Astronomers call this the “synchronicity” or “life islands” problem, and it seems defeating except for one loophole: Say that long ago, this neighboring civilization, realizing it was cooked—imminent nuclear war, a dying planet, a robot rebellion, whatever—constructed a permanent radio beacon to outlast it, one that would seed the cosmos with detectable signals long after the species that made it was gone. It could still be there now, just waiting for someone to tune in. Nothing about this is science fiction; in fact, locating an interstellar beacon is the best chance Earth has of finding a neighbor. We just have to know where to look.
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The physicist Michio Kaku seems to believe that anything is eventually possible, which is why I called him to talk about intergalactic lighthouses. Kaku is a respected theoretical physicist and strong proponent of string theory, but he’s also a worthy heir to Carl Sagan for his ability to popularize physics and astronomy. His book Hyperspace: A Scientific Odyssey Through Parallel Universes, Time Warps, and the 10th Dimension first tuned me in, during the 10th grade, to the very real weirdness of how the universe works, and a more recent book of his makes the scientific case for force fields and teleportation, among other things. Naturally, he is a big Star Trek fan.
In fact, Star Trek came up right away when we got on the subject of whether there is any reason to think an advanced civilization would ever build some form of beacon to preserve its memory after all other traces of its splendor are gone. Kaku recalled a The Next Generation episode called “The Inner Light,” in which a strange probe zaps Captain Picard with a beam that knocks him out and sends him into a dream existence as a weaver on a distant, unknown planet, unaware of his real identity. He lives out his simple life on that planet, which is rapidly heating and becoming inhospitable to life. His last memory, as an old man, is that of a probe being launched that contains the history of the dying civilization, which will replay its final years in the mind of whomever it encounters. (Picard, meanwhile, awakes to discover that only 25 minutes have passed.)
“That was its way of preserving its collective memory,” Kaku said. “That meant he had a tremendously intimate understanding of this civilization.”
For us humans, there’s something attractive about the idea of leaving some trace of ourselves for posterity, in the same way that we're programmed to propagate our genes down the generations. Might some long-dead society of extraterrestrials have had the same impulse? One widely-cited “working definition” of life calls it “a self-sustaining chemical system capable of Darwinian evolution,” which would arguably produce the same instincts. Of course, many in the astrobiology community find this definition woefully inadequate and see no reason to believe aliens would have the same desire to leave something behind. When I ran the idea by Paul Davies, an Arizona State University professor who once chaired the committee on how to break the news when aliens are first detected, he was doubtful that the self-propagating instinct would persist as a species became more and more technologically advanced.
“This need to preserve something for posterity—that’s something we’ve inherited from evolution,” he said. “If we’re dealing with intelligence elsewhere in the universe, it may long since have abandoned its organic roots.”
It is a maddening idea: To think that all these years we could have been pointing our radio telescopes in the exact right direction, only to be listening in on a long-dead race of aliens that never bothered to erect a grand memorial to itself, or even to scribble out some galactic graffiti for our benefit. Who knows if it’s even possible for a civilization to construct the kind of beacon that would beam out its epitaph for millions or billions of years? If our aliens had possessed the will to create such a thing, would they even have had the skill?
Whether or not your evolutionary impulses are tweaked by thoughts of leaving behind a gravestone, we ought to hope that other civilizations were so moved. It's the best chance we have with present technology of discovering anyone else in the universe. But that line of thinking has a way of turning back on itself: If another civilization was so kind as to send a few signals our way, we ought to return the favor. We ought to build our own beacon. It’s a simple matter of interstellar courtesy.
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At press time, the planet Earth has about 5 billion years left before our sun becomes a red giant, probably swallowing us up in the process. There are any number of ways that our fate could be hastened. The moon could take a hit, throwing us off tilt; we could succumb to a super virus; global warming could bake our planet to a crisp; or we could nuke one another into oblivion. There is a distinct possibility that we are living out the final act of the human race. This is not some gloomy assessment of humanity. It is a basic fact of the uncaring randomness of the universe, not to mention our stunning incompetence at preserving our finely-tuned habitat. As those investment commercials say, it’s not too early to start thinking about our retirement.
This is the first half of a two-part article on Earth's legacy and the search for extraterrestrial life. Read Part 2 on how to help the aliens find us.