The Newtonian constant of gravitation is one of the most fundamental constants of classical physics. Recent measurements of G are in disagreement, with discrepancies that are roughly ten times the quoted uncertainties in some cases. A graph of the measured values is given here.
The disagreement calls into question our ability to measure small forces on a laboratory scale. It also raises the question of whether the Newtonian force law is a complete description of gravity at these distances.
An international consortium is being formed to address this problem. The objective is to carry out a series of measurements that will eliminate bias that may have existed in earlier measurements.
In addition, an international advisory board will be formed made up of people who have already carried out measurements of G as a resource to answer questions on the design and construction of the experiments as well as the interpretation of the data and calculation of the results.
A Royal Society scientific meeting was held on 27-28 February 2014 that explored possible reasons for the descrepancies and generated some proposals for new measurements that might resolve the present impasse.
A workshop to refine the terms of the proposed consortium was held at NIST on 9-10 October 2014.
A National Science Foundation (NSF) sponsored Ideas Laboratory will be held at NIST on 7-11 December 2015. The objective is to generate new approaches to measure G in order to help resolve the discrepancies.