Researched
SI Units Redefined (New Kilogram)
On 20 May 2019 all SI base units are defined by fixed constants of nature; the kilogram no longer rests on a metal cylinder.
Open in the interactive tree →The kilogram, ampere, kelvin and mole were tied to the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, while the second and metre rest on caesium and the speed of light. No single object defines a unit any more, so any well-equipped lab can realise it.
Prerequisites
- Metric System1799
- Quantum Mechanics1925
- Atomic Clock1955
- Josephson Effect & SQUIDs1962-1964The volt is realised with Josephson junction arrays, whose constant 2e/h becomes exact
- Quantum Hall Effect1980-1982The ohm is realised with the quantum Hall effect, whose constant h/e² becomes exact once h and e are fixed
Sources
More in Foundations of Civilization · Present
- Open Access & Open Science2018-2026
- AI Tutors in Schools2023-2026
- Global Literacy at 88%2024
- AI as Research Partner2025-2026