Where Are the Aliens?
There may be a few reasons that we haven't met anybody yet.
In 1950, Enrico Fermi went to lunch with his friends. It was a good time to be a physicist at Los Alamos National Laboratory. Science was cracking the shell of an entirely new discipline, one with terrible potential and unlimited government funding. The mood was light and everybody at the table was a genius. The scientists joked about a recent rash of UFO spottings over their sandwiches. Suddenly, Fermi exclaimed, "Where is everybody?"
Fermi, of course, was referring to the aliens. He wasn't the first person to wonder, but he might have been the first scientist to voice the question. About twenty years earlier, a Soviet rocket scientist named Konstantin Tsiolkovsky had pondered the same problem in an unpublished manuscript. He himself was probably responding to conversations that had been fermenting in the research community for a while.
The universe is 13.8 billion years old and contains up to two trillion galaxies. Statistically speaking, aliens ought to have evolved somewhere other than Earth, taken to the skies, and become a commonly accepted fact of life long ago. It's improbable that this hasn't happened. Yet there was, and still is, no incontrovertible proof of alien involvement on Earth. There are no invasions or peace envoys, no artifacts or space garbage, no radio signals or resource grabs or—the true elephant in the room, when everyone carries a camera in their pocket—clear photographs.
So where are the aliens?
Theory 1: They're hiding
Fans of Star Trek will already be familiar with the Prime Directive. For non-Trekkies, the Prime Directive is the rule that advanced, spacefaring species shall not make themselves known to or intervene in the affairs of non-spacefaring planets. Obviously, this is a boring rule that makes for poor ratings, so the various Captains of the Starship Enterprise break it constantly.
There's another name for the Prime Directive, and it's a little less noble. Welcome to the Zoo Hypothesis, a darling of science fiction writers. Arthur C. Clarke is probably the most notable zoovian, beginning 2001: A Space Odyssey with an alien artifact on the moon. In this case, aliens are waiting and watching for our evolution into something smart enough to relate to them.
However, this scenario assumes not only that the aliens are fairly ethical, but that they are all ethical. It also posits that alien societies don't experience the kind of resource demand or economic pressures as we do.
In a universe as large as ours, it doesn't make sense that no interstellar corporation has ever mined through in service to their fourth quarter investors' meeting. Several planets in our solar system contain valuable resources - Europa even has water. Even without ever having mined them there ourselves, we know that iridium, gold and platinum exist on asteroids. Still, we don't see open pits on Ganymede and abandoned shafts on Callisto. In a universe of two trillion galaxies, what are the odds that there are no other capitalists—or, for that matter, no planet experiencing resource shortage?
Ever since Galileo pointed his homemade telescope at the sky in the early 1600s, there have been myriad opportunities to see alien mining and resource operations at work. The leavings of those mines ought to have been pretty apparent. None have appeared.
It's a reasonable possibility that some ethical aliens might hide from us. But all aliens? Impossible. Even here on Earth, profiteers regularly perform end runs around regulators, NGOs, and other ethical do-gooders. In a universe of two trillion galaxies and potentially thousands of alien life forms, there's no way that there wouldn't be a single spoiler in the bunch.
The aliens aren't hiding.
Theory 2: They're incomprehensible or inaccessible
Trees are conscious. To a degree, anyway. They react to touch and emit chemical "screams" in response to injury. Some of them may have memory capability. Think about that. After four million years on this planet, humans are just coming around to the bare possibility that plants could be at all mentally sophisticated. They're alien intelligence literally sitting in our backyard.
Human perception is notoriously weak. Human assumptions are notoriously strong. Put those together and you might have a recipe for aliens. If they're different enough from ourselves, we might look right at them and not realize that they're there.
Ever since the 1960s, researchers have been trying and failing to figure out a single rubric for what qualifies as alien life. Does life need to breathe? If something talks to us but doesn't have a metabolism, does that count? There are lots of examples of questionable life forms even on Earth. Viruses are one of the thorniest, and the question of whether or not they're alive has dogged science for a century. If intelligent interstellar life has been trying to communicate by giving us pneumonia, then we're never likely to notice its advancement.
In fact, we may be as inscrutable to alien life as it is to us. For all we know, the universe of advanced intelligence may be heavy on protozoa. If they're here, they may be as oblivious to our presence as we are to theirs. Unlikely? At best. Impossible? Who knows?
Even if we ever solve the problem of our own human bias toward life that's like ourselves, we may never reach areas where interstellar life is flourishing. There's no reason that aliens couldn't be swimming around in Jupiter right now. As implausible as it may seem that anything could thrive on the 864-degree-Fahrenheit surface of Venus, there are terrestrial extremophiles that can handle worse. A Russian scientist made waves a few years ago by insisting that something was living in Venus's clouds. It's not implausible, but it's also not verifiable. Places like Venus and Jupiter are currently out of bounds for us clunky little apes. We may have aliens right next door. We might eventually see them, recognize them, get excited about them, and then never have a chance to meet them.
That brings us to our final theory of the day.
Theory 3: They're homebodies.
Space travel takes resources. Not a few resources. Not a smidgen of resources. A lot of resources. It's a venture that requires crazy amounts of raw materials, which need to be mined, researched, and refined. Never mind the years of training and scientific advancement societies require to generate rocket scientists. A world of 500,000 people living a sustainable hunter-gatherer lifestyle isn't likely to stumble upon a fuel powerful enough to escape orbit. Whether aliens husband their resources or not is anyone's guess. They could be grand champion re-users on par with the most gung-ho of zero waste Facebook moms. But even if they did, there's a good chance they'd eventually run out or run themselves into the ground.
If you watch the news for signs of life, you may already know that models predict that aliens tend to die out. Either they expire in a few million years, or their rapacious resource use and poor waste management snuffs them. The fact that we're currently raking our own environment over the coals in the name of progress, potentially to the point of changing the climate beyond our own ability to adapt, suggests that extraterrestrial people like us may be prone to wrecking themselves ecologically. Human civilizations have a long and dramatic history of crashing their environments directly into a wall. Ask a Roman, a Mayan, or a resident of the Dust Bowl how fast resource mismanagement gets you to the moon.
Even if a civilization were to survive the pitfalls of climate change and resource waste, there's no reason that it ought to last forever. Nothing else does. In all of the universe's billions of years, there may have been millions of life forms as smart as we are. They might have just finished their natural runs. According to Alan Weisman's amazing book, The World Without Us, it might not take much time for nature to eliminate evidence of intelligent life. There's even some plausible speculation that intelligent life has evolved on Earth before.
Finally, there's a decent chance that the aliens have just gone home. Who says it's smart to leave the verdant paradise where you evolved and venture into the unlivable void? The Earth is about 4.5 billion years old. Humans evolved in less than 0.1 percent of that amount of time. If we survived another hundred million years, we still wouldn't approach the day when the sun begins to die. If we wanted to stay home, we could engineer asteroid redirection programs, emergency plague enclaves, and mass environmental management to ensure that our stay on this beautiful rock is lengthy, safe, and comfortable. That might be exactly what the aliens are doing.
Maybe they went through a resource-heavy phase and saw the light. Maybe they ventured out into space, decided that home is where the heart is, and returned to the nest. Maybe they never got past the bow and arrow. One way or another, they're not here. And maybe that's OK.
Human beings aren't alone in the universe. We have each other, a fact that we sometimes miss, and the other life forms that inhabit our unusual world. It's tempting to suggest that we ought to focus our energies on making life good for each other rather than pining for alien friends. Knowing the fates, that would be exactly when E.T. would drop by for coffee.