This article details the global shift from measuring mass using physical artifacts to defining it through fundamental natural laws, specifically Planck’s constant, a core value in quantum mechanics. The standard was developed and coordinated by international bodies like the General Conference on Weights and Measures, with significant contributions from NIST and laboratories across more than 50 countries. It officially moved from proposal to implementation over a 20-year period: NIST initially suggested the approach in 1999, the scientific community finalized the exact numerical value in 2017, and the new standard was formally adopted and implemented in May 2019.
Technically, the change replaces the old physical kilogram prototype with methods that either compare mechanical weight to electrical energy or count atoms in ultra-pure silicon spheres. To ensure reliability, independent labs had to produce matching results within extremely tight error margins before approval. This update creates a permanent, universally reproducible measurement system that scales accurately from everyday objects to atomic-scale particles. By anchoring measurements to unchanging quantum constants rather than degrading physical objects, the standard provides the precise calibration foundation required for advanced fields like quantum computing, where exact energy and mass measurements are critical for device performance and research.
Keywords: Planck’s constant, Kibble balance, SI unit redefinition
