Avoiding “Sagan Syndrome.” Why Astronomers and Journalists should pay heed to Biologists about ET.


A new paper using data from NASA’s Kepler telescope came out recently, estimating that 22% of Sun-like stars harbor Earth-sized planets. This is a big increase over previous estimates. It’s very cool work. Love it. But the news spin was predictable:

  • New York TimesThe known odds of something — or someone — living far, far away from Earth improved beyond astronomers’ boldest dreams on Monday.
  • USA TodayWe are not alone.

You get the idea. Aliens under every rock. The existence of extraterrestrial intelligence (henceforth ETIs, or just ETs) is normally discussed in the context of the Fermi Paradox, which Wikipedia describes as “the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity’s lack of contact with, or evidence for, such civilizations.” Now I’m a strong advocate for there being no ETs in our galaxy, as explained in this recent post. In fact I’ve gotten so tired of hearing about ETs I’ve started thinking of it as “Carl Sagan Syndrome.” Name checking the deservedly well regarded astronomer and advocate for the Search for Extraterrestrial Intelligence (SETI). With this latest news cycle I got to wondering. Why so much Sagan Syndrome? What am I missing?

A good starting point is Stephen Webb’s book “If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life.” It’s a fun romp through the history of the Fermi Paradox. From page 23: “it was a 1975 paper by Michael Hart in the Quarterly Journal of the Royal Astronomical Society that sparked an explosion of interest in the paradox. Hart demanded an explanation for one key fact: there are no intelligent beings from outer space on Earth at the present time.” Hart’s explanation was “we are the first civilization in our Galaxy.

Hart’s 1975 paper is short and clear, and worth a quick read. Hart runs various scenarios, but for me the key insight is one of time scale. It takes (only) millions of years for intelligent life to completely fill the galaxy, but billions of years for it to evolve. So first out the gate should be everywhere before second out the gate. Logically if ETs exist they should be here. And they aren’t. So case closed. The Fermi Paradox literature since Hart could arguably be characterized as nonstop special pleading to avoid a common sense conclusion. Besides my recent posts, you can find similar views from Robin Hanson, Ian Crawford, Leonard Ornstein. And in particular I want to cite Stephen Ashworth, both for his article “Alien Civilisations: Two Competing Models“, plus an email exchange where he was generous enough to spend time answering questions. Finally of course we have Stephen Webb himself (spoiler alert) finishing his book of 50 explanations by concluding ETs aren’t there. So while this is a minority view, it’s not uncommon. Back to discussing Hart’s impact, Webb goes on:

Hart’s paper led to a vigorous debate, much of it appearing in the pages of the Quarterly journal. It was a debate that anyone could enter — one of the earliest contributions came from the House of Lords at Westminsterlz. Perhaps the most controversial offering came from Frank Tipler, in a paper with the uncompromising title “Extraterrestrial Intelligent Beings Do Not Exist.” Tipler reasoned that advanced ETCs could use self-replicating probes to explore or colonize the Galaxy cheaply and in a relatively short time. The Abstract to Tipler’s paper sums it up: “It is argued that if extraterrestrial intelligent beings exist, then their spaceships must already be present in our Solar System.” Tipler contended that the SETI program had no chance of success, and was therefore a waste of time and money.

Now unfortunately later on Tipler became a crackpot. But at the time he wrote his 1980 paper he was doing good work. In particular Tipler was an early and forceful advocate for self-replicating robotic probes as the best way for humans or ETs to explore the galaxy. This scenario makes exploration and expansion faster, cheaper and far more plausible. But by directly attacking SETI, Tipler naturally annoyed Carl Sagan.

In response, Sagan co-wrote a paper with William Newman “The Solipsist Approach to Extraterrestrial Intelligence” which right from the title attacks Tipler for believing Earth to be unique. Sagan is of course citing the Copernican Principle, which roughly states the Earth is NOT the center of the heavens. The Copernican Principle is the modern foundation for Astronomy, Cosmology and Relativistic Physics. Sagan thought anyone claiming the Earth to be special must be doing bad science. Here’s a typical quote: Despite the utter mediocrity of our position in space and time, it is occasionally asserted, with no sense of irony, that our intelligence and technology are unparalleled in the history of the cosmos. It seems to us more likely that this is merely the latest in the long series of anthropocentric and self-congratulatory pronouncements on scientific issues that dates back to well before the time of Claudius Ptolemy.

So how did Sagan and Newman make Earth typical? By concluding ETs were common in galaxy. Then they resolved the Fermi Paradox by assuming every single ET civilization decided to expand slowly. Very, very slowly. So none have reached Earth yet. As Webb points out in his bookNewman and Sagan assumed very low population growth rates – rates that many people find too conservative…… A final criticism: even if advanced ETCs are not driven to expansion by population pressure, would they not explore the Galaxy out of curiosity?

Now unlike Astronomy, the discipline of Biology takes a highly favorable view of uniqueness. Evolution constantly discovers quirky and highly contingent historical paths. Biology takes it for granted that everybody is a special snowflake. In fact the third sentence of Tipler’s 1980 paper calls this out:

The contemporary advocates for the existence of such [extraterrestrial intelligent] beings seem to be primarily astronomers and physicists, such as Sagan (2), Drake (3), and Morrison (4), while most leading experts in evolutionary biology, such as Dobzhansky (5), Simpson (6) Francois (7), Ayala et al. (8) and Mayr (9) contend that the Earth is probably unique in harbouring intelligence, at least amongst the planets of our Galaxy.

And as quoted in Mark A. Sheirdan’s book, we have eminent Evolutionary Biologist Theodosius Dobzhansky (“Nothing in Biology Makes Sense Except in the Light of Evolution“) joining the fray:

In his article Dobzhanksy turned Sagan’s argument on its head. Dobzhansky cited the fact that of the more than two million species living on Earth only one had evolved language, extragenetically transmitted culture, and awareness of self and death, as proof that it is “fatuous” to hold “the opinion that if life exists anywhere else it must eventually give rise to rational beings.” 

Now we’ve nailed it. It’s Evolutionary Biologists versus Astronomers. In table format:


Obviously I’m harshing on Astronomers to make a point. And while I’m at it, I want to harsh on science journalists as well, for narrowly talking to Astronomers about ETs, without paying enough heed to Biologists. But full disclosure, I took Astronomy 101 at Cornell University in the 1980’s when Carl Sagan was there. Now of course Sagan obviously never taught Astronomy 101, but it turns out I was at Cornell in the year he wrote his paper with Newman that trashed Tipler. Furthermore I love Cosmos, and plan to watch the reboot series with my kids. So I have a genuine fondness for Sagan’s work. And when I attempt to summon my inner Carl Sagan, it does feel extremely discomforting to claim the Earth is unique. Sagan Syndrome is contagious.

But perhaps some perspective shifts will allow us to restore the Copernican Principle to its rightful place. Recall from my previous post how we have three wildly disparate time scales in play: millions, billions and trillions. Rounding to the nearest 20, we have:

  1. Time for intelligent life to fill a galaxy: super short 20 million years
  2. Time for intelligent life to evolve in a galaxy: moderate 20 billion years
  3. Time of universe to keep having stars: super long 20 trillion years

The first perspective shift is to step back in time, and realize the universe is very young. With 20 trillion years of star generation ahead, the universe has only covered 13.7 billion years or roughly .07% of its life span. Compare this to a person who expects to live 70 years, and you’d get  .07% * 70 years = roughly 18 days. So in human terms the universe is a three week old baby. No wonder there’s not too much life out there yet.

The second perspective shift is to step back in space. Our Milky Way galaxy is part of the Local Group, which contains 54 galaxies. In turn this is part of the Virgo Supercluster. And on we go until we hit 100 billion galaxies in the universe. Now nearly all the Fermi Paradox literature I’ve come across limits itself to just our Milky Way galaxy. Though if you read closely you’ll see Hart and many others after him considered larger scales, as we’re doing now. Why limit to our local galaxy? Because communicating between distant galaxies would take millions or even billions of years. Not much fun. But what happens if assume intelligent life is so rare, and the universe is so young, we only have a few examples within the Local Group? Or worst case the Virgo Supercluster? At this scale our Fermi Paradox problem goes away. We’re now talking billions of years, if it’s possible at all, to travel and expand between galaxies. Sagan’s solution of ETs needing more time to arrive can be made to work. What does all this mean? Well, nobody for millions of years will meet ETs face to face. But we can expect our billion year distant cyborg descendants to do so. There’s lots of time, trillions of years in fact, for this to happen.

I’d like to think Carl Sagan would prefer this approach, which recovers the Copernican Principle, to Tipler’s idea of defunding SETI. Our pale blue dot can be mundane at the scale of galactic clusters, while simultaneously being the crown jewel of the Milky Way. SETI has shown it’s unlikely there’s anyone else here in our galaxy to talk to, so perhaps it’s time for SETI to look outward. Much, much farther outward.

Hubble Ultra Deep Field 2014

Image credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team

By Nathan Taylor

I blog at http://praxtime.com on tech trends and the near future. I'm on twitter as @ntaylor963.


    1. The Fermi paradox is based on the assumption that we will continue the explosive growth of our population and yet as societies become more wealthy they reduce or eliminate their population growth. Without immigration many western countries would have negative birth rates.

      If you scattered our current population through the galaxy they’d be damn hard to find.

      There’s no reason to think we should be hip deep in aliens.

      1. if we scattered ourselves among the stars we’d have expect frontier birth rates rather than developed country ones. and people on the frontier have a dozen kids.

      2. This is a good point.
        However there is no reason to think that all societies will reach western levels of affluence.
        If there is an ecological niche for people who merely subsist and who reproduce at rates traditional for people in such circumstances then as more become affluent, others should move in to fill the void.
        Global population growth is slowing, but that may more reflect a lack of available resource in poor countries, rather than conscious choice in developed ones.

  1. The consequences are a telescope. Flip the opinion and put it to your eye and

    1. We are not unique. We are of infinitesimal importance.
    2. We are unique. We are of supreme importance.

  2. Perhaps, the likeliest explanation for the lack of extraterrestrials in our universe that should be swarming with them, is that we and this world are a digital construct, programmed to feature only us, perhaps as a thought experiment.

  3. I think it’s strong to say that SETI has demonstrated that there’s no one to talk to. Between SETI’s limitations, and the limitations of our technology AND the limitations of radio for communication, all we’ve established is that we can’t detect intelligent life. We’ve established that nobody is being super overt about broadcasting their existence to the galaxy.

    Look at the Earth- our peak radiation happened during the Cold War (massive radar deployments). That’s a narrow spike, a traveling wavefront that announces our existence to the galaxy. Since then, our radio transmissions have largely become more efficient and more encrypted- becoming weaker and more similar to random noise.

    Assuming that we’re not unique (yes, a big assumption), and projecting our current radiation path as a model- well, we could have nearby neighbors that we wouldn’t think exist because their radiation doesn’t peak above the natural background loudly enough.

    That said, I don’t really think this is the case- I think life is both far more common (I suspect that there is other life in our stellar system that evolved independently of Earth (and ETs that evolved on Earth and relocated to Mars, mostly by our own doing)), and I think “intelligence” is defined too much as “like humans” (I’d argue that humans aren’t the only intelligent life on Earth, and that maybe we’re too excited about our tool using to notice).

    I think alien intelligences would be… well… alien. Imagine organisms that arise from interactions of plasma clouds in stars. Imagine massive colonies of single-cells, that are able to coordinate and think- albeit on very long time scales.

  4. There is absolutely zero evidence that aliens are not present (either directly or via probes) in our solar system, simply because there is no sign of them that is obvious to us. In fact, this major argument of “anti-ET” scientists seems so firmly rooted in an assumption that we have no way of knowing the legitimacy of, we might as well just sit back and chill a bit. If they can get here, they can choose to remain totally hidden if they want to. Or, crazy thought, maybe the solar system is pretty big, and we have barely begun to scratch the surface of what is out there? For all we know, there are alien fish swimming in the water ocean of some moon in our very own solar system. Or maybe not. But it seems like we have so little evidence either way at our disposal, it makes almost no sense to come down so hard on one side of the argument or the other.

  5. 1. Not to argue, but the idea it would take millions of years to fill the universe required a set of unrealistic assumptions, including no statement of “why” or cost or size of population needed, etc. If you were to back through these assumptions, particularly the cost and the as yet impossible mechanisms of sustained very, very long distance travel for large groups of people (who somehow maintain a “civilization” despite relativity, etc.), I suspect you’d be back to saying there may be tiny bubbles of intelligent life, likely on individual worlds, maybe spread slightly. (And I note the original papers made strange statements like there’s no reason to believe other species would have similar lifespans. Huh? I can think of dozens of reasons, mostly related to lifespans on our planet, what we know about the mechanism of evolution and the internal “lifespans” of cell mechanisms, etc. To say there’s no reason is what I consider an intentionally dumb statement designed to obfuscate a difficult area.)

    2. We could assume life at roughly our stage is relatively rare and still have hundreds of billions of intelligent life species. They could be distributed at the galactic scale, something you mention but without a number (as I remember). We may be the only species at our stage now in this galaxy and there may be other galaxies where there are 10 species or none or some other number. This isn’t a word game but a question of determining the correct probability space, something we can’t actually do with this question.

    1. The estimated time to fill the galaxy with intelligent life is based on the cheapest and fastest idea, which is to send off some self-reproducing machine intelligence which is very small and light and easy to transport. Then when our mechanical seed arrives at a planet of a new star, it reproduces by building copies of itself and sends some of them off to other stars. A few million years after we start this process, it has filled all inhabitable planets of the galaxy. That time is so short compared to the time it took life to evolve on Earth that it would be a miracle if the first intelligent life to follow this plan didn’t fill the galaxy with its spawn. And the universe is so young, compared to it’s full lifespan, that it would not be surprising for us to be the first in our galaxy to have the opportunity to do this.

      1. How do we know one has not already arrived in our solar system? It might well be programmed to avoid interfering with habitable planets. There is no reason why, if its prime mission is to observe, report and send off copies of itself, it has to reproduce to its full capacity within our system.

      2. And *why* do we want to fill the universe with self-replicating machines, again? Sure it’s cheap and fast, but in the end, what’s the point?

  6. “Dobzhansky cited the fact that of the more than two million species living on Earth only one had evolved language, extragenetically transmitted culture, and awareness of self and death”
    Except this paper is from 1973 and by now we are pretty sure that every single one of those assumptions was wrong.

    1. Unless you’re talking about our extinct cousins, it’s pretty likely nothing else on earth has language as we define it. But culture and awareness of death? Yeah, other animals have that.

  7. There is the other fact that few people site: intelligent lifeforms, though not inevitable in favorable environments, can become extinct on a planet as quickly as they evolve whether by circumstances or by their own actions, making detection or contact even less likely.

  8. After reading the article you cited regarding the unlikelihood of intelligent life existing elsewhere in the universe, I would point out that I perceive a few logical omissions. Firstly, the source article announces that it has taken 3 billion years for intelligent life to form on our planet, and then compares this to the total life span of our star. It is true that the first few billion years of our planet’s existence was filled with single-celled microbes in sheets on ocean floors, but it’s important to acknowledge that life appeared nearly immediately, implying that if it is possible, it is likely to happen. Further, throughout those first couple billion years, the earth experienced many disastrous global upheavals, with life surviving each time (evidence suggests that life formed while the earth was still bombarded with inter-planetary objects and planetoids) and there is [as yet unproven] evidence that the earth experienced at least one total global glaciation. With that, we can establish the resilience of life. Further, it was only just over half a billion years ago that life started taking forms that we might consider familiar, multi-cellular organisms with organs with specific functions and uses. Since then, life has diversified explosively. Throughout earth’s history, we can classify the world biologically by the dominant animal species on the planet, the synapsids controlled the planet for most of the permian, followed by dinosaurs and after their extinction, mostly mammals. Each group has distinct behaviours and physical traits that made them the dominant kingdom or species for their time. If we look at our own species, humans or homonids or however you want to group us, we are mammals. It was the rise of mammals on the planet that positioned us to become the intelligent species we are today, and of our traits which make us so good at dominating the planet, many of them can be traced back to those that make mammals so successful, such as how we raise and care for our young, pass knowledge to future generations, have higher metabolisms and our ability to adapt to different climate types and locations on the planet. On a cosmological or geological timescale, we moved from tree-dwelling apes to ground-based hunters in a matter of a few million years, and further, from basic hunter-gatherers with simple oral traditions to a species that has visited their planet’s moon in a few thousand years. Therefore, I submit that if life is able to form on a planet, it very likely will. From there, it would be incredibly difficult to get rid of, and will likely progress far enough (however long that takes) to become multi-cellular. From there, it will continue to progress and adapt. Eventually, a clade of life which focuses on care-giving and rearing as opposed to flooding the eco-system with offspring will form, and given the opportunity, dominate the global eco-system. After that, a species merely needs to be placed in the position to become intelligent to nearly guarantee that it will do so.

    Given enough time, intelligent life can be considered inevitable, and on planets which did not experience such dramatic ecological catastrophes as earth, it might rise much sooner.

    Finally, how can we assume to understand how and why a more advanced civilization behaves as it does? It’s likely that the initial basal needs and desires of such a race would match our own, but they too may have had much more time to come to terms with it. Will a space-age civilization advanced enough to cross stars still be burdened by problems of over-population and the desire to conquer and own? It’s very well possible that once they attain the ability to do so, they may no longer have the drive for it.

    Consider this: when Europeans first arrived in North America, disease, racism, and conflict lead to the eventual demise of much of the culture and people that once dominated the continent. In the modern world today, such killing, disease and racism would be considered abhorrent, (of course there are many modern instances of peoples meeting the civilized world and still dying from disease, such as in the amazon rainforest) yet, we are no where near as eager to wipe out masses of people simply for our own gain. Consider then, that a race which has traveled across the stars may take as much care as they could muster with any civilizations or life that they met. They may believe in the right for such life to exist on it’s own and to not have to deal with an invasive species.

    Are we right to assume that a civilization so advanced would still be subject to desires over their own reason? Humanity has only turned to logical thinking on a scale measurable in thousands of years.

    Still, compare modern society to life 200 years ago. Our methods of communication would be completely alien to them, the ability to talk instantly over distances or observe actions from orbit around the planet- can we assume that all forms of communication and travel are even comprehensible by us, or that such beings in possession of them would make themselves known to us?

    I just believe that there are variables in your argument to which you have assigned values as if they are constants, and which I believe are very much open to debate.

  9. What if there are many space faring species, but none are intelligent? They just have evolved to survive in space. Maybe they only visit the gas giants, so we never see them.

  10. Who the hell would want to be around a civilization so self-destructive they have enough nukes to obliterate their own species.

    All jokes aside, this assumes that intelligent life lives within the same biological and physical constraints we do.

  11. I’m gonna go with physics on this one. By sheer probability there is likely other intelligent life in our galaxy, who cares if they haven’t visited us yet? We haven’t exactly visited them… Evolutionary biology has only been a legit scientific discipline for the last decade, with the emergence of high-throughput sequencing. And half these studies we take for “truth” are probably based on poor statistical models that were accepted into a high impact paper because the reviewers thought it sounded cool. For all we know ETs came to earth billions of years ago and cooked up the “primordial soup” themselves. Biologists have way to much huberus for a discipline where half the experiments are unreplicable (c’mon guys, isn’t that like one of the commandments from the holy Scientific Method?). if “Sagan syndrome” means humbly accepting that we know almost nothing about our universe then I’m definitely a “Saganite”.

  12. Interesting argumentation, but it relies one some premises that may be false. For one thing, that galactic expansion is easy for a sufficiently advanced civilization. As far as we know, interstellar travel is only possible at a small fraction of light-speed, which means centuries to reach the closest star system; planets that are habitable by any particular species may be spaced by many thousand years of travel. Sci-fi movies propose gigantic spaceships with a self-contained ecosystem and a multi-generational (or hybernating) crew that could colonize other worlds, but this may not be very easy even for an arbitrarily-advanced civilization. It’s more likely that only unmanned probes can spread through the galaxy, but then, proposing that such probes would have the ability to bring life or intelligence to other worlds in a reliable way (a la 2001’s monolith) is just another big leap of faith in SF plots. Sure the probe could carry some bacteria everywhere, but even if it gets lucky and its life seeds thrive, that panet would only produce a new generation of intelligent life some billions of years in the future. Alternatively, we could have a single civilization that carpet-bombs the whole galaxy with its seeds; this could reach everywere in a few million years, but you still need to wait billions of years before even a single planet evolves advanced life, and the civilization of origin would need to send billions of probes which doesn’t seem like a reasonable effort. You can speed up the process with much bigger probes that, a la Noah’s Ark, carries more advanced and varied life; but then their adaptation would be exponentially more difficult, unless the probe also has some ability for terraforming (another staple of Sci-fi but not real science yet), or gets super-lucky and finds planets with perfect environments (but these would already contain life, as a biologist will certainly realize — so the best result you get is that of an invasion, but not creation of life where it didn’t exist).

  13. Some other explanations for why they are not here, yet exist:
    1) We are at the beginning of our evolution.
    The chances of other intelligent species in any neighboring planet being at the SAME stage of evolution as us is what is remote. Life has not yet evolved intelligently, OR it is so much more highly evolved (100,000 years is nothing in the cosmic timeline) we wouldn’t recognize them or see them.

    2) Its harder to travel to other worlds than we think.
    We like to imagine starships or even life ships traveling to other worlds. What we may discover is that it is beyond practicality to do so – the most we will ever have is probes. We will likely find it is impossible to travel Star Trek like distances.

    3) Given these two-
    It may be in our “neighborhood” (300 light years) we are unique.

    and I will add
    4) Maybe “Independence Day” was right about one thing – the perspectives and understandings held by other intelligent species may be highly different from our own. Its unlikely they will be malevolent, but they may have as much trouble communicating with us as we do communicating with Dolphins and chimps.

  14. Let me try a FAQ format to respond to questions about my post:
    1. How do we know aliens will expand? We don’t. But… Darwinian evolved life tends to fill ecocsystems. And it only takes ONE who wants to expand to flood the galaxy very quickly. So either you argue that NONE ever will attempt it with self-replicating robotic probes, which seems presumptuous. Sine we’ll likely do it. Or you are back to square one saying it’s very rare.
    2. won’t it take more than 20 million years to expand? Surprisingly not, even with relatively slow ships travelling 10% of speed of light. Math here
    3. What about the great filter? An obvious great filter is multicellular life, which is behind us. There are strong biological reasons to believe this, plus the timeline of life’s development on Earth (multicellular life coming very late) supports it. More in my post here

    Thanks for reading. An interesting topic, with little data to go on.

    1. No. 1’s a good point. Assume at least one Klingon-like species evolved at some point, it might be compelled to spread across the galaxy and likely leave evidence of their former (possibly current) existence. Assuming interstellar travel is feasible within the lifespan of a civilization. (One could also envision a species incapable of the level of cooperation or imagination necessary for galactic expansion.) Of course, a species compelled to simply distribute robot probes would not necessarily be visible.

    2. Nathan Taylor : “So either you argue that NONE ever will attempt it with self-replicating robotic probes, which seems presumptuous. Sine we’ll likely do it. Or you are back to square one saying it’s very rare.”

      Err… You’re leaving one argument out, in fact the argument that seems to be held by most serious (and many not so serious) SF authors and used again and again in their stories: Any intelligent, high technology civilization is going to be bowel looseningly terrified of star faring self-replicators, and with very good reason.

      The first high technology civilization (or first couple) that arise and stabilize to become long-term viable in this galaxy is almost certainly going to put the prevention and destruction of star faring self-replicators towards the very top of their civilization’s mission statement.

      Oh! And I suspect they will be just as scared of any sort of star faring-self replicator, multi generation ships full of humans included.

      In fact, looking at humans, I reckon they are far more dangerous than self-replicating robotic probes.

      Of course, in a few galaxies the first long-term viable civilization may make different choices, but hey, vive la difference, even if it does not turn out happily for them.

      Stephen Heyer

  15. I really don’t like talking to the pro-ET people, as they insist that they know the probability of life forming, as well as the probability of intelligent life forming. Where did they get these probabilities? From their rears. And so they’ll insist that since there’s so many planets in the universe that there MUST be intelligent life, based on the probability that they invented. And well…that’s not how things work. I can believe that the probability of me winning the lottery is 95%, but that doesn’t make it true. If you don’t know the probability, you don’t know the probability, no matter how much you claim otherwise.

    And really, any time you don’t know the answer to a question, just admit you don’t know. There’s no prize for guessing right, and to assume that your guesses are fact is downright unscientific. Science isn’t about accepting everything until proven false. It’s about accepting nothing until it’s proven, and knowing that even that is likely to change over time. It’s like someone who reads murder mysteries and can’t skip to the end, so they make up their own ending and move on to the next book, assuming they already know who did it.

  16. I’m sorry but I don’t find Fermi’s paradox terribly embarrassing. The following is an excerpt from a book name of Contact with Alien Civilizations: Our Hopes and Fears About Encountering Extraterrestrials. And, no, this is nothing like Whitley Strieber:

    Consider the challenges that radio searches face: the vast number of stars to be surveyed and the wide range of possible frequencies on which a signal might be transmitted. Even the best SETI programs are limited in their coverage; no system looks for everything.

    The vast majority of search space remains unexplored. Search space does not just mean the three-dimensional volume of the Galaxy. As the Jet Propulsion Laboratory’s Michael Klein explained, it is a multidimensional space that includes source location, signal frequency, power level, time of arrival, signal modulation, and polarizations.[9]

    The NASA program, if it had been carried to its planned conclusion, would have explored only one ten-billionth of the cosmic haystack. That haystack is so immense, said Drake, that no theory, no amount of dedication, no endless hours at the typical radio telescope is going to produce a thorough search.[10]

    Jill Tarter reminded us of the scale. “We’re going out now 155 light years in a galaxy that’s one hundred thousand light-years in diameter. It’s way too early to get discouraged.”[11]

    The book has a little more to say about this, but I omitted it for brevity. I will however add the factors of encryption and/or compression, which will tend to make a signal look like noise. While I share Sagan’s assessment that there is a high probability of the existence of extraterrestrial beings, even in abundance, I do not share his attitudes about things like pacifism, particularly the inevitability of pacifism in the interstellar arena. I can thus think of quite good reasons to make a message alerting the whole Universe to your presence as imperceptible as possible.

    It is also entirely possible that communication through media other than electromagnetic transmissions that we don’t yet know about, or can’t even comprehend with our feeble simian intellects, may be preferred greatly to the means of communication we have now, which seem virtually useless over distances where the apparent speed limit of the Universe truly comes into play.

  17. I like the Neil deGrasse Tyson quote on extra terrestrial life: It is possible that other life in this universe is so advanced that we have actually witnessed them but were unaware because we didn’t have the intelligence or understanding to comprehend them. And maybe they haven’t stopped to say hi because, if they are that sufficiently advanced and intelligent, we would be like uninteresting worms to them. How often have you stopped on the sidewalk to have a real conversation with a worm?

  18. We humans are unique as a species. Other “species” most likely and probably exist, but not exactly like us. Conditions are unique here on Earth. I wonder why everything that occurred was “accidental” or “lucky” or “fortunate” or coincidental.” How many coincidences can there be before we believe that something greater and far more Divine can exist?

  19. We humans are unique as a species. Other “species” most likely and probably exist in the universe, but not exactly like us. Come on…think of each nuance of time and development. Nothing can replicate our growth and development! How many coincidences, or luck, or fortune, or accident can there be before we believe that something greater and far more Divine in the universe exists?

  20. There are many things that are imperceptible to us because of the limitations of our senses unless/until we discover the technology to detect them. There are creatures on earth that can perceive light at different wavelengths or sound at different frequencies. We can’t assume that we have the ability to detect ET.

  21. SETI is finally learning where to aim. They need more funds since Kepler. We also need more Kepler missions.

  22. No civilization, no matter how advanced, can populate the galaxy. The stars are too far apart. Even with the best propulsion systems, it takes tens of thousands of years to travel to the nearest stars. It seems inconceivable to me that any life form could sustain a search and settle strategy in the face of the time constraints that distance imposes. Perhaps at the center of the galaxy, it might be possible, but not at the outer reaches where Earth is located.

  23. With our fastest and biggest rockets, we could get a small payload to our nearest star (obviously excepting the sun) in about 50,000 years. To assume that within 20 million years a species can fill a galaxy is to ignore the fact that life as we know it is, simply put, incapable of travelling away from its host star using point a to point b travel. I mean it would take light longer to make its way across the galaxy. The whole post hinges on the idea that life automatically and magically figures out faster than light travel – in other words, wormholes etc. Whilst I know that’s possible according to Einstein, it just seems that the author is ignoring the scale of a galaxy. A galaxy is not an ‘ecosystem’ by any stretch! If our proposed aliens were as advanced as us, we would never, ever see them…

    1. I think you may have confused the size of the galaxy with the size of the universe.

      The milky way is only 100,000 light years across. If we master interstellar travel, even at sublight speeds, 20 million years is plenty of time to populate a galaxy.

      That is a reasonable sized ‘if’ though!

  24. I’m still on the fence on this one.

    It’s unlikely I’ll ever be fully convinced the galaxy is devoid of intelligent life, but that is just because it’s impossible to prove a negative. There’s no way to prove there’s nothing out there until we’ve looked everywhere.

    However what would get me wandering toward the ‘aliens should be everywhere’ camp would be the discovery of life within our own solar system. Once we find life that has evolved completely separate to ours, even just simple bacteria, it becomes more difficult to cling to our position as unique in the cosmos. If we can find simple life under a rock on a jovian moon, there almost certainly has to be something more complex ‘out there’.

    Till then though I’m quite happy to sit here with no set opinion either way.

  25. There’s a strong assumption that aliens would be like us, and would find our world interesting to visit. But what if they aren’t? What if they are entities that float around the atmospheres of gas giants. Why would they come to earth? Why would they care? Or what if they are pan dimensional beings that manifest themselves to us as an occasional feeling of irritation? For all we know, the universe is full of intelligent travelling entities that simply aren’t interested in us or our world.

  26. ET’s are already here. They “heard us” detonating our atom bombs in the 50’s. They came, they said take me to your leader, and that was that. They’re been working with our military ever since. We don’t see them because their ships are invisible to the naked eye. Light bends around your ship when it’s surrounded by a gravitational field. Infrared picks them up nicely though (see STS-80 or other NASA mission footage from the 90’s).

    Any time a visible “UFO” is spotted (like the Chicago O’Hare sighting) it’s most likely a government created, human piloted ship.

    “We already have the means to travel among the stars, but these technologies are locked up in black projects and it would take an Act of God to ever get them out to benefit humanity…Anything you can imagine, we already know how to do.” -Ben Rich, Lockheed

  27. Expanding through space in no way equates to expanding across an ocean. There’s food in an ocean and after falling from the sky.
    I can’t see any civilisation. Having enough energy available to viably get to their nearest star system …

  28. I don’t think the issue is “whether” or not there is life out there. I just don’t think they or we have the technology to see each other.

    Take for instance the “old” and “new” worlds. Until Europe had ships that were capable of making it to the “new world” there was no way for them to tell that there was a new world.

    Yes there were those that calculated the circumference of the earth and through that calculated that there maybe land there that we didn’t know about. But that sounds a lot like now. Right?

    Also keep in mind that with our telescopes we are seeing thousands of years back in time. Where were _we_ back thousands of years ago. We had Egypt that was a super power of its day but it wasn’t like Egypt had space ships that could travel to another planet. We still don’t have that. Okay, we don’t have one yet that has traveled to another galaxy yet. So where really does that put us?

    Keep in mind that if it hadn’t been for wars we wouldn’t have had the technology that we have now. It’s amazing that we haven’t had world war 3 which could have easily put us back into the dark ages or living in caves. Only because of the very fragile peace that we’ve had have we gotten this far. If other people on other planets are made up of the same DNA they could be having this same problem. And who’s to say that in twenty years we won’t be in the middle of WW3. Looking at the sudden cooling of relations between Russian and the U.S. and how they could cut us off from the space station if they wanted to.

    The odds of there _not_ being other people as we know them on other plants, if DNA there is the same as here, is zero to none in my book. The question is what _percentage_ of planets have people on them.

    It’s not a matter of _if_ we can see or communicate with them. People is so fragile that we can’t stop getting into fights just like with siblings. The question is whether on each one it helps us make gains in technology like rockets or whether we end up blowing each other up and sending us backwards.

    Why haven’t we seen or heard from them yet? Radio waves take time. It could be thousands of years before they hear or see ours and vis versa. It might take thousands of years before their and our radio waves cross each others let alone reach each other.

    What about space ships and aliens on our planet?

    I’m laughing about this one. I see the chance of this being so close to zero percent that it really isn’t a laughing matter. I don’t think that we’ll create the technology to bridge that big of space in the next three hundred years. I could be wrong of course. But it is more than just the propulsion systems too.

    We have a _lot_ to learn when it comes to shielding ourselves from radiation in space. Then there is what happens to us in the vacuum of space without gravity. What about food? We would have to have a big enough ship to make it possible to grow food. That big of a spaceship takes money and would cost billions even if we knew how to keep out radiation that would kill the plants along with killing us.

    Humans on our planet like to think we are so smart when we are still babies when it comes to space exploration. Even our brightest minds still bicker instead of working together.

    Just like it took thousands of years to go from grabbing onto a floating tree to making a raft to eventually making a boat to a ship to the bicycles and hot air balloons and then motorcycles and cars … I still think we are a long ways away from being able to go from Earth to Mars without dying of radiation and/or starving to death. How do we expect to get to the stars?

    If people on other planets were ten times further along then us they still wouldn’t have what it takes to make it here. And if they could, we should be VERY afraid as humans with our DNA have shown that whenever we find something new we get afraid and when we are afraid we kill it. If they can make it from their planet to ours and they act the same way, they will get afraid and kill us or they will catch our germs and die of disease like the people of the “new world” did when Columbia “discovered” the “new world”.

  29. how long would it take before a civilisation develops the weapons technology to allow every home to easily and cheaply have its own stockpile of nuclear weapons and how long would it last after that point if it hasn’t already wiped itself out? Intelligent life may have developed many times all over the universe and in cosmological time scales instantly disappeared in the very moment it came in to being, each and every one may have gone in a flash.

  30. Copied from Pharyngula, where I first saw this post, with slight edits:

    “Now we’ve nailed it. It’s Evolutionary Biologists versus Astronomers. In table format:”

    Oh hey, I skipped over this the first time I read this, but wow, this table bugs me. Hell, even before getting to this bit the entire post was patronising, but this takes the cake. Do you honestly believe this to be a reasonable, non-smarmy summary of astronomical thought?

    “Earth life is unique.”
    This statement can be read in at least two ways.
    1: Earth life is unique in the sense that none of the species here will be repeated on another planet with another evolutionary history. It’s possble that organisms occupying a similar ecological niche might have some similarities through convergent evolution, but they will still be different in other ways.
    2: Earth is unique in that it harbours life at all.
    In my reading of the respective summaries from biologists and astronomers, the biologist is answering reading #1, while the astronomer is answering #2.

    Thus, I think these comparisons are unequal, but this disagreement has nothing on the astronomy caricature in response to the second proposition.

    “Can’t be. If this is true, then the aliens should already be here.”
    Loads of reasons why this is not a necessary conclusion, several of which are astronomical / physics in nature: space is big, FTL is probably impossible, sublight travel is inadequate etc etc.
    “And since they aren’t this implies Earth is unique.”
    No, that’s a stupid conclusion given the variety of reasons why an alien visit is unlikely; and given that plenty of those reasons are well known to astronomers, the author of this image is basically calling astronomers idiots.
    “Copernican violation. Error. Error…”
    And from here on it gets nakedly insulting.

    Given the very basic nature of the logical errors masquerading as a summary of astronomical thought, it follows that A) you (and the author) think the state of astronomical thought has not changed since Sagan (which is similar to saying evolutionary biology has remains in lockstep with what [famour biologist] said 40 years ago), or B) your appraisal of astronomy is overly simplistic.

    1. This is one of the best comments in this thread. It’s a direct and fair criticism of the piece. I should have done better on this when writing. Sorry about that.

      Unfortunately I think Pharyngula overplayed this flaw in his commentary, making a moderately bad mistake a far worse one. In my piece I was trying to develop a contrast of world views, of which there is a tendency for astronomers to be more in one camp then the other, which I think is not just historically true but still true. The idea that replicating probes would swamp the galaxy quickly is a very biologic idea, and that’s really what I’m attempting to contrast, those who support it and those who don’t. In the real world that won’t split cleanly along astronomer/biologist lines. Then in the next paragraph after the table I talk about taking an Astronomy class in college at Cornell where Sagan was when I was in school (which was great by the way). The goal of the entire post was to make the search for ETI recognized as an interdisciplinary problem. Yes there is some strawman aspects to drive the writing narrative, but ultimately I was hoping the point would be that astronomers and biologists need to work together on this. Yet in practice you see astronomers (who are doing the hard work of finding exoplanets) getting interviewed about life elsewhere more so than biologists. Mostly this is lazy journalism, not astronomers fault for answering questions when asked. Hence the title of the post: astronomers should “pay heed” to biologists. If you go from the table to the very end of the post, I try to reconcile the two views as supportive, but only if SETI considers more strongly looking beyond this galaxy for life.

      The last paragraph is a direct call to the hope that Carl Sagan (and by implication current astronomers) would not be averse to working together.

      Along those lines, I was glad that Astrophysicist Sean Carroll was favorable to the piece on twitter. Though if you click through, obviously some negative responses. But sure to scroll down as Astronphysicist Brant Robertson had some suggestions. Likely I will do a follow up along those lines.

      In any case, a good criticism. It stings, but is deserved. Just trying to explain a bit more. Thanks.

  31. Intelligent life will probably be extremely rare. Most stars will likely not hold any life-bearing planets, and most of the ones that do will have bacteria worlds, which is what Earth was for the vast majority of it’s existence.

    Off the bat, I’d be quite comfortable for example, eliminating red dwarf stars as havens for intelligent life. Perhaps the more stable and clement ones will have planets hosting something akin to a black algae bloom, but I suspect even that is rare. Red dwarf stars, though they make up 8 out of 10 stars in the galaxy, just have to many unfortunate properties that make them unlikely to host life, and certainly complex life.

    But of course some stars will have the right properties, the right chemistry, the right planets on which this chemistry can happen, that some type of life will arise there… And they’ll by far most likely be microbes.

    Not to mention that if we look at the earth, most of the period with complex life would make earth a wildlife world without intelligence.

    But lets say that we then take this small group of planets where intelligence does come around. It does not need to get technological. Humanity spend most of it’s existence in the stone age and some tribes still live roughly like that in distant rainforests. Or perhaps the intelligence lacks a body with fine dexterous tool.

    And further still, humanity seems quite keen on always skirting around it’s own extermination. Perhaps humans will wipe themselves out one day, and perhaps so will alien races.

    Now on the scale of the universe, this still would result in millions and millions of species of technology using aliens… BUT… they may well be two galaxies away from us, where we’d never encounter any of them.

    All in all, these people who claim that red stars will host advanced civilizations because of camelot zones inbetween the night and day half of the tidally locked world, to me seem like the people who used to draw dragons and people with dog heads or one leg on ancient maps, assuming there’d be strange beasts out there.

    The truth almost certainly is… any life at all will be tiny islands in a vast ocean of dead chemistry and physics. And it’ll mostly just be sludge.

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