So, according to the Wall Street Journal*, says Jon Pratt, a mechanical engineer with the U.S. National Institute of Standards and Technology (NIST). He was speaking about a cylinder of platinum-iridium forged in 1889, known as “Le Grand K”, which on May 20 went out of service as the kilogram standard.
Metrologists worldwide now will define this weight by non-physical methods based on non-changing constants of the universe. It will be measured by a high-tech tool called the Kibble balance.
For a detailed explanation of the new kilogram standard and a fascinating video of NIST’s Kibble balance in action, see the Wired magazine post by physics professor Rhett Allain on The Basic Physics of the Kilogram’s Fancy New Definition. Weighty stuff! (A bit too dense for me—I just like the Kibble…mesmerizing.)
*(“The Numbers” by Jo Craven McGinty, “The Kilogram Faces a New Test of Metal”, 6/8/19)