Earth: Eternal or Vulnerable?

Earth. For most of our history, we have thought of it as The World. The place created for life. The canvas upon which the drama of history takes place. As far as we knew or cared, Earth was pretty much the whole Universe. Sure, the sun, moon, stars, and planets were out there, but they were there to serve as signs and sources of light, and to mark the passage of time. There was a purpose to the world; it was there for us. It was eternal. Sure, we supposed it had been created some time in the forgotten past, and would end sometime in the inscrutable future, but for us, for our grandparents, and for our grandchildren, it was what it was.

Only recently have we begun to wake up from this fantastic dream. New methods of observing the heavens and Earth opened our eyes to the vast context of space and time we exist within. We learned that the Earth and the Universe are not anywhere near as close in size as we thought. The Earth is a planet, one among an uncountable number; the sun, merely another star. And we learned that for every star we can see, there are billions upon billions in our galaxy alone, and our galaxy is just one among billions upon billions. In universal time, all of human history is but a fraction of an eyeblink. And in the eons before us, the world has changed dramatically, many times.

We still usually think of the world as what is real. We say that all that stuff about stars and galaxies is real too, but it feels distant, like it’s somehow less real than the ground we stand on. This is put into words by the phrase, “down-to-Earth,” which describes someone who is focused on the tangible present. It is our natural inclination to pay the most attention to things we can see and touch, and treat everything else as if it is less real. We talk about “the real world,” meaning the place we find ourselves in, with an emphasis on our social and economic environment. And even though we know objectively that Earth is one tiny planet around one middle-sized star, we struggle to break away from the narrative of The World upon which we stand as the foundation of the universe.

From Voyager 1, amongst a background of stars and the glare from the sun, Earth appears as merely a fraction of a pixel.

We have plenty of stories of the world coming to an end, from the gods and demons of mythology, to invasions from aliens, to nuclear war, to giant asteroids, to plagues, to just about anything we can imagine. Yet we know these are just stories—or at least most of us do, anyway—and at the end of the day, The World will still be here. Always has been, always will be.

Except that isn’t so. The sun is heating up, and in about a billion years this will cause Earth to follow in Venus’ footsteps with a runaway greenhouse effect, boiling away the oceans and making the planet inhospitable to any life. Unless our descendants are around for some planetary engineering, The World will end.

In our planet’s history, life has faced several major extinction events and survived. First, there was the Great Oxygenation Event 2.5 billion years ago, when photosynthesis evolved and gave our atmosphere the large amounts of oxygen that keeps us alive today. While that was good for the life that evolved later on, it was toxic to the life at the time, and killed most of it off. During the past billion years, there have been five famous mass extinction events, each of which killed off more than half the species on Earth. And right now, we’re in the middle of another mass extinction, this time caused by a fun little species called homo sapiens, first by lots and lots of hunting, and nowadays by irresponsible pollution.

In the past, despite toxic atmospheres, ice ages, supervolcanoes, and mountain-sized meteorites, life has always bounced back. This has led to the Gaia Hypothesis, which proposes that Earth is a self-regulating system, which always brings itself back to equilibrium when the balance is disturbed, like a living body keeping itself in homeostasis. The Gaia Hypothesis is a prominent theme in David Brin’s 1990 near-future science fiction novel, Earth, which is really good and I highly recommend it.

While the Gaia Hypothesis might help us sleep easier with the belief that we will solve our current global problems and The World is going to be okay, much of the evidence supporting it may be an illusion. Take the Fermi Paradox; the universe has been around long enough that alien civilizations could have gotten billions of years’ head start on us, and enveloped noticeable chunks of the galaxy in Dyson spheres. Yet when we look out into the universe, we don’t see big empty spaces in the Milky Way, nor in any of the other thousands of galaxies we have looked at, suggesting technological life is extremely rare.

One answer for why we see no signs of alien civilizations is the idea of filters, events standing between non-replicating matter and technological civilizations, which most planets never get past. Perhaps it is unimaginably rare for non-replicating matter to form replicating molecules. Perhaps it’s the leap from single-cells to multicellular life. Or maybe, most mass extinctions in the universe wipe out all life on their planet, and we happen to be the one place where life got lucky six times in a row.

This implication of the Fermi Paradox suggests that maybe we shouldn’t let ourselves become complacent about the continuation of the Earth. In addition, we have something today the Earth has never seen before in its 4.5 billion year history: rapid technological progress. Through science and economics, more and more power has become available to the average person. For example, the internet is only a few decades old, and now almost anyone can view the vast stores of human knowledge stored on it, to which the great libraries of the past pale in comparison.

The present-day philosopher Nick Bostrom put forth a thought experiment: imagine the set of all possible inventions as an urn full of balls on a scale from white to black, white being something that can only be used for good, and black being something that can destroy the world. Throughout human history, we have been pulling balls from this urn with varying shades of gray, from airplanes to vaccines to nuclear bombs. But there may be, unknown to us, a possible technology that would be extremely easy for anyone to make and destroy the world with. A black ball technology. Perhaps a self-replicating swarm of drones tasked with destroying all humans, or an unstoppable virus, or an easy method of creating black holes. The fact that we cannot rationally rule out the possibility of a black ball technology 100% has led to an alternative to the Gaia Hypothesis, the Vulnerable World Hypothesis.

The fact that neither humanity nor life on Earth has been wiped out in the past is not sufficient to say it won’t happen in the future. That would be survivorship bias. We cannot rule out the possibility that a large-scale natural disaster or a powerful technology could end it all. However, there is a bright side. The fact that it is possible for The World to end does not mean it is guaranteed. Taking the Vulnerable World Hypothesis seriously could make it a self-defeating prophecy. If we accept that our choices could mean the difference between fading away into nothing and a legacy of life that goes on into the deep future of the universe, then we will be spurred to reduce our existential risks as much as possible. Just like technology has given us more power to destroy the world than ever before, it has also given us unprecedented power to save it.

We need not despair at our impending doom, but neither should we live on as usual, casting our faith blindly at Nature or Fate or God or aliens. We are the caretakers of this world, the sole beings with the ability to rationally assess the risks and design methods to mitigate them. We have strong narrative attachment to The World. But if we want to be faithful to truth, we must treat it analytically, just like everything else. It is our responsibility to learn, to gather information, and to work to preserve our precious home in this vast, empty universe.