Illustration of Kepler-186f, a recently-discovered, possibly Earthlike exoplanet that could be a host to life. (NASA Ames, SETI Institute, JPL-Caltech, T. Pyle)

Why Haven’t We Heard From All The Aliens? Because They’re All Dead!

Article Updated: 23 Jan , 2016


In 1950, physicist Enrico Fermi raised a very important question about the Universe and the existence of extra-terrestrial life. Given the size and age of the Universe, he stated, and the statistical probability of life emerging in other solar systems, why is it that humanity has not seen any indications of intelligence life in the cosmos? This query, known as the Fermi Paradox, continues to haunt us to this day.

If, indeed, there are billions of star systems in our galaxy, and the conditions needed for life are not so rare, then where are all the aliens? According to a recent paper by researchers at Australian National University’s Research School of Earth Sciences., the answer may be simple: they’re all dead. In what the research teams calls the “Gaian Bottleneck”, the solution to this paradox may be that life is so fragile that most of it simply doesn’t make it.

To put this in perspective, let’s first consider some of the numbers. As of the penning of this article, scientists have discovered a total of 2049 planets in 1297 planetary systems, including 507 multiple planetary systems. In addition, a report issued in 2013 by the Proceedings of the National Academy of Sciences of the USA indicated that, based on Kepler mission data, there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way, and that 11 billion of these may be orbiting Sun-like stars.

So really, there should be no shortage of alien civilizations out there. And given that some scientists estimate that our galaxy is over 13 billion years old, there’s been no shortage of time for some of that life to evolve and crate all the necessary technology to reach out and find us. But according to Dr Aditya Chopra, the lead author on the ANU paper, one needs take into account that the evolutionary process is filled with its share of hurdles.

Dr. Aditya Chopra of the ANU Research School of Earth Sciences. Credit:

Dr. Aditya Chopra of the ANU Research School of Earth Sciences. Credit:

“Early life is fragile, so we believe it rarely evolves quickly enough to survive,” he says. “Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.”

Consider our Solar System. We all know that planet Earth has all the right elements to give rise to life as we know it. It sits within the Sun’s so-called “Goldilocks Zone” (aka. habitable zone), it has liquid water on its surface, an atmosphere, and a magnetosphere to protect this atmosphere and ensure that life on the surface isn’t exposed to too much radiation. As such, Earth is the only place in our Solar System where life is known to thrive.

But what about Venus and Mars? Both of these planets sit within the Sun’s Goldilocks Zone and are believed to have had microbial life on them at one time. But roughly 3 billion years ago, when life on Earth was beginning to convert the Earth’s primordial atmosphere by producing oxygen, Venus and Mars both underwent cataclysmic change.

Whereas Venus experienced a runaway Greenhouse Effect and became the hot, hostile world it is today, Mars lost its atmosphere and surface water and became the cold, desiccated place it is today. So whereas Earth’s microbial life played a key role in stabilizing our environment, any lifeforms on Venus and Mars would have been wiped out by the sudden temperature extremes.

In other words, when considering the likelihood of life in the cosmos, we need to look beyond the mere statistics and consider whether or not it may come down to an “emergence bottleneck”. Essentially, those planets where lifeforms fail to emerge quickly enough, thus stabilizing the planet and paving the way for more life, will be doomed to remain uninhabited.

In their report, “The Case for a Gaian Bottleneck: The Biology of Habitability” – which appears in the first issue of Astrobiology for 2016 – Dr. Chopra and his associates summarize their argument as follows:

If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable.

While potentially depressing, this theory does offer a resolution to the Fermi Paradox. Given the sheer number of warm, wet terrestrial planets in the Milky Way Galaxy, there ought to be at least a few thousand civilizations kicking around. And of those, surely there are a few who have climbed their way up the Kardashev Scale and built something like a Dyson Sphere, or at least some flying saucers!

Cyanobacteria Spirulina Credit:

Oxygen-producing bacteria like Cyanobacteria Spirulina (shown above) played a major role in stabilizing Earth’s environment. Credit:

And yet, not only have we not detected any signs of life in other solar systems, but the Search for Extra Terrestrial Intelligence (SETI) hasn’t detecting any radio waves from other star systems since its inception. The only possible explanations for this are that either life is far more rare than we think, or that we aren’t looking in the right places. In the former case, an emergence bottleneck may be the reason why life has been so hard to find.

But if the latter possibility should be the case, it means our methodology needs to change. So far, all of our searches have been for the “low-hanging fruit” of alien life – looking for signs of it on warm, watery planets like our own. Perhaps life does exist out there, but in more complex and exotic forms that we have yet to consider.  Or, as is often suggested, it is possible that extra-terrestrial life is taking great pains to avoid us.

Regardless, Fermi’s Paradox has endured for over 50 years, and will continue to endure until such time that we make contact with an extra-terrestrial civilization. In the meantime, all we can do is speculate. To quote Arthur C. Clarke, “Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.”

Further Reading: ANU, Astrobiology

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26 Responses

  1. Bryan says:

    How can our galaxy be “16 billion years old” when the universe is only about 14.3 billion yrs. old?

  2. bactuniv says:

    I’ve brought this up before, but no one seems to get it. The Fermi’s Paradox is based on wrong data. It is not adding in the fact that evolution of life beyond pond scum may require mixing of the reagents. This means active diurnal tides caused by a large rocky moon, similar to Luna.
    I don’t know if our current planet search can even “see” a moon spinning around a planet, but I would think that the criteria should be added to the parameters to narrow down the # of possible intelligent life planets. I expect that this would result in a very low number of candidate planets. for a web page with that and more theories

    • qedlin says:

      Thank you. Did you see the recent UT blog on the need for a moon? I posted the same fact that a moon is essential to support life (not initiate it) and there was heck to pay for even suggesting what you have posted. Except – my concern is you seem to imply (the fact that evolution of life…”) Chemical evolution is one of many Darwinian myths: There is no naturalistic mechanism or physical process that can generate metaphysical realities. Also, the lack of a viable, comprehensive theory of abiogenesis is because there will never be one, period. Fermi’s paradox is real but based on much more than what was known when he first posited it.

  3. robst247 says:

    Good question, Bryan. Obviously it cannot be. In this article (dated 3 Dec 2014) Matt Williams himself states:
    “The most recent estimates place the age of the Universe at about 13.7 billion years. Our Milky Way has been around for about 13.6 billion of those years, give or take another 800 million. The oldest stars in our the Milky Way are found in globular clusters, and the age of our galaxy is determined by measuring the age of these stars, and then extrapolating the age of what preceded them.
    “Though some of the constituents of the Milky Way have been around for a long time, the disk and bulge themselves didn’t form until about 10-12 billion years ago. And that bulge may have formed earlier than the rest of the galaxy.”
    — Please clarify this point, Matt, by referring to the latest insights on the age of the universe and our home galaxy.

  4. Random Sample says:

    Geez, you’d think none of these scientists ever heard of the Prime Directive…

  5. Random Sample says:

    Geez, you’d think none of these scientists ever heard of the Prime Directive.

  6. robst247 says:

    Dr Chopra says: “Early life is fragile, so we believe it rarely evolves quickly enough to survive,” he says. “Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.”

    It seems to me that Dr Chopra and other planetary scientists are trying to extrapolate from one data point: our knowledge of processes on Earth. Every aspect of his standpoint is based on our well nigh infinitessimal understanding of the cosmos. It’s like staring at your own belly button for a lifetime and then asserting that you know the shape of your entire body. What has been and is still valid on Earth says nothing or very little about what goes on elsewhere in the universe. I refuse to believe that “all the aliens are dead”. It’s too depressing. Yesterday I read an article about a ‘dead galaxy’, and now this. Why are astronomers such depressing people? Are alien astronomers equally depressing? How shall we rid ourselves of such dreary people?

    • leasjahasr says:

      AHA! THAT’S what happened to them. They advanced to such a state that some of them began to consider others of their kind depressing and dreary, so they undertook a program of ridding themselves of all that dead weight….

  7. UFOsMOTHER says:

    The Universe is Full of Life look up to the Heavens for we are there.. It wont be long now before positive contact will be made. We are getting close but life on Earth is still primitive and we can not see what is realy going on in the Milky Way or the rest of the Cosmos, But we are nearly there now and any person that believes we are alone is demented the numbers are infinite on the side of Life if you dont believe it look in the mirror.. We are All Stardust.

  8. BlackWolfStanding says:

    The Galaxy is a very big place. 100k light years across. Evidence of human life has not even reached the other side of our own galaxy. In fact, it has barely reached the limits of unaided observable stars. We have as much of a chance being the first intelligent life in our galaxy as being the last intelligent life in the galaxy. And if Stephen Hawking is to be believed, we could annihilate ourselves before evidence of human life even gets 1/3 the way across our own galaxy. Think about that. By the time we find evidence of intelligent life, that life could already be extinct. With such a small time frame on a galactic scale to find intelligent life, we may have already “seen” intelligent life and that life annihilated itself and now it would take a probe to see the reminisce of that life which won’t even get to the target planet before we ourselves go extinct. The size of our own galaxy is working against us. So, there is no doubt that life abounds in our galaxy. There is no doubt intelligent life occurs in our galaxy. Just it could very well only be occurring in our little corner of the galaxy in one location, and that’s right here. And the equation for life would still be valid.

  9. Bob Andersson says:

    It’s probably way too early for this analysis. Mars and Venus are bad examples of life “failing”. The former was too small to hang onto its atmosphere and the latter rotates too slowly to generate a protective magnetic shield with the consequent loss of hydrogen. Life could have prevented neither. Life did succeed on the one planet in our solar system which was “just right”, and in my opinion that includes the need for a stabilising large moon, but a sample size of one is obviously useless when it comes to drawing conclusions.

    I don’t believe the current absence of evidence for aliens can be used to pray in aid of the posited Gaian Bottleneck. Lack of SETI results may simply mean that alien civilisations are so widely spaced on average that undirected broadcasts are too expensive and that we are too far away from any civilisation minded to talk to us, assuming they’d even want to from what they’ve seen so far, for them to have realised we might have the technological capability to reply. As for aliens visiting us, space is an incredibly hostile environment to organic life: even a round trip to Mars has considerable health implications. Any lack of little green beings waving their antennae at us and demanding to be taken to our leaders is much more likely to be evidence that warp drives can’t exist than that aliens don’t exist. Generation ships or, if a biology supports it, suspended animation might be ways of crossing interstellar distances but both have severe ethical issues. Quite apart from enforcing the impoverished environment of a generation ship on countless unborn beings what is the point? Arriving somewhere where there is a vibrant biosphere means a risk either of contaminating it or being unable to survive in it without a protective suit. And then, assuming they don’t intend to destroy it and create a new home for themselves, they turn around and go home?

    Maybe the universal principle in place to explain the lack of alien presence is not a Gaian Bottleneck but boring old economics? For less than the cost (probably a lot less) of an interstellar voyage which results in no payback within the lifetime of the contributing members of a society think what one could build in terms of spaceborne remote sensing which could be directed at multiple star systems. If the economics are good for us then why not for any aliens?

    Just my two penny worth, totally unsupported by experiment and so totally unscientific. 🙂

  10. Not only are they not dead but they’re all over the Universe, going back and forth, and back and forth, like a ping-pong ball. We don’t know how and they haven’t told anyone how they do it. There are several sighting cases involving reliable witnesses, the most well-known being the Lubbock Lights Case. Those who saw them were four professors from the Texas Technological College. The space aliens will never approach us openly –“land right on the White House lawn” and tell the hefty security apes “take us to your Leader”, like in the comic books — because at their stage of evolution everyone is telepathic, a mindreader, and most of us would find their presence intolerable and embarrassing. Their elusiveness is their way of respecting our intimacy. They make themselves available to anyone who has already reached an advanced stage of moral evolution. If your life is “an open book” then just go out on a clear night somewhere in the boondocks and call on them. Meanwhile you can count the shooting stars or watch the heavens through your telescope. Would Enrico Fermi have been brave enough to do such a thing? Anyway, he would’ve laughed all the way over to the encounter.

  11. jjb says:

    Reading this and looking at planetary magnetic fields.


    What would have happened to the Earth / or would happen to the Earth if – Mercury – Venus – Mars had a magnetic field equal or just slightly greater or lesser to Earth’s?

    Would it through Earth’s ‘equilibrium’ so totally out of balance; heat, radiation and such, that we would not have had life here?

  12. chfosmith says:

    Fermi’s paradox is resolved, and not just by “The Prime Directive”.
    Stephan Hawking’s warning is the second reason any ET would approach Earth “cloaked” (Stealth Technology in military jargon), and not make contact.
    If you consider what any ET that is advanced
    (Here I am considering moderately ahead, say 35,000 years, not 6 million years such as between us and Lucy)
    would think and do when it saw news reels of Stalin, Hitler, and Mao Zedong or more recently the Islamic State, or North Korea, or Eritrea, or Somalia, or Libya, or The list goes on.
    It would not be positive, and they might have to consider a quarantine of Earth until the situation improved.
    The reason for the lack of radio signals is probably due to the fact that radio communication is a primitive means of communication compared to Quantum Entanglement,
    and radio signals are limited to the speed of light.
    Fermi’s paradox is resolved for at least three reasons.

  13. chfosmith says:

    Hi JJB,
    The simple answer is no.
    Only the sun can generate magnetic storms of such intensity that the magnetic field of the earth is affected.

  14. Pvt.Pantzov says:

    “But what about Venus and Mars? Both of these planets sit within the Sun’s Goldilocks Zone and are believed to have had microbial life on them at one time…”

    …based on flimsy circumstantial evidence combined with a great deal of hope.

  15. mewo says:

    I think another reason is that the Universe as a whole is more habitable now than in the past. The amount of heavy elements like C,N,O,P, is are increasing (which life forms are made of), and the rate of planet-killing disasters like nearby supernovae and gamma ray bursts is decreasing. It may be that we are among the first civilisations in the Universe.

    Also, the analysis in this paper does not take into account subterranean habitats on, say, Enceladus or Europa. Almost nothing the Sun can do will have any effect on a well-shielded, tidally heated water cavern. The only real danger is that life there will end up poisoning itself; remember the cyanobacteria on Earth, which killed almost everything with all that horribly toxic corrosive oxygen?

  16. weeasle says:

    It’s important to remember that this paper’s premise is based on “Life as we know it.” To truly answer the Fermi Paradox we would need to take into account ‘Life as we don’t know it.’

    It may be a long time until we can make any statements on ‘Life as we don’t know it’ … Until we develop the capacity to send probes interstellar (or develop some other technology capable of studying unknown lifeforms many light years distant), it will be impossible to make a definitive statement…

  17. weeasle says:

    It’s important to remember that this paper’s premise is based on Life as we know it. To truly answer the Fermi Paradox we would need to take into account Life as we don’t know it.

    It may be a long time until we can make any statements on Life as we don’t know it … Until we develop the capacity to send probes interstellar (or develop some other technology capable of studying unknown lifeforms many light years distant), it will be impossible to make a definitive statement…

  18. weeasle says:

    Sorry for the duplicate posts.. Also worth pointing out that if there is intelligent life, perhaps, like us, they haven’t worked out a way to reliably communicate or broadcast across vast distances (many tens/hundreds/thousands of light years).. It is questionable that radio waves sent from hundreds/thousands of light years would even be detectable with SETI after having to pass through gas clouds in interstellar space….

  19. daveb81 says:

    We, as a civilization, haven’t even convinced ourselves that we are capable of being responsible with the power that we’ve obtained. We may be too flawed a species to obtain the power that a more advanced alien species has without their interference without destroying ourselves….and this planet. Even if they didn’t directly give us knowledge, if we were simply contacted by aliens, would it not serve as motivation for us? Instead of us competing with each other for power, we would, silently, be a more united world to obtain the knowledge that they have. Would we deserve that motivation?

    If I made the choice for that alien civilization, I would wait until at least humans detected us before contacting them. I would want to see that human CIVILization egg hatch, so to speak. Imagine the amount of damage we could do if we became a multi-star system species? Or how about intergalactic? by obtaining that power before we’ve matured. Lord of the Flies anyone? Even if they could put us in our place, why even put themselves in that position? And Lord knows what ramifications we could have that they didn’t realize. It’s not worth contacting us.

  20. Takojohn says:

    There is always the possibility that INTELLIGENT aliens exist. They may have taken a sharp look at us and placed warning beacons around the Solar system to keep everyone away. Reading the history of Homo Sapiens(??) explains it.

  21. Mich48 says:

    If all life in this universe is assumed, to have started in the same universe that we now live in; Then we should all have had the same starting point. Given that our radio waves have only existed for around one hundred years. We are and will be blind to other intelligent life for millennia. Early stars may have been to big and explosive to support life. And it would be only the very early life that we could detect. Someone has to be first. Why not us!

    • Our Solar System formed 4.5 billion years ago. Our Universe is 13.8 billion years old, and the Milky Way Galaxy is over 13 billion years old. We didn’t all start at the same point in time. In fact, there is no reason to assume that intelligent life elsewhere would not have had a multi-million or even billion year head start on us. Which is one of the main challenges posed by Fermi.

  22. Tibsam says:

    Given 12 billion years, I would venture that there’s a also a very small window in which intelligent life overlaps. We’ve had the ability to signal and search for barely half a century and – given the rate at which we’re exhausting earth’s resources – it’s all too likely that our ability to communicate with other worlds will cease within the next couple of centuries. If life on other planets is equally improvident with their resources, the odds on our communication windows overlapping is remote.

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