Why the World Just Redefined the Kilogram

You might think you know what a kilogram is - it sounds pretty obvious, right? Well this story might get you thinking a little deeper. You see scientists say the exact weight of a kilo has actually been changing over time and they've made a plan to fix it.

What is a kilo? Six apples, five blocks of chocolate, or 122,000 feathers?

In the old days, measuring things was really complicated. People tended to use real objects to measure things by like grains for weight and body parts like arms and feet for length.

The problem here is obvious; grains come in different sizes and so do feet. There were hundreds and hundreds of units of measurement and thousands of ideas of what those units actually meant.

As years went by, people got better at measuring. By 1889, the metric system had gone global.

Scientists from around the world got together and created the International Bureau of Weights and Measures. They created artefacts out of platinum that everyone agreed to measure by, including this; Le Grand K or the kilogram. It sits in a vault in France, and it's been used ever since to set scales around the world. You see, over time the big K has lost some atoms and while atoms are obviously really, really small, it means a kilo isn't quite what it used to be. And the ministry still in charge of weights and measures does not take this stuff lightly. After all, measurements need to be really specific in fields like science and medicine, so it voted to scrap the old hunk of metal.

So say hello to this perfectly tuned electromagnet. It'll be set using something called Planck's constant, which involves energy and photons of light and frequency of electromagnetic waves.

Basically, it's super complicated. But the important thing is it doesn't change and that means a kilo now won't either. So, while you won't notice any difference at the gym, in the supermarket or at home; you can still imagine scientists, past and present, quietly cheering the next time you're weighing feathers.

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