Where Are The Aliens? How The ‘Great Filter’ Could Affect Tech Advances In Space

Article Updated: 23 Dec , 2015

“One of the main things we’re focused on is the notion of existential risk, getting a sense of what the probability of human extinction is,” said Andrew Snyder-Beattie, who recently wrote a piece on the “Great Filter” for Ars Technica.

As Snyder-Beattie explained in the article, the “Great Filter” is a response to the question of why we can’t see any alien civilizations. The “Great Filter” deals with similar issues as the Drake Equation, which talks about the probability of communicating civilizations outside of Earth, and the Fermi Paradox, which asks where the civilizations are.

Simply speaking, the idea is that if a civilization continues to expand (especially at the technological pace we humans have experienced), it wouldn’t take all that long in the lifespan of the universe for artificial processes to be visible with our own telescopes. Yes, this is even taking into account a presumed speed limit of no more than the speed of light. So something could be preventing these civilizations from showing up. That’s an important part of the Great Filter, but more details about it are below.

Here are a few possibilities for why the filter exists, both from Snyder-Beattie and from the person who first named the Great Filter, Robin Hanson, in 1996.

‘Rare Earth’ hypothesis

Maybe Earth is alone in the universe. While some might assume life must be relatively common since it arose here, Snyder-Beattie points to observation selection effects as complicating this analysis.  With a sample size of one (only ourselves as the observers), it is hard to determine the probability of life arising – we could very well be alone.  By one token, that’s a “comforting” thought, he added, because it could mean there is no single catastrophic event that befalls all civilizations.

Artists impression of an asteroid flying by Earth. Credit: NASA

Artists impression of an asteroid flying by Earth. Credit: NASA

Advanced civilizations are hard to get

Hanson doesn’t believe that one. One step would be going from modestly intelligent mammals to human-like abilities, and another would be the step from human-like abilities to advanced civilizations.  It only took a few million years to go from modestly intelligent animals to humans. “If you killed all humans on Earth, but you left life on Earth — and the animals have big brains — it wouldn’t necessarily be that long before it came back again.” Some of the filter steps leading up to that would have taken longer, though, including the emergence of multicellular animals and the emergence of brains, roughly on the timespan of a billion years each per stage.

‘The Berserker Scenario’

In this scenario, powerful aliens sit hiding in wait to destroy any visible intelligence that appears.  Hanson doesn’t believe that would work because if there were multiple berserker species, there would be opposing parties. “As an equilibrium, you’d have these competing teams of these berserkers all trying to smash each other.”

Maybe natural activities are masking the extraterrestrials

Maybe the big natural activities of those beyond Earth just happens to look exactly as if they are not there. Hanson said it seems rather unlikely, as it would be a “remarkable coincidence” if advanced artificial processes were actually responsible for all the astronomical phenomena we do explain from natural occurrences,- from pulsars to dark matter

Artist's conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde

Artist’s conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde

A natural disaster

There certainly is an inherent risk to just being an Earthling. One asteroid strike, a stream of radiation from a nearby supernova, or a large enough volcano could end civilization as we know it — and possibly much of life itself. “But the consensus is we have a track record of surviving these things. But it’s unlikely that all life would be destroyed forever. “If those humans who were left, it took them 10,000 years to come back to civilization, that’s hardly a blink of an eye, that doesn’t do it,” Hanson said. The next is that statistically speaking, although these events happen, they don’t happen often. “It is unlikely one of these very rare events would happen in the next century or 300 years,” Snyder-Beattie said.

A ‘fundamental technology’ that ends civilization

This is open to complete speculation. For example, climate change could be the catalyst, although it would seem extraordinary for all civilizations to encounter such similar political failures, Snyder-Beattie said. More generalized possibilities could be the rise of machine intelligence or distributed biotechnology, a force that is self-replicated. Hanson, however, points out that even that has its limitations — presumably then it would be the robots that head out through the cosmos and leave traces of civilization themselves.

The solution

For the fate of our own civilization, the key is to focus on what we can control, Hanson says. This means drawing up a list of the things that could kill us — however theoretical — and then work on ways of addressing those.

The question of why other civilizations are not visible still persists, however. What are your thoughts about the Great Filter? Let us know in the comments.

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25 Responses

  1. joker365247 says:

    Why not take in to account the possibility that aliens are already here? Is it not just as likely aliens already found Earth and are using some kind of signal jammer? I know that sounds far fetched, but we can do it with the technology we currently have, whats to stop an advanced civilization? If they are studying us they would want to keep evidence of their existence to a minimum. It would be even easier if the governments of the world know about them.

    • Beckler says:

      Or even more low-tech (and possibly terrifying), they could just be hiding in our solar system somewhere. Behind a big planet, or even the sun, briefly peeking around to observe Earth at will. There could even be quite a large base on a distant dark moon, say of Saturn, and I don’t think we’d ever notice. Or just a big dark ship out in the open at quite some distance (maybe 10AU for example) from Earth, would just fade into the blackness and never be noticed. With any of these methods, a sizable fleet of alien destroyers could easily be massing as we speak…

  2. psieti says:

    Regardless of whether there is a ‘Big Filter’ or a ‘Really Big Filter’, the ‘Paradox’ which is the basis of this discussion is nonsense.

    The answer to Fermi’s question (‘Paradox’) was known to elements of the U.S. Government, and others, several years before Fermi asked the question.

    If you have any doubt that some of the UFO sightings represent ‘ETs’ who are willing to talk to us now–to begin the Contact process –and that the U.S.G. knows this, then try asking a SETI researcher or a NASA astrobiologist this simple question: Would NASA–speaking for the U.S.G.–welcome an undeniable appearance, or a message from any ETs who are already here, interacting with our civilization?

    Do you think NASA could answer this question with a simple ‘Yes’ or ‘No’? [They can’t, and they won’t.] Or would they evade and dismiss the question? Do you think SETI researchers can even openly discuss this question? [They won’t.]

    Here’s an explanation:

    • Beckler says:

      Your UFO link is nothing but wild speculation and not even particularly relevant. But since you characterize the (Fermi?) paradox as nonsense (i.e. aliens are already here) please provide a simple link that shows proof of that. Actual evidence-based proof please, not just more speculation. I believe you’re the one making the claims here.

      • Jim Krug says:

        Actually Beckler, psieti is correct. In the opening pages of SETI researcher Paul Davies’s book, The Eerie Silence, he admits that if SETI ever DOES uncover an extraterrestrial signal, there top priority is to……..report it to the US government, and then the government decides how to “best disseminate the information”, which would obviously include not disseminating it at all.

        So there you have an actual well-known SETI scientist admitting that they still report directly to the government, even though the government no longer funds it.

  3. TheUnone says:

    I do not expect to see any signs of extraterrestrial life in our neighborhood. If they’re out there, they probably fled the galaxy long ago. It’s too dangerous here. It would be a shame to spend a million years advancing your civilization, just to watch it get decimated by a stray gamma-ray burst. I’d pack up the robot kids and flee to some artificial paradise between the galaxies as soon as I could.

    • cacarr says:

      *If* there are numerous gigayear-old technological civs in our Hubble volume, then your explanation (which has occurred to me in the past) makes as much sense as any I can think of. A Very Old civilization is, I think, necessarily highly averse to risk. Galaxies may be intolerably risky — and as I understand it, it would be very, very difficult to locate (much less get to) such civilizations if they are out in intergalactic space. I would assume they could cloak themselves such that they blend into the background radiation.

      But compared to the universe’s expected lifespan, we happen to be just a sliver away from its beginning — someone has to be first, eh?

      I’m not an astrophysicist, but if it’s the case that the universe is only quite recently (relatively speaking) suitable to the development of life (not enough necessary elements cooked up in the past?) then perhaps the universe looks about how you would expect it to look. Or, perhaps biospheres have existed from much earlier in the existence of the universe, but have only recently been able to exist for a long enough period of time for Darwinian process to generate technologically smart things (maybe GRBs were more frequent in the past?).

      I’ve also wondered if we should expect to have noticed tech-saturated (with a high percentage of stars being matrioshka brains, or whatever) galaxies if they are only, say, one in 30 million, or so.

      It’s also been suggested that technological civs invariably disappear up their own arses, so to speak — plenty of room at the bottom, as Feynman put it.

      • TheUnone says:

        I really think Feynman’s point is the key to this topic as well…

        When you’ve mastered the atom, and everything is synthetic and artificial, then why would your risk exploration and expansion? That just sounds like busy work. Why seek-out something new when you can create a more interesting version right at home?

        In fact, I really wonder what would motivate any advanced civilization (..or AI for that mater..) to go on when you strip out all of the uncertainties and excitement of life. Until we know that, then we are not going to know where to look.

        BTW – any civilization that decides to stay in this buzz-saw that we call the Milky Way, despite the long-term risk, is probably completely insane and worth avoiding.

  4. Pete says:

    Conspiracy theories aside, I tend to believe that life is just much rarer then we have been assuming. Sure, once the process gets going, its march is inexorable. But just getting to that first crude form of archaic life may be so rare an event that it takes an entire universe to see it happen once or twice, or even a few dozen times. Then too, there could easily be on the order of 1000 or so advanced civilizations in this great cosmos without any of them ever detecting signs of the other.

    • Beckler says:

      I’d tend toward that line of thinking as well, but still it’s just guessing. I think it’s clear we simply don’t have enough information about how life starts, the conditions required, and the conditions of the average planet/solar system to make any judgement just yet. In the development of human life though, there appears to be some seemingly unlikely chain of events which at least suggests the possibility of extreme rareness.

    • FarAwayLongAgo says:

      An argument against the rarity of life, is that life consists of the very most common *elements* in the universe, in the solar system, in Earth, in living beings: “CHNOPS”. And on Earth life is intimately living with 3 of the 6 or so most common *molecules* in the universe: H2O, CO2, CH4. And life uses the most common energy sources such as sunlight and some chemical reactions between the most common molecules and elements (such as H and Fe).

      If life on Earth were dependant on a rare self eliminating element such as plutonium, then the argument for us being rare would be very convincing. But we instead indeed consist of only that which is most common in the entire universe. Even our star type and planet size/orbit are common. If we are uncommon, then it is a mystery what about us which would make us uncommon. If that proposition could be proven, it might be an ever greater discovery than the discovery of extreterrestrial life!

      I think “they” are all over the place. We just haven’t looked for “them” enough yet in order to see them. We today see their home planet as a regularly orbiting dimmening of a star by 1/10000 for a few minutes. We’re far from seeing their space engineering…

      • Windfall says:

        To add to FarAwayLongAgo’s replay, we must also acknowledge the speed of light. Given everything we see is light and light has a speed limit, we would be unable to see any “signs” of advanced civilizations that formed sufficiently far enough away that the light simply hasn’t had time to reach us.

        For those worrying about the signals we put out there, just remember that this works both ways. Considering we’ve only recently advanced to a point where we are putting radio signals and such out there for other intelligent life to discover, the evidence has traveled a comparatively short distance that only a nearby civilization could find us anytime soon.

    • gopher65 says:

      Doing some basic math, and making some assumptions on how long a civilization lasts, you discover something “disturbing” (I don’t find it disturbing, but some here clearly do).

      Life is everywhere we can think of,
      Intelligent life pops up fairly often,
      Technologically advanced life isn’t common, but isn’t rare, and
      The average civ lasts a million years after it invents spaceflight.

      Using those assumptions, you find out that there will be very little – if any – overlap of intelligent space-faring civilizations in a galaxy the size of ours. It turns out that space is just very, very big, and the timespan we’re talking about is very, very long. Barring the existence of faster-than-light travel, it’s unlikely two civilizations will cross paths in both time and space. It probably happens, but it’s relatively rare.

      There is no need to assume apocalypses, or rare Earth, or hostile aliens, or self-replicating machines maliciously destroying every biological organism they come across (why would they bother expending the energy necessary to do that?).

      All that you ultimately need to assume to explain the “paradox” of us not seeing aliens is that, 1) everything dies eventually… even long lived civilizations, and 2) FTL travel is either impossible in our universe or impractical at any reasonable level of technology. Once you make those assumptions, the lack of aliens is not just explainable, it’s likely.

  5. psieti says:

    Dear @Beckler,

    Insult the question if you wish, but you can’t openly pose it, much less invite an open discussion. Do you know why that is?

    If you truly wish to know–and you don’t, of course–then invite an *open* discussion of the question. You can’t, of course.

    Best Wishes…

  6. sangos says:

    Here is why we have ‘A great filter’ if there is such a thing

    1. Just our galactic neighborhood is HUGE. And we are still completely oblivious of it in spite of all our science.

    2 It also points to the fact that our galactic neighbors are not much ahead of us. Matter of fact they would be at the level of ‘Pandora’ like creatures. Certainly not the angels and UFOs cool stuff.

    The only way we are going to run across ET is we find them. At least there is no one using radio for the number of light years radius since we had SETI.

  7. Greg says:

    I would say that based on what we know about this galaxy is that the likelihood of advanced civilizations capable of communication arising in the universe is about 1 per every 300 billion stars every 13.8 or so billion years. I would hazard a guess that an advanced civilization can be found in the Andromeda galaxy. The main problem as I see it, is that a civilization has to advance far enough technologically to achieve interstellar travel before a mistake happens with it’s advanced technology that destroys all life on a planet or causes a regression in technology such that interstellar travel is never achieved. This milestone may be more difficult to achieve than thought and is an existential problem that we are facing right now. The more power you have at your disposal the more likely that a single mistake or single series of mistakes could kill everyone on a planet or at least set it back to the stone age.

  8. Greg says:

    To the extra-terrestrial enthusiasts I would like to run some basic logic by them as I customarily do on threads that they post on. If there was an advanced civilization capable of interstellar travel in this galaxy, they realistically could colonize the entire galaxy in 20 million years. That is a blink of an eye cosmologically. So if they exist and this were their intent there would be evidence of them everywhere. Most likely they would have exploited/terraformed this planet long ago such that our civilization would never have had a chance to develop. Otherwise they must be xenophobic or not intent on exploiting the entire galaxy. This would mean that they simply don’t care about us. If they did they would have an embassy here already with the intent to steer us away from technological and natural pitfalls that they are already aware of. So we should be content not to care about them. That might change if we were to achieve interstrellar travel in our current state of ethical development. Then they would be forced to reveal themselves in order to prevent us from exploiting the entire galaxy which would inevitably threaten their existence. If that day comes then it would be very wise for us to cooperate with their demands.

  9. Greg says:

    One side note for conspiracy enthusiasts. If there is an advanced xenophobic civilization in this galaxy, even though their leaders could care less about our civilization until it achieves interstellar travel, it’s biologic scientists would likely be very interested in us. Like true scientists, of course, they would not like knowledge of their existence to contaminate any of results of the experiments that they might be running here.

  10. UFOsMOTHER says:

    When the Drake Equation first came about we had not even found other Planets orbiting other Stars, Since then we have found Thousands of these Planets, My guess is there are Millions of inhabited Planets in our own Galaxy, None of which uses radio waves to communicate because they have much better tech than us, Earth is not alone where there is liquid water (and other liquids) there is life look up to the Heavens for they are there the Cosmos is Full of life we just have to find it and im sure that some of these civilisations are way more advanced than us, I believe that (they) will make contact with us in the near future but in the mean time keep looking up The Truth Is Out There…….

  11. aquaone41 says:

    One trait of higher intelligence on this planet is curiosity. I am afraid another is sadism. Both arose from the need to survive. Can there be an advanced intelligence that is not curious or sadistic ? Would an advanced civilization become less sadistic like we think we have ? Would they lose their curiosity ? Even if you have been around for a 100 million years would there still not be discoveries to be made in this vast universe or multiverse. I don’t think that they would lock themselves away behind some magic curtain. Perhaps we should proceed like we are the only intelligent race and try and secure our future until we find out different.

    • Greg says:

      Sadism is function of ignorance and is pathologic. It is not a marker of higher intelligence but rather for a lack of understanding and a lack of tolerance for differences. Humans outgrow their capability for sadism when they acquire and use abstract reasoning which enables them to understand abstract principles that comprise the code of ethics we are supposed to practice in our everyday lives. The solution to sadism is for an individual to look for commonality in other beings first, understand what is different from the norm that you innately expect, and then appreciate diversity as a strength and not a weakness. These are the abstract principles and need to be put into practice within the mind for sadism to go away. A civilization that has evolved above the need to fight for basic subsistence will lose such barbaric traits over time.

  12. anubis_lab says:

    I’m sure we will find evidence eventually if there are technological societies out there. But nobody said it was going to be easy. The great filter might just be patience.

    I’m not sure if it’s a fair comparison, but I’d suggest we could use the hunt for extrasolar planets as a rough guide to how good we would be at locating another civilization. That’s something that is at least measureable and we can tell how much progress we’ve made.

    Obviously it’s not an apples-to-apples comparison, but I have to believe that SETI is even harder than the search for other planets. And we have made some amazing progress in the hunt for extrasolar planets–but let’s face it, we haven’t scratched the surface of what’s out there. The kepler satellite is no longer fully functional, and even when it was working it was only able to tell a tiny fraction of what was out there. And for that matter, how many of the objects in our local neighborhood have we really found? We are just starting this journey.

    Also, if we were looking for our own civilization, does anyone know how close would we have to be to see it? That would put a rough floor to the probability, because if you assume that civilization is just out of reach, then you can calculate the number of stars within the volume of space we can detect (ourselves), we could have a lower bound for the probability of other civilizations. It’s crude but it would be a starting point.

  13. fatman6502002 says:

    I think simple life, as in single cell organisms will eventually be found in abundance all over the Universe due to the fact that simple life as we know it is made of the most abundant materials and uses the most abundant energy sources a solar system has to offer – (H/t to “FarAwayLongAgo”). However I also think the filter is the very rare combination of events that must happen in order to allow for the evolution of intelligent life, as in Human Life here on Earth, as the article suggests. Such as a planet has to be in the Goldilocks Zone of a star and stay there for very long periods of time; it has to support the presence of liquid H2O; it must have a moon or some other environmental stabilizer that allows for very long relatively stable climate conditions; it have occasional natural disasters such that as evolution experiments with different forms of intelligent life the process can be virtually started over several times such that eventually an intelligent species learns to reason rather than just survive by instinct. So it seems to me at least, that the most likely scenario that is now playing out is that simple life is common; complex intelligent life at the relative earthly human level is probably very rare; advanced civilizations that have mastered interstellar travel orders of magnitude rarer; and advanced civilizations that have mastered intergalactic travel orders of magnitude rarer still as to be probably nonexistent. I would suspect, considering the various scientific indicators we have, that life at the human intelligence level or above will be found to be nearly in the same proportion as the number of solar systems that produce a planet with those combinations of events that allow for its evolution. Find out how often a solar system produces that kind of a planet and you have your answer as to how many civilizations have advanced to our level or above, IMHO. Wherever life can exist, it will exist; life will only evolve as far as the environmental conditions present on the host planet or moon allows it to evolve, and it will evolve to it’s maximum intelligence virtually every time because the processes of life’s creation; it’s will to survive; and evolution are likely to be relentless natural forces.

  14. Davies says:

    If the ETs are that advanced in technology, why do they hide? We’re nothing to them…..powerless. They can destroy our planet in few hours…..yet, they hide in darkness, strange. Unless if there is code, a planetary code to never invade other planets.

  15. JFA says:

    If your interested in these issues check out a excerpt from my current film project at http://www.thecrossofthemoment.com The website includes a rough cut of the chapter on Fermi’s Paradox that features Robin Hanson discussing The Great Filter Theory and Don Brownlee and Peter Ward on Rare Earth theory.

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