[runarberg]

von Neumann probes are a fantasy. I see no reason why any civilization in the entire universe will ever build a successful self replicating probes, let alone ones that are still replicating dozens of millennia later. The reasons include that targeted probes and telescopes can give you pretty much the same amount of knowledge for far cheaper and much quicker then random walking probes across the galaxy. There is also a technical limitation to self replicating probes, even if a civilization will build one, we cannot expect the self-replicating mechanism to last dozens of millennia. Some generations will fail to replicate, and in the vastness of space that may mean the entire lineage will go extinct.

I think you may be expecting an exponential growth when population dynamics almost always favor logistical growth. At some point your machines, or your colonial behavior hits a limit and your growth starts to slow down. I suspect that limit is within the solar system for the vast vast vast majority of civilization. And even if one escapes their own solar system and starts anew on a new home world, they most likely will not colonize another. The space is just so big, and habitable worlds so far away from each other that I find it extremely improbable that any civilization (and their ancestor civilization) will survive more than 5-6 colonization (by far most will see 0).

> Living beings are the same.

They are not. You are describing living beings like viruses (fair enough; viruses are worthy to be considered lifeforms) that spread from host to host until they infect everybody. But viruses don‘t behave like that. The vast majority of them only infect their closest neighbors, and those that do spread towards the limit of all members of the species (like Covid) still fall short and eventually start to slow down their spread in a logistical manner. Growth only looks exponential while you are at the initial stages of spread. This behavior is not only common among viruses, but in fact most population dynamics can be described with logistical growth.

[pfdietz]

> von Neumann probes are a fantasy.

Well pack it up folks, we've been told what would be possible for any alien civilization, even given millions of years of effort.

[runarberg]

Yes, theorizing a future possibility that has no president is, by definition, fantasy. I mean, you can do fantasy, it makes good science fiction, but until we have evidence that von Neumann probes exist and are capable of colonizing the entire galaxy, it remains fantasy. Theoretically we could build a high speed rail between Seattle and LA, we could build a permanent settlement on Antarctica, and we could replace our jet-planes with hydrogen powered flying wings, but until we do, a world with those things are just fantasy.

The only argument for von Neumann probes that I can think of is as a specific answer to the Fermi paradox. The universe should be filled with these probes, but since it obviously isn’t, we can infer that no civilization has reach the interstellar age.

I reject this framing, the Fermi paradox is only a paradox if you assume that space colonization is a thing that is not just possible, but inevitable. My solution to the Fermi paradox simply rejects this assumption. Civilization will not colonize definitely, they will do their space explorations with telescopes and targeted probes, and they won‘t build any von Neumann probes (at least not ones continue to replicate for dozens millennia).

Aside: I am aware of the irony that my description of civilizations outside of our solar system is also a fantasy.