The Kilogram to be Redefined After 130 Years as Part of Metric System Overhaul21.05.2019

From now on, the kilogram will be defined by fundamental physical and atomic properties, rather than a material, man-made object. The redefinition, unanimously approved at the 26th General Conference on Weights and Measures last November, came into force on May 20.  

Representatives from International Bureau of Weights and Measures (BIPM) member states have unanimously approved the plan to redefine basic SI units. The comprehensive overhaul, the BIPM explains, will change the definitions of four SI units—the ampere, mole, kelvin, and kilogram. From 1889 until now, the latter was defined by a one-kilogram cylinder made from a platinum-iridium alloy, kept in an underground vault located in Sèvres, a suburb of Paris. 

Le Grand K, as the cylinder was commonly known, ceased to function as the standard kilogram, on May 20. “The redefinition of the SI draws on fundamental physical constants, universal for the entire universe. When the overhaul is complete, the basic units of measure and those derived from them will be based on the pillars of our world—physical constants. Science and technology will no longer be constrained by mutable material artifacts,” writes the Polish Bureau of Weights and Measures. 

Nową definicję kilograma stworzono z wykorzystaniem tzw. stałej Plancka – jednej z podstawowych stałych, często pojawiającej się w równaniach mechaniki kwantowej. Ma ona wartość 6,626070150 × 10^-34 kg·m2/s i wiąże kilogram z prędkością światła oraz podstawową jednostką czasu, czyli sekundą. Oznacza to, że definicja kilograma, choć odnosi się teraz do zupełnie innego systemu miar, jest teraz dużo bardziej precyzyjna.
The new kilogram will be based on the Planck constant, one of the most fundamental constants in quantum mechanics. The value of the constant is set to 6,626070150 × 10^-34 kg·m2/s, thus binding the kilogram to the meter and the second. This means that although dependent on other units, the definition of the kilogram much more precise now. 

The Central Office of Measures was quick to add that the redefinition will have basically no impact on our everyday lives. The numbers on our kitchen scales will not change—the redefinition will, however, be important to scientists worldwide as it will make the data underpinning their research efforts that much more precise.