A decade-long experiment by the National Institute of Standards and Technology (NIST) has yielded a new measurement of the universal gravitational constant, known as big G. The result differs from another leading measurement, deepening a 225-year-old physics puzzle. This discrepancy is small, but it is significant for one of nature's fundamental constants.
Physicist Stephan Schlamminger led the NIST team. He aimed to replicate a 2007 experiment conducted by the International Bureau of Weights and Measures (BIPM) in France. The goal was to clarify inconsistencies in previous big G measurements. Schlamminger blinded his experiment by having a colleague scramble part of the data, preventing bias.
After ten years of work and analysis, the NIST team's value for big G was 6.67387 × 10^-11 meters cubed per kilogram per second squared. This measurement is 0.0235% lower than the value obtained in the French experiment. This difference is negligible in everyday life but holds significant implications for fundamental physics.
Scientists have measured big G for over two centuries, yet it remains less precise than other fundamental constants. Gravity is an extraordinarily weak force, making it difficult to measure accurately in a laboratory setting. Modern instruments are highly sensitive, but measurements of big G continue to produce slightly different answers.
The persistent mismatch suggests either overlooked experimental errors or an unknown aspect of gravity itself. The NIST experiment used a torsion balance, a technique dating back to Henry Cavendish in 1798. They also used two different materials, copper and sapphire, for the experimental masses, obtaining consistent results with both.
This continued inability of precision experiments to converge on the same value keeps the mystery surrounding big G alive. While experimental error is the most likely explanation, historical precedents show that small discrepancies can sometimes reveal new understandings of how nature works.
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