IUPAP Working Group 13 (WG13) was created in 2016 for the primary purpose of supporting experimental efforts to measure the Newtonian constant of gravitation, G.

To achieve this goal the working group will:

  • Provide a group of individuals who are willing to work with experimenters on various technical questions and issues,
  • Convene regular meetings on the subject of G measurements,
  • Serve as a forum to discuss future experiments, proposals and new ideas,
  • Consider and discuss possible mechanisms that might explain the existing discrepancies between at least some of today’s measurements and
  • Evaluate possible strategies for performing G experiments blindly to avoid unconscious bias


Stephan Schlamminger,
 is a physicist at the National Institute of Standards of Technology (NIST). He currently works on the watt balance. Previously, he has measured the gravitational constant using a beam balance. He will serve as the chair of the IUPAP working group on big G.

Markus Aspelmeyer is a researcher at the University Vienna in Austria. His research interests are centered on the fundamental of quantum optics, quantum information processing, and quantum entanglement. He is currently applying these techniques to measure gravitational forces.

James Faller, a Fellow Adjoint of the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, has worked in precision measurements and gravitational physics his entire career.  He was instrumental in developing absolute gravimeters that are now commercially available. In the last two decades he was involved in at least two of determinations of the gravitational constant.

Gabriela Gonzales, a Professor at the Louisiana State University, is the spokesperson of the LIGO scientific collaboration. She is an expert in the thermal noise limits of sensitive detectors such as torsion balance and gravitational-wave detectors.

Jen Gundlach is a Professor at the University of Washington. He has performed the most precise measurement of the gravitational constant to date. He has been involved in a series of other gravitational experiments.

Mark Kasevich, a professor at Stanford University, was the first to measure the gravitational acceleration using atom interferometry. He is interested in using atom interferometers to measure acceleration, rotation, and to test General Relativity.

Jun Luo is the director of center for gravitational experiment at Huazhong University of Science and Technology in China. Under his leadership several measurements of the gravitational constant have been performed.

David Newell is a physicist at National Institute of Standards and Technology and the chair of the Task Group on Fundamental Constants within the Committee (CODATA) on Data for Science and Technology. He has worked on vibrational isolation for gravitational wave detectors, the watt balance, and more recently on graphene.

Riley Newman, a professor at the University of California Irvine, has been involved in gravitational physics is entire career. Recently, he has measured the gravitational constant using a cryogenic torsion balance.

Harold Parks is a physicist with the National Research Council (NRC) in Canada. He was involved in two big G experiments, one carried out at JILA, the other at BIPM.

Bill Phillips, a physicist at NIST and professor at the University of Maryland, won the Nobel Prize in physics in 1997. Bill serves as liaison to IUPAP.

Terry Quinn, FRS, is the director emeritus of the Bureau International de Poids et Mesures (BIPM). He conducted two experiments to measure the gravitational constant. Terry will serve as liaison to the CIPM steering committee.

Christian Rothleitner is a physicist at the Physikalisch Technische Bundesanstalt (PTB) in Germany. He has experience in building free fall gravity gradiometers and is interested in using this instrument to measure the gravitational constant.

Clive Speake is a professor at the University of Birmingham in the United Kingdom. He has performed several precision measurements in gravitational physics. Recently he was involved in both experiments to determine the gravitational constant at the BIPM. He will serve as the vice chair of the IUPAP working group on big G.

Guglielmo Tino is a professor of physics at the University di Firenze in Italy. In the past decade he has been leading an experiment to measure the gravitational constant using an atom interferometer.


Report to the IUPAP Council and Commission Chairs/General Assembly: 2016, 2017, 2018, 2019