K. Eric Drexler in Engines of Creation says: Among the cognoscenti of nanotechnology, this threat has become known as the "gray goo problem." Though masses of uncontrolled replicators need not be gray or gooey, the term "gray goo" emphasizes that replicators able to obliterate life might be less inspiring than a single species of crabgrass. They might be "superior" in an evolutionary sense, but this need not make them valuable.

One of the many scary scenarios of Nanotechnology. Basically it is self-replication gone awry, causing mass destruction on levels we've never seen. You think the bomb is bad (okay, it is :) at least it can be controlled. We've been lucky to escape the Cold War, but will we escape the next one? The scary thing about nanotechnology is that one could destroy the world (no, really, no more life on earth) in a laboratory accident. Nobody, of course, would know about this lab experiment, because it could be done with a few simple tools, unlike the massive amounts of uranium needed for the bomb. At least in the Cold War, we (the US) knew who our enemies were, if nanotechnology is left on the backburners as far as our lawmakers go, we will see a "whole new can o worms."

grault = G = gray hat

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.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.