One of the theories for extraterrestrial intelligence is that it would most likely be postbiological societies where technology is more prevalent than biology. This would require von Neumann machines which are computers that are capable of self-replication. These self-replicating probes (SRPs) would be able to travel the galaxy and mine for raw resources. The parent probe would then be able to build more probes and pass down their knowledge and even making improved versions. The new probes could then travel to other systems while the parent probe could remain and explore the local system. This could continue for generations until there are probes observing every system. Using von Neumann machines would allow a civilization to span the galaxy in a relative short amount of time. 

Postbiological civilizations could have a wide variety of reasons for employing SRPs. They could avoid contact and observe the evolution of other civilizations or even just observe space. They could also function as Bracewell probes which have messages and attempt to communicate between distant intelligent species. There is also the possibility that they could interfere to either prevent extinction events. Berserker probes or another possibility whose purpose would be to exterminate other intelligence whether due to design or an evolved error. The machines could be used to construct engineering projects such as a Dyson sphere. Another potential use would be to find places to start colonies which could involve terraforming planets. Police probes could be waiting to interfere if a civilization evolved to a point where it appeared that it would be a danger to others.
Calculations suggest that it could take as little as half a million years for SRPs to reproduce to millions and explore the galaxy if traveling at a tenth of the speed of light although there is reason to believe it would be closer to ten million years. They can also increase their speed by taking advantage of slingshot maneuvers around stars. Fuel sources could come from the atmospheric gas of a planet or using mined resources to construct solar panels. These machines could be built on a micro-scale where little fuel is required and they would be able to travel close to the speed of light. The best location for self replication would be dead moons where it is easy to take off and land. They would also have the metal deposits necessary to build more machines.
The problem with the concept of SRPs is the Fermi Paradox. If von Neumann probes exist then why haven't they been encounter? Earth life has not been uplifted or berserked and we have not detect and communication from SRPs. This could mean that they do not exist at all because other intelligence does not exist. Alternative solutions propose that they would eventually consume most of the mass in the galaxy so intelligent civilizations would not send them out. This can be worked around by programming the probes not to replicate beyond a certain point to limit their numbers and mass.

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The idea of von Neumann machines and SRPs seems like a logical means for any ultra advanced species to search the cosmos for the raw materials needed to sustain the life such a civilization must be accustom to. Assuming one such race of beings exists, what would be the probability that another similar race exists also searching for similar resources. Would the two compete for the resources? Would such competition spark intergalactic warfare? Is searching for evidence of such galactic battles a means to search for life? Interesting!

In line with the Fermi Paradox, the why haven't we had an encounter question, how would we look to detect the communication between SRPs and their command? 

I think you explore the topic of von Nueman machines very well and explore the implications of these machines on a galactic level. The most interesting aspect to me is if they would propagate so fast through the galaxy, why don't we see or encounter any of them. I found your response that they could be limited as not too reproduce too extensively to be a good answer. If I could make a recommendation, it would be explaining what a Dyson sphere is and why a galactic civilization would like to create one. 

Hey there Alyssa, overall this was a great read and really interesting. You included a lot of great potential benefits of SRP's such as them serving as Bracewell probes and since i don't have a strong background knowledge in astrobiology i'm glad to know now that there is a term for that concept.

I'm not sure if i follow what you mean exactly by the "Berserker probes". While reading that part I imagined it would be something as your suggested Police probes. when you mention exterminating intelligence " due to design or an evolved error." are you referring to things such as illnesses and viruses or something closer to the idea that well since this one species needs blank chemical to survive and will cause the depletion of said chemical than that species should be eliminated instead?

I clicked to find out what a Von Neumann machine was. I like them. You explored the idea pretty thoroughly, even t the point of why we don't see them. These would be a great way for humans to explore the galaxy. They could go to new planets, collect data, if there is not much to find they could use whatever resources are available to make new machines and outposts for stopping points for humans. If hey don't exist we should make them exist. 



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