It’s been the topic of a weighted discussion for quite some time, but today it has been decided: “Le Grand K” will no longer be used to define a kilogram.
“Le Grand K” is not a big box of Special K, but a platinumiridium cylinder stored by the International Bureau of Weights and Measures in an underground vault in Paris that has defined a kilogram of mass since 1889. There are a few official copies, and many more copies, so each country has their own kilogram to calibrate to.
Last Friday (November 16th) the kilogram has been redefined so it no longer depends on a material object. Because a material object can be scratched, chipped or destroyed. Or stolen. Or accidentally thrown into the bin. And it can degrade – in fact, “Le Grand K” weighs about 50 µg lighter than its six official copies. You don’t really want to gold – ahem, I mean platinumiridium – standard for weight to change in weight, right?
So now the kilogram will be defined based on a universal, unchangeable constant. Much better, I think you would agree. The constant of choice here is the Plank’s constant, a number that converts the macroscopic wavelength of light to the energy of individual constants of light. Representatives from 58 countries universally agreed on this new definition, so from next year, the kilogram will be constant forever.
The ampere (electrical current), the kelvin (temperature) and the mole (amount of chemical substance) have also been redefined. That means that all seven units in the International System of Units (S.I.) will be defined by universal constants:
meter  unit of length 

kilogram  unit of mass 

second  unit of time 

ampere  unit of electrical current 

kelvin  unit of temperature 

mole  unit to describe the amount of substance 

candela  unit to describe the intensity of light 

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Sources/Further reading:
The international system of units: en.wikipedia.org/wiki/International_System_of_Units
The new kilogram was in the news: www.nytimes.com/2018/11/16/science/kilogramphysicsmeasurement.html and www.theregister.co.uk/2018/11/17/amp_kelvin_kilogram/
Comic from xkcd.com
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* Avocado’s number, however, states that 6.02214076 × 10^23 guacas make up one guacamole. (I knooooow, I already made this joke).
** I have to be honest and say that I have no idea what this all means