The Eerie Silence: Renewing Our Search for Alien Intelligence


Paul Davies




Date Reviewed:

August 10, 2011

his book is more than a review of the SETI (Search for ExtraTerrestrial Intelligence)project. Davies pretty much covers all sorts of issue pretaining to the possibility of life elsewhere in our universe.

There are a lot of interesting points about alien life that Davies makes in the book, so it is hard to summarize what I found interesting (a lot), but I'll highlight some of the best material:

The famous Drake equation tries to predict how many technologically advanced civilizations might be in our galaxy right now, and capable of communicating with us. One of the terms in the equation is Fl - the fraction of planets upon which life does arrive. Right now, we have no idea what percentage to assign to Fl - we only know of life arising once, which obviously is here on Earth. Some scientists like Carl Sagan argued that life was sure to arise quickly - Sagan pointed out that just a few hundred million years after Earth formed, it had bacterial lifeforms, so therefore Fl should be a large number. The opposite camp says life is very unlikely, so Fl should be vanishingly small. Davies points out in his book that if Sagan is right, and new life forms easily, then it ought to start spontaneously multiple times right here on Earth. He proposes that we search here on Earth for a "Shadow Biosphere" - looking in extreme environments where life-as-we-know-it can't survive. Perhaps deep in the ocean, or at the extremes of temperature or surviving as unrecognized microbes that safely consume arsenic or life in high radiation environments, there is indeed alternate lifeforms. Of course, recognizing an alternate lifeform is extremely difficult - you can't just do a DNA sequence on it, because the alternate lifeform won't have a DNA basis, or it might be based upon a different set of amino acids (all DNA here on earth is based upon G, C, A and T) but there are 21 amino acids, so perhaps the alternate lifeform uses four different nucleotides, or maybe it uses 6 or 8 in its DNA.

Or maybe the alternate lifeform are based upon opposite "chirality". The molecules of amino acids have a left-handed and a right-handed orientation - the two molecules that have exactly the same molecular components (same number of carbon atoms, hydrogen atoms, etc), but their structures are mirror images of each other. All of life here on Earth is based upon right handed amino acids, we can not digest "left-handed" food. But there is no apparent reason for Earthlings to use the right instead of the left molecules. Lifeforms that are based upon left-handed amino acides would be opposite-chirality organisms. Indeed, if alternate lifeforms did subsist on left-handed amino acids, they wouldn't have to compete with the other lifeforms in our environment, so that would be a sustainable niche.

Even if we do some day find evidence of life on Mars, Davies points out that is not conclusive proof that life has arisen more than once. Bacteria can survive in rocks and in the harshest environments - it is possible that early in the solar system, life first arose on Mars (which, being smaller than Earth, cooled sooner and had a thick atmosphere and liquid oceans). Asteroids colliding with Mars could have knocked bacteria rich rocks off of the surface of Mars, and some of these rocks could have fallen to earth and seeded the biosphere here (even today, scientists find Mars rock fragments in the Antarctic ice). We might all be Martians.

Davies talks about SETI, which uses radio telescopes to try and detect signals from aliens, but he says we need to widen our search beyond radio waves for signs of intelligence. Might aliens subtly warp a powerful neutron star to send signals? Might aliens build self-replicating von Neumann machines to sweep across the galaxy? Might aliens embedded messages in the "junk" portion of self-replicating/self-repairing DNA? Maybe aliens already have visited Earth in the past and we need to look for signs of their visit - Davies mentions a "natural" reactor at Oklo in Africa. If our telescopes spotted a solar system that was missing it's Oort cloud, then that might be a sign that an alien civilization had found a use for those raw materials. There are a lot of ideas in this book. I like how he mentioned that scientists now suspect that there may be billions of rogue planets roaming through our galaxy - and who knows what might be riding on them. (A rogue planet is one that has been ejected from its orbit around a sun and now roams freely through the galaxy)

There is a really interesting section about "The Great Filter" - about each of the "Hard Steps" that has to occur for an intelligent civilization to arise somewhere in the galaxy. Hard Step One - Life must form (on Earth, this occurred 3.5 billion years ago). Hard Step Two - Eukaryotes (large cells with complex functions such as nuclei and mitochondria) must evolve (on Earth, occurred 2.5 billion years ago). Hard Step Three: sexual reproduction (on Earth, this began 1.2 billions years ago). Hard Step Four: Multi-cellular life most form (600 million years ago). Hard Step Five: Intelligent life must form (a couple hundred thousand years ago). We don't know how likely each of these difficult steps are - here on Earth, it seems to have taken about 800 million years for each step - but maybe Earth was extraordinarily lucky (after all, life seems to have started within just a few hundred million years of the planet forming - but Davies points out that maybe we got a head start by having life form first on Mars and then transferring to earth via meteorites), and on typical planets their sun will burn out before enough time passes for intelligent life to form. Intelligence may be really rare - after all, useful adaptations such as eyes, wings, camouflage have evolve multiple times, but only once has intelligence evolved. On the other hand, Davies points out that perhaps the early Milky Way was troubled with huge gamma ray bursts from exploding suns as the violent galaxy formed - the gamma rays would wipe out any nearby life forms, but now that the galaxy has quieted down, life may spring up all over. To quote the last words of Paul Davies book: "We just don't know".

Davies seems to think that the normal progression of an advanced civilization will be to move to machine based intelligence. He speculates that any developing culture will eventually make machines that are smarter than the alien lifeforms, and from then on the machines will advance themselves. Eventually the machines will be super smart, and nearly immortal - Davies postulates that the machines will sit around solving advanced mathematical theorems for their hobby, which may be why we can't contact them; they have no interest in lowly earthlings. But what happens to the alien lifeforms that built the machines? They would still exist. The super machines would have no reason to exterminate them. Although the aliens may replace some crucial organs with synthetic devices, I doubt any alien would willing upload its consciousness into a machine (even if such a thing were possible) Would any human give up the five senses, the delights and wonders of being alive, to sit as a conscious entity inside a network? I doubt it. So I think these alien civilizations ought to be out there, aided by their super machines, and perhaps curious to contact us.

I thought it Eerie Silence was a good book, I think I'll try to find more books from Davies at the library.