142
Scientists have been searching for evidence of extraterrestrial life for decades. So where are all the aliens? Here are 12 intriguing theories. One night about 60 years ago, physicist Enrico Fermi looked up at the sky and asked, "Where is everyone?"
He was talking about aliens.
Scientists today know that there are millions, possibly billions, of planets in the universe that could support life. So, in the long history of everything, why has none of this life made it far enough in space to shake hands (or claws… or tentacles) with humans? Maybe the universe is just too big to walk through.
Maybe the aliens are deliberately ignoring us. It's even possible that every growing civilization is irrevocably doomed to self-destruction (something to look forward to, earthlings). Or it could be something much, much weirder. How what, you ask? Here are 12 unusual answers scientists have come up with for the Fermi paradox.
We're looking in the wrong universe
Maybe we haven't found aliens because our universe isn't very conducive to life. Perhaps Earth is an anomaly—a happy blue speck adrift in a vast ocean of darkness and dead worlds. Perhaps we would be lucky enough to look for life in the next universe.
This last idea is the premise of the 2024 study, which suggests that our cosmos is just one possible universe in an infinite "multiverse" of realities, each slightly different from the rest. To test whether our universe has the optimal conditions for the emergence of life, the researchers compared the rate of star formation with the rate of star formation in many hypothetical parallel universes with different concentrations of matter and energy.
The main factor the team looked at was the density of dark energy in the universe, a mysterious force that drives the constant, accelerated expansion of space. A universe with too much dark energy would expand too quickly, scattering star-forming material and stunting the growth of large-scale structures such as galaxy clusters. But in a universe with too little dark energy, gravity can become overwhelming, causing large structures to collapse before habitable planets form.
The team's models showed that the optimal density of dark energy in the universe would allow up to 27% of ordinary matter to turn into stars. But in our universe, only about 23% of the matter turns into stars—meaning there are fewer stars than there could be, and as a result, fewer places for extraterrestrial life to appear. Good luck in the next universe!
Aliens do not live on planets
Every alien species needs a habitable planet, right? Surprisingly, a 2024 study says this isn't always the case.
In a paper accepted for publication in the journal Astrobiology, the researchers proposed a scenario in which an alien colony could survive by floating freely in space, without the need for a planet. This may sound strange, but it is not without precedent in the real world; humans, for example, can live for hundreds of days without a planet while on the International Space Station (albeit with constant supplies of critical resources from their planet), and hardy slow-walkers can survive in the vacuum of space.
A theoretically planet-free alien colony would have to overcome many challenges, including a lack of resources, exposure to cosmic radiation and the vacuum of space, and access to sufficient sunlight. With that in mind, the researchers paint a picture of a species that could withstand these tests: a free-floating colony of organisms up to 330 feet (100 meters) across, encased in a thin, hard, transparent shell that could maintain acceptable temperatures and pressures through a greenhouse. effect.
It takes a long time to find such a species, but it is not impossible. A free-floating alien colony may also explain why no intelligent aliens return our calls: they don't have a landline.
Aliens are hiding in the underground oceans
If humans hope to communicate with aliens, we need to have some icebreakers on hand. No, seriously—alien life is probably trapped in secret oceans buried deep inside frozen planets.
Subsurface oceans of liquid water splash beneath several moons in our solar system and may be common throughout the Milky Way, astronomers say. NASA physicist Alan Stern believes that subterranean water worlds like these could provide an ideal platform for life to develop, even if the inhospitable conditions on the surface take a toll on these plants. "Shocks and solar flares, nearby supernovae, what orbit you're in, and whether you have a magnetosphere, and whether you have a poisonous atmosphere — all of that doesn't matter" to life underground, Stern said.
That's great for aliens, but it also means we'll never be able to detect them just by looking at their planets through a telescope. Can we expect them to contact us? Hell, said Stern, these animals live so deep that we can't even expect them to know there's a sky above their heads. Fortunately, NASA's Europa Clipper spacecraft is headed to one of these moons to find evidence of life up close. Clipper will arrive at Jupiter's frozen moon Europa in 2030.
Aliens are imprisoned on "super-earths"
No, "super-Earth" is not Captain Planet's dumb cousin. In astronomy, this term refers to a type of planet whose mass is 10 times the mass of Earth. Studies of the stars have revealed a bunch of these worlds that could have the right conditions for liquid water. This means that extraterrestrial life could develop on super-Earths throughout the universe.
Unfortunately, we will probably never meet these aliens. According to a study published in 2018, a planet with a mass 10 times the mass of Earth would also have an escape velocity 2,4 times that of Earth, and overcoming this drag could make rocket launches and space travel nearly impossible.
"For more massive planets, spaceflight would be exponentially more expensive," study author Michael Hippke, a researcher at the Sonneberg Observatory in Germany, previously told Live Science. "Instead, [these aliens] will be somewhat arrested on their home planet."
We're looking in the wrong places (because all aliens are robots)
Humans invented the radio around 1900, built the first computer in 1945, and are now mass-producing handheld devices capable of billions of calculations per second. Full-fledged artificial intelligence could be just around the corner, and futurist Seth Shostak said that's reason enough to rethink our search for intelligent aliens. Simply put, we should be looking for machines, not little green men.
"Any [alien] society that invents radio so that we can hear them has been inventing successors for several centuries," Shostak told the Dent:Space conference in San Francisco in 2016. "And I think that's important, because heirs are machines."
A truly advanced alien society could be populated entirely by superintelligent robots, Shostak said, and that should inform our search for aliens. Instead of focusing all our resources on finding other habitable planets, perhaps we should also look for places that would be more attractive to machines—say, places with lots of energy, like the centers of galaxies. "We're looking for counterparts," Shostak said, "but I don't know if that's the majority of intelligence in the universe."
We already found aliens (but we were too distracted to realize it)
Thanks to pop culture, the word "alien" probably makes you think of a creepy humanoid with a big bald head. That's good for Hollywood, but these preconceived images of aliens may be sabotaging our search for extraterrestrial life, a team of psychologists from Spain wrote earlier this year.
In a small study, researchers asked 137 people to look at pictures of other planets and scan the images for signs of extraterrestrial structures. Hidden among several of these images was a tiny man in a gorilla suit. When participants were asked what they imagined alien life to be like, only about 30% spotted a human-gorilla.
In fact, the aliens probably won't be ape-like at all; they cannot even be detected by light and sound waves, the researchers write. So what does this research tell us? Essentially, our own imaginations and attention spans limit our search for extraterrestrials. If we don't learn to expand our frames of reference, we may miss the gorilla staring us in the face.
Humans will kill all aliens (or have already killed)
The closer we get to finding the aliens, the closer we get to destroying them. In any case, this is one likely possibility, said theoretical physicist Oleksandr Berezin.
Here's his take: Any civilization capable of exploring the limits of its own solar system must be on a path of unlimited growth and expansion. And as we know on Earth, such expansion is often at the expense of smaller organisms that get in the way. Berezin said this "me first" mentality probably won't stop when alien life is finally encountered — if we even notice it.
"What if the first life to achieve the ability to travel interstellar necessarily destroys all competitors to fuel its own expansion?" Berezin wrote in an article published in 2018 in the preprint journal arXiv.org. "I do not claim that a highly developed civilization will deliberately destroy other forms of life. Chances are, they just won't notice, the same way a construction crew demolishes an anthill to build real estate, because they have no incentive to protect it. (Whether humans are the ants or the bulldozers in this scenario remains to be seen.)
Aliens caused climate change (and died)
When the population burns resources faster than the planet can provide them, disaster looms. We know this quite well from the current climate change crisis here on Earth. So, isn't it possible that an advanced energy-absorbing alien society could face the same problems?
According to astrophysicist Adam Frank, this is not only possible, but extremely likely. Earlier this year, Frank ran a series of mathematical models to simulate how a hypothetical alien civilization might rise and fall as it increasingly converts its planet's resources into energy. The bad news is that in three of the four scenarios, the society collapsed and most of the population died. Civilization was able to survive only when society noticed the problem early and immediately switched to sustainable energy. This means that if aliens do exist, there is a pretty good chance that they will destroy themselves before we meet them.
“In space and time, you're going to have winners—who managed to see what was going on and find a way through it—and losers who just couldn't get their act together and their civilization collapsed. curb, said Frank. "The question is, what category do we want to be in?"
Aliens used clean energy, but still caused climate change (and died)
A sufficiently advanced alien species will inevitably heat up its planet as its society and energy needs grow. This could trigger rapid climate change, as humans do on Earth, and could doom these aliens to early extinction. But what if a fast-growing alien society switched to clean, renewable energy early? Can it save them, allowing the aliens to grow, prosper and expand throughout space without consequence?
Sorry, but no, according to a grim theoretical study published in the arXiv database in September 2024. The study found that an exponentially growing alien species using 100% renewable energy would still heat its planet with the waste heat that is inevitably produced from any energy expenditure according to the second law of thermodynamics. This waste heat will continue to accumulate as long as society's energy needs increase, eventually leading to catastrophic climate change within 1000 years of that society's industrial revolution.
If true, it means that an alien energy-absorbing race will likely never survive long enough to venture into space and set up shop on nearby planets. This is not only a sad prospect for aliens, but an urgent wake-up call for Earth.
Aliens couldn't evolve fast enough (and died)
File another excuse in the "aliens are already dead" category. The universe may be teeming with hospitable planets, but there is no guarantee that they will remain so long enough for life to develop. According to a 2016 study by the Australian National University, wet, rocky planets like Earth are very unstable early in their careers; if any alien life hopes to develop and thrive on such a world, it has a very limited window (a few hundred million years) to budge.
"Between early heat pulses, freezing, fluctuations in volatiles, and [greenhouse gas] emissions, sustaining life on an initially wet, rocky planet in the habitable zone could be like trying to saddle a wild bull—most life disappears," the study said. the authors wrote. “Life may be rare in the universe not because it is hard to get started, but because a habitable environment is hard to sustain for the first billion years.
Dark energy divides us
As we have already established, the universe is expanding. Slowly but surely, galaxies are moving away from each other, and distant stars appear dimmer to us, all thanks to the action of a mysterious invisible substance that scientists call dark energy. Scientists predict that within a few trillion years, dark energy will stretch the universe so much that Earthlings will no longer be able to see the light of any galaxy except our closest cosmic neighbors. It's a scary thought: if we don't explore as much of the universe as possible by now, such explorations may be lost to us forever.
"Stars are becoming not only unobservable, but completely unobservable," Dan Hooper, an astrophysicist at the Fermi National Accelerator Laboratory in Illinois, wrote in a study earlier this year. That means we have a serious deadline to find and meet any aliens—and to stay one step ahead of dark energy, we'll have to expand our civilization to as many galaxies as possible before they all fly away.
Of course, fostering that kind of growth won't be easy, Hooper said. This may involve rearranging the stars.
Ending: We are aliens
If you left your house today, you saw a stranger. Does the woman deliver the mail? Alien Your nearest neighbor? Nose alien. Your parents, siblings? Aliens, aliens, aliens .
At least that's one implication of a fringe astrobiology theory called the "panspermia hypothesis." In a nutshell, the hypothesis says that most of the life we see on Earth today did not originate here, but was "seeded" here millions of years ago by meteors carrying bacteria from other worlds.
Proponents of this theory have variously suggested that octopi, slow-walkers, and humans were settled here from other parts of the galaxy, but unfortunately, there is no real evidence to support this. One big counterargument: If the bacteria carrying human DNA evolved on another nearby planet, why haven't we found traces of humanity anywhere but Earth? Even if this hypothesis turns out to be plausible, it still won't help us answer Fermi's nagging question… where is everyone
