Next year, the kilogram will be officially redefined but don’t worry it won’t change how much a kilogram is, only how we actually measure it.
Since 1889, the kilogram has been measured by comparing it to a special cylinder of platinum-iridium but in 2018 we’ll finally move to a measurement that is only related to the fundamental constants of the universe, the Plank constant.
The new approach needed a new type of scales, known as the Kibble Balance, which accurately measures the Plank constant, and researchers are now busy improving on the design. The Technical University of Ilmenau in Germany has just announced their work in the creation of new, more sensitive scales which they are calling the "Plank Balance". They hope to unveil the new prototype at the end of the year.
All future scales will be calibrated against the Planck constant, one of the fundamental quantities of physics that connects the energy of a particle to its frequency. It is found in many physical formulas and has been key to creating a new way to measure mass.
Researchers were able to connect electrical measurements to a mass thanks to the existence of certain quantum effects that connected the physical quantities that we can measure to the Planck constant.
The second and the meter are both defined in terms of constants. The second is related to the hyperfine oscillation of a cesium atom while the meter is a fraction of the distance covered by light in one second. Anyone in the world (or the universe) can measure those values and calibrate their instruments.
Currently, though, to calibrate kilogram scales one needs to use a copy of the one-kilogram platinum-iridium block. While this specific metal alloy is pretty sturdy and resistant to corrosion, the kilogram prototype is still a physical object and it has had variations over time. Those changes are tiny if we think in terms of following, say, a cake recipe but they become huge when you’re doing high-precision measurements.
So, the measurement change is welcome, and that requires high-precision scales. Kibble balances are already in use in several institutes of metrology around the world and theoretically, anyone could build their own. But the German group is promising to push the limit of this technology and to develop their Planck Balance, which can proudly measure the kilogram more accurately than ever before.
The new way to measure the kilogram will be officially accepted at the 26th General Conference of Weight And Measures taking place in November 2018.