Solution to the Fermi paradox?

[18-Till-I-Die]

The second would require either great distances (like: life bearing planets are VERY rare) or some kind of unknown mechanism (dark matter) preventing those signals/other stuff (unlikely).

You know i recall a video game, where the explanation was actually rather morbid in retrospect, the idea being that the universe is covered in this caul of extreme radiation (called the "Nectar Barrier"...it was a Japanese game) that killed anything that left a planet's atmosphere for more than a few months. So interstellar travel by ship was impossible, and no signals of any sort could readily penetrate this "Nectar" stuff.

Which is, like i said, rather morbid and dead-endish.

[Sky Captain]

The fermi paradox simply points out that there are questions we have to ask.
There is simplynot enough data to answer it.

As for solutions, there are only two:

-We are the only lifeform in our galaxy intelligent enough to send signals/do the other stuff descrived.

-There is something preventing those signals/other stuff

The first is arrogant, but it IS a viable solution - whether there are not enough planets, intelligence is rare for some reason or there is something wiping out civilisations - we simply do not know.

The second would require either great distances (like: life bearing planets are VERY rare) or some kind of unknown mechanism (dark matter) preventing those signals/other stuff (unlikely).

This is what I have always thought regarding Fermi paradox - we simply do not have enough data to generate viable answer. We don`t know how common terrestrial planets are, how many of those planets can sustain some sort of life, how likely it is for inteligence to develop, how likely it is for those intelligent beings to develop technological civilization capable of radio communications and so on.

It`s unlikely but possible that we are the only technological civilization in this corner of our galaxy. And I don`t think it`s bad if it turns out to be true. At least no need to worry about giant colonization ship from Type II+ civilization arriving in our solar system and treating us like construction workers treat ant nest.

[kinnison]

Some possible solutions:

1) Either biogenesis, or development of multicellular life, or same of intelligence, or same of technology, are more unlikely than we think at present - and we are it. Chilling thought. Posible reasons for the difficulty include the requirement for a large moon, and the event that created it, for life development. Or possibly that our solar system is unusually free of catastrophic events for some reason.

2) The religious types have been right all along, and life was created - just once, and right here - by some superior intelligence which might as well be called God. This does not have to mean that the Earth was created complete with all its life forms, fossils, radioactive decay products, etc. in 4004 BC.

3) There is some physical process, which we haven't discovered yet but will soon, which once discovered inevitably leads to the destruction of the world it is found on. (Something like the wilder imaginings of the anti-LHC fraternity, for example.)

4) Any technological civilisation inevitably discovers computers and solid-state circuitry and not much later nanotech, and promptly disappears up its own backside into some virtual universe.

5) The entire visible universe is actually a simulation run by some godlike entity for its own purposes, and the entity simply hasn't included other intelligent life forms in the simulation.

Any more?

[cosmicalstorm]

Ontologic transcendense combined with life being exceptionally rare always seemed like a good explanation to me.

[Dooey Jo]

Any more?

• Omnidirectional radio signals from a civilisation will be very weak and hard to detect at interstellar distances. Focused signals are very unlikely to be aimed at Earth, and it's even more unlikely that we currently will be listening in the right direction at the right time. Even then, there's no guarantee that we will be listening at the right frequency, and even then there's no guarantee that the signal will not be compressed and look very much like any other white noise. (SETI makes quite a few assumptions in order to narrow down their search, see)
• Could turn out radio signals are crap compared to some future technology, and most civilisations only use them for a few hundred years on average.
• ETs were here a while ago but they didn't like it, or had better things to do, and left. Since there were only a few of them, any artefacts they may have left behind were destroyed by the environment, or we just haven't found them yet, or we found them but thought they were something else and melted them down to make swords.

It's not really a paradox unless you assume that our knowledge in these areas is somewhat complete. The "no artefacts, therefore no aliens" argument assumes that we have a fairly complete archaeological record of the whole solar system, which is clearly ludicrous. We don't even have anything near that for our own planet.

[kinnison]

Dooey Jo, the problem with your answer is that radio signals and left-over alien junk are assumed to be the only possible evidence of ET civilisations; and that is simply not true. As an example; exponential growth (which has held here at least for several centuries) leads to a Dyson swarm here in maybe 300-400 years - which is an absurdly short time on the timescale of stellar lifetimes. A Dyson swarm is detectable from interstellar distances. It would probably show up as an extremely anomalous object that looks a lot like a red giant or supergiant - except that just about all its radiation is in the far infrared, and there are no spectral lines.

One more possible explanation of the paradox is that we are surrounded by type II civilisations, but interstellar travel (though not impossible) is only worth doing (because of energy expenditure and/or time required) if you have a really good reason - and we just haven't looked in the right places or in the right way.

With 2% growth per annum, assuming we don't kill ourselves off (and just read the news to find out how likely that is) and in 300 years or so we will be a type II. Assuming Moore's Law holds as it has for 50 years or so, and Earth will be transapient in less than 50. After that, the same power law works out to, at that same 300-year mark, 2^83 or about 1E25 times human-brain processing power in something the size of a desktop PC. Natural laws do not prevent this. And the growth is likely to be more than exponential, anyway.

If something like that wants, for some unfathomable reason, to hide then it will. In such a way that mere human-level intelligences will never find it.

[Dooey Jo]

As an example; exponential growth (which has held here at least for several centuries) leads to a Dyson swarm here in maybe 300-400 years - which is an absurdly short time on the timescale of stellar lifetimes.

That has as many implicit assumptions as the radio signals/visitation arguments; they're just centred around their energy needs and means of production, instead of their preferred means of communication or behaviour. And compared to broadcasting radio or sending lots of probes everywhere, building Dyson swarms that cover a star to such a degree as to be detectable is really difficult. They're more easily seen once they're there, but that doesn't help much if there are only a bunch of them in the whole galaxy.

[Ariphaos]

The Fermi Paradox, as others have already pointed out, goes beyond signals.

Now, the Milky Way has had enough heavy elements to form large terrestrial planets since ~9.3 billion years (reference). Our sun is ~4.6 billion years old. That means that there are (or should be) large terrestrial planets over 4 billion years older than Earth. Put it another way, if there are aliens out there, the oldest ones should logically have had a head-start on us of over 4 billion years.

They started forming en masse about 4.4 billion years ago. IE the Earth has a ~150 million year head start.

Not only that, but the Solar System coalesced rather quickly from its parent supernova.

So no... the hypothesis that we are relatively unique in the Milky Way is not a bad one, nor would it be terribly surprising. It may well be that we find complex life forming on thousands of other worlds, and the few that started before us were simply stunted for one reason or another.

Edit: Gah. Read the article. Still, an important part of the balance on Earth is that it formed quickly from the parent supernova and that there are studies that indicate the Galaxy only became 'habitable' 4-5 gya ago.

[The Duchess of Zeon]

Even if they died out long ago for some reason, they would probably have left detectable artifacts.

Possibly us? I would find it very amusing if life on Earth started because some alien spaceship from a civilization now a few billion years dead flushed their sanitation system into the ocean on Earth because the captain in charge of the exploratory mission was a lazy bastard who ignored the environmental contamination protocols. A few simple proto-bacterium get lose, and....

How's that for a created origin to human life? *snicker*

[Junghalli]

They started forming en masse about 4.4 billion years ago. IE the Earth has a ~150 million year head start.

Do you have a source for that? Cause it contradicts what the papers I've read say.

Any more?

1) Sapience is an evolutionary trend "run amok", like a peacock's tail, and therefore rare. Usually, the point of diminishing returns stops animals from getting intelligent enough to be sapient. Personally, this is my favorite.

2) Development of multicellular life is rare.

3) Most sapient species never make it past preindustrial level due to environmental reasons. There are a variety of possible ways this could happen, such as most Earthlike planets having much more water than Earth (a species restricted to tiny islands would be unlikely to industrialize), or having a more stable and lush climate (hence no incentive to become farmers) or having a harsher climate that discourages agriculture (think Australian aboriginals).

4) Most sapient species never think of the scientific method.

5) Most technological civilizations are not expansionistic because STL interstellar colonization is an expensive and unrewarding proposition.

6) Most technological civilizations collapse before they can colonize a tiny fraction of the galaxy's disk, or maybe even before they escape their own star system.

7) There is a hostile technological intelligence in our galaxy that methodically patrols the galaxy and destroys newly emerging technological civilizations.

8] They already colonized our solar system and then died out long ago, but they stayed in the Kuiper belt, which we haven't explored.

...

If you want more I could probably do this all day. Really, you could write a book with nothing but possible explanations for the Fermi Paradox of differing likelihood in it.

There's also the possibility that the true answer is a combination of different factors, which is where my money would be. Honestly, I don't understand why people always talk in terms of one Great Filter. Why not a dozen lesser filters that add up to one great filter?

It's worth noting that explanations like 3 through 6 work best if you assume that sapient species are already relatively rare (i.e. in combination with another filter further down the line). The problem with them is all it takes is one outlier to get back to having a paradox, and outliers are much less of a problem in a small sample size than a huge one.

[Ariphaos]

Do you have a source for that? Cause it contradicts what the papers I've read say.

I misread what you wrote - see edit.

[GrandMasterTerwynn]

They started forming en masse about 4.4 billion years ago. IE the Earth has a ~150 million year head start.

Do you have a source for that? Cause it contradicts what the papers I've read say.

Any more?

1) Sapience is an evolutionary trend "run amok", like a peacock's tail, and therefore rare. Usually, the point of diminishing returns stops animals from getting intelligent enough to be sapient. Personally, this is my favorite.

This one has some validity to it.

2) Development of multicellular life is rare.

This one I'm skeptical about. Multicellular life ought to turn up once there's enough free oxygen to support the level of metabolism required to sustain it. What may be more likely is that complex life doesn't always get the foothold on land needed to spawn intelligent animals. Presumably this happens because the planet in question is exposed to a higher level of meteoric bombardment than Earth is, has much greater orbital eccentricity, or not adequately stabilized about its axis of rotation, leading to drastic climate shifts of severe intensity.

3) Most sapient species never make it past preindustrial level due to environmental reasons. There are a variety of possible ways this could happen, such as most Earthlike planets having much more water than Earth (a species restricted to tiny islands would be unlikely to industrialize), or having a more stable and lush climate (hence no incentive to become farmers) or having a harsher climate that discourages agriculture (think Australian aboriginals).

This one has some merit as well. Up until about 10,000 years ago, Earth's dominant sapients were mired in the Stone Age. For that matter, the most successful obviously sapient species on Earth, in terms of extent, and duration of the species, was Homo erectus and his various subspecies, which originated around two million years ago and survived clear up to just 50,000 years ago.

5) Most technological civilizations are not expansionistic because STL interstellar colonization is an expensive and unrewarding proposition.

This one has been among my personal favorites. The only reason for any Type II aspiring species to attempt interstellar colonization is as an insurance policy for the ongoing survival of their species. Expanding because you're running out of room at home isn't going to work for a Type II, because given the carrying capacity of an entire solar system, you can't possibly export sapients fast enough to put any appreciable dent in the system's population.

6) Most technological civilizations collapse before they can colonize a tiny fraction of the galaxy's disk, or maybe even before they escape their own star system.

Given how many pitfalls a civilization seems to have to be able to survive just to get over the threshold of being a Type I, this may have some merit.

7) There is a hostile technological intelligence in our galaxy that methodically patrols the galaxy and destroys newly emerging technological civilizations.

No. Homogenizing the galaxy just doesn't work. Logically, such an intelligence should wipe out planetary ecosystems before they show signs of technological civilization, since between the time you see a technological civilization's birth cry, and the time your STL berserker fleet turns up to kill it, they'll likely have progressed to the point of effectively shooting back. The fact that we're here tends to suggest that there hasn't been an interstellar xenocidal civilization around in hundreds of millions of years.

8] They already colonized our solar system and then died out long ago, but they stayed in the Kuiper belt, which we haven't explored.

Why would they do that? Better to get into the inner solar system, where the insolation is much higher. If any other civilization colonized the solar system sometime in the murky past, then evolution here would've taken a noticeably different track. Not to mention once you get above Type I and start working your way to Type II, there isn't a whole lot out there that could kill you.

[Samuel]

Even if they died out long ago for some reason, they would probably have left detectable artifacts.

Possibly us? I would find it very amusing if life on Earth started because some alien spaceship from a civilization now a few billion years dead flushed their sanitation system into the ocean on Earth because the captain in charge of the exploratory mission was a lazy bastard who ignored the environmental contamination protocols. A few simple proto-bacterium get lose, and....

How's that for a created origin to human life? *snicker*

Another fan of Venus in a Half Shell?

1) Sapience is an evolutionary trend "run amok", like a peacock's tail, and therefore rare. Usually, the point of diminishing returns stops animals from getting intelligent enough to be sapient. Personally, this is my favorite.

I don't think so. Remember why it runs amok? It forms a positive feedback loop, which encourages the development of more intelligence. That would encourage, not discourage the formation of intelligence.

or having a more stable and lush climate (hence no incentive to become farmers) or having a harsher climate that discourages agriculture (think Australian aboriginals).

People don't become farmers because the climate sucks. The Mayans became farmers in a tropical rainforest, New Guinea developed farming independantly in the same climate, etc.

As for Australia, it is so resource poor due to the lack of recent volcanic deposits or glacier grinding down rocks. A whole planet cannot be like that unless it was both without tectonic activity and without variation in its tilt.

4) Most sapient species never think of the scientific method.

If there are multiple competing powers on a planet, one of them will in order to get an endge over its neighbors. Remember that the foundation of Western philosophy and thought came from Athens... which only had a free male population in the tens of thousands.

5) Most technological civilizations are not expansionistic because STL interstellar colonization is an expensive and unrewarding proposition.

Why not send out slow probes just to look around? The cost is much cheaper.

6) Most technological civilizations collapse before they can colonize a tiny fraction of the galaxy's disk, or maybe even before they escape their own star system.

How can an interstellar civilization collapse

If you want more I could probably do this all day. Really, you could write a book with nothing but possible explanations for the Fermi Paradox of differing likelihood in it.

There's also the possibility that the true answer is a combination of different factors, which is where my money would be. Honestly, I don't understand why people always talk in terms of one Great Filter. Why not a dozen lesser filters that add up to one great filter?

Because most of the answers given simply don't work. Which is why it is a paradox.

[Guardsman Bass]

People don't become farmers because the climate sucks. The Mayans became farmers in a tropical rainforest, New Guinea developed farming independantly in the same climate, etc.

As for Australia, it is so resource poor due to the lack of recent volcanic deposits or glacier grinding down rocks. A whole planet cannot be like that unless it was both without tectonic activity and without variation in its tilt.

I think you are missing the point of the argument. One of the reason why humanity was able to develop as far as we did, arguably (I say "arguably" because there may be alternative paths to technological civilization that I'm not considering), is because we are land-based (meaning fire and other technologies are available full-time), sentient, tool-using (including that we have appendages to use tools), omnivorous (meaning that we can form sedentary populations that do agriculture and the like, and grow our numbers) primates. Even then, for the vast majority of both human and hominid existence, we were wandering bands of nomadic tool-users, only really settling down (as far as we know) in the past 12,000 to do agriculture and the like.

Even then, we spent nearly 11,000 years where most of us lived as peasant farmers in even the most advanced civilizations of any era, only really starting to escape from that in the past 1,000 years. Several civilizations over the past 3,000 years may have discovered at least different parts of the technology to escape from that via industrialization, but only one of them really did end up escaping it independently (the Europeans), and they either spread it to the rest of the world or caused other civilizations under threat to take advantage of it to do it themselves (I'm thinking Japan here).

Now apply that to a situation in which actual sentience may be very rare due to what Junghalli mention. To start with, your friendly sentient may not live on land - in fact, considering that most life on Earth lived in the oceans for billions of years before life gained any significance on land, sentients may be more prone to develop in the sea for all we know. Living in the sea means no fire, which severely limits your available tools (particularly tools that lead up to things like radio contact and space travel).

Your sentient could be an exclusive carnivore, meaning that anything like sedentary agriculture is out of the question. Perhaps they could get around that, though, if what they ate was something like bugs that cluster in cultivatable colonies in a single place at a time, but that's just a guess.

Your sentient may have no appendages for manipulating tools (particularly if they are sea-based), or possibly no need for them. Perhaps your sentient is something akin to a Utah raptor, and they don't need tools to hunt meat - they're born with their tools.

Even assuming that your sentient develops technology, there is absolutely no guarantee that they'll end up at radio communications and space travel. Perhaps many civilizations never go through the equivalent of an industrial revolution, either because they find a way to stabilize their numbers that doesn't involve disease, war, and starvation, or because they just never discover and make use of the technology, like several civilizations did in our case.

Can you see how this would narrow things down a bit, particularly if sentience is already rare?

[Junghalli]

This one I'm skeptical about. Multicellular life ought to turn up once there's enough free oxygen to support the level of metabolism required to sustain it.

Wasn't there a big spike in oxygen levels just before the development of complex life, probably caused by (IIRC) a major cooling event? Maybe such events are rare?

I don't think so. Remember why it runs amok? It forms a positive feedback loop, which encourages the development of more intelligence. That would encourage, not discourage the formation of intelligence.

Intelligence requires a big brain, which is metabolically expensive, and so may be selected against before it gets far enough for true sapience. Also, a hunter-gatherer species only really needs to be smart enough to make basic stone tools and fire. They don't need the intellect to build starships. You could have a species where the adult has intelligence comparable to a human 2-4 year old, and it would probably have simple tools and maybe fire and a simple pre-language and be very successful, but a species like that will never build a starship or a radio transmitter. And, as I said, a big brain is metabolically expense, so you don't want to be any smarter than you need to be.

It is worth noting that evolution had plenty of opportunity to make intelligent species before us, but as far as we can tell never did so.

As for Australia, it is so resource poor due to the lack of recent volcanic deposits or glacier grinding down rocks. A whole planet cannot be like that unless it was both without tectonic activity and without variation in its tilt.

Most planets could have much less water than Earth. With a sea level a couple of kilometers lower, the continents become high plateaus with a mostly uniform high desert/semi-desert climate. A culture living on such unproductive land would be hard pressed to develop agriculture. And there won't be any mountain glaciers either, which means no rivers, so no Nile, Fertile Crescent etc. type areas where a civilization could develop.

Alternately most planets could have much more water than Earth. A sapient species would be restricted to small islands (think Polynesia, but on a planetary scale). I doubt such a species could develop a high tech civilization. Intelligence could emerge in the water, but they'd be even worse off (no fire).

Just two possibilities I can think of, there are probably more. For instance, a lot of planets are likely to have extreme axis tilts (we don't because of our moon, which is probably a rarity). What would sub-zero winters and 150 degree summers mean for a sapient species living there? I imagine any primitives on such a world would have to spend a lot of their time storing up food or fat for the winters and summers.

And as well as environment, there's behavioral factors of the sapients themselves to consider. What if they're carnivores? You might get pastoral nomads, but the road to settled agriculturalism would be a lot harder.

If there are multiple competing powers on a planet, one of them will in order to get an endge over its neighbors. Remember that the foundation of Western philosophy and thought came from Athens... which only had a free male population in the tens of thousands.

The scientific method doesn't seem to come naturally to people, humans at least. Just look at how long it took for people to realize heavy and light objects fell at the same rate. In an alternate history, I wouldn't at all be surprised if it never developed until the next regularly scheduled ice age came along. As for the Greeks, I think they'd be a good example of a failure in this respect, except insofar as they laid intellectual groundwork for people who came after them. Remember, their intellectual tradition was dominated by abstract logic, not experimentation.

Why not send out slow probes just to look around? The cost is much cheaper.

People "just having a look around" aren't really a problem. A small probe could have passed through our solar system in Napoleon's time and we probably wouldn't know about it. The solar system could have been visited by millions of expeditions "just having a look around" before humans evolved or in our prehistory and we'd have no idea. It's colonization that's the problem.

How can an interstellar civilization collapse

The colonies collapse one by one for various reasons, faster than they send out new colonial expeditions. View it as a percolation problem.

[GrandMasterTerwynn]

This one I'm skeptical about. Multicellular life ought to turn up once there's enough free oxygen to support the level of metabolism required to sustain it.

Wasn't there a big spike in oxygen levels just before the development of complex life, probably caused by (IIRC) a major cooling event? Maybe such events are rare?

Development of complex life on Earth started right at the end of the so-called "Snowball Earth" era. But, even without that, if you've got photosynthesizing single-celled organisms converting the planet's CO2 to O2, you will eventually reach a situation where you've run out of readily available oxidizable minerals, causing a buildup of O2 in the atmosphere. Provided the planet is big enough to hang on to its atmosphere, and doesn't have anything happen to it to strip it of its atmosphere, a life-bearing planet will hit an oxygen crisis sooner or later.

Just two possibilities I can think of, there are probably more. For instance, a lot of planets are likely to have extreme axis tilts (we don't because of our moon, which is probably a rarity). What would sub-zero winters and 150 degree summers mean for a sapient species living there? I imagine any primitives on such a world would have to spend a lot of their time storing up food or fat for the winters and summers.

The extreme climate shifts caused by a wildly variable axis of rotation would tend to keep the most complex organisms confined to the oceans, I suspect.

And as well as environment, there's behavioral factors of the sapients themselves to consider. What if they're carnivores? You might get pastoral nomads, but the road to settled agriculturalism would be a lot harder.

It's hard to get a sapient pure-carnivore. By the time a species has 'picked' that route, it's become highly specialized in the art of chasing down and killing things for food. While the extra protein tends to fuel larger brains, the body modifications needed to get it tend to preclude tool-use, and the demands of chasing down all that protein serve to limit how big a brain a carnivore gets. Tool-using sapients will likely be highly-social omnivores. Mind you, this prediction is mildly anthropocentric, but these two factors would tend to produce an animal with a more generalist body plan with a brain suited to the conceptualization and transmission of large sums of data.

How can an interstellar civilization collapse

The colonies collapse one by one for various reasons, faster than they send out new colonial expeditions. View it as a percolation problem.

Barring Post-Biological Singularity/Nanotech/Bleeding-Edge Physics Experiment Gone Horribly Wrong(tm), an STL interstellar civilization should be nigh-on-unkillable. And even then, even if a civilization succeeded in converting its home system to paperclips through profound incompetence in self-replicating AI directives programming, its daughter colonies should be unaffected (assuming they get the memo to not install that last software patch.)

The only thing that might kill an interstellar civilization is ennui. They might decide that living in the real universe is a drag, and convert everything they can into planet-massed supercomputers, digitize themselves, and begin experimenting with some truly bizarre and incomprehensible trans-biological shit. And to ensure nobody bothers them, they might make these computers operate off of low-density, ambient energy sources, and distribute the processing power to a ridiculous degree, so as to make it indistinguishable from the background. Of course, the civilization wouldn't actually be dead, per se. Just no longer involved in the universe as we know it.

[Junghalli]

Barring Post-Biological Singularity/Nanotech/Bleeding-Edge Physics Experiment Gone Horribly Wrong(tm), an STL interstellar civilization should be nigh-on-unkillable.

It would be nearly impossible for it to all collapse in one go, but the various colonies could independently collapse one by one for unrelated reasons (from the usual things; probably chiefly war).

Like I said, it can be thought of as a percolation problem. The homeworld sends out X number of colonies before eventually its civilization collapses. The colonies are still there. Some of the colonies fail or eventually collapse for one reason or another without sending out new colonies of their own, others repeat the homeworld's pattern. As long as more colonies fail to send out colonial expeditions than do send out colonial expeditions, the colonization wave will fizzle out eventually.

Alternately, instead of collapsing they might simply give up colonization. Considering how expensive and economically unrewarding interstellar colonization is, that would hardly be a surprising thing for people to do.

[Samuel]

Now apply that to a situation in which actual sentience may be very rare due to what Junghalli mention. To start with, your friendly sentient may not live on land - in fact, considering that most life on Earth lived in the oceans for billions of years before life gained any significance on land, sentients may be more prone to develop in the sea for all we know. Living in the sea means no fire, which severely limits your available tools (particularly tools that lead up to things like radio contact and space travel).

I'm not seeing how this is different from Earth- whales and dolphins fall into this category.

Even assuming that your sentient develops technology, there is absolutely no guarantee that they'll end up at radio communications and space travel. Perhaps many civilizations never go through the equivalent of an industrial revolution, either because they find a way to stabilize their numbers that doesn't involve disease, war, and starvation, or because they just never discover and make use of the technology, like several civilizations did in our case.

Any group that finds a way to stabilize their numbers will be conquered by ones who don't and swarm them.

Intelligence requires a big brain, which is metabolically expensive, and so may be selected against before it gets far enough for true sapience. Also, a hunter-gatherer species only really needs to be smart enough to make basic stone tools and fire. They don't need the intellect to build starships. You could have a species where the adult has intelligence comparable to a human 2-4 year old, and it would probably have simple tools and maybe fire and a simple pre-language and be very successful, but a species like that will never build a starship or a radio transmitter. And, as I said, a big brain is metabolically expense, so you don't want to be any smarter than you need to be.

Except a bigger brain allows you to outhink your fellows and have more offspring. It is a trend that feeds upon itself.

The scientific method doesn't seem to come naturally to people, humans at least. Just look at how long it took for people to realize heavy and light objects fell at the same rate. In an alternate history, I wouldn't at all be surprised if it never developed until the next regularly scheduled ice age came along. As for the Greeks, I think they'd be a good example of a failure in this respect, except insofar as they laid intellectual groundwork for people who came after them. Remember, their intellectual tradition was dominated by abstract logic, not experimentation.

True, but lets not underestimate it- they discovered the existance of the atom and the like. Abstract logic is good for producing theories with experiments pruning them. Still, it isn't like the conditions in Europe that created the birth of the scientific method were extremely abnormal- given enough time they could happen almost anywhere.

People "just having a look around" aren't really a problem. A small probe could have passed through our solar system in Napoleon's time and we probably wouldn't know about it. The solar system could have been visited by millions of expeditions "just having a look around" before humans evolved or in our prehistory and we'd have no idea. It's colonization that's the problem.

I'm talking about large self-replicating probes that stay around. At least one civilization might have used that strategy- where are theirs?

It would be nearly impossible for it to all collapse in one go, but the various colonies could independently collapse one by one for unrelated reasons (from the usual things; probably chiefly war).

Why would they fight wars of extermination? Habitats are ridiculously fragile- I don't think any group would push it that far.

Alternately, instead of collapsing they might simply give up colonization. Considering how expensive and economically unrewarding interstellar colonization is, that would hardly be a surprising thing for people to do.

We are talking about a stage where there is enough energy available for individuals to carry it out on their own.

[Junghalli]

Except a bigger brain allows you to outhink your fellows and have more offspring. It is a trend that feeds upon itself.

It also means you need more food, and probably reproduce more slowly since you take longer to mature (all that brain development). If you're viviparous, it also means you're more likely to die in childbirth if you have any offspring that inherit the trait. There are disadvantages to it as well, heavy ones.

True, but lets not underestimate it- they discovered the existance of the atom and the like. Abstract logic is good for producing theories with experiments pruning them. Still, it isn't like the conditions in Europe that created the birth of the scientific method were extremely abnormal- given enough time they could happen almost anywhere.

Maybe, maybe not. It failed to emerge in other, older societies.

I'm talking about large self-replicating probes that stay around. At least one civilization might have used that strategy- where are theirs?

Well, that gets us back to the Paradox.

Why would they fight wars of extermination? Habitats are ridiculously fragile- I don't think any group would push it that far.

A lot can happen in thousands or millions of years... Civilizations self-destructing has plenty of precedent in human history.

[Samuel]

Maybe, maybe not. It failed to emerge in other, older societies.

Except the conditions were different... okay, that is obvious. In other, more static societies, there will still advance though. It just was slower. There were few truly static cultures.

A lot can happen in thousands or millions of years... Civilizations self-destructing has plenty of precedent in human history.

Mostly because the food runs out. Not going to happen to a space-faring civilization

[Junghalli]

Mostly because the food runs out. Not going to happen to a space-faring civilization

We almost fought a MAD-style conflict with the Soviets. We were smart enough not to do it, that time, but I'd say when it comes to the likelyhood of a technological civilization not engaging in MAD-type conflicts over timescales of millenia, I'm less optimistic than you. I can easily see it happening. And a war in space would be considerably worse than a nuclear war in terms of its ability to send civilization to its knees hard enough that it doesn't quickly recover, or even destroy the species entirely (in that solar system anyway).