Civilization / Foundations of Civilization

SI Redefined by Constants

On 20 May 2019 all SI base units are defined by fixed constants of nature; the kilogram no longer rests on a metal cylinder.

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.