The kilogram will be redefined this week as representatives from over 60 nations will meet in Versailles, France, in order to formally approve the change.
For almost one and a half centuries the unit of mass has been defined by the weight of a platinum iridium cylinder which is kept under heavy security in a special vault. The vault itself is located inside the International Bureau of Weights and Measures in Sevres, France.
By convention the cylinder weighted exactly one kilogram and vice versa a kilogram was equal to the weight of the cylinder. Any marginal change meant that the weights used around the world had to be adjusted accordingly.
In order to remove any future changes, the kilogram will be now linked to a feature of quantum physics, namely Planck’s constant, a theory that defines the smallest amount of energy that can exist. Since energy and mass are deeply interconnected according to Einstein, researchers are able to use Planck’s constant in order to precisely calculate mass, with the added benefit that it will not change over time.
The change won’t affect the way in which ordinary measurements take place but it will help industries and research that require a high percentage of accuracy.
The event is charge with symbolical value as it concerns a topic on which everyone agrees and the shared acknowledgment of a truth that cannot be changed.
The International System of Units was established in order to eliminate conflict among merchants, as they struggled to converse one local measuring unit to another. In 1875, the Treaty of the Metre was signed and two etalons made of platinum and iridium were created: a bar measuring one meter in length and the previously mentioned cylinder which weights one kilogram. Copies were distributed among the participant nations.
Science advance has allowed researchers to finally determine the exact value of Planck’s constant. The vote will take place on Friday.
Nora Reynolds is a major in biology and a minor in Biological Basis of Behavior, writing about science in general. She also likes to try new gadgets and sports about the AI new era.