gray goo

n. A hypothetical substance composed of sagans of sub-micron-sized self-replicating robots programmed to make copies of themselves out of whatever is available. The image that goes with the term is one of the entire biosphere of Earth being eventually converted to robot goo. This is the simplest of the {nanotechnology} disaster scenarios, easily refuted by arguments from energy requirements and elemental abundances. Compare {blue goo}.