Is Anyone Out There?: The Fermi Paradox, Explained

Jennifer Leman
Photo credit: Space Telescope Science Institute Office of Public Outreach

From Popular Mechanics

For thousands of years, we've cast our gaze toward the stars, opining about what awaits us out there. Our telescopes have scanned the skies in search of life, and, in some instances, we thought we'd discovered it.

In 1877, astronomer Giovanni Schiaparelli discovered a series of deep trenches carved into the Martian surface. He called them "canali." His discovery was mistranslated, leading people to believe these that aliens had constructed a series of canals on the Red Planet.

⚠️Spoiler: there are no canal-carving aliens on Mars.


There are a lot of galaxies out there in the universe. We know life exists in ours. In this sprawling universe the chances that some form of life exists out there on some exoplanet circling a distant star are pretty high. So why haven’t we found them? Or, conversely, why haven’t they found us? Enter the Fermi Paradox.

Child prodidgy-turned-physicist Enrico Fermi invented the atomic reactor, sparked the first controlled nuclear chain reaction, and won the Nobel Prize in Physics in 1938. Just 12 years later, he posed the famous question while lunching with colleagues at the Los Alamos National Laboratory: ”Where is everybody?”

Our galaxy consists of 400,000,000,000 stars. The Fermi paradox works under the assumption that the number of possible locations where extraterrestrial civilizations might exist—a seemingly infinite number of cosmic hotspots—is high enough that we should have detected at least one of them.

Do You Read Me?

Photo credit: Barcroft Media - Getty Images

The SETI Institute in Mountain View, California, for example, has set out to explore the question. The non-profit has probed the universe for the call signs of intelligent life since it was founded in 1984 by Jill Tarter and Thomas Pierson.

Researchers—like those at the SETI Institute—have used radio telescopes like the one at Arecibo Observatory in Puerto Rico or the those at the National Radio Astronomy Observatory in Green Bank, West Virginia to hunt for signals. And the hunt is on.

In September, China's newly built FAST radio telescope will start poking around the cosmos for signs of extraterrestrial life. Just recently, NASA funded research into an especially bold plan to construct a radio telescope dish in a crater on the far side of the moon. This giant ET-hunting soup bowl, proponents say, could probe farther out into the universe than those on Earth.

But it's not just radio astronomy that's doing the heavy lifting. There have also been efforts to physically get the message out there. Both of the Voyager crafts have left the solar system and are carrying a shiny gold record etched with snapshots of humanity. The Breakthrough Initiatives have funded Breakthrough Message, a competition to develop ways to broadcast our existence out into the universe. As we

The Nitty-Gritty on SETI


Photo credit: NASA, ESA, M. Kornmesser

The radio astronomer Frank Drake’s ground-breaking SETI experiment, Project Ozma, ran from April to July in 1960 and marked the very first attempt to detect radio transmissions from extraterrestrial life. In 1961, he developed the the Drake Equation (an alphabet soup of the ages) to explain the probability that life might exist elsewhere in our galaxy.

N = RfpneflfifcL

In this equation, R is the rate of star formation per year, fp is the fraction of stars with planets, ne is the number of habitable planets per planetary system, fl is the fraction of these planets with life, fi is fraction of life that develop intelligence, fc is the fraction of intelligent civilizations that we can see or contact and L is the average longevity of detectable civilizations in years.

It's a lot to digest. We know there are over 400 billion stars in our galaxy alone—20 billion of which are sun-like. A fifth of those sun-like stars, according to recent estimates might have planets lying within the habitable zone, where conditions that enable life exist.

But these variables are constantly shifting. New research published last month in the journal Nature Astronomy found, for example, that certain types of bacteria here on Earth could actually survive on a planet with a hydrogen-dominated atmosphere, thus expanding our definition of "habitable." Still, if just .1 percent of the habitable planets in our galaxy harbored alien life, we'd still have 1 million planets teeming with life.

Now, let's say that life is more than just a couple of microbes swimming around in a toxic soup. What might a complex civilization look like? According to the Kardashev Scale, developed in 1964 by the Soviet astronomer Nikolai Kardashev, there are three different types of potential civilizations we might come into contact with.

Type I civilizations have mastered all of the energy on their planet. Here on Earth, we're pretty close to achieving Type I status. Type II civilizations have harnessed the energy of their home star. (Dyson sphere, anyone?) And Type III civilizations control all of the energy within their galaxy.

Given what we know about the Milky Way so far, there might be anywhere from 1,000 and 100,000,000 civilizations lurking in the distant corners of our galaxy who have the ability to "phone home."

Ok...But Where Are They?

Photo credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA), F. Summers, G. Bacon, Z. Levay, and L. Frattare (Viz 3D Team, STScI)

Since Fermi proposed the idea in 1950, researchers have spent the decades proposing solutions to the Fermi paradox, hoping they might have the best answer as to why aliens haven’t yet reached out.

Scientists have put forth a number of bizarre hypotheses about our status in the universe. Some, like the astronomer Frank Tipler or astrophysicist Michael Hart, have suggested that the solution to the Fermi Paradox might be that complex civilizations elsewhere in the universe simply don’t exist.

Others believe that complex extraterrestrial civilizations exist, but blame logistics for their lack of communication. Maybe they’re just too far away or, like us, don’t have the technology yet to travel or communicate across great distances. The astronomers Carl Sagan and William Newman suggested just this in a 1981 paper. Could it be too costly for other worlds to travel to greet us? Or perhaps their methods of communication are too complex for our puny brains to understand.

One hypothesis, the zoo hypothesis, suggests that our cosmic companions, are observing us from a distance like caged animals. Another hypotheses suggests that maybe we’re trapped in some sort of simulation created by these ultra-powerful beings.

A quirky 2018 hypothesis posited by Alexander Berezin and dubbed the “First In, Last Out” solution suggested that perhaps the “the first life that reaches interstellar travel capability necessarily eradicates all competition to fuel its own expansion.” Berezin argues in his paper, which was posted to the preprint site arXiv.org, that these beings likely wouldn’t notice the consequences of their actions in “the same way a construction crew demolishes an anthill to build real estate because they lack incentive to protect it.”

Others have suggested something even more disconcerting: that maybe they've been here the entire time and we just haven't noticed. Call it the "Men in Black" hypothesis. Perhaps they've mastered a way to tap into our consciousness, as stated by the transcension hypothesis.

And then there's the Great Filter Theory, which suggests that life has had to slip past a series of "filters" in order to evolve. Perhaps we've gotten lucky and surpassed the majority of these great filters while other civilizations have not? Or maybe the final filter is just ahead of us.

How's that for bleak?

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