Author: Stephen Johnson / Source: Big Think
- The new definition of a kilogram is based on a physical constant in quantum physics.
- Unlike the current definition of a kilogram, this measurement will never change.
- Scientists also voted to update the definitions of several other measurements in physics.
Since 1889, the definition of a kilogram has been the mass of one particular chunk of platinum-iridium alloy called the International Prototype Kilogram, stored at the International Bureau of Weights and Measures in Sèvres, France.
This cylindrical hunk of metal, nicknamed Big K, has many copies around the world that are used to calibrate scales and keep society in agreement on what constitutes a kilogram and other units of measurement. This helps the global economy to function smoothly.
But this system has a fundamental problem: Big K loses mass over time, about 50 micrograms since its creation, or the mass of an eyelash, as Vox reports. Strangely, when this happens, the definition of a kilogram stays the same. (After all, a kilogram is defined simply as the mass of Big K.) This causes headaches for industries and fields of study that have to account for the miniscule changes.
That’s set to change. On Friday morning, scientists at the General Conference on Weights and Measures in Versailles voted to change the definition of a kilogram, opting to affix it to a physical constant that will never change, whether you’re measuring it on Earth or light years away in the cosmos.
“Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense,” said Barry Inglis, director of the International Committee for Weights and Measures. “We will now no longer be bound…
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