(Science Week – Day 2!)

I remember being impressed and satisfied to learn a metre was defined as the distance light travelled in a minuscule fraction of a second (one 299,792,458th) – a definition that seemed immune to wavering by its tetheredness to nature. So, finding the kilogram was defined as “the weight of a particular chunk of platinum and iridium stored at the International Bureau of Weights and Measures in France” (an upgrade from its historical definition of “the mass of one cubic decimetre of water”), felt like learning not just a fact, but something about the state of humanity. The best it had done was to select an object as prototypical.

But last year, the kilogram and several other units were successfully defined in terms of natural constants. It makes the present feel like another piece of history, and labs will begin using these definitions in May.

And it’s an interesting story, reaching back to derpier times. The chosen link for today is this charming report.

• The Verge article