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Extraterrestrial Life: The Need for an Answer

An article in Time Magazine’s latest issue caught my eye as I thumbed through it while waiting in line at the grocery store. The magazine is running a feature called ‘10 Ideas That Will Change the World,’ and they tend toward being optimistic takes on huge problems. Thus the deficit gets an essay about how we’re going to fix it, while Afghanistan gets a thumbs-up for progress in the right direction. The article finds gold in everything from direct mailings (OK because they help charities raise money) to modern airports, which are creating a new kind of community.

And in the midst of this is a puzzling piece by Jeffrey Kluger called ‘Relax: You Don’t Need to Worry About Meeting E.T.’, where the upshot is: ‘Don’t worry about contact with extraterrestrial civilizations. It will never happen.’ Here’s a quote:

Humans and aliens haven’t connected yet, but with 1022 stars out there (that’s 1 with 22 zeros), it’s just a matter of time — right? Wrong. If exobiologists have learned anything, it’s that you and your kids and their kids’ kids will probably never hear the slightest peep from an alien. If E.T. the movie star is your idea of what extraterrestrial life might be like, you will be disappointed. If your thoughts run more to War of the Worlds, you can breathe easy.

Breathe easy? Let’s assume for a moment that Kluger is right, that contact with an extraterrestrial civilization is simply not going to happen at any time soon or in the future. If we knew that to be the case, would it be a cause for relief? For optimism? Maybe I travel with the wrong crowd, but most of us would be disappointed at the thought that we might never know whether intelligent civilizations exist around other star systems. Even those of us who think a confirmed SETI signal is unlikely any time soon — and I am one of these, believing that intelligent life is extraordinarily rare — would still hope to be proven wrong, and thrilled if we were.

Failure Is Not an Option

Kluger mentions both ‘E.T.’ and ‘War of the Worlds,’ so he’s not just reacting to disaster-oriented invasion films like ‘Battle: Los Angeles.’ The magazine seems to be implying that just the knowledge that we are either alone or unable to communicate with other civilizations is the solution to what Time bills as one of our worst problems. That phrase is used in the lead-in to these ten essays: ‘Our best shots for tackling our worst problems…’, of which knowledge of an alien culture is billed as number three on the list. And I’m wondering, since when is the idea of failing in our attempts to gain scientific knowledge considered the solution to a problem?

The essay goes through the difficulty in finding ETI, including our reliance on a sample of one to construct theories about life’s development on a planet, our uncertainty about how likely life is to develop even on worlds similar to our own, and the difficulty in finding an alien culture through SETI. That last point gets a quote from Don Brownlee (University of Washington), who notes the distances involved in going from star to star in the galaxy and says, “If the nearest hundred or thousand stars don’t have life, we probably won’t ever, ever, ever know about it anywhere else.”

That’s an interesting point if you strip it down to its basic assumptions. Picking up signals from a civilization something like our own would be a hugely difficult proposition even if they were being broadcast from a place as nearby as Centauri B. Pushing the distance out to a thousand light years makes things even more problematic. But we don’t know how long civilizations can exist, and the possibility of one living long enough to be thousands of years — if not millions — more sophisticated than our own can’t be ruled out. The factors that make a chance reception of a signal from a civilization like ours so tricky would be negligible to such an advanced species.

That possibility is one reason why we continue to look. And the fact that we have a sample of just one living planet to base our conclusions about life on is why we continue to look for life elsewhere, to broaden the sample and learn more about life’s mechanisms. So I don’t find any of this convincing in terms of making our detecting an alien civilization less likely to occur.

SETI, Distance and the Odds

But the point about stellar distances is still an interesting one. For one thing, we have a new paper by Joseph Catanzarite and Michael Shao (JPL) analyzing the Kepler science results that attempts to extract an estimate on how common Earth-like planets are. Let me quote from its summary:

Kepler’s science team has determined sizes, surface temperatures, orbit sizes and periods for over a thousand new planet candidates. Here, we show that 1.4% to 2.7% of stars like the Sun are expected to have Earth analog planets, based on the Kepler data release of Feb 2011. The estimate will improve when it is based on the full 3.5 to 6 year Kepler data set. Accurate knowledge of nEarth is necessary to plan future missions that will image and take spectra of Earthlike planets. Our result that Earths are relatively scarce means that a substantial effort will be needed to identify suitable target stars prior to these future missions.

We’re dealing with results that will be improved as the Kepler mission continues, but the figures so far cited indicate that planets like ours aren’t terribly common. Yes, it’s true that even with these low percentages, the option is still open for millions of Earth-like planets throughout the galaxy, given the sheer number of stars involved. But that other big imponderable — the question of how long civilizations last — still faces us. If they don’t tend to survive very long after they develop the ability to destroy themselves through technology, then Brownlee’s point has more resonance. And certainly these numbers say the nearest Earth-like planet may be a substantial distance away, a fact that will make studying it even more challenging than we first thought.

So yes, looking for ETI is difficult. But I can hardly share Kluger’s certainty in Time. He ends the essay, having looked at the possibility of alien extremophiles on Earth, by saying this:

Of course, even such aliens would hardly be the kind we either crave or fear — those who could regale us with tales of what things look like on the other side of the cosmos on the one hand, or conquer us with their superior intellects on the other. Too bad — or maybe very good — you’re never going to see them.

‘Never’ is a curious word to use in the midst of a great scientific investigation, one in which we hope to start assigning some reasonable values to the Drake Equation and find out just where we stand in terms of our place in the galaxy. We know so little, and Kepler and CoRoT are only the beginning of our space-based exploration of exoplanets increasingly like our own. We all have our views on this, and some of us are going to be proven wrong, but our investigations into extraterrestrial life are among the most energizing scientific projects in the history of our species. How could anyone possibly regard a failure to learn the answer as a good thing?

The paper cited above is Catanzarite and Shao, “The Occurrence Rate of Earth Analog Planets Orbiting Sunlike Stars” (preprint).


Comments on this entry are closed.

  • Bob Steinke March 22, 2011, 10:52

    It’s also curious that the article is in a feature named ‘10 Ideas That Will Change the World’. How can not discovering something new change the world? Wouldn’t it just leave us in the same state we are now?

  • Richard March 22, 2011, 10:53

    Some studies are indicating billions of earth-like planets:
    Scientists at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., focused on roughly Earth-size planets within the habitable zones of their stars — that is, orbits where liquid water can exist on the surfaces of those worlds. [The Strangest Alien Planets]

    After the researchers analyzed the four months of data in this initial batch of readings from Kepler, they determined that 1.4 to 2.7 percent of all sunlike stars are expected to have Earthlike planets — ones that are between 0.8 and two times Earth’s diameter and within the habitable zones of their stars.

    “This means there are a lot of Earth analogs out there — two billion in the Milky Way galaxy,” researcher Joseph Catanzarite, an astronomer at NASA’s Jet Propulsion Laboratory, told SPACE.com. “With that large a number, there’s a good chance life and maybe even intelligent life might exist on some of those planets. And that’s just our galaxy alone — there are 50 billion other galaxies.”

  • Alex Tolley March 22, 2011, 10:57

    The Time article was another reflection of the “two cultures” divide. My wife, who was a history major, was quite relieved about the conclusion of the article and was somewhat upset when I explained how it wasn’t as “safe” as the article suggested. People with a science mindset see the universe in a very different context than those with humanities education. Where we see discovery and new knowledge, they see threats to hide from. After 70 years of movies depicting the consequences of visitors from space, should we be surprised at that reaction?

    As the US is also quite religious, with a growing fundamentalist fraction, the presence of intelligent aliens represents a possible threat to their world view, so a suggestion that aliens won’t make their presence felt is going to be somewhat comforting.

  • Erik Anderson March 22, 2011, 11:08

    Let me confess here that I share Kluger’s certainty for two main reasons:

    1) The purely evolutionary arguments posed by the likes of Ernst Mayr, Steven Pinker, and others convince me that the process of human-like intelligence evolving out of simple life are deeply dependent upon very particular historical accidents for which the probabilities of occuring are inestimably small.

    2) The basic tenet of the Fermi Paradox is well-formulated. If the Galaxy already abounds with technologically-advanced civilizations, they would have already colonized Earth long ago. SETI experiments which target stars in the immediate solar neighborhood are thus particularly hopeless.

    It therefore seems most reasonable to assume that we live in a Asimovian “Foundation” universe rather than a “Star Trek” universe. A shift in experimental focus should be taken towards searching for habitable worlds rather than inhabited worlds. This will cost big bucks (e.g., TPF, Darwin). Unlike SETI, it can’t be done on the cheap. But the actual discovery of an extraterrestrial planet with an oxygen-enriched atmosphere, oceans of water, and large continents would definitely qualify an ‘Idea That Will Change the World.’ If such a world could be imaged at high-resolution with space-borne optical interferometry, as Daniel S. Goldin once mused, that one image alone will change the outlook of human culture forever.

  • the other adam March 22, 2011, 12:03

    ok… here are my thoughts on the matter…


    Whenever an alien invasion is described in fiction it has mostly been because of two factors: either the aliens want our resourses (water, etc) or they want to take over the Earth so they can live here. In a way that kind of makes sense (assuming the aliens are not TOO alien) because those are the reasons behind basically all of our wars.

    But think of it: why take over a planet for its resources? Whatever you are looking for (water, metals, etc.) exist in quantities of several orders of magnitude more on uninhabited planets, asteroids, planetoids, etc. You can pretty much find whatever you want in the ort cloud, so why start a war which could cost lives and waste time and expense?

    As for taking over the Earth for its real estate, once again this doesn’t make sense. Assuming that they could even live here, I think it’s a safe assumption that “M-class” planets without intelligent once again outnumber ours by many orders of magnitude. It would be easier to find and settle on one of them.


    As mentioned above, “never” is a pretty strong word. There have been lots of “nevers” that have become reality. But I’d say given how big the universe is I bet it’s an amost-never.

    As for finding any sort of life, maybe it’s a horse of a different color. Basically how much we’re willing to invest in research (more powerful telescopes, more probes, etc.) Who knows how far and long we’ll go?

  • kurt9 March 22, 2011, 12:26

    If 2% of sun-like stars have Earth-type planets, this means there are two additional Earth-like planets within 50 lys of us, 8 within a 100 lys.

    Then there is the issue of the Hydrogen Hypothesis of Endosymbiosis of the Eukaryote. This is thought to be a rare event.

    I think the two of these answers Fermi’s question for the galaxy at least.

  • Stephen Ashworth March 22, 2011, 12:37

    Paul, your quote from Catanzarite and Shao is garbled — I think you’ve accidentally transposed a phrase.

    Yes, the Time piece is strange. Failing to find aliens is more an idea that won’t change the world, rather than one which might.

    One idea which could change the world(s) is the idea of human space colonisation. This could make our civilisation’s heritage immortal, and make the Drake equation (and Brownlee’s skepticism) irrelevant. But despite dating, in its modern form, from O’Neill’s “High Frontier” (and ultimately from thinkers going back to Tsiolkovsky), that’s clearly a world-changing idea whose time has not yet come!

    Oxford, UK

  • Istvan March 22, 2011, 12:57

    “How could anyone possibly regard a failure to learn the answer as a good thing?”

    Perhaps I’m taking this too far, but I think the sentiment you’re troubled by is actually a symptom of our “popular culture” in America, and one of the things we need to change if we are going to survive.

  • David March 22, 2011, 13:24

    Paul Time causes brain damage be careful!
    I just mentioned it bby passing once in a college paper got a C and never went near it again

  • Paul Gilster March 22, 2011, 13:35

    Stephen Ashworth writes:

    Paul, your quote from Catanzarite and Shao is garbled — I think you’ve accidentally transposed a phrase.

    Yes, the quote was indeed garbled. Sorry. I cut and paste directly from the PDF, but there must have been a rogue character in there, because I just did the same thing again and got the same result. So I went back and typed the thing in letter by letter — looks OK now. Thanks for seeing this!

  • Mark Presco March 22, 2011, 13:57

    What is the current thinking on instantaneous communication?

    Years ago, I read an article in Scientific America that said photons are emitted in pairs. If one is annihilated, so is the other, instantaneously (if I remember correctly).

    All I can find recently, is that the Uncertainty Principle limits the speed of communication because the first measurement must be compared to the second measurement and this is light speed. However, if you can modulate a star though photon annihilation or some other parameter which can be measured statically, this comparison is not necessary.

    Thus anyone located slightly farther from a star than the modulator will get information instantaneously.

    Has any thought to look for modulated stars?

  • kurt9 March 22, 2011, 14:02

    The paper defines an Earth-analog based exclusively on size and being in the HZ. It does not account for density. The Kepler-11 findings suggests that many (most?) planets that are Earth-sized may still be gaseous or ice planets. Call them ice and gas miniatures. If the majority of “Earth-analogs” are indeed ice and gas miniatures instead of rocky planets, true Earth-like planets may be even rarer than the paper suggests. In such case, it is likely that the nearest “garden” world is no closer than 100 lyrs from us.

    This possibility, along with Eukaroyic evolution, does effectively explain Fermi’s paradox. Compared to other explanations, this one is rather prosaic, and therefor likely.

  • kzb March 22, 2011, 14:03

    Erik Anderson -completely agree with what you said. I like the term “Asimovian”, however Asimov largely confined himself to our own Galaxy in his writings, so I propose “Asimovian galaxy” rather than “Asimovian universe” :)

    I too think the Rare Earth hypothesis, and the even rarer evolution of our kind of technological intelligence, is the most credible explanation of the Fermi paradox.

  • Bynaus March 22, 2011, 14:36

    I agree that one cannot speak of certainty – but I guess this the article in the times is more a strongly worded “hunch”. As science progresses, we learn more and more about the universe – and at some point, a person knowledgeable in the relevant matters can utter a “hunch” that, while not provable at this point, has the ring of truth to it. To be honest, I have the same “hunch”. If we are ever to meet aliens, then it would be in the deep cosmological future, as explored from the present by, say, wormholes (but this is another topic).

    Think of it:
    1) The emptiness of space: The universe is vast, and we know there should be billions of “Earth-like” in our galaxy alone. However, it is also, as far as we know, devoid of any intelligence-like activity. Where are the type-III civilizations? Where are the dyson swarms? Where are the signals of ancient automated beacon systems? No where to be found. A universe that looks empty very probably is.

    2) The emptiness of time: Human existence is just a footnote on the histoy of our planet, and form the principle of mediocrity we can claim that this will, with high probability, not change significantly in the future. There is not a single indication that Earth has been visited or settled at any point, and it seems we are the very first civilization to arise on this planet, indicating that civilizations do not form easily, and may even be prone to destroy themselves (if that were the case, every civilization would observe to be the first on its home planet).

    Yes, we cannot exclude anything, but just as in the question whether there is a god or not, this should not qualify as a rational argument in favor of the existence of “contactable” ETI.

    3) The unsustainability of human civilization: at no point did humankind develop a truly sustainable civilization that could stay stable for the eons necessary to overcome the interstellar/intergalactic vastness, and our own does not seem to be different in that respect. Think global warming, resource shortings, dangerous technology. Civilization is, by its very nature, volatile, and the history of civilization could also be seen as a history of repeated failure. I do not mean to be utterly pessimistic: I just try to look at the facts the way they are. Just because we haven’t failed yet, does not mean we can’t and won’t. And just because we can imagine a bright future, that does not mean it will come true.

    4) The only way to some sort of long-term survival of civilization might be artificially intelligent machines adopted to the environement of space. Such AI may, however, not be interested in colonizing Earth-like planets, or getting into contact with biological civilizations.

    From all this: While I can’t prove it, I think we will have to live with the idea that we are and will always be, in a very broad sense, alone. Considering the ~100 years of intense discussions, books, movies, conspiracy theories, scientific papers on aliens, this conclusion is, I think, indeed a world-changing idea.

  • Greg March 22, 2011, 15:55

    There is only one reason I could see any intelligent life attacking another in a different star system or planet. That would have to be a extreme form of Xenophobia, perpetuated by technology. I say this because, if the technology to travel between stars is difficult then the “fear” an intelligence would have of meeting another competing intelligence would be small. But, and its a big one, if the technology to travel between stars is simple (as simple as some form of FTL can get) then the fear would be much greater, causing a highly xenophobic intelligence to attack others life forms before they develop the technology to travel between star systems.

  • Greg March 22, 2011, 16:08

    Bynaus said,

    “1) The emptiness of space: The universe is vast, and we know there should be billions of “Earth-like” in our galaxy alone. However, it is also, as far as we know, devoid of any intelligence-like activity. Where are the type-III civilizations? Where are the dyson swarms? Where are the signals of ancient automated beacon systems? No where to be found. A universe that looks empty very probably is.”

    This isn’t true, even now we are just starting to use meta-materials , allowing us to bend light. I have no doubt a civilization that has had thousands of years of advancement could do some amazing things such as re-direct the entire light spectrum of it’s star, making it impossible for us to view with our limited technology.
    I think it’s a lack of imagination when we begin not to see possibilities when there are several just right in front of us.

  • The Cosmist March 22, 2011, 17:01

    I’m wondering if folks like Sagan and the SETI founders were operating from a faulty model of the universe. What if the new picture that’s emerging in physics and cosmology is correct, that we live in a multiverse and we need to invoke the anthropic principle to explain the basic facts of our particular universe? In this model, life may be such a freak occurence that we are literally the only intelligent species in the universe, so the Fermi paradox isn’t a paradox at all. It’s all speculation at this point, but it seems plausible that the anthropic multiverse could be just another step in the expansion of our cosmic horizons that began with Copernicus. Maybe this universe was, in a sense, made just for us (just as perhaps we will some day create universes of our own), and the expectation of aliens is just an artifact of our faulty models!

    This is a pretty mind-blowing idea, but I don’t find it too disappointing. If it’s true it just means the universe is ours for the taking, and all its intelligent life will be branches of our biosphere. This doesn’t make a Foundation-type future less interesting, because as Freeman Dyson said: “The question that will decide our destiny is not whether we shall expand into space. It is: shall we be one species or a million? A million species will not exhaust the ecological niches that are awaiting the arrival of intelligence.”

  • Ronald March 22, 2011, 17:14

    Apart from the minor detail that the number of stars in the observable universe is closer to 3 * 10^23, according to recent estimates, it is both remarkable and annoying that so many people keep confusing ‘life’, ‘intelligent life’ and ‘technological civilization’, mentioning them as almost synonymous.

    The universe may be teeming with life, most of which is likely to be relatively simple single-celled or undifferentiated cell-colony, with advanced (complex, specialized organs) life being much rarer, intelligence extremely rare and technological civilization near-absent.

    Almost needless to say by now, the Time article is plain dumb. But is does indicate one important thing: first things first, foremost we need to search for (potentially) habitable planets and terrestrial planets with biosignatures, by means of spectroscopic analysis by large space-based interferometers. We can’t cut corners.

  • Malcolm Ramsay March 22, 2011, 19:16

    Cosmist, you contradict yourself when you say “we live in a multiverse and we need to invoke the anthropic principle to explain the basic facts of our particular universe”. One of the points of a multiversal model is that all possible combinations of initial conditions give rise to universes- in those where they are conducive to life and intelligence arising, it does: we live in one of that sheaf of universes.

    No creators, alien or deistic required- just good ol’ fashioned causality.

  • Michael March 22, 2011, 20:01

    that the other adam said.

    However regarding the Asimovian universe….the Robots came before the Empire. In one of the novels, I cannot remember which, the Robots, ever subject to the Laws of Robotics, decided that Mankind would do best in a universe that was inhabited only by man. So after withdrawing from the scene they set out to make it so.

    The implications have always scared me.

  • Rob Henry March 22, 2011, 20:59

    Ronald, and kurt9, you both allude to the pivotal issue of whether the development of complex life is rare. At first glance the record of life on Earth may seem to back you decisively. There may or may not be a shadow biosphere on Earth, but of one thing we can be certain – there is only one extant form of transition from the complexity level of ‘bacterial grade’ to ‘eukaryote grade’ organisation among ‘ribosomal life’, and that is we eukaryotes ourselves. But now take a second look.

    At least the heterocyst cynobacteria and myxobacteria are also comparable in the complexity of their multicellularity to lines of primitively asexual Eukaryotes. The most complex line of eukaryotes developed sexual reproduction (possible as an anti-parasite strategy) – a means of reproduction that is known to be a powerful inhibitor of the transition from single celled to a multicellular lifestyle. Its descendants occupied the niches of the most complex creatures on Earth prior to the rise in oxygen levels. As such they would have inhibited the further development of asexual eukaryote, cyanobacterial and myxobacterial lines. As for sexual reproductions advantage in retaining potential genetic complexity, this seems to rest on Muller’s ratchet and this only conveys any advantage at all in cases of small populations.

    I put it to you that abiogenesis is a very rare event, but the development of higher life from lower occurs rapidly wherever possible (such as when oxygen levels rise past a certain point), with our case being on the slower side due to the untimely displacement by sexually reproducing eukaryotes of others that were better placed for multicellular development.

  • Eniac March 22, 2011, 21:44


    Apart from the minor detail that the number of stars in the observable universe is closer to 3 * 10^23, according to recent estimates, it is both remarkable and annoying that so many people keep confusing ‘life’, ‘intelligent life’ and ‘technological civilization’, mentioning them as almost synonymous.

    I count myself among this “annoying” group.

    The universe may be teeming with life, most of which is likely to be relatively simple single-celled or undifferentiated cell-colony, with advanced (complex, specialized organs) life being much rarer, intelligence extremely rare and technological civilization near-absent.

    I consider this very unlikely. The history of life on Earth has been an unrelenting march towards higher complexity, driven by the principles of evolution. With some fits and false starts, to be sure, but with a dogged persistence nevertheless that makes the result all but inevitable.

  • Rob Henry March 22, 2011, 21:45

    Sorry, I realise now I was unwise to commit so many heresies simultaneously. What I should have stated above is that we only have one example of biology and where it leads down one path on Earth we have no reason to believe that it will in another example. This problem is exacerbated by evolutionary selection, which ensures that once one transition is made that confers a huge advantage in particular niches, a similar transition will never happen again. This makes such transitions appear rarer than they are. Worse still this misreading can be exaggerated if these niches are ones where complexity would be likely to subsequently slowly accrue

  • Eniac March 22, 2011, 21:56


    This possibility, along with Eukaroyic evolution, does effectively explain Fermi’s paradox. Compared to other explanations, this one is rather prosaic, and therefor likely.

    As has been said, 1% number of habitable planets still leaves billions, a far cry from explaining the Fermi paradox. Remember the Fermi paradox is that there is not a single, not ONE intelligent race that set out to spread across the galaxy. You are left with 9 orders of magnitude to go, and mitochondria are certainly not the answer.

    The Cosmist has it right: Our universe is one of the ones that just BARELY allow for our existance, not one of the much fewer ones that more generously allow for our AND other’s existence. Simply by the laws of probability, or by the principle of Occam’s razor.

  • Aerospace Engineer March 23, 2011, 0:06

    Excellent commentary, Paul. The bottom line is we really don’t know. The only intelligent thing for homo sapiens to do is keep looking and keep learning and resist the urge to draw conclusions based on thought experiments.

  • henk March 23, 2011, 5:46


    no it is very likely that most life is simple life. because from the earth history 4 billion years of it it had only simple life. That it evolve on earth to complex life does not mean it will happen everywhere. The moon could play a great role for complex life

  • Michael Spencer March 23, 2011, 6:47

    On reading Greg’s notion that only xenophobia would lead to an invasion I am reminded of the story about the scorpion and the frog, in which the scorpion, despite assurances, stings the frog in the middle of the stream, dooming them both. Why? “It’s what I do. I’m a scorpion”.

  • tesh March 23, 2011, 7:04

    I’m not sure I would agree with the statement below.

    I consider this very unlikely. The history of life on Earth has been an unrelenting march towards higher complexity, driven by the principles of evolution. With some fits and false starts, to be sure, but with a dogged persistence nevertheless that makes the result all but inevitable.

    Once multicellular life appeared, has it really become more complicated? It is maybe semantics but by complicated do you mean more cell types or the niches occupied or something else? Also, evolution drives adaptation and not more complexity.

    I’d also like to add, that in all the time that has elapsed since life on earth appeared, has there been any other technologically capable species? Probably not and if it did then it died out and left nothing behind. It would seem more likely that tech-capable species are a fluke and therefore likely very rare indeed!

  • Bynaus March 23, 2011, 7:16

    @Greg: As long as civilizations do not disappear deliberately, it is very implausible that they would do so just by natural evolution of their technology. But why should they want to hide? Do we try to hide from the ants? No, and why should we… As I said: I cannot exclude anything, and this is why I stated this as a “hunch”. But as we look out for signs of other civilizations, and can’t find any, the most simple answer is not that they all somehow hide and erase all possible trace of their existance, but that they plain simply do not exist. This may be sad (if you belong to the “E.T.”-crowd) or good (if you belong to the “War of the Worlds”-crowd), but whether we like it or not was never the question.

  • kzb March 23, 2011, 8:43

    Bynaus, I have the same hunch. There are of course all kinds of possible explanations of Fermi’s paradox, and these have been discussed at length on here -many times over. But by Occam’s razor you have to select the simplest explanation, and that is “they” just are not there.

    I’ve also wondered about the anthropic universe for a long time, and I find it an attractive theory. There is some quantum -level connection between us and the beginning of the universe, which crystallised OUR universe into reality, all others remaining “virtual” universes because there is no-one to observe them.

    Personally I find it reassuring that we are not in a crowded galaxy with lots of races competing for resources.

  • Bill B. March 23, 2011, 9:34

    A lot of folks have made up their minds about the likelihood of ETL and/or ETI. While I would love to know the absolute truth on the matter, I also enjoy the great mystery of it. We are now just scratching the surface from pure speculation (outside of the example of our own planet, and the small amount we know of the potential for life in our own planetary system) to hard data, so why rush to draw conclusions? If there are ancient advanced civilizations out there, perhaps they are just doing stuff that is so beyond us, we can not adequately project what they would be doing. Maybe they do not have a need for giant Dyson spheres, powerful radio beacons, or colossal power sources, or maybe they can just hide it all really well. If the galaxy is teeming with life we need to get out there and discover it, and if its mostly or completely barren then we should get out there and spread it. Win win situation. Should there be hostiles out there it wouldn’t be the first existential threat to humanity and it probably wont be the last. Even a hostile encounter could be beneficial to the advancement of humanity, assuming we survive it. So again win win right?

  • Ronald March 23, 2011, 9:36

    Eniac, I often agree with you but now I am almost a bit disappointed ;-), agreeing with henk and tesh;

    – Life and evolution are all about survival and adaptation, this is not an opinion but a rock-hard and verifiable principle, a driving mechanism.
    Intelligence (i.e. big brains) is NOT an inevitable outcome of this driving mechanism, but just a possibility, just like wings, flippers, gills, long necks, …

    – With regard to complexity, life on earth has done successfully without it for more than 3 billion years, without intelligence for some 4 billion years. And even where higher intelligence has arisen (primates, cetaceans, some bird families such as crows and parrots, elephants) only one lineage has led to truly self-aware and technological intelligence.

    – A relevant question is whether the Eukaryote cell and further complexity (multicellularity, sexual reproduction, specialized organs) arose as a pure chance event or soon when certian necessary conditions were met and thresholds reached (such as atmospheric oxyygen levels). The latter case would be particularly interesting, because it would imply a kind of clockwork mechanism and a certain degree of predictability.

    – Even avoiding the discussion about the inevitability of complex life and intelligence, it is an objective and observable fact that complex life was absent on earth for about 80 – 90 % of life’s history, while higher intelligence is, needless to argue, an extremely recent phenomenon.

    Also bear in mind that our planet will become too hot for any higher life (actually any life but some extreme thermophiles) in about 0.5 gy and for any life in about 1 gy. So complex life is about halfway its history (since the early Cambrium) and all life is at about 80% of its potential lifespan.

    So, concluding, it is apparently very well possible for a planet with life to ‘avoid’ complexity (not even mentioning intelligence) for by far most, if not all, of its lifespan.

  • Ronald March 23, 2011, 10:06

    Cosmist (and Eniac quoting): strongly disagree, physically and logically wrong and contradictiry, Malcolm Ramsay is right about this;

    The anthropic principle is nothing more than an observed result, an outcome of natural processes, a seeming near-impossibility about which we wonder, like a pseudo-religion, and hence scientifically an antiquated fallacy.

    What is truly observable is the cosmological principle, the observation that matter and the laws of nature are universal. Hence, what applies here, in principle applies anywhere.

    Our sun and earth are not special classes apart from all others but rather specific conditions in a continuum of existing conditions, some very similar, others gradually different. Specimens in a long row of specimens. All observations confirm that and increasingly so. The way I often exp0lain this to friends ia by saying that our sun is only unique in the same way that every grain of sand is, in some way or another, unique.

    Hence, the mere fact that life is here on earth, inevitably means that it can also be elsewhere. This isn’t a belief or even wishful thinking, it a scientific possibility based on the observed facts that support the cosmological principle.

    Therefore also, Eniac is factually wrong (again, sorry) when he states that our universe *barely* allows for our existence “Simply by the laws of probability, or by the principle of Occam’s razor”.

    This is not only wrong, it is a contradiction: either we (life) can exist, survive and flourish, the laws of nature allowing for it, or we can’t. And then we (life)wouldn’t be here at all, and not so soon after the earth originated, not so abundant, not so long-time, etc.
    If the ‘laws of probability’ (I would rather say the laws of nature, with a certain probability) allow life to be here, and (a gradually varying range of) similar conditions exist elsewhere, then this implies that life may exist elsewhere. That *is* Occam’s razor.

    And it is our challenge to discover how (un)common that life is in the universe, not to fatalistically acquiesce in the pseudo-religious and meaningless idea that we, as a solar system, are somehow ‘unique’.

  • Greg March 23, 2011, 10:20

    @Bynaus, I agree I don’t see why they would do it intentionally. But I do see them doing it by technology. As any technology becomes more efficient it means less energy lost, meaning less energy that can be detected. If we extrapolate this natural progression, it should mean the higher the level of technology the harder to detect. Although I still think distance makes it even harder to detect. Any advanced civilization 1000 light years away would never know we exist, and won’t for another 900 years, if they could even detect our “presences” from such a distance.

  • Ron S March 23, 2011, 12:00

    I have a hunch that everybody else’s hunches and speculations are wrong. This feels absolutely true to me, so I will conclude that it is indeed true.

  • The Cosmist March 23, 2011, 13:38

    Ronald, my point was that the multiverse model gives us a way to understand why we might be the only life in the universe without becoming religious or abandoning Copernican thinking. The space of possibilities is no longer just this Hubble volume, but an infinity of universes, so the emergence of complex life *in this universe, with it’s laws of physics* could be a 1 in 10^500 per planet fluke and that’s still OK! In the vast majority of universes no intelligent life exists to wonder about these questions, so that’s what I mean by the anthropic principle. Is there something wrong with this reasoning?

  • coolstar March 23, 2011, 13:44

    @Kurt9 Catanzarite and Shao picked their limits on size PRECISELY because it would lead to results of “mostly” rocky worlds. Earth sized “jupiters” can’t exit and the proportion of “sub-neptunes” is likely to be small, given the size constraints chosen. Even the proportion of water worlds is likely to be only a small fraction of the population. A few of the earth-sized, habitable zone planets ultimately found by Kepler will have masses measured, either by radial velocity work on K & M stars (thru new spectrographs on either existing 8 meter class telescopes or the next generation of ELTs) or thru planet-planet interactions for some of those in multiplanet systems.
    Since the total predicted by Catanzarite and Shao is only about 12 though, here “few” could mean just one or two. The news is already depressing enough, without making it worse!

  • kzb March 23, 2011, 14:02

    Only the other week we were enthusiastically discussing the possibility of life on Enceladus and in ice-covered oceans on wandering interstellar planets. This brings up the possibility of Panspermia also.

    However, all the evidence (= essentially the Fermi Paradox) says that technological intelligence is at best extremely rare. The evidence we have currently points to us being unique in this regard. That’s in accord with the Anthropic universe (but it does not prove it of course).

    Hopefully we will get some information to work with within our lifetimes, in that the following questions may be answered:

    (1) Is there life elsewhere in the solar system, and did it arise separately in each location?
    (2) Are there signs of life on exoplanets?

    This will at least give us something to work with !

  • Greg March 23, 2011, 14:13

    @Ron S,
    You may very well be correct. But like in science we await to be proven wrong or right and then we move on.

  • intercostal March 23, 2011, 19:49

    I find it quite likely that we will not meet or detect intelligent alien life in the next, say, 500 years.

    This is not to say that I think intelligent alien life doesn’t exist — but I think it is unlikely that civilizations capable of large-scale interstellar travel exist near us.

    I think the Fermi Paradox is explained by a series of small filters rather than one ‘Great Filter’ — not every planet with life gets complex life, not every planet with complex life gets life with sapience /civilization-capable intelligence, not every planet with sapient / intelligent life in fact develops a technological civilization, not every technological civilization in fact attempts interstellar communication or exploration.

    I think interstellar *transmitting* by a civilization not capable of large-scale interstellar activity is an extremely bad gamble (you’re likely to make yourself visible to hostile civilizations, for no reward save pure curiosity — light-speed times make actually getting useful knowledge to solve a problem ridiculously unlikely). This logic is one that is likely to develop *even if there are no actual hostile civilizations*, since you can’t ever be sure there *aren’t*. The calculus changes once you already have a complex interstellar civilization, or have built a Dyson swarm… something detectable from large interstellar distances ALREADY… however.

    @The Cosmist: assuming 10^500 extra universes just seems counter-Occamian. If anything, if we NEED 10^500 extra universes to maintain the ‘Copernican thinking’… to me, that’s strong evidence to trash ‘Copernican thinking’ .

  • Bounty March 23, 2011, 20:01

    It’s possible that advanced (us) life forms are common in the galaxy. Using the only example I know of (us) we’re mostly undetectable to any other equally advanced life forms nearby. One day we may detect anomalies in some other atmosphere and start sending big signals that way. Or not. It may be happening between other stars already. Of course that doesn’t make star travel any more practical.

    I think maybe, because of resources, technological progress happens on a curve that we’re on the other side of. I don’t think we can assume the aliens are somehow super advanced. (If they exist.) If so, setting up decent beacons and useful METI is expensive. I would understand if nearby ET only did METI sweeps once every 500 years.

  • Rob Henry March 23, 2011, 23:34

    When Eniac states that this universe barely allows life, he is just speaking how different our universe could be and still allow life and of abiogenesis. I wish to speak to that second aspect.

    In any world that is completely driven by logical process, if we want to create a self-replicating entity whose survival depends on its stored information content in such a way that its line of descent can acquire continuing advantage with time, we have a major problem. It took all of von Neumann’s ability to demonstrate that life was even possible in such a universe. His proof implied that the reality of such a ‘machine’ was far to complex for him to outline in design, even within the mathematical universe that he had specially designed to facilitate the task. So, is our universe of that logical rule nature?

    Before about 60 years ago, biologists were uniform in their belief that the simplest life was very simple indeed, and, if so, our universe could not be of this nature. Now we know the incredible complexity of the simplest organism. Ronald is right evolution does not select for complexity. Organisms that remain in the niche of simplest organism should only retain the minimum complexity that is consistent with their existence. Eniac is only looking at organisms ensconced in tricky niches when he states that complexity increases naturally with time. If he has a failure it is in acknowledging that such tricky niches do not always exist.

    Objective evidence points to abiogenisis being an overwhelming problem, with no know mechanism that could bridge the gap. By contrast, Explaining complex life only requires us to postulate the existence of tricky niches for sufficient time.

  • Anthony Mugan March 24, 2011, 6:35

    Another interesting debate! I think it is fair comment to conclude that, applying strictly scientific criteria we simply can not yet say if life, intelligent life or advanced technologicial civilisations exist or how numerous they would be if they did. As the end of this comment will get into dangerously controversial territory I’d best start with a couple of testable predictions which stand some chance of being resolved over the next twenty years or so. First though – my assumptions…
    Given that life did appear on earth very rapidly and the weak anthropic principle illuminates that the fundamental constants of nature are well atuned for a universe in which life occurs (I am not a fan of the strong anthropic principle), combined with theoretical developments such as complexity theory and panspermia, it would appear likely that microbial life is widespread. Suitable habitats appear to be quite common (in numerical terms), based on the Kepler and other exoplanetary data and the wider range of possible habitats than pure earth analogues that have been widely discussed.
    How often life evolves towards species capable of technological development is clearly uncertain. As we exist we can logically conclude the probability is not zero. Given the available time and space any non-zero probability tends to lead to the conclusion that the phenomena will occurr many times in the universe. Clearly we can not refine that conclusion very much in terms of a more quantitative estimate without building in lots of assumptions (Duncan Forgan’s 2009 paper using Monte Carlo methods would seem a good starting point for example of a serious attempt to refine the numbers down a bit more (refs below)).
    The above would suggest that the two most probable solutions to Fermi’s paradox are either ‘they can’t get here from there’ or the ‘zoo hypothesis’, which suggests that we may be embedded within a wider civilisation which chooses to ignore emergent cultures such as ours. Given the main focus of this forum I would suggest that the ‘they can’t get here from there’ possibility may not be totally secure and the zoo hypothesis should be considered if strong evidence emerges that life is common (given the probabilistic arguments outlined above). Olum (2004) wrote an interesting paper, which I’m not entirely in agreement with, but the main point seems reasonable around the implications of inflationary cosmology for this debate. So…a couple of predictions for future testing.
    1) Spectroscopic analysis of ‘earth analogue’ exoplanets will reveal some oxygen rich atmospheres.
    2) Sample return missions and other data will show evidence of microbial life in most potential habitats in the solar system.
    These may take some decades to get the results in, but other, less conclusive lines of evidence are looking promising in terms of prediction (2).

    now for the really controversial bit. If the predictions are in time supported by the evidence, perhaps it is worth revisiting the proposal of Deardoff et al (2005) which argues that there may be evidence to support the Zoo hypothesis, and this deserves further study…

    Deardoff, J., Haisch, B., Maccabbe, B., and Puthoff, H. E., 2005, ‘ Inflation theory implications for extraterrestrial visitation’, Journal of the British Interplantary Society, 58, 43-50
    Forgan, D., 2009, ‘A numerical testbed for hypothesis of extraterrestrial life and intelligene’, International Journal of Astrobiology, 8,121
    Olum, K., 2004, ‘Conflict Between Anthropic Reasoning and Observation’, Analysis, 64, 1 (gr-qc/0303070)

  • Ronald March 24, 2011, 6:59

    Ref. Kurt9 and coolstar: the Catanzarite and Shao paper (very relevant and fascinating paper btw) defines ‘Earth analog’ as a planet with a radius of 0.8Re < R < 2Re (and within its star's HZ).
    Note well: this includes the so-called super-earth category!

    The 0.8Re lower limit corresponds with a mass of 0.5Me, considered the minimum required to hold an oxygen rich atmosphere. This seems a slight bit low to me, I would lower that to about 1/3 Me.
    However, on the high end, 2Re seems rather high to me, since it would correspond to a mass of roughly (3) 5 – 8 (10) Me (depending on whether it's an iron, silicate, carbon, water or water-and-gas planet).
    Kurt9 is right about that such a planet could still be of various composition and origin and hence not necessarily very earth-like.

    The concept of 'Super-earth' should be (or actually is) defined on the basis of mass and not purely radius.

    I would rather limit the definition of earth-like to iron/silicate planets able to hold on to a sufficient O2 (or rather O2/N2) atmosphere but not to a very dense atmosphere dominated by other gasses (He, H2, CH4, NH3), in other words excluding the real super-earths.
    This would limit the mass to something between about 0.3Me < M < 3Me.
    And R would then be limited correspondingly to roughly between 2/3 Re and 1.5 Re.
    Since we know from Kepler that super-earths and Neptune class subgiants are (much) more common than earth-sized planets, this would further reduce the fraction of sunlike stars with earth-like planets in the HZ, possibly to something in the order of 1% (0.5-2%).

  • Bynaus March 24, 2011, 7:08

    @Greg: I agree that some of the unintentional “leak out” of intelligent signals will fade away as they get more efficient (as seem to be the case for the Earth’s TV signals). But others do not, as for example planetary defense radar, because in some cases the broad dispersion of a source signal is the very nature or purpose of the activity.
    And then, there are the intentional attempts at communication: I guess, if there was a radio telescope accessible for the broad public (for free or little fee) over the internet, it would be constantly sending signals to the stars. Think of that, scaled to the power of a interplanetary or even interstellar civilization: they could build self-repairing beacons that could send their signals (automatically) for billions of years. Yet again, nothing.

    Concerning the other discussion: I am no fan of the anthropic principle in general, i.e., I don’t really like the idea that the universe is here because we observe it. But I think it is important to realize that we have a strong anthropic bias when we look at the Earth, the solar system and the universe as a whole. We might be typical observers of the universe, but that doesn’t mean observers themselves are typical for universes. We could very well be the only observers in the observable universe. This would be just as compatible with our observation as the idea that civilizations are much more common, but shortlived and long and far inbetween.
    Considering the emptyness, the more civilizations there are out there, the more pessimistic we have to be about the prospects of long-term survival of civilizations in general, and humanity in particular.
    So it’s either many civilizations, or a long-term future for humanity, certainly not both, and possibly neither.

  • Ronald March 24, 2011, 7:22

    Cosmist: see also intercostal, your way of reasoning is per definition not Copernican nor in accordance with the cosmological principle.

    The great Greek philosopher Epicurus already postulated that in a field with many grains it is highly unlikely that only one grain will germinate.

    Your additional reasoning about 10^500 universes in a multiverse required for our (or intelligence’s) existence makes things even worse, because it woulf imply not just an anthropic universe but an anthropic multiverse!

    Why do so many people have such difficulty with accepting the mundane scientific facts or at least indications as often mentioned by Kurt9 (with which I fully agree): that there are so many huge gaps and barriers on the way from a potentially habitable planet to a technological civilization?!

    Abiogenesis (first living cells), complex (symbiotic, Eukaryote-analogue) cell, sexual reproduction, multi-cellular organism, specialized organs, land-dweller/atmospheric oxygen breather, intelligence, higher (self-aware) intelligence, culture/civilization, technology, high tech capable of inter-stellar communication, long-term survival of the same.
    And I may still have missed a few hurdles.

    According to 3 or 4 recent guesstimates, discussed on this site on a few occasions, the number of habitable earth-like planets near solar-type stars in the galactic disc of our MW galaxy is probably in the order of 100 million (50 – 200 million).
    That is a lot of potential breeding grounds for life to arise. Also a lot of potentially habitable real-estate for any interstellar-capable colonizing civilization.
    However, it is not such a lot to end up with (more than one) techno-civilization, if all the above-mentioned barriers have to be passed.
    Modern attempts to fill in the Drake equation almost invariably end up with VERY few or at most a few civilizations co-existing in out MW galaxy.

  • Ronald March 24, 2011, 8:31

    @Anthony Mugan: interesting and well-founded post!
    You limit yourself to two main explanations for the Fermi paradox (inability to bridge the interstellar gaps, zoo hypothesis), of which I tend to agree with the first one as one likely solution.
    However, like some others, you seem to almost equate life to advanced intelligent life, whereas I, as may be clear from my previous posts, strongly prefer to consider the huge difference between those two as another likely solution to Fermi.
    I think that both of your predictions, particularly 1) being most relevant, have a good chance of being supported in due time.
    That would still leave another possible solution for Fermi: life is common, but intelligence exceedingly rare.
    Here on earth, in its life’s history, we can also see that: even if and when conditions for life and its explosive (post-Precambrian) evolution are favorable, life branches off in many, many possible directions and diversity, but very few of those branches ever lead to (higher) intelligence.

  • kzb March 24, 2011, 8:43

    So what is the biggest hurdle? Is it biogenesis itself, or is it evolution of a technology-capable species after life has begun?

    The interesting thing to me is, we should get some answers to the first question -is biogenesis common or is it unique to Earth -within our lifetimes.

  • Eriks March 24, 2011, 9:13

    Very interesting discussion and a promising website! Shame I find it just today – but plenty of interesting material to read ahead.

    As to discussion about intelligent extraterrestrial life forms I have always felt a bit uncomfortable by making a persumptipons conclusions based on a todays science. From one point that is the best we’ve got. From the second point of view I always rememeber a tale about transport problems in Paris – in the 19th century they were pretty pesimistic about a development of public transportation system in 20th century because of lack oats to secure a horse trams… My point is that it is wrong to make a categorical statements based upon current knowledge as an absolute limit.
    As to the question about why we haven’t see any advanced life forms visiting us – there an be a thousands of potential answers. Maybe theye are here already but we don’t see them (impossible? try to tell somebody in 15th century that humans will step on the Moon). Maybe they see us but don’t see a need to come here. Maybe their agendas are so different we would never understand.
    Again, it is right that we are trying to discuss this problem using our current knowledge and science. However, it is wrong to fundamentally exclude the possibilities that are not fully in line with out knowledge up to date. And that is what a Time Magazine article seems to do.

  • Eniac March 24, 2011, 9:47


    There is nothing religious about the anthropic principle or should we call it the multiverse model, if understood properly. Cosmist says it very well:

    Ronald, my point was that the multiverse model gives us a way to understand why we might be the only life in the universe without becoming religious or abandoning Copernican thinking. The space of possibilities is no longer just this Hubble volume, but an infinity of universes, so the emergence of complex life *in this universe, with it’s laws of physics* could be a 1 in 10^500 per planet fluke and that’s still OK! In the vast majority of universes no intelligent life exists to wonder about these questions, so that’s what I mean by the anthropic principle. Is there something wrong with this reasoning?

    As to whether it is Copernican or Cosmological, consider this: Clearly, our physical reality, has many aspects that are what they are, but could easily be different. There is an infinite number of possibilities for it to be different. The laws of physics could be different, or its constants, or even just the initial conditions. If you want to be truly Copernican, you have to postulate that the laws and constants of physics that we happen to observe are nothing special, and this universe is just one possibility among others (Tegmark’s multiverse). In fact, you have to renounce the notion that there is such a thing as reality. What we perceive as real is distinguished ONLY by our point of view, the “existence” of the universe is predicated on our own existence, such as it is (cogito ergo sum?).

    Life, or self-replication, is very complex, and only a vanishingly small subset of possible realities (or universes, if you prefer) can support it. The one we see as “the” reality is naturally one of them. It has to be, or else we wouldn’t be there to see. There is nothing religious about this, it is pure logic. Now, it is reasonable to assume that the subset of realities in which life is possible, but very, very unlikely is hugely larger than that in which life is common. This is why: If it takes a lot of tuning to make life possible, it takes even much more to make it likely. The only thing we know is that we exist, therefore our reality is likely to be the most common type that allows for that. This would be the type where life is rare.

    I have tried to keep this as logical and free of “religion” as I can, and I would be interested in having any flaws in the argument pointed out.

    Of course, I’ll have to eat my words if we do find independent life somewhere, but I’ll be happy to do so when it happens.. :-)