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, a scenario that has been called ecophagy. The original idea assumed
machines were designed to have this capability, while popularizations have assumed that machines
might somehow gain this capability by accident. 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 gray goo was coined by nanotechnology pioneer Eric
Drexler in his 1986 book Engines of Creation. In 2004 he stated, "I wish I had never used
the term 'gray goo'." Engines of Creation mentions "gray goo" in two paragraphs and
a note, while the popularized idea of gray goo was first publicized in a mass-circulation
magazine, Omni, in November 1986.
Definition The term was first used by molecular nanotechnology
pioneer Eric Drexler in his book Engines of Creation. 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, a contrasting idea 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 gray 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 "gray 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.
Risks and precautions 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. None of these measures
would prevent a party from creating a weaponized gray goo, were such a thing possible.
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 media
commentary on gray goo. The Royal Society's report on nanoscience was released on 29 July
2004, and declared the possibility of self-replicating machines to lie too far in the future to be
of concern to regulators. More recent analysis has shown that the danger
of gray 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 gray goo hypothesis, in an effort to focus the debate on more realistic
threats associated with knowledge-enabled nanoterrorism and other misuses.
In Chris Phoenix and Eric Drexler's paper Safe Exponential Manufacturing, which was
published in a 2004 issue of Nanotechnology, it was suggested that creating manufacturing
systems with the ability to self-replicate by the use of their own energy sources would
not be needed. The Foresight Institute also recommended embedding controls in the molecular
machines. These controls would be able to prevent anyone from purposely abusing nanotechnology,
and therefore avoid the gray goo scenario. Ethics and chaos
Gray goo is a useful construct for considering low-probability, high-impact outcomes from
emerging technologies. Thus, it is a useful tool in the ethics of technology. Vallero
applied it as a worst-case scenario thought experiment for technologists contemplating
possible risks from advancing a technology. This requires that a decision tree or event
tree include even extremely low probability events if such events may have an extremely
negative and irreversibile consequence, i.e. application of the precautionary principle.
Dianne Irving admonishes that "any error in science will have a rippling effect....".
Vallero adapted this reference to chaos theory to emerging technologies, wherein slight permuations
of initial conditions can lead to unforeseen and profoundly negative downstream effects,
for which the technologist and the new technology's proponents must be held accountable.
Limitations Gray goo nanobots need a source of energy
to drive their replication. For efficiency reasons, the energy would likely come from
oxidation and other chemical reactions on the organic matter itself—a process which
in organic life is known as digestion—rather than from an external power source.
In such a scenario, gray goo replication is self-limiting. The more organic material that
the grey goo consumes, the less remains available for further consumption. After exhausting
available organic material within a local area, grey goo would experience a population
crash in that area, slowing or ending its outward spread.
Some organic organisms may prove more resistant than others to gray goo. As with all environmental
stresses, natural selection would favor their survival, and amplification of their resistance
traits. If gray goo nanobots could also evolve through
the course of their replications, they might gain the ability to consume one another, as
an additional source of energy to drive replication. Further from there, they could evolve resistance
to consumption by gray goo nanobots. Under such evolutionary pressure, gray goo nanobots
would become subject to speciation, inter-species competition, and specialization to occupy
ecological niches. However, engineered machines like those which Dexler has proposed are fundamentally
simpler and less susceptible to evolution than biological systems.
See also Self-reconfiguring modular robot
Programmable matter Utility fog
Smartdust Claytronics
Ice-nine Alkahest
The Blob Benderama - Futurama episode about the issue
References
Further reading
External links Some Limits to Global Ecophagy by Biovorous
Nanoreplicators, with Public Policy Recommendations Safe exponential manufacturing Paper critical
of "grey goo," summarized in article Nanotechnology pioneer slays "grey goo" myths
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
Nanotechnology: Drexler and Smalley make the case for and against 'molecular assemblers'
Nanotechnology and the Grey Goo Problem Be Amazing! – Humorous animation that involves
a grey goo scenario