The Arxiv blog highlights a post on John Scalzi’s favorite science question: the Fermi Paradox:
We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?
The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.
That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.
I’m a little surprised that nobody has tried to account for this before, but maybe I shouldn’t be. It seems like a fairly obvious effect– the intensity of a signal drops off as the distance squared– but it’s not nearly as much fun to talk about as the other terms in the “Drake Equation.” If you use the lack of detectable alien civilizations to talk about the probability of life evolving or the probability of technological civilization surviving, you’re a Deep Thinker; if you start talking about detectable signal strengths and propagation delays, you’re a great big nerd.
The cited paper is freely available on the arxiv, if you’d like to read more..