So....where are they? (Fermi Paradox)

Great Debates
61

SPOOFE

It does say something about the existence of other intelligent species. It indicates they are at best far more rare than we originally thought. As mentioned here, many of the early SETI scientists were confident we would obtain confirmation of ETs existence within a few years. This diagram summarizes the results of SETI searches thus far. As it shows, even Earth-level Arecibo-class transmitters have been ruled out to about 1000 light-years.

As to the possibility of slightly less-grand empires, well let’s just say the odds are against it. If the semi-empire had a 1 million year advantage, that still places it within 0.01% of our development cycle. Unless there are only a precious few ET civilizations, you still would have another ET that would just expand around it.

Look at it from the other angle. If ET only had a 10% advantage, that would equal a 1 billion year headstart. If life began near a star like 47 Ursae Majoris, then followed the exact same development pattern as Earth, it would have a 2.5 billion year advantage. That’s a lot of time to get your act together.

There is currently no known scientific or economic principle that rules out interstellar spaceflight. Species evolving well outside the galaxy proper can be dropped from consideration without changing the conclusion, again unless there are only a precious few ETs. Now about the way humanity smells, I’ll just point out that not everyone shares your legendary personal hygiene exploits. :wink:

Finally, without sounding too much like a gushing schoolgirl, I have to admit how honored I am to have someone like The Bad Astronomer drop in and dispense some valuable wisdom.

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Hmmm. I am not sure how far back in the past you can extrapolate. Planets form from heavier elements, which are in turn formed in supernovae. So long time ago stars were all metal poor, and were gradually enriched. Our Sun may well be the part of the first generation capable of forming planets. The big question is just how long ago metals were common enough to form planets. My gut feeling is that it could have happened long ago (more than 2 or 3 billion years certainly) under special conditions, like in dense clusters, where supernovae would have been common. But this is not really my field.

Anyway, I am sure that planets could have formed more than tens of millions of years before our own. I honestly wonder if either we are the first. Disconcerting.

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Finally, without sounding too much like a gushing schoolgirl, I have to admit how honored I am to have someone like **The Bad Astronomer
** drop in and dispense some valuable wisdom.
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A gushing schoolgirl named harcdcore? Hmmm… maybe I’ll refrain from commenting. Anyway, that’s sweet. I’ve been thinking about this very issue a lot lately, because it’s so interesting, and for the first time we can actually back up assumptions with hard numbers. I can’t wait for the 1000th star to be found to have planets. By then we’ll have real statistics on planet forming, and maybe we can get a grip on how it works.

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D’oh! Within minutes (starting here: http://exoplanets.org/index.html), I found that 47 UMa is about 6.9 billion years old, 2.4 billion years older than the Sun. Now, we don’t know if the planet is rich in metals (it might just be a big hydrogen/helium gasbag) but it means planets do form that far back at least.

64

One is reminded of dear departed Pogo. “Either we are the most intelligent species in the Universe, or we aren’t. Either way, its a mighty sobering thought.”

Elucidators Conjecture of Universal Paranoia: In an infinite set of possible galactic civilizations, it is unlikely that each and every one is comprised of gentle Buddhists. Therefore, there is at least one Kzinti/Klingon civ. Radiating messages announcing your existence would be like spreading chum in the water where you swim. And that would account for the narrow timeframe, a new and naive civilization would broadcast its message only as long as it takes for the predators to detect such and arrive.

65

We’ve had a few classes of solutions to Fermi here. One I want to dispense with, the “they don’t feel like colonizing the galaxy” solution. Yes, if there are only a few dozen intelligent species in our galaxy it is certainly possible that humans are extremely atypical. But even if we are atypical that only matters if the number of intelligent species is very small. If the number is large, then there must be many such atypical species.

All it requires is ONE species in our galaxy that wanted to spread out. Since we know that life has existed on our planet for billions of years, it seems likely that life has existed on othe planets for billions of years also. So, if we assume that earth is somewhat typical, or at least not more than a few standard deviations from the mean, then it seems likely that some intelligent species would evolve on other planets sooner than on earth, and some later than on earth. What would be unlikely would be if they evolved at the same time. If there are aliens on Alpha Centauri then they are likely to be either more advanced than us, or less advanced than us. They are unlikely to have similar tech levels to us.

So, since SOME aliens likely evolved sooner than humans, and some fraction of those will be ABLE to colonize the galaxy, then it follows that one would have already.

Let’s examine the assumptions for what such a colonization would entail. It does not entail FTL travel or communication. It does not entail some sort of interplanetary government. It simply means that some people decide to take off and go to another solar system. If you are going on a space voyage to Alpha Centauri at .10c, then it will take you 40 years. Which means that you have to be able to build a space habitat that will function without resupply for 40 years. Which means that in order to colonize other solar systems you’d have to have the technology to live in space for extended periods…lifetimes in fact.

So, these galaxy hoppers aren’t exactly looking to colonize other planets. No, they are likely to want to colonize other solar systems. They already live in space, they just want the raw materials and energy from a different solar system. If we imagine that their original solar system is filled with habitats, then they just attached a rocket to a habitat and left, taking their home with them.

Anyway, the point of the Fermi paradox is to wonder which of it’s apparently plausible postulates aren’t true. I sincerely doubt that every other intelligent tool-building species in the galaxy wants to stay at home. Which means that perhaps there are many fewer intelligent tool-building species out there. Perhaps most intelligent species live under ice-capped moons of gas giants, and don’t ever develop the concept that other planets exist. Maybe most evolve in the ocean, and never use fire, and thus never get rockets. Perhaps life exists in riotous abundance in the universe, but “intelligent” life is freakishly unlikely. Perhaps there life exists everywhere but 99.9999% of it is only at the prokaryotic level. Perhaps life itself is freakishly unlikely. Well, chose your own assumptions.

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Then again, why do we assume that ET life forms have the same lifespans as we do? Planet-hopping to places 2,000 lightyears away is only impractical if one doesn’t live that long. This Island Earth is the only biological system we have ever seen, and things on this planet live from a few hours to a thousand years or more. Maybe ET life lives longer!

Just another wrench to throw into the machine :smiley:

-Soup

67

It’s not a bad assumption. Most large life forms on this planet have a lifespan measured in years. A small mammal might live just a few, through say 80 years for humans to 150 or so for some birds, turtles, etc. Given our chemistry and environment I think this is a fair assumption. Any life that is intelligent by our definitions will either live long enough to pass information down to later generations or have an efficient enough system to teach young that the lifespan is not as much an issue.

As I said before, I have a gut feeling that either we are alone, or there are lots of other civilizations. In things like this there are rarely just a few of something; there is either a singular event or lots of events. This isn’t scientific of me. However, if there is only one (us!) civilization, or are only a few civilizations, we have a trivial solution to Fermi’s paradox. Otherwise the question gets a lot more interesting… and more ambiguous.

68

Oh yeah, I forgot to mention the Saberhagen solution: Berserkers. Any civ that sticks it’s neck out with radio signals gets smashed and smashed hard by a xenophobic and nasty species. The only way to stay alive is to not make radio broadcasts. Too bad it’s already too late for us and the berserkers are already on the way since we’ve been radiating like a small star for a century. The other friendlier species would have warned us, but the only way to do that would be to send a radio message, which would bring the berserkers down on them. They are sad we’re going to be destroyed, but there’s nothing they can do about it.

69

Yes, the galaxy is very, very large. It’s also very, very old. So, any solution to the Fermi Paradox which just says “Hey, it’s a big galaxy” is probably insufficient.

Okay, here a hypothetical solution which I don’t think anyone has thrown out for discussion yet. At the Dawn of Time, billions of years ago, various forms of intelligent life evolved. Perhaps some of them were “stay at home” types. Others were ravening xenophobes bent on the subjugation or destruction of all other life. Others weren’t quite so bad as that, but were expansionist, and, left to go their own way, would have filled up the whole galaxy, and pre-empted later forms of life (i.e., us) from evolving in the first place without any need for messy xenocide. Finally, some species evolved certain ethical beliefs, namely that backwards primitive savages like ourselves should be left alone and given a chance to develop to least some level of their own quaint little native civilizations. Furthermore, life-bearing worlds, even ones without sapient life, should be left alone and given a chance to develop intelligent life. (Possibly star systems with no native life might still be open to interstellar colonization or exploitation.) There was some sort of conflict–military, political, or economic, or something we don’t even have the concepts for yet–and the last group won out. They established a Galactic Empire, or a Galactic Federation, or a Galactic Community, and they’ve been out there ever since. Note that, in this scenario, we don’t have to postulate that this particular set of ethics will be universally evolved by all intelligent species. It only has to evolve once, billions of years ago, and ever since, some species or group of species has been enforcing it on everyone else.

Although the Galactic Empire/Federation/Community clearly wouldn’t be utterly malevolent, in an Independence Day sense–because if it is, we’d already be dead–we might or might not like it very much. They might not let us colonize other star systems. Maybe even nearby systems are already taken. Maybe they’re sort of ethical, but also a little bit hypocritical and arrogant–i.e., they’re willing to leave us our own Solar System, and they were even kind enough to not move in and exploit it when the first survey ships reported the existence of native lifeforms billions of years ago–but they have already colonized and exploited all the other systems which didn’t develop native life. Sorry, humanity–no interstellar colonies for you!

Also, we can’t totally rule out the possibility that the Galactic Empire/Federation/Community has a system of ethics which states that all species of life should be allowed to develop their own culture, up to the point of inventing radio or interplanetary colonies or interstellar probes or whatever the cutoff point is, because Q’toonpharg doesn’t want a single sterile galactic monoculture; Q’toonpharg wants a glorious tapestry of cultures and peoples, all striving to achieve Q’toonpharg Nature and develop Q’toonpharg Thought, all for the Greater Glory of Q’toonpharg. Of course, once a civilization reaches the point where it may ethically be brought the Good News about Q’toonpharg–the invention of radio or interplanetary colonies or interstellar probes or whatever it might be–then naturally that culture will be brought the Good News about Q’toonpharg. And, naturally, Q’toonpharg does not permit Q’toonphargless heathens to run around polluting the Universe with their vile, Unq’toonphargly ways.

There’s no way of telling what the Galactic Empire/Federation/Community’s cutoff point for making First Contact with backwards species is. Maybe it’s radio, and the Galactic diplomatic team (or transmission) is already on its way, but they don’t have FTL, so it’s taking them a while. (If they don’t have FTL–and from everything we know, FTL is impossible–it will take tens of thousands of years for news to get around to the whole Galaxy. This is no big deal for a civilization that’s five or ten billion years old, but it probably does rule out any really highly centralized form of decision-making.) Maybe they’re waiting for us to contact them. Maybe the Galactic Federation already has a First Contact team of diplomats and exosociologists sitting on some planet orbiting Alpha Centauri, playing the super-advanced equivalent of Solitaire on their super-advanced equivalents of PC’s, saying “Well, they’ve had radio for over 2[sup]4[/sup] half-lives of cobalt-60 now–they’ll probably be here in another couple of microgalacticrotations.”

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MEBuckner, the main problem I have with the Cosmic Zoo hypothesis is the uniformity of purpose it requires from the alleged Galactic Empire. How could the entire empire mask all its movements and communications so effectively? Not everyone is likely to even care about doing so, even if it is possible. I can’t begin to imagine how they would mask the enormous energy outputs from the starship movements. Besides, we don’t appear to have any problem with affecting the development of other species right here on our home planet. It just seems too much like an ad hoc hypothesis.

Lemur866, I have a similar problem with the Dangerous Neighbor hypothesis you and elucidator put forth. It should also require a fairly massive empire to be able to kill off neighbors in a reasonable timeframe, and even if they all maintain radio silence, we should still be able to notice the starships. Furthermore, why not just colonize every system and “exterminate” any near-intelligent species long before they have a chance to pose a threat? This would seem to be a far simpler way to accomplish the same thing.

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I’m not imagining a malevelent empire here…just killer robots with radios and a lot of patience. They cruise through interplanetary space at .1c until they catch a radio signal. Then it’s a hard right at the nearest neutron star, and send a rock half as big as Ceres straight towards us. Of course, a couple of guys ride rock down to make sure it hits, but there goes the biosphere! That’s how the dinosaurs bit it. Of course, it wasn’t the dinosaurs they were after, but a species of intelligent ammonites. And the Permian extinction sure did a number on those crafty trilobites! Well let’s just hope they don’t figure out that the Earth is home to dolphins or we’re all finished.

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Well, if they don’t build an empire, they risk obliteration from another ET who does. Besides, why have the robots wait on radio signals? Why not just assign one to each system, and have them repeatedly reign down havoc once every 100,000 years per planet? Otherwise, they risk someone like us developing the ability to deflect incoming asteroids and learning of their dastardly devices before they can exterminate us. Then we most likely would set off on an expansionist campaign in order to eradicate them.

73

What I meant to say was:

  1. It’s likely that the central region encompasses many if not most of the 200 billion stars in the Milky Way Galaxy, and life as we know it cannot exist in this area, too much radiation, gas clouds, heat, etc., etc.

  2. Of the stars that are left, how many can support life? tens? hundreds? a few thousand?

  3. Of those stars, what is the mean time to cataclysmic events likely to push the evolutionary clock back significantly (like the ones that wiped out the dinosaurs several times).

  4. How many of the species that made it to scientience evolved into creatures that used tools (i.e. had hands, developed the inclination, discovered the required materials in workable form), and lived long enough to develop the technology to explore space. Our technology is driven by competition within the human race, without the crucial conjunction of technological and social development, we may have killed each other off or never have reached the moon.

  5. Who’s to say we’ll make it to the stars? We seem to have at least a few hundred years and perhaps many wars (chemical? biological? nuclear?) before we even get started, much less develop the technology and infrastructure for multi generational space flight.

  6. What are the chances that a civilization that starts a star trek will finish it. One giant x-ray pulse, or even a high speed rock during the trip could pretty much end it. How long does it take the home planet to find out? Do they still use the same language? Do they send replacements?

  7. What’s the START time for life in this galaxy? Could some event have occurred in the last 500 million years that would have exterminated all life in this galaxy, thus resetting the evolutionary clocks for all life to zero.

  8. Assuming someone makes it into space, you’d have to consider that they’d take the best and brightest, and continue to evolve technologically, socially, and physically as they travelled. By the time they get here, they may not be anything like the one’s who started the journey.

  9. Last one. Maybe they got our transmissions first, and decided to either go stealth or steer clear. Perhaps we’d be considered too violent to risk stopping by and saying hello. The neanderthals or the Egyptians may have made an interesting arthropological study, but we seem to be in the teenage years of our sociopolotical development.

We’re left with four possibility: There’s nobody there, They’re on the way, They already left, or, We can’t see 'em. I never took statistics, but it seems that the odds could be anywhere from really small to 50-50, determined by a host of factors we may not even be able to conceive of. It may be a thousand years before we have enough information to find an answer.

BTW, thanks for the welcome. Nice to find out there are others who think for themselves out here.

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AND

I understand & can cope with most of your arguments, but this one is driving me up a wall! We can have no idea of what type of technology is required for intersteller travel, so why do you assume we could detect the energy output of a starship? We haven’t even been able to detect Earth sized planets outside our solar system yet! This assumption seems to be an unwarrented leap, and it’s dragging your whole argument down. Can you either justify it, or please stop using it???

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I see people assuming that mankind would spread out across the galaxy given the chance, and using that to justify the position that some alien races would do the same. I don’t see it. Man only seems to expand when there is pressure to do so. Long before we have the technology to colonize other star systems we will either have our population under control or have ways of handling it. Maybe we will all be absorbed into our computers before then, it seems logical.

Any spacefaring race will have computers of some kind. Being intelligent they will realize the many uses computers have. Finding better ways to interface with said computers would be desirable to any race that has them. Considering processing power doubles every 18 months, who can predict what influence this technology will have on our lives and ways of thinking in the future. Why expend so much energy exploring space when people can simulate their own, much more interesting universe to explore and be able to ignore the laws of physics when traversing it?

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From what I have read here, I think it is fair to say that the Fermi Paradox is a statistical problem – that is, there have to be N ET civilizations, each with a certain probability of spreading at a certain rate for a very long time. What parameters will lead to a high probability that we would notice this spreading (by being visited, or intercepting transmissions, or by seeing any kind of large scale distant activity, or whatever)?

The real trouble with this kind of argument is the inability to quantify these parameters. I mean, the number of potentially life bearing planets is something you can take a crack at, but how do you determine the most probable rate at which a potential galactic civilization can spread?

At any rate, we are trying to estimate N. We know that the time involved is very very long, and if N were very very big, it’s probably fair to say the other parameters don’t matter that much. In that case, we should have noticed something. We haven’t, so N isn’t very very big.

So what? I mean, suppose N is four. It doesn’t seem to be a great inevitability, for all of the evolutionary, political, etc., etc., arguments already described, that they would be spreading at all, so we wouldn’t notice anything. But come on – four intelligent civilizations is enough to blow my mind.

All there has to be is one besides us for it to be interesting. If there is at least one other galactic civilization, and we stick around enough, and both of us are doing our expansion thing as fast as possible, then we have a chance of encountering each other. But even a race much older than our own has many obstacles in the way of total expansion.

The main point here is that we may need a large sample size for Fermi’s Paradox to have any validity, but large sample size isn’t necessarily what we’re trying to establish.

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frinkboy, I think if you will read all of my posts in this thread, you will find that I have justified my reasoning for starship detection. First, the light from the planet’s nearby star is what prevents us from being able to detect an Earth-sized planet outside our solar system. This is why NASA proposes to build an interferometer to “cancel out” the light from the star and allow the planet to be observed directly. Interstellar starships by definition travel far from their original star system and would not suffer from this problem. Second, I have referenced the well-respected Dr. Zubrin, whose ideas form the very basis for the current Mars Direct plan in favor at NASA. Starting with the assumption that ET would not be able to mask the tremendous energy output from a starship(or even care to), he then outlines the detectable ranges for various combinations of starship types and telescope sizes. If you care to, pick up a copy of his book I cited for a more detailed explanation.

Badtz Maru, the Lotus Eater stay at home hypothesis would seem reasonable if there were only a few ET civilizations. If, as Yumanite notes, the number N of ETs is large, we expect that somebody would have decided to venture forth. And as The Bad Astronomer so aptly noted, if N is not large, then it starts to become far more likely that N=1. Not conclusive mind you, but certainly the most probable solution. Regardless, we must continue with our search for ET, for even a negative result is important.

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I think there are plenty of reasons why intelligent life hasn’t come knocking on our door. I’m sure most of these examples fall into one or another of the above theories, but just in case we’ve missed a few, here’s the short list.

The Greg Bear Hypothesis #2: Intelligent life abhors competition. Start buzzing around in the electromagnetic spectrum and someone will notice, and kill you. We’ve only been prattling on for a century, but the planet-eating singularities may already be on the way.

Non-electromagnetic spectrum communication: The Galaxy Overlords communicate by means other than those which we now suspect. Possibilities might include as-yet undiscovered gravity waves, tachyons, separated particle pairs, etc. We don’t hear them, and they don’t listen for us because we compete with all those loud heavenly bodies.

Faster-than light travel: In two hundred years we’ve gone from nearly undetectable (to our own devices) wooden sailing ships as our fastest means of travel to chemical rockets. Are we so arrogant as to believe that there is no other means of travel yet to be discovered, one for which we are not currently searching? Why should we, as observers, be able to see the aliens flitting about? And why would aliens allow us to see them if the universe is in fact a dangerous place?

Seen 'em, misinterpreted 'em, wrote books about 'em: What would a Bussard Ramjet look like to non-technological humans? A comet? The Star of David? A nova? A warning of the coming plague? Certainly the last explanation a historian would choose while poring over ancient Chinese astronomical observations is an alien spacecraft. So one hasn’t come by in the past 500 years, since we’ve really started looking hard. Well, we are kind of far away from the center of the action.

Who’s the observer, anyway? The aliens have a thriving galactic society, and are careful to allow the Earth Nature Preserve to develop largely on its own (save for the occasional visit by proctologists), to the delight of quintillions. The aliens communicate in the microwave band, so the Solar system is orbited by a cloud of noisemakers which mask the signals at 3-5 deg. K. This has led the so-called “humans” to create elaborate and highly entertaining myths regarding the creation of the universe…

Hydrogen, you fools! It’s plainly obvious that the debris surrounding the life-nourishing suns are not suitable for propagating intelligent life, and contain below-minimal levels of hydrogen needed to form any kind of life at all. Besides, how would intelligent creatures guide the path of their sun through the dangerous starfields?

Get a sense of perspective, Korg: A mere fifty thousand years ago, we did bump shoulders with another intelligent race, H. neandertalis. We forgot about them for 49,800 years. Heck, many of us don’t even know how to use significant figures. Perhaps we should be less confident about our ability to spot intelligence, here on earth as well as elsewhere.

“Pi” is baby-talk: What do you say to a toddler on the subway when he points at you and says, “da da?” All the really swinging aliens know that the hot chat is in the e-multiples.

(And an infinitude of other explanations.)

I can guarantee you one thing. The Critters will be found in a most unexpected way. Why? The chances of finding intelligent life that thinks or acts anywhere near the way we do are far lower than finding intelligent life that does things completely differently.

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I’m totally in Hardecore’s camp on this one. I think life is probably common, but intelligent, technological life is very, very rare and we are probably the first in our galaxy.

There may be too many bottlenecks. Life gets stuck as bacteria. If it makes it past that then it gets stuck on something else, etc, etc. Consider that mammals and dinosaurs developed at the same time and that if they weren’t wiped out completely, they would still be here. Didn’t they go through some major extiction events and still came back? When we get out there, I think we’ll find worlds stuck in bottlenecks.

However,

Whoever posted the ‘percolation theory’, thanks! I have not heard that one but it makes sense to me and maybe it is possible. I still find it unlikely but it is the first theory beyond the ‘we are alone in our galaxy’ that I feel has a possibility essentially not very close to zero.

Blink

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I am starting to doubt this hypothesis, to be honest.

If I abhor all other life, then the thing to do is make sure it’s destroyed before it can develop technology, right? That’s not too hard: design von Neumann machine, little spacecraft that are semi-intelligent. Scatter them throughout the Galaxy. They can even go sub-light. When they get to a planet, they scan for life, of any kind, or a planet that is able to support life. The little machines find a nice nickel iron asteroid in the system and then replicate themselves a few million times. They spread throughout the belt, strapping little rockets to the asteroids.

Then they set the rockets to bomb every planet in the system. There are enough asteroids in our belt to scour the life off of the Earth once a year for many, many years.

Then some of the machines spread out, finding more systems. They spread exactly like a virus. Even at 0.1c they hit every planet in the Galaxy in a few million years. Less, really, because they can scatter far better than humanity can. The diffusion math usually predicts us humans taking a megayear or so to populate the Milky Way at 0.1c. I bet it would take less than a million years for the machines, using just marginally extrapolated technology, to raise the temperature of every terrestrial planet in the Galaxy to the melting point of tin.

So I don’t believe in Berserkers, either, as much fun as the stories are.