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Grey goo refers to a hypothetical end-of-the-world scenario involving molecular nanotechnology in which out-of-control self-replicating robots consume all living matter on Earth while building more of themselves (a scenario known as ecophagy).
The term is usually used in a science fiction or popular-press context. In the worst postulated scenarios (requiring large, space-capable machines), matter beyond Earth would also be turned into goo (with "goo" meaning a large mass of replicating nanomachines lacking large-scale structure, which may or may not actually appear goo-like). The disaster is posited to result from a deliberate doomsday device, or from an accidental mutation in a self-replicating nanomachine used for other purposes, but designed to operate in a natural environment.
Definition of grey goo
The term was first used by molecular nanotechnology pioneer Eric Drexler in his book Engines of Creation (1986). In Chapter 4, Engines Of Abundance, Drexler illustrates both exponential growth and inherent limits by describing nanomachines that can function only if given special raw materials:
- "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 describes grey goo in Chapter 11 Engines Of Destruction:
- "...early assembler-based replicators could beat the most advanced modern organisms. 'Plants' with 'leaves' no more efficient than today's solar cells could out-compete real plants, crowding the biosphere with an inedible foliage. Tough, omnivorous 'bacteria' could out-compete real bacteria: they could spread like blowing pollen, replicate swiftly, and reduce the biosphere to dust in a matter of days. Dangerous replicators could easily be too tough, small, and rapidly spreading to stop - at least if we made no preparation. We have trouble enough controlling viruses and fruit flies."
Drexler notes that the geometric growth made possible by self-replication is inherently limited by the availability of suitable raw materials.
Drexler used the term "gray goo", not to indicate color or texture, but to emphasize the difference between "superiority" in terms of human values and "superiority" terms of competitive success:
- "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."
Grey goo has several whimsical cousins, differentiated by color:
- Golden Goo is the backfiring of a get-rich-quick scheme to assemble gold or another economically valuable substance.
- Black Goo is goo that has been designed to carry a plague and intentionally unleashed into a populated area.
- Red Goo is goo unleashed intentionally by terrorists, a doomsday weapon, or a private individual who wishes to commit suicide with a bang.
- Khaki Goo is goo intended by the military to wipe out somebody else's continent, planet, etc.
- Blue Goo is goo deliberately released in order to stop some other type of grey goo. It might well be the only solution to such a disaster, and would hopefully be better controlled than the original goo.
- Pink Goo is a tongue-in-cheek alias for humanity, as the human species as a whole could be characterized as relentlessly self-propagating, planet-consuming, and potentially interstellar in scope. This metaphor has often but not exclusively been used to characterize human space expansion as a catastrophe, opening up the possibility of an entire galaxy or universe ultimately 'digested' by Pink Goo, perhaps at the expense of previous, less gregarious inhabitants.
- Green Goo is goo deliberately released, for example by ecoterrorists, in order to stop the spread of Pink Goo, either by sterilization or simply by digesting the pink goo. Some form of this, along with an antidote available to the selected few, has been suggested as a strategy for achieving zero population growth. The term originates from the science fiction classic, Soylent Green.
One convenient analogy for the grey goo problem is to consider bacteria as the most perfect example of biological nanotechnology. As they have not reduced the world to living goo, some consider it unlikely that some artificial construct will manage to do so with grey goo.
Even so, some people argue that living goo, or even a combination of nanotechnology and biotechnology to create organic replicators, is a more realistic threat than grey goo. Arguing that bacteria are ubiquitous and extraordinarily powerful, Bill Bryson (2003) says that the Earth is "their planet" and that we only exist on it because "they allow us to". Margulis and Sagan (1995) go further, arguing that all organisms, having descended from bacteria, are in a sense bacteria. Many kinds of bacteria are in fact essential for human life and are found in large quantities in the human digestive tract, in a symbiotic relationship.
Thus a living goo could be a multicellular organism that obtains its raw materials to grow through ecophagy, and then grows through a process of exponential assembly such as cell division.
Risks and precautions
It is unclear whether the molecular nanotechnology would be capable of creating grey goo at all. Among other common refutations, theorists suggest that the very size of nanoparticles inhibits them from moving very quickly. While the biological matter that composes life releases significant amounts of energy when oxidised, and other sources of energy such as sunlight are available, this energy might not be sufficient for the putative nanorobots to out-compete existing organic life that already uses those resources, especially considering how much energy nanorobots would use for locomotion. If the nanomachine was itself composed of organic molecules, then it might even find itself being preyed upon by preexisting bacteria and other natural life forms.
If self-replicating machines were built of inorganic compounds or made much use of elements that are not generally found in living matter, then they would need to use much of their metabolic output for fighting entropy as they purified (reduce sand to silicon, for instance) and synthesized the necessary building blocks. There would be little chemical energy available from inorganic matter such as rocks because, aside from a few exceptions (coal, for example) it is mostly well-oxidized and sitting in a free-energy minimum.
Assuming a molecular nanotechnological replicator were capable of causing a grey goo disaster, safety precautions might include programming them to stop reproducing after a certain number of generations (but, see cancer), designing them to require a rare material that would be sprayed on the construction site before their release, or requiring constant direct control from an external computer. Another possibility is to encrypt the memory of the replicators in such a way that any changed copy would decrypt to a meaningless, random bit string.
Drexler has 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. His 1992 technical book on advanced nanotechnologies Nanosystems: Molecular Machinery, Manufacturing, and Computation  describes manufacturing systems that are desktop-scale factories that specialized machines in fixed locations and conveyor belts to move parts from place to place. Popular culture, however, remains focused on imagined scenarios derived from his older ideas.
In Britain, the Prince of Wales called upon the Royal Society to investigate the "enormous environmental and social risks" of nanotechnology in a planned report, leading to much delighted media commentary on grey goo. The Royal Society's report on nanoscience was released on 29 July 2004, and dismisses the idea as impossible.
Recently, new 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.
- "We cannot afford certain types of accidents", Eric Drexler, Engines of creation, 1986
- "I wish I had never used the term 'grey goo'", Eric Drexler, Nature 10 June 2004
- "Autofac" is a 1955 science fiction short story by Philip K. Dick that features one of the earliest treatments of self-replicating machines.
- In Stanisław Lem's Ciemność i Plesń (Darkness and Mildew), 1959, spores of an engineered lifeform that can use nuclear energy escape the lab. In order for the spores to activate, they need to be in the dark and near a rare species of mildew (hence the title), after which they grow exponentially.
- In Michael Crichton's The Andromeda Strain (1969), also made into a movie, a rapidly evolving virus/prion-like chemical consumes many types of organic molecules with catastrophic results. This story overlaps both the grey goo and the out-of-control virus scenarios. The same author's Prey (2002) presents a somewhat less limited scenario where a company in Nevada accidentally/purposely releases self-assembling nanobots into the desert, which quickly replicate and evolve and threaten all of the human protagonists.
- The plot of John Sladek's 1968 novel The Reproductive System (British title Mechasm) is based on small (but not nano-scale) machines who scour the world for material to make more of themselves. The phrase "grey goo" is not used but the idea is the same.
- In the Adam Warren-penned Dirty Pair manga (1979-), mankind has ventured out into the stars as a result of the Nodachi Nanoclysm (often referred to as just "the Nanoclysm"), where nano absorbed most of the solar system before gaining sentience and annihilating itself to save its creators. As a result, with rare exceptions, nanotechnology is universally banned in human civilizations.
- Greg Bear's novel Blood Music (1983) is a classic of the field, depicting a form of grey goo originally derived from human lymphocytes.
- Frank Miller's graphic novel, Ronin (1983-84), is set in a future New York that is being overtaken by a post-singularity computer complex capable of physically replicating itself.
- Alan Moore's comic book, Promethea, takes place in a technologically-futuristic modern world, where the synthetic "Elastagel" is ubiquitous. In one issue, a Y2K malfunction causes all the Elastagel to melt and run together, essentially creating a Blob-like creature that causes havoc before being destroyed by the protagonist.
- In Jeffrey Carver's 1989 novel, From a Changeling Star, medical NAGs (nano-agents) capable of healing a human body from severe trauma run dangerously amok, causing amnesia and bizarre behavior. Competing NAGs, known collectively as an intelligence named Dax, help to reconstruct the memories and reveal a conspiracy regarding an attempt to cause Betelgeuse to go supernova.
- Walter Jon Williams's novel Aristoi (1993) features a future wherein Earth was consumed and destroyed by runaway nanorobots, referred to as "mataglap", from an Indonesian expression, "Mata Gelap," meaning "cloudy eye," "dark eye," or "dilated eye." Mata Gelap is considered to be an indication that one is blind to reason, and possibly about to run amok.
- In Ken Macleod's The Stone Canal (1996), blue goo is a generic anti-nanomachine antiseptic.
- In Iain M. Banks's "Culture" series, specifically in Excession (1996), the major possible threat to the Culture is considered to be something called an "Aggressive Hegemonizing Swarm", selfish self-replicating devices intent on turning all matter in the Universe into copies of themselves.
- In Stephen Baxter's Moonseed (1998), Venus and the entire earth are engulfed by grey goo. This forces the inhabitants of Earth to flee to the Moon, which is immune to the goo because of an alien presence.
- Wil McCarthy's science fiction novel Bloom (1999) is set in a future in which a grey goo has overwhelmed the entire inner solar system, with the only remaining colonies of humans surviving in the asteroid belt and on Jupiter's moons.
- In Yukito Kishiro's Battle Angel Alita: Last Order (2000-), grey goo is mentioned by a Venusian councilor during a LADDER meeting. Apparently the result of bored teenagers messing with common nanotechnology, it is the reason LADDER has made very strict laws concerning the use of nanotech in the solar system.
- James Alan Gardner includes a grey goo incident in his science fiction novel Ascending (2001). A spy on a starship intentionally causes the incident using a computer-sabotaging nano agent.
- In Jasper Fforde's Thursday Next novel Lost in a Good Book (2002), the entire world is (and later is not) turned into a sweet-tasting pink goo by nanomachines designed to manufacture strawberry Dream Topping.
- Patrick Larkin's contribution to the Robert Ludlum Covert-One series, called The Lazarus Vendetta (2003), is about nanotechnology initially that was derived for benevolent purposes but then intentionally set loose by terrorists, using biological signals. Victims are turned into "organic soup": piles of goo and bone fragments.
- Alastair Reynolds' book Century Rain (2004) describes an Earth decimated by an eruption of nanotechnology (an event referred to as the "Nanocaust"). Although not a strictly traditional "grey-goo" scenario, it is still an outline of an apocalypse arising from uncontrolled nanomachinery. (The scenario starts with gray goo for the purposes of cleaning the environment, which gets smart enough to rebel and does so, and attempts to control the situation with blue goo fail, resulting in a grey-goo catastrophe.)
- Kurt Vonnegut's Ice-nine from the novel Cat's Cradle has similar properties to grey goo and is capable of "freezing" liquid water instantly if it touches it. It is accidentally dropped into the ocean and causes all the world's water to crystallize. It is, in essence, a Doomsday device.
- Isaac Asimov's short story Found is about a "virus" that lives off metals. The viruses infect large computers in orbit around earth, and begin to "eat" them. The immediate conflict is resolved when it is discovered that vibrations kill the virus; however, the protagonists worry that earth's civilization has been "found" by extraterrestrial civilizations.
- In Neal Stephenson's novel The Diamond Age, the air is choked with vast clouds of nanobots referred to as "toner" because of the black residue they leave on clothes and the lung damage they cause over time, if inhaled.
- Joan D. Vinge's book The Summer Queen contains a chapter with a "universal solvent", a horde of carbon-based nanobats that turn any source of carbon into diamonds. Being partially diamond themselves, they are almost indestructible.
- Nano-disasters of varying sizes seem to be a common thing in Warren Ellis's Transmetropolitan, as nearly every home has a "Maker" that uses nanomachines to create products from raw materials. Makers have code to prevent them from building certain items, but these codes are sometimes broken by the curious or the malicious.
- Scott Westerfeld's third book in the Uglies Trilogy Specials uses an accident in a war museum with a grey goo weapon as a key plot point.
- The Deathstalker (novel) series of novels by Simon R. Green makes mention of the planet Zero-Zero, where nanotech experiments were carried out and where self-replicating nanites eventually broke free to transform the world into a ball of gray goo. A team eventually revists Zero-Zero (protecting themselves via energy fields) to find that one of the researchers has incorporated the nanites into his body and become a sort of god of the world, able to manipulate the nanites to create anything he desires.
In film and television
- In the science fiction television series Lexx, self-replicating robot arms called Mantrid drones wind up consuming the mass of an entire universe. Mantrid drones were macroscopic machines, but they apparently used nanotechnology as part of their means of manufacturing new parts for themselves.
- Stargate SG-1 also fought a form of macroscopic self replicating machines. This enemy was known as the "Replicators". The basic building block of the Replicators is a 1cm trapezoidal block containing its own power supply and computing/memory capacity. These blocks could be then organized into structures as simple as six-legged arachnoid scout bot to faster-than-light capable star ships of unlimited size. The first replicators were built by a defective gynoid, but due to their immense computing power and hive mind, they quickly became sentient and began executing their own agenda of converting the entire universe into replicators. The initial replicators were macroscopic, but more advanced nanoscopic versions appeared that could mimic humanoid lifeforms.
- In The Matrix Reloaded, the program Agent Smith becomes a data-based form of grey goo--a self-aware virus that copies itself over other programs, be they human minds or fellow Agents.
- Star Trek: Enterprise has an episode entitled "Vox Sola" in which the Enterprise is being overtaken by a biological entity. A strange, symbiotic alien creature boards Enterprise and captures several crew members and Hoshi has to decipher the creature's complex language. On the entity's planet, T'Pol, Reed, Phlox and Hoshi land in a shuttlepod and release the entity at the coordinates given earlier. Phlox also releases the tendril severed in the Cargo Bay, which is reabsorbed. As the shuttlepod returns to the Enterprise, dawn breaks and the area is revealed to be covered with one huge grey organism. Granted this "organism" would be labeled "green goo" due to being biological and not a nanotechnological (mechanical) entity, but the entity is related to grey goo due to appearance and hyper-assimilation actions.
- In Babylon 5 's spin-off Crusade, a race called the Drakh have released a nanovirus plague on Earth, which will destroy all life on Earth within five years if it is not stopped.
- An episode of Cartoon Network's series Justice League Unlimited entitled "Dark Heart" pitted the comic book heroes of the DC comics universe against a nanotechnological weapon of mass destruction created by an ancient alien race designed to defeat its enemy by literally devouring the planet from under them. It is stopped when The Atom is sent inside the central mass to examine and attack it at the source.
- One fanciful depiction of a grey goo crisis was in an episode of the Gargoyles animated series where the protagonists face an advanced form of artificially intelligent nanotechnology. They stop it by making contact and convincing it to stop its spread.
- The Blob, a 1958 science-fiction film, depicted a jelly-like mass emerging from a fallen meteor and dissolving every living thing it came into contact with. Although it was probably not intended, this is a perfect example of what grey goo would be capable of (at the end of the film the Blob is hit with carbon dioxide from fire extinguishers and, in a harmless frozen state, was shipped to the Arctic).
- The computer-animated cartoon series ReBoot featured a computer virus called 'Medusa' that was stolen by Megabyte from Hexadecimal and accidentally unleashed, spreading in a manner similar to grey goo, turning everyone and everything in mainframe save for Bob and Hexadecimal to stone. Bob then confronts Hexadecimal and convinces her to release the antivirus, returning mainframe and its inhabitants to normal.
- An episode of Sci Fi Channel's series Eureka (aired in the UK and Ireland on Sky One as A Town Called Eureka) entitled "Primal": Nanoids have been spreading across Global Dynamics and creating clones of the employees, especially Nathan Stark. The Nanoids reproduce at an exponential rate and harvest human matter for energy and materials.
- The 2001 sci-fi/comedy Evolution revolves around an actual grey goo, introduced to Earth via a metorite, which rapidly evolves, grows, differentiates into multiple species, and merges back together as it spreads throughout an Arizona town's underground cave system.
In other media
- In the virtual world Second Life, it is a popular term referring to player-coded objects that self-replicate out of control and thus (intentionally or otherwise) consume server resources and end up as a Denial of Service attack. This has happened at least once..
- In the PlayStation game Xenogears, the opening FMV depicts an attack by an technologically advanced, self-replicating goo-like entity which overwhelms a large space ship, causing it to crash into the planet on which the game takes place. Near the end of the game (10,000 years later in the game's history) most of humanity is converted into biological parts for the same entity by way of nanomachines. The being literally reforms itself at one point from a mass of grey goo.
- Sierra Entertainment's computer game Outpost 2 was a Civilization-like game which theme was based on a space colony where a lab exploded, creating a plague that consumed everything in its path, called 'the Blight'. As a side effect, the entire planet was transformed into a huge computer.
- Sid Meier's Alpha Centauri, the unofficial sequel to Civilization 2, had one "Secret Project" called The Nano-Factory. When built, units can be repaired in the field, even in enemy territory. The premise was of a nanomachine fluid that can absorb and reprocess any items to which it is exposed and use that raw material to produce weapons and equipment. "Industrial Grade Nano-Paste, Planet's most valuable commodity, can also be one of its most dangerous. Simply pour out several canisters, slide in a programming transponder, and step well away while the stuff cooks. In under an hour the nano will use available materials to assemble a small factory, a hovertank, or enough impact rifles to equip a regiment. — Col. Corazon Santiago, 'Planet: A Survivalist's Guide'" A cutscene begins once the project is completed, showing a futuristic battlefield littered with organic material (corpses) and destroyed implements of war. The nanomachines are then introduced to the area and dissolve everything present, before producing a new hovertank out of the material.
- Also seen in Alpha Centauri was a colony upgrade called a Nanoreplicator, which ostensibly used nanomachines to perfectly replicate any item down to the atomic level.
- In the introduction sequence of Ion Storm's futuristic PC and Xbox game Deus Ex: Invisible War, a nanotechnology bomb called a nanite detonator is detonated by a terrorist cell to destroy the city of Chicago. The result of the bomb being detonated is a wave of purple goo that consumes and destroys the entire city. Victims are transformed into brittle sand-like (salt?) statues of themselves.
- Activision's computer strategy game Civilization: Call to Power contained a military unit called the 'Eco Ranger', which could be used under an 'Ecotopian' government to completely destroy a city and its surroundings, almost like a nuclear weapon. Unlike a nuclear weapon, which halved a city population, destroyed all military units and tile improvements around the city as well as polluting several adjacent tiles, this unit was supposed to use nanomachines, 'grey goo', to completely destroy the city and its surroundings, converting the area into pristine wilderness.
- The Zerg in Blizzard Entertainment's StarCraft series have a structure called a Creep Colony, it is a building sized organ that produces "Creep". Creep is a layer of purple tissue that all Zerg buildings are built on. It functions as connective, circulatory and nervous tissue tying all the structures into one organism.
- On Mr. Bungle's 1999 album California the song "None of Them Knew They Were Robots" contains the lyrics, "I feel the Grey Goo boiling in my blood."
- The Konami game Nanobreaker has an opening sequence in which nanomachines reduce all the living organisms on an island to grey goo.
- In the Marvel Universe, there is a sentient, highly-advanced race spawned from such Grey Goo known as the Technarchy. These are self-replicating, parasitic techno-organisms whose civilization invaded Earth spawning a techno-organic pathogen, known as the Transmode Virus.
The most famous Earth-616 member of this techno-organic race is perhaps "Douglock," the fusion of Doug Ramsey's (Cypher) consciousness and Warlock's technological form into a techno-biological hybrid. Note also that Jean Grey's sister Sara was assimilated and killed by the Technarchy.
- Also in the Marvel Universe, Apocalypse created a supervirus/pandemic version of the TMV from the original template, with much the same techno-assimilatory result.
- ^ Center for Responsible Nanotechnology (June 9, 2004). Leading nanotech experts put 'grey goo' in perspective. Press release. Retrieved on 2006-06-17.
- ^ Current Results of Our Research. Center for Responsible Nanotechnology. Retrieved on 2006-06-17.
- Lynn Margulis and Dorion Sagan - What is Life? (1995). Simon & Schuster. ISBN 0-684-81087-5
- Bill Bryson A Short History of Nearly Everything (2003)
- Green Goo: Nanotechnology Comes Alive!
- Green Goo: The New Nanothreat from Wired
- Clanking replicator (often called von Neumann machine)
- Technology assessment
- Von Neumann Probe
- Some Limits to Global Ecophagy by Biovorous Nanoreplicators, with Public Policy Recommendations
- Drexler dubs "grey goo" fears obsolete
- Nanotechnology pioneer slays "grey goo" myths
- Online edition of the Royal Society's report Nanoscience and nanotechnologies: opportunities and uncertainties
- Nanotech guru turns back on 'goo'
- U.S. robot builds copies of itself
- Exit Mundi article on the grey goo doomsday theory
- The First Church of the Grey Goo - humorous new apocalyptic religion
- Could nanobots destroy us? - The Telegraph (UK newspaper) on Grey Goo
- A look at the exponential nature of grey goo population growth