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The paradox is that if we make seemingly reasonable assumptions/estimates about all the factors required for advanced aliens to occur, there should be many such

The paradox is that if we make seemingly reasonable assumptions/estimates about all the factors required for advanced aliens to occur, there should be many such civilizations - and if we observe that there aren't any, then it implies that some of these assumptions are very, very wrong. However, since the initial Fermi discussion we have gathered some more evidence about the universe and these assumptions/estimates still seem reasonable, in some cases (e.g. the number of exoplanets) even larger than originally. So there is a contradiction, or paradox about that.

q1w2 4y ago
The unreasonable assumption is that aliens with hundreds of millions of years of additional development, would "colonize" planets like organic creatures and fly around like Star Trek. It's entirely unreasonable to assume that we would be able to see aliens at all nor that they'd have any interest in US.
joe_the_user 4y ago
The paradox assumes "advanced aliens" having abilities we've never observed and which are impossible given current human technologies. These aliens have been imagined by essentially linearly extrapolating human technological progress and, European expansion across the Earth. Humans have explored the solar system and it's becoming clear to most people that off-earth settlements are unlikely to in the foreseeable future (despite certain people's claims). Colonizing near-space, if it happens, won't be like colonizing earth. Moreover, our current exponential increase in resource usage seems more like to destroy our species than to get us to space - if we fix that, the perceived need to get to get to space may much less once technology reaches the point it would allow us to do so. Basically asking "why can't we see the interstellar empires?". Well, maybe these don't exist even if many earth-like societies exist. Maybe "colonizing" other stars is uninteresting to any society that reach level where it would be possible. Maybe there really are hard limits to such endeavors or maybe we're alone at the moment (the limited time in the universe is a factor. Life on earth took a significant fraction of the universe' lifetime to develop and the earlier universe might have been life hostile).
- PeterisP 4y ago
  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.
mr_mitm 4y ago
> seemingly reasonable assumptions/estimate I challenge the idea that all the assumptions hidden in the claim that life is ubiquitous are seemingly reasonable. For instance, we don't have the faintest idea of how likely it is that eukaryotic life evolves from prokaryotes or if prokaryotes can themselves become complex life forms. Next, we don't know the likelihood of complex life becoming intelligent. It's not like this is some natural goal of evolution, at least as far as we know. It may have been an extremely rare accident here on earth. There are many more such assumptions, some of which Fermi could not have known about. But we shouldn't ignore all the progress we have made since then.
MrScruff 4y ago
I really don't see how we estimate f_l in Drake's equation? Other than knowing it's >0 I mean.

q1w2 4y ago

The unreasonable assumption is that aliens with hundreds of millions of years of additional development, would "colonize" planets like organic creatures and fly around like Star Trek. It's entirely unreasonable to assume that we would be able to see aliens at all nor that they'd have any interest in US.

joe_the_user 4y ago

The paradox assumes "advanced aliens" having abilities we've never observed and which are impossible given current human technologies. These aliens have been imagined by essentially linearly extrapolating human technological progress and, European expansion across the Earth. Humans have explored the solar system and it's becoming clear to most people that off-earth settlements are unlikely to in the foreseeable future (despite certain people's claims). Colonizing near-space, if it happens, won't be like colonizing earth. Moreover, our current exponential increase in resource usage seems more like to destroy our species than to get us to space - if we fix that, the perceived need to get to get to space may much less once technology reaches the point it would allow us to do so. Basically asking "why can't we see the interstellar empires?". Well, maybe these don't exist even if many earth-like societies exist. Maybe "colonizing" other stars is uninteresting to any society that reach level where it would be possible. Maybe there really are hard limits to such endeavors or maybe we're alone at the moment (the limited time in the universe is a factor. Life on earth took a significant fraction of the universe' lifetime to develop and the earlier universe might have been life hostile).

PeterisP 4y ago
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.

mr_mitm 4y ago

> seemingly reasonable assumptions/estimate I challenge the idea that all the assumptions hidden in the claim that life is ubiquitous are seemingly reasonable. For instance, we don't have the faintest idea of how likely it is that eukaryotic life evolves from prokaryotes or if prokaryotes can themselves become complex life forms. Next, we don't know the likelihood of complex life becoming intelligent. It's not like this is some natural goal of evolution, at least as far as we know. It may have been an extremely rare accident here on earth. There are many more such assumptions, some of which Fermi could not have known about. But we shouldn't ignore all the progress we have made since then.

MrScruff 4y ago

I really don't see how we estimate f_l in Drake's equation? Other than knowing it's >0 I mean.