Where is everyone?
That simple question is the essence of the
Fermi Paradox, posed (if only, perhaps, apocryphally) by nuclear physicist Enrico Fermi. More expansively: if life arises naturally on suitable planets, then why -- with so MANY stars around us -- hasn't intelligent life contacted or visited Earth? If aliens haven't, maybe the premise about life arising naturally and then intelligent life following naturally is suspect.
(Regular readers of this blog know that as an SF author I'm interested in the search for extraterrestrial intelligence (SETI) and in First Contact scenarios. This post is about one small aspect of the science of SETI. If you're curious about my fictional uses of SETI, check out my
InterstellarNet series and
Moonstruck posts.)
Traditional SETI, based on listening for radio signals, has been noticeable for its lack of success. It turns out listening isn't the only SETI option. There's a SETI offshoot called search for extraterrestrial artifacts (SETA). A subset of SETA is search for extraterrestrial vehicles (SETV). The dressed-up term for it is
xenoarcheology. Like astrobiology, xenoarcheology is a science for which, to date, there is no proof of the existence of its subject matter.
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Finding (or thinking one has found) physical evidence of aliens is an SF staple. Consider, for example, the black monoliths in the acclaimed
2001: A Space Odyssey. And I've always been partial to the cover at left, from James P. Hogan's
Inherit the Stars.
The SETV argument goes like this. Signaling across interstellar distances takes a
lot of energy. Sending that (expensive) signal yields a benefit only if someone hears it. Sending a space probe is much more energy efficient -- albeit slower -- than beaming across the light-years. The visiting probe can gather data independent of the tech level of any creatures in the visited solar system. The probe can also choose to announce itself with a locally transmitted signal. Proponents of SETV advise us to look around our solar system for alien spacecraft.