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I disagree that this requires "advanced aliens" having abilities we've never observed. Let's assume that a fictional alien race has the technology level we hav

I disagree that this requires "advanced aliens" having abilities we've never observed. Let's assume that a fictional alien race has the technology level we have right now and no significant advances happen after that, just the buildup of the infrastructure that we could build today but haven't yet built because we just invented it a few years ago. With this level of technology it seems entirely plausible that a planet will spare the resources to prepare a single 'generation ship' once every 1000 or 10000 years - like, if once every hundred generations a crazy billionaire decides to spend their wealth on this, it should be in the ballpark of what's possible; it doesn't require a consistent effort of the whole civilization, sporadic one-off actions every few millenia are enough. And within 10k-100k years of settlement, that planet definitely can gain the same capability. And that's enough - with this stagnant level of tech, and with this conservative rate of expansion, that alien race would still be expected to populate the whole galaxy long before the first hominids appeared on Earth. Of course, the species destroying itself is a valid argument - that's why this chance is an explicit factor in the Fermi Paradox.

joe_the_user 4y ago
Things that don't currently exist: * "Suspended animation" technology about preserve living humans indefinitely * Means of human being living a lifetime or giving birth in zero gravity. * Human made, fully self-contained, large-scare ecosystems, even on earth. Which is to say a "generation ship" would require considerable progress in either reliability of systems or the self-healing of systems. Moreover, such a ship with minimal tech would take even longer than the slow, slow movements of Voyager spaceship. And finally, if alien did occasionally put out things, by the huge cost and slow speed, it would be plausible to none have reached us yet. I mean, the hypothesis that Oumuamua is alien space junk seems plausible given that space junk would be first alien technological product one could expect. Maybe in 1000 years or 100,000 years, some slow, slow ship will limp into the solar system. That would be interesting.
- PeterisP 4y ago
  My point is that "one colonization of a neighbouring planet every 100k years" is a fast speed, not a slow one. A hypothetical alien civilization who got to intelligent life and space-capable technology 1% faster then we did would have a 45 million year head start on us. A hypothetical alien civilization whose development happened exactly like on Earth but on a star which is not as young as ours could easily have a 500 million year head start on us - those are the timeframes on which we have to judge whether they have enough time to reach us; and that is time enough to colonize every planet in the galaxy many times over even at those "slow" speeds. If we ever meet alien life and it turns out that their level of development is just 10000 years behind or ahead of ours, that would be a more unlikely coincidence than having the first stranger you meet have the exact same age and birthday as you do.

joe_the_user 4y ago

Things that don't currently exist: * "Suspended animation" technology about preserve living humans indefinitely * Means of human being living a lifetime or giving birth in zero gravity. * Human made, fully self-contained, large-scare ecosystems, even on earth. Which is to say a "generation ship" would require considerable progress in either reliability of systems or the self-healing of systems. Moreover, such a ship with minimal tech would take even longer than the slow, slow movements of Voyager spaceship. And finally, if alien did occasionally put out things, by the huge cost and slow speed, it would be plausible to none have reached us yet. I mean, the hypothesis that Oumuamua is alien space junk seems plausible given that space junk would be first alien technological product one could expect. Maybe in 1000 years or 100,000 years, some slow, slow ship will limp into the solar system. That would be interesting.

PeterisP 4y ago
My point is that "one colonization of a neighbouring planet every 100k years" is a fast speed, not a slow one. A hypothetical alien civilization who got to intelligent life and space-capable technology 1% faster then we did would have a 45 million year head start on us. A hypothetical alien civilization whose development happened exactly like on Earth but on a star which is not as young as ours could easily have a 500 million year head start on us - those are the timeframes on which we have to judge whether they have enough time to reach us; and that is time enough to colonize every planet in the galaxy many times over even at those "slow" speeds. If we ever meet alien life and it turns out that their level of development is just 10000 years behind or ahead of ours, that would be a more unlikely coincidence than having the first stranger you meet have the exact same age and birthday as you do.