This thread reminded me of the idea of von Neumann machines.

Someone do the math here, I’m bad at it.

If I were to make one machine the mass and size of a baseball and released it into the earth (for simplicity let’s say it can consume any materials), and it reproduced itself exactly twice a day… how long would it take to “eat” the world?

It can consume lava and survive under high pressure as well.

The mass of the earth is 5.9742 × 10[sup]24[/sup] kg, and the mass of a baseball is roughly .145 kg. So there are 4.12 × 10[sup]25[/sup] baseball mass equivalents in the earth, which is roughly 2[sup]85[/sup]. So it’d take about 42.5 days, assuming the earth to machine conversion is perfectly efficient.

Ah, but that assumes the “offspring” are just as hungry. If it’s just the one machine chomping away, and it doesn’t eat any of its children:

4.12 × 10[sup]25[/sup] baseball mass units in Earth =
2.06 × 10[sup]25[/sup] days (@ 2 meals/day) =
5.64 x 10[sup]22[/sup] years =
4.03 x 10[sup]12[/sup] universe lifetimes (@ 1.4 x 10[sup]10[/sup] years/universe)
Yeah, yeah, I know that’s not what the OP meant, but I threw it in for laughs.