07/17/2015

Redefining the Kilogram

16:37 minutes

Researchers are using this spherical crystal of silicon in their quest to redefine the kilogram. Photo by Enrico Massa and Carlo Sasso
Researchers are using this spherical crystal of silicon in their quest to redefine the kilogram. Photo by Enrico Massa and Carlo Sasso

All the scales in the world—from those at your local deli to the big ones at the junkyard—are ultimately calibrated against a 125-year-old chunk of metal in a vault on the outskirts of Paris. Its mass is the definition of a kilogram. There’s just one problem: That chunk of metal seems to be losing weight. We talk to Derek Muller, creator of the Veritasium science education series, about the race to redefine the kilo in less slippery terms—and what a near-perfect silicon crystal sphere has to do with it. And Jon Pratt, an engineer at the National Institute of Standards and Technology, tells us about his team’s alternative “watt balance” strategy to lock down the kilo in terms of Planck’s constant.

Segment Guests

Jon Pratt

Jon Pratt is leader of the Fundamental Electrical Measurements Group at the National Institute of Standards and Technology in Gaithersburg, Maryland.

Derek Muller

Derek Muller is creator of Veritasium and is based in Los Angeles, California.

Meet the Producers

About Christopher Intagliata

Christopher Intagliata is Science Friday’s senior producer. He once served as a prop in an optical illusion and speaks passable Ira Flatowese.

About Elah Feder

Elah Feder is co-host and producer of Undiscovered. She’s also Science Friday’s resident Canadian.