The Straight Dope on Fermi's Paradox...

[njtt]

@Chronos

Just noticed this from the last page:You have to pick a definition of “civilization”, and then stick to it. You can argue that “humans” constitute a civilization, in which case we’ve already lasted for hundreds of millenia. Alternately, you can call, say, Rome a civilization, but then you’ve got to add a new factor in Drake’s equation for the number of civilizations an intelligent, tool-using species will form, and history seems to show that that factor is very large. What you can’t do is say “Well, civilization has arisen once on Earth, and history shows that civilizations on Earth only last a few hundred years”.

Nonsense, I am using the word “civilization” in a perfectly conventional sense and my argument does not depend on any equivocation on the term. Anyway, even if we use the utterly non-standard definition that you suggest, and call the whole of human history a civilization, my conclusion still follows: we have only very weak reasons to believe that a civilization’s technological progress typically continues indefinitely because we only know know of one example, it has not developed the technology to travel or communicate effectively over galactic distances, and there are good reasons to believe its period of rapid technological advancement will soon be ended by ecological collapse or nuclear holocaust.

On a more conventional definition of “civilization,” we know of lots of examples (precisely how many will depend on niceties of definition, but that is not the issue here) and none of them have lasted. In every case except the one still ongoing, we see a period of advancement (technological and otherwise) followed by decline, collapse, and a loss and forgetting of most of the accumulated knowledge and technology. We happen to be in the midst of a period of rapid advancement right now, but all the evidence shows that this is not typical, and that such periods end. A reasonable induction is that technological progress does not continue indefinitely. A more cautious conclusion (reasonable given all the unknowns) is that we simply have no idea of how probable it is that an intelligent species, given enough time, would develop galactic level technology, but it may well be extremely improbable.

But Fermi, and everyone else in this discussion, seems to assume that it is virtually inevitable that if an intelligent species is around long enough it is sure to develop its technology to the requisite level. That is simply an induction based upon extrapolation from the last few centuries of ‘Western’ civilization. A slightly wider view of what we know about the history of the human species - i.e., actually taking account of all the available evidence instead of just that portion that you happen to know best and that makes you feel good - soon shows that that induction is entirely unwarranted. Civilizations decline and collapse. Periods of technological advancement come to an end, and the knowledge is lost (until some later civilization rediscovers it). Thus, there is no reason to believe that intelligent aliens who have been around longer than we have will have, or even are likely to have, a significantly more advanced technology than we do now. I am not saying that it not possible that they would, but we have no good reason to think it likely.

[levdrakon]

@Triskadecamus

OK, how about a question we probably can answer.

How far away could we detect ourselves? What percentage of the heavens have we examined with sufficient detail to detect life exactly like our own?

Tris

Using our own equipment? I’ve read it’s no more than 20-40 light years before our signals fade into the CMB, and probably not at all since as you suspect, we haven’t searched but a small % of the heavens. Here’s another fun little article discussing the likelihood of someone as close as Alpha Centauri actually happening across something we’ve deliberately sent at them. The short answer: “hahahahahaha!”

[Voyager]

@njtt

But Fermi, and everyone else in this discussion, seems to assume that it is virtually inevitable that if an intelligent species is around long enough it is sure to develop its technology to the requisite level. That is simply an induction based upon extrapolation from the last few centuries of ‘Western’ civilization. A slightly wider view of what we know about the history of the human species - i.e., actually taking account of all the available evidence instead of just that portion that you happen to know best and that makes you feel good - soon shows that that induction is entirely unwarranted. Civilizations decline and collapse. Periods of technological advancement come to an end, and the knowledge is lost (until some later civilization rediscovers it). Thus, there is no reason to believe that intelligent aliens who have been around longer than we have will have, or even are likely to have, a significantly more advanced technology than we do now. I am not saying that it not possible that they would, but we have no good reason to think it likely.

The Drake equations take the lifetime of a civilization into account.

For the purposes of this discussion, I think it makes more sense to consider humanity as a civilization. Political systems and religions may vanish for ever, but science, math and technology build. There have been many civilizations that rose and fell over the past 2500 years, but we are still using math straight from the Greeks. While the state of Europe was such that the Greek and Roman knowledge couldn’t be used, most of it was locked away in monasteries for eventual rediscovery.

Barring a nuclear war, I think this will hold for most worlds.

[levdrakon]

@njtt

On a more conventional definition of “civilization,” we know of lots of examples (precisely how many will depend on niceties of definition, but that is not the issue here) and none of them have lasted. In every case except the one still ongoing, we see a period of advancement (technological and otherwise) followed by decline, collapse, and a loss and forgetting of most of the accumulated knowledge and technology. We happen to be in the midst of a period of rapid advancement right now, but all the evidence shows that this is not typical, and that such periods end. A reasonable induction is that technological progress does not continue indefinitely. A more cautious conclusion (reasonable given all the unknowns) is that we simply have no idea of how probable it is that an intelligent species, given enough time, would develop galactic level technology, but it may well be extremely improbable.

I really don’t think you can compare the human species with a tiny little subset of humanity called a “civilization.” Civilizations are nothing more than little experimental pockets of humanity, and it’s natural for some of those pockets to fail. The human species taken as a whole however, has marched inexorably to where we are now, and there are certainly good reasons to assume we’re going to make at least a little more progress before we fail, and it doesn’t really take much more progress for us to become capable of really amazing things.

[Shawn1767]

I keep thinking about this and I still think people aren’t taking into account simply how BIG the universe is. From what a lot of the discussions I’ve seen about this, it seems like most people are only considering our own Milky Way galaxy. When in reality a civilization could arise in any of the many billions of galaxies in the universe. Then, not only would they have to pick our star out of billions in the Milky Way, but they’d have to pick our GALAXY out of the billions of galaxies out there in the first place. It takes light to reach us from the furthest reaches of the universe billions of years at light speed, in other words, the entire life of the universe. Why assume a technological civilization would be able to colonize enough of the universe in the same amount of time, when even light takes billions of years to get here?

[levdrakon]

@Shawn1767

It takes light to reach us from the furthest reaches of the universe billions of years at light speed, in other words, the entire life of the universe. Why assume a technological civilization would be able to colonize enough of the universe in the same amount of time, when even light takes billions of years to get here?

I don’t think anyone is concerned with what might be going on billions of light years away. No one is assuming a civilization born 14 billion light years away would have anything to do with our finding life here in our galaxy.

[AdmiralCrunch]

I’ve always assumed that the Rare Earth hypothesis was a satisfying solution to the paradox, since we don’t know much either way. And there’s always been a kind of anti-Fermi paradox about getting contact from advanced civilizations. If intelligent life is rare, and only arises on earth-like planets orbiting Sun-like stars, then there’s probably no one close and advanced enough to find us. If it’s common enough that it arises on a wide range of planets, then there’s no reason to think we stick out as noticeable to anyone outside of 70 or so ly, and a notice and contact within 35 ly with the absolute best case scenario.

[levdrakon]

@AdmiralCrunch

I’ve always assumed that the Rare Earth hypothesis was a satisfying solution to the paradox, since we don’t know much either way. And there’s always been a kind of anti-Fermi paradox about getting contact from advanced civilizations. If intelligent life is rare, and only arises on earth-like planets orbiting Sun-like stars, then there’s probably no one close and advanced enough to find us. If it’s common enough that it arises on a wide range of planets, then there’s no reason to think we stick out as noticeable to anyone outside of 70 or so ly, and a notice and contact within 35 ly with the absolute best case scenario.

One problem I have with the Rare Earth Hypothesis, is conditions on early Earth were pretty crappy, with no O2, lots of volcanism, and frequent sterilizing impacts. Some scientists think life not only began much sooner than it should have, but life may have gotten started a few more times even earlier, and got snuffed. Conditions on Earth really weren’t all that special and Goldilocks was screwed. Life appears to be pretty tenacious, beginning the moment it possibly can, anywhere it can, and we keep finding life in places that surprise us.

[Tibby]

I, like a few others here, believe that the main problem with Fermi’s Paradox lies with erroneous assumptions: be it one, or in combination. For example:

Intelligence: we assume that alien intelligence (biological or technological), given enough time, will become advanced enough to master the vastly complicated engineering feat of interstellar travel. We look at the evolutionary growth of intelligence on Earth’s tree of life and assume that given the same time frame, the rate of growth will continue unabated. If it took 500 million years to go from the intelligence of a flounder to that of human being, then we should expect the intelligence potential of beings 500 million years more advanced than us to be as different from us as ours is to fish, right? Not necessarily, that’s just our biased assumption. Either the rate of change in intelligence potential could slow down significantly or worse, there could be an intelligence ceiling in the universe. Perhaps no alien species, even those with a billions of years head start on us, is smart enough to visit or even communicate with us.

Technology: We assume that technology will someday be capable of transporting matter or information over extremely large stretches of space in time frames and efficiently enough to serve the purposes of advanced civilizations wishing to make contact, right? It only took us, what, a few tens of thousands years to advance our rocket technology from thrusting spears into bison to a Saturn V rocket thrusting Armstrong, et al, to the moon. Our technology is advanced enough to visit our intra-solar system planetary brethren, and to do so in manageable time-frames and not inconceivably cost prohibitive. We tend to assume that the next step, local interstellar travel, is simply another technological hurdle to be easily mastered in due time, no longer, say, than the time it took us to get to where we are now from chucking spears. But, what if there are real limits to how far and how fast technology can advance? Perhaps a ship capable of carrying anything of importance hits a universal speed limit wall of only ~20% light speed. That would make visiting even our closest stellar friends every bit as boring as driving to ugly Aunt Betty’s way out in the country–something to be avoided at all costs. And, odds are good, I believe, that we’ll need to look further than locally interstellar before we can expect to find advanced civilizations. At non-local interstellar or intergalactic distances should we really just assume that technology, no matter how advanced, has the potential to transport matter or information with any type of accuracy and in time frames useful to any civilization? Perhaps not.

Our universe may be awash with civilizations much more advanced than ours, but if none exist who are smart enough, or have gadgets sophisticated enough, to contact us…well, don’t waste your time waiting by the phone.

[AdmiralCrunch]

@levdrakon

Life appears to be pretty tenacious, beginning the moment it possibly can, anywhere it can, and we keep finding life in places that surprise us.

On Earth. But Earth is one of eight planets in our solar system, the only one we have found with life on it. And we’ve only had technologically advanced life for 70 years. And 85 percent of the stars in our galaxy are red dwarfs. And any star that isn’t made of supernova remnants can’t have elements we know are necessary for life. And stars close to galactic centers are under too much radiation to support life. And elliptical galaxies don’t have a habitable zone. And planets without a magnetosphere aren’t shielded long enough to foster life. No matter how bad things get on Earth, it’s more conducive to space faring life than every other planet and star around us. I’m not saying the Rare Earth hypothesis is bulletproof, but it’s certainly plausible, ergo no paradox.

[Voyager]

@Tibbytoes

Technology: We assume that technology will someday be capable of transporting matter or information over extremely large stretches of space in time frames and efficiently enough to serve the purposes of advanced civilizations wishing to make contact, right? It only took us, what, a few tens of thousands years to advance our rocket technology from thrusting spears into bison to a Saturn V rocket thrusting Armstrong, et al, to the moon. Our technology is advanced enough to visit our intra-solar system planetary brethren, and to do so in manageable time-frames and not inconceivably cost prohibitive. We tend to assume that the next step, local interstellar travel, is simply another technological hurdle to be easily mastered in due time, no longer, say, than the time it took us to get to where we are now from chucking spears. But, what if there are real limits to how far and how fast technology can advance? Perhaps a ship capable of carrying anything of importance hits a universal speed limit wall of only ~20% light speed. That would make visiting even our closest stellar friends every bit as boring as driving to ugly Aunt Betty’s way out in the country–something to be avoided at all costs. And, odds are good, I believe, that we’ll need to look further than locally interstellar before we can expect to find advanced civilizations. At non-local interstellar or intergalactic distances should we really just assume that technology, no matter how advanced, has the potential to transport matter or information with any type of accuracy and in time frames useful to any civilization? Perhaps not.

You seem to be assuming that technology progresses linearly - however it actually progresses exponentially, at least so far. It took a lomg time to get from ox-carts to spaceships, but almost as long to get from ox-carts to trains. Trains to spaceships happened very quickly, aircraft to spaceships even more rapidly.

500 years ago explorers set off on multi-year expeditions. Today we send our robots on them. There is nothing impossible about us going.
Except resources - and if this world ever gets its act together and stops spending a large portion of its surplus wealth on guns and bombs, there will be plenty for going to the stars.

[levdrakon]

@AdmiralCrunch

On Earth. But Earth is one of eight planets in our solar system, the only one we have found with life on it.

It’s the only planet we’re aware of that has life, but that’s not the same thing as the only planet we’ve found, since we haven’t really looked yet. If we can find life over a mile underground encased in volcanic rock we’ve got a lot of searching to do before we make assumptions about the ubiquitousness or rarity of life in our system. Also, if we believe in habitable zones then it’s unfair to expect much life outside of Sol’s habitable zone.

And 85 percent of the stars in our galaxy are red dwarfs. And any star that isn’t made of supernova remnants can’t have elements we know are necessary for life.

Red dwarfs have habitable zones, and we’ve found planets around them already. We have found no red dwarfs without metallicity, which means most red dwarfs probably are the scions of supernovae. I’m not saying red dwarfs will be teeming with life, but there are lots and lots of candidate stars besides dwarfs.

And stars close to galactic centers are under too much radiation to support life. And elliptical galaxies don’t have a habitable zone.

I don’t really care about other galaxies, and our galaxy’s habitable zone is vast.

And planets without a magnetosphere aren’t shielded long enough to foster life.

You make it sound like magnetospheres are rare, but they aren’t in planets our size or larger, and it looks now like Super Earths are probably quite common.

[Tibby]

@Voyager

You seem to be assuming that technology progresses linearly - however it actually progresses exponentially, at least so far. It took a lomg time to get from ox-carts to spaceships, but almost as long to get from ox-carts to trains. Trains to spaceships happened very quickly, aircraft to spaceships even more rapidly.

500 years ago explorers set off on multi-year expeditions. Today we send our robots on them. There is nothing impossible about us going.
Except resources - and if this world ever gets its act together and stops spending a large portion of its surplus wealth on guns and bombs, there will be plenty for going to the stars.

Yes, I buy that technology has progressed more exponentially than linearly thus far, but I posit that it may not continue to do so and, furthermore, perhaps even grind to a halt with regard to significant improvement in intergalactic/interstellar travel or communication—and, not just for us, but for any and all advanced civilizations. We can’t simply assume that, since we’ve increased our travel speed from ~40mph (horse) to 252,792 km/h (Helios ll) in a little over a century, that it’s just a matter of time until we reach manned or even unmanned space flight speeds close to the speed of light. What if, for all practical purposes, space flight speed universally hits the ceiling at a mere fraction of light speed. With that type of restriction, it would certainly turn humankind off from the idea of intergalactic travel (committing mega-abundant resources on a project with no potential payoff for at least many millions of years is illogical—chances are we won’t even be the same species upon completion of the first leg of such a journey). Can we assume with any degree of certainty, if other advanced civilizations do exist in our universe, any of them will feel any differently or can play under vastly different rules than we do now or in the foreseeable future?

Perhaps intergalactic travel/communication is universally cost prohibitive. Perhaps multi-million year journeys are just too long for any advanced civilization to seriously entertain. Perhaps given millions of years to evolve past the point of humans, no civilization can reach the exponential or even linear growth potential many of us assume they will: instead of being the nearly omnipotent beings we imagine the most advanced beings in the universe to be, maybe they’re more like the Jetsons, enjoying their flying cars, video phones and robot maids, but scoffing at the frivolity of intergalactic/interstellar space travel. Just because we took an impressive evolutionary journey from single cell organism to human in ~3 billion years doesn’t mean we can turn into near gods in another ~3 billion.

[billfish678]

@Voyager

. It took a lomg time to get from ox-carts to spaceships, but almost as long to get from ox-carts to trains. Trains to spaceships happened very quickly, aircraft to spaceships even more rapidly.

.

On the flip side, basic spaceship and aircraft technology/performance has remained virtually stagnant for the the past 3 or 4 decades. They have both hit a real wall due to the fundamental laws of nature and which will only fall back IF we find some nearly magical power source that may well not exist.

If that power source does NOT exist, IMO about the only way we will get to even the very nearest of stars is if we can build space ships that last from anywhere from 100s to 10s of thousands of years. Thats a pretty tall order.

[BlinkingDuck]

@Chronos

You have to flesh it out a bit more before the paradox becomes evident. First of all, even at very conservative estimates, there should be a few civilizations per galaxy, or so (possibly millions or billions of civilizations). Second, it would only take a few tens of millions of years for a civilization to colonize the entire Galaxy. Third, tens of millions of years is not a very long time at all, compared to the time it would take a civilization to arise on its own on a planet, so for the vast majority of planets, one would expect civilization to come from elsewhere.

All that said, I’m not sure of a resolution, either.

Your very conservative estimates might not be conservative enough.

Solution to Fermi Paradox could be - we are alone.

The universe could be so hostile, so unfavorable to complex life that we are just some so extreme fluke that it just hasn’t happened elsewhere. If we do get out there all we may find is bacteria.

I hope this isn’t true but people that talk about this seem unwillling to face the possibility that it could be true.

What can stop a tech civilization…

Is is formation of stable planetary systems?

Is it that planets favorable to live get pasted so much?

Is it the development of life itself?

Is it the development of multi-cellular life?

Is it development of a ‘land’ life (or equivalent - where they can possibly harness energy our equivalent of fire)?

Is it the development of intelligence?

Is it the development of civilization?

Is it the development of technology?

Is it the stability of that civilization?

Is it the spreading of the civilization out into space?

===

All of these things, except 2 or 3 would fall to a large number numerical argument. However, my ‘gut feeling’ tells me that:

• The hard to get over step is the development of multi-cellular life. Life develops but stays simple and hardy because the universe is so harsh for more complicated life to develop.

• possibly the development of intelligence. This would be the best for us because this would mean life-filled worlds are out there.

I hope the above is wrong…but it could very well be true.

[Tibby]

Interstellar vs. intergalactic may be the most important factor to Fermi’s Paradox

Personally, I’m in the conservative camp of believing there are just a few civilizations per galaxy. So perhaps, here in our Milky Way: we have us Earthlings with our feeble supra-terrestrial modes of communication and our pathetic and barely utilized intra-solar system space travel (i.e. we’re not likely to find them); maybe a very advanced, technology-rich civilization who, though they could make contact, choose not to because they’re apathetic about non-productive endeavors (i.e. they won’t find us); and a couple of fully liquid-habitated civilizations (probably more common than land-living creatures in the universe, IMO) whose communications and modes of travel , though quite advanced for the medium they were designed for, simply don’t propagate through air or space—I doubt advanced whale-type beings, even if they evolved opposable fins, would or could make technology to be used in anything other than their water environment—(i.e. they can’t find us).

So, if those are the few civilizations we have in our galaxy, then, for all intents and purposes, the only space traveling/communicating civilizations, with interests in contacting other civilizations are inhabitants of other galaxies. And, while I believe Fermi’s paradox holds if there are supposedly large numbers of advanced civilizations within our galaxy (surely some would have mastered interstellar travel/communication and be in contact with us), I believe inter-galaxy travel is a whole ‘nother kettle o fish. Is it reasonable to expect to make contact with any of the few civilizations that may inhabit even our next closest galaxy, at a distance of ~2.54 million light-years, or any civilization in galaxies of greater distance, no matter how many there may be? As mentioned up-thread, I believe it’s reasonable to assume some universal restrictions to travel and communication exist and if one or more does (e.g. exceptionally long periods of time are important and prohibitive to any life form; multi-million light-year travel is prohibitively resource-expensive for any civilization; technology, no matter how advanced, has to abide by a sub-light speed limit, etc.).

That leaves the door open only for those civilizations that don’t mind committing hurtful amounts of resources and numbing amounts of time on a project they, and perhaps even their ancestors—if they speciate in a predictable time-frame—are likely to benefit from. If a civilization needs to spread out in preparation for its sun dying or even leave its region due to a local star going nova, surely it will simply travel to another sector of its own galaxy where it’s safe and peppered with enough planets to harbor all emigrants and their progeny. Even if a civilization had to flee a threatened galaxy, surely it would just skedaddle over to the next closest. So, unless a big black hole is about to eat Alpha Centauri, I don’t think we’re going to be visited any time soon.

[levdrakon]

@Tibbytoes

I believe inter-galaxy travel is a whole ‘nother kettle o fish. Is it reasonable to expect to make contact with any of the few civilizations that may inhabit even our next closest galaxy, at a distance of ~2.54 million light-years, or any civilization in galaxies of greater distance, no matter how many there may be?

Minor nitpick, but the nearest large galaxy is 2.5 mly away. Our nearest galaxy of at least 1 billion stars is actually very close. Canis Major Dwarf Galaxy is currently only 25K ly away, and only 42K ly from our galactic center. There are other close dwarf satellite galaxies too. The reason I bring it up is because we’re eating these galaxies, and they’re orbits swing pretty far around the Milky Way. A lot of stars end up in our galactic halo, extending the outer boundaries of our galaxy pretty far. If we were a spreading civilization, we could reach nearby galaxies much sooner than the other side of our own galaxy. Additionally, we could basically hitch a ride in nearby galaxies and let their orbits carry us to even more distance galaxies. So, if we ever encounter alien technology, I wouldn’t assume it has to be from our galaxy. Self-replicating probes could reach us from other galaxies in reasonable timeframes, relatively speaking.

[Naxos]

@Jim_B

This is something I have wondered for some time. What is the solution to Fermi’s Paradox? …

It’s not a paradox.

This is like a carbon molecule on a plant leaf on the plains of Siberia asking why they have not come in contact with other intelligent entities.

[njtt]

@Voyager

For the purposes of this discussion, I think it makes more sense to consider humanity as a civilization. Political systems and religions may vanish for ever, but science, math and technology build. There have been many civilizations that rose and fell over the past 2500 years, but we are still using math straight from the Greeks.

Knowledge does get lost when civilizations collapse. We cannot read Inca quipu or Minoan Linear A. The scientific knowledge of the Greeks only survived in part, and through luck, on the slenderest of threads. Many of the works of Aristotle, the most important source of such knowledge, may have only survived in one buried and forgotten copy for a couple of centuries. Most of the works of most of the Greek intellectuals are known only via small fragments quoted by later authors (if we know of them at all).

Anyway, from the Greeks to us is still only a tiny fragment of human history.

Barring a nuclear war, I think this will hold for most worlds.

And why bar that? It seems to me (as I said in my original post in this thread) that our current civilization is quite likely to end in either nuclear war of global ecological catastrophe (or both) before very long. Alien civilizations that get to our sort of level would probably face the same dangers.

@levdrakon

The human species taken as a whole however, has marched inexorably to where we are now

Nothing inexorable about it.

@levdrakon

and there are certainly good reasons to assume we’re going to make at least a little more progress before we fail, and it doesn’t really take much more progress for us to become capable of really amazing things.

Useful interstellar travel, or effective interstellar communication, calls for a lot more progress. Indeed, our current best science strongly suggests that they are impossible. That might not really be the case, but finding otherwise call for a major scientific revolution, which is not visible on the horizon.

[levdrakon]

@njtt

Useful interstellar travel, or effective interstellar communication, calls for a lot more progress. Indeed, our current best science strongly suggests that they are impossible. That might not really be the case, but finding otherwise call for a major scientific revolution, which is not visible on the horizon.

Well, define useful and effective. The technology we have today is more than capable of carrying on communication with a star 4 ly away. As for useful travel, I’m not sure words like useful or profitable are going to be primary motivators for humanity in five or ten thousand years. I highly doubt we’re going to be intra-galactic gold prospectors or anything. People have this romantic notion of humans being these wonderful, intelligent, curious, explorative naked apes who will invariably pack up the family in the covered wagon and head off looking for land and opportunity. That’s what is going to get us spread out around the solar system perhaps, but it’s hard to predict what will motivate us in the future.