Factories make things. They use machines to position parts so they combine into bigger parts. Those parts are then combined into even bigger parts.

This goes on until the thing you want to make is finished. Then it gets packed up and sent to the store.

The parts factories start with, the smallest parts, are made by taking a chunk of material and cutting out what's not needed. There's a limit to how small the parts can get before you start having trouble putting them together. If the parts are too small, you won't be able to control them. Or they just won't stay together.

It would be like trying to put together Lego blocks while wearing thick gloves.

Because the smallest parts can't get too small, the things you can make aren't perfect. It's like working with huge Lego blocks because that's all you can handle with thick gloves. The cars, buildings, and people you can make with huge Lego blocks won't be very detailed, or as easy to carry around.
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With huge blocks, you can probably make something that looks like a car, but only roughly.*

If the smallest parts a factory can control are atoms, then you can control just about any feature a product can have, including its shape, strength, mass, texture, etc. This includes products the size of cells, or smaller. So we could make devices that mimic and improve on the body's cellular processes, repairing damaged tissue, curing disease, and fighting infections.

Every product we use in daily life is made by arranging atoms, but in large chunks. Because we can't decide exactly where these atoms go, some products have defects, are weak, inefficient, or cost a lot to make. With a factory that can arrange atoms just the way we want, products wouldn't have these issues.

On top of all that, such a factory could fit in a box—like a printer—that sits on the table next to your computer. Or next to your virtual assistant. Or the coffee table. Or kitchen counter. Or... you get the idea.

We're building this today, in fact. It's called atomically precise manufacturing (APM).

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* Of course, this is part of the appeal.. like Minecraft.

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Further Reading

Drexler, K. Eric. "Radical Abundance".

Saadeh Y, Vyas D. Nanorobotic Applications in Medicine: Current Proposals and Designs. Am J Robot Surg. 2014;1(1):4–11. doi:10.1166/ajrs.2014.1010

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