8. Nano Technology

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The pace with which mankind is discovering new ways to accomplish amazing things on a tiny scale is rapidly accelerating. Nano technology, which essentially means really small stuff, holds great promise for the future by giving us medical procedures that would allow tiny nanobots to be injected into our bodies to seek out and destroy disease, among other things. On the other hand, making these nanobots too smart could be a problem as well. What if they decided to band together and start replicating themselves? In theory, they could replicate fast enough to create a mass that would outweigh the Earth in a matter of days.