Self-replicating probes are also sometimes called von Neumann probes or von Neumann machines after the famed mathematician who first created the concept.
Self-replicating probes are usually regarded as a "Low C" option of exploring interstellar space. Low C options assume that achieving significant fractions of lightspeed are impossible or highly impractical, forcing voyages between the stars to take centuries or millennia.
SELF-REPLICATING INTERSTELLAR PROBE
Tech Level: 15
In essence, self replicating probes work as follows: A fully-automated probe with a sophisticated AI is launched toward a nearby star. When it enters that star system decades or centuries later, it exhaustively surveys what lies there. It transmits what it learns back to its homeworld. It then uses the material resources of the star system present in asteroids, comets, moons, and/or planets to construct replicas of itself, which it sends to other nearby star systems to repeat the process. They would be in essence miniature flying factories, designed to use advanced robotic systems to mine and process ore, harvest raw materials, fabricate individual components, and assemble all the varied parts into a whole probe. Depending on the complexity of the probe and the sophistication of the robotic systems involved, the process to produce a single daughter probe can vary from a few days to several years.
The original probe may stay in the system or continue on, depending on its mission parameters. If it stays, it may act as a communication relay between its "children" and its homeworld, or it may begin processing the systemís resources for anticipated follow-up colonization ships from the homeworld, or it may launch said resources back to its point of origin for its building raceís material needs.
Using this method and assuming an average crusing speed of the probes at a few percentage points of light speed, some postulate that the entirety of the Milky Way galaxy could be charted and explored in less than a few million years. More advanced propulsion technology can considerably cut this time.
While self-replicators are ostensibly connected with exploration, they can be used for other purposes, as many science fiction writers have demonstrated in their stories. In the novels Life Probe and Procyonís Promise by Michael McCollum, an advanced alien race sends out probes to specifically contact other sentient species, to trade all their scientific and cultural knowledge for the secret of a possible FTL drive. In The Ring of Charon and The Shattered Sphere by Roger McBride Allen, probes were sent out armed with wormhole technology to hijack entire worlds for their material and organic resources. And in the most famous example in sci-fi, the many Berserker stories by Fred Saberhagen, the self-replicators were created to be the ultimate weapon, an ever-growing and adaptable weapon system programmed to seek out and exterminate all organic life it encountered.
Self-replicating probes in many ways resemble living organisms; they consume resources, produce waste, reproduce, and spread out to fill a specific niche. In fact, some would say the distinction is arbitary, and that they would, quite by accident, also inherent the one other distinctive trait of living creatures: evolution.
Small errors in the replication of daughter probes are bound to occur every once in a while; in many ways, these can be considered analogous to mutations. Like mutations in living creatures, most mutations in replicators would be non-viable, and either of no consequence or would reseult in the destruction of the probe. However, every once in a great while, a bit error will carry over into the next generation of daughter probes, who will in turn pass that on to their offspring, and so on. After many millions of years of this, the probes drift away from their original manifestation. Some may just drift into extinction, some may become nothing more than feral organisms focused purely on surviving and reproducing, and some may develop ideas and purposes far beyond what they were originally programmed to do. In fact, in The Ring of Charon and The Shattered Sphere, this is exactly what happened to the Charonians, which started out as Voyager-style exploration probes and ended up after millions of years as immense dyson sphere intelligences who had completely forgotten their origins and treated human-level sentients as microbes.
Both the Charonians and the Berzerkers represent the all-too-easy-to-achieve Frankenstein-like aspect of this scheme. Self-replicating probes can all too easily overwhelm any organic species of lesser technology, and become the dominant form of life, artificial or otherwise, in the galaxy. Though the purposes of the building species may have been benign, their self-replicating probes could, after eons of reproducing and evolution, become a danger without equal to any organic civilization in the galaxy.
In the novels Forge of God and Anvil of Stars, by Greg Bear, the star-faring species of the galaxy consider self-replicating probes to be a menace without equal and formed a very loose alliance called the Law, whose purpose was to hunt down and destroy not only any self-replicating probes it finds but also to punish their building species with extinction.
One method that can be used to avoid the potential explosion of evolved self-replicators is to use a programmed limitation to the number of generations the probes can go through. A dozen or so generations (resulting in a total of a few thousand probes) would be enough to explore a local interstellar neighboorhood without incurring any serious statistical risk of replicator evolution.
SELF-REPLICATING INTERSTELLAR NANO PROBES
Tech Level: 18
Iíve encountered this idea primarily through the novel Assemblers of Infinity by Kevin J. Anderson. Instead of a single, large, factory-like macroscopic probe, the building race instead shoots out many millions of microscopic nanites (nanotech robots) in the direction of a nearby star system. The majority of these probes will most likely be lost, passing through the system without encountering any physical body, or falling into the star or gas giants and meeting their destruction.
However, the trajectories of a small fraction will intersect solid bodies such as moons, planets, and asteroids. The nanites, of course, would be built in such a way as to withstand high-speed impacts with material bodies. After landing, the nanites begin replicating themselves, and when enough of them are present they begin construction of larger-scale structures to complete whatever task their builders meant for them to do at the target system. When this is done, they assemble a nanite launcher to shoot their daughter units at a nearby star system to repeat the process.
The power and versatility of a nanotech-based mineral extraction and fabrication process can be near-unlimited, allowing the nanoprobes to accomplish tasks that are generally considered to be beyond macroscopic probes. In Assemblers of Infinity, for example, the nanite assemblers that had landed on the Moon completed not only a macroscopic launch facility to signal its building race but by the novelís end had recreated their creators biologically by building them up molecule by molecule.
The "Frankenstein" capacity of nano probes are also that much higher than macroscopic probes.
Berserker, et al, by Fred Saberhagen
The Ring of Charon and The Shattered Sphere by Roger McBride Allen
Life Probe and Procyonís Promise by Michael McCollum
Forge of God and Anvil of Stars by Greg Bear
"Lungfish" by David Brin
Assemblers of Infinity by Kevin J. Anderson
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