5 ms·

> "The change also means that the constants on which the new definitions rely — the charge of the electron for the ampere, Avogadro’s constant for the mole, Bol

by pkulak 7y ago

> "The change also means that the constants on which the new definitions rely — the charge of the electron for the ampere, Avogadro’s constant for the mole, Boltzmann’s constant for the kelvin and Planck’s constant for the kilogram — are from today fixed values with zero uncertainty." Does anyone know what that last paragraph means? Why would defining new constants in terms of existing ones make the existing ones have zero uncertainty?

gmueckl 7y ago
The constants on which the SI units rely have been assigned fixed numerical values by definition. This is so that you can now build a certain type of experiment and calibrate it so that it measures this defined numerical value for that constant. And in doing the calibration, you actually produce a reference for an SI unit.