I’m not talking about self-replicating nanobots. IF all intelligent civilizations accidentally produce self-replicating chemical ecophages well before they would develop a space-surviving, ecophagic nanobot then this would be consistent with Fermi’s Paradox.

> And what self replicating chemical did you mean?

Obviously this is unknown since we don’t have a self-replicating ecophagic chemical in existence right now. But, if you program a tabletop molecular manufacturing machine to produce chemical of ever increasing size, I think that there is a possibility that at some point it will produce a self-replicating ecophage.

But it seems as though we are rapidly approaching self-replicating technology on a number of fronts (e.g. biotech, nanotech, AI, and self-replicating chemicals). At the same time we are still very far from interstellar travel. So if our existential even also makes our solar system uninhabitable then this seems to me to be a plausible explanation for Fermi’s Paradox.

The EGR mission is a near-term interstellar mission proposal to deal with this scenario:

http://www.peregrinus-interstellar.net/index.php?option=com_…;Itemid=60

I think this may in effect be a sort of selection filter. I would like to be hopeful that we’ll survive this stage but sadly I fear the odds are not on our side.

For those that do, there could be many reasons why they then don’t expand or choose to limit their expansion. They could have achieved some sort of long term stable, static society. Or they might consider that those who left would develop soon to be unlike them (their own aliens) and so at best they might lack the motivation. They might fear the future potential risk of extinction from them would outweigh any benefit, including reduced risk from solar flare, supernova ect. Or they might choose to limit their expansion in order to try and remain ‘hidden’ and reduce the risk of coming into contact with other aliens even knowing that they themselves might be the first. Or they might have developed some form of Unity, which limits them from expanding over too large a volume or too high a population.

It’s possible that some do expand more widely, maybe throughout their whole galaxy and beyond. They or their probes could be observing us now. They might intervene or make contact with us as we become more technologically advanced. Again, there are many reasons why they may not, at least during our current stage of development.

They may have developed to be non — violent (through the earlier selection filter — and their internal unity and even survival may depend on applying that even to us). Related to this they may not want to interfere with us in any way which might bias the way that filter applies to us one way or the other. Or being so far ahead of us, it is possible that we can’t ever compete with or threaten them (which needn’t necessarily limit our expansion, as they may be using different resources, or only a limited proportion of them, or leave for some reason) Another possibility is that our greatest value to them, is to be able to observe us and our ‘natural’ development without them damaging, limiting or ‘polluting’ it. Perhaps they are comparing us to others and their own distant history.

That last would be my preferred scenario. Or that we might even be first, and can survive our risks of extinction (greatest currently being from ourselves) and find we can still develop and expand and be doing this ourselves.