For more than 140 years, the kilogram has been defined by a hunk of metal called the International Prototype. It’s the thing against which every scale is calibrated.
On Monday, a group of metrologists, or people who study measurement, redefined the kilogram. Without getting too deep into the numbers, they decided back in November that the world should define the kilogram based on a fundamental constant of nature called Planck's Constant — partly, in case of contact with aliens.
"It's a much better system because it's artifact-free," said Stephan Schlamminger, a physicist at the National Institute of Standards and Technology, who was part of the American team that helped make the change happen. "If you want to talk to an alien civilization — and what are you going to talk about with these people? You talk about physics because there's no other topic worthwhile talking about."
VICE News went to Versailles, France, to speak to the scientists who spent decades working on redefining the kilogram.