The search for alien life must heed this lesson from Stephen King

Here on Earth, at least 3.8 billion years ago and perhaps even earlier in our planet’s history, life emerged on our world, and has persisted ever since. We’ve had photosynthetic life for at least the last 2.7 billion years. We’ve had eukaryotic life, with differentiated organelles inside its cells, for more than 2 billion years. Multicellular life and sexual reproduction have been around for over a billion years. And plants, animals, and fungi all emerged more than 500 million years ago. More recently, our own species emerged on Earth: not only intelligent, but technologically advanced, transforming our world and having taken our first steps into space beginning in the 20th century.

Uncovering this story, coupled with the recognition that the raw ingredients that led to life on Earth are found in billions of star systems across our galaxy and in trillions of galaxies across the observable Universe, has led to some tremendous questions and some equally tremendous speculations.

• How many other worlds in our Solar System had life arise on them?
• How many inhabited planets are there in our galaxy right now?
• How many planets are teeming with life the way Earth is?
• How many intelligent alien species are out there, and how many are more technologically advanced than we are?
• And, perhaps most fundamentally, are we alone in the Universe?

These are among the biggest existential questions one can ask, and perhaps later this century we’ll finally, for the first time in history, have an answer to one or more of them. But until then, there’s a vital lesson against drawing premature conclusions from an unlikely source: the novelist Stephen King. Here’s what everyone, from professional astrobiologists to laypersons, ought to know.

The prospect of detecting and characterizing the atmosphere of a true Earth-like planet, i.e., an Earth-sized planet in the habitable zone of its star, including both red dwarf and more Sun-like stars, is within our reach. With a next-generation coronagraph, a large ultraviolet-optical-infrared mission could find dozens, or even hundreds, of Earth-sized worlds to measure.

In Stephen King’s epic story The Stand, a weaponized virus gets accidentally released from a military lab and causes a devastating global pandemic. This bioweapon of a virus — known both as the superflu and also by its codename, Captain Trips — is highly infectious, and in short order, the initial outbreak in Arnette, Texas has now spread to every country on Earth. The superflu, over the span of just a few weeks, proves to be fatal to nearly everyone: killing over 99% of the world’s population. After only about a month has elapsed, nearly all of the humans that once existed on Earth have died.

However, one of the people present at the “ground zero” scene of the initial outbreak in Arnette, Texas turns out to be Stuart Redman: a remarkable individual for a single reason, the fact that he appears to be immune to the virus. He’s forcibly detained as researchers and government officials hope to use his body’s seemingly unique properties to find a treatment and cure, but as more and more people succumb to the virus, he escapes. He eventually meets up with several other survivors, where many of them join together to try to create a new society from the remnants of the old, and to make humanity’s “stand” against a series of dark forces led by the story’s antagonist: the supernatural Randall Flagg.

In Stephen King’s novel “The Stand,” all humans become exposed to, and more than 99% of them die from, a new superflu virus known as Captain Trips. The rare human who survived the virus, largely unaffected by it at all, would potentially have to go a very long while before finding a second survivor. Until they do, they would legitimately worry about whether they were, indeed, the only remaining living human on Earth.

What makes this story so important when we think about the search for alien life, as King artfully outlines in several different storylines, is what each of the (rare, but not unique) survivors of the pandemic must have been wondering: am I alone? Am I the last, and perhaps only, surviving human on Earth?

He has a character — one who’d been living in an isolated, rural area rather than the urban or suburban population centers where there were often multiple survivors — explore the possibility for themselves. “Am I alone? What would it take to convince me that I’m not alone?”

The character (correctly!) assesses that they have no way of knowing how many people survived, or whether they were the only one remaining on Earth or not. In fact, there’s no way to know whether they’re alone or not until they find a second example of a living person: without a second example, the odds could range anywhere from:

• well, the few people I knew to look for in my area are all dead, and I’m the only survivor among the very small sample that I’ve collected,
• to there is something very, very special and rare about the traits and properties that I have, and even if Earth were previously filled with trillions or even quadrillions of humans, I would be the only one who survived.

From both a scientific and also a mathematical point of view, this is an incredibly responsible way to approach the puzzle.

If you were to walk down the street and find large numbers of bodies laying down, still and unliving, you would begin to wonder whether any humans other than you were alive at all. It wouldn’t be until you spotted another living human that you would be correct to be convinced you weren’t the only living human remaining on Earth.

Imagine yourself in the following scenario: you wake up one morning, only to discover, much to your horror, that no one else around you has woken up this morning. The people you normally live with in your household are all in their beds, but their bodies are cold and motionless. You go to your neighbor’s, but there’s no answer there. You call the people in your phone, one after another, going down the line, but nobody picks up. You get into your car and start driving, but don’t see any other cars on the road. They’re all parked, all empty, and no stores are open. You open up your social media apps and start messaging everyone, looking for a response or even a “seen” status, all to no avail. You start looking for new posts, but aren’t seeing any, save for what looks like automated postings or the ramblings of bots.

From a mathematical point of view, what you’re doing as you cast your net wider and wider, looking more broadly for any signs of life outside of your own self, is increasing the sample size of “potential people” who could be showing a sign that they are alive: that it’s not just you.

• When you’ve surveyed your first 10 people and find that you’re the only survivor, you could reasonably infer that the survival rate is low: likely to be no more than 1-in-10.
• After your first 100 people, if you’re still the only survivor, you’re likely to infer that the survival rate is even lower: no more than 1-in-100.
• After 1000 people, a million people, or a billion people, if you’re still the only survivor, you’d infer the survival rate is likely to be 1-in-1000, 1-in-a-million, or 1-in-a-billion, at most.

These four graphs show the expected number of successes one would be likely to achieve in 18 trials of a fair sample, for success probabilities per trial of 10% (upper left), 25% (upper right), 50% (lower left), and 75% (lower right). Note that observing exactly 1 success does not rule out any of these four possibilities, and also does not necessarily imply that the true success rate would be 1/18.

That’s not a mathematically rigorous statement, however. Mathematically, when you survey 10 people and find only one example of success, that doesn’t mean the probability of success is 1-in-10. In fact, if your “odds of success” are actually 1-in-10 and you perform 10 independent trials, you’ll only wind up with exactly one success about 39% of the time. 34% of the time, you won’t have any successes at all, 17% of the time you’ll have two successes, and about 10% of the time you’ll have three or more successes.

The fact that you conducted 10 trials and observed 1 success doesn’t mean the odds of success are 1-in-10 in a general sense.

• First off, if you knew the “true probability” of success, and took a fair sample of any number of trials, you wouldn’t necessarily get a number of successes that equaled the true probability multiplied by the number of trials. (You would expect a binomial distribution of successes instead.)
• Second off, the “one” observed success is a necessary condition of this trial; if there were no successes, the experiment could never have been performed, meaning you have to make inferences based on the use of Bayesian statistics, which is limited in its helpfulness in situations such as this.
• And thirdly, you have no way of knowing what your sampling bias is: whether the trials you’ve conducted represent a fair sample of the overall population, or whether they represent a biased sample, where the sample could be biased either higher or lower than the true distribution.

At top, the Powerball ticket sales projections dependent on the size of the Jackpot; over half a billion tickets are expected for each Jackpot over $1 billion. At bottom, the expected value of a $2 Powerball ticket, which, when accounting for taxes and split Jackpots, peaks at Jackpot values of around half a billion dollars and decreases thereafter.

By surveying a larger and larger sample, for as long as you yourself represent the only known success thus far, all you can do is place more and more stringent constraints on the maximum inferred probability of any success at all. If you want to gain a better estimate of the true probability of success, however, there’s only one way to get there: by actually finding a second example of success.

King noted this as well, as the survivor in his story recognized that as long as they were the only living human that they knew of, they had no way of knowing whether they were alone or whether there were others. However, as soon as a second living person was discovered, the survivor could then rightfully conclude that there were more than two total survivors: likely there was a population of many others that had also survived.

Again, statistics backs King up on this one. If you have a large number of samples but only one success — especially if you’re in a situation where that one success (i.e., yours) is necessary for the study to even begin — you do not know what the odds of success are. However, if you find a second success while the vast majority of all possible samples remain uninvestigated, you can be confident there are going to be many other instances of a successful outcome. If you have a winning lottery ticket, and after surveying 10,000 other tickets you find a second winner, then if you know there are a billion total tickets to choose from, there are most likely many other (likely several thousand more) winning tickets as well.

Although Earth contains the most liquid water on its surface of any of the 8 planets, the most water in any form is found on Jupiter’s moon Ganymede. Next in order is Saturn’s Titan, Jupiter’s Callisto, and Jupiter’s Europa. Planet Earth has only the 5th most water, placing it ahead of Pluto, Dione, Triton, and Enceladus, which land in 6th through 9th place in the Solar System, respectively. Other, more poorly explored Kuiper belt objects, such as Eris, may yet deserve a place on this list.

In the search for alien life, we’re still in that very early stage of asking whether we’re alone or not. Here in our own Solar System, we know that there aren’t world-transforming aliens on any of the places that we’ve searched that could possibly house them, including Mars, Venus, Titan, Europa, Ganymede, Callisto, Triton, Enceladus, or Pluto. We haven’t found any solid evidence for present life on any of these worlds, and even evidence for past, ancient life is both scant and dubious. But we also haven’t looked very hard or very well; there could yet be microbial life forms thriving on, above, or within several of these worlds.

We haven’t found any signatures of intelligent aliens, through direct searches and the efforts of SETI, although again, our power to search for their presence is limited to only a few detection methods and to a relatively small search radius within our galaxy.

And despite recently crossing the threshold for 6000 discovered exoplanets, nearly all of these known worlds are wildly unfriendly to life, as the majority of worlds:

• are much larger than Earth, with thick hydrogen and helium atmospheres,
• are much hotter and closer to their parent stars than Earth, and too hot to house liquid water on their surfaces,
• or, for the smaller, Earth-sized worlds, are likely to orbit around small, faint, still-actively flaring red dwarf stars.

Although more than 6,000 confirmed exoplanets are now known, with more than half of them uncovered by Kepler, there are no true analogues of the planets found in our Solar System. Jupiter-analogues, Earth-analogues, and Mercury-analogues all remain elusive with current technology. The overwhelming majority of planets found via the transit method are close to their parent star, are ~10% the radius (or, equivalently, ~1% the surface area) of their parent star or more, and are orbiting low-mass, small-sized stars.

In fact, despite all the worlds we know of, there are no known “Earth twin” candidates out there: an Earth-sized world at Earth-like distances from Sun-like stars.

And yet, despite the lack of any signs of life out there despite all the ways that we’ve looked so far, there are good reasons to believe that the galaxy is actually a very life-friendly place. The raw ingredients for life — the heavy elements that lead to the formation of rocky planets, organic molecules, and living creatures — are ubiquitous throughout the plane of the Milky Way: where most of its stars reside. Most of the known stars have comparable heavy element fractions to those found in the Sun, and when we’ve looked at newly forming stellar systems, they tend to produce planet-forming disks.

Over 80% of the stars, based on our surveys, are suspected to have planets. Earth-sized planets are common around stars at all distances, and Earth-sized planets at the right distances from their parent stars to support liquid water on their surfaces (assuming they have Earth-like atmospheres) are anticipated to be common: present in between 1-10% of all star systems. Sun-like stars, as well, are common, representing between 1-10% of all stars. We know of many such stars, some of which are strongly suspected to have planets, right in our own backyard, such as Tau Ceti, Alpha Centauri A, Epsilon Eridani, 61 Cygni, and Epsilon Indi. Although there are many others, these five stars are all located within a mere 12 light-years of Earth.

In the early 21st-century, we’ve successfully mapped out practically all the stars in our neighborhood in three-dimensional space. The closest stars to us don’t always align with the stars we can see, as what’s visible is determined by a combination of distance and intrinsic brightness, but all stars beyond the Sun are at a much, much greater distance than anything within our Solar System. The Alpha/Proxima Centauri system is a trinary, and has the three closest stars to our Sun at present; Barnard’s star is the fourth closest, and is the nearest singlet star system to our own.

The reason stars like these are important, however, is because humanity is on the precipice of designing, building, and operating our first telescopes that will be capable of measuring the light from Earth-sized worlds at Earth-like distances around (roughly) Sun-like stars.

• If those worlds have atmospheres, we can use the science of spectroscopy to break that light up into its component wavelengths, revealing what types of gases, hazes, clouds, and chemical compounds are present.
• If that world has seasonal variation in its atmospheric contents, the way Earth’s carbon dioxide levels fluctuate seasonally, we’ll be able to detect it.
• If the world changes color or brightness over time, even from just a single imaged pixel, we can use those changes to infer things like the planet’s rotation period, the presence of clouds, the existence of continents and oceans, the retreat or advance of icecaps, and whether land masses change color with the seasons. (The last of which would be an analogy to Earth’s continents greening and browning periodically.)

Those observatories include the ground-based Extremely Large Telescope and the Giant Magellan Telescope, already both under construction, as well as the planned Thirty Meter Telescope. They include the concept of ExoLife Finder, which is under development, and NASA’s planned flagship mission for the 2030s: the Habitable Worlds Observatory. If there’s life on planets surrounding any of the nearest Sun-like stars to Earth, the next generation of ground-based and space-based telescopes will have an excellent shot at finding it.

Left, an image of Earth from the DSCOVR-EPIC camera. Right, the same image degraded to a resolution of 3 x 3 pixels, similar to what researchers will see in future exoplanet observations (assuming the light from the central pixel bleeds into adjacent ones). If we were to build a telescope capable of obtaining ~60–70 micro-arc-second resolution, we’d be able to image an Earth-like planet at this level at the distance of Alpha Centauri. Habitable Worlds Observatory, with a novel coronagraph, as well as the ground-based ExoLife Finder, could image Earth-sized worlds at Earth-like distances from Sun-like stars, albeit only as a single pixel.

But not finding it, which is also an option, doesn’t necessarily mean that we’re alone. It doesn’t even necessarily mean that life or inhabited planets or even intelligent aliens are rare; it means that we haven’t yet looked with sufficient precision to find the key piece of evidence that will teach us that we aren’t alone: a second example of success, somewhere else beyond Earth in this Universe. As we look with more and more precision, casting not just a wider net for where life could be but looking more deeply and comprehensively into the possible locations where signatures past or present life could be hiding, we can expect two periods:

• a period where we don’t have a detection of definitive life beyond Earth, where our constraints become better and better, allowing us to place more stringent upper limits on the frequency and abundance of life in the Universe,
• followed by a discovery that will forever change how we view our place in the Universe: the discovery of a second instance of life somewhere in the Universe.

Until we have that second instance of life, we have no way of ruling out the most horrifying possibility of all: that we truly are alone in all the Universe. But when that critical moment does come — and like many scientists, I am convinced that someday it will — and we do find our first robust instance of life beyond Earth, we’ll not only know that we aren’t alone in the Universe, we’ll be able to conclude that there are plenty of examples out there. Until then, we should all remember Stephen King’s lesson: that one example might mean there’s only one in all of existence, but if we can find two, we can be confident there are many others.