Physicist Stephan Schlamminger of the National Institute of Standards and Technology spent approximately a decade attempting to precisely measure big G, the universal gravitational constant that defines the strength of gravitational attraction throughout the universe. To avoid unintentionally biasing his analysis based on expected results, Schlamminger arranged with colleague Patrick Abbott to blind the experiment by obscuring part of the data. Abbott subtracted a secret number from the measured weights of the experimental masses, which was then sealed in an envelope that only he knew the contents of.
The measurement of big G has proven remarkably difficult despite centuries of scientific effort. Gravity is extraordinarily weak compared to other fundamental forces in nature—a small magnet can easily lift a paper clip against the gravitational pull of the entire Earth. This means laboratory measurements must detect gravitational forces between small objects approximately 500 billion trillion times smaller than Earth, requiring extraordinarily sensitive instruments to capture such faint signals.
Schlamminger initially postponed opening the envelope in 2022 after realizing the team had not fully accounted for air pressure effects. The envelope was finally opened on July 11, 2024, during a presentation at the Conference on Precision Electromagnetic Measurements in Aurora, Colorado. While the correction needed was as large and negative as anticipated, subsequent analysis revealed a problem: the NIST measurement did not align with a comparable French experiment conducted in 2007.
The NIST team’s final measurement, reported in Metrologia, yielded a value approximately 0.0235% lower than the French result. While such a small difference would be imperceptible in everyday applications, it represents a significant discrepancy for fundamental physics research. Other fundamental constants are known to six or more significant digits, while big G remains less precisely determined. Historically, small measurement mismatches have occasionally indicated previously unknown aspects of nature, though scientists cannot yet determine whether the disagreement over big G signals new physics or reflects overlooked experimental factors.
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