RUI: Search for Non-Newtonian Gravity Using A High-Sensitivity Torsion Balance, A Continuation

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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 description of 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) pioneered by Newton 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 50 micron. Specific results obtained from this research in collaboration with SU students 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. This project aims to test the inverse-square law of gravity in the parallel-plane configuration by directly quantifying the contributions from non-gravitational interactions. The proposed strategy allows for conducting a high-precision experiment below 70 micron 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 strength α-parameter of the Yukawa space at least by a factor of four at the 10-μm range. Another novelty of the proposed research is to probe gravity above 1 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. The completed torsion balance experiment will provide an excellent experimental platform for students to gain critical laboratory skills and make significant contributions to the integration of teaching and research in the SU physics department. The research will greatly benefit from technical resources and expertise provided by the Eöt-Wash group at the University of Washington (UW), a pioneering group renowned for their precise studies of the ISL for many decades.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.