Measurement of Planck's constant and redefinition of the kilogram
Medida de la constante de Planck y redefinición del kilogramo
- Date
- 2018-2019 · confidence high
- Place
- General Conference on Weights and Measures, Versailles, France (Kibble balances at NIST and NRC)
- Credited to
- Bureau International des Poids et Mesures; NIST; NRC Canada; PTB (silicon sphere)
- Field
- Cosmos & Earth
What was discovered
After measuring h with an uncertainty of 10 parts in a billion using Kibble balances and silicon-28 spheres, the SI fixed in 2019 the exact values of h, e, k and N_A, and the kilogram ceased to be a platinum-iridium cylinder. Every unit is now defined by constants of nature.
Approved on 16 November 2018 at the 26th CGPM and in force since 20 May 2019.
What it led to
- International System defined entirely by constants
- Quantum metrology (Josephson and quantum Hall standards)
- Realisation of the kilogram in any laboratory
- End of artefact standards
Built on
- Kibble balance1975
- Planck's constant (1900)
- Josephson effect and quantum Hall effect
- Avogadro Project
Made possible
- Kibble balance1975
- Kibble balance
- Monoisotopic silicon-28 spheres