Yes, of course
Well I have never seen one, but I am one hundred percent certain they exist. Why? Just do the sums. Planets orbiting distant stars (in the trade extrasolar planets) are two a penny. Current methods of detection are very ingenious but they favour finding the bigger planets and those closer to their suns. Nevertheless, the statistics point in only one direction: Earth-like planets are numbered in their billions. This is not to deny that solar systems come in all sorts of shapes and sizes and where the Jupiter-clones (the giant planets) end up can make a huge difference to everybody else. So too, many planets will fall outside the so-called Habitable Zone (HZ), either searingly hot (no tourists on Venus) or toe-stampingly cold (try Mars for a vacation), but like dear old Earth many, many will be like Goldilocks, just right.
Along with solar HZs, but there is also a Galactic Habitable Zone (GHZ). This is delineated by the ferocious core of the Milky Way, where black holes have stars for breakfast, and the lonely marginal wastes. We are on the outer edges of the GHZ, but despite added dangers the majority of habitable worlds lie much further in. Good arguments also exist for the universal nature of biochemistry with a pre-biotic inventory of organic molecules largely determining the available substrates for life. Some argue that once life is established, the evolutionary trajectory on each planet will be fascinatingly different. Most unlikely. Convergent evolution shows that there will be few surprises. But let’s not be too narrow-minded. Orthodoxy states all life to be carbaquist, employing multipurpose carbon and that very strange liquid, water. Any alternatives? Even on Earth might there be a “shadow biosphere?” And across the Milky Way? What about silicon-based life-forms? Certainly in a terrestrial setting, the silica-analogues of carbaquist compounds have the tiresome habit of exploding, but at the sort of temperatures we might find on Saturn’s moon Titan and in an ocean composed of liquid ethane, then things look more promising. Either way, who cares? Extraterrestrials are three a penny.
No, don’t be ridiculous
It is lunch-time in Los Alamos, summer 1950. At a table, a group of physicists, including Enrico Fermi. The discussion is wide-ranging, including the possibility of ET. Then Fermi asks “So where are they?” A deceptively simple question, aka The Fermi Paradox or if you prefer “The Great Silence”. Not a chirp from our radio-telescopes, no giant-brained visitors turning up at Lords to watch the cricket, not even a set of alien footprints beside the dinosaur trackway, let alone an extraterrestrial goldfish that was illegally released into that Carboniferous lagoon. The Fermi Paradox has moved from awkward to downright embarrassing. The central problem is that innumerable extra-solar systems far, far predate us. Combine this with the inevitability of advanced cognition – after all if it has evolved multiple times on Earth so too it will happen “out there” – and even modest estimates of colonization rates across the galaxy, then either we would be toast or on toast, literally. It is 511,789,855 years ago, October 15th if you want to know. The aliens have arrived on a lovely Cambrian evening. They adore fish and have a special weakness for narthi (what we call whitebait). Up comes the net, full. An hour later a decent Soothma (Meursault to you and me), a quadrant of lemon (by an odd coincidence, lemon), and narthi on toast. Delicious. Only one problem: narthi are our ancestors. Had the aliens not arrived, we would have called them Pikaia.
It all depends on the question
So who’s right? Fermi or the extraterrestrial equivalent of Trip Advisor? If Fermi, then there are plenty of escape clauses. Perhaps the origin of life is not difficult, but practically impossible, occurring once or twice in the visible universe? Even if life is everywhere, may be the Big Evolutionary Jumps (eukaryosis, multicellularity, nervous systems, language) are collectively very, very improbable, with most planets stuck in the zone labelled “pond scum”? Or we can establish the Department of Extraterrestrial Sociology (would anyone notice?) and show that clever civilizations always blow themselves up? All common currency, but maybe we can be more subtle – or mad. The night sky the dinosaurs enjoyed looked almost identical. Sure, different constellations but the same then as today, and tomorrow. But can we be sure the Universe is really at equilibrium? Fortunately, we live in a quiet corner of the Milky Way, pretty safe from dangers such as exploding stars (supernovae). But that is small beer in comparison to so-called gamma-ray bursts (GRB). They may be the result from two neutron stars getting too intimate, but the energy (say 1052 ergs) released in a few seconds is stupendously large. It would spoil not only your holiday, but the entire galaxy’s weekend.
Happily as time goes by GRBs become rather less common. So from a time when emerging intelligences could begin to enjoy the night sky, only to be promptly knocked for six, the intervals of relative safety became long enough to guarantee that we can do more than gaze at the stars. And when does this happen? Funnily enough, just about now. So it is a phase tran n: across the Milky Way sentient individuals with names like Fermi are popping up and saying “That’s very odd, where is everybody?” Soon our galaxy will be awash with people, all asking “Another drop of Soothma?” A neat solution, but not the correct one. The real answer to the Fermi paradox hardly bears contemplation. We are not alone because we do not exist: we live in a virtual universe. Sure it takes a lot of computing power by whoever “they” are, but there are limits, roughly equivalent to a diameter of 100 light years. Up until now that hardly mattered. For Galileo the Moon and Jupiter were virtual; now we have visited them they have to become “real”. As we approach the limits of our “Universe” the system will begin to creak. Read Stephen Baxter’s Touching Centauri; it has a horrible ring of truth.
Text copyright © 2015 Simon Conway Morris. All rights reserved.
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