Physicist Stephan Schlamminger at the National Institute of Standards and Technology completed a ten-year effort to precisely measure the universal gravitational constant, known as big G. This fundamental value determines the strength of gravitational attraction throughout the universe, yet remains one of the least precisely known constants in physics despite over 225 years of measurement attempts.
The primary challenge in measuring big G stems from gravity’s extreme weakness compared to other fundamental forces. Researchers must detect gravitational attraction between laboratory-scale objects that are roughly 500 billion trillion times smaller than Earth, making the forces extraordinarily faint despite increasingly sensitive modern instruments. Past measurements have consistently produced slightly different answers, with disagreements roughly one part in 10,000—larger than expected from ordinary experimental uncertainty.
To address potential sources of error, Schlamminger designed the experiment using a blinding technique. A colleague scrambled part of the data by subtracting a secret number from measured masses, preventing Schlamminger from knowing the actual result during analysis. The correction was sealed in an envelope, originally planned to be opened after preliminary analysis. However, concerns about unaccounted air pressure effects prompted a delay from 2022 until July 11, 2024, when Schlamminger presented findings at a precision measurement conference in Colorado.
Upon opening the envelope and analyzing the complete data, the NIST team obtained a measurement of 6.67387 × 10-11 cubic meters per kilogram per second squared. While this differed from a comparable French measurement by only 0.0235 percent, such tiny discrepancies hold significance in fundamental physics. Other fundamental constants are known to six or more significant digits, while big G remains considerably less precise. Historically, small mismatches between measurements and expectations have occasionally revealed previously unknown aspects of nature, though researchers emphasize this discrepancy does not necessarily indicate new physics.
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