Since the late 19th century, the official standard for the weight of a single kilogram has been the International Prototype Kilogram (IPK), a small cylinder of platinum and iridium that is sometimes called "Le Grand K" and always kept locked in a vault outside Paris. There are copies of the IPK, but metrologists (measurement-y type scientists) have recently been seeking standards more stable than vulnerable, pathetic physical objects.
Now, as Nature reports, there is finally a solution to the dilemma of physical matter's inevitable deterioration, at least as it pertains to Le Grand K. Metrologists are ready to replace the IPK with a mathematical constant that will standardize the weight of a kilogram without reference to a vigilantly safeguarded physical object.
The plan answers a question that has been at the forefront of the international measurement community for decades now. After all, it was in 1989 that Le Grand K was first determined to be losing mass at a troubling (by scientific standards) rate. Over time, objects just lose atoms. That's life.
The plan to replace the IPK is elegant but has required three independent confirmations of an intricate series of calculations. The International Committee for Weights and Measures (CIPM) approved a method whereby the original kilogram was expressed first using Plank's constant, which, roughly speaking, is the ratio of energy over frequency for any particle. That result was then calculated as a mass using Einstein's famous E=mc2. Voilà: the new kilogram!
Of course, there is still some final work to be done, including development of a protocol enabling researchers anywhere to use the new kilogram measure. A redefinition of other measurement standards, such as the mole, is scheduled for 2018, and the kilogram will now join them. All hail imaginary quantities made real by international decree!
Source: Nature
