[puglr]

It routinely bothers me a bit that, IME, most IRL discussions of the Fermi paradox tend to omit this rather simple explanation.

Half the time it's brought up, FTL is offered as the solution. Which as best we can tell is fundamentally impossible.

That squishy or otherwise organic bodies are generally unable to travel interstellar distances has always seemed to me to be the simplest solution.

Assuming intelligent life is out there, surely there are civilizations that have destroyed themselves and so on. But lack of FTL travel would be a common constraint, regardless of all other scenarios.

[jjoonathan]

It routinely bothers me a bit that, IME, most IRL discussions of the Fermi Paradox settle on this rather simple explanation when the whole idea was that this "simple explanation" was extremely unlikely, pushing speculation to more complicated and interesting hypotheses.

Emergence of life on Earth took 13.7 billion years, galactic colonization should only take millions of years. We should not expect to find the galaxy half-colonized, as this would be a staggering feat of synchronization. We should find the galaxy completely full or completely empty. It seems to be completely empty.

[withinboredom]

I doubt a civilization could survive being multi-starred.

If you can expend that kind of energy, a pilot with a bad day can destroy the whole planet. A pissed off colony in the asteroid belt can sling asteroids at the home planet, etc.

I also think you’re making a lot of assumptions but the speed of light is quite limiting in every aspect. If it takes 40 years to send a message, you need to either live a ridiculously long time — in which case your birth rate will be quite low — or figure the colonization as a one-way trip. No one would colonize another star system just for kicks, there would need to be a reason and I can’t think of a reason to colonize an entire galaxy that would make sense for a whole civilization, especially when it takes multi-decades just to send a message one way.

[chrononaut]

> Emergence of life on Earth took 13.7 billion years

13.7 billion years? Isn't that the age of the universe, and didn't life emerge on Earth only after about a billion years?

[pmontra]

Even with FTL you have to know where to go. Let's say you do 100 solar systems per year (going somewhere close to the star and some local jumps to look around.) There are 100 billion stars in the Milky Way. It takes a billion years to sequentially scan the galaxy. Optimizations in the search algorithm to cut that number down to 100 years are left as an exercise ;-)

[bottled_poe]

Branching factor of two means around 30 hops to visit every star.