The Fermi Paradox and Why It Matters
As a science fiction writer I have what may be called a professional interest in aliens. I read every popular science article or technical paper that comes to my attention about detecting or communicating with extraterrestrial civilizations. But I'm always a little surprised at how many people aren't interested in the subject. To me it seems incomprehensible: how can you not wonder about the possibility of life and intelligence elsewhere in the Universe?
One cannot argue about matters of taste. But one can argue about priorities, because I also happen to believe that studying the topic of extraterrestrial intelligence may be of tremendous importance for the survival of humanity here on Earth.
First, some background: the "Fermi Paradox" is the term we use to describe the puzzling lack of any sign of extraterrestrial intelligence. It's named for the physicist Enrico Fermi, and apparently came from a discussion he was having over lunch with some colleagues at Los Alamos during World War II. They'd been talking about the possibility of life on other worlds, and interstellar travel, and then on the way back to work after eating Fermi burst out with the question "Where are they?"
Of course, in the 1940s, the answer was actually pretty obvious and comforting: they're too far away to visit us. Beings on Mars or other planets of our Solar System might be able to build spaceships to reach Earth, but even then it was pretty obvious that neither planet had much in the way of life, let alone intelligence. As to civilizations on planets circling other stars, the distances were (and are) dauntingly vast. And at the time, the question of whether space travel was even possible still had yet to be answered.
In the decade following the war, radio telescopes began to search the skies, picking up the emissions of distant stars, nebular clouds, active galaxies, and even the echoes of the Big Bang. But one thing they didn't pick up were signals coming from alien civilizations. (At least, nothing that anyone has recognized as a signal in the past half-century.) In 1959 Philip Morrison and Giuseppe Cocconi published a paper discussing the possibility of detecting interstellar radio signals, doing some theoretical work on how it could best be accomplished.
Fermi's Paradox came roaring back. Even if interstellar travel remains forever impossible, it shouldn't be that hard to send messages to other star systems. Why hasn't someone broadcast a big hello to the Galaxy? Where are they?
And that's where the subject has remained for the past half-century. We've got more sensitive detectors, vastly better signal-processing methods, and many more radio telescopes. Private donors and governments have sponsored time on big instruments to listen for alien signals. There's even a dedicated SETI radio observatory, the Allen Telescope Array, searching the sky every day for signs of alien activity. The SETI@home project uses the donated computer time of millions of volunteers to process radiotelescope data in search of patterns which might indicate signals from other worlds. Nothing. Where are they?
There are reasons to be glad rather than disappointed at the lack of any sign of extraterrestrial intelligence. Back in 1998 economist and futurist Robin Hanson wrote an article about what he called "The Great Filter." Hanson's idea was that there must be some "filter" which stops most worlds from developing an advanced civilization capable of building radiotelescopes and broadcasting to the Galaxy. So far, we are the only civilization we know of to make it through the filter.
The big obstacle could be any of the terms in Frank Drake's famous "Drake Equation" to estimate the abundance of extraterrestrial civilizations (and thus calculate how far away they might be). Maybe planets with the right conditions are rare, maybe life doesn't form easily, maybe multicellular life is uncommon, maybe intelligence and tool-using are unlikely. But we made it past all those hurdles, so the Universe is ours! Right?
Maybe. Maybe not. See, for most of those potential filters, we don't really know the answers. Planet-finding telescopes like the Kepler mission have demonstrated that planets are extremely common, so the odds of finding worlds with the right conditions turn out to be pretty high. The history of life on Earth suggests it didn't take that long for life to evolve once the surface of our planet was no longer a sea of molten rock pounded by asteroids. (But, to be fair, we have no evidence that life has evolved elsewhere in the Solar System, so maybe Earth really did get lucky.) We have no way to tell if multicellular life or intelligence were flukes or inevitable.
And . . . there's still the possibility that the Great Filter isn't in our past at all. Maybe life evolves on lots of planets. Maybe complex organisms capable of using tools and communicating and inventing things are common in the Universe. And maybe something very bad tends to happen to them right around the time they become able to build radiotelescopes. That very bad thing must be something which alien minds as good as our own have been unable to foresee or prevent ��� even if they could come up with the idea of the Great Filter themselves. And maybe that very bad thing is about to happen to us! Isn't that a good enough reason to search for extraterrestrial life and civilizations? So we can figure out if something's about to make us extinct?
