When Virginia Postrel asked her Facebook followers for science writer recommendations, I immediately suggested Sean Carroll, Caltech research professor in physics. And that was when I was only part way through the second book I've ever read from him. He's a very good writer at the dilettante level (which is where I am these days, even though I was a physics major), writing with insight and wit.
Richard Feynman, in his day, famously said that he was confident that nobody really understood quantum mechanics. It's just weird. And it hasn't gotten any less weird since then. Part of the problem is that a key feature in QM's standard "Copenhagen" interpretation is kind of loosey-goosey: the act of observing a quantum state causes its Schrödinger wave function to "collapse" to some definite value. But unless that state is (somehow) measured, asking what it "really" is is nonsensical: it's in a superposition of its possible states. This gives rise to the good old half-dead Schrödinger cat, the Einstein-Podolsky-Rosen "paradox", and other oddities. And there's a lot of handwaving about the nature of wave function collapse; when does it "really" happen, how long does it take, etc.
That doesn't sit well with some scientists, even though decades of experiments don't contradict it, and much modern technology relies on it being correct down to many decimal places. There have been alternate explanations offered. One of the most thought-provoking was offered by Hugh Everett back in the 1950s: quantum events spawn, literally, multiple universes, one for each possible outcome. That's the version of QM Carroll prefers and he explicates it well.
So, for example, Schrödinger's cat isn't half-dead. He's alive in one universe, dead in another. (Carroll, being a more humane physicist, dinks the experiment so the cat is asleep/awake instead of dead/alive.)
The book made me aware of the Universe Splitter©, an iPhone app you can get for a mere $1.99. Need to make a binary decision? Well, just fire up the app and…
Universe Splitter© will immediately contact a laboratory in Geneva, Switzerland, and connect to a Quantis brand quantum device, which releases single photons into a partially-silvered mirror. Each photon will simultaneously bounce off the mirror and pass through it — but in separate universes.*
Good news: if you use the app to make all your decisions (and you can always break down complex decisions into binary ones), then there will be a universe out there where you've made all the right decisions!
And, unfortunately, there will also be a universe where you've made all the wrong ones.
Anyway, I've babbled enough. The book is a lot of fun, and Carroll goes into other areas as well, like (see subtitle) where time and space "come from". He argues that they may not be fundamental, but emergent properties of "something deeply hidden". Fine. His argument is (unfortunately) at the layman level, so there's a lot of handwaving over what in actuality is some pretty, very serious math. Still, the book is full of "did I just blow your mind?" arguments and descriptions.