The Global Unit of Mass in the Metric System Just Changed

Guest: Wolfgang Ketterle, Professor of Physics, MIT When you step on a scale or put some apples on the little one at the grocery store, how does the scale know exactly what a pound is? If you can believe, there’s actually a chunk of platinum in a vault in France that is the official kilo against which every scale in the world is calibrated. But this is 2019 and the world’s scientists have decided they can define the precise weight of a kilogram in a way that’s more high-tech (and hard for regular folks to understand).