DARK MATTER AND THE DINOSAURS by Lisa Randall ★★★★

I very much enjoyed Lisa Randall’s Knocking on Heaven’s Door, which provided a layperson like me with a cogent explanation of the Standard Model that underpins modern particle physics. Randall is a physicist with a knack for explaining things both enthusiastically and clearly; she’s a good storyteller who doesn’t get too bogged down in trying to get all the details right for us. So I was intrigued enough to put Dark Matter and the Dinosaurs on my to-read list, even if that was years and years ago. Now that I’ve read it, all I can say is: wow. What an interesting take on a popular physics book.

The title hints at how different this book is going to be. How could the dinosaurs be connected at all with dark matter? Randall has a plausible scientific theory—this book is not science fiction or fantasy—but I want to be up front with anyone considering reading this book: this is a thought experiment. Randall and her collaborator, Matthew Reece, decided to investigate the possibility that the solar system’s passage through a hypothetical disk of dark matter embedded in the galactic plane might disturb comets from the Oort cloud and periodically send them into the solar system in a way that could lead to a devastating, extinction-level impact on Earth. Their work is built on decades of investigations into extinctions, the theory of periodic impacts from space, and of course, the nature and distribution of dark matter in our universe. Everything they say here is (as far as I can tell) plausible from a scientific perspective but also highly theoretical. Just keep that in mind as you read.

Also be aware that much of this book discusses neither dark matter nor dinosaurs! Never fear, they do come up, especially towards the end. But there is a lot of build-up first. In this respect, the book’s subtitle—The Astounding Interconnectedness of the Universe—is quite apt, and this is probably the make-or-break selling point of the book for people. Either you appreciate how Randall tells the story or you don’t. The first few parts of the book develop our basic understanding of the universe itself and our particular corner of it. In particular, Randall explains where impactors—asteroids, comets, meteoroids—come from. She does a good job helping us wrap our heads around the vastness of our solar system as well. Those school models of the planets all neatly lined up at distances not to scale warp our ideas about how big the solar system is—Randall makes it clear that our solar system is vast and mostly empty, but there is a lot about the composition of its fringes (like the Oort cloud) that we’re still unsure of because it’s so far away and hard to probe.

The middle of the book is mostly about the effects of impacts on Earth. While the dinosaurs come up here and there, they aren’t the main story. Randall is more interested in explaining about craters, how we investigate their properties, and what they can tell us about the nature of the impact and impactor itself. This part was extremely interesting and valuable to me. Randall strives to help us understand that science is a fallible but hopefully self-correcting process. As with the story in Fossil Men, this is a story about people’s egos and different theories running up against each other, looking for evidence either way. Things I took for granted growing up, like the fact that the extinction of the dinosaurs was kicked off by an impact off the coast of the Yucatán Peninsula, were only accepted very recently! And the story of how these theories were formed and investigated in incredibly interesting and full of drama. (Hearing about all the messy drama is probably my favourite thing about reading popular science books, let’s be real!)

So it’s a lot of setup before we finally arrive at the end of the book, where Randall unspools the theory she and Reece have cooked up. I explained it above, and that’s about all the detail I can give, because I am not an astrophysicist! I appreciate the care with which Randall explains competing models of dark matter and how she reminds us, over and over, that what she and Reece are proposing is just one idea among many. Sometimes scientists become too invested in promoting or hyping up their own theories when the evidence isn’t there yet. Randall doesn’t do this, and it makes me respect her all the more.

Yes, it might seem silly to some people to write an entire book about a hypothetical scenario. Yes, it might seem odd that Randall has spent so much time investigating a connection between physics and extinction events that doesn’t seem to have any practical consequences for humans here and now. In my opinion, however, this book has a great deal of merit. It demonstrates how science is a creative process. I love the way Randall describes how she and Reece went about forming their theory, from reviewing existing literature to gathering datasets to forming their hypotheses. She makes it clear that this is a fun project for them, but she also explains its value: by searching for evidence that supports or rules out their theory, they might further refine our understanding of dark matter in general. Similarly, if their theory helps us to understand impact events and whether or not they are periodic, this might help paleontologists further refine our understanding of the history of life on Earth! None of this would happen if two physicists didn’t decide one day to get creative. I know any physicist (or scientist in general) who reads this review might not be surprised—I bet all of you are a fairly creative bunch! But that isn’t the picture we’re painted, especially in schools where we are not taught science in a creative, messy way like we were from The Magic School Bus. And that’s a shame.

Dark Matter and the Dinosaurs might not hold a revolutionary new discovery within. But it shows us the value of looking at connections, of being interdisciplinary, and of creative thinking. These are qualities scientists need, and this book helps you think a little more like a scientist.