Some experts warn against contacting aliens. Are the fears of an extraterrestrial invasion valid?

The concept of interstellar beings is pretty ancient, with even Greek philosophers pondering about the idea. But the concept of these beings acting maliciously is a relatively new one, which really took hold at the turn of the 19th Century thanks to H.G. Wells and his 1898 book "War of the Worlds." Today, aliens feature in many popular horror films such as the "Alien" series and "A Quiet Place" and action blockbusters like "Independence Day." First we invent extaterrestrial monsters, then we imagine them killing us.

But this fear has true scientific merit: Legendary theoretical physicist Stephen Hawking warned his fellow scientists to stop trying to contact alien civilizations because he believed they would likely be hostile. Two years ago, a Washington Post editorial warned "Contacting aliens could end all life on earth. Let’s stop trying." And earlier this summer, four scholars were invited by the SETI Institute (Search for Extra-Terrestrial Intelligence, the world's premiere organization for seeking intelligent life off-planet) to release an Indigenous studies working group statement on the issue. They cautioned "First contact with aliens could end in colonization and genocide."

To understand the root of this question, we need to start with physicist Enrico Fermi, who questioned why we don't see evidence of aliens amidst the stars — a puzzling prospect given the seeming likelihood that life should exist somewhere else in the universe. There are endless possible explanations for the so-called Fermi paradox, among them that aliens may be as exploitative and violent as we are.

These fears may be rational. According to Dr. Franck Marchis, a senior planetary astronomer at the SETI Institute, we don't know a lot for sure, but certainly there is some reason for concern. "If they can travel to visit us, their technology is probably way ahead of ours, including maybe having a way to travel faster than light," Marchis wrote to Salon. "If they don't like us or don’t consider us to be intelligent, they could probably wipe us out quickly, so yes, this is a frightening prospect."

To best guess how these such aliens might act if they visited Earth and chose to be hostile, Marchis suggested comparing hypothetical aliens to real animals that humans encounter on a regular basis.

"They could be like ants, with a queen in charge, like in the movie 'Aliens,'" Marchis speculated. "Or they could be like big cats that hunt alone and might come to our solar system to hunt, like in the movie 'Predator.' They could also be like the aliens in the TV show 'V,' who see our planet as a resource and want to use us and our water. Or, they might see us as a threat and want to destroy us before we get too advanced, like in the movie 'Independence Day.'"

Dr. Ethan Siegel, an astrophysicist and science writer, takes a completely opposite position.

"This is a completely fear-driven approach from a human perspective, with no basis in reality," Siegel wrote to Salon. "Why would a technologically superior alien species, of all the planets with all the resources to choose from for whatever they required, choose to visit an inhabited, life-rich planet with a species in their technological infancy? And why, as these depictions tend to show, would their goal be to wipe out the infant species (us) rather than just acquire the resources they were seeking?"

Siegel compared this to humans intentionally annihilating a group of single-celled organisms in Europa's sub-surface oceans. "Of all the very real threats we face, from ourselves and from the Universe, this is just one case where our egocentrism has grabbed hold of our instinct to flee-and-hide as prey, and run amok in popular culture," Siegel said, ticking off movies like "Mars Attacks!" as examples of films that are as realistic as the Loch Ness monster, Sasquatch or Godzilla.

"Therefore, I put my trust in Godzilla to protect us from the invading aliens, just as she has successfully protected planet Earth from all similar alien invasions in the past," Siegel joked.

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Dr. Steve Desch, an astrophysics professor at Arizona State University, was also skeptical of the prospect that aliens would be hostile to Earth. As he noted, "it's a completely silly premise once you realize the amount of technology and the magnitude of effort it would take to cross light years of space to fight a war like that."

Just as humans need for their investments to be worth the allocated resources, aliens would need it to be worth their while to travel all of this distance just to invade Earth. "Lifting just one of those city-sized destroyer spaceships from a hover position to Earth orbit would require more energy than the entire human civilization produces in a year (roughly 30,000 TWh). The aliens clearly have so much more resources. What do we have to offer?"

Desch added, "Sending in spaceships is so stupidly inefficient, too. Aliens intent on killing us and taking our planet would just crash an asteroid into every major city at once. If they could wait a millennium for the planet to recover, just send in a giant asteroid like the one that killed the dinosaurs. To really do the job right, just blow up the Sun, as in the book 'Dark Forest' by Cixin Liu."

While these possibilities may seem absurd, one must recall the basic premise of the Fermi paradox — if the universe is infinite, and therefore intelligent life is overwhelmingly likely to exist, any civilization capable of reaching Earth would have to be exponentially more advanced than our planet-bound species. 

"The Galaxy is over 12 billion years old," Desch wrote to Salon. "An alien civilization easily could have had a 100,000 year head start. At current rates of economic growth, human civilization could have powers literally 10 million times greater than it does today, in just 1,000 years. We just cannot imagine these discrepancies. The gap in resources and technology between the Spanish and the Aztecs was substantial, but absolutely trivial compared to the gap that would exist between us and an alien civilization."

When asked if any pop culture representations of aliens are accurate, Siegel pointed to movies that show benign representations of alien encounters: Robert Zemeckis' "Contact" (based on a novel by Carl Sagan of the same name), Steven Spielberg's "Close Encounters of the Third Kind" and "E.T." and John Carpenter's "Starman."

"It is more likely to be a case of 'Hey, who are you?' than 'Now that I found you, I'm coming to destroy you," Siegel said. For his part, Desch pointed to the Denis Villeneuve "Arrival" (based on a short story by Ted Chiang) because it succeeded in "depicting how advanced the aliens' technology is, but more so for how it depicted how difficult it would be to communicate with the aliens, understand their thought process and discern their purpose. I also love that the aliens are not here to destroy us, and even need our help." He also praised the Vernor Vinge book "A Deepness in the Sky" for likewise showing "that it's just as rational and likely that aliens would want to symbiotically help us when they arrived."

Marchis theorized that aliens who visited Earth would be closer to those "shown in the movie 'Men in Black' or the Lanthnites in 'Star Trek.'" His premise is that they would be "here, living with us, and learning about us without us even knowing it. If they are belligerent, they may even try to destroy us and our society while pretending to be humans."