Improved Measurement of the Newtonian Gravitational Constant G

The Newtonian gravitational constant, G, is one of the oldest known fundamental constants, but despite this, it is the least precisely known of all the fundamental constants to date. In the past 200 years, a wide variety of experimental methods have been used to measure G but consistently producing widely varying results even among recent measurements of high precision. Recently, two improved experiments have produced results that are consistent at the 12 ppm level. After examination of the methodology used in previous measurements, the research group at IUPUI, in collaboration with Cal Poly Humboldt, will use multiple approaches within a singular torsion pendulum apparatus to investigate sources of error between the incorporated techniques. Measurements of G will be made using both the angular acceleration feedback and time of swing methods in the apparatus. At Cal Poly Humboldt, further sources of error are being addressed through the development of an additional integrated optical system designed to detect residual simple pendulum motion aside from the angular rotational motion used to measure G. We expect to obtain a measurement at the 2 ppm level using these new methods. By continuing the use of a torsion pendulum apparatus, we also hope better to understand the current discrepancies among previous experimental results.