As of today, the kilo no longer weighs one kilo. The change affects not only the kilogram, but also the Ampere, the Kelvin and the Mole (which are all different measuring units).
What is a kilogram?
In the 19th century a mould in the shape of a cylinder would be the original shape in which the "Great Kilo" would be born; in 1889. Ever since then the international prototype of the kilogram has been the reference of the basic unit of mass.
For nearly 130 years, this piece of metal has been locked up in a secure vault in the Pavillon of Breteuil, Saint-Cloud, near Paris. However, representatives of 60 nations, including Australia, have now voted on a proposal to define humble unity using pure and unadulterated physics.
It is not a change we will notice when shopping, but it is necessary if we want to keep pace with technology now and in the future.
History of the kilogram
In the 18th century, one kilogram was equivalent to a certain volume of water, but in 1889 it was replaced by a platinum and iridium cylinder known as the international prototype kilogram or Big K, the Big Kilo.
"We are only talking about micrograms. Not enough to worry about our daily life measurements, but enough to see, and enough to want a better kilogram," explains Bruce Warrington, CEO of the National Measurement Institute.
So what's going to change?
Instead of using the classic kilogram, as a criteria, scientists will use one of nature's fundamental laws known as the Planck constant to define one kilogram, which varies by about 50 micrograms less. The new kilogram value is derived from the Planck constant thanks to a power balance.
The Planck constant is the amount of energy released in light when electrons in atoms jump from one energy level to another. That number will now be exactly 6.62607015 x 10 ^ -34 J-s. To make their measurements, scientists will use a sensitive electromagnetic instrument known as the Kibble Balance.
A historical redefinition
"It's a historic step, it's bigger than any similar change made in the past," says Warrington.
The International Bureau of Weights and Measures, which regulates changes in measurements, has already updated several of its units.
Following the approval of the changes, these will come into effect on the next World Metrology Day: 20 May 2019. The objective is, therefore, to achieve the numerical accuracy of the kilogram and, with this, the International System of Units will adapt better to new technologies.
-The second, which occurs at a fixed frequency of 9,192,631,770 Hz.
-The meter, the distance traveled by light in a specific fraction of a second, defined using the speed of light in a vacuum of 299,792,458 meters / second.
-The Kelvin is the unit of temperature, defined by the Boltzmann constant for the energy of gas particles at a given temperature, set at: 1.380 649 × 10-23 joules / Kelvin
-The kilogram is a quantity of mass, defined using the Planck constant established at: 6.626 070 15 × 10-34 joules-second
-The ampere is a current flow, quantified using the elemental charge of electrons established in: 1.602 176 634 × 10-19 Coulomb.
-The candle measures the intensity of light and is defined using the constant Kcd: the brightness, per watt, of monochromatic radiation at a specific frequency (540 × 1012 Hz), i.e. 683 lumen / watt.
-The mole is a quantity of atoms or particles, defined by the Avogadro constant set at: 6.022 140 76 × 1023 mol - 1