“If the Universe Is Teeming with Aliens… Where Is Everybody?” –Stephen Webb
As egocentric as we are, we know that not only are we but one planet of many orbiting our Sun, but that when we look up in the heavens, every point of light we see is another chance — another opportunity — for planets, for life, and even for intelligence.
With hundreds of billions of stars (visible here in infrared wavelengths) in our galaxy alone, we have many, many chances for life to have evolved similarly to how it did here on Earth. With hundreds of billions of galaxies in the Universe, it seems unfathomable to us that we would be alone as the only self-aware, intelligent, sentient lifeforms in the Universe.
The question atop — where is everybody — is known today as Fermi’s Paradox.
Is there really anything paradoxical about it at all? Let’s take a look.
This is Earth, our home, and (so far) the only place we know of that harbors life in the Universe, much less intelligent, sentient, self-aware and (possibly) capable-of-communicating-with-alien life. We assume that if there are intelligent extra-terrestrials out there, they’ll be made of the same chemical elements we are. Not because it’s the only way to store information, or because we think any other methods are prohibitive, but because this is something we understand, and we know at least one way that it works.
And if it works this way here, for us, perhaps it works elsewhere, too, for someone else. Other than the right elements (which are all over the galaxy and Universe by this point), what we need is actually pretty simple.
We need to be the right distance from the Sun in order to have liquid water. In other words, we need the temperature to be a particular value. If it were too cold, everything would freeze, and if too hot, everything would boil (and too many chemicals would denature).
Fortunately, we’re not speculating about this like Frank Drake had to fifty years ago. We know of thousands of planets that orbit around other stars now!
As best as we can tell — extrapolating what we’ve discovered to what we haven’t yet looked at or been able to see — there ought to be around a trillion planets in our galaxy, and somewhere around ten to a hundred billion of them are candidates for having liquid water and Earth-like temperatures on their surfaces!
So the worlds are there, around stars, in the right places!
What about the building blocks of life?
Believe it or not, these are unavoidable by this point in the Universe. Enough stars have lived and died that all the elements of the periodic table exist in fairly high abundances all throughout the galaxy.
But are they assembled correctly? Taking a look towards the heart of our own galaxy is molecular cloud Sagittarius B, shown above. In addition to water, sugars, benzene rings and other organic molecules that just “exist” in interstellar space, we find surprisingly complex ones.
Like ethyl formate, above, the compound responsible for the smell of raspberries, among others. So with tens of billions of chances in our galaxy alone, and the building blocks already in place, you might think — as Fermi did — that intelligent life is inevitable.
But there is a big difference between an organic molecule and an intelligent lifeform. On Earth alone — the one place where we know it worked — it took over four billion years and a slew of unlikely events to bring us about.
What was it that needed to happen, and what are the odds of it happening? Let’s go through it, both liberally and conservatively, and see what we get.
First, we need to make life from non-life. This is no small feat, and is one of the greatest puzzles around for natural scientists in all disciplines: the problem of abiogenesis. At some point, this happened for us, whether it happened in space, in the oceans, or in the atmosphere, it happened, as evidenced by our very planet, and its distinctive diversity of life.
But thus far, we’ve been unable to create life from non-life in the lab. So it’s not yet possible to say how likely it is. (Although we are taking some amazing steps.) It could be something that happens on as many as 10-25% of the possible worlds, which means up to 25 billion planets in our galaxy could have life on them. (Including — past or present — others in our own Solar System.)
But it could be far fewer as well. Was life on Earth likely? Or, if we performed the chemistry experiment of forming our Solar System over and over again, would it take hundreds, thousands, or even millions of chances to get life out once? Conservatively, let’s say it’s only one-in-a-million, which still means, given the conservative end of 10 billion planets with the right temperature, there are still at least 10,000 planets out there in our galaxy alone with life on them.
And we need that life to stick around for — as best as we can tell — at least for billions of years, in order to evolve into something interesting enough to be considered intelligent. Large, specialized, multicellular, tool-using creatures are what we’re talking about. So while, by many measures, there are plenty of intelligent animals:
We are interested in a very particular type of intelligence. Specifically, a type of intelligence that can communicate with us, despite the vast distances of the stars!
So how common is that? From the first, self-replicating organic molecule to something as specialized and differentiated as a human being, we know we need billions of years of (roughly) constant temperatures, the right evolutionary steps, and a whole lot of luck. What are the odds that such a thing would have happened? One-in-a-hundred? Well, optimistically, maybe. That might be how many of these planets stay at constant temperatures, avoid 100% extinction catastrophes, evolve multicellularity, gender, and eventually learn to use tools.
But it could be far fewer. Even one-in-a-million seems like it might be optimistic; I could easily imagine that it would take a billion Earths (or more) to get something like human beings out just once. Because at the end of the day, here’s what we need to see.
We need to see the sky in radio wavelengths, and we need for other aliens to have broadcast signals in those wavelengths we’re looking for. (Other methods may be possible, but this is one example we know would work.) In order to do that, we need for them to build transmitters of some variety,
and for us to have build detectors of some variety.
We have both of those capabilities of course, but how many other worlds do? If we take the optimistic estimate, perhaps 250 million worlds are out there capable of communicating with us, in our galaxy alone. But if we take the conservative estimate, above, there’s only a one-in-100,000 chance that our galaxy would have even one such civilization.
And we’re not done yet.
Because human haven’t been around forever, and we won’t be around forever. Neither will humanity’s equivalent on another world. Whether it’s nuclear war, natural disasters, or a slow poisoning of our own environment, at some point there will not be humans on Earth any longer. For what percent of our star’s lifetime will humans be around? Or, of all the civilizations that may have existed over the history of the Universe, what are the chances that there are aliens out there now, capable of communicating with us?
Humanity has only been around for a little over a hundred thousand years, or about 0.001% of the history of the Universe. Optimistically, perhaps we will thrive for another million years before we either evolve into something completely different or destroy ourselves. But pessimistically, we may only be around — in our able-to-communicate-phase — for a few hundred years.
Taking the million-year estimate and our prior optimistic figure, that means there may be as many as 25,000 civilizations ready to communicate with us right now in the Universe. (Clarification: this is 25,000 civilizations in our galaxy, which are the only ones in the Universe we’ll be able to communicate with on sub-million-year timescales.)
But taking the pessimistic number and applying our pessimistic estimate? There’s only about a 10% chance of there being one Earth-like world, today, with a species like us on it, in the entire Universe.
Regardless of whether the optimists or the pessimists are closer to being right, there is no paradox. If the pessimists are right, it’s because there isn’t anybody out there for us to talk to. And if the optimists are right, there’s still almost nobody out there for us to talk to! 25,000 civilizations in our galaxy, right now, still means that the nearest one is probably hundreds of (if not closer to one or two thousand) light-years away.
But we have to look. There’s too much to know, too much to gain, and too much to learn for us to not ask these questions. Some would have you fear the unknown, but any civilization that talks to us will likely have been around — as you can tell from the estimates — in a technologically advanced state for thousands or years, if not hundreds of thousands (or more). When you think of all the social and political problems that we’ve solved (and are solving now) just over the past few hundred years, and the hurdles we have coming up over the next few hundred (including population, pollution, energy, resource management, human rights, and more), any civilization that talks to us has likely already solved those problems.
So where is everybody? If they exist at all, they’re very far away. But life, in some form or another, is sure to be close by, and we wouldn’t be doing justice to the curious, investigative nature of humanity — the very nature that’s led us this far — if we stopped looking now.
After all, as Carl Sagan so beautifully said,
I guess I’d say if it is just us… seems like an awful waste of space.