So, it happened. And you probably didn’t notice. But the long-awaited, new definition of the kilogram went into effect this past week.
The metal cylinder that has defined the kilo for over a century has now been replaced with a mathematical equation based on a number known as the Planck constant.
It was the last physical artefact defining any unit of measurement in the international system, so its replacement marks an important point in efforts to define those units in ways that are permanent and immutable – based on constants of nature, rather than somebody’s foot or a hunk of metal. But it’s certainly not the end of the effort.
Now they’re taking on the second with renewed vigor. You know, the base unit of time in the International System of Units. That second.