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Science Behind the Fiction: If aliens existed, would they hunt us down, like in Predator?

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Sep 12, 2018, 2:10 PM EDT

For decades, we’ve been fascinated with the question of what might happen should we encounter intelligent life from elsewhere in the universe. The answer, according to the stories we tell one another, is that either they’d attempt to wipe us out or we’d become best friends and ride bikes into the moonlight.

Scores of books, movie franchises, and television shows have explored the potentially terrible consequences of first contact with an alien society. And while there are exceptions to the rule, the overwhelming commonality is that intelligent life from beyond our solar system would come here with one true intention — to take what’s ours and leave us dying in the rubble.

There’s a pretty compelling reason for these sorts of fictional narratives: Guilt.

We, as modern humans, are painfully aware of the types of behavior we’ve taken part in, as a species, in pursuit of expansion, advancement, and survival. In the unending effort to improve the quality of life for us and ours, we’ve committed unspeakable atrocities against our own species and against non-human animals, often dehumanizing outgroups in an attempt to justify maliciousness. It’s easy, after examining our own sins, to imagine a superior species from elsewhere and project our own behaviors onto them. Should travelers come from the stars, why shouldn’t they be conquerors? And would we deserve any less if they were?

These are the thoughts that have spawned an entire sub-genre of science fiction, including such enduring franchises as Alien and Predator, the latter of which has a new film opening in theaters this week.

Our most primal fear, after all that we’ve done, is that we might be thrust back into the food chain, subject to the sorts of evils we’ve unleashed upon others. These sorts of stories allow us to explore those feelings and fears in thrillingly visceral technicolor. They allow us to examine our own history through a fictional lens, softening the blow while still asking hard questions. Actually answering those questions is complicated, mainly because right now, they're theoretical. Is there life elsewhere in the universe? Is that life complex? Is that life intelligent and space-faring? Is it benign or malicious? And is it capable of reaching us?

Sadly, we have exactly zero empirical evidence for answering any one of these questions, let alone all of them. But that hasn’t stopped some of humanity’s greatest minds from tackling them.

Is there life elsewhere in the universe?

This is a question of considerable intrigue. There are moderately good reasons to suspect there might be life elsewhere in our very own solar system.

We know that the environment of Mars was once, billions of years ago, similar to that of Earth and that it still has liquid water today. While more extreme in its environment than we’re used to, it’s not entirely outside the realm of possibility that life might exist there today, if it ever did at all. It is, at the very least, a point of interest in our local neighborhood, and it isn’t the only one.

There are several moons around Saturn and Jupiter that may have the basic necessities for life. In 2005, the Cassini spacecraft sent back incredible photos of Enceladus, showcasing its geysers. We have reason to believe that liquid water exists beneath the surface, warmed by gravitational forces. And where water and energy exist, life has the opportunity to take root.

Europa has a similarly intriguing environment, with its global liquid ocean hiding under ten miles of ice. Any life hiding beneath its frozen shield would never see the light of the sun, but geothermal vents could provide the energy needed to sustain alien life.

Perhaps the most interesting candidate in our solar system is Saturn’s moon, Titan. Like Earth, it has liquid bodies of methane on its surface, but you wouldn’t want to beach there. While Earth exists at the tripling point for water (allowing water to exist as a solid, liquid, and gas) Titan’s temperature resides at the tripling point for Methane. There are lakes of methane, methane rain, and methane clouds.

Such an environment would be deadly to life on Earth, but it supports organic chemistry that could give rise to a form of life entirely different to anything we would recognize at home.

Finding life within our own solar system would blow the lid off the alien life debate. If we could prove that life arose not once, but twice, within our own solar system, it would go a long way toward supporting the idea that life is common in the universe. Putting local candidates aside, is there any good reason to believe there might be life somewhere out there?

This is one of the questions, alongside what happens, if anything, after we die. It speaks to the very nature of our reality and has intrigued humanity for as long as we can remember.

For a long time, it wasn’t really a scientific question. The notion of whether there was life elsewhere in the universe wasn’t something we could tackle through designed and regimented experimentation. Instead, it was left to philosophers and storytellers. But in the last several decades, that’s changed.

The last century saw human-kind slipping the bonds of our own gravity to visit other worlds, or at least, another world. We sent men to the Moon, we launched satellites and created permanent orbital science stations. We sent probes beyond the boundaries of our solar system, we designed radio telescopes capable of listening to the sounds of the universe, landed rovers on other worlds, and built telescopes capable of mapping the edges of known space.

For the first time in our species’ long history, we’re doing the work that could potentially answer that grand question. We’ve announced our presence to the universe, thrown our calling card on the table, and we’re waiting for a response. As yet, no one has answered, but in the meantime, we’ve gone knocking door to door. And while no one has answered, we’ve found, if not vacant homes, at least tenable real estate.

For much of human history, it was the common belief that Earth, and by extension, our solar system were unique in existence. That belief held for a long time. Many people, scientists included, thought that perhaps planets weren’t all that common and that planets capable of sustaining life (rocky bodies inside their parent star’s Goldilocks zone) were even less so. All of that has gone out the window in recent years, thanks in large part to the Kepler spacecraft.

Before Kepler, the most common method of identifying planets around foreign stars was by measuring their wobble. Despite common belief, the center of a solar system isn’t actually the star around which everything else orbits. That would require that stars be entirely stationary and that isn’t the case. Gravity works on all bodies, massive stars included, in equal measure. That means that while stars pull on planets, planets pull back.

This relationship means that when a massive planet orbits near a star, there is a measurable wobble in the star’s position that we can see from Earth. Before Kepler, most of the discovered exoplanets were detected by measuring the wobble of distant stars. This method was limited in that we could only see massive bodies near their parent stars. The wobble had to be sufficient to be seen from a vast distance.

Kepler changed the game in that it allowed us to find objects much smaller than gas giants, including planets that are considered to be Earth-like. Kepler measures the amount of light that reaches Earth from distant stars. And it’s good enough to detect tiny changes in the apparent light, such that when an object transits (passes between the star and Earth) it can tell.

Since the beginning of the Kepler mission, thousands of exoplanets have been discovered, putting to rest the notion that planets, even Earth-like ones, are rare in the universe. Box checked.

Despite the confirmation of suitable locations scattered throughout the galaxy and the universe, we have failed to find any confirmed evidence for life off our own world. This has caused many people to wonder where the cosmic party is and why we haven’t been invited.

In 1961, astronomer Frank Drake proposed, around the lunch table, a way to estimate the number of intelligent species in the universe by plugging in a set of variables based on the information we have. This has become commonly known as the Drake equation, and it suggests that, even with less than preferable odds, the universe should be entirely littered with intelligent species. The fact that we haven’t encountered evidence of any such species is the root of another common concept in the realm of alien intelligence, the Fermi Paradox. It asks, in short, since we should expect to find evidence of life outside our solar system and haven’t yet, what gives?

There are several popular explanations for the Fermi Paradox. Some thinkers believe there must be what they call the Great Filter, something that prevents most or all species from making the transition to space-faring, intelligent societies. Others believe intelligence is out there and they’re avoiding us on purpose. Others believe that the answer lies in our own hubris; why should any sufficiently advanced alien species communicate or operate in a way that would be easily recognizable to us? Maybe we’re like ants trying to understand skyscrapers.

Is extra-terrestrial life intelligent?

Let’s assume, for the sake of argument, that complex life exists somewhere out there. Even when you take the Fermi Paradox into account, it seems incredibly unlikely that in all of existence, Earth represents the one and only time that life arose. As Carl Sagan was famous for saying in his novel Contact, “The universe is a pretty big place. If it’s just us, seems like an awful waste of space.”

Assuming that life exists, what might it be like? The common suspicion is that there are species out there conquering space, wiping out lesser beings with their grand technology. Or, as is suggested in the Predator series, hunting us for sport.

The late, great Stephen Hawking had some pretty doom-and-gloom predictions for what might happen should humanity finally encounter intelligence life from beyond the stars: “Meeting an advanced civilization could be like Native Americans encountering Columbus. That didn’t turn out so well.”

Maybe he was right. If we did encounter an advance society we would certainly be at their whims, whether they be malicious or not. The real question is what is the likelihood that we encounter an advanced species? Is it more likely that we’re behind the cosmic eight ball or, as is suggested by some, that we are early and might be one of the first space-faring species in the universe?

On one hand, there is the school of thought that says the universe is almost 14 billion years old and intelligence only arose on Earth very recently. The math doesn’t look good and puts us at a severe disadvantage when compared with a species that industrialized even a thousand years before us, saying nothing about millions or billions of years.

But some scientists think this sort of thinking might be without merit. Avi Loeb, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics has a different point of view. He believes that Earth might actually be an early example of complex life in the long-term view of the universal lifespan: “We used the most conservative approaches to understanding the appearance of life in the universe, and our conclusion is that we are very early in the process and that it is likely to ramp up substantially in the future. Given the factors we took into account, you could say that life on Earth is on the premature side.”

Loeb’s premise considers the long view, that the lifespan of the universe is measured not in billions of years but trillions, and that the most common types of life supporting systems might arise around the long-lived red stars as opposed to stars like ours. He suggests that the probability of life might increase by 1,000 times in the distant future.

This line of thinking suggests that we might, in fact, be alone in the universe, not by virtue of the universe being innately sterile, but because we arrived to the party too early. Maybe we’re not the only life looking to the stars and wondering if we’re alone, but due to the incredibly vast distances involved and our early place at the table, we might as well be.

While it’s comforting to know that we’ll likely never encounter violent trophy hunters from the vast reaches of space, it’s also a little disappointing to know we might miss out on encountering other intelligent beings because we jumped the gun.

While we’re waiting for ET to land on the White House lawn, we can sate our desires under the glow of the sliver screen. As such, The Predator opens in theaters Sept. 14.