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16th Nov 2018

The definition of a kilogram is set to change

Alan Loughnane

kilogram definition

Wait, what?

The world is on the verge of a weighty moment as the end is nigh for the kilogram as we know it.

On Friday, scientists from more than 60 nations will convene in Versailles, France, to approve a new definition for the kilogram.

Researchers will vote to get rid of the current method in favour of defining a kilogram in terms of an electric current.

Up to now, it has been defined by a weight of a platinum-based ingot called “Le Grand K” locked in a vault in France, but now the baseline measure is “going electronic”.

A kilogram was equal to the heft of this metal, and the cylinder, by definition, weighed exactly a kilogram. If the cylinder changed, even slightly, then the entire global system of measurement had to change, too.

So the plan is to redefine the kilogram by tying it to a fundamental feature of the universe called Planck’s constant. This is where it gets tricky.

So basically, Planck’s constant is a quantity that relates weight to electrical current.

Friday’s change is the result of decades of research into Planck’s constant to measure it precisely enough so the change could be made.

Accurate measurement is critical in many areas of the world today, such as in drug development, nanotechnology and engineering and is among reasons the Le Grand K rule is being changed.

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