Figure: Sketch of the experiment (left) and comparison of this work with previous results (right). In the left picture, a is the time-of-swing method, and b is the angular-acceleration-feedback method. The black dots in the right picture represent fourteen measurement results and recommended G values relevant to CODATA-2014 adjustment. Two blue points in the bottom represent measurement results of G by using two independent methods, the uncertainties are both about 11.6 ppm.

With the support of the National Natural Science Foundation of China (Project Approval Number: 91536223, 11722542, 11325523, 11605295), Prof. Luo Jun and his team have made significant progress in precision measurement of the gravitational constant G. They measured G with record precision up to date by using two independent methods. The relevant research results were published in Nature on August 30, 2018, entitled "Measurements of the gravitational constant using two independent methods" (http://www.nature.com/articles/s41586-018-0431-5). Prof. Yang Shanqing, Shao Chenggang, and Luo Jun are corresponding authors. Dr. Li Qing, Dr. Xue Chao, Dr. Liu Jianping and Dr. Wu Junfei contributed equally as first authors.

The gravitational constant G, which is introduced to describe the strength of the gravitational interaction between objects, is the first fundamental constant discovered by human beings,  while it remains the least precisely known among all fundamental physical constants. Although the values of G determined by different groups around the world are considered with relative uncertainties nearing the level of 10-5, they agree with each other within a level of only 10-4. As a result, many fundamental scientific problems can’t be solved with the limited accuracy of G. Recently, Prof. Luo Jun and his team measured G by using two independent methods: the time-of-swing method and the angular-acceleration-feedback method. These values of G have the smallest uncertainties reported until now, and both agree with the latest recommended value within a level of 10-5, these results would provide a substantial contribution to nail down the true value of G.

Prof. S. Schlamminger of the National Institute of Standards and Technology (NIST) published a comment entitled "Gravity measured with record precision" in "News and Views" of Nature. He said that "The study is an example of excellent craftsmanship in precision measurements." In addition, Prof. James E. Faller, the former president of JILA laboratory and Presidential Rank Award winner, commented on the achievements of Prof. Luo Jun and his team: “I think the work of this team is excellent and represents an important contribution towards obtaining a value for G. Discovering why a few measurements are discordant would provide the 'frosting' for this cake. Luo Jun and his team constitute a very capable and enthusiastic working group on this hardest to measure fundamental constant. Luo Jun is, simply put, a first rate scientist. China can be very proud of having both Luo Jun, his group, and this wonderful laboratory. 

Beyond that, the team developed a number of high-end instruments over the research period, and some of them have played an important role in the measurements of gravity field and geological exploration. For example, the precision torsion balance technology developed by the team has been successfully applied to the micro-thrust calibration of satellite micro-propellers and the ground calibration of space inertial sensors. These instruments will lay a good foundation for National Precise Gravity Measurement Facility and space gravitational wave detection.