On May 20, 2019, the World Metrology Day, the measurement of a kilogramme was redefined. Earlier, the kilogramme was measured according to the weight of was measured according to the weight of a block of platinum-iridium alloy housed at the International Bureau of Weights and Measures in France. But post May 20, the weight of the kilogramme would be defined by the Planck Constant – a constant of nature that relates to how matter releases energy.
The main problem with using Big K as a universal standard for mass is that Big K, being a manmade object, is imperfect and subject to change over time. Indeed, it is estimated that Big K has lost about 50 micrograms since the time it was created. Since 1 kilogram is defined as exactly the value of the mass of Big K, if Big K’s mass changes then the value of the kilogram must also change. Obviously, having a standard for mass that changes its mass is not a good idea for science. The ideal set of units should be static and unchanging.
Hence the reason for redefinition. The new definition of the kilogram ties the value of the kilogram to a fundamental constant of nature that will never change. Even billions of years from now when Big K has disintegrated into dust, this new constant the defines the value of the kilogram will be exactly the same—because the value of the unit is tied to a fundamental aspect of reality.
Picture Credit : Google