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Scientists vote to change the kilogram

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Scientists from around the world are gathering in France today to decide the fate of the kilogram.

For nearly 130 years, the kilogram has been based on a lump of metal called the Big K, locked in a vault near Paris.

But at 11:00am Paris time (9:00pm AEDT), representatives from 60 nations, including Australia, will vote on a proposal to define the humble unit using pure, unadulterated physics.

Paul Hetherington from the National Standards Authority of Ireland said it will not change what you see on your bathroom scales, but it will make measurements more stable for the future.

He said: "Because it's a piece of metal, even though it's handled very carefully and stored very, very carefully, being metal it is subject to contamination. So from that point of view, it's changing by very small amounts, but it is subject to change

"So there has been work ongoing for the last 10 to 20 years in various science laboratories around the world to see can we move away from having a physical artefact so it won't be subject to this change that is ongoing and that is what we voted for."

Back in the 18th century a kilogram was equivalent to a certain volume of water, Dr Warrington explained.

But in 1889, it was replaced with a cylinder of platinum and iridium known as the international prototype kilogram (IKP) — or the Big K.

Today the original Big K is held under lock and key in the Pavillon de Breteuil, Saint-Cloud, near Paris.

There are six copies in the same vault, and many more around the world.

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