Deafening Silence

Why we don't want find life on Mars or Europa

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In a universe that we now understand to be both unimaginably vast and ancient, where are the aliens? Surely, with modern technology we would see signs of intelligent life everywhere we look, but we don’t. This apparent contradiction, known as the Fermi Paradox, has many theorized solutions. Some of those potential answers are encouraging, others are frightful, but all embody the importance of continued human progress here on the pale blue dot.

The Paradox

The Big Bang, the first moments of the creation of the universe, set into motion the immutable laws of physics. Chief among these laws, of course, is the Second Law of Thermodynamics, which lays out what we know as “entropy.” Under the second law, the universe will naturally trend from order to disorder, or more specifically, toward the dispersion of energy. As we will see life on Earth, paradoxically, conforms to the second law and accelerates the process of entropy on the universe’s behalf. Indeed, the emergence of life may have been a natural and inescapable consequence of physics.

This begs the question then, why do we not find a universe teeming with life? The aliens need not make contact with us. Our telescopes are now capable of analyzing the atmospheric composition of distant planets, which could illuminate the presence of bacterial life via chemical fingerprint. Intelligent life, on the other hand, would probably be easier to spot, as they would likely use radio waves for communication, as we do. Yet, our radio telescopes have scanned the skies for decades: hearing only silence.

Sure, the precise temperature and chemical conditions that allowed for the formation of life on Earth are probably not common, but there is no requirement that life be so constrained to these parameters either. Earth’s own oceans, for example, harbor life that survives harsh acidic, high-temperature environments…in total darkness to boot. There is also no inherent reason that life must be “carbon-based” either. Scientists believe that silicon-based life is possible, if less probable, and this greatly broadens the environments where life could survive and thrive. Surely, in the vastness of the universe, there are many others. The universe is incomprehensibly large, with trillions upon trillions of planets. The silence of the heavens begs us to ask….where are they? This was the question posed in 1950 by Enrico Fermi, in what became known as Fermi’s Paradox.

Several solutions to Fermi’s question have been proposed. Among the more unique was posited by John Allen Ball in 1973, known as the “Zoo Hypothesis.” This theory holds that intelligent life exists and knows that we are here, but is hiding from us, preferring to observe from afar. Not unlike a nature reserve or a zoo, observing our development serves a scientific purpose for them. Should our civilization become sufficiently advanced, they may indeed make contact with us. If you ask me, this seems far-fetched. Not actively making contact is one thing, but hiding their entire civilization (and others), including their radio transmissions, spacecraft, laser communications…etc is another.

The approx. reach of human radio broadcasts is represented by the small red dot on the right.

Others have more plausibly suggested that the universe is simply too vast. Travel and communication are limited by the speed of light or nearly 300,000,000 meters a second. That’s fast, but our galaxy is some 150,000 light-years across. This means radio transmissions leaking from Earth would take tens of thousands of years to reach the ends of our just our own galaxy. Since we humans invented radio only <150 years ago, even our earliest signals have barely touched the smallest fraction of our galactic home (see image above). The same applies to “them;” we don’t hear them because their signals haven’t reached us yet. But in a universe that is 14 billion years old, that too seems unlikely. It took only ~300,000 years for humans to invent radio, 14 billion years is plenty of time for many civilizations to have done the same.

Nonetheless, others have suggested that we are, in fact, very early to the party. Despite its age, we humans may be among the first intelligent organisms to emerge in this universe. Early stars were short-lived, exploding in supernovas that sterilized much of the young universe over and over again. Indeed, astronomers from the Space Telescope Science Institute have estimated that the probability that the universe harbors other civilizations is an astonishing 92 percent. The problem is that these estimates are based on the entire lifespan of the universe; most of the planets that would harbor these civilizations do not yet exist.

This fact is further compounded by the universe’s size. When we look into the night sky, we do not see the universe as it is, but rather as it was. Alien civilizations could be emerging everywhere alongside us, but their light and radio waves have yet to reach us. In the same way, an alien civilization on the other end of our galaxy observing Earth might see a planet with promising oceans and reasonably intelligent mammals, but certainly no signs of civilization, at least not for another 100,000 years.

The Great Filter

In the 1990s, another possible explanation for the silence was formulated by Robin Hanson, in what became known as the “Great Filter” theory. This theory holds that while the universe’s vastness creates countless opportunities for life to emerge, one or more of the rungs on the “ladder” between chemical evolution and the emergence of intelligent, civilized life, must be highly improbable. This rung, or rungs, is called the Great Filter since it appears to block the advancement of life beyond a certain point.

The question becomes, what could the Great Filter be? Is the emergence of life itself extremely unlikely? Or perhaps the universe is filled with life, but the development of intelligent, multi-cellular organisms is rare? Or maybe intelligent life emerges but fails to develop and sustain progress as we have? Or maybe, most ominously, civilized life has emerged many times, but like the stars themselves, their efflorescences quickly burn out. Perhaps they, like us, become hopelessly dependent on fossil fuels and never find a viable workaround. Like us, perhaps they never overcome their biological limitations and eventually and inevitably wage wars between them that extinguish the light of their civilization.

Or perhaps one of these advanced civilizations gave birth to super intelligent AI that wiped out the mother species. Perhaps this all-knowing AI is still out there, hidden in the darkness beyond our detection, with no need for radio communication and lacking the telltale chemical signature of life. Maybe it’s out there, harvesting energy from stars as it ceaselessly expands like a cancer upon the universe, mopping up every potential threat to its survival the moment it detects competition for energy. Maybe, just maybe, this AI is coming for us, and we don’t know it.

These questions form what is perhaps the greatest unanswered mystery in the story of progress, where along the progress timeline does the Great Filter lie? Is it behind us, or in front of us? If it is behind us, then human civilization has, against all probability, done something truly special here on Earth. Something that we should celebrate, enhance, and protect. If it is in front of us, then, more likely than not, lessons unheeded, doom awaits us all at some point in the future, which makes advancing and accelerating progress that much more important.

Life on Europa

Mars and Europa are the leading candidates for finding life in our Solar System. Mars is fairly Earth-like and was more so in times past. Europa has warm oceans underneath a thick blanket of ice that could harbor life similar to that found in the deepest depths of the Earth’s oceans. We humans have sent probes to Mars and have not (yet) found evidence of life there. We have not yet explored the oceans of Europa, but we will soon. We don’t want to find life on either celestial body.

Why should we not want to discover alien life? If we find another instance of biological life so close to Earth, it suggests that the emergence of life itself is not at all improbable. This means that the Great Filter is that much more likely to be in front of us instead of behind us. It means the universe is likely brimming with bacterial life but that most become extinct between the evolution of intelligent life and the emergence of advanced civilization, or shortly after.

We may never know whether or not we are alone in this universe and perhaps we are better off simply not knowing. On the other hand, the vastness of space may mean that it doesn’t matter much either way. The light and radio waves we see in the night sky took millennia to reach us. Even if, one day, we hear “them” and reply, it will take millennia for our reply to be returned. Should they hear us and come to meet their interstellar pen pals, what will they find when they arrive thousands of years later? Will they find a prosperous and advanced civilization or the ruins of what was and could have been? That choice is ours.

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