Physicists at the National Institute of Standards and Technology have completed a decade-long effort to measure the gravitational constant, only to deepen the mystery surrounding one of nature’s most fundamental numbers. The new measurement, published April 16, 2026, in the journal Metrologia, differs from the previous reference value by 0.0235%, a significant gap in metrology that fails to align with the internationally agreed CODATA estimate.
Led by Stephan Schlamminger, the NIST team replicated a 2007 experiment originally conducted by the International Bureau of Weights and Measures in Sèvres, France, using a torsion balance to detect the faint gravitational pull between masses. To avoid bias, Schlamminger enlisted colleague Patrick Abbott to alter the data by subtracting a secret number from measured masses, ensuring the result remained unknown until the envelope was opened.
The experiment was conducted twice — first with copper weights, then with sapphire weights — yielding consistent results that did not match the French data. Schlamminger described the work as “soul draining,” yet said he was driven by the belief that “it must be possible for humans to measure this number.”
Despite its role in governing planetary motion and galactic structure, the gravitational constant remains the least precisely known of the four fundamental forces. Its extreme weakness — a slight magnet can overcome Earth’s pull on a paperclip — makes laboratory measurement extraordinarily tricky, requiring detection of forces between masses quadrillions of times lighter than Earth.
Efforts to measure G date back to Henry Cavendish’s 1798 experiment, and modern techniques now include pendulums, balanced masses, and atom interferometry. Yet with an uncertainty of about 1 part in 5,000, Big G continues to elude precise determination, and known experimental errors cannot explain the spread of values across studies.
Richard Brown, a metrologist at the UK National Physical Laboratory, called the NIST team’s meticulous work “a great leap forward” for future experimenters, even as it fails to resolve the core discrepancy. Christian Rothleitner of the German National Metrology Institute labeled it “the most challenging laboratory experiment of all.”
The inability to shield experiments from external gravitational influences further complicates isolation of the signal, leaving physicists to question whether persistent inconsistencies point to unseen errors or a deeper misunderstanding of gravity itself.
While the discrepancy of 0.0235% has no perceptible effect on everyday scales or satellite orbit calculations, its persistence challenges the precision of fundamental physics and underscores the difficulty of measuring nature’s weakest force.
Why is the gravitational constant so difficult to measure?
Gravity is trillions of trillions of times weaker than the other fundamental forces, requiring detection of extremely faint interactions between small masses that are quadrillions of times lighter than Earth, and experiments cannot be shielded from interfering gravitational signals.
What does the NIST result signify for the accepted value of Big G?
The NIST measurement does not match the CODATA value or previous results, leaving the true value of the gravitational constant unresolved and highlighting ongoing inconsistencies in precision measurements.
How did the team avoid bias in their measurement?
Physicist Stephan Schlamminger used a blind data analysis method, having colleague Patrick Abbott alter the data with a secret number known only to Abbott, so Schlamminger remained unaware of the result until the envelope was opened.