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Scientists applaud and weep as cylinder that has been the world's sole true kilo since 1889 is retired

The change represents decades of work - REUTERS
The change represents decades of work - REUTERS

In a historic vote, nations on Friday unanimously approved a ground-breaking overhaul to the international system of measurements that underpins global trade and other vital human endeavors, uniting behind new scientific definitions for the kilogram and other units in a way that they have failed to do on so many other issues.

Scientists, for whom the update represents decades of work, clapped, cheered and even wept as the 50-plus nations gathered in Versailles, west of Paris, one by one said oui to the change, hailed as a revolution for how humanity measures and quantifies its world.

The redefinition of the kilogram, the globally approved unit of mass, was the mostly hotly anticipated change.

For more than a century, the kilogram has been defined as the mass of a cylinder of platinum-iridium alloy kept in a high-security vault in France.

That artefact, nicknamed "Le Grand K," has been the world's sole true kilogram since 1889.

But now, with the vote, the kilogram and all of the other main measurement units will be defined using numerical values that fit handily onto a wallet card. Those numbers were read to the national delegates before they voted.

Scientists celebrate after the vote on the redefinition of four base units of the International System of Units - Credit: REUTERS/Benoit Tessier
Scientists celebrate after the vote on the redefinition of four base units of the International System of Units Credit: REUTERS/Benoit Tessier

Scientists at the meeting were giddy with excitement: some even sported tattoos on their forearms that celebrated the science.

Nobel prize winner William Phillips called the update "the greatest revolution in measurement since the French revolution," which ushered in the metric system of meters and kilograms.

Jon Pratt of the US National Institute of Standards and Technology said the vote left him "a basket case" and "extremely emotional."

"Those units, those constants chosen now, include everything we know, everything we have always known and provide that springboard for us to go pursue those things that we don't know," he said. "That was just leaving me in a puddle of tears."

The Grand K and its six official copies, kept together in the same safe on the edge of Paris and collectively known as the "heir and the spares," will be retired but not forgotten. Scientists want to keep studying them to see whether their masses decay over time.