As we discover more and more planets around other stars, the Fermi Paradox is becoming, well, more paradoxical.
The Fermi Paradox simply asks the question "where are they?" Our Milky Way galaxy is so big and so old - and we are estimated to be accompanied by at least 100 billion planets - that aliens should have visited us by now.
Instead, when we peruse the heavens, we are faced with the Great Silence, which is one of the biggest challenges to modern astronomy.
There have been numerous solutions to the Fermi paradox, but none of them are satisfactory.
A few diehards like Harvard astronomer Howard Smith are emphatic that we are completely alone in the universe. As much as I disagree, there isn't a shred of evidence to the contrary. Nevertheless, I do wholeheartedly agree with my colleague Seth Shostack of the SETI Institute who says that it would be a miracle if we didn't find advanced life out there.
Picking up on this idea, Canadian science fiction writer Karl Schroeder has come upon a novel solution to the failure of astronomical observations to solve the Fermi Paradox. He proposes: "any sufficiently advanced technology is indistinguishable from nature." (This is a takeoff on Arthur C. Clarke's posit: "any sufficiently advanced technology is indistinguishable from magic.")
In other words, smart aliens have "gone green" and generate no waste products that we could detect. They therefore blend into the galaxy. Therefore, "artificial and natural systems are indistinguishable," writes Schroeder.
This implies that no astronomical observations could offer convincing evidence for the handiwork of E.T. The principle of Occam's Razor will insist that we stick with a natural explanation for space phenomena.
This undermines an extraterrestrial search strategy called SETT (Search for Extraterrestrial Technology). The idea is that we might pick up the spectral signature of nuclear fission waste that extraterrestrials dump into their star, or the leakage of tritium from alien fusion powerplants.
However, "green aliens" have reached a Utopian state of being in balance with nature. Short of finding a directed message, or a leaked radio signal, we could be surrounded by advanced societies that are camouflaged within our galaxy. Maybe only ecologically-balanced civilizations survive in the long run.
Another Fermi Paradox solution is that intelligent life might be inherently unstable and destroys itself in any number of doomsday scenarios: nuclear war, bioterrorism, or nanotechnology run amok. But even if that is the case, their technological progenies should survive forever.