“He’s dead, Jim.”
So sayeth Leonard “Bones” McCoy, the plainspoken doctor in the original “Star Trek” television series, to Captain James Kirk whenever an alien croaks in their high-tech sickbay. Expired extraterrestrials have been frequent players in many sci-fi potboilers, and for obvious dramatic reasons.
But how about entire alien societies? A research team under the leadership of French astronomer Claudio Grimaldi recently published a paper suggesting that any extraterrestrial civilization we discover is likely to be long dead.
This possibility may sound bizarre. After all, how could we possibly tell whether a culture is still around when it’s hundreds or thousands of light-years away? In general we can’t. And yet there are reasons why Grimaldi and his team may be right. In fact, their argument is reminiscent of one I often hear in connection with the search for extraterrestrial intelligence (SETI).
Since any alien radio message we might receive would have been lumbering through space at the finite speed of light — and since space is big — many folks assume that the signal must have been sent “millions of years ago.” The obvious corollary is that the alien broadcasters may have long since cashed in their chips.
My response to this melancholy logic is to note that most of the star systems examined by SETI scientists are less than a few hundred light-years away. So a signal from one of these wouldn’t be a million years old. And since a few centuries isn’t really much time, I usually offer an analogy: It takes the postal service three days to deliver a letter from my aunt. But it’s unlikely that she died in the interim because three days is brief in comparison to the average lifetime of aunts.
The new paper offers a similar argument, mathematically elaborated. The authors assume a simple scenario in which extraterrestrial societies spring up at random places in the galaxy at random times, and that they broadcast their talk shows (or whatever) into space. You can imagine these transmissions spreading like ripples across the plane of the Milky Way, reaching more and more star systems as time goes on.
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SOURCE: NBC News, Seth Shostak