Gravity Group Seminar, Stephan Schlamminger (NIST)

Fri, Nov 18, 2016, 12:00 pm to 1:30 pm
Joseph Henry Room

TITLE Measurements of the gravitational constant – why is a precise measurement so difficult? ABSTRACT In this presentation, I will summarize measurements of the Newtonian constant of gravitation, big G, that have been carried out in the last 30 years. I will describe key techniques that were used by researchers around the world to determine G. Unfortunately, the data set is inconsistent with itself under the assumption that the gravitational constant does not vary in space or time, an assumption that has been tested by other experiments. Currently, several research groups have reported measurements with relative uncertainties below 2 x 10^-5, however, the relative difference between the smallest and largest reported number exceeds 5x10^-4. It is embarrassing that after over 200 years of measuring the gravitational constant, we do not have a better understanding of the numerical value of this constant. I will discuss why it is so difficult to measure G and what can be done to get a better understanding of these experiments.