Gravitational constant G: NIST repeated the BIPM measurement on the same torsion balance and obtained (6.67387 ± 0.00038) × 10⁻¹¹ m³ kg⁻¹ s⁻² — lower than the French result by 2.5 × 10⁻⁴
On 16 April 2026 the US NIST announced the result of a ten-year measurement of the gravitational constant G, published in the journal “Metrologia”. The team repeated the experiment of the International Bureau of Weights and Measures (BIPM) in Sèvres using the same torsion balance, at NIST’s campus in Gaithersburg, but did not reproduce the BIPM result.
- NIST’s result: G = (6.67387 ± 0.00038) × 10⁻¹¹ m³ kg⁻¹ s⁻², a relative standard uncertainty of 5.7 × 10⁻⁵. According to the paper it is lower than the BIPM determination by 2.5 × 10⁻⁴ in relative terms; the NIST announcement gives the difference as 0.0235 %. Earlier precise measurements of G differed from one another by about one part in 10,000 — too much to be explained by routine experimental errors.
- The torsion balance designed and built at the BIPM about three decades ago (BIPM measurement of 2007) has eight cylindrical masses: four on a rotating carousel and four smaller ones on a disk suspended from a copper-beryllium ribbon. G was determined by two methods: from the twist angle under the gravitational torque, and from the voltage on electrodes whose electrostatic torque exactly balances the gravitational torque.
- The NIST team added a third variant: measurements first with copper masses, then with sapphire masses, to check the influence of the material — the results were virtually identical. To avoid unconsciously steering the result towards the BIPM value, the measurement was blinded: another team member subtracted a number known only to that person from the measured weights of some of the masses; in 2022 the unblinding was postponed after an overlooked factor related to air pressure was found.
- The number was revealed on 11 July 2024 at the Conference on Precision Electromagnetic Measurements; after two more years of analysis the result was published. According to NIST, the measurement does not resolve the puzzle of discrepant G values but adds an independent result, and the paper says the replication helps assess the reproducibility limits of current techniques for measuring the gravitational constant.
Source: NIST — NIST Weighs In on the Mystery of the Gravitational Constant (16.04.2026)