Book review: “Dark Matter and the Dinosaurs” by Lisa Randall

On the one hand, we have the elusive dark matter particles, dispersed throughout the universe across billions of light-years; on the other, we have the sorely missed dinosaurs, who lived in our own proverbial backyard but were driven extinct by a mysterious impactor 66 million years ago. What if these fascinating yet disparate phenomena, separated by so much space and time, were somehow related?


That, in essence, is the premise of Lisa Randall’s book, “Dark Matter and the Dinosaurs.” Maybe the “vanilla” cold dark matter model we have isn’t the only possible explanation of observations of the expanding universe and the cosmic web of millions of surveyed galaxies, she argues. It’s more fun to consider other more exotic models, even if they turn out to be wrong.

Dark matter particles don’t interact with each other the way our familiar atoms do. In fact, they hardly interact at all. They mostly just move apart with the growing universe and then clump together as they feel the effects of gravity over time. As a result, we end up with nearly spherical dark matter clumps throughout the universe, and we and the rest of the Milky Way are living inside one of those clumps. But if some dark matter interacts like normal matter, it could form a dense and thin disk—even thinner than the disk of our own galaxy. (Picture a compact disk hidden inside a bagel. Here’s a good composite image of our galaxy, on edge, which would be the bagel.)

If that’s the case, then as our solar system moves up and down through the disk, we’ll experience an extra little gravitational nudge each time we go through. This could periodically dislodge comets traveling in tenuous orbits in the Oort cloud in the distant realms of our solar system, flinging one comet away forever and sending another in an unfortunate Earthbound direction, where the consequences of its destructive impact in the Yucatan kills off the dinosaurs some 66 million years ago, thus finally linking dinosaurs to dark matter.

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