The Eerie Silence

In 2010, the SETI - Search for Extra-Terrestrial Intelligence - initiative celebrated its 50th anniversary. And so physicist/cosmologist/astrobiologist Paul Davies was asked to write something. Rather than just write a simple back-patting congratulation, he decided to try and write about the whole concept: Why are we looking for signs of alien intelligence, how are we looking for it, how likely is it to exist, how likely are we to find it (or they to find us), what would we be likely to find, how would we react...? Is it possible that the big fat Zero that's been the result of our search so far means that we really are all alone in the universe, or are we just looking for a very tiny needle in a very large haystack? To do this, obviously, he can't just write about radio telescopes, he needs to go back and revisit the fundamentals: how does life arise and evolve, how would you travel or communicate across large distances, how would we even recognise technology that's thousands or millions of years beyond our own?

The Eerie Silence is a great little primer on most of these subjects, though at 210 pages you'll probably find yourself wanting to dig deeper in some areas. Some of the stuff that fascinated me:

Our telescopes keep finding more and more planets outside the solar system - 846 identified ones as of today - and with all the stars out there, it stands to reason that there could be millions of habitable planets in our galaxy alone; ie planets made of rock, in the "goldilocks zone" (not too hot, not too cold), with liquid water and an atmosphere. Theoretically, there could be a lot of aliens out there. But habitable doesn't mean inhabited; the problem when trying to figure out how likely that is, is that we simply don't have any indication of how easy the step is from "theoretically habitable" to "practical rocket scientists". As far as we know for sure (though Davies presents some interesting speculations), life has arisen in the universe exactly once (around 3.5 billion years ago on Earth) and evolved intelligence exactly once (Homo, about 2 million years ago), and one single data point doesn't give us any indication of how likely the same thing is to happen on other planets; it could happen every time, or never. For all we know, the universe could be empty, or it could be teeming with life that never evolved "past" bacteria or dinosaurs (going with the common fallacy that some animals are "more evolved" than others), or the 6-7 billion years that the average planet has before its sun supernovas simply isn't enough time to perfect interstellar travel. If there are aliens out there to communicate with, why wouldn't they have already done so? It's a bit like Stephen Hawking's question: if time travel is possible, why have we never seen any tourists from the future?

What would we be looking for, and how would we recognise it when we see it? We take for granted that communication from other civilisations would come as, say, a radio signal carrying prime numbers, because that's what we can hope to read. If there are others out there, they may well be trying to communicate in ways we haven't even conceived of yet.

For that matter, what would other, more advanced civilisations even want with us? Science fiction is full of aliens looking to humans as cheap sources of food, labour or concubines, which is just silly - if you're able to communicate across light years, you can't have much need for manual labour. How do we know they haven't noticed us and decided not to bother with us until we show some sign of intelligence? After all, we've only been broadcasting weak radio signals for about 100 years (and have pretty much stopped by now, since we're mostly using fiberoptics and satellites these days), and anyone looking at us from more than 110 lightyears away wouldn't even know that we've mastered flight.

What would members of an ancient civilisation even be? Even assuming they started out roughly like us, we're already edging into cyborg territory ourselves; would a species that's had another 40,000 years of "civilisation" even be biological anymore? (Yes, Davies is an Olaf Stapledon fan.) Would we even recognise them as life? Would we recognise their technology as artifice?

For all the high-flying speculations, The Eerie Silence is a sober and realitic look at the possibility of finding and communicating with hypothetical extraterrestrial civilisations. In the end, Davies is very sceptical that they even exist, but that's not his worst nightmare, nor a reason to stop looking. The worst-case scenario, he claims, is this: we keep looking, and we discover that there's plenty of life in the universe, and that it's occasionally evolved into intelligent beings... and that none of them have survived long enough to communicate with others before they wiped themselves out. If that's the case, then that's definitely something we need to know.

Or, as xkcd put it:

The universe is probably littered with the one-planet graves of cultures which made the sensible economic decision that there's no good reason to go into space--each discovered, studied, and remembered by the ones who made the irrational decision.