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.

Questions & Answers

Q: How is the roundness of the silicon sphere achieved?

The silicon sphere is created by grinding an oversized sphere progressively finer using abrasives, reaching the atomic level to control its shape. It is massaged at the atomic level.

Q: How is the diameter of the sphere measured accurately?

The diameter is measured using a laser. The sphere is placed in the center of a cavity, and a laser hits both sides, measuring the gap. This allows for precise determination of the sphere's diameter.

Q: How will redefining the kilogram affect measurements?

Redefining the kilogram will eliminate its dependence on a physical object, ensuring a consistent and unchanging unit of mass. This will have implications on various measurements in science and everyday life, such as weight, energy, and force.

Q: What is the alternative approach to redefine the kilogram?

The alternative approach involves fixing Planck's constant using a device called a Watt Balance. This approach is complementary to the silicon sphere method and provides a check on its accuracy.

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.