November 16th 2018, a very important day you've probably never heard about

TIFO that november 16th 2018 marked the end of the SI system as we knew it, and most of us never even noticed. 

In most countries around the world, barring Burma, Liberia and the United States, the SI system is a universal system of measure. For those who aren't aware, the SI system is a system that gives universal units of measurement for temperature(kelvin), distance(metres), electric current(amperes), time(seconds), amount of substance(moles), mass(kilograms), and intensity of light(candelas). By making these units universal, it becomes easier for people working in different fields to easily interpret this information without having to convert units or spend time interpreting the meaning. Before the implementation of SI units, it was very difficult for researchers and especially scientists from different countries to use or build on research done by others, and errors made while converting values caused large time losses and created far too many problems. Therefore, when SI units were introduced in 1960, they provided us with a way of making our knowledge easy to access and understand. 

In 2018, on the 16th of November, the SI system underwent a huge change. It was found that out of the 7 units, 4 were inaccurate - kilograms, moles, kelvin and amperes. This all stemmed from a problem created by the way we calculated the value of 1 kilogram. You see, unlike what most of us would imagine, before 2018, a kilogram was not defined by some complex formula or decimal. Instead, until then, it was defined by physical objects. Till 1879, it was defined as the mass of 1 litre of water. In fact, 1 litre of pure water is just about 1 kilogram, but that is only if the water is pure. Because of this, in 1879, a platinum-iridium cylinder was forged. This cylinder, named Le Grand K, became the new definition of a kilogram and was kept in a vault in France. This cylinder's mass was the exact definition of 1 kilogram. No failsafe, no equation or other object, just this one cylinder. To be fair, in the 139 years of its existence, it lost no more than 0.00005 grams. To put it in perspective, 20kg of material in 1879 was just around 1 gram heavier than 20kg of material in 2018. Doesn't really make much of a difference to you and me, but caused a lot of trouble with scientists. Therefore, in 2018, the Kg was redefined based on a constant called the Planck's constant. They assigned a fixed value to the constant and then formed an equation to calculate the Kg. 

Prior to 2018, the mole, the kelvin and the ampere were all based on the Kg. However, now that the definition of the Kg had changed, all 3 of these had to change too. Before 2018, the mole was defined as the number of atoms in 12 grams of carbon-12. However, this shared the same problem as the old definition of the Kilogram, and so it had to change. From 2018 onwards, the definition of the mole became 6.02214076*10²³ particles. As for the kelvin, it was defined based on the triple point of pure water. The triple point of pure water is simply the temperature at which a substance can be present in solid, liquid or gaseous form. For water, at 0.01°C, it can exist as a liquid, solid or gas. However, this shared the same issue as using water to define kilograms, and so the kelvin was redefined in an equation with a constant called the Boltzmann constant. The ampere was also redefined. Before 2018, it was defined with relation to force. As newton's second law states, force is found by multiplying mass by acceleration.  This too had to be changed after the unit for mass was changed. Therefore, after 2018, current was instead defined with relation to charge, instead of mass. 

These 4 changes don't play a role in most of our lives. However, they were critical steps in science. They helped us move away from defining measurements through physical objects, and instead improved our mathematical definitions of these units. Our measurement of quantities was no longer hindered by physical objects, but by equations and mathematics, and I for one find that very reassuring. 

What about you? What's your favourite TIFO moment? Tell me down in the comments below.