What a very strange book this is, and what a very strange guy Richard Panek seems to be. I know many autistic-spectrum people, and I wonder if he isn't a little autistic. One of the most characteristic things about autistic people is the unevenness in their range of abilities. They are usually extremely good at some things and staggeringly incompetent at others. Panek is definitely a bit in that direction.
Panek sets out to tell us about the most recent chapters in the exciting history of cosmology, the discovery of dark matter and dark energy. As everyone now knows, most of the universe is invisible. The 4% in the title is the part we can see: planets, stars, nebulae, things like that. Then there's about another 25% which is dark matter - we can't see it, but we can quite easily see the gravitational effects it causes - and the rest is dark energy, the evidence for which is considerably more indirect. The greater part of the book is about the discovery of dark energy during the 90s. Its presence is detectable by the fact that it acts to stretch the universe apart over time (you sometimes see it called "anti-gravity"), and finding proof that the stretching existed was very difficult. It involved accurately measuring the distances to galaxies which are many billions of light years away, obviously a challenging thing to do.
But scientists can be ingenious when there is a good reason for displaying ingenuity. The brightest things there are (simplifying a little) are the huge stellar explosions called supernovae, and it turns out that a certain type of supernova has predictable enough behavior that it can be used to carry out the accurate measurements that were needed. A supernova is so bright that you're able to see it more or less literally from the other end of the universe, and because their behavior is well understood you can also figure out from careful examination of the rate of change of intensity what their true brightness is. Comparing the true and apparent brightness gives you their distance. But the details are complicated.
So why are Panek and the book strange? Well, let me start with the good news. He is an incredibly dogged and hardworking journalist. He seems to have talked with virtually everyone who was involved in the story, he has read their papers, he has looked at their emails and PowerPoint slides, and he is certainly able to present you with some rather striking details. Where Vera Rubin was standing when she received a critical phone call; Alan Sandage's loss of his sense of balance causing him problems on the high telescope platform towards the end of his career; how the cosmology community reacted when they heard that David Schramm's private plane had crashed. He's got all the gossip, and, given that the discovery of dark energy was an acrimonious race between two teams, there's plenty to write about. On all of this, I can't fault him. He's booked you a ringside seat, and you can see the drops of blood flying every time someone lands a solid punch.
Now for the middling news. Panek, alas, is not a particularly gifted writer. His prose is cliché-ridden and pedestrian. He is not good at sketching character. There are a bewildering number of people in the story, and it's frequently impossible to tell them apart. A lot of the time, you just have to remember that X is the person who's responsible for Y on the blue team, and Z is the person responsible for W on the red team. Luckily, a few people are such appalling assholes that their personalities shine through. (I hasten to add that there are also some truly admirable characters; the one I liked best was Vera Rubin). But they're the exceptions.
And finally for the bad. Oddly enough, for someone who's an award-winning science journalist, Panek seems to be rather sketchy on science. There are some remarkable bloopers. He says that the Casimir effect integrally involves gravity. He tells us that the hypothetical neutralino (important to dark matter theorists) is the supersymmetric partner of the neutrino. Most astonishingly of all, he misquotes Kepler's Third Law - something your average scientist learns in their early teens - and even gives some incorrect examples of how to apply it. So, unfortunately, when he's explaining something I don't already know, I'm never sure whether to trust him. I doubt I've spotted all the glitches.
To summarize, then, a mixed bag. But despite the weaknesses, I give him a clear thumbs-up. He's got an incredible story to tell you about how science actually gets done.