I enjoyed Caleb Scharf's previous book, Gravity's Engines a good deal, so I was happy to get email from a publicist offering me his latest. I'm a little afraid that my extreme distraction of late hasn't really treated it fairly, but then again, the fact that I finished it at all in my current state of frazzlement may be the best testament I can offer to its quality. This is a sweeping survey of what we've learned about our place in the universe over the last five hundred years or so.
Now, a grandiose description like that often portends a bunch of wifty philosophizing that poses grand questions but doesn't answer any. Happily, Scharf's book is largely free of that-- it's not that he actually has concrete answers for questions about the origin of life in the universe, but he resists the worst sort of speculation, and grounds everything in solid modern science.
In fact, if anything, it's a bit anti-philosophical, starting with the title. Scharf spends a good deal of time arguing against more extreme versions of the Copernican principle, the idea that the Earth isn't special. This is one of those meta-scientific ideas, like Occam's Razor, that are perfectly sensible in a simple form, but are sometimes stretched well beyond their natural domain, as if they were built into the very structure of the universe.
The mis-application of the Copernican principle that Scharf argues against is the idea that the Earth has to be perfectly mediocre, unexceptional in every regard. You'll sometimes hear this trotted out in arguments that there must be bazillions of inhabited planets out there, just like Earth, and therefore we need to spend more on the favored space exploration schemes of whoever's talking. Scharf dismantles this line of thinking with a clear and thorough survey of modern astronomy, showing that the Earth is, in fact, special. Our Sun isn't an average star, but a type that's a little bit unusual. Our solar system, with rather circular and relatively stable orbits, looks unusual when compared to the many exoplanet systems that have been discovered-- we don't even have any examples of the most common planet types we've seen around other stars. And Earth itself is a little unusual, with our large Moon stabilizing the rotation axis. Given what we now know about astronomy, there are lots of ways in which the Earth is, in fact, special.
At the same time, though, he's careful not to go too far the other way, into asserting that our uniqueness indicates that life is exceedingly improbable and therefore rare. After all, as he points out, everything is unique in some sense. If you flip a fair coin twenty times, writing down the sequence of heads and tails, the resulting string will be literally one in a million (1,048,576, if you want to get pedantic). But that's true of absolutely any string of coin-flips-- they're all unique. Similarly, any life-bearing world out there will have a large number of features that make it unique, and would allow alien bloggers to hold forth about the improbability of such a combination occurring elsewhere. Just as the improbability of a particular string of coin-flips doesn't tell you all that much about the general operation of flipping coins, the contingent factors associated with our particular brand of life don't tell us all that much about life in general.
The main weakness of the book isn't a weakness of the book itself, but the underlying science. Scharf goes through as much detail as he can about what we can say about the conditions for life and the possibility of life elsewhere, but it's necessarily an incomplete picture. We don't yet have enough information to make many sensible statements about what's really going on with life in the universe, and that constrains what he can do with this book. But he does muster a good argument that we're really close to having enough information to address these questions in a concrete manner, thanks to ongoing developments in exoplanet searches and robotic probes and all that sort of thing. It's a fun time to be in science.
This is, in many ways, a book that's pitched just right for me. It engages in speculation about some fun subjects, but it's appropriately constrained speculation, with Scharf looking askance at the more excessive sorts of speculation in a manner I find very congenial. If you're an enthusiastic follower of the wilder sort of Fermi paradox/ anthropic principle/ "rare Earth" stuff that's out there (or an "Ancient Aliens" theorist, for that matter), you won't find much to like. But if you want a compact and engaging survey of what we actually know about the possibilities involved with life in the universe, this is an excellent read.