At first sight, Dark Matter and the Dinosaurs looks like a title thought up by the marketing department. “Hmm, what interests the public? Dark matter is trendy. And who doesn’t love a dinosaur, right?” To be fair, physicist Lisa Randall does make a tenuous connection between a new dark matter theory and the comet that is thought to have caused the extinction of the dinosaurs, but that is by no means the most interesting aspect of this book.

Much of the content takes us on a solid, if surprise-free, tour of the history of the Universe, zooming in to see how far the Solar System reached in its present form, and exploring the nature of comets, meteors, and asteroids. But where Randall really triumphs is with her coverage of extraterrestrial impacts on the Earth. The detective story that led to the identification of the Chicxulub crater as the site of the dinosaur-killing meteoroid strike is extremely engaging.

Better still, the chapters on dark matter go far beyond most other popular books on the subject. Randall paints a truly fascinating picture of the possibility that dark matter is as rich and varied as normal matter, perhaps forming dark matter suns that pour out dark light, or are even orbited by dark planets hosting dark life.

Where the book could do better is in hitting the right level of detail. Randall dismisses modified Newtonian dynamics (MOND)–the alternative to dark matter based on a tweak to Newton’s laws–with an example of a star cluster unsupported by the modified theory. Yet she continues to support dark matter, despite listing four or five examples where it fails to match observation, and it’s never made entirely clear why dark matter is given the benefit of the doubt but MOND isn’t. Elsewhere, it seems as if the book hasn’t been adequately edited–it isn’t unusual for Randall to take a page to say something that only required a couple of lines.

The climax of Dark Matter and the Dinosaurs is the discovery that a possible regular cycle of comet strikes–for which the evidence, it should be pointed out, is rather thin–combined with an unsubstantiated dark matter theory just might explain the extinction of the dinosaurs. But to consider this the highlight misses the point. This book is not about the destination, but the journey. And that is often delightful.

This review is by Brian Clegg for BBC Focus magazine on page 106.

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