The concept of self-replicating spacecraft , as envisioned by mathematician John von Neumann, has been described by futurists and has been discussed across a wide breadth of hard science fiction novels and stories. Self-replicating probes are sometimes referred to as von Neumann probes. Self-replicating spacecraft would in some ways either mimic or echo the features of living organisms or viruses. [1]
Von Neumann argued that the most effective way of performing large-scale mining operations such as mining an entire moon or asteroid belt would be by self-replicating spacecraft, taking advantage of their exponential growth. [2] In theory, a self-replicating spacecraft could be sent to a neighbouring planetary 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 planetary 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 Self-replicating machines in fiction), 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, [2] 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 produce 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 [3] that a self-replicating starship utilizing relatively conventional theoretical methods of interstellar travel (i.e., no exotic faster-than-light propulsion, and speeds limited to an "average cruising speed" of 0.1 c .) could spread throughout a galaxy the size of the Milky Way in as little as half a million years.
In 1981, Frank Tipler [4] put forth an argument that extraterrestrial intelligences do not exist, based on the fact that von Neumann probes have not been observed. 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 [5] came from Carl Sagan and William Newman. Now known as Sagan's Response,[ citation needed ] 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 [6] has pointed out, the assumed capacity of von Neumann probes described by both sides of the debate is unlikely in reality, and more modestly reproducing systems are unlikely to be observable in their effects on our solar system or the galaxy as a whole.
Another objection to the prevalence of von Neumann probes is that civilizations that could potentially create such devices may have a high probability of self-destruction before being capable of producing such machines. This could be through events such as biological or nuclear warfare, nanoterrorism, resource exhaustion, ecological catastrophe, or pandemics. This obstacle to the creation of von Neumann probes is one potential candidate for the concept of a Great Filter.
Simple workarounds exist 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), analogous to the Hayflick limit in cell reproduction. 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 (which in turn could lead to probe-on-probe space wars if faulty probes first managed to multiply to high numbers before they were found by sound ones, which could then well have programming to replicate to matching numbers so as to manage the infestation). Another workaround is based on the need for spacecraft heating during long interstellar travel. The use of plutonium as a thermal source would limit the ability to self-replicate. The spacecraft would have no programming to make more plutonium even if it found the required raw materials. Another is to program the spacecraft with a clear understanding of the dangers of uncontrolled replication.
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.
A von Neumann probe is a spacecraft capable of replicating itself. [2] It is a concatenation of two concepts: a Von Neumann universal constructor (self-replicating machine) and a probe (an instrument to explore or examine something).[ citation needed ] 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". [2] Such constructs could be theorised to comprise five basic components (variations of this template could create other machines such as Bracewell probes [ jargon ]):
Andreas M. Hein and science fiction author Stephen Baxter proposed different types of von Neumann probes, termed "Philosopher" and "Founder", where the purpose of the former is exploration and for the latter preparing future settlement. [7] [ better source needed ]
A near-term concept of a self-replicating probe has been proposed by the Initiative for Interstellar Studies,[ clarification needed ] achieving about 70% self-replication, based on current and near-term technologies. [8]
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),[ jargon ] or even interfere with or guide the evolution of life in some way.[ citation needed ]
Physicist Paul Davies of University of Adelaide has "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, a concept that, per Michio Kaku, was what Stanley Kubrick used as the basis of his film, 2001: A Space Odyssey (though the director cut the relevant monolith scene from the movie). [9] Kubrick's work was based on Arthur C. Clarke's story, "The Sentinel", expanded by the pair in the form of a novel that became the basis for the movie [10] and so Davies' lunar probe/observatory concept is also considered reminiscent of Clarke.[ citation needed ]
A variant idea on the interstellar von Neumann probe idea is that of the "Astrochicken", proposed by Freeman Dyson.[ citation needed ] 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.[ citation needed ]
Anders Sandberg and Stuart Armstrong argued that launching the colonization of the entire reachable universe through self-replicating probes is well within the capabilities of a star-spanning civilization, and proposed a theoretical approach for achieving it in 32 years, by mining planet Mercury for resources and constructing a Dyson Swarm around the Sun. [11]
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 the Berserker series of novels by Fred Saberhagen which describes a war between humanity and such machines. 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 in fiction that Berserkers could be created and launched by a xenophobic civilization (see Anvil of Stars , by Greg Bear, in the section 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 – could be interpreted as attacking previously inhabited planets, killing their inhabitants in the process of changing the planetary environment, and then self-replicating to dispatch more ships to "attack" other planets.
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 or from stored information using molecular nanotechnology to build zygotes with varying genetic information from local raw materials. [12]
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. Seeder ships would be a suitable alternative to generation ships as a way to colonize worlds too distant to travel to in one lifetime.
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The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 55 astronomical units (AU), stars are typically separated by hundreds of thousands of AU, causing these distances to typically be expressed instead in light-years. Because of the vastness of these distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer.
The Kardashev scale is a method of measuring a civilization's level of technological advancement based on the amount of energy it is capable of harnessing and using. The measure was proposed by Soviet astronomer Nikolai Kardashev (1932–2019) in 1964 and was named after him.
A sleeper ship is a hypothetical type of crewed spacecraft, or starship in which most or all of the crew spend the journey in some form of hibernation or suspended animation. The only known technology that allows long-term suspended animation of humans is the freezing of early-stage human embryos through embryo cryopreservation, which is behind the concept of embryo space colonization.
The Berserker series is a series of space opera science fiction short stories and novels by Fred Saberhagen, in which robotic self-replicating machines strive to destroy all life.
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible uncrewed interstellar probe. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use existing or near-future technology and had to be able to reach its destination within a human lifetime. Alan Bond led a team of scientists and engineers who proposed using a fusion rocket to reach Barnard's Star 5.9 light years away. The trip was estimated to take 50 years, but the design was required to be flexible enough that it could be sent to any other target star.
Xenoarchaeology, a branch of xenology dealing with extraterrestrial cultures, is a hypothetical form of archaeology that exists mainly in works of science fiction. The field is concerned with the study of the material remains to reconstruct and interpret past life-ways of alien civilizations. Xenoarchaeology is not currently practiced by mainstream archaeologists due to the current lack of any material for the discipline to study.
In Arthur C. Clarke's Space Odyssey series, Monoliths are machines in black cuboids whose sides extend in the precise ratio of 1 : 4 : 9 (12 : 22 : 32) built by an unseen extraterrestrial species whom Clarke dubbed the Firstborn and who he suggests are the earliest highly intelligent species to evolve in the Milky Way. In the series of novels (and the films based on these), three Monoliths are discovered in the Solar System by australopithecines and their human descendants. The characters' responses to their discoveries drives the plot of the series and influences its fictional history, particularly by encouraging humanity to progress with technological development.
Astrochicken is the name given to a thought experiment expounded by theoretical physicist Freeman Dyson. An Astrochicken is a small, one-kilogram spacecraft, a self-replicating automaton that could explore space more efficiently than a crewed craft could due to its innovative mix of technology.
The zoo hypothesis speculates on the assumed behavior and existence of technologically advanced extraterrestrial life and the reasons they refrain from contacting Earth. It is one of many theoretical explanations for the Fermi paradox. The hypothesis states that alien life intentionally avoids communication with Earth to allow for natural evolution and sociocultural development, and avoiding interplanetary contamination, similar to people observing animals at a zoo. The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence. A variant on the zoo hypothesis suggested by the former MIT Haystack Observatory scientist John Allen Ball is the "laboratory" hypothesis, in which humanity is being subjected to experiments, with Earth serving as a giant laboratory.
The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
A self-replicating machine is a type of autonomous robot that is capable of reproducing itself autonomously using raw materials found in the environment, thus exhibiting self-replication in a way analogous to that found in nature. The concept of self-replicating machines has been advanced and examined by Homer Jacobson, Edward F. Moore, Freeman Dyson, John von Neumann, Konrad Zuse 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 is 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 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 be able to evolve and which he formalized in a cellular automata environment. Notably, Von Neumann's Self-Reproducing Automata scheme posited that open-ended evolution requires inherited information to be copied and passed to offspring separately from the self-replicating machine, an insight that preceded the discovery of the structure of the DNA molecule by Watson and Crick and how it is separately translated and replicated in the cell.
The mythology of the Stargate franchise is a complex and eclectic fictional backstory, which is presented as being historical, of the Stargate premise. A "rich mythology and world-building" are used to establish "a vast cosmology and an interesting alternate take on the history of Earth"; a defining feature is "its use of ancient mythology, with stories that take inspiration from multiple places around the globe". Narratives center around xeno-mythology as experienced by humans during episodic contact with alien races. Audiences across a variety of platforms - including TV series, novels, comics and movies - witness the people of Earth exploring a fictional universe using the Stargate. Species established early on in the franchise recur throughout, with one adversary often dominating a particular story arc, which can continue across several seasons.
Manifold: Space is a science fiction book by British author Stephen Baxter, first published in the United Kingdom in 2000, then released in the United States in 2001. It is the second book of the Manifold series and examines another possible solution to the Fermi paradox. Although it is in no sense a sequel to the first book it contains a number of the same characters, notably protagonist Reid Malenfant, and similar artefacts. The Manifold series contains four books, Manifold: Time, Manifold: Space, Manifold: Origin, and Phase Space.
A Bracewell probe is a hypothetical concept for an autonomous interstellar space probe dispatched for the express purpose of communication with one or more alien civilizations. It was proposed by Ronald N. Bracewell in a 1960 paper, as an alternative to interstellar radio communication between widely separated civilizations.
Ancient astronauts have been addressed frequently in science fiction and horror fiction. Occurrences in the genres include:
The cultural impact of extraterrestrial contact is the corpus of changes to terrestrial science, technology, religion, politics, and ecosystems resulting from contact with an extraterrestrial civilization. This concept is closely related to the search for extraterrestrial intelligence (SETI), which attempts to locate intelligent life as opposed to analyzing the implications of contact with that life.
Death's End is a science fiction novel by the Chinese writer Liu Cixin. It is the third novel in the trilogy titled Remembrance of Earth's Past, following the Hugo Award-winning novel The Three-Body Problem and its sequel, The Dark Forest. The original Chinese version was published in 2010. Ken Liu translated the English edition in 2016. It was a finalist for the 2017 Hugo Award for Best Novel and winner of the 2017 Locus Award for Best Science Fiction Novel.
The Berserker hypothesis, also known as the deadly probes scenario, is the idea that humans have not yet detected intelligent alien life in the universe because it has been systematically destroyed by a series of lethal Von Neumann probes. The hypothesis is named after the Berserker series of novels (1963–2005) written by Fred Saberhagen.
The Hart–Tipler conjecture is the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System. This idea was first proposed in opposition to the Drake equation in a 1975 paper by Michael H. Hart titled "Explanation for the Absence of Extraterrestrials on Earth". Assuming that the probes traveled at 1/10 the speed of light and that no time was lost in building new ships upon arriving at the destination, Hart surmised that a wave of Von Neumann probes could cross the galaxy in approximately 650,000 years, a comparatively minimal span of time relative to the estimated age of the universe at 13.7 billion years. Hart’s argument was extended by cosmologist Frank Tipler in his 1981 paper entitled ‘Extraterrestrial intelligent beings do not exist’.