Aww, no alien empires yet

[Rynn]

Your point about birth control and the like is well taken, but we can't know that it applies to all lifeforms.

Yeah that is a key condition of the fermi paradox: it just takes one species to try and colonise and in a relatively short amount of time they're everywhere. That mostly applies to the galaxy rather than intergalactic but doesn't change much. They needn't even colonise directly; another way of putting it is that it would just take one self replicating probe, tasked with building up the industry to dismantle all the planets and build a matrioska, and we have a K3 situation also in no time.

I remember when I first heard of the fermi paradox as a kid I thought it must be wrong because no species could have had the time to colonise the entire galaxy, even if they were a billion years old. Then it was pointed out to me that on the scale of the universe even slow speeds lead to the same effect. For example:

- Assume a VN probe situation
- Average travel time 100,000 years
- A 100,000 year Matrioshka construction time (assume for now every star is suitable)
- Only two (successful) probes sent out once the Matrioshka is complete

Even with that it only takes 7.8 million years to convert the entire milky way, a time scale 8 times less than that of the gap between now and the dinosaurs.