What if the programming of billions of tiny self-replicating robots—nanobots in the technical parlance—suddenly went awry? And instead of doing the job for which they were built (like mopping up an oil spill), they started consuming all matter on Earth—while building more of themselves? In his 1986 book, Engines of Creation, nanotech pioneer Eric Drexler describes it this way: "Imagine such a replicator floating in a bottle of chemicals, making copies of itself... the first replicator assembles a copy in one thousand seconds, the two replicators then build two more in the next thousand seconds, the four build another four, and the eight build another eight. At the end of ten hours, there are not thirty-six new replicators, but over 68 billion. In less than a day, they would weigh a ton; in less than two days, they would outweigh the Earth; in another four hours, they would exceed the mass of the Sun and all the planets combined."