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    Where Are The Extraterrestrials? The People Speak...
    By David Brin | July 19th 2012 07:30 PM | 54 comments | Print | E-mail | Track Comments
    About David

    David Brin is a scientist, public speaker, technical consultant and author of books including The Postman, Startide Rising, The Uplift War and Existence...

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    We live in times of extraordinary discovery. Exoplanets appear to be quite common in our galaxy. NASA’s Kepler Telescope has identified over 2,000 planetary candidates orbiting other stars. And yet the universe appears to be silent – at least when it comes to any detectable signs of alien civilizations, either at present in our galaxy or their remnants from the last couple of billion years.  

    And let’s be clear: it isn’t just the failure of SETI  (the Search for ExtraTerrestrial Intelligence) to detect radio signals that constitutes “silence.” Indeed, there are strong reasons to believe that they have been looking in the worst possible way. No, the greatest SETI Observatory has been our own planet Earth, which had an oxygen atmosphere for up to two billion years but with no inhabitants higher than a slime mold to defend it against external colonization.  Had alien visitors ever flushed a toilet or dropped a sandwich wrapper into Earth’s seas, the bio changes would have been huge and visible in our rocks.

    Physicist Enrico Fermi famously asked, “Where is everybody?” The Fermi Paradox or The Great Silence refers to this quandary of why we have never encountered extraterrestrial civilizations. I've written about all this extensively in scientific papers and in fiction, and my latest novel, Existence reveals dozens of scenarios about first contact.

    Many experts have weighed in with explanations for the Fermi Paradox, and I’ve observed a strange phenomenon among smart fellows like Stephen Hawking, Michio Kaku,  Paul Davies and such.  They all-too often seem to leap upon just one  hypothesis – a bizarrely premature thing to do, especially in the only scientific field without any subject matter.  I have chosen instead to spend the last 30  years cataloging and categorizing up to a hundred theories for the Great Silence.  But I won’t list them here.

    Instead, I recently crowd-sourced this question on the web; the top responses are presented here, ranging from the serious and thoughtful to the humorous and ironic.  Here are the top vote-getters… followed in each case by my comments.


    #1 We don't have the capabilities to detect anything but a tightly beamed signal. And like detecting the sound of a jet in the sky, where you can see it, is not where you can detect signals from it. You have to point your microphone behind it. With tightly beamed signals over galactic distances, you have to know the proper motion of the planet and its sun and they have to know our proper motion to beam it to us. If they are ten light years away, they have to beam it to where we were ten years ago and we have to point our detectors to where they were ten years ago. All the SETI searches ignore this and hope a civilization is sending out a ridiculously powerful beam in all directions.  –Tony Farley

    In fact, Tony, you are partly on-target with this one. But first, where you are wrong. SETI searches engaged in by the top group near Berkeley do compensate for motions and Doppler shifts and orbital variations to a degree that would amaze you.  They can detect a signal that is spectrum-varying with time and compensate for that as the source spins and rotates and revolves around a noisy star. These are clever folks.

    But you are right that they still make untenable assumptions. They search the sky with narrow listening beams... looking for aliens who might be BROADcasting hello signals in all directions, or else leaking their own broadcast conversations, prodigiously, into the sky.  But our own noise leakage has declined fantastically as human communications grew more efficient and channeled, since the 1980s.  

    As for those gigantor beacons, meant to teach newcomers? Well, there's no reason that even a beneficent race would do that, around the clock, for eons.  Horribly expensive.  They would, as you say, "ping" likely targets like our solar system, maybe once a century.  To detect such pings, we would need a system very different than the one that billionaire Paul Allen funded for the SETI Institute. Instead of one expensive SETI program in one place, aiming pencil-thin listening beams at one narrow patch of the heavens after another, we should have a thousand backyard receivers, networked, scanning the whole sky at once.  Look up Project Argus of the SETI League!


    #2 The universe is big in space AND time. It would be a major accomplishment for a technological society to remain intact for a million years, yet that is just a blip on the scale of the universe. How many galactic empires came and went before the Earth was even capable of supporting life? –Thomas Nackid

    A good question.  And yes, we might simply not overlap with the others in time!  But note, Thomas, your assumption is that the numbers of tech races must be very small (and that may be the case) in order for the statistical non-overlap idea to work.  But if there are numerous long-lived species, then we get the Fermi Paradox. And if they travel?  A lot?  Possibly colonizing as they go? Then all goes crazy in the numbers. Colonization changes everything!

    Even if they just explore and don't colonize, then the Earth would likely have been visited.  But even one toilet flush during the Archaean would have changed life on Earth in ways we'd detect in the rocks.


    #3 Life, even intelligent life, is common in the universe, but advanced civilizations are rare, and hard to find in the small window of time that we have been looking, and not all advanced civilizations are nice. Getting between stars and communicating between stars is hard, and having someone close enough to communicate with at the same time you're communicating is rare, and sometimes perilous. We have not found anyone yet because we can only shout at our nearest neighbors, and our local neighborhood is currently empty, probably by chance and possibly by malice. –Ilithi Dragon

    I am one of the SETI experts who has been arguing that the Great Silence may be telling us something.  "If all the races more advanced than us are being quiet... maybe they know something we don't know?"

    Several major voices in the field, Like former NASA SETI chief John Billingham, have joined me in resigning from major committees in protest over the SETI Institute's high-handed role in helping clear a path for METI or "MESSAGE to ETI" – actively beaming messages to space. See our complaint: Shouting at the Cosmos -- or How SETI has taken a Worrisome Turn into Dangerous Territory.


    #4 They won't unscramble the signal until we put a deposit down.  –Lone Hanks

    Along those same lines: We haven't yet chosen a intergalactic long distance carrier. --Christopher R. Vesely.

    Heh, you two may be saying this tongue in cheek.  But read Existence!  These thoughts can be re-expressed as real hypotheses that have a chance of explaining the Great Silence.  (I hope those passages will both make you laugh and make you think.)


    #5 The "Do Not Feed the Humans" sign just past Pluto deters all but delinquents making crop circles.  –Kevin King

    Uh-huh.  See my answer to #4.  Also a short story about alien “teasers” I wrote, called Those Eyes.


    #6 Civilized people do not just drop in uninvited. –Eli Roth

    We've been inviting!

    Along those same lines: There may be a "Prime Directive" ethos that they stick to. --Glenn Brockett

     

    That's the "Zoo Hypothesis" that comes in dozens of variations... all of which assume either that the ETIS are few and share the same value system, or else they have one heckuva police force...

    And here’s an intriguing variant on the same idea:


    As society gets rich enough and technologically sophisticated enough, eventually everyone is able to live in their own personal Matrix, customized to provide them with their ideal life. Soon after the civilization stops bothering to expand any further, as the perfect existence can already be found on their home planet and nothing more could be wanted. Humans have a rare neurological structure that prevents them from being satisfied with this sort of simulation. –Eneasz Brodski

    See also a discussion of The Great Filter: Does a Galaxy Filled with Habitable Planets Mean Humanity is Doomed? on io9 -- Robin Hanson’s concept that there may be some obstacle that consistently prevents species from reaching the technological stage where they can traverse interstellar distances.  Also, if you really hunger for more deep mind games, try the Transcension Hypothesis of John Smart.  Both very very very brainy guys.

    #7 We're an evolutionary simulation coded into some incredibly complex computer, and while there's enough computing power to model the behavioral and biological processes and interactions of all the life on planet Earth, there isn't enough to model intelligent (or otherwise) life for the rest of the universe, so they have to rely on simpler astrophysics algorithms. Maybe if that next grant gets approved, they'll be able to add in another few clusters and work on a "First Contact" situation... —Carter Boe

     

    A big concept, but also a bit of a Giant Waffle.  I have put some creative thought into it.  We’re all in a simulation is becoming clichéd… like all great ideas… even as it draws a growing following.  Speaking of which --

     

    #8 Our universe is part of a very advanced simulation in another universes cutting edge computer system. The system is designed to test out various theories of creation i.e. a big bang based on whatever the prevailing theories are - they then watch it all unfold and see how closely the results are to what these beings perceive in their "real" universe. this simulation has been tweaked and rerun many times because the results didn't quite match - the last time has been amazingly successful so they let it keep going and add memory and processing power as time goes by and as the simulated cosmos coalesced into our universe. They kept it running but tweaked it here and there and eventually decide to help form a world that can contain life similar to their own. Most of the computers' processing power in concentrated on resolving the detail and simulated life on that single simulated world. Every individual being, their thoughts and dreams, every bird that falls from the sky... They simply don't have enough memory and drive space yet to create "aliens" for us. (spoiler alert) in the "real" universe they never generated any speculative fiction so they haven't wondered in any important way at the coincidence... why are there no radio signals coming from intelligent life in their space? Until they read some sci fi created by the folks in their simulation...—Jim Simbrel

     

    Hmmmm you folks certainly glom onto a fashionable idea!  It was pretty fresh a decade a go!

     

    #9 We are, in fact, alone in the Universe. We are the first, We are the Progenitors of the great galactic civilizations yet to come. It's lonely at the top. –Tom Owoc

     

    For a related scenario, take a look at my short story:  "The Crystal Spheres."  And I don’t say it isn’t so.  A variant is this: we may be the first to survive our adolescence and move onward.  That is… supposing that we do.

     

    #10 Most societies evolved real-time communications using a fundamental principle or particle of physics we never discovered and thus never had to leverage the electromagnetic spectrum in this way. Radio is our solution to a problem no one else has and thus unique in the universe.  –Adam Maxwell

     

    Hm... well, maybe.  And yet when we found  out about and started using radio, did we completely abandon drums?  Completely?  Or even at all? New Guinea natives might not notice the radio waves all around them, but they'd recognize the thumping on a passing ocean liner as having human origins!

     

    #11 There are one or more paranoid, raptorial spacefaring species who attack, pillage, and destroy any civilizations whose electromagnetic radiation they detect. The only civilizations to escape destruction are those who have shielded their EM radiation sources from detection, by virtue of natural, innate caution, or from having learned of the dangerous aliens prior to developing electronic technology. For all other civilizations, they are detectable only in a narrow time window, until they are discovered and annihilated by the aggressors. This produces a relatively silent galaxy that may in fact harbor hundreds of sentient species. –Ed Uthman

     

    Very much a theme in Existence.  But also, again, have a look at this missive against METI: Shouting at the Cosmos…or How SETI has taken a worrisome turn into dangerous territory. We aren't saying this is likely.  We are saying that sensible people should discuss it before arrogant fools scream into the cosmos "Yoohoo!" on our behalf.

     

    #12 Given the scale of just our own galaxy, much less the vastness of the universe, the likelihood of anyone being in our celestial "neck of the woods" is slim at best. I'd propose that there's no paradox...if they're out there, they're just too far away.  –Jared Freeman

     

    True, we might simply not overlap with the others! But this assumes that the number of advanced races is very small in order for the statistical non-overlap idea to work.  But if there are numerous long-lived species, then we get the Fermi Paradox. And if they travel?  A lot?  Colonization changes all the numbers!

     

    #13 The civilizations that are advanced enough to communicate with us are too advanced to want to communicate with us. —Derek Whittom

     

    Hrm. So we're like ants to them?  Well there are still plenty of human scientists who are interested in ants.  You neglect how inherently interesting we are!  The number of new tech races appearing in the galaxy at any time is not comparable to ant colonies on Earth.  At absolute maximum it might be one or two a year. Any truly advanced race would deputize specialists, or robots, or lesser selves to look into and see what such newbies might have that's interesting or entertaining to offer.  And to inspect them for potential danger.

     

    Of course, they might do that in secret… 

     

    Good stuff.  What impresses me most among those of you who answered – and those of you who will continue the discussion here - is your mental agility and verve. Keep at it! Stay interested and lively.  And make sure that our politicians are forced to discuss issues of science and the future.  

     

    Never let us stop being a vigorously future-facing and scientific civilization.

    Comments

    my take

    there really is a God

    and he's like super slippery

    when he started we had like this little world floating in the firmament

    as soon as some schmucks start to question the nature of things God picks the coolest idea and extends the universe accordingly

    when someone thinks up the best way that aliens might appear and interact - pzzzzszzzttt - they'll be right there

    so the reason that there has not been any aliens is that nobody has come up with a sufficiently imaginative way for them to fit into the scheme of things

    God, being infinitely patient,

    is waiting

    pop

    Could you get in touch with your God for me because i my own world without all you murdering religious people. It only takes six days, is that right.

    I guess that means you did not like my idea then?

    It's funny - here i am an Atheist and highly educated (and old enough to know what that was worth)

    and i am watching a new paradigm emerge in the (mostly American) world - the screaming violent nutcases are swapping from being "Christians" to "Atheists" - like the person who commented on my comment - no brains, just violence - very much what i have come to expect of fundamentalism

    If the world moves to where the fundamentalists are the same nasty violent people waving an "evolution" flag it's time to stop being an Atheist at least by name.

    I've met almost 0 "New Atheists" who understand evolutionary science

    whats the difference between such people and the other wackos?

    zip

    pop

    Why would we be using radio communication in 2050? Today, most data goes through glass fibres, and local data is low power radio above 1Ghz. If we had dozens of colonies orbiting the sun, we would use lasers to send data. Most of that light would travel in the planetary plane, and not be noticed by anyone outside that plane. The ancient Voyager probes use radio, but how many light years away is that detectable?

    Hi. David Brin replying.
    First to PeakOil - you appear to be quoting almost directly from my Hugo nominated short story "The River of Time." Seriously You'd be amazed at the closeness of the wording, even! http://www.davidbrin.com/riveroftime.html

    Mr. Gisin I agree with you that efficient comms make it harder to detect leakage. On the other hand, when we become a race that expands into the solar system, colonizing moons and planets and asteroids, we will be using radio and lasers a lot! This is not a topic in which pat "answers" are often rewarded if you look at the big picture.

    With cordial regards,

    David Brin
    http://www.davidbrin.com
    blog: http://davidbrin.blogspot.com/
    twitter: http://twitter.com/DavidBrin1

    :-)

    i'll read it

    but i thought up the idea like 40 years ago - i guess it's like we all know - when an idea is ripe someone is bound to think of it

    pop

    Gerhard Adam
    I think the discussion overlooks one major issue; the organizational structure of the life forms.

    We tend to think in terms of intelligence, yet it is unlikely that humans are significantly more/less intelligent than our ancestors of thousands of years ago.  Yet, our civilization isn't a result of our intelligence, but rather our social organization.  The extreme division of labor is what has given rise to our achievements.  In effect, it is harnessing the human capabilities as a type of parallel processing [parallel brains] rather than depending on individual serial processing [individual intellect] to achieve results.

    Therefore, one of the key elements in finding an advanced civilization is that it must also have followed an evolutionary trajectory giving rise to such an extreme division of labor. 

    So the universe could easily be filled with intelligent life, but without the proper level of organization, it could never achieve a sufficiently sophisticated technology for space exploration.
    Mundus vult decipi
    Thor Russell
    There are three main possibilities that it could be, and some things that you can rule out.

    1. There is no other technological life (perhaps intelligent exists however) in our galaxy or nearby ones.

    2. Enforced non-interference. For whatever reason, the first civilization in the galaxy spread out and controls everything to the extent it stops other civilizations from interfering with each other. It could do this for ethical reasons, or simply curiosity to see how other civilizations develop. When such civilizations become space faring, they would either be forced to follow such rules themselves, or more darkly could outlive their "usefullness" and now become a nuisance from the point of view of the controlling civilization.

    3. Some kind of transcendence like situation where all civilizations lose the desire to expand. e.g. Matrix like cyber heaven etc. 

    I don't see how you can be sure which one of these three is the case, but its easy to have an opinion.

    In all logical scenarios, SETI is a waste of time. In #1 its obvious, in situation 2 it will be ignored by the controlling civilization, and other advanced civilizations will be forced/agree not to respond. In #3, no-one will be listening or care.

    Calcualtions with signal strengths from distant stars etc show that If aliens wanted to be found we would have found them, (and they would have found us much earlier) however if they don't want to be found or don't care, we won't be able to find evidence of thier existence.


    Some comments on the scenarios presented in the article:

    #1 No. If aliens are there they would have grown to control the whole galaxy and would know we exist millions of years ago. The scenario where aliens have been around for millions of years but not explored/colonized by some method but still listen to radio transmissions seems very unlikley. Sure interstellar travel is hard, but not that hard. There are no reasons to believe that replicating robot probes are fundamentally impossible.

    #2 Not true, once a civilization can spread to another star system, it can spread to many, nothing internal can wipe it out. Light speed limit etc would mean that even if things go wrong on one world its not going to stop it spreading. Even if all civilizations eventually collapse, it would have visited practically all the galaxy at some point.

    #3. Any advanced civilization could easily tell from miles away whether a planet has life from its atmosphere etc. There is no point in being quiet. It can't be dangerous, its just a waste of time.  Either the galaxy is completely mapped out by an advanced race by now or not at all. Other situations are statistically very unlikely.

    #7-8 etc, You can't disprove a scenario like this, not much point in saying anymore

    #10, No. They would still know we are here and would have decided not to interfere.

    #11. Very unlikely. Such a agressive civilization would have already colonized the galaxy or their part of it. They would know we exist millions of years ago. If they wanted advance notice of a technological race then their probes etc would already have detected that easily by our effect on the planet. They would have millions of years experience and wouldn't need radio signals to tell.

    #12. No, exponential growth would have made any expansionist civilization spread across the galaxy millions of years ago.

    Thor Russell
    Bonny Bonobo alias Brat
    There is plenty of evidence that there are Extra Terrestrials but they seem to be very wary of mankind, who can blame them?
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Interesting stuff. Can you explain this though:
    "Had alien visitors ever flushed a toilet or dropped a sandwich wrapper into Earth’s seas, the bio changes would have been huge and visible in our rocks."
    Is this just a humorous exaggeration? I can understand how E.T's creating monumental structures, or with a prolonged and/or numerous presence would almost certainly have left telltale signs behind (i.e. everything makes garbage), but why would micro-colonization, missions of exploration, accidental/unplanned visitation necessarily leave traces? Especially considering the use of local materials (as opposed to hauling it in) would be obvious.

    Thanks

    I think he means: Without life, rocks would be very monotonous and fairly uniform. The huge interesting variety of rocks we have on Earth is due in large part to the influence of microscopic life on the formation (and re-formations and re-combinations, etc etc.) of those rocks. If an ETI merely visited (say) a billion years ago, they would have "infected" the life already here and changed the course of the development of rocks going forward (getting in on the ground floor, so to speak). So we would have a different huge interesting variety of rocks. (I contend, there's no way to know if it did or did not happen, because I don't think we can know what the difference would be in the other; if it happened, we don't know what it would have looked like with only Earth-raised bacteria, and if it didn't happen, we don't know what it would have looked like with ETI infection).

    Gerhard Adam
    I contend, there's no way to know if it did or did not happen...
    Perhaps not, but even when we examine the most extreme micro-organisms, there is nothing to suggest that there is any different biology at work.  This means that there is nothing to suggest that biology was different before such a visit, nor that it changed after such a visit.

    This would suggest that either (1) any alien visitors shared exactly the same biology as existing life forms, or (2) alien visitors actually "seeded" life on Earth.

    So, while we can't know definitively, it does place a few parameters around the problem to consider.
    Mundus vult decipi
    I agree.

    I think looking at the makeup of rocks (that is, not looking or needing to look directly at the microorganisms themselves) pushes it even further removed from a place where you can tell if there is a difference (between flush/no flush). I think if ETI flushed a toilet here, we would have some differences in rocks than if he hadn't, but there would still be a lot of overlap (chemistry is apparently same everywhere), and no way to tell which was the case (flush or no flush). Let's say the flush happened: if the biology was not inherently different, then it might influence the rock formations and provide some kinds of rocks and minerals that wouldn't have happened otherwise (but there's no way to tell). If the biology was different (from what we have now), then it may have had some influence then died off; whatever rocks we have from such an episode must then be very rare indeed. If the biology was different and didn't die off, then we would now have two incompatible life systems on Earth. Another response from the author points out: we can see exactly when the life explosion started; if so, there was only one (not a flush, then die-off, then native emergence). Whether that explosion was native only, or native/ETI (or for that matter, ETI-only, a-la pan-spermia), I don't think we can tell, because we don't have anything to compare it to. Unless we find ETI, find out he definitely flushed here in the past, then compare our planet to his, we cannot know.

    Gerhard Adam
    Well, bear in mind that if an E.T. could leave microscopic traces, then the exchange would be two-way.  In other words, that would mean that any micro-organisms that existed on this planet would be picked up.

    This would be highly dangerous for any biological system, so it seems likely that no such exchange took place.  This reduces the likelihood of E.T. having "seeded" the Earth unless such an action were intentional.

    In that instance, then it begs the question as to where they have been, since it seems implausible that an advanced civilization would have invested the time and technology only to disappear?  Bear in mind that an intentional act of "seeding" would essentially question why no follow-up missions occurred.

    I don't accept the notion that such an advanced civilization would be terribly shy about announcing themselves even to our modern society.  Why should they be any more shy about it, then we are when we investigate any other species habitat or environment? 

    Of course, it is highly unlikely that a civilization could've "seeded" the Earth and still survived the billions of years as a society.  That would practically require a miracle.

    So, again, there is little reason or evidence to suggest that such an early visitation occurred.  It doesn't make it impossible, simply implausible.
    Mundus vult decipi
    They are here and they are communicating with mankind, one just needs to know where and how to look for them!
    http://www.educatinghumanity.com/2012/07/ET-on-Video-Communicating-with-...

    Gerhard, I do not ignore organizational structure; indeed I talk about it extensively. e.g. in Existence I speak to the coincidence of sapience developed by gregarious apes instead of, say, tigers or bears. But in this piece I was responding to a survey.

    There are hundreds of Fermi explanations. See more at: http://www.scoop.it/t/seti-the-search-for-extraterrestrial-intelligence

    Thor, thanks for being broad in your approach. My sole quibble is that you declare only three high plausibility Fermis. Sorry, there are about a dozen top-ranked ones... and more than 80 that descend into less and less plausibility,

    Error: Earth's TV broadcasts dissipate well before one light year.
    Error: " nothing internal can wipe it out" Sorry... a race that depletes the worlds it colonizes, callously and thoughtlessly, will be like a prairie fire sweeping the galaxy, dying out at each site, leaving ruin. It is a top-ranked "explanation."
    Error: " no point in being quiet. It can't be dangerous, its just a waste of time." Now you are just displaying lack of imagination.

    Helen: what evidence to you speak of? I have been investigating this all my life and have seen nothing even remotely credible, just nonsense eagerly clasped by the credulous.

    Elohein: We can see in our rocks almost the very moment that eukaryotic cells on Earth appeared, and then when they became capable of clustering in organisms. It changes the nature of the sediments. Believe me, we can tell when it happened on Earth. Question, was THAT episode the result of an alien toilet flushing? Ah, genealogy! ;-)

    Oh... but ALL of this... and much much more (!!) can be found (amid an exciting adventure novel) in EXISTENCE. (See the trailer: tinyurl.com/exist-trailer )

    Let's hope for good luck in the cosmos.

    With cordial regards,

    David Brin
    http://www.davidbrin.com
    blog: http://davidbrin.blogspot.com/
    twitter: http://twitter.com/DavidBrin1

    Bonny Bonobo alias Brat
    Helen: what evidence to you speak of? I have been investigating this all my life and have seen nothing even remotely credible, just nonsense eagerly clasped by the credulous.
    Unlike you David I had no interest in Extra Terrestrials until I saw a UFO very clearly with my own eyes and then closer up through a telescope. I described this incident on Science20 blogs here and here since then my own investigations have convinced me that ETs do exist but I can't be bothered to convince anyone else.
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Helen, every year the number of cameras and telescopes on earth approximately doubles. Doubles. Yet the "images" of UFOs remain always just a blurry, just as vague and ambiguous and subject to the mind's wild ability to exaggerate and amplify. And that isn't suspicious to you?

    Recall whom you are talking to. No one on Earth has explored the notion of the alien - both scientifically and in fiction - than I have. I do not dismiss the UFO thing completely. But if they are little green men, their BEHAVIOR toward us merits nothing but utter contempt.

    Bonny Bonobo alias Brat
    Helen, every year the number of cameras and telescopes on earth approximately doubles. Doubles. Yet the "images" of UFOs remain always just a blurry, just as vague and ambiguous and subject to the mind's wild ability to exaggerate and amplify. And that isn't suspicious to you?
    Did you read my links to Hank and Gerhard's blogs about UFO's above, in which I explained what I saw? It wasn't a blurry, vague or ambiguous image and two of us saw it at the same time, if it was subject to the mind's wild ability to exaggerate and amplify then how did we work together to focus the telescope on it?
    Recall whom you are talking to. No one on Earth has explored the notion of the alien - both scientifically and in fiction - than I have. I do not dismiss the UFO thing completely. But if they are little green men, their BEHAVIOR toward us merits nothing but utter contempt. 
    Really, I'm afraid I don't know much about you David, I hardly get much chance to read science fiction these days, I'm too busy listening to depressed and suicidal people, managing interventions and commenting here in between these and other pressing duties, I used to write blogs but no longer have that privilege here now, I am also studying at uni. 

    Anyway, who said they are little green men, not me and how does their behaviour towards us merit utter contempt? We are a very dangerous warring species that oppresses our own vulnerable people and is also causing massive extinctions of vulnerable plant and animal species worldwide. 

    UNICEF tells us that every year over a million children die from either lack of medicine or food that would cost less then a few dollars for each child to remedy. Globally, over 20 million people attempt suicide annually, millions of little girls worldwide are still having forced clitoridectomies and genital mutiliation without anaesthetics and with dirty knives and we kill millions of our young men and civilians in wars every century. 




    We spend billions on manufacturing weapons and hegemonic wars to utilise them and upon machines to smash particles but we can't even stop people from cutting down what's left of our native, indigenous forests, the lungs of the world. If I was an extraterrestrial I would also steer very clear of us and use my advanced technology and skills to evade detection by the authorities in charge of this collective global mess that we call humanity.
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Thor Russell
    Hi,There may be dozens of apparently possible fermi's put forward but that doesn't mean they don't fail because of some elementary error. Ones that aren't the 3 mentioned by me do fail for reasonably obvious reasons as I will point out. 

    Firstly #1. Nothing internal can wipe it out. A race that depletes the worlds it colonized would still colonize practically all worlds in the galaxy, and obviously leave a presence! Furthermore if you are putting that forward as a solution then obviously you are saying that is common, i.e. thousands of races follow this pattern. If you are saying there was just one race that did that, it doesn't count as a solution. Now if thousands of races had, then there would be an undeniable record of it on earth, and more likely we wouldn't be here at all because our planet would have been damaged too much for us to evolve. This cannot be a solution.
    #2. No I am not displaying lack of imagination. Put forward a believable hypothesis that disproves that. Any civilization with any kind of space faring capabilities that is interested would have known we exist for ages.

    #3. Why do you mention earths broadcasts dissipating at about 1 light year? what is your point, I never said they wouldn't. 

    In order for radio signalling to be worthwhile, it has to be so incredibly difficult to travel between stars that civilizations will sit in their local star system for thousands of years and signal rather than just sending exponentially replicating probes out if they desire contact. There is no reason to believe that interstellar travel is impossible so signalling is going to be a waste of time. 

    The idea of not attracting the attention of a race capable of interstellar travel is obviously illogical. If they are capable of travelling to one star system, then they can travel to them all. Their telescopes/sensors would be able to pick up that earth had life from light years away because of our atmospheric composition and they would have known that for ages.
    Thor Russell
    "How big and how old is the universe?"
    Well, let's say 1.5*10^13 lyrs. And about as much lightyears wide, as we can't see any further.
    What's interesting is however how many stages of development are necessary to achieve a level of complexity as we now indulge in. It's hard to beleive that any life can exist without 'metallic' elements. I've checked the solar granula, no life, because no significant sex.
    Metallic elements are only made in a significant amount after 2 times recycling in a supernova. That,s little chance, and a long time.
    10 billion about. So you got 5.000.000.000 yrs to place a possible planet in orbit. That's the time you'll find (or they) to meet an IT. Other constraints welcome
    . What's a Fermi anyway? A refutation of?

    Isn't it the case that nothing in the universe can travel faster than the speed of light? If that's the case, then wouldn't that set a "cosmic speed limit" on an alien civilization's ability to travel across the physical space of the universe? Given the enormous distances between the nearest stars of any type, perhaps the time involved in travelling the distances between Earth and the nearest other planets bearing any type of complex species capable of interstellar space travel or communication is such that not enough time has passed for them or their attempts at communication to reach us.

    To me, this explanation also seems likely given that a species would have to first evolve to the point where it is capable of even sending a spaceship or a communication, and then it would take possibly billions of additional years for any ship or signal it would send to actually traverse the distances involved. How big and how old is the universe? Has there been enough time in the history of existence to allow this to happen?

    Perhaps it is also possible that a complex alien civilization, knowing this, might conclude long before they ever reach the point of technological feasibility that the probability of achieving any results from such an effort is so miniscule and remote that it just isn't worth the expenditure of effort and resources that would be involved.

    Gerhard Adam
    ...might conclude long before they ever reach the point of technological feasibility that the probability of achieving any results from such an effort is so miniscule and remote that it just isn't worth the expenditure of effort and resources that would be involved.
    Sure, especially since the details of such an effort aren't typically considered very thoroughly, imagine the expense and commitment to find an alien civilization that in all likelihood would be pathogenic [i.e. everything about them would be biologically dangerous to you].

    Despite all the times the topic comes up, I have yet to hear of a single benefit that such an encounter would actually provide [other than the knowledge that there is other life in the universe].
    Mundus vult decipi
    [i]"an alien civilization that in all likelihood would be pathogenic [i.e. everything about them would be biologically dangerous to you]"[/i]

    That makes no sense.

    (1) If they (or their micro organisms) can eat us, then so can we eat them. And there are more of us than there are of them. Keep in mind that life on this planet has had a minimum of 3.5 billion years to explore, adapt to, and occupy nearly every niche in the environment.

    (2) Much more likely is that their form of life will be different, either subtly or tremendously, down to the very building blocks of life (DNA). In other words, their "life" is no more likely to interact with ours than inorganic rocks are.

    (3) However, if time is not of the essence to them, "they" (i.e., the artificial intelligence in command of their colonization spaceship) could patiently work on changing Earth's ecology over millenniae until it becomes a more suitable habitat for them, cut broad enough swathes in our environment ("clear cutting") to put down roots here, and when that's accomplished the robotic wombs on their spaceship start incubating the first generation of settlers from germ cells carried aboard. This would require vastly less machinery, time, and expense than turning a barren, deadly planet (life Mars or Venus) into a planet supporting life. Some ("They Live" by John Carpenter) think this is already happening...

    "like", not "life" Mars or Venus

    Gerhard Adam
    If they (or their micro organisms) can eat us, then so can we eat them.
    What are you talking about eating?  The likelihood of being infected by a harmless micro-organism would be quite high.  That's what makes an invasive species such a risk.
    Much more likely is that their form of life will be different, either subtly or tremendously, down to the very building blocks of life (DNA). In other words, their "life" is no more likely to interact with ours than inorganic rocks are.
    Based on what?  Are the organic molecules that arrive on meteors vastly different?  What basis do you have for believing that life would be vastly different to the point of where the two biological entities would be inert to each other?
    This would require vastly less machinery, time, and expense than turning a barren, deadly planet (life Mars or Venus) into a planet supporting life.
    Not true, except in the movies.  The reality is that unless you completely obliterated life, you'd only be exerting selection pressure on organisms too numerous to keep track of.  So, the risk would be much higher on a planet that already has life versus one that can shaped from sterile beginnings.

    You talk as if changing the Earth's ecology is like turning the switch on a thermostat.  There are hundreds of millions of organisms that would be subject to the selection pressures of such changes and absolutely no way for an alien civilization to determine which might be deadly, other than recognizing that they have no natural exposure.  Of course, even if it were directly deadly to them, presumably they would also have to modify the environment for their food [plants and animals] ... and of course all the micro-organisms that they would have to bring along that would now be competing with Earth-specific micro-organisms.

    It's insane and can't possibly work.
    Mundus vult decipi
    Gerhard you big German lummox!
    An infection *is* getting eaten from the inside by micro organisms. See "flesh-eating bacteria".
    Are you a nucleotide chauvinist? Why four nucleotides, why not five or six? Why A C G T, why not others? Why not a radically different design than the double helix?
    Think!

    Gerhard Adam
    Why not indeed?  Other than speculation, why should I presume that anything other than our finely functioning version of biology is required?  It's been amply demonstrated to operate under some rather extreme conditions.

    In short, it doesn't matter because (1) if the biology isn't different then we're still at risk from pathogens and (2) if the biology is different, we don't know anything about it, including whether or not it would still be capable of negatively interacting with our biology.

    In fact, the latter might be significantly more dangerous, because there's no reason to believe that biological systems are inert because of such differences.  They evolve to exploit their environments, and Earth biology is simply another environment.  There would be nothing inert about it, if any of the constituent parts were biologically usable.
    Mundus vult decipi
    Also see "The Screwfly Solution" by Raccoona Sheldon.

    The einsteinian universe slows things down but it still allows many kinds of star travel and even colonization. Only half a dozen are mentioned in Existence (some in passing). But there are others.

    Or, perhaps they have attempted contact, and our governments have kept it from us, for fear of overturning the social order that has empowered the ruling classes? Isn't that a pretty popular conspiracy theory?

    Re #11: "...arrogant fools scream into the cosmos "Yoohoo!" on our behalf." Whoever they are and however disposed, the proof they do exist is worth all the risk, even the risk of extermination: that catastrophe, hopefully, will take a while to unfold, letting us savor that amazing "communication" with a highly developed life form. Better that than a self-immolation, or an asteroid what not. Come to think of it, today the humanity has technology to kill itself many times over. For sure, it is a more likely event than finding extraterrestrials who may yet turn out quite benign.

    When you say "But even one toilet flush during the Archaean would have changed life on Earth in ways we'd detect in the rocks", what changes would we detect? This statement is based on the assumption that A) toilet flush didn't happen and we know what it would look like if it did, or B) toilet flush did happen and we know what it would look like if it didn't. I don't see how we could tell which case it is, A or B (great silence assumes A).

    I already answered Knom in an earlier reply.

    " proof they do exist is worth all the risk, even the risk of extermination" - Ilya

    So YOU say Ilya. As a father of three, I must take a balanced approach and I want to talk it over before guys like you scream skyward based upon unwarranted assumptions. The unwillingness to consult the greatest human minds on this topic is stunning arrogance, especially since EVERY encounter in human history between cultures resulted in (at minimum) staggering pain for the less developed society. Every single one.

    I want to learn more about the cosmos. But we should listen and look and learn first. And before shouting, we concerned ones have a right to be heard and to discuss it more deeply than a blog comments section.

    Helen, your complaints about human behavior are both justified and short-sighted. So obsessed with self-rebue, you cannot accept how vastly we've improved in the last generation, with violence plummeting since 1945, everywhere and in almost every way, while today the vast majority of kids get all their meals and go to school, almost everywhere. You MUST get Steven Pinker's THE BETTER ANGELS OF OUR NATURE.

    I AGREE with your compassion and desire to make rapid progress! That does not mean we must refuse, obstinately to accept that some progress HAS HAPPENED.

    Now dig this. Your UFO guys have refused to help us in this time of crisis, at all, in any way. And don't give me how dangerous we are. We have been to our moon, barely, 5 fimes. Puh lease. If they are aliens, they are bastards. There is no excuse for their behavior.

    david brin

    Gerhard Adam
    Whoever they are and however disposed, the proof they do exist is worth all the risk, even the risk of extermination...
    To what end?  What possible difference does it make in any meaningful way?  Bear in mind that there are already people that are quite convinced and have what they consider proof, so again ... what possible difference does it make to anyone?

    It is ultimately no different than the argument about God, which also has people claiming various types of proof, and yet what difference does that make?

    If communication is established, what conversation do you think you're going to have?  If physical contact occurs, what makes anyone think that it will turn out well for either party?  Given the resources that will need to be expended for such missions, does anyone truly believe that we [or aliens] would traverse half the galaxy just to stop by and say ... "Just happened to be in the area, so we thought we'd say hi!"

    What makes anyone think that communication will be possible?  What about the risks of pathogens?  As I said before, I would really like to understand what possible benefit anyone thinks any of this brings.  Beyond the mystical, "saving humanity" crap, I don't understand what the fascination is beyond simple curiosity.
    Mundus vult decipi
    There is another most likely situation that really hasn't been understood yet, nor articulated very well. We are just beginning to understand our world as a quantum one, and just understanding that the world as we see it classically is largely built by our perception. (e.g. the world as we see it is an interpretation created by our brain in response to quantum events, that we share similar pictures of how the world looks is more related to our common evolution). Although this has similarities to various "Matrix" type interpretations, it differs in the sense that we really can not disengage our independent identities from the signal. In this world, each individual represents a universe in themselves, since each individual represents a particular solution to the particular constraints placed by the universe. This highlights the particular mathematical uniqueness of individuals.

    The obvious answer is that the signals decay from the origin at a 1/d^2 amount. For us to actually see a signal from the distances we are talking about, the signal would have to be orders of magnitudes above a safe emmission level at the source. To contact our satellites or even our mars missions, we have to have dishes pointed very directly at them and they radiate directly at us. Secondly, at the edge of our solar system we have the heliosphere which is a layer of charged particles which would help shield our signals from getting out and theirs from getting in. Anyway, its actually a simple problem with obvious answers.

    The idea of moral objections to our looking or trying to be found should be explored further. In that vein, I offer the thoughts in this post.

    In what follows I present the case as a lawyer in court might; because in the interest of justice and truth, opposing reasons ought to be stated as strongly as possible.

    (1) If actively broadcasting our existence to extraterrestrial intelligences is wrong...
    a. because the ET's could invade and destroy our future generations...
    (2) Then seeking extraterrestrial life is also morally wrong.
    a. because our future generations might well invade and destroy them.
    b. that we now cannot do it is no justification, because:
    c. we cannot guarantee for certain that our future generations who can do it, will not have that murderous intent.
    d. as evidence, consider the murderous, genocidal history of humankind.
    e. the idea that mankind has shown sufficient moral progress in the last few generations to justify the search for extraterrestrial intelligence:
    1. requires a blind faith in inevitable progress which is obviously wishful thinking; mere special pleading aired to give some plausibility to a predetermined conclusion.
    (3) This could also explain why we haven't detected ET's:
    a. because any ET civilization advanced enough to be possibly detectable...
    is morally advanced enough to regard both of these as being binding:
    1. refrain from letting other galactic civilizations know they are there, for reason stated as (1) above.
    2. refrain from seeking other galactic civilizations, for reason stated (2) above.
    (4) The "juvenile" nature of our civilization could be just as much moral as technical; perhaps more so.

    What if SETI is looking at the wrong phenomena entirely? There are hundreds of unexplained UFO sightings a month and unexplained observations, and do none of these merit at least scientific curiosity? Dr. Steven Greer of the Disclosure project has been working on securing eyewitness testimony of (literally) thousands of high-credibility witnesses of close encounters, including encounters of beings. Most of these are people in military and aviation, not armchair theorists. If you haven't watched their testimony, you are missing the action happening here on the planet. http://disclosureproject.org There are a couple thousand or more witnesses - most of whom have very similar observations of contact and flight patterns.

    And perhaps the beings associated with these craft aren't using the EM spectrum (at least the spectrum as we know it) to communicate. At near-light speeds wouldn't a quantum tunnel be more likely?

    But try Occams' razor, Why would they use RF if they could just visit directly? When you see some these flight patterns yourself, you would start to question the phenomena and observe more carefully. I've seen absolutely inexplicable flight patterns, some quite close, on about 9 occasions. And there are some well documented events from news footage, such as the New Jersey expressway flyover of about 4 craft - slow and low - that shut down traffic for an hour, captured by video and narrated by bewildered highway patrol officers. August 15, 2001 - the footage stayed on ABC News' website for a while, then was disappeared from archives. Are human observations actually disregarded in our SETI science because it may not pass the paradigm test?

    Bonny Bonobo alias Brat
    Very good points Peter, I'm looking forward to David's reply.
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    As the person who has explored the concept of alien life probably more extensively than anyone else on the planet, I have often been asked onto talk shows (e.g. Larry King) and Radio Shows (e.g. Art Bell) about UFOs. People are surprised how little truck I hold with this "field". And it isn't because I disbelieve that folks "see" or encounter something strange!

    Finally, after years, I put down my thoughts about UFOs in a story that relates to you some of the things that I have said TO UFOs when I am on late night radio shows! Yes, I have interrupted the show to aim my remarks right at the little green assholes who buzz our towns always at the edge of blurriness, kidnap farmers and anal probe them, and all the other idiocies attributed to these critters.

    Here's the story, from the point of view of a guy on radio, substituting for the regular host:
    http://www.davidbrin.com/thoseeyes.html

    In fact though, if you really are interested in this topic, and broadening your horizons and asking better questions, you'd do well to read EXISTENCE!

    See tinyurl.com/exist-trailer

    or the reviews at http://www.davidbrin.com/existence.html

    More concepts than you could shake a stick at!

    It's been fun. If you have further questions, follow me to http://davidbrin.blogspot.com/

    And thrive in a life of ideas, in a civilization of courage and calm.

    With cordial regards,

    David Brin
    http://www.davidbrin.com
    blog: http://davidbrin.blogspot.com/
    twitter: http://twitter.com/DavidBrin1

    David, what is your opinion of this testimony by Donna Hare saying that NASA repeatedly edited or destroyed UFO photographs and also that Apollo astronaut Neil Armstrong appeared to confirm what Donna Hare was saying when he said that he was a parrot, which implies he was not allowed to talk freely and could just repeat what he was told and he also talked about truth's protective layers. Buzz Aldrin also talks about the UFOs that they saw on their Apollo mission. See 'Secrets Revealed - Donna Hare (Disclosure Project Witness)'at http://www.youtube.com/watch?v=JkIYpWtpLs8 and 'Neil Armstrong Nasa Lies' at http://www.youtube.com/watch?v=rfCzUuA8M4U&feature=related and 'aliens exist says buzz aldrin' at http://www.youtube.com/watch?v=KpfvhdmhQy4&feature=related

    The sign they may be waiting to see from us, is when we finally unlock the purpose of the Great Pyramid. My guess is, when we have unwrapped this technology, we will have achieved the peace-milestone they are waiting to see from us. It would be highly unintelligent for any intelligent extra-terrestrial species to communicate with us until then we have reached peace amidst ourselves. Buuut! Governments rule this planet for personal benefit, not collective benefit.

    Gerhard Adam
    Governments rule this planet for personal benefit, not collective benefit.
    ... and who are these governments of which you speak?  The people?  ... or are we waiting for a collection of benevolent dictators to take our hands and guide our planet to nirvana?
    Mundus vult decipi
    Since government is all about 'power' and controlling it, then if humans could find a way to wean themselves from the addiction to oil and the massive tax source it retains. We'd have it licked! But in the meantime, government will do whatever it can to successfully muzzle true alternative energy efforts. This includes all governments...Democratic, Communist or Dictatorships. Governments are more afraid of sweeping changes than the people are.

    Gerhard Adam
    So,. you think that some future society with be based on anarchy?
    Mundus vult decipi
    There is so much secrecy about true oil reserves, that investors have little idea how to gauge supply and demand in order to best evaluate 'worth'. The only sure shot method is by closely watching the closure of oil refineries on a worldwide basis. When closures begin to accelerate, then we know we're approaching a very critical moment in human history. Governments worldwide depend on energy tax revenues and oil to grease the economy. Invest in 'lead' because bullets will be flying in all directions. No sign of intelligent life yet on this planet.

    David, I'm sorry to receive such a mundane response. If you believe there's any correlation at all between what I've reported and talk radio, then you misjudge the seriousness of your (perhaps fleeting) audience. If you don't know of Dr. Greer's two-decade composition of eyewitness accounts from military, flight line, and policy specialist from the US government and around the world. Not a single one of these 2000+ witnesses speaks of the sensational garbage that's used for misinformation. Most of them are trained operators of humanity's most risky machinery - aircraft, missile fields, space ops, ATC, flight line control. They observe the skies all the time for their jobs, and they are objectively specific in their accounts,

    If you don't know of the National Press Club presentation of the highest credibility presentations of these accounts in May, 2001. If you haven't seen such phenomena yourself - then you're just disrespecting the quality of data which you have no access to yourself. These are not concepts, or "alien concepts" these are actual phenomena that you may not have an explanation for. Most good empirical scientists withhold judgment until they have investigated the data for themselves. Theoretical scientists, on the other hand, often operate from belief systems that blind them to the phenomena or data that do not fit the model.

    Respectfully, Peter Jones

    Gerhard Adam
    Theoretical scientists, on the other hand, often operate from belief systems that blind them to the phenomena or data that do not fit the model.
    Don't know much about science, eh?
    Mundus vult decipi
    A good analogy would be our days of seafaring exploration. If one of the great explorers came across an island filled with incredibly destructive, savage, and violent primates, even though less technologiacally advanced, that explorer would have noted that island on his charts, and kept on sailing.
    An e.t. species, fluttering past our little mud ball would encounter the exact same thing. We're the tweeked out trailer park of the universe. The sheer volume of artificial energy signatures produced here is like a big neon sign at the edge of our solar system; "Shady Palms Trailer Co-rt".
    Lets face it, none is going to make their presence known to us, until we start cleaning up, and acting like at least potentially responsible members of a cosmic community..

    Gerhard Adam
    What a parochial view of history.
    If one of the great explorers came across an island filled with incredibly destructive, savage, and violent primates, even though less technologiacally advanced, that explorer would have noted that island on his charts, and kept on sailing.
    Yes ... I suppose it's too bad the ships didn't also have signs on them.
    Mundus vult decipi
    Michael Martinez
    The Fermi Paradox fails in so many ways to be a true paradox, it's a shame there are still highly educated intelligent people willing to invest any time and thought in it.
    Are there or have there been other intelligences in the universe?  We have shown that intelligent species besides our own exist all over Earth.  If life exists out there the chances are pretty good that it has become intelligent in some ways.

    But do all intelligences behave like humans?  No, they have managed to diverge in some interesting patterns.  And we who have only barely stepped on our own moon are unqualified to know what it really takes to explore the galaxy.

    False logic holds that if space aliens have really visited the Earth we should know that by now.  How are we supposed to know?  Maybe 10% of all UFO sightings represent space alien insectologists dropping by to take a look at life on our rock.  The absurd assumption that they should, would, or must land on the front lawn of the White House or some other authoritative structure simply deludes people into assuming that we must not have been visited.  Absence of confirmation of stupid assumptions doesn't prove anything any more than a shaky video of a light in the sky.

    When was the last time one of our entomologists attempted to communicate with a queen ant or bee?  "Oh, but the queens don't actually RULE these inect societies."  Maybe, maybe not.  Until we communicate with the ants in a meaningful, abstract way we're at a loss to understand how and why they organize themselves.  We have high expectations for efficient ant colonies but then they surprise us with horrific inefficient behavior.  Who knows the mind of an ant let alone the mores and taboos of an ant colony?

    Ants may not be intelligent enough to converse with us about the probability of life out in the universe but we have not yet mapped the genomes of all life on Earth.  Our ignorance leaves a huge gap in probability estimates about whether some alien sandwich wrapper or toilet flush changed the course of life on Earth.  For all we know, we ARE the results of a toilet flush.

    Radio signals are our way of communicating across various atmospheric and ex-atmospheric distances.  We haven't ruled out all other forms of long-distance communication.  We haven't even imagined them all as we're stuck in one relatively small area of the electromagnetic spectrum.  Maybe there are extradimensional wave patterns that allow for intergalactic communication.

    Our inability to map the universe beyond a few hundred light-years with any degree of certainty leaves us muddled in a huge geometric fog.  Maybe there is plenty of space traffic zooming by us and we just cannot yet see it.  Why are they supposed to zoom in on the Earth?  How many planets could they have colonized?  When is life supposed  to have arisen elsewhere?

    We make assumptions and then complain loudly that there are no aliens to back up our ideas -- or that our imaginations are running wild and concocting fake aliens because we're lonely.  I'm not ready to buy into the mass insanity of an entire ecosystem; nor am I ready to believe that space alien taught us how to build pyramids.  But just because we don't know what to look for doesn't mean we should be disappointed in not finding anything.

    Presumably finding space aliens will become much, much easier after we actually capture one and study it and its technology.  Stephen Hawking and others say we should fear an advanced civilization because they may do to us what the Europeans did to the Native Americans.  And it's true that the Europeans eventually won out, but at the very beginning of these encounters that outcome was not nearly so certain for the people living at the time.  The Europeans had one thing working to their advantage which space aliens may not: they unwittingly brought with them diseases that were adapted to feed off the human biosystem.

    Just because a microbe evolves elsewhere doesn't have to guarantee that it will be the death of us; we have our own microbes.  Perhaps any space aliens wandering around the universe have already learned that what goes around comes around, and perhaps they take great care not to interact with biosystems they have not carefully evaluated and devised sufficient protections to allow them to safely land and chat with the local bee queens.
    SETI won't find an intelligent artifact because it is looking for humanoid intelligence - which is highly unlikely to have evolved elsewhere - and not looking for messages from the large numbers of plausible non-humanoid intelligences that scientists and others (including Mr. Brin) have been imagining with increasing frequency since about the 1970s.

    All the gory details can be found in my PhD dissertation, posted in David Darling's (superb) on-line encyclopedia:
    http://www.daviddarling.info/encyclopedia/S/SETI_critical_history_cover....

    Sagan and Spielberg instated the name of Contact for what the Fermi paradox declares missing. But the "Great Silence" points to a more generic definition for "Contact": the point where an intelligent civilization for the first time gains conclusive evidence to the existence of at least another similar civilization.

    The noun of "contact" itself describes the naive expectation. We'd want to be literally in touch with E.T.We would like to shake their hands. Failing direct, physical touch, something approaching it. Like radio signals from a nearby solar system. Or - as David Brin suggests above - microbes that visitors would inadvertently leave on a visited planet.

    But it is possible to imagine Contact (as defined by the paradox) to occur in a way that most radically denies the expectation promoted by the instated noun, "contact".

    Two ways I see:

    (1) Let's suppose "Contact" is attained from what's most in contrast with touch as far as geometric distance of sampling the Universe is concerned. The most wide-ranging physical signals we know to exist in the Universe are supernovae explosions. So suppose that studying patterns of explosions over dozens of centuries should reveal, in a select multitude of distant and unrelated galaxies, the gradually compelling signs of interstellar warfare. It costs nothing to assume further, that this same form of "third party contact" is standard for our own galactic neighborhood. A picture then emerges of a Universe were intelligent civilizations coming later on would learn not to risk e.g. physical contact - would learn the latter from observing the most spectacular failure of early and faraway civilizations cohorts to achieve fruitful physical contact.

    (Challenge: write a scifi narrative turning dark energy into an observational artifact due to ET warfare biasing the standard candle in a systematic way).

    (2) "Contact" is effected by replacing it with a mathematical equivalent. The capsule form of this idea is best provided by an analogy. We can in principle by rigging the language education of a cohort of children born at place X, turn them (as speakers of the appropriate language) into an approximation to a cohort of children born at any other place/time Y on Earth. And this - the important point - without moving anybody across space or time. The proposal here is that by rigging mathematical education instead of language education, we can obtain a similar effect that will not act over just planetary but over cosmic virtual distances!