Gray goo

Grey goo (alternatively spelled gray 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, 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, stating that "we cannot afford certain types of accidents." He later changed his position, in 2004 stating "I wish I had never used the term 'grey goo'."

Definition

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.

In a History Channel broadcast, grey goo is referred to in a futuristic doomsday scenario: "In a common practice, billions of nanobots are released to clean up an oil spill off the coast of Louisiana. However, due to a programming error, the nanobots devour all carbon based objects, instead of just the hydrocarbons of the oil. The nanobots destroy everything, all the while, replicating themselves. Within days, the planet is turned to dust."

Drexler describes grey goo in Chapter 11 of Engines Of Creation:

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 "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.

Bill Joy, one of the founders of Sun Microsystems, discussed some of the problems with pursuing this technology in his now-famous 2000 article in Wired magazine, titled "Why the Future Doesn't Need Us". In direct response to Joy's concerns, the first quantitative technical analysis of the ecophagy scenario was published in 2000 by nanomedicine pioneer Robert Freitas.

Living goo

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.

The cell is the archetypal nanomachine and in fact does have many of the properties ascribed to grey goo, particularly, the ability to transform unstructured materials into copies of the replicating agent. Hence, the cell is able to incorporate carbon dioxide, molecular nitrogen gas, and water into complex, multifunctional biomolecules, as well as incorporating solid materials such as hydroxyapatite, and other calcium and phosphorus containing compounds. While certainly not the ecocatastrophe posited by grey goo alarmists, the transformative and contaminative nature of cells is impressive. Earth would certainly be a different place without the appearance of the cell (the most impressive of which would be the lack of an atmosphere containing large amounts of oxygen), and the possibility of seeding and contaminating the rest of the Solar System with cells is a real consideration when planning space missions.

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.

A more literal biological analogy to grey goo are prions, which have been implicated in such diseases as kuru, Mad Cow disease, Creutzfeldt-Jakob disease, and fatal familial insomnia. In all of these conditions, an abnormal protein possesses the ability to unfold and refold other normally functioning proteins into copies of itself. Prions are extraordinarily contagious and difficult to destroy, but their relatively sluggish rate of transformation has prevented them from successfully overrunning the biosphere.

Risks and precautions

It is unclear whether 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, it is mostly well-oxidised 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 (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 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 with 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. None of these measures would prevent a party creating a weaponised grey goo, were such a thing possible.

Oxford based philosopher Nick Bostrom discusses the idea of a future powerful superintelligence, and the risks that we/it face should it attempt to gain atomic level control of matter.

In Britain Prince Charles 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.

More 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 Template:Noredlink and other misuses.

Popular culture

Fiction

The term grey goo is often used in a futuristic or science fiction context, as the required technologies do not yet exist. 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 only for other purposes, but designed to operate in a natural environment.

Notable examples of such a work can be found in the novel Blood Music by Greg Bear (1985), the 2002 Michael Crichton novel Prey and Wil McCarthy's novel Bloom.

In the video game Deus Ex: Invisible War, a limited form of "grey goo" has been weaponized to create so-called Nanite Detonators, a potent weapon which uses self-replicating nanites to consume an entire city, yet which is not capable of running amok across the Earth's surface.

Computing

Denial-of-service attacks in the virtual world Second Life which work by infinitely replicating objects until the server crashes are referred to as grey goo attacks. This reference refers to the self-replicating aspects of grey goo. It is one example of the widespread convention of drawing analogies between certain Second Life concepts and the theories of radical nanotechnology.

Further reading

• 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—Life in the Era of Humane Genocide by Nick Szabo
• Green Goo: Nanotechnology Comes Alive!
• Green Goo: The New Nanothreat from Wired

Self-reconfiguring modular robotics is the research field that is working on this, you will find much more information on the wikipedia page for the area.

External links

• Some Limits to Global Ecophagy by Biovorous Nanoreplicators, with Public Policy Recommendations
• Nanotechnology pioneer slays "grey goo" myths Paper critical of "grey goo"
• Online edition of the Royal Society's report Nanoscience and nanotechnologies: opportunities and uncertainties
• Goo and Paste Directory
• UK Government & Royal Society commission on Nanotechnology and Nanoscience