NIST Physicist Completes Decade-Long Measurement of Universal Gravitational Constant

Stephan Schlamminger, a physicist at the National Institute of Standards and Technology (NIST), has concluded a 10-year effort to measure the universal gravitational constant, a fundamental quantity that determines the strength of gravity throughout the universe. The measurement campaign culminated in the opening of an envelope containing a secret reference number used to unscramble the experimental data—a blinding technique employed to prevent unconscious bias during the lengthy measurement process. The gravitational constant, denoted as G, remains one of the least precisely known fundamental constants in physics, making high-precision measurements like Schlamminger's critical for testing theories of gravity and cosmology.

The universal gravitational constant has proven notoriously difficult to measure with high accuracy, with different experimental approaches sometimes yielding results that disagree beyond their stated uncertainties. NIST's decade-long campaign represents one of the most sustained efforts to pin down this elusive value. The use of a sealed reference number—revealed only after data collection was complete—reflects the extreme care required to avoid systematic errors and experimenter bias in precision metrology.