PSA: The Kilogram Is Changing

What is a kilogram? It’s a base unit of measurement, but one that’s hard to define in definite terms without having something to base it off. Kilograms are currently marked by a cylindrical lump of platinum and iridium known as the ‘Big KG’ in Paris, but scientists are seeking to redefine it by far more, well… scientific means.

The Big KG that currently rules our entire system of weight measurement is a 19th Century artifact, crafted in 1889. While the original was kept locked up in the Pavillon de Breteuil, Saint-Cloud in France, many copies were distributed around the world – though over the years those copies have changed weight from the original.

The differences are miniscule, but even tiny changes can be notable when used in science. So now, scientists and national representatives from more than 60 countries have gathered to vote on changing the kilogram to a measurement that will never change.

Time is already measured atomically, and the standard meter is based on a formula using the speed of light — so now, the proposal is to do the same with the kilogram.

The new measurement would be based on something called the Planck constant, a physical constant that can be used to calculate the energy in a light particle. And, since energy and mass are equivalent, it can also be used to measure the latter.

While physical standards like the Big K will inevitably change in mass over the years, even if just in the tiniest increments, a measurement tied to the Planck constant will never change. To measure weight in this way, scientists use an electromagnetic device called a Kibble balance.

But not to worry, you won’t have to go buying electromagnetic scales for your kitchen now, and nor is the 1kg of apples you buy at the supermarket going to change. If voted through tonight, the change will come into play on May 20, 2019: World Metrology Day. Most people will likely be none the wiser: but sometimes it’s just nice to know how things work.

[ABC News]


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