What is Grey Goo?

Grey goo is an apocalyptic scenario involving molecular nanotechnology in which self-replicating robots lose control and consume all matter on Earth while building more of themselves. This scenario is also known as ecophagy (“eating the environment”)

Macroscopic Self-replicating machines 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.”

How soon will molecular manufacturing be developed?

Molecular manufacturing could be successfully developed and deployed within 10 to 15 years. In about twenty five years, devices similar to Star Trek replicators will be present in our everyday lives however the build process will not be as instant. We can already buy $1500-$25 3D printers, such as the MakerBot, that can build small computer designed objects out of plastic. Larger, more expensive 3D printers can build prototypes or  usefull objects directly from a variety of materials. These are not Nanotechnology devices, but the same concept could eventually be done with nanotechnology.

What happens?

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.

It is proposed that In less than a day, they might weigh a ton and in less than two days, they could outweigh the Earth; in another four hours, they would exceed the mass of the Sun and all the planets combined . The problem with this is that they will likely out of suitable materials to use before ever reaching these levels. It is more likely that once the goo becomes too heavy it will sink into the Earth and the heat will render the nano replicators in-operable or the mass itself will alter the spin of the Earth and cause other effects that will also destroy the grey goo and all life on the planet.

Here’s another problem…the only nanobots that can make more of themselves and replicate will be the ones on or near the edge of the grey goo. Those inside the grey goo can’t get to any materials (other than themselves) to use depending on how dense the goo is. It could be more of a swarm rather than a blob, in which case they will all be active for some time but will likely fight over the same materials.  This will slow the growth rate down substantially.

Finally, someone is going to notice this growing mass and even at the fast rate of growth, people could potentially destroy the mass before it’s too late. Not an easy task.

Stargate Replicator

Stargate Replicator

Something to Consider: How fast can grey goo really grow?

People assume that a nano replicator can build anything instantly, but consider the fact that at the nanoscale your hair is always growing and it’s doing so very fast. Right now your hair is likely growing rapidly, but you can’t actually watch your hair grow. You can’t see it.  This is because it’s growing at the nano-scale. Let me put this another way. Imagine you have various sets of building blocks like LEGO. You need to build a 10ft x 10ft x 2ft house out of each set of blocks. You have nano sized blocks, inch-sized blocks and large 1foot blocks.  Which house will be built faster?  The big blocks right?  The nano blocks would take a very long time to build but if you had a thousand units building it at once then it would speed up the process.  The speed at which a unit is able to function or move from A to B also comes into play.  How fast a nanobot can replicate itself is yet to be seen.   Stargate Replicators are not nanoscale but offers a look into the grey goo problem.

Counter measures?

Here are some commonly referenced ideas..

  • Air.   Require a vacuum or inert gas environment for them to operate within. Open air then becomes the defense.
  • Water.  There are many properties of ordinary water that could potentially neutralize molecular nanobots, such as, oxygen deprivation, high thermal conductivity, solvent action, cohesivity, cooling effect, rust and corrosion.
  • Concussion force.  A high compression or concussion force could destroy them. Also a change in air pressure itself could render them harmless.
  • Heat.  Heat or cold would most likely  alter the chemical reactivity of the materials, melt nano circuitry, or melt them altogether.
  • Cold.  Cold makes many materials brittle, can cause some fluid-filled compartments to either burst or implode due to pressure changes. It will often also alter the chemical reactivity of various materials and/or catalysts. Extreme cold can also produce superconductivity in metals and certain other materials.
  • Glycerine/Soap.  Soapy water will quickly suffocate any insect or flame as well as make many surfaces quite slippery. Soapl tends to heavily weigh down any fine mesh or grating.
  • Oils (low cohesivity liquids)  Oils can penetrate many cavities and materials which are impervious to water.
  • Salt or Saline.   The characteristics of salt and saline is their ability to dehydrate, strong corrosive effects (particularly on metals), electrical/chemical effects when brought into contact with other materials.
  • Electrical Current.   Various devices might be fried by applying or inducing an electrical current.
  • EM Radiation.  UV, Infra-Red, microwaves, x-rays, and gamma rays are the most typically destructive wavelengths of EM radiation, but virtually any wavelength could potentially neutralize or at least impair some variety of device.
  • EMP.  (Electro-Magentic Pulse)
  • Strong Magnetic Fields.   One use of magnetic fields would be to gather or direct metallic objects for containment and eventual neutralization. Magnetic fields might also produce destructive mechanical stresses in some objects/devices. Magnetic fields can also interfere with electrical operation of unshielded devices, especially if the magnetic fields are made to fluctuate.
  • Sound.   At least down to a certain scale, sound at resonant frequencies of undampened rigid bodies can have devastating effects when of sufficient amplitude. Whether this will be a common exploitable vulnerability in many micro- or nano-scopic devices remains to be seen. Load sounds can also rip or deform membranes and/or cables, beams, or threads at a wide range of frequencies. Sound may also be used to move or channel particles within a gas or liquid or loosely placed on a smooth, non-dampening surface.
  • Anti Matter.  Anti-matter will vaporize any ordinary matter it comes into contact with.
  • Counterbots.  Theoretically you can build nanobots that are designed to destroy those that are  out of control.

Stop Grey GooI came across a number of other ideas but I felt they where simply too ineffective to list.  Even some of these methods would only put dents in a constantly growing mass of grey goo while others suggest that the environment itself may limit or destroy the mass. There’s actually a lot working against the grey goo. It can’t endlessly grow and destroy the Earth without encountering major difficulties.  Several other approaches could include an on off switch triggered by remote commands or even time travel based foreknowledge which could warn us of any such event before it happens. This assumes a number of ideas about Time Travel though.

Drexler, an American engineer best known for popularizing the potential of molecular nanotechnology, 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.

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 on more realistic threats associated with knowledge-enabled nanoterrorism and other misuses.

Additional Scenarios

Other scenarios which may lead indirectly to global ecophagy have been identified. In all cases, early detection appears feasible with advance preparation.

Gray Dust (Aerovores)

Traditional diamondoid nanomachinery designs have employed 8 primary chemical elements, along with the associated atmospheric abundances of each element. The requirement for elements that are relatively rare in the atmosphere greatly constrains the potential nanomass and growth rate of airborne replicators.

The most efficient cleanup strategy appears to be the use of air-dropped non-self-replicating nanorobots equipped with prehensile microdragnets.

Gray Plankton

Some researchers are studying the possibility of reducing greenhouse gas accumulations by storing liquid or solid CO2 on the ocean floor, which could potentially enable seabed replibots to more easily metabolize methane sources.  Oxygen could also be imported from the surface in pressurized microtanks via buoyancy transport, with the conversion of carbon clathrates to nanomass taking place on the seabed below. The subsequent colonization of the land-based carbon-rich ecology by a large and hungry seabed-grown replicator population is the “gray plankton” scenario. (Phytoplankton, 1-200 microns in size, are the particles most responsible for the variable optical properties of oceanic water because of the strong absorption of these cells in the blue and red portions of the optical spectrum.)

Gray Lichens

In theory, replicating nanorobots could be made almost entirely of nondiamondoid materials including noncarbon chemical elements found in great abundance in rock such as silicon, aluminum, iron, titanium and oxygen. The subsequent ecophagic destruction of land-based biology by a maliciously programmed noncarbon epilithic replicator population that has grown into a significant nanomass is the “gray lichen” scenario.

Continuous direct census sampling of the Earth’s land surfaces will almost certainly allow early detection, since mineralogical nanorobots should be easily distinguishable from inert rock particles and from organic microbes in the top 3-8 cm of soil.

Malicious Ecophagy

More difficult scenarios involve ecophagic attacks that are launched not to convert biomass to nanomass, but rather primarily to destroy biomass. The optimal malicious ecophagic attack strategy appears to involve a two-phase process.

In the first phase, initial seed replibots are widely distributed in the vicinity of the target biomass, replicating with maximum stealth up to some critical population size by consuming local environmental substrate to build nanomass. In the second phase, the now-large replibot population ceases replication and exclusively undertakes its primary destructive purpose. More generally, this strategy may be described as Build/Destroy.

Policy Recommendations

Specific public policy recommendations suggested by researchers include but not limited to:

  • An immediate international moratorium on all artificial life experiments implemented as nonbiological hardware. In this context, “artificial life” is defined as autonomous foraging replicators, excluding purely biological implementations (already covered by NIH guidelines tacitly accepted worldwide) and also excluding software simulations which are essential preparatory work and should continue. Alternative “inherently safe” replication strategies such as the broadcast architecture are already well-known.
  • Continuous comprehensive infrared surveillance of Earth’s surface by geostationary satellites, both to monitor the current biomass inventory and to detect (and then investigate) any rapidly-developing artificial hotspots.
  • Initiating a long-term research program designed to acquire the knowledge and capability needed to counteract ecophagic replicators, including scenario-building and threat analysis with numerical simulations, measure/countermeasure analysis, theory and design of global monitoring systems capable of fast detection and response, IFF (Identification Friend or Foe) discrimination protocols, and eventually the design of relevant nanorobotic systemic defensive capabilities and infrastructure.

Written by: Richard D. Green


1. Bill Joy, “Why the future doesn’t need us,” Wired (April 2000); response by Ralph Merkle, “Text of prepared comments by Ralph C. Merkle at the April 1, 2000 Stanford Symposium organized by Douglas Hofstadter“.

2. K. Eric Drexler, “Engines of Creation: The Coming Era of Nanotechnology,” Anchor Press/Doubleday, New York, 1986. See:.

3. Joshua Lederberg, “Infectious History,” Science288(14 April 2000):287-293.

4. K. Eric Drexler, Nanosystems: Molecular Machinery, Manufacturing, and Computation, John Wiley & Sons, NY, 1992.

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