World's Roundest Object!

TL;DR

A silicon sphere, considered the roundest object in the world, is being used to redefine the kilogram, eliminating its dependence on a physical object.

Transcript

Can I hold it? 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 ready? I'm about to touch a 1kg sphere of silicon-28 atoms. There are about 2.15x10^25 of them. It feels absolutely incredible. Wow, that is amazi... Read More

Key Insights

• 🏪 The kilogram is the only SI unit still defined by a physical object, the International Prototype Kilogram, stored in Paris.
• 🫀 The roundest object in the world, a silicon sphere, is being used to redefine the kilogram by counting the number of silicon-28 atoms in it.
• 💦 The kilogram was originally intended to be the mass of a liter of water at its densest temperature, which was achieved with remarkable accuracy.
• 🪡 Redefining the kilogram will have significant implications for various measurements and eliminate the need for a physical object as the standard.

Summary & Key Takeaways

• The silicon sphere, valued at 1 million Euros, is the roundest object, with a diameter measured using lasers and its volume calculated using the known atom spacing in silicon.

• The sphere contains a specific isotope of silicon, silicon-28, making it extremely pure and perfect for redefining Avogadro's constant.

• By redefining the kilogram using the number of silicon-28 atoms in the sphere, the kilogram's value will no longer be tied to a physical object but based on a concept.

• Another approach to redefine the kilogram involves fixing Planck's constant using a Watt Balance.