On Friday, scientists redefined the value of kilogram. A kilogram has been defined by a shiny lump of platinum-iridium kept in a special glass case and known as the International Prototype of the Kilogram. It is housed at the headquarters of the International Bureau of Weights and Measurements (whose French acronym is BIPM), just outside Paris, as reported by Reuters. After a week-long meeting, members of the BIPM agreed to redefine a kilogram in terms of a tiny but unchanging value called the ‘Planck constant’. Take a Weight Off: Tears, Joy as Kilo Gets Historic Update.
Not just kilogram but they also decided to update definitions for the ampere (electrical current), the kelvin (thermodynamic temperature) and the mole (amount of a substance). Rather than basing the unit on this physical object, henceforth, the measurement will be based on a fundamental factor in physics known as Planck’s constant. The problem is the prototype doesn’t always weigh the same. Even inside its three-glass bell jars it picks up microparticles of dirt and is affected by the atmosphere. Sometimes it needs cleaning which can affect its mass.
Martin Milton, director of the BIPM said, “The SI redefinition is a landmark moment in scientific progress.” Barry Inglis who heads the committee for weighs and measures said the implications were immense. He said, “We will now no longer be bound by the limitations of objects in our measurement if the world but have universally accessible units that can pave the way to even greater accuracy and even accelerate scientific advancement,” he said. The new definitions agreed by the BIPM will come into force on May 20, 2019.