What If We Haven’t Met Aliens Yet Because They’ve Messed Up Their Planets Too?

Enrico Fermi is one of the most important figures in modern nuclear physics. Among the many programs he was involved in was the Manhattan Project, in which he helped establish the conditions for a sustained nuclear reaction, a key component in the atom bomb. During a visit to Los Alamos, where the first bomb had been built less than ten years before, Fermi joined a casual conversation with Edward Teller and other scientists around a lunch table. This was at the height of the 1950s space race, and they were discussing the physical and technical barriers to traveling at near light speed. Most of the scientists eventually agreed that such rapid transit would one day be invented, and the conversation turned to guesses about when, not if, humans would achieve these great speeds. Most of those around the lunch table assumed that it would be a matter of decades, not centuries.

Suddenly, Fermi did some quick calculations on a napkin demonstrating that the galaxy had millions of planets similar to Earth. If interstellar travel was theoretically possible, then—“Where is everybody?” he suddenly blurted out.

The shocking realization that Fermi had while chatting over lunch that day was that the universe was eerily absent of non-natural radio signals. He and other scientists had been analyzing electromagnetic waves throughout the cosmos for many years. They had detected signals from very far away—millions and billions of light years away. But they had heard only the regular, repetitive signals from stars and other celestial bodies. They’d never heard anything that could possibly be a form of communication, as far as they could tell.

That realization was more than 60 years ago, and we still haven’t heard anything but the background buzz of stars, planets, quasars, and nebulae, nor have we been visited by alien life (that we know of). Which leaves us with the uncomfortable question: If we do turn out to be the only intelligent life in the universe, what does that say about life in the first place—and what does it say about us?

As Fermi knew, the universe is billions of years old and contains billions of galaxies. Even our own Milky Way, a run-of-the-mill spiral galaxy, contains hundreds of millions of stars, each one of which could be orbited by a planet harboring intelligent life. Furthermore, from what we can tell from the fossil record, life on Earth started almost as soon as conditions were favorable. There was very little delay after the Earth cooled before life began buzzing along, well on its way toward evolving into complex organisms. This argues that life not only can evolve but will evolve on a lifeless planet when the temperature and chemical composition are right.

The vastness of the universe inspired Dr. Frank Drake to develop a mathematical formula, now known as the Drake equation, that attempts to estimate how many civilizations exist in the universe. There are many variables in the Drake equation, including the number of galaxies in the universe, the number of stars per galaxy, the rate of new star formation, the percentage of stars that have planets, the fraction of those planets that exist in the habitable zone (which allows liquid water), the odds that life will begin, the chances that life will evolve to the point of having intelligent beings capable of transmitting signals into space, and so on. None of these are perfectly knowable variables but all can be estimated using current knowledge and the laws of probability. While there are huge disagreements about the utility of the Drake equation, some current estimates predict that the universe harbors around 75 million civilizations. The estimates constantly change, of course, as our knowledge of the universe improves.

Even before the Drake equation was articulated, with so many billions of stars and planets, Fermi reasoned that the universe should be teeming with life. Moreover, alien civilizations could be very far ahead of us in terms of technological development. Most sci-fi movies imagine aliens that are just a couple hundred years beyond where we are now, but the universe is nearly 14 billion years old, and stars and planets have existed for most of that time. Our solar system is relatively young at 4.6 billion years of age. There could be civilizations with billions of years on us in terms of their technology. They might be able to travel enormous distances the way we travel through cities.

Enrico Fermi’s question became known as the Fermi paradox, summed up as “In a universe as old and vast as ours, why have we not yet heard from alien life?” There are many possibilities to this as yet unanswered  question.

One possible explanation is that alien civilizations take care to hide their presence from us. An extreme expression of this notion is the planetarium hypothesis, which states that some sort of protective sphere has been built around us to filter out the noises from extraterrestrial civilizations but allow the background cosmic signals through.

Even if advanced alien civilizations have the ability (and desire) to keep us from hearing them, they would certainly be able to hear us. After all, we have been transmitting radio waves into space continuously since the 1930s. Traveling at the speed of light in all directions, our transmissions exit the solar system within a couple of hours and have been reaching other stars and their planets for decades. There are at least nine stars within ten light years of Earth and at least one hundred stars within 25 light years. Though our signals would be very weak by the time they reached that far, we would expect that an advanced civilization would also be advanced in its ability to monitor the signals coming from the surrounding stars and galaxies. They would know that we exist as well as quite a bit about us. (I wonder if that’s why no one’s come.)

Another explanation is that our assumptions are wrong and life is exceedingly rare in the universe. Maybe the rapid germination of life on Earth was an incredibly unlikely fluke and the other rare places that have been so lucky are so far away that radio signals have not had time to travel between them and us. Nevertheless, just in our local neighborhood of the Milky Way, we know that there are hundreds of thousands of planets in the sweet-spot range of temperatures necessary to sustain the kind of chemistry we see on Earth. Planets with the chemical composition of Earth and near the same temperature range are pretty common in the universe. While we don’t have nearly enough information to determine much about what those planets are like, there is no reason to think that Earth was special in any way at the time that life got started. Perhaps the most boring possible explanation is that every science-fiction book and film is wrong and our current barriers to interstellar travel are ultimately insurmountable. Stars are very far from one another, and at this time, we know of no way to exceed the speed of light—or even get anywhere near it. In fact, the conversation in which Fermi raised his question was actually an argument about the odds of humans having vehicles that could approach light speed in 10 years’ time. Fermi guessed 10 percent. That was more than 65 years ago, and we’re no closer now than we were then to traveling at speeds anywhere close to light speed. If there simply aren’t any solutions and standard jet propulsion is the best we’re ever going to do, the many civilizations throughout the universe are destined to remain isolated from one another forever. We will stare at the stars, bored and lonely, while other beings stare back, but we’ll never actually meet each other.

But still, why aren’t we at least hearing their signals?

There is another explanation, an even darker one, that many scientists, myself included, are starting to worry about. It may be that life is relatively commonplace in the universe, but it appears—and disappears—over unfathomably immense timescales during periods that rarely if ever overlap. In other words, advanced alien civilizations are not out there waiting to be found because they no longer exist. And in all likelihood, the fate that befell them will also befall us: developmental implosion.

Think about it: Human beings are on a collision course with our own industrialization. We are consuming nonrenewable (or very slowly renewable) resources at an unsustainable pace. Coal, oil, and gas are finite resources. Even if there is a lot left, there is not an infinite amount left. We are converting rainforests, which produce the majority of our breathable oxygen and consume the majority of the carbon dioxide, into land for farming or housing. Our population is growing so fast that our ability to provide food for each person will be in serious doubt within a generation, despite all of our scorched-earth efforts to extract more and more sustenance from the planet. Meanwhile, climate change is threatening major coastline developments, some ocean ecosystems are in all-out collapse, and biodiversity throughout the globe is plummeting. We are in the midst of a mass extinction caused almost exclusively by our own actions. Who knows how bad things will get before we bottom out?

That’s not even the worst of it. Weapons of mass destruction have raised the specter of mutually assured destruction, which was actually a delicate deterrent for a time but may not hold for long. Radical messianic and apocalyptic ideologues may be impervious to deterrence, and it seems inevitable that they will one day get their hands on the ultimate weapon. What will restrain them from using it? In addition, when world resources become scarce, strife will abound. Strife brings forth the worst in us, and economic and cold wars culminating in hot wars seem almost certain—with the stakes far higher than ever before.

Add to these dangers the very good chance that a pandemic could strike at any point. Humans now exist in such density that infectious diseases spread like wildfire. When we add to this the ease of global travel, a doomsday scenario is not hard to imagine.

All of these factors compound the others, increasing the danger that one or another of these tragedies will someday occur. Lack of farmable land raises food prices. Strain on energy resources raises all prices. High prices cause strife and unrest, which tends to favor the rise of dictators. Global warming will place the most pressure on the least developed regions, exacerbating their problems. Continued invasion of the rainforest will tap previously dormant viruses and provide them with a new and densely populated host. Bringing all of this together produces a grim picture. Are we on a clear path to our own demise?

There are literally thousands of ways to imagine how our species could suffer tremendous setbacks in the coming century, but at this point, extinction of Homo sapiens seems very unlikely. Given that humans live basically everywhere on the planet, there will always be people with the forethought, tenacity, and luck to get through whatever crises may come. Sure, without a complete redirection of our species’ current trajectory, major economic and political collapse may be likely. But I have little doubt that some humans would survive an apocalyptic scenario and the species would go on, even if the destructive implosion causes mass death and suffering as well as huge setbacks in technology and development.

The risks we now face as a species—dangers that are completely attributable to our own ambition—might very well be the normal way of things in the universe. If life has emerged on another planet, we can only assume that natural selection shapes that life more or less the same way it does ours. This is because natural selection is an extension of simple logic: Those who survive and reproduce well will leave more offspring than those who do not. It’s hard to imagine life working any other way on another planet, despite how different everything (and everyone) might appear on the surface. However, never have we seen—and never, alas, could we predict—the evolution of disciplined self-control, long-range foresight, rampant selflessness, generous self-sacrifice, or even something as simple as willpower. Evolution has never shown an ability to plan ahead more than a generation or two.

Evolution has made us entirely selfish. Of course, as a social species, we have an expanded sense of self that includes children, siblings, parents, and anyone else we are closely affiliated with. We make sacrifices for our children because we see them as part of “us.” But with this expanded sense of self comes limits. Our siblings and even our friends might be “us,” but certain strangers aren’t. Maybe we can expand further and say that people of one’s race, religion, or nationality constitutes “us,” but that still leaves a “them.” In the same way that humans evolved to feel parental love, we evolved to hate or fear those who are not “us.” This is true in all social mammals, so we have every reason to believe that life on another planet would follow this same logic.

It may be that we have never seen, heard, or been contacted by aliens because their civilizations simply collapsed under the weight of their own selfishness, technological advancement, and a host of other exacerbating factors before they gained the ability to leave their solar system. We ourselves are tantalizingly close to unlocking the secrets of space travel, harnessing endless energy from the sun, and keeping our bodies healthy indefinitely, but we also may be just as close to catastrophic collapse. Perhaps the same scenario repeats itself throughout the history of the universe, endless boom-and-bust cycles where a civilization almost takes the crucial next steps before blowing itself back to the agrarian days (if it’s lucky) and starting all over again.

Our impending collapse may be unavoidable, given our evolutionary design. Our desires, instincts, and drives are the product of natural selection, which does not make long-term plans. Chaos, death, and destruction may be the true natural state of the universe and of all species, including ours. To borrow a quote from the legendary science-fiction writer Arthur C. Clarke, “Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying.”

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From Human Errors, by Nathan H. Lents, courtesy Houghton Mifflin Harcourt. Copyright 2018, Nathan H. Lents.