People are familiar with things that are round all the time, right? The Earth, basketballs, ball bearings, and countless other things. But just how round are they?

When it comes to looking at them on an atomic level, not very round at all. So, what is the roundest thing in the world?

It turns out that it is the silicon spheres of the International Avogadro Project.

What?

Yes, there are several spheres made of 100% silicon that were made specifically to be as round as possible. The National Institute of Standards and Technology (NIST) describes them this way:

“Their surfaces are so smooth that if they were blown up to the size of the Earth, the distance between the tallest mountain and the deepest ocean would be just 3-5 meters (10-15 feet).”

That is incredibly round. NIST has more information about how they are measured, and how much they cost:

“Devices known as optical interferometers have allowed researchers to measure the sphere’s width to nanometer precision. They each cost about $3.2 million and had to be handcrafted by a master lens maker.”

But why would anyone ever spend so much money to make an (almost) perfectly round sphere of silicon?

Simple, to more precisely define what a kilogram is.

People throughout the world (yes, even some in America) have used Kilograms as a unit of measurement for generations. It has served us well, but the exact weight of a kilogram has not always been very precise. When standard weights for the metric system were first introduced, they used things found in the natural world. This was good for the most part, but as more precise measurements were needed, it became a problem.

Efforts have been made over the years to more precisely define things used in the metric system.

This silicon sphere is just one of the latest efforts in this direction. The International Avogadro Project wanted to make these spheres and use them to provide a precise measurement of a kilogram. To that end, multiple copies of this silicon ball were made.

Sadly, the International Committee for weights and Measurements decided against using it as the standard, opting for a standard based on the Planck Constant instead.

NIST says that this was not a wasted effort though:

 “though measurement scientists chose the Planck constant as the basis for redefinition, other constants of nature can also be used. if for no other reason than to provide a check that the Planck constant definition is correct.”

If you want to see these round balls, check out this video:

Wow, those are some amazingly round balls you got there.

If you enjoyed that story, check out what happened when a guy gave ChatGPT $100 to make as money as possible, and it turned out exactly how you would expect.