Self-replicating spacecraft

The idea of self-replicating spacecraft has been applied — in theory — to several distinct "tasks". The particular variant of this idea applied to the idea of space exploration is known as a von Neumann probe. Other variants include the Berserker and an automated seeder ship.

Contents

Theory

In theory, a self-replicating spacecraft could be sent to a neighbouring star-system, where it would seek out raw materials (extracted from asteroids, moons, gas giants, etc.) to create replicas of itself. These replicas would then be sent out to other star systems. The original "parent" probe could then pursue its primary purpose within the star system. This mission varies widely depending on the variant of self-replicating starship proposed.

Given this pattern, and its similarity to the reproduction patterns of bacteria, it has been pointed out that von Neumann machines might be considered a form of life. In his short story, "Lungfish" (see Examples in fiction below), David Brin touches on this idea, pointing out that self-replicating machines launched by different species might actually compete with one another (in a Darwinistic fashion) for raw material, or even have conflicting missions. Given enough variety of "species" they might even form a type of ecology, or — should they also have a form of artificial intelligence — a society. They may even mutate with untold thousands of "generations".

The first quantitative engineering analysis of such a spacecraft was published in 1980 by Robert Freitas,[1] 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, over a 500 year period, and then use the resulting automated industrial complex to construct more probes with a single seed factory on board each.

It has been theorized that a self-replicating starship utilizing relatively conventional theoretical methods of interstellar travel (i.e., no exotic faster-than-light propulsion such as "warp drive", and speeds limited to an "average cruising speed" of 0.1c.) could spread throughout a galaxy the size of the Milky Way in as little as half a million years.[2]

Implications for Fermi's paradox

In 1981, Frank Tipler[3] put forth an argument that extraterrestrial intelligences do not exist, based on the absence of von Neumann probes. Given even a moderate rate of replication and the history of the galaxy, such probes should already be common throughout space and thus, we should have already encountered them. Because we have not, this shows that extraterrestrial intelligences do not exist. This is thus a resolution to the Fermi paradox—that is, the question of why we have not already encountered extraterrestrial intelligence if it is common throughout the universe.

A response[4] came from Carl Sagan and William Newman. Now known as Sagan's Response, it pointed out that in fact Tipler had underestimated the rate of replication, and that von Neumann probes should have already started to consume most of the mass in the galaxy. Any intelligent race would therefore, Sagan and Newman reasoned, not design von Neumann probes in the first place, and would try to destroy any von Neumann probes found as soon as they were detected. As Robert Freitas[5] has pointed out the assumed capacity of von Neumann probes described by both sides of the debate are unlikely in reality, and more modestly reproducing systems are unlikely to be observable in their effects on our Solar System and the rest of the Galaxy.

Another objection to the prevalence of von Neumann probes is that civilizations of the type that could potentially create such devices may have inherently short lifetimes, and self-destruct before so advanced a stage is reached, through such events as biological or nuclear warfare, nanoterrorism, resource exhaustion, ecological catastrophe, pandemics due to antibiotic resistance, etc.

A simple workaround exists to avoid the over-replication scenario. Radio transmitters, or other means of wireless communication, could be used by probes programmed not to replicate beyond a certain density (such as five probes per cubic parsec) or arbitrary limit (such as ten million within one century). One problem with this defence against uncontrolled replication is that it would only require a single probe to malfunction and begin unrestricted reproduction for the entire approach to fail — essentially a technological cancer — unless each probe also has the ability to detect such malfunction in its neighbours and implements a seek and destroy protocol.

Applications for self-replicating spacecraft

The details of the mission of self-replicating starships can vary widely from proposal to proposal, and the only common trait is the self-replicating nature.

Von Neumann probes

A von Neumann probe is a self-replicating spacecraft designed to investigate its target system and transmit information about it back to its system of origin.[6] The concept is named after Hungarian American mathematician and physicist John von Neumann, who rigorously studied the concept of self-replicating machines that he called "Universal Assemblers" and which are often referred to as "von Neumann machines". While von Neumann never applied his work to the idea of spacecraft, theoreticians since then have done so.

If a self-replicating probe finds evidence of primitive life (or a primitive, low level culture) it might be programmed to lie dormant, silently observe, attempt to make contact (this variant is known as a Bracewell probe), or even interfere with or guide the evolution of life in some way.

Physicist Paul Davies of Arizona State University has even raised the possibility of a probe resting on our own Moon, having arrived at some point in Earth's ancient prehistory and remained to monitor Earth (see Bracewell probe).

A variant idea on the interstellar von Neumann probe idea is that of the "Astrochicken", proposed by Freeman Dyson. While it has the common traits of self-replication, exploration, and communication with its "home base", Dyson conceived the Astrochicken to explore and operate within our own planetary system, and not explore interstellar space.

Oxford-based philosopher Nick Bostrom discusses the idea that future powerful superintelligences will create efficient cost-effective space travel and interstellar Von Neumann probes.[7]

Autonomous synthetic life

Similar to a von Neumann probe, the only intelligent beings capable of traveling the huge distances of space are synthetic and self replicating life forms. These life forms are not single probes, but groups of life forms who are teaming together to achieve their goals in space.

Berserkers

A variant of the self-replicating starship is the Berserker. Unlike the benign probe concept, Berserkers are programmed to seek out and exterminate lifeforms and life-bearing exoplanets whenever they are encountered.

The name is derived from a series of novels by Fred Saberhagen which feature an ongoing war between humanity and such machines (see: Berserker). Saberhagen points out (through one of his characters) that the Berserker warships in his novels are not von Neumann machines themselves, but the larger complex of Berserker machines — including automated shipyards — do constitute a von Neumann machine. This again brings up the concept of an ecology of von Neumann machines, or even a von Neumann hive entity.

It is speculated that Berserkers could be created and launched by a xenophobic civilization (see Anvil of Stars, by Greg Bear, in Examples in fiction below) or could theoretically "mutate" from a more benign probe. For instance, a von Neumann ship designed for terraforming processes — mining a planet's surface and adjusting its atmosphere to more human-friendly conditions — might malfunction and attack inhabited planets, killing their inhabitants in the process of changing the planetary environment, and then self-replicate and dispatch more ships to attack other planets.

Replicating "seeder" ships

Yet another variant on the idea of the self-replicating starship is that of the "seeder" ship. Such starships might store the genetic patterns of lifeforms from their home world, perhaps even of the species which created it. Upon finding a habitable exoplanet, or even one that might be terraformed, it would try to replicate such lifeforms — either from stored embryos (see: embryo space colonization) or from stored information using molecular nanotechnology to "build" zygotes with varying genetic information from local raw materials.

Such ships might be terraforming vessels, preparing colony worlds for later colonization by other vessels, or — should they be programmed to recreate, raise, and educate individuals of the species that created it — self-replicating colonizers themselves.

As a side note, this pattern of terraforming and colonization need not be "automated". Manned interstellar colony ships could follow a similar pattern — and might be considered a sort of a combined von Neumann probe/seeder ship in which replication can be performed by the living inhabitants.

Some proponents of space habitats suggest that planets would be entirely unnecessary to a civilization using this approach. Taken to its extreme, this concept could combine self-replicating habitat ships with technologies such as virtual reality, envatted brains and tissue regeneration to efficiently transform cosmic resources into meaningful subjective lives free from suffering.

Examples in fiction

Von Neumann probes

Berserkers

Replicating "seeder" ships

See also

References

  1. ^ Freitas, Robert A., Jr. (July 1980). "A Self-Reproducing Interstellar Probe". J. Brit. Interplanet. Soc. 33: 251–264. http://www.rfreitas.com/Astro/ReproJBISJuly1980.htm. 
  2. ^ Comparison of Reproducing and Nonreproducing Starprobe Strategies for Galactic Exploration
  3. ^ "Extraterrestrial Beings Do Not Exist", Quarterly Journal of the Royal Astronomical Society, vol. 21, number 267 (1981)
  4. ^ Sagan, Carl and Newman, William: "The Solipsist Approach to Extraterrestrial Intelligence", Quarterly Journal of the Royal Astronomical Society, vol. 24, number 113 (1983)
  5. ^ Freitas, Robert A., Jr. (November 1983). "Extraterrestrial Intelligence in the Solar System: Resolving the Fermi Paradox". J. Brit. Interplanet. Soc. 36: 496–500. http://www.rfreitas.com/Astro/ResolvingFermi1983.htm. 
  6. ^ A Self-Reproducing Interstellar Probe
  7. ^ Nick Bostrom 2003 Ethical Issues in Advanced Artificial Intelligence — section 2
  8. ^ The complete text of the story has been placed on the author's website at davidbrin.com
  • Boyce, Chris. Extraterrestrial Encounter: A Personal Perspective. London: David & Charles, Newton Abbot (1979).
  • von Tiesenhausen, G., and Darbro, W. A. "Self-Replicating Systems," NASA Technical Memorandum 78304. Washington, D.C.: National Aeronautics and Space Administration (1980).
  • Freitas Jr., Robert A. "A Self-Reproducing Interstellar Probe," Journal of the British Interplanetary Society, 33, 251–264 (1980). rfreitas.com, also molecularassembler.com
  • Valdes, F., and Freitas, R. A. "Comparison of Reproducing and Non-Reproducing Starprobe Strategies for Galactic Exploration," Journal of the British Interplanetary Society, 33, 402–408 (1980). rfreitas.com