The idea of self-replicating spacecraft has been applied in theory to several different “tasks.” The particular variant of this idea applied to the idea of space exploration is known as a von Neumann probe after the mathematician John von Neumann, who originally designed them. Other variants include the Berserker and an automated terraforming seed ship.
Von Neumann proved that the most effective way to carry out large-scale mining operations such as mining an entire moon or the asteroid belt would be through self-replicating spacecraft, taking advantage of their exponential growth.
In theory, a self-replicating spacecraft could be sent to a neighboring planetary system where it would seek raw materials (extracted from asteroids, moons, gas giants, etc.) to create replicas of itself.
These replicas would then be sent to other planetary systems. The original “mother” probe could then pursue its primary purpose within the star system. This mission varies widely depending on the variant of self-replicating starship proposed.
Other people have said yes antimatter rockets are the way to go and we’ve all had this mental vision of the Enterprise going to nearby star systems… But this is another way to do it. Think about Mother Nature.
When Mother Nature wants to propagate life one possibility is to send seeds, not just one or two, but millions of seeds. Most seeds never make it, but one or two do, and as a result, this is how trees propagate in forests. So why not create a nano ship using nanotechnology? How big would that be?
Some people like Paul Davies say it could be as big as a bread box. Other people say it could be even smaller than that. Why not something the size of a needle? And because they’re so small it wouldn’t take much to accelerate them to close to the speed of light.
Realize that a very small tabletop accelerator can accelerate electrons to nearly the speed of light so it wouldn’t take long for us to accelerate nanomolecules to very, very fast speeds close to the speed of light using electric fields.
Now, these probes would be different from ordinary probes. They would be nanobots. They would have the ability to land on hostile terrain and create a factory like a virus. That’s what viruses do. They replicate themselves.
A virus can create maybe a thousand copies, then a thousand, a thousand copies, then a million, a billion, a trillion, and suddenly you have trillions of these things propagating through outer space.
And how would you do that? One possibility is to use the field, magnetic fields around Jupiter. Calculations have shown that you can go around Jupiter using what’s called the Faraday Effect to spin the particles up to perhaps close to the speed of light.
The first quantitative engineering analysis of such a spacecraft was published in 1980 by Robert Freitas, in which the non-replicating Project Daedalus design was modified to include all the subsystems necessary for self-replication.
The design strategy was to use the probe to deliver a “seed” factory with a mass of about 443 tons to a distant location, have the seed factory replicate many copies of itself there to increase its total manufacturing capacity over a period of 500 years, and then use the resulting automated industrial complex to build more probes with a single seed factory on board each.
It has been theorized that a self-replicating starship using relatively conventional theoretical methods of interstellar travel (i.e., no exotic faster-than-light propulsion and speeds limited to an “average cruising speed” of 0.1c.) could spread across an entire galaxy the size of the Milky Way in just half a million years.
Implications for the Fermi Paradox
In 1981 Frank Tipler presented an argument that there are no extraterrestrial intelligences 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 therefore we should have encountered them by now.
Because we don’t, that shows that there are no extraterrestrial intelligences. This is therefore a resolution to the Fermi paradox – that is, the question of why we haven’t found extraterrestrial intelligence yet if it is common throughout the universe.
An answer came from Carl Sagan and William Newman. Now known as Sagan’s Reply[citation needed], it pointed out that Tipler had in fact underestimated the replication rate and that the von Neumann probes should have already begun to consume most of the galaxy’s mass.
Any intelligent race therefore reasoned Sagan and Newman would not design the von Neumann probes in the first place and would attempt to destroy all found von Neumann probes as soon as they were detected.
As Robert Freitas has pointed out the assumed capability of von Neumann probes described by both sides of the debate is unlikely in reality and more modestly reproduced systems are unlikely to be observed 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 of the type that could create such devices may be inherently short-lived and self-destruct before such an advanced stage is reached through events such as biological or nuclear warfare, nanoterrorism, resource exhaustion, ecological catastrophe, or pandemics.
There are simple workarounds 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 in a century), analogous to the Hayflick limit in cellular reproduction.
One problem with this defense against runaway replication is that it would only take 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 malfunctions in its neighbors and implements a search-and-destroy protocol (which in turn could lead to probe-on-probe space wars if faulty probes first manage to multiply to high numbers before being found by solid ones, which might then have a program to replicate to matching numbers. This is how the infestation is controlled).
Another alternative solution is based on the need for spacecraft heating during long interstellar journeys. The use of plutonium as a thermal source would limit the self-replication capacity.
The spacecraft would not be programmed to produce more plutonium, even if it found the necessary raw materials. Another is to program the spacecraft with a clear understanding of the dangers of uncontrolled replication.
Applications for self-replicating spacecraft
The mission details of self-replicating starships can vary widely from proposal to proposal, and the only common feature is their self-replicating nature.
And again, we don’t have these nanobots yet. We have to wait until nanotechnology becomes sufficiently developed, but when that happens, perhaps the 100-year-old starship won’t look like the Enterprise.
Maybe they look like tiny needles by the billions sent into outer space, and maybe just a handful of them land on a distant moon to create factories.
And doesn’t that sound familiar? This is the plot of the movie 2001. Remember that giant obelisk on Mars? That was the Von Neumann probe, a virus, a self-replicating probe that can then explore the universe at close to the speed of light.
