"Grey goo" is a hypothetical end-of-the-world scenario involving molecular nanotechnology in which out-of-control self-replicating robots consume all matter on Earth while building more of themselves. This scenario is known as "ecophagy" -- the literal consuming of an ecosystem. The term "grey goo" is usually used in a science fiction context. In the worst postulated scenarios, matter beyond Earth would also be turned into goo, a large mass of replicating nanomachines. The disaster is posited to result from a deliberate doomsday device, or from an accidental mutation in a self-replicating nanomachine used only for other purposes, but designed to operate in a natural environment.
A simple form of self-replicating machine (Credit: NASA)Self-replicating machines were originally described by mathematician John von Neumann. They are artificial constructs capable of autonomously manufacturing copies of themselves using raw materials taken from their environment. The concept of self-replicating machines has been advanced and examined by Edward F. Moore, Homer Jacobsen, Freeman Dyson, and in more recent times by K. Eric Drexler. The future development of such technology has featured as an integral part of several plans involving the mining of moons and asteroid belts for ore and other materials, the creation of lunar factories and even the construction of solar power satellites in space. Von Neumann also worked on what he called the universal constructor, a self-replicating machine that would operate in a cellular automata environment.
Ecophagy is a term coined by Robert Freitas. He used the term to describe a scenario involving molecular nanotechnology gone awry. In this situation out-of-control self-replicating nanorobots consume entire ecosystems, resulting in global ecophagy. However, the word "ecophagy" is now applied more generally in reference to any event -- nuclear war, the spread of monoculture, massive species extinctions -- that might fundamentally alter the planet. These events might result in ecocide in that they would undermine the capacity of the earth's biological population to repair itself. Some scientists suggest that more mundane and less spectacular events -- the unrelenting growth of the human population, the steady transformation of the natural world by human beings -- will eventually result in a planet that is considerably less vibrant, and one that is, apart from humans, essentially lifeless.
In his original paper Freitas wrote:
Perhaps the earliest-recognized and best-known danger of molecular nanotechnology is the risk that self-replicating nanorobots capable of functioning autonomously in the natural environment could quickly convert that natural environment (e.g., "biomass") into replicas of themselves (e.g., "nanomass") on a global basis, a scenario usually referred to as the "grey goo problem" but perhaps more properly termed "global ecophagy".
As the use of industrial automation has advanced over time, some factories have begun to approach a semblance of self-sufficiency that is suggestive of self-replicating machines. Since safety is a primary goal of all legislative consideration of regulation of such development, future development efforts may be limited to systems which lack either control, matter, or energy closure. Fully-capable machine replicators are most useful for developing resources in dangerous environments which are not easily reached by existing transportation systems -- such as outer space. An artificial replicator can be considered to be a form of artificial life. Depending on its design, it might be subject to evolution over an extended period of time. However, with robust error correction, and the possibility of external intervention, the common science fiction scenario of robotic life run amok will remain extremely unlikely for the foreseeable future.
