Title: Weighing the Earth: The Quest to Measure the Gravitational Constant at NIST
Abstract: The discovery of gravitation by Isaac Newton in the 17th century is often referred to as the beginning of physics as we know it. More than two centuries later, the value of the gravitational constant, “the big G,” serves as the fundamental basis for understanding large-scale cosmic structures, while providing the essential theoretical foundation for general relativity. Yet, despite centuries of experimentation, the global dataset for G remains frustratingly inconsistent. Compared to the strength of the electromagnetic interaction, known to a relative uncertainty of 0.2 parts-per-billion, G is only known to 22 parts-per-million. This staggering five-order-of-magnitude gap highlights the unique stubbornness of gravity. Two primary factors contribute to this: (1) unlike its dimensionless electromagnetic counterpart, G is a dimensioned quantity tied to our macroscopic units, and (2) the gravitational force is extremely weak compared to other fundamental forces and impossible to shield. In this talk, I will discuss the recent NIST measurement that we undertook to better understand the global dataset. I will attempt to answer three central questions: Why is G so difficult to pin down? How did we measure it? And what now for the future of the gravitational constant?