Ever since scientists began to grasp the staggering scale of the universe, we’ve wondered if there was other intelligent life out there. It certainly seems like there’s space. No one has come calling from another planet, or even sent a signal we can detect, though. This prompted famed physicist Enrico Fermi to speculate on the reason for this lack of contact. The so-called Fermi Paradox comes up whenever we talk about the search for life outside our solar system, but what does the Fermi Paradox say about our place in the universe? It might predict our doom, or perhaps a bright future. It asks one simple question: where is everybody?

The mathematics of loneliness

In the immortal words of Douglas Adams, “Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is.” We inhabit a planet orbiting a star that is just one of at least 100 billion stars in our Galaxy. The Milky Way is just one galaxy of… well, we aren’t sure. The old estimates were in the neighborhood of several hundred billion, but new data suggests there may be as many as 2 trillion galaxies in the observable universe. So, that’s a whole lot of space.
From a sheer mathematical perspective, it seems likely that life of some sort would evolve on other planets out there. We know there are other planets, too — a lot of them. There’s an interesting thought experiment known as the Drake Equation that can be used to estimate the number of detectable intelligent species. It includes factors for the number of stars, the probability of habitable planet formation, the development of intelligent life, and so on. You can see it below. Of course many of these values are complete guesses, but even if you plug very small numbers into the Drake Equation you come up with large numbers of detectable civilizations.
seti-drake-equation
In addition to being large, the universe is also extremely old. Our sun is 4.5 billion years old, but that’s rather young. The universe itself is believed to have come into existence just shy of 14 billion years ago. There could be other planets around other stars that formed a billion or two billion years before us. Imagine what a species a billion years more advanced than us would be like. You can’t really. Even a few centuries of progress on Earth has resulted in amazing advances in technology. As Arthur C. Clarke pointed out, “any sufficiently advanced technology is indistinguishable from magic.”
In just 100,000 years, humans have gone from tribal beings numbering in the thousands to the dominant species on the planet with a population in excess of 7 billion. With a billion-year head start, a species from another star could have expanded considerably more with technology we can’t even begin to imagine. Even if this hypothetical intelligence just decided to stay home and send self-replicating robotic explorers out into the galaxy, those robots would be everywhere by now.
So, that leads us to the big question: where is everybody?

The Great Filter

The first answer to that question is a troubling one. The math says there could be super-advanced civilizations given the scale and age of the universe. So, maybe there’s nobody (or almost nobody) else there because intelligence like ours doesn’t last long. We could be rare in the universe. This idea assumes what’s known as The Great Filter, an evolutionary hurdle that few species clear. So where’s the filter? That’s the troubling part.
Let’s assume that we’ve already passed The Great Filter. It’s more or less clear sailing for humanity now because we’re one of the rare civilizations that made it — maybe the only one. It doesn’t really matter what The Great Filter is. All that matters is we defied the odds and beat it, and that’s why there isn’t more intelligent life out there.
It’s also possible for there to be little intelligent life in the universe without a Great Filter. For this to be true, the only filter is the development of life. In this scenario, the conditions needed for intelligent life to develop in the universe were only recently met. That means no ancient aliens with a billion year head start on us ever existed. We would simply be one of the first intelligences to arise, and there could be others on the rise with us. I suppose you could call this one a positive scenario.
An asteroid hurtling towards Earth
For every best case there’s a worst one as well. That’s what you’d call it if The Great Filter is ahead of us. That means humanity is neither rare nor first in the universe, and there is some substantial evolutionary hurdle ahead of us that almost no species can clear. That would explain why we haven’t seen any super-intelligent ancient aliens, because they are the rare ones — the precious few to clear The Great Filter. In this scenario, humanity is probably doomed. Maybe an asteroid wipes us out before we develop the technology to deflect it. Or perhaps we’re running into The Great Filter right now, and it’s climate change or the exhaustion of natural resources that knock most civilizations back.

Maybe they’re everywhere

All that talk of The Great Filter is a bummer, but there’s another potential answer to the Fermi Paradox that’s more upbeat. We might not be rare, but just haven’t been able to spot intelligent life yet. There could be many advanced civilizations in the universe that simply don’t want to have contact with us for one reason or another.
When we wonder about the motivations of aliens, we assume they think like us. That’s far from certain, though. Perhaps the idea of exploring the cosmos is a uniquely human one. A hyper-advanced alien race might lock themselves up tight in a Dyson Sphere and stay put. They may not have the same need to expand as their population grows like humans do, so it’s reasonable that we would never have seen evidence of them.
Another possibility in this realm is that intelligent life is so common that we’re intensely uninteresting, and no advanced species would bother communicating with Earth. We could be in the galactic backwater of the Milky Way far away from all the important stuff. Aliens in this scenario might occasionally pass by and say, “look at those ape descendants, so boring and primitive.” Or maybe they aren’t even physical anymore, having long since moved beyond the need for corporeal bodies. If they’ve uploaded their minds to some sort of communal super-intelligence, then the very idea of beings living on a planet could seem blasé.
dyson
A Dyson Sphere.
A darker version of aliens being everywhere is a science-fiction staple — space is a dangerous place, and broadcasting your presence is a bad idea. By making yourself easy to find, you’re inviting invasion by aggressive hyper-advanced aliens. That would explain why we don’t see anybody — they’re all keeping their heads down because they know something we don’t.
Another possible explanation for a universe teeming with intelligence we can’t see is what I like to call the “Prime Directive” scenario. Here, advanced alien life exists all around us, but they are intentionally hiding themselves from lesser beings. In Star Trek, the Prime Directive dictates that humans not interfere with the internal workings of alien worlds. That means concealing their existence from primitive civilizations. So, maybe the aliens are watching us, but they don’t want to be involved directly until we’re a bit more mature.
It’s not unthinkable that the Fermi Paradox only exists as an idea because we aren’t ready as a species. I don’t mean that aliens are concealing themselves a la the Prime Directive. Consider this one last thing: What if intelligent life is common in the galaxy, and the evidence for it is all around us? The only problem is we’re not smart enough to realize it.
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