In 1950, famed astrophysicist Enrico Fermi posed a profound question during a casual lunch with colleagues: Where is everybody? In other words, if there’s an extremely high probability that advanced alien civilizations exist somewhere, why haven’t we found evidence of them?
That’s how the story goes, at least. But regardless of the circumstances surrounding its utterance, that question—known today as the Fermi paradox—has captured the minds of researchers ever since. In a new paper, which has not yet been peer reviewed, astrophysicist Robin Cordet proposes “radical mundanity” as one possible explanation.
Cordet, a senior research scientist at the University of Maryland, Baltimore County, who is based at NASA’s Goddard Space Flight Center, suggests the galaxy is home to a modest number of alien civilizations that aren’t that much more advanced than our own. Because their technology is similarly limited, neither civilization can detect the other.
“The idea is that they’re more advanced, but not much more advanced. It’s like having an iPhone 42 rather than an iPhone 17,” Corbet told The Guardian. “This feels more possible, more natural, because it’s not proposing anything very extreme.”
An alternative explanation for “the great silence”
Calculations using the Drake Equation—a formula that estimates the number of civilizations in the Milky Way that are capable of transmitting radio signals—suggest a fair few should exist. Our civilization has been bleeding radio signals for decades, so we know the answer to the Drake Equation must be at least one. More radically, astrophysicists have proposed that it would take a relatively short amount of time, on astronomical timescales, for advanced civilizations to spread across the entire galaxy.
If aliens accomplished this feat, humanity should be able to detect their presence through a number of different technosignatures. These might include an artificial electromagnetic beacon, signs of astro-engineering such as heat emanating from Dyson spheres (hypothetical energy-harvesting megastructures built around stars), or extraterrestrial artifacts on Earth. So far, however, we haven’t found any of these.
Astrophysicists have come up with many different hypotheses to explain this lack of evidence, also known as “the great silence.” Maybe intelligent extraterrestrials are just too advanced for humanity to detect them, or perhaps they choose to stay away from Earth? Maybe we really are alone in the galaxy after all? Or more pessimistically, maybe all sufficiently advanced civilizations end up destroying themselves.
To Corbet, these possibilities seemed extreme, so he decided to ask a different question: What if civilizations have a natural technological limit that stops them from becoming advanced enough to create detectable technosignatures or to detect us?
The galaxy may be more boring than we think
According to Corbet’s hypothesis, humanity may be near the upper limit of technological progress. Alien civilizations could hit a similar plateau, never advancing far enough to easily detect or contact others.
This idea, known as the radical mundanity principle, suggests that alien societies aren’t building massive space structures or traveling at light speed. Instead, they’re probably a lot like us—and just as limited in their ability to find others in the galaxy. And they stay that way, eventually losing interest in cosmic exploration over time.
Even if this hypothesis is correct, that doesn’t mean we’ll never find evidence of an alien civilization. In his paper, Corbet explains that a technologically mundane world may still be detectable via leakage radiation, and such a discovery “may not be too far off” if radio telescopes continue to advance.
But don’t get too excited. “Although this would have profound implications in many ways, it may not lead to a huge gain in our technology level, and could leave us somewhat disappointed,” Corbet concludes.