The Fermi Paradox and SETI

The Atacama Compact Array
The Atacama Compact Array

In 1950, amidst the UFO hoopla that was sweeping the world, Italian physicist Enrico Fermi posed a simple question, Where are they? By that he meant with lots of people making the argument that in a universe full of stars presumably with planets there should be lots of intelligent life out there. That seems plausible. So, he wondered, how come there isn’t a shred of evidence for it? After all, if we lived in a city full of people, wouldn’t we see them or at least see evidence of them being there? So why don’t we?


In 1961 astronomer Frank Drake, interested in that very question, made an estimate of how many intelligent civilizations should exist inside our galaxy. The Drake Equation has seven terms, each a guess, from how many stars are born per year and how many of those have habitable planets through how many of those planets have developed technologies (like radio) that allow them to be detected. In 1961 there was not enough data to give reliable estimates to any of the terms. In the intervening 50 years we’ve accomplished enough basic research to apply actual values to the first few terms.

The Milky Way produces about seven new stars per year. Virtually every star forms within a disc of gas and rock/metal dust called a protoplanetary disc that eventually condenses into planets. According to research derived from data collected by the Kepler spacecraft, at least 22% of Sun-like G type stars have an Earth-like planet in the habitable zone, the habitable zone being defined as the distance at which water neither boils off or is continuously frozen. Result: the number of habitable Earth-like planets in the Milky Way is at least 50 billion.

Stars are not all the same, they come in a range of sizes and temperatures. The large hot ones, the OBA blue giants, burn through their hydrogen fuel very quickly and so have short life spans. At the other end of the range are the M type red dwarfs, the fuel efficient econo-cars of stars, which live for so long that not a single one since the birth of the universe has yet died. And like everything in nature, when given a pile of stuff from which to make things, you will make a lot more small things from the same amount of stuff than large things, so there are many, many times more red dwarf stars than blue giants, and that number goes up continuously since they keep on living while the blue giants burn through their fuel at a rapid pace, collapse, and then detonate into supernovae.

Why does that matter to this question? Because every red dwarf with planets in the habitable zone born since the formation of the universe has had all that time to develop life and intelligent civilization. Red dwarf stars form 76% of all main sequence stars, Sun-like stars form about 7% and all three types of blue giants together less than 1%. From an odds point of view, planets circling red dwarf stars are the most likely place to find intelligent life.

Spectral Classification
Spectral Classification

One thing to consider in the search for extraterrestrial intelligence (SETI) is that should we ever locate another intelligent civilization it will most likely be more advanced than we are. Consider, there are three possibilities:

1. They are less advanced and have not developed technology like radio. If we locate a planet with life that is not technologically advanced, we will do it by analyzing the spectra of their atmosphere for things like oxygen. How else would you even find them if they are not emitting radio waves or other form of energy that indicate intelligence?

2. They are exactly advanced as we are. Considering the age of the universe, the likelihood of our randomly locating another civilization at the exact same level of development as us is extremely small.

3. Since we have just reached the point where can even begin searching, if we encounter another civilization it will almost certainly be one that is more advanced, one that developed radio and spaceflight hundreds, thousands or even millions of years ago.

Seth Shostak is an astronomer and the current director of the nonprofit SETI Institute in California. He has spent much of his career involved in SETI research and believes that, despite the glaring failure of 50 years of SETI to produce a smidgen of evidence, that the numbers are too compelling to be wrong. Maybe we’re not looking for the right things. Or maybe life spends only a short time as protoplasm before developing machine-like replacements for themselves. Maybe ET is a machine.

The Fermi Paradox: Why Are There No Tourist from Other Worlds?

Preparing for Discovery: A Rational Approach to Finding Life Beyond Earth

22 thoughts on “The Fermi Paradox and SETI”

  1. Hundreds of commerical and military airline pilots have seen UFOs.
    Are they all wrong?? hallucinating? observing natural phenomena?

    Why did/does the military investigate UFO sightings/crashes if it is all a hoax/baloney?

    If you called the police/authorities to report that an elephant is hovering above your house/head/car, would they bother showing up to investigate??

    The idea that IF intelligent life exists outside of planet earth, then well, they should have revealed themselves to us mere earthbound mortals, is simply conjecture/opinion.

    Maybe these “beings” have a very good reason to avoid earthlings. Who says they have an obligation to reveal themselves to earthings? Who says they should think as we think? Maybe they consider humans on par with ants or groundhogs.
    IF they exist, we have absolutely no idea how/why they think as they do or why they do the things (or not) they do.
    Because we may have no clue as to their motivations, this has ZERO bearing on the fact of their existence or not.
    When was the last time a colony of ants or fish or groundhogs or deer or bears or whatever, decided, well, let’s introduce ourselves to those funny two legged creatures to announce our presence.
    We have seen them not because they wish to be seen, but because their normal places to hang out just happens to conflict where we may be.

    Think about it; why should earthlings be the only living, thinking beings in ALL the solar systems ?
    Frankly, if you wish to believe in the totally impossible, then you would think we are alone in all the universes.

    Look, there have been way too many sitings of UFOs by pilots or other reliable people to think that it is all a hoax or misinterpretation of natural phenomena.

    Lastly, the dept of defense, etc., would NOT have AT ALL any info labelled as classified pertaining to UFOs.

  2. >>When was the last time a colony of ants or fish or groundhogs or deer or bears or whatever, decided, well, let’s introduce ourselves to those funny two legged creatures to announce our presence.

    Yes, that point is made by the SETI folks themselves. Once an ET civilization reaches a certain level of development, they may simply have no reason to interact with us. We don’t invite squirrels and field mice over for pizza and cards and they don’t invite us over for nuts and acorns. Consider that we no longer remember who invented the wheel or domesticated horses. Imagine a civilization so advanced they don’t remember the invention of radio or spaceflight. Seems crazy at first, since it seems like once a civilization begins recording and copying data en masse it would never lose track of that information again. But consider wars and societal collapse over millions of years and vast distances and maybe that can occur.

    >> Hundreds of commerical and military airline pilots have seen UFOs. Are they all wrong?? hallucinating? observing natural phenomena?

    I agree that’s compelling. I read a book on UFOs about 25 years ago that used a lot of those reports as evidence. I’m willing to concede that some or even many are mistaken identity or research projects or whatever. But all of them? Many by experienced pilots who aren’t just seeing a light in the distance or something but describe aircraft maneuvering around them and behaving in ways that defied aerodynamic laws. Maybe they are ALL explainable, but it’s an interesting point.

    On the other hand, Frank Drake makes the argument that when you consider the energy costs to get between star systems, why would anyone choose to do it? And Seth asks, Why send living beings, why not send robotic probes? Valid points.

  3. >> One of my duties on the web is to point out that aliens tend to avoid us because last time one lived among us we nailed him to a cross.

    Yes. Never underestimate the deterrent effect of that sort of thing.

  4. We may be one of the early pioneers according to this study that came out last year

    The study, which focuses purely on the likelihood of the evolution of habitable worlds (and not speculation of alien intelligence, the Fermi Paradox implication is my own), finds that when our planet was born from our young sun’s protoplanetary disk some 4.6 billion years ago, it was born into an era when only “8 percent of the potentially habitable planets that will ever form in the universe existed.” This means that the universe has 92 percent to go until it runs out of the necessary material to produce the stars that go on to produce planets, some of which will be small and rocky and orbit in just the right location for life (as we know it) to thrive.

    This is actually good news. We’ve got so much more universe ahead of us. Its an empty canvas. Let’s make the best of it.

  5. Red Dwarf stars have a habitable zone so small that the planet will be tidally locked to the star, and very vulnerable to the flares that can double the brightness of those stars when they happen, which for the larger red dwarfs is fairly often. I do not hold much hope for habitable planets around those stars. I think we should be looking mostly at K, G, and F type stars.

  6. I think we may very well find life on Mars and maybe even in a comet or two. It will probably consist of microscopic creatures called Archea which are capable of living in harsh environments. They will probably be deep in the soil where they are shielded from cosmic rays.

    I expect that we will find some about six feet below the surface although it may be more.

    The question of intelligence is more difficult.

    David, your essay is interesting and I fear may be predictive. On the other hand, we may not need that many scientists and those really motivated and with the IQ to accomplish something might be enough. I don’t know if the IQ distribution curve will shift much.

    The trouble is finding those with the possibility and helping them with education and opportunity. My own life makes me more interested in that aspect of it. I was accepted to Cal Tech and had my dorm room assigned but my National Merit Scholarship did not come through. I was too inexperienced to think of contacting Cal Tech and seeking other aid. That, of course, was 60 years ago but I see all emphasis on helping the unqualified to fail. Depressing, actually,

  7. Red dwarfs have small habitable zones. They are much less likely to form livable planets than sun like stars. Still it should be possible, although conditions are more stringent, for the smaller zones.

  8. Swiping a comment directly from the link Michael provided:
    “As many skeptics have pointed out, the Drake equation can give a very wide range of values, depending on the assumptions. ….the values one may attribute to each factor in this equation tell more about a person’s beliefs than about scientific facts.”

    Take, for example, the coefficient n sub e, the probability of an earth like planet. Pretty big, right? Spock says, “Class M planet, Captain.” We all know that means he describes one of Sagan’s millions of earth like planets. So ubiquitous that one easily finds ’em not merely anywhere, but everywhere. But once one leaves fun with sci fi, what does physics (rather than faith) say?

    Needs right size mass (else looses atmosphere), right size distance from right size star. Odds start going down rapidly already. But then add that it must have right rotation speed on its axis: too fast, get monster winds (tornadoes, hurricanes); too slow, get monster winds (temp differentials). Odds going down rapidly again. Must have tilt on axis, else no seasons (evolutionary necessity). Odds go down more. Must have right size moon at right distance. Else a bunch of problems, among them, eg, tides, said problems any one of which quashes evolution. Odds go down more. Must have a strong enough magnetic field that solar radiation doesn’t zorch life, wreck mechanics of mutation. Must have right composition of elements. Too much oxygen, for example, everything oxydizes, including life; too little, no life.

    Drake eqn and Fermi paradox help give a veneer of probability to that which is actually, even given qazillions of plantet, not so likely. One can appreciate the philosophical problem, yea, the faith problem, without buying the snow job.

  9. The Drake equation and the Fermi Paradox both depend on the assumption that the universe is an empty stage on which randomly colliding particles occasionally produce something interesting. The assumption is the atomic theory of the ancient Greek Epicurean philosophers. It is the dominant theory among our “educated” classes, particularly scientists. If the theory is not true, the whole question of extra-terrestrial intelligence may be malformed.

    At this point, all I am willing to commit to is the belief that the Epicurean philosophy is a very narrow version version of what the world is really like, and one that I doubt encompasses any large portion of the truth.

    “There are more things in heaven and earth, Horatio,
    Than are dreamt of in your philosophy.”
    Hamlet (Act I Sc. 5 L. 167-8)

  10. The CIA’s collection of declassified UFO related documents

    To the answer the question why we investigated them

    CIA closely monitored the Air Force effort, aware of the mounting number of sightings and increasingly concerned that UFOs might pose a potential security threat. (10) Given the distribution of the sightings, CIA officials in 1952 questioned whether they might reflect “midsummer madness.” (11) Agency officials accepted the Air Force’s conclusions about UFO reports, although they concluded that “since there is a remote possibility that they may be interplanetary aircraft, it is necessary to investigate each sighting.”

    Necessary because this was in the deepest depths of the Cold War. We were investigating things like whether the Soviets were capable of mind control or fomenting mass hysteria, so we weren’t going to give a pass to even the most unlikely threats.

    The midsummer madness comment was due to the fact that sightings spiked in July

  11. ” Once an ET civilization reaches a certain level of development, they may simply have no reason to interact with us. ”

    Or, there may be a “rule of thumb” that states: “once a civilization reaches a certain level of development (with the ability to actually search the heavens, amongst other things) it self destructs.

    A corollary to that might be related to the time factor. Say life has been on earth a billion(?) years; let’s say that we have had the above mentioned “ability” for 50 years…or about .00000005 of that billion years. If that ratio is anything like typical, the chances of two alien and developed civilizations being around at the same time are exceedingly remote (a probability of .00000005 squared, if I’m not mistaken).

    The chances of finding an “undeveloped” civilization would only be slightly greater. The chances of finding life of, some sort, much greater.

  12. “The chances of finding life of, some sort, much greater.”

    I think we will find life soon but the chances of intelligent life are remote.

    The premise of the movie “Close Encounters” was that there were three kinds of encounters. Two are hostile. Maybe we are better off.

  13. Something no one has taken into account. From our experience here on earth over the last 500000 million years there has been numerous die offs that restarted our evolution.

    We have to take into account that the same processes are happening on these other worlds. Life starting over again every 100 million years of so kind of puts a damper of our ever finding another advanced race.

  14. It may be that there are intelligent beings that have been around for thousands or millions of years longer than us, and that they simply have no interest in us and nothing to say to us. As Jonathan said “How do we treat insects?” If they are pests we poison them, but otherwise we ignore them.

  15. I’ve read a bit on the environment necessary for life to develop, including:

    1. Liquid on the surface is a must. Liquid water may be the ideal medium, plus it’s easy to make; just hydrogen and oxygen and both are plentiful in the galaxy. Liquid allows organic chemistry reactions to happen more easily since the molecules are mobile and can interact easily.

    2. Elements that appear to be necessary are hydrogen, oxygen, nitrogen, sulphur and phosphorus.

    3. Hydrocarbons can form many different kinds of complex molecules and long molecular chains, which is necessary for complex life. Carbon is also abundant.

    4. A reasonably stable climate in terms of temperature in the correct range.

    5. Sufficient gravity to hold an atmosphere in place.

    6. Recently the argument is being made that an active planetary core and plate tectonics may also be required. The active core generates a magnetic field which shields the Earth from particles ejected by the sun. Plate tectonics continuously refreshes the sea floor with minerals necessary to support primitive lifeforms which form the bottom of the food chain.

    I’ve read speculation that an ammonia atmosphere might develop life, though I don’t understand the chemistry. I also remember Carl Sagan speculating that gas giants might harbor drifting lifeforms in certain layers of their atmosphere. That’s an interesting idea.

    I’d like to see a space mission to explore the atmospheric layers of Jupiter and one to put a rover on Titan’s surface. Both of those would break new ground.

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