Grey goo is a hypothetical end-of-the-world scenario involving nanotechnology in which out-of-control self-replicating robots consume all matter on Earth while building more of themselves, a scenario known as ecophagy (‘eating the environment’).
Self-replicating machines of the macroscopic variety were originally described by mathematician John von Neumann, and are sometimes referred to as von Neumann machines.
The term ‘grey goo’ was coined by nanotechnology pioneer Eric Drexler in his 1986 book ‘Engines of Creation’: ‘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 — if the bottle of chemicals hadn’t run dry long before.’
Drexler used the term ‘grey goo’ not to indicate color or texture, but to emphasize the difference between ‘superiority’ in terms of human values and ‘superiority’ in terms of competitive success: ‘Though masses of uncontrolled replicators need not be grey or gooey, the term ‘grey 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.’
Drexler more recently conceded that there is no need to build anything that even resembles a potential runaway replicator. This would avoid the problem entirely. In a paper in the journal ‘Nanotechnology,’ he argues that self-replicating machines are needlessly complex and inefficient. Recent analysis has shown that the danger of grey goo is far less likely than originally thought. However, other long-term major risks to society and the environment from nanotechnology have been identified. Drexler has made a somewhat public effort to retract his grey goo hypothesis, in an effort to focus the debate on more realistic threats associated with knowledge-enabled nanoterrorism and other misuses.
The Daily Omnivore 
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