Worlds Roundest Object
Can I hold ité Only if you promise to be really, really careful. I promise I will be so incredibly careful.I will be incredibly careful with it. I promise. So, it's slippery, be careful.Alright, are we readyé I'm about to touch a 1kg sphere of silicon28atoms. There are about 2.15x10^25 of them. It feels absolutely incredible. Wow, thatis amazing. Besides its creators, I am one of only a handfulof people ever to hold this sphere. The raw material used to make it was worth1 million Euros but now that it has been so
precisely sculpted How much is that worthé It's priceless. . This you are looking atnow is the roundest object in the world. How can you say for sure it's the roundestobjecté I mean the Earth is pretty round, isn't itéIf this was the Earth. If this were the Earth then the highest mountainto the lowest valley would be. about 14m apart. That is shocking. That is shockingly round.
But why would you invest one million Eurosand thousands of manhours perfecting a pure, polished silicon sphereé Well the answer is grave. Or rather 'grave'as it would have been pronounced in the original French. You see the grave was the original name forthe base unit of mass in the metric system, which became the Systeme International d'unitesor SI units. In 1793, a commision which included notable scientist and aristocrat Antoine Lavoisier,defined the base unit of mass as the weight of a cubic decimeter of water at the meltingtemperature of ice essentially just a litre
of ice water. The name grave came from theLatin gravitas, meaning weight. But it wasn't to last. It sounded too similarto the aristocratic title 'graf' which is the equivalent of an earl or a count. Andwith the French revolution in full swing with the rallying cry of equality for all, youcouldn't exactly have one unit nobler than the others. At this Lavoisier lost his head,literally, not because he helped devise one of the greatest systems of measurement ofall time, but because he was collecting taxes as a nobleman. So things really were grave.
The new republican government believed a gravewould be too big for the things they wanted to measure anyway and and so they settledon the gramme, which was just a thousandth of the grave. But soon they realized that a gram was toosmall and so they returned to the grave, but since they couldn't call it that, they inventedthe kilogram a thousand grams. And that is why out of the seven base SI units, thekilogram is the only one to have a prefix in its name. In 1799 the kilogram definition was refinedto be the mass of a litre of water at 4 degrees
Celcius the temperature at which it isdensest. But water itself is obviously not the most sensible thing to use as a mass standard.So a pure platinum cylinder was created to have the same mass as the water definitionand it was declared Kilogram of the Archives. Now it's important to note at this point thekilogram is no longer tied to the mass of a volume of water the kilogram of the archivesis by definition THE kilogram. 90 years later, in 1889 the kilogram was upgradedto a platinumiridium alloy cylinder. Now it was much harder than the original but wasotherwise basically identical. And to this day, it remains the definition of the kilogram.It is officially called the International