Ten-year NIST measurement of gravitational constant adds to long-standing discrepancy

After a decade of experiments, NIST physicist Stephan Schlamminger and colleagues produced a new value for the gravitational constant that differs from another leading result. The tiny mismatch is significant for such a fundamental constant, leaving scientists uncertain whether hidden errors or new physics are involved. The work continues a 225-year effort to measure gravity's strength precisely.

The experiment's difficulty stems from gravity's extreme weakness relative to other forces. A pinhead-sized magnet can lift a paper clip against the gravitational pull of the entire Earth, demonstrating how easily electromagnetism overcomes gravity. In the lab, researchers must measure attraction between masses roughly 500 billion trillion times smaller than Earth, producing forces that are incredibly faint and difficult to isolate from environmental noise.

The new NIST value differs from another leading result by about one part in 10,000, a mismatch larger than ordinary experimental uncertainty would predict. This discrepancy continues a 225-year effort to measure big G, which remains less precisely known than constants for other fundamental forces. Scientists face an uncomfortable choice: either subtle experimental errors have been overlooked, or our understanding of gravity itself may be incomplete.