Gray goo (or, in British spelling, "grey goo") is a term used to describe what life on our planet might become if self-replicating robots or nanomachines got out of control and began to use up life forms for their own energy needs in some unstoppable way.
The term was first used in K. Eric Drexler in his seminal book about Nanotechnology, Engines of Creation. Michael Crichton's Prey is one of several science fiction novels about gray goo catastrophes. The possibility of all of us becoming a lifeless conglomeration of gray goo, whether by accident or by robotic intent, is considered exceedingly unlikely. However, it has been taken seriously enough by one researcher, Robert Freitas, to suggest some public policy recommendations.
In self-replication at the "nano" or molecular level, some source of energy would be needed and it would seem that these would be the same sources used by life forms or from life forms themselves (just as human beings derive energy from eating other animals that have obtained their energy from lower life forms). In the competition for energy with nanomachines, human beings might find themselves unable to adapt quickly enough through natural evolution, ultimately falling prey to their own intellectual creations.
A significant argument against the possibility of a gray goo situation is that engineers should be able to build in limiting conditions for self-replication. One writer, Chris Phoenix, says that it is as unlikely that a molecular manufacturing system could degenerate into unstoppable self-replication as that a drill press or lathe might self-replicate. Phoenix refers to nanorobots that self-replicate only for the limited purpose of a specific task, such as cleaning and closing a wound.
Variations on this term include:
- Black goo or red gloo, the use of nanomachines by terrorists or nihilist to destroy all or some segment of humanity.
- Pink gloo, a view of humanity itself, which can be seen as a self-replicating entity with a tendency to fill up existing space.
- Green gloo, the idea of some antidote to the tendency of pink gloo to spread, perhaps limiting its ability to reproduce.