4 ms·

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,

by puglr 4y ago

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.

pmontra 4y ago
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 4y ago
  Branching factor of two means around 30 hops to visit every star.
  - pmontra 4y ago
    2^30 probes at the final hop. Maybe those FTL ships will turn out to be cheap to build like in Vance's Demon Princes novels.
jjoonathan 4y ago
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.
- chrononaut 4y ago
  > 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?
  - yreg 4y ago
    Yes, but the parent means we are 13.7B years late to the party. Other civs should have been spawned before Earth was formed.
  - jjoonathan 4y ago
    The formation of Earth wouldn't have been the starting gun for alien life evolving somewhere other than Earth.
- withinboredom 4y ago
  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.
  - jjoonathan 4y ago
    > A pissed off colony in the asteroid belt can sling asteroids at the home planet If planets become indefensible then people simply won't colonize them. Problem solved. They'll stay in artificial habitats, and I would expect this to accelerate the colonization of the galaxy, if anything, because then they wouldn't need to wait for a planet to fill up before sending out the next generation of colony ships, they would just need to wait for the prime asteroids to be claimed. > the speed of light is quite limiting in every aspect Yes, exactly, and the non-interaction limit only needs one ship of space mormons to become exponential growth Diffusion-limited exponential growth, to add the next layer of modeling sophistication, but the ultimate point is that you still don't need all that many generations before the galaxy is full. Just multiply the number of steps by generation time, and if you are tempted to pick a really long generation time, remember that space mormons get a vote. > 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 Come on, the reason is resource competition.

by puglr 4y ago

pmontra 4y ago

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 4y ago
Branching factor of two means around 30 hops to visit every star.
- pmontra 4y ago
  2^30 probes at the final hop. Maybe those FTL ships will turn out to be cheap to build like in Vance's Demon Princes novels.

jjoonathan 4y ago

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.

chrononaut 4y ago
> 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?
- yreg 4y ago
  Yes, but the parent means we are 13.7B years late to the party. Other civs should have been spawned before Earth was formed.
- jjoonathan 4y ago
  The formation of Earth wouldn't have been the starting gun for alien life evolving somewhere other than Earth.
withinboredom 4y ago
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.
- jjoonathan 4y ago
  > A pissed off colony in the asteroid belt can sling asteroids at the home planet If planets become indefensible then people simply won't colonize them. Problem solved. They'll stay in artificial habitats, and I would expect this to accelerate the colonization of the galaxy, if anything, because then they wouldn't need to wait for a planet to fill up before sending out the next generation of colony ships, they would just need to wait for the prime asteroids to be claimed. > the speed of light is quite limiting in every aspect Yes, exactly, and the non-interaction limit only needs one ship of space mormons to become exponential growth Diffusion-limited exponential growth, to add the next layer of modeling sophistication, but the ultimate point is that you still don't need all that many generations before the galaxy is full. Just multiply the number of steps by generation time, and if you are tempted to pick a really long generation time, remember that space mormons get a vote. > 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 Come on, the reason is resource competition.