Self-replicating Machine

Advanced Automation

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A self-replicating machine is an artificial construct that is theoretically capable of autonomously manufacturing a copy of itself using raw materials taken from its environment, thus exhibiting self-replication in a way analogous to that found in nature. The concept of self-replicating machines has been advanced by Homer Jacobsen, Edward F. Moore, Freeman Dyson, John von Neumann, and in more recent times by K. Eric Drexler in his book on nanotechnology, ‘Engines of Creation,’ and by Robert Freitas and Ralph Merkle in their review ‘Kinematic Self-Replicating Machines,’ which provided the first comprehensive analysis of the entire replicator design space.

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. The possibly misnamed von Neumann probe (a self-replicating spacecraft) 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 (a computer simulation of life).

A self-replicating machine is, as the name suggests, an artificial self-replicating system that relies on conventional large-scale technology and automation. Certain idiosyncratic terms are occasionally found in the literature. For example, the term ‘clanking replicator’ was once used by Drexler to distinguish macroscale replicating systems from the microscopic nanorobots or ‘assemblers’ that nanotechnology may make possible, but the term is informal and is rarely used by others in popular or technical discussions. Replicators have also been called ‘von Neumann machines’ after John von Neumann, who first rigorously studied the idea. But this term 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’ to describe such self-replicating machines.

Historians of machine tools, even before the numerical control era, sometimes spoke figuratively of machine tools as a class of machines that is unique because they have the ability ‘to reproduce themselves,’ by which they meant the ability to make copies of all of their parts. However, implicit in such discussions is the fact that a human would be directing the cutting processes (or, later, at least planning and programming them) and then assembling the parts. The same is true of RepRaps, which are another class of machines sometimes mentioned in reference to such non-autonomous ‘self-replication.’

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. Further, for a complete self-replication, it must, from scratch, produce its smallest parts, such as bearings, connectors and delicate and intricate electronic components. It is unlikely that this would all be contained within a single structure, but would rather be a group of cooperating machines or an automated factory that is capable of manufacturing all of the machines that comprise it.

The factory could produce mining robots to collect raw materials, construction robots to assemble new machines, 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 the basic technologies necessary for some of the more detailed proposals and designs already exist.

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.’ Several other variations on this anecdotal response also exist. Samuel Butler proposed in his 1872 novel ‘Erewhon’ that machines were already capable of reproducing themselves but it was man who made them do so, and added that ‘machines which reproduce machinery do not reproduce machines after their own kind.’

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. Scientific study of self-reproducing machines was anticipated by John Bernal as early as 1929, 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.

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. 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. His original kinematic concept remained obscure until it was popularized in a 1955 issue of ‘Scientific American.’

In 1956 mathematician Edward F. Moore proposed the first known suggestion for a practical real-world self-replicating machine, also published in ‘Scientific American.’ 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.

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. 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 and the ‘Astrochicken’ (a one-kilogram spacecraft based on biology, artificial intelligence and modern microelectronics—a blend of organic and electronic components).

In 1980, inspired by a ‘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 proposed system would have been capable of exponentially increasing productive capacity and the design could be modified to build self-replicating 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.’

A 2004 study supported by NASA’s Institute for Advanced Concepts took this idea further. Some experts are beginning to consider self-replicating machines for asteroid mining. 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.

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. 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. They named their machines ‘Auxons,’ from the Greek word ‘auxein’ which means ‘to grow.’

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 some or 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. The RepRap approach uses fused deposition modeling to manufacture plastic components, possibly incorporating conductive pathways for circuitry. Other components, such as steel rods, nuts and bolts, motors and separate electronic components, would be supplied externally. In 2006 the project produced a basic functional prototype and in 2008 the machine succeeded in producing all of the plastic parts required to make a ‘child’ machine.

Partial construction is the concept that the constructor creates a partially constructed (rather than fully formed) offspring, which is then left to complete its own construction. The von Neumann model of self-replication envisages that the mother automaton should construct all portions of daughter automatons, without exception and prior to the initiation of such daughters. Partial construction alters the construction relationship between mother and daughter automatons, such that the mother constructs but a portion of the daughter, and upon initiating this portion of the daughter, thereafter retracts from imparting further influence upon the daughter. Instead, the daughter automaton is left to complete its own development. This is to say, means exist by which automatons may develop via the mechanism of a zygote.

The idea of an automated spacecraft capable of constructing copies of itself was first proposed in scientific literature in 1974 by Michael A. Arbib, 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. The first quantitative engineering analysis of a self-replicating spacecraft was published in 1980 by Robert Freitas, 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.

In his short story ‘Crabs on the Island’ (1958) Anatoly 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.

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 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 labor and the manufacture of spare parts and other components locally becomes more economical than transporting them from elsewhere. As Samuel Butler has pointed out in ‘Erewhon,’ replication of partially closed universal machine tool factories is already possible. Since safety is a primary goal of all legislative consideration of regulation of such development, future development efforts may be limited to systems which lack either control, matter, or energy closure. 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).

An artificial 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 foreseeable future.

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