NIST Physicists Conclude Decade-Long Effort to Refine Measurement of Universal Gravitational Constant
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Researchers at the National Institute of Standards and Technology (NIST) have published a new, highly precise measurement of the universal gravitational constant, known as 'big G'. The result, achieved after nearly 10 years of work and a blind analysis to prevent bias, closely aligns with a prior international measurement but reveals a small, unexplained discrepancy. This work represents the latest step in a centuries-long scientific quest to pin down the fundamental strength of gravity.
Facts First
- A new value for the universal gravitational constant (big G) has been published by a team at the National Institute of Standards and Technology (NIST).
- The measurement took nearly a decade and involved a blind analysis where part of the data was secretly scrambled to prevent researcher bias.
- The NIST result is 0.0235% lower than a key 2007 measurement from the International Bureau of Weights and Measures (BIPM) in France.
- The experiment used a modern torsion balance, a technique pioneered in 1798, alongside an independent electrostatic measurement method.
- Modern measurements of big G still vary more than expected, with differences of about one part in 10,000 across experiments.
What Happened
Physicist Stephan Schlamminger and his team at the National Institute of Standards and Technology (NIST) have completed a nearly 10-year experiment to measure the universal gravitational constant (big G). The team replicated a 2007 experiment conducted by the International Bureau of Weights and Measures (BIPM) in France. To ensure objectivity, a colleague secretly scrambled part of the data by subtracting a hidden value, a number that was only revealed at a scientific conference in July 2024 after two additional years of analysis. The NIST team's final measured value for G is 6.67387x10^-11 meters^3/kilogram/second^2, which is 0.0235% lower than the BIPM's result.
Why this Matters to You
The universal gravitational constant is a fundamental number that defines the strength of gravity everywhere in the universe. While this measurement does not directly change your daily life, refining such constants is essential for the precision of modern technology and science. More accurate values for fundamental constants could, over time, improve the reliability of technologies that depend on ultra-precise measurements, such as satellite navigation (GPS) and deep-space mission planning.
What's Next
The persistent discrepancy between high-precision measurements like those from NIST and BIPM—differences larger than expected experimental uncertainties—suggests an unknown source of error or a deeper physical mystery may remain. Schlamminger's team tested whether the material of the experimental masses (copper vs. sapphire) influenced the result and found it did not. Future experiments will likely need to investigate other potential hidden variables to resolve this long-standing puzzle in physics.