The Weight of History
a little heavier lately, don’t blame that extra slice of pizza. The kilogram—to which our familiar pound is pegged—was slightly redefined in 2019, a landmark in the long history of scales and weights. Instead of a platinum-iridium bar locked in an underground vault in the outskirts of Paris, the kilogram is now based on the Planck constant, an immutable concept in quantum mechanics. The kilogram was the last international unit of measure still based on a human-made
