Awhile back, I wrote a review of Perfect Rigor by Masha Gessen. It was ok. Not the most thrilling read I'd had. The publisher found my review and suggested that another book from their company might be more up my alley. So they sent me a review copy of Paul Davies The Eerie Silence. This book is a 50 year retrospective on the SETI program, written by the head of it's post detection taskforce.
The role of the post detection taskforce is to lay out the recommended policy for the procedure to follow if we ever do discover any sort of extraterrestrial life. But the book isn't about what we'll do, it's about why we haven't found any yet and what possible improvements can be done to improve the program in order to up our chances of actually detecting something.
The main argument of the book is that we've been far too narrow in both our methods of looking as well as our definition of life and intelligence.
One of the first things Davies asks is how likely is it that there is some other form of life out there? We know all life on Earth had a common origin, so we've really only got one example to study and try to understand. Small number statistics impress no one (aside from the pseudoscientists). Thus, to even begin to get a reasonable predictive handle on such things, we'd like to try to find another example of life. SETI could stumble across this in the heavens, or it's possible that it's right here on Earth.
Davies suggests that we look for forms of life on Earth that don't use the same base pairs (or amino acids) that life as we know does. Or life that has an opposite "handedness" (chirality) to it. If these were discovered, it would likely imply a second example of biogenesis and we could start getting a feel for how likely life is to originate in the first place. Although attempts have been made to look for such life (by looking in the most extreme environments in which "normal" life was not expected to exist), the only life that's been found has always been of the same base pairs and the same chirality.
But even without forming full fledged life, Davies points out that amino acids are plentiful in space, including ones that aren't used for life as we know it, as indicated by the Murchinson Meteorite.
Of course, even if weird life were discovered here on Earth (or in rocks from space) it doesn't necessarily prove a completely separate biogenesis. While it would lend credence to it, there's always the possibility that it came from a different branch of our own evolutionary tree or due to some sort of horizontal gene transfer. This would obviously muddy the waters.
On top of that, Davies suggests that looking for odd lifeforms like this may be another way to find messages from extraterrestrial civilizations. ET may use life as a carrier since it's essentially a self sustaining message that can propagate itself. And even if not life, then perhaps nano-machines that can self replicate to spread. Such methods would be more enduring than a short radio message.
If this all starts sounding too close to Intelligent Design, Davies is quick to assure us it's not. In fact, one of the very first parts of the book discusses the difference between good science and pseudoscience, namely that good science must actually work through the math to show just how closely the evidence fits the hypothesis through use of Bayes rules. Although the Discovery Institute is desparate to be similar to SETI, they've never done any such analysis, or even made a hypothesis to be actually testable.
Davies concludes by briefly discussing the post detection sequence, affirming an open and honest dispersal of the information, but a quiet one so as not to get the media all fired up over the possibility of a false positive (as they have before). After all, we've seen the devastation that the media misportraying science can have of the public view with the recent "Climategate" nonsense.
Overall, this book was pretty good. The extreme edge of what Davies proposed (super computer AI taking over in place of life, growing into quantum computers and living in deep space, not communicating with the outside world), goes a bit beyond the believable, but that's the point. We don't have enough information to truly make any good predictions about intelligent life so we need to keep an open mind and open eyes.