The famous Fermi Paradox is one of the central concerns of research on the Search for Extra-Terrestrial Intelligence (SETI). Just to summarize quickly: we know of no good reason why technological civilizations can't emerge on other worlds in our Galaxy, but we see no signs of any. Paradox!
"Where is everybody?" Enrico Fermi asked plaintively.
But it's not a paradox. We see no signs of extraterrestrial civilizations because we've barely looked.
The Milky Way contains 100 to 400 billion stars (and the fact that the possible range is that large should be suggestive — there's a lot of things we don't know). How many of those stars have we searched for signs of advanced civilizations?
Not many. To spot a civilization like our own, you couldn't just glance at the Solar System with a radio telescope and instantly detect some old sitcom broadcast. That's not how it works. You'd have to watch over a long period — months or years. You'd have to detect the faint radio emissions and link them to the orbit of Earth around the Sun and Earth's own rotation.
According to Jill Tarter's index at technosearch.seti.org, the biggest search so far covered 290,000 targets. The SERENDIP survey looked at 30 percent of the sky, but that was all piggybacked observations on other astronomers' observing sessions, so very few of those examined the same target repeatedly or over a long period. The Breakthrough Listen project aims to study 1 million objects over the next decade.
That would be . . . one percent of the Galaxy. Maybe less. At this rate it'll take millennia to finish the job.
These are all good and valuable projects, but they're woefully limited. The real solution to the Fermi Paradox is a very simple one: we don't know enough. We don't know if there are stars wrapped in alien Dyson Sphere megastructures. We don't know if there are tiny, heavily Doppler-shifted point sources in interstellar space burning the exact color of deuterium fusion rocket exhaust. We don't know if there are stars with rosettes of co-orbital worlds in their habitable zones, all with identical atmospheres and surface temperatures. We don't know!
I do expect the pace of SETI to pick up as techniques are refined and infrastructure expands. There's also the heartening fact that the "giggle factor" of searching for "little green men" among the stars seems to be waning. After decades of after-hours bootleg research, SETI is finally getting serious support. All this means that it probably won't take a thousand years to search the other 99 percent of stars in our Galaxy. Maybe not even a hundred years.
What then? What happens when we have made a serious effort to search the sky?
Well, the results can be generalized into four cases.
Case 1: Nothing! It's 2124 and we've given the Galaxy a thorough going over and found no sign of intelligence other than our own. Maybe signs of life here and there, but no radio signals, no energy emissions, no artificial structures. Apparently we really are the only minds in the Galaxy.
This could go either way. It might cause a turning away from space exploration because nobody really likes to consider awful, infinite emptiness. Maybe over time some eccentric tycoons will fund colony projects on the Moon or Mars, and maybe the resources of near-Earth space will attract robot miners, but the bulk of humanity will stay on one planet for the foreseeable future. Some people may find this idea appealing, but I don't. To my mind, it's one small step from that to suicide.
Or perhaps the certainty that there's nobody out there would stimulate expansionist ideals among humanity. Unlike exploration and colonization projects on Earth, this time there's nobody to get hurt or displaced. Manifest Destiny on a cosmic scale! The Universe is our sandbox and we can play with it as much as we like! It's something to hope for, I suppose.
And either way I expect a hard core of diehards will insist that we just haven't searched enough. This will become an increasingly hard line to sell, but people are persistent, and those lonely SETI researchers will keep listening . . . to silence.
Case 2: We Are Not Alone, Barely. Our searches turn up one or two civilizations. They're thousands of light-years away and are modest in scale. This would naturally spur interest in the idea of communicating with them, even though it may take centuries to even get a reply. In effect, alien intelligence would be a cool science fact but little more than that. Space exploration and astronomy will still be driven by commercial concerns, national pride, and scientific curiosity, probably at about the same levels of funding as today. Crackpots will finally have a name to put on their imaginary alien friends, but otherwise life goes on as before.
The biggest winners in this case will be SETI and astrobiology researchers, because finally they'll have some data to work with! Humans can learn about alien life and intelligence in relative safety.
Case 3: They're Everywhere! Turns out we picked the wrong 1 percent to search at first. Once you learn the trick, finding alien civilizations is easy. Disturbingly easy. There's scores of them in the Milky Way, and some of those civilizations are big.
As with Case 1, the response could go in one of two ways. Either humanity will try to hide, masking and muting our emissions, putting strict (and probably un-enforceable) restrictions on transmissions to the stars, and generally doing our best to avoid attracting the attention of beings who can move stars around.
Or our insatiable curiosity will prevail, and we'll listen and learn and eventually try to make contact. Whatever happens, this is a turning point in human civilization. It's going to affect government policy, education, everything. The night sky will never look the same again.
SETI — and planetary protection — will become national security priorities. Radiotelescopes will sprout like mushrooms, both on Earth and the far side of the Moon. Whether we're hiding or trying to join the interstellar club, learning about alien civilizations, figuring out their goals and especially how close they are will be of capital importance.
Case 4: They're Here! The crackpots were right. They were here all along. Somebody finds a probe on the Moon, or the seabottom, or on a near-Earth asteroid. They've been watching us, maybe for decades or maybe for millennia.
The take-away is simple: they're real, they know we're here, and they can reach us. As with the above scenario, expect a massive push to discover as much as possible, this time without the option of trying to stay hidden.
Ironically, the big losers in this latter case would be the UFO crackpots. Because now defense agencies, universities, governments, and international organizations will be taking the concept of life beyond Earth very seriously. There will be a lot of research, done rigorously and systematically. No more blurry photos, no more woo. Astrobiology and SETI will become as serious, well-funded, and no-nonsense as nuclear power or genetics research.
Which will it be? My money's on Case 2. I don't think we're alone, but I think it's a lot harder to create and maintain a technological civilization than astronomers think it is. Our views are biased, because we live on a world where it did happen, so of course it looks practically inevitable. Whichever proves to be the truth . . . we'll see! And I hope it's sooner rather than later.
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