Self-replicating machine

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The concept of self-replicating machines has been advanced and examined by, amongst others, Homer Jacobsen, Edward F. Moore, Freeman Dyson, John von Neumann and in more recent times notably K. Eric Drexler in his seminal book on nanotechnology, Engines of Creation. The future development of such technology has featured as an integral part of several plans involving the mining of moons and asteroid belts for ore and other materials, the creation of lunar factories and even the construction of solar power satellites in space. A von Neumann probe is one theoretical example of such a machine. Von Neumann also worked on what he called the Universal Constructor, a self-replicating machine that would operate in a cellular automata environment. In fiction, they have also featured heavily in various successful Hollywood film franchises such as The Terminator series and The Matrix trilogy.

A self-replicating machine is, as the name suggests, an artificial self-replicating system that relies on conventional large-scale technology and automation. The term "clanking replicator" is sometimes used to distinguish such systems from the microscopic nanobots or "assemblers" that nanotechnology may make possible.^[1] They are also called "von Neumann machines" after John von Neumann, who first rigorously studied the idea. This last term ("von Neumann machine") is less specific and also refers to a completely unrelated computer architecture proposed by von Neumann, so its use is discouraged where accuracy is important. Von Neumann himself used the term Universal Constructor.

Contents 1 Basic concept 2 History of the concept 2.1 von Neumann's kinematic model 2.2 Moore's artificial living plants 2.3 Dyson's replicating systems 2.4 Advanced Automation for Space Missions 2.5 Lackner-Wendt Auxon replicators 3 Recent work 3.1 Self-replicating rapid prototypers 3.2 NIAC studies on self-replicating systems 4 Self-replicating spacecraft 5 Other references 6 Self-replicating machines in fiction 6.1 Other notable works containing replicators 7 Prospects for implementation 8 See also 9 References 10 External links

[edit] Basic concept

A self-replicating machine would need to have the capacity to gather energy and raw materials, process the raw materials into finished components, and then assemble them into a copy of itself. It is unlikely that this would all be contained within a single monolithic structure, but would rather be a group of cooperating machines or an automated factory that is capable of manufacturing all of the machines that make it up.

The factory could produce mining robots to collect raw materials, construction robots to put new machines together, and repair robots to maintain itself against wear and tear, all without human intervention or direction. The advantage of such a system lies in its ability to expand its own capacity rapidly and without additional human effort; in essence, the initial investment required to construct the first self-replicating device would have an infinitely large payoff with no additional labor cost.

Such a machine violates no physical laws, and we already possess the basic technologies necessary for some of the more detailed proposals and designs.

If proof were needed that self-replicating machines are possible, the simple fact that all living organisms are self replicating by definition should go some way towards providing that proof, although most living organisms are still many times more complex than even the most advanced man-made device.

[edit] History of the concept

The general concept of artificial machines capable of producing copies of themselves dates back at least several hundred years. An early reference is an anecdote regarding the philosopher René Descartes, who suggested to Queen Christina of Sweden that the human body could be regarded as a machine; she responded by pointing to a clock and ordering "see to it that it reproduces offspring."^[2] Samuel Butler proposed in his 1872 novel Erewhon that machines were already capable of reproducing themselves with the assistance of the humans that operated them, and analogized this to flowering plants that were only capable of reproducing with the assistance of pollinating insects.

In 1802 William Paley formulated the first known teleological argument depicting machines producing other machines, suggesting that the question of who originally made a watch was rendered moot if it were demonstrated that the watch was able to manufacture a copy of itself.^[3] Scientific study of self-reproducing machines was anticipated by John Bernal as early as 1929^[4] and by mathematicians such as Stephen Kleene who began developing recursion theory in the 1930s. Much of this latter work was motivated by interest in information processing and algorithms rather than physical implementation of such a system, however.

[edit] von Neumann's kinematic model

A detailed conceptual proposal for a physical non-biological self-replicating system was first put forward by mathematician John von Neumann in lectures delivered in 1948 and 1949, when he proposed a kinematic self-reproducing automaton model as a thought experiment.^[5] Von Neumann's concept of a physical self-replicating machine was dealt with only abstractly, with the hypothetical machine using a "sea" or stockroom of spare parts as its source of raw materials. The machine had a program stored on a memory tape that directed it to retrieve parts from this "sea" using a manipulator, assemble them into a duplicate of itself, and then copy the contents of its memory tape into the empty duplicate's. The machine was envisioned as consisting of as few as eight different types of components; four logic elements that send and receive stimuli and four mechanical elements used to provide a structural skeleton and mobility. While qualitatively sound, von Neumann was evidently dissatisfied with this model of a self-replicating machine due to the difficulty of analyzing it with mathematical rigor. He went on to instead develop an even more abstract model self-replicator based on cellular automata.^[6] His original kinematic concept remained obscure until it was popularized in a 1955 issue of Scientific American.^[7]

[edit] Moore's artificial living plants

In 1956 mathematician Edward F. Moore proposed the first known suggestion for a practical real-world self-replicating machine, also published in Scientific American.^[8] Moore's "artificial living plants" were proposed as machines able to use air, water and soil as sources of raw materials and to draw its energy from sunlight via a solar battery or a steam engine. He chose the seashore as an initial habitat for such machines, giving them easy access to the chemicals in seawater, and suggested that later generations of the machine could be designed to float freely on the ocean's surface as self-replicating factory barges or to be placed in barren desert terrain that was otherwise useless for industrial purposes. The self-replicators would be "harvested" for their component parts, to be used by humanity in other non-replicating machines.

[edit] Dyson's replicating systems

The next major development of the concept of self-replicating machines was a series of thought experiments proposed by physicist Freeman Dyson in his 1970 Vanuxem Lecture.^[9] He proposed three large-scale applications of machine replicators. First was to send a self-replicating system to Saturn's moon Enceladus, which in addition to producing copies of itself would also be programmed to manufacture and launch solar sail-propelled cargo spacecraft. These spacecraft would carry blocks of Enceladean ice to Mars, where they would be used to terraform the planet. His second proposal was a solar-powered factory system designed for a terrestrial desert environment, and his third was an "industrial development kit" based on this replicator that could be sold to developing countries to provide them with as much industrial capacity as desired. When Dyson revised and reprinted his lecture in 1979 he added proposals for a modified version of Moore's seagoing artificial living plants that was designed to distill and store fresh water for human use^[10] and the "Astrochicken."

[edit] Advanced Automation for Space Missions

In 1980, inspired by a 1979 "New Directions Workshop" held at Wood's Hole, NASA conducted a joint summer study with ASEE entitled Advanced Automation for Space Missions to produce a detailed proposal for self-replicating factories to develop lunar resources without requiring additional launches or human workers on-site. The study was conducted at Santa Clara University and ran from June 23 to August 29, with the final report published in 1982.^[11] The proposed system would have been capable of exponentially increasing productive capacity and the design could be modified to build Von Neumann probes to explore the galaxy.

The reference design included small computer-controlled electric carts running on rails inside the factory, mobile "paving machines" that used large parabolic mirrors to focus sunlight on lunar regolith to melt and sinter it into a hard surface suitable for building on, and robotic front-end loaders for strip mining. Raw lunar regolith would be refined by a variety of techniques, primarily hydrofluoric acid leaching. Large transports with a variety of manipulator arms and tools were proposed as the constructors that would put together new factories from parts and assemblies produced by its parent.

Power would be provided by a "canopy" of solar cells supported on pillars. The other machinery would be placed under the canopy.

A "casting robot" would use sculpting tools and templates to make plaster molds. Plaster was selected because the molds are easy to make, can make precise parts with good surface finishes, and the plaster can be easily recycled afterward using an oven to bake the water back out. The robot would then cast most of the parts either from nonconductive molten rock (basalt) or purified metals. A carbon dioxide laser cutting and welding system was also included.

A more speculative, more complex microchip fabricator was specified to produce the computer and electronic systems, but the designers also said that it might prove practical to ship the chips from Earth as if they were "vitamins."

Much of the design study was concerned with a simple, flexible chemical system for processing the ores, and the differences between the ratio of elements needed by the replicator, and the ratios available in lunar regolith. The element that most limited the growth rate was chlorine, needed to process regolith for aluminium. Chlorine is very rare in lunar regolith.

[edit] Lackner-Wendt Auxon replicators

In 1995, inspired by Dyson's 1970 suggestion of seeding uninhabited deserts on Earth with self-replicating machines for industrial development, Klaus Lackner and Christopher Wendt developed a more detailed outline for such a system.^[12][13] They proposed a colony of cooperating mobile robots 10-30 cm in size running on a grid of electrified ceramic tracks around stationary manufacturing equipment and fields of solar cells. Their proposal didn't include a complete analysis of the system's material requirements, but described a novel method for extracting the ten most common chemical elements found in raw desert topsoil (Na, Fe, Mg, Si, Ca, Ti, Al, C, O₂ and H₂) using a high-temperature carbothermic process. This proposal was popularized in Discover Magazine, featuring solar-powered desalination equipment used to irrigate the desert in which the system was based.^[14] They named their machines "Auxons", from the Greek word auxein which means "to grow."

[edit] Recent work

[edit] Self-replicating rapid prototypers

Early experimentation with rapid prototyping in 1997-2000 was not expressly oriented toward reproducing rapid prototyping systems themselves, but rather extended simulated "evolutionary robotics" techniques into the physical world. Later developments in rapid prototyping have given the process the ability to produce a wide variety of electronic and mechanical components, however, making this a rapidly developing frontier in self-replicating system research.^[15]

In 1998 Chris Phoenix informally outlined a design for a hydraulically-powered replicator a few feet in volume that used ultraviolet light to cure soft plastic feedstock and a fluidic logic control system, but didn't address most of the details of assembly procedures, error rates, or machining tolerances.^[16]

In 2005, Adrian Bowyer of the University of Bath started the RepRap Project to develop a rapid prototyping machine which would be able to manufacture most of its own components, making such machines cheap enough for people to buy and use in their homes. The project is releasing its designs and control programs under the GNU GPL.^[17] The RepRap approach uses fused deposition modeling to manufacture plastic components, possibly incorporating conductive pathways for circuitry. Other components, such as motors and discrete electronic components, would be supplied externally. As of 2006 the project has produced a basic functional prototype.

[edit] NIAC studies on self-replicating systems

In the spirit of the 1980 "Advanced Automation for Space Missions" study, the NASA Institute for Advanced Concepts began several studies of self-replicating system design in 2002 and 2003. Four phase I grants were awarded:

• Hod Lipson (Cornell University), "Autonomous Self-Extending Machines for Accelerating Space Exploration"^[18]
• Gregory Chirikjian (Johns Hopkins University), "Architecture for Unmanned Self-Replicating Lunar Factories"^[19]
• Paul Todd (Space Hardware Optimization Technology Inc.), "Robotic Lunar Ecopoiesis"^[20][21]
• Tihamer Toth-Fejel (General Dynamics), "Modeling Kinematic Cellular Automata: An Approach to Self-Replication"^[22] The study concluded that complexity of the development was equal to that of a Pentium 4, and promoted a design based on cellular automata.

[edit] Self-replicating spacecraft

Main article: Self-replicating spacecraft

The idea of an automated spacecraft capable of constructing copies of itself was first proposed in scientific literature in 1974 by Michael Arbib,^[23] but the concept had appeared earlier in science fiction such as the 1967 novel Berserker by Fred Saberhagen or the 1950 novellette trilogy The Voyage of the Space Beagle by A. E. van Vogt (see self-replicating machines in fiction, below). The first quantitative engineering analysis of such a spacecraft was published in 1980 by Robert Freitas,^[24] in which the non-replicating Project Daedalus design was modified to include all subsystems necessary for self-replication. The design's strategy was to use the probe to deliver a "seed" factory with a mass of about 443 tons to a distant site, have the seed factory replicate many copies of itself there to increase its total manufacturing capacity, and then use the resulting automated industrial complex to construct more probes with a single seed factory on board each.

[edit] Other references

• A number of patents have been granted for self-replicating machine concepts. The most directly relevant include U.S. Patent 4,734,856  "Autogeneric system" (March 1988), U.S. Patent 5,659,477  "Self reproducing fundamental fabricating machines (F-Units)" (August 1997), U.S. Patent 5,764,518  " Self reproducing fundamental fabricating machine system" (June 1998), and U.S. Patent 6,510,359  " Method and system for self-replicating manufacturing stations" (January 2003).

• Macroscopic replicators are mentioned briefly in the fourth chapter of K. Eric Drexler's 1986 book Engines of Creation.^[1]

• In 1995, Nick Szabo proposed a challenge to build a macroscale replicator from Lego(tm) robot kits and similar basic parts.^[25] Szabo wrote that this approach was easier than previous proposals for macroscale replicators, but successfully predicted that even this method would not lead to a macroscale replicator within ten years.

• In 2004, Robert Freitas and Ralph Merkle published the first comprehensive review of the field of self-replication, in their book Kinematic Self-Replicating Machines, which includes 3000+ literature references.^[26]

[edit] Self-replicating machines in fiction

In fiction, the idea dates back at least as far as Karel Čapek's 1921 play R.U.R. (Rossum's Universal Robots). A fundamental obstacle of self-replicating machines, how to repair the repair systems, was the critical failure in the automated society described in The Machine Stops.

A. E. van Vogt used the idea as a plot device in his story "M33 in Andromeda" (1943), which was later combined with four other General Semantics stories to became the novel, The Voyage of the Space Beagle. The story describes the creation of self-replicating weapons factories designed to destroy the Anabis, a galaxy-spanning malevolent life form bent on destruction of the human race.

An early treatment was the short story Autofac by Philip K. Dick, published in 1955, which precedes von Neumann's original paper about self-reproducing machines. Dick also touched on this theme in his earlier 1953 short story Second Variety. Another example can be found in the 1962 short story Epilogue by Poul Anderson, in which self-replicating factory barges were proposed that used minerals extracted from ocean water as raw materials.

In his short story "Crabs on the Island" (1958) Anatoli Dneprov speculated on the idea that since the replication process is never 100% accurate, leading to slight differences in the descendants, over several generations of replication the machines would be subjected to evolution similar to that of living organisms. In the story, a machine is designed, the sole purpose of which is to find metal to produce copies of itself, intended to be used as a weapon against an enemy's war machines. The machines are released on a deserted island, the idea being that once the available metal is all used and they start fighting each other, natural selection will enhance their design. However, the evolution has stopped by itself when the last descendant, an enormously large crab, was created, being unable to reproduce itself due to lack of energy and materials.

Stanisław Lem has also studied the same idea in his novel The Invincible (1964), in which the crew of a spacecraft landing on a distant planet finds a non-biological life-form, which is the product of long, possibly of millions of years of, mechanical evolution. This phenomenon is also key to the aforementioned Anderson story.

John Sladek used the concept to humorous ends in his first novel The Reproductive System (1968, also titled Mechasm in some markets), where a U.S. military research project goes out of control.

NASA's Advanced Automation for Space Missions study directly inspired the science fiction novel Code of the Lifemaker (1983) by author James P. Hogan.

The movie Screamers, based on Dick's short story Second Variety, features a group of robot weapons created by mankind to act as Von Neumann devices / berserkers. The original robots are subterranean buzzsaws that make a screaming sound as they approach a potential victim beneath the soil. These machines are self-replicating and, as is found out through the course of the movie, they are quite intelligent and have managed to "evolve" into newer, more dangerous forms, most notably human forms which the real humans in the movie cannot tell apart from other real humans except by trial and error.

The concept is also widely utilised in science fiction television. Cult series Lexx featured an army of self replicating robots known as Mantrid drones. Similarly the Replicators are a horde of self-replicating machines that appear frequently in Stargate SG-1, and Star Trek's Borg could also be considered as self-replicating machines.

[edit] Other notable works containing replicators

• "Autofac" by Philip K. Dick
• "The Necessary Thing" by Robert Sheckley, in which a universal replicator is tricked into replicating itself
• The Berserker series of books and short stories by Fred Saberhagen
• The Forge of God by Greg Bear
• 2010: Odyssey Two by Arthur C. Clarke
• The World at the End of Time by Frederik Pohl
• Recursion by Tony Ballantyne ISBN 0-330-42699-0
• Evolution by Stephen Baxter
• Spin (novel) by Robert Charles Wilson

[edit] Prospects for implementation

As the use of industrial automation has expanded over time, some factories have begun to approach a semblance of self-sufficiency that is suggestive of clanking replicators (another name for self-replicating machines). However, such factories are unlikely to achieve "full closure" until the cost and flexibility of automated machinery comes close to that of human labour and the manufacture of spare parts and other components locally becomes more economical than transporting them from elsewhere. Fully-capable machine replicators are most useful for developing resources in dangerous environments which are not easily reached by existing transportation systems (such as outer space).

A clanking replicator can be considered to be a form of artificial life. Depending on its design, it might be subject to evolution over an extended period of time. However, with robust error correction, and the possibility of external intervention, the common science fiction scenario of robotic life run amok will remain extremely unlikely for the forseeable future.

[edit] See also

• Conway's Game of Life
• Gray goo

[edit] References

[edit] External links

• The Clanking Replicator Project: Bootstrap your own self-replicating, rapid prototyping machine
• Cornell's Self-replicating machine
• The RepRap Project: Creating wealth without money...
• Terraforming Mars and Venus using machine self-replicating systems (SRS)