ranging from astrophysics to elementary particle and nuclear physics.

The proposed research aims to test short-range gravity in the parallel-plane configuration by directly quantifying the contributions from non-gravitational interactions. The strategy makes it possible to conduct a high-precision experiment below 70 micrometers for which the roughness and planarity of the interfacing surfaces are the only limiting physical barriers. The approach will thus substantially improve the current limits on the Yukawa space at the 10 micrometer range by a factor of four. Another novelty of the proposed research is to probe gravity above one cm in the Yukawa space, a previously unexplored range. From a technical perspective, with an electrostatic screen inserted between the test bodies, probing gravity at this scale would significantly reduce the near-field effects, such as the electric patch effect and the Casimir force. Finally, the proposed research will provide on-campus, hands-on research opportunities for students, enhancing an existing research program in the area of precision force measurements in the PI's lab. Examples of the laboratory techniques routinely taught in undergraduate research in the past include: low-noise lock-in measurements, design and construction of electronic circuits, interferometric techniques, such as fiber-optic and Michelson's interferometer to perform precision displacement measurements, various scanning probe microscopy techniques, such as STM, AFM, and KPM, that are accessible at the NSF-funded Washington Nanofabrication Facility (WNF) at the University of Washington.