Planets, Life, and the Fermi Paradox
By Bryan Caplan
Since junior high, I’ve believed that the galaxy is full of planets and intelligent life. But it wasn’t until I was in my thirties that I heard of the Fermi Paradox. You can boil the paradox down to a sentence: “Where is everybody?” In other words, “If there’s intelligent life anywhere else in the galaxy, why don’t we see any sign of it?”
It turns out that at least the first of my junior high guesses was right on target. The galaxy is indeed full of planets. The New York Times:
Three studies released Wednesday, in the journal Nature and at the
American Astronomical Society’s conference in Austin, Texas,
demonstrate an extrasolar real estate boom. One study shows that in our
Milky Way, most stars have planets. And since there are a lot of stars
in our galaxy — about 100 billion — that means a lot of planets.
“We’re finding an exciting potpourri of things we didn’t even think
could exist,” said Harvard University astronomer Lisa Kaltenegger,
including planets that mirror “Star Wars” Luke Skywalker’s home planet
with twin suns and a mini-star system with a dwarf sun and shrunken
“We’re awash in planets where 17 years ago we weren’t even sure there
were planets” outside our solar system, said Kaltenegger, who wasn’t
involved in the new research.
Astronomers are finding other worlds using three different techniques
and peering through telescopes in space and on the ground.
Confirmed planets outside our solar system — called exoplanets — now
number well over 700, still-to-be-confirmed ones are in the thousands.
These discoveries seriously undermine the Fermi Paradox. If we’ve only recently confirmed the existence of extrasolar planets, why on earth should we be surprised by the fact that we’ve failed to confirm the existence of extrasolar intelligent life? Clearly our powers of detection remain extremely limited if we could overlook the existence of hundreds of billions of entire planets. To refuse to believe that any of these planets sustain intelligent life dumbfounds me.
Several people have objected, “The Fermi Paradox doesn’t ask why we haven’t found extraterrestrial life. It asks why they haven’t found us.” Maybe because they face the same problem we do: Detecting intelligent life is extremely difficult. But shouldn’t they already be here? Not if space travel (including the value of time) permanently remains extremely costly relative to the value of raw materials. It’s a lot easier to believe that space travel will forever remain a rare luxury for intelligent life than that intelligent life exists on Earth alone.
When people discuss the Fermi Paradox, a common rhetorical tactic is to say, “Whatever intelligent life usually does, surely one species of intelligent life would be the exception that proves the rule.” Facile. When you multiply independent, rare events together, you quickly reach situations with zero examples. There are seven billion people on earth. But how many people named Bryan Douglas Caplan are watching Citizen Kane and eating butterfingers right now? Almost certainly zero. As Google often tells me, “Your search did not match any documents.”
Similarly, even if there are seven billion species of intelligent life in the galaxy, there could easily be zero species that entered our solar system during the last century, approached the earth, and stayed long enough for the scientific community to detect and confirm. Your search did not match any documents.
I don’t expect science to vindicate my other junior high guess in my lifetime. Our powers of detection are bad enough to overlook hundreds of billions of planets. Detecting intelligent life will be vastly harder than detecting planets – maybe prohibitively harder. But until we actually do the leg-work of examining a thousand random Earth-like planets, concluding that we’re the only intelligent life in the galaxy is an astronomically implausible leap of logic.