The universe is not like a clock, where well-understood parts tick in predictable ways, nor like a balloon expanding or contracting. It is in fact pushing itself apart with a strange kind of energy, and 96% of it is made of an unknown kind of matter. How we discovered this is the subject of The 4% Universe, which condenses the complex, messy and startling tale – people, science, instruments, events – into an easily digestible, fast-paced 243 pages. That is a startling achievement in itself. To the connoisseur of popular science, indeed, the way author Richard Panek tells the tale is as interesting as the events: half drama, half detective story.

The prologue begins with a one-page “wow!” moment. On 5 November 2009 scientists at 16 institutions around the world dropped their collective jaws as they seemed to catch a first-ever glimpse of an entirely new structure of the universe. Two pages follow explaining its significance. Referring to the year when Galileo first used the telescope to reveal entire new worlds previously unknown to humankind, Panek writes “It’s 1610 all over again.”

What follows in Act One is the story of how cosmology went from speculation to science: how astronomers discovered that the furniture of the universe was more than planets and stars, and was on the move to boot. The universe “had a story to tell”, Panek writes. “Instead of a still life, it was a movie,” he says. We learn how scientists uncovered this movie’s plot by peering over the shoulders of Act One’s two main characters: theoretical physicist Jim Peebles, author of the classic textbook Physical Cosmology on the physics of the early universe; and astronomer Vera Rubin, whose work on the galaxy-rotation problem pointed the way to the idea that the universe contains some amount of “dark” matter, invisible to present-day instruments.

Act Two introduces more characters and “the game”, in which two different teams of scientists vie to unravel the plot by finding distant “Type 1a” supernovae. The game is played with telescopes equipped with charge-coupled devices, which revolutionized astronomical photography, and with the Hubble Space Telescope, which peered into hitherto invisible corners of the universe, among other equipment. The first team, the Supernova Cosmology Project (SCP), was led by Saul Perlmutter and Carl Pennypacker, particle physicists at the Lawrence Berkeley National Laboratory who applied the tools of their trade to astronomy. In doing so, Panek observes, “[T]hey weren’t drifting towards a new discipline. The discipline was drifting towards them.”

The second team was known as High-Z, where Z is a term for redshift. Highly redshifted objects are among the oldest and most distant in the universe, meaning that they would bear the clearest traces of any expansion or contraction. High-Z‘s main members were Adam Reiss and Brian Schmidt, who hailed from Harvard University and viewed supernovae as their area of expertise. They saw the Berkeley group as being out to “beat them at their own game”. While SCP had a six-year head start, High-Z recruited the “old-boy network” to, in effect, beat the Berkeley group at beating them at their own game.

In 1997 the two teams converged – simultaneously, yet reluctantly – on two wild, toothfairy-like ideas: that the universe contained “dark matter they couldn’t see and [a] new force they couldn’t imagine”. In Act Three, all the main characters introduced so far in the drama gather at a meeting where the SCP’s results (picked up by discerning newspaper reporters) suggest that “SCP was beating [High-Z] at beating the SCP at beating [High-Z] at their own game”. Then High-Z outdid that by securing full credit in the media. The discovery of this new force – soon dubbed “dark energy” – became Science magazine’s “breakthrough of the year” in 1998.

The new idea – that the universe’s expansion is accelerating – both simplifies things, by explaining a lot of puzzling data, and makes them more complex, by raising a lot of questions.

In Act Four, SCP and High-Z make plans to hunt for answers to one question – dark matter – while struggling over credit for the other, dark energy. The existing picture of the universe turns “preposterous”. But as Perlmutter remarks on the final page of the book, what usually attracts physicists to their field is “not the desire to understand what we already know but the desire to catch the universe in the act of doing really bizarre things”. And so, at the book’s conclusion, while one chapter in astronomy ends, another begins.

Panek tells the story briskly yet warmly, capturing personalities and not overlooking controversies. He chooses characters carefully. Through Rubin, for instance, we not only learn about dark matter, but also what it is like to be a woman in science, literally balancing child and career: textbook in one hand, pram in the other. Panek also has a knack for summarizing developments concisely and efficiently, such as in the following passage about how astronomy became more specialized over time:

You couldn’t just study the heavens anymore; you studied planets, or stars, or galaxies, or the Sun. But you didn’t study just stars anymore, either; you studied only the stars that explode. And you didn’t study just supernovae; you studied only one type. And you didn’t study just Type 1a; you specialized in the mechanism leading to the thermonuclear explosion, or you specialized in what metals the explosion creates, or you specialized in how to use the light from the explosion to measure the deceleration of the expansion of the universe – how to perform the photometry or do the spectroscopy or write the code.

Inevitably, Panek makes some compromises, and the seams of his crisp storytelling occasionally show. Galileo is mentioned once too often, and Panek’s apothegmatic style can ring precious, as in this remark about the signal from a radio antenna: “[T]his time the source wasn’t a radio broadcast from the West Coast. It was the birth of the universe.” The reader sometimes feels manipulated, too. That “wow!” moment that kicks things off so dramatically in the prologue? You don’t find out until page 197 that it was phoney – not a discovery after all.

Another author might have explored why it initially seemed to be a discovery, why its announcement was hyped even after problems were uncovered, and what this says about science and scientists. But by this time, you are so absorbed in the story that you do not care that much. And the book does convey a good picture of scientists in the act of catching the universe doing really bizarre things – while also showing that this is why they took the job. Give this book to your non-scientist friends to show them what it is all about – and to fellow scientists as a model of how to write popular science.