NIST spent a decade replicating a divergent 2007 BIPM torsion balance experiment, yielding 6.67387e-11 m³/kg/s² – 0.0235% below BIPM’s original result, without resolving the discrepancy.
Key Takeaways
Paper in Metrologia reports a decade-long NIST effort to replicate the 2007 BIPM torsion balance result, one of the largest outliers in Big G measurements.
The discrepancy across all modern Big G measurements is roughly 1 part in 10,000 – large relative to other fundamental constants, which are known far more precisely.
NIST used two mass materials (copper and sapphire) and two independent measurement methods (gravitational torque and electrostatic compensation), ruling out material-dependent artifacts.
Gravity’s extreme weakness relative to other fundamental forces makes lab measurement noisy; Earth’s own gravitational field dominates as background noise.
Physicists argue continued precision efforts produce better instruments for measuring small forces and torques, with broad scientific benefit beyond the G value itself.
