William Herkewitz, writing for Popular Mechanics: Physicists have just built the smallest working engine ever created. It's a heat-powered motor barely larger than the single atom it runs on. Designed and build by a team of experimental physicists led by Johannes at the University of Mainz in Germany, the single atom engine is about as efficient as your car at transforming the changing temperature into mechanical energy. While scientists have previously created several micro-engines consisting of a mere 10,000 particles, Johannes's new engine blows these out of the water by paring down the machine to a singular atom housed in a nano-sized cone of electromagnetic radiation. The project is outlined today in the journal Science. "The engine has the same working principles as the well-known [combustion] car engine," Johannes says. It follows the same four strokes; expanding then cooling, contracting then heating.There's some confusion here. The article says it's a "four-stroke" engine. But as we know, a four-stroke engine consists of an intake stroke, a compression stroke, a power stroke, and an exhaust stroke -- things that the engine in the article doesn't seem to have. The article doesn't mention how a single atom is able to mimic all the effects of a combustion engine. Update: 04/15 18:24 GMT by M :The article appears to have been updated for clarification.