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von Neumann probe

Introduction to von Neumann probes

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, repeating the process in an exponentially increasing pattern. After the replication process has started the probe would eventually spread to every part of Universe, if given enough time.

How could this self-replicating entity work? The simplest example would be a huge space ship that is loaded with mining robots, construction robots and repair robots. When the space ship arrives to a suitable planet or other astronomical object, it releases the robots who then start to search and harvest raw materials. When they are found and collected, the constructor robots start to build more robots, and finally, a new space ship. Repair robots keep the other robots working. When the new spaceship is ready, it is loaded with all three kind of robots and sent aboard to find other suitable astronomical objects. Enough robots are left behind to build another spaceship. And another - and so on. This of course was a highly simplified example of a von Neumann probe but I hope the main idea become clear.

As pretty much every else technology, von Neumann probes could be used for both constructive and destructive purposes.

Bad news first...

The simplest von Neumann probe possible is a design that just keeps replicating, as long as there are raw materials available. This design is inherently destructive, because it turns anything it could to copies of itself as it replicates exponentially. This means it will also destroy habitated places, or at least steal the resources form inhabitants, as it progress. It is unlikely anyone would build such a probe since it would also threaten it's creator. It is possible, however, that a badly designed probe could begin such a replication, even if it is not intended for it.

This design could be deliberately made even more destructive by adding weapons to it. After that it would be the ultimate weapon of mass destruction: destructive enough to threaten entire galaxies. Could there be something in the universe that has both intelligence, ruthlessness and motivation to build something like that? I have tried to answer the question here.

...and then the good news

Althought the idea sounds rather depressing there is no need for anxiety.

If someone/something releases a destructive probe mentioned above there is a possibility to counter it: another von Neumann probe that is designed to hunt down and eliminate destructive von Neumann probes. I'm afraid however that it is mandatory to lauch this defensive probe before aggressive probes enters the vicinity of your solar system. Otherwise it is too late, as the power of von Neumann probe is bind to the time and space it has for self-replication.

Of course a civilization could fortify the solar system of it. It could build something like proposed SDI but on vastly greater scale. The logic would be that whatever happens in other parts of galaxy, the possible aggressions could be thwarted at local scale with advanced weapons.

But there are some problems on this strategy. Given the amount of raw materials of even a one galaxy, aggressive von Neumann probes could attack the solar system at rate of billions of probes per minute. And if attacking probes are advanced enough, they can their attack defence system.

It is hard to imagine a defence system that is reliable against such an attack.

Therefore, there are good changes that at least one civilization in our galaxy has been cautious enought to send a defensive von Neumann probe to keep aggressive von Neumann probes away from Milky Way. Please read more about he possible motives of extraterrestials here.



What is von Neumann probe

Von Neumann probe is a hypothetical robotic space probe. It is programmed to search space for raw materials and energy in order to build copies of itself. It can be considered as a mechanical bacterium or virus. Besides self-replicating, von Neumann probes will execute tasks they are programmed to do. You can read more about von Neumann probe on Wikipedia.