Collaborative Research: Measuring G with a Magneto-Gravitational Trap

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Gravity was the first force mathematically described by scientists as an explanation for the motion of the moon, planets, and stars. Hundreds of years later, gravity is still considered to be the most poorly understood force. It cannot be consistently described across different theories in physics, and even its strength is poorly known. The Newtonian constant of gravitation, which quantifies the strength of gravity, is perhaps the most poorly measured fundamental property of the universe. This project seeks to greatly improve our knowledge of this constant with the most significant change in technique since the experiments of Henry Cavendish in 1798, who used a torsion balance for his measurements. The measurement funded by this award may be of value across many areas of physics and astronomy, and the new experimental tools being developed may lead to new instruments for measuring extremely small forces and accelerations for use in studying the earth and for inertial navigation. Further, the attention to detail required in these experiments makes them an exceptional training ground for tomorrow's STEM workers.The ultimate goal of this project is to develop a new system for measuring the Newtonian constant of gravitation G, and to make a measurement of G to unprecedented accuracy (10 parts per million or better). The approach leverages a recently-developed optomechanical system: a silica microsphere suspended in a magneto-gravitational trap under ultra-high vacuum. The mechanical oscillation of the microsphere will be used in the time-of-swing method to determine G from the change in oscillation frequency when field masses are brought near the trapped particle. The system has multiple features that make it nearly ideal for precision measurements, including an oscillation frequency that can be made less than 1 Hz, isolation from the surrounding environment, and other degrees of freedom to act as a built-in probe to correct for drifts. The proposed measurement strategy was chosen for its transparency to the scientific community. First, the simplicity of the system makes it simple to understand and analyze. Second, most of the data will be contained in sequences of images which are recorded; there are almost no hidden feedback loops or other difficulties in reanalyzing components. To ensure confidence in the new measurement, all data and analysis code will be stored and made freely available to other researchers in their entirety.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.