The machines we’re familiar with operate on some pretty obvious principles. It’s easy to supply them with energy, whether it’s chemical or mechanical. Given parts we’ve carefully arranged, that energy gets converted into some form of useful work, like pumping water or moving a car. While the environment can have an effect on the machine’s performance, the machine can usually operate over a wide range of conditions.

Absolutely none of this is true at the level of individual molecules, yet people have figured out how to make machines out of little more than a few dozen atoms. This year’s chemistry Nobel honors three pioneers in this field.

Nearly everything about building a molecule-sized machine is hard. You can’t put the parts in their proper places by hand or even with a small machine; they have to be built by chemical synthesis. The environment dominates at the molecular level, with Brownian motion tending to force molecules to move about at random rather than in the directed manner needed to perform work. And providing energy to a molecule is much more challenging than giving an internal combustion engine something to burn—the energy for a molecular machine needs to be precisely tailored to act at specific chemical bonds.