A research team at the National Institute of Standards and Technology has completed a decade-long effort to measure the universal gravitational constant, known as big G, which describes the strength of gravitational attraction throughout the universe. The measurement campaign was prompted by a persistent discrepancy in how different laboratories have calculated this fundamental number over the past 225 years of scientific investigation.
Physicist Stephan Schlamminger led the project to replicate a precision measurement originally conducted by the International Bureau of Weights and Measures in Sèvres, France, in 2007. To minimize unconscious bias in interpreting results, Schlamminger asked a colleague to scramble part of the experimental data by subtracting a secret number from measured masses. This blinding technique meant Schlamminger could analyze the experiment without knowing the target value, with the correction sealed in an envelope.
The envelope was not opened until July 11, 2024, when Schlamminger presented the findings at a precision measurement conference. The NIST team’s calculated value for the gravitational constant was 6.67387 × 10-11 meters3/kilogram/second2, approximately 0.0235% lower than the French reference measurement. While such a difference would be negligible in everyday applications, it represents a significant discrepancy in fundamental physics research.
The disagreement is particularly noteworthy because gravity remains far less precisely known than other fundamental forces in nature, despite centuries of scientific effort. The persistent inconsistency between independent measurements has led physicists to consider two possibilities: either subtle experimental effects remain unaccounted for, or scientists may be overlooking something fundamental about how gravity itself operates. The team’s findings were published in the journal Metrologia.
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