If, like me, you've tended to think of string theory as a way that applied mathematicians and theoretical physicists can have endless fun without ever contributing anything practical to our understanding of the universe, Joseph Conlon's is a useful book to remind us that string theory isn't quite so unlikely and useless as it can seem.
I must admit I've been strongly influenced by anti-string theory books such as Not Even Wrongand The Trouble with Physics. After reading Why String Theory? I have a more balanced view (if still being pretty doubtful of the theory's value). One thing that Conlon does, which I've never never seen elsewhere, is give a detailed description of it how the theory came into being, including the original, 26-dimensional approach that was an attempt to deal with the strong interaction. When this was trumped by quantum chromodynamics, it was almost as if the string theorists were so enamoured with their theory, which has some mathematically beautiful aspects, and a tendency to suddenly fit quite well with other mathematical constructs in physics, that they seem to have a spent a lot of time thinking 'Okay, what can we do with it?' And apart from the possibility of quantum gravity, it's remarkable in how many places it seems to have offered some use, despite its infamous lack of testable predictions to whittle down the vast numbers of potential solutions.
I won't say that this is an ideal popular science title. Like Not Even Wrong, it constantly throws out material that you just have to take the writer's word for being meaningful. It's not that there's heavy maths - there are pretty well no equations - but there's an awful lot you have to take on trust, or glaze slightly as meaningless (to the reader) terms are thrown at you. This isn't helped by a style that sometimes reminds me of a elderly schoolmaster (I was amazed that the author is considerably younger than me) with examples like referring to a person's bottom as a 'derrière' (something my grandma might have done) and throwing in 'crossing the Rubicon of physics' occurring within 2 lines of each other. I'm surprised their weren't Latin tags. Elsewhere we get 'I will, for now, let sobriety be the better part of speculation and be silent whereof I cannot speak...' Note that this is while calling pre-Big Bang ideas 'bad speculation' because they're not based on observation - unlike string theory?
There's also a touch of iffy history of science (we are told that Gell-Mann named the quark after a word in Finnegans Wake, for instance, where it was only the spelling that came from there), and the author rather sneakily compares string theory to astronomy as being 'pursued for the value of intrinsic understanding' rather than anything so grubby as commerce - but doesn't note that at least we know that what astronomers (as opposed to cosmologists) study exists. (Not to mention Conlon being unnecessarily sniffy about practical applications.)
However, I do still recommend this book for everyone who wants to get an up-to-date picture of the state of string theory with a lot of background, and is prepared to take the rather heavy approach, lacking much of an attempt to explain things in words most of us can understand. If, like me, you've tended to the anti-camp, this title (sadly, priced more like a textbook than a popular science title) is a very valuable antidote.