Kilogram Redefined by the Planck Constant, ‘A Fundamental Constant of Nature’
(Engadget) The definition of the kilogram as well as three other units of measurement — the ampere, the kelvin and the mole was recently changed at the General Conference on Weights and Measures in Versailles, France. The kilogram will now be defined by the Planck Constant. After May 20, 2019, the value of the Planck constant will be fixed at exactly 6.62607015 × 10−34 kilograms times meters squared per second.
The new definitions will be based on “what we call the fundamental constants of nature,” according to Estefanía de Mirandés of the International Bureau of Weights and Measures (BIPM). Those unchanging numbers — which include the speed of light and the charge of the electron — are the same everywhere in the universe, making them useful pegs upon which to hang the metric system’s hat. “It’s a very big change of paradigm, and now it’s complete,” de Mirandés says. While the changes won’t necessarily be reflected in your day to day life, they’ll help scientists make more accurate measurements going forward.
Until this change, every measurement of mass made anywhere on Earth has been tied back to one cylindrical object known as “Le Grand K,” the cylinder, cast in 1879, that has been carefully sequestered in a secure, controlled environment outside Paris.