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Dark Matter and the dinosaurs: A quest for grown-ups

HOW do you know if you’re onto something in science? According to University of Manchester physicist Andre Geim, it starts with a feeling: a nagging pull in your gut tells you that your crazy idea is worth exploring. So, with bated breath, you give it a try. The result is usually failure – whether or not the idea has merit. “Then, you may or may not try again,” says Geim in his autobiography.

Throughout his career, Geim has tried again with many different projects. Just occasionally, he says, “failures sometimes failed to materialise”. And if you are far enough out from the mainstream when your project fails to fail, it’s far more likely that your surprise success will have some significance – hence Geim’s Nobel for the discovery of graphene.
Lisa Randall is certainly far from the mainstream in Dark Matter and the Dinosaurs. She has an as-yet unproven idea about the nature of the as-yet undetected dark matter that may (or may not) make up 80 per cent of the universe’s mass. Then physicist Paul Davies at the University of Arizona suggested this idea might account for the demise of the dinosaurs. Should that have been the point where she walked away?

“Meteoroid hits are challenging enough to investigate,” Randall says. “Coupling them with uncertainties about extinction events is bound to go down a convoluted rabbit hole of trouble.” But she went down the rabbit hole anyway. And, thanks to this fascinating account of the story so far, we can too.

It takes a particular kind of nerve to expose your research before it is shown to be right. That’s doubly true when the ideas seem ridiculously implausible at first glance. Perhaps Dark Matter and the Dinosaurs is a sign that readers of popular science have finally grown up and no longer need pureed “triumph” narratives of science.

“Randall has invited us to the process… We see the script, dress rehearsals, rewrites, fluffed lines”
After all, it is easy to digest happy-ending stories of derided speculations that turned out to be right all along. The uncompleted stories are more demanding. However, as Randall ably demonstrates here, they are ultimately more satisfying: there is something to chew on. Biologist Peter Medawar once ticked off scientists for giving the impression that research is always neat by adopting what he called “the postures we choose to be seen in when the curtain goes up”. Randall has invited us to the process, not the performance. We can see the script, the dress rehearsals, the rewrites, the fluffed lines. And this idea may not even make it to opening night.

Dark Matter and the dinosaurs: A quest for grown-ups
Randall’s proposal is that our galaxy contains a disc of dark matter with unusual properties. Instead of interacting solely through gravity, as dark matter is thought to, the dark matter in the disc has its own set of interactions. Occasionally, the disc exerts a pull on some of the rocky inhabitants of the Oort cloud beyond the solar system’s planets – perhaps enough to dislodge a rock and send it hurtling towards a cataclysmic collision with Earth.
Clearly the idea is not without merit, because it has now been published in what might be the most prestigious journal in physics, Physical Review Letters (although without mention of dinosaurs). The idea that dark matter did for the dinosaurs is “speculative”, Randall admits, but in a good way.

After all, if every idea in science were sensible, we would be without quantum physics and relativity. Randall even questions the value of sticking with Occam’s razor, the principle that the simplest explanation is usually the best. “Although scientists tend to prefer simple ideas, they are rarely the whole story,” she says.

That said, to her credit she doesn’t fall into the trope of painting herself as a maverick fighting the mainstream. Nowhere in these pages does she give the impression she thinks she and her colleagues are right – except in pursuing something that is both intriguing and (so far) plausible. As a world-renowned theoretical physicist and her own harshest critic, she has the self-confidence to lay out the ideas without being overly defensive of the argument.

She happily pokes fun at herself, in fact. The stars aligned for this project, she says, and just before it began, a fortune cookie asked her: “What is the speed of dark?” As she says: “I didn’t know then that the words were indeed a sort of fortune, in that they more or less prophesied the research project I was about to commence.”

The day she asked her collaborator Matthew Reece if he wanted in on the project was the day the Chelyabinsk meteor entered Earth’s atmosphere – and that was three days after Davies’s question about dark matter and the dinosaurs. And then there’s the simple joy of the idea: “dark matter (yay!), meteoroids (yay!), dinosaurs (yay!). The five-year-old in all of us was intrigued,” she says.

“If every idea in science were sensible, we would be without quantum physics and relativity”
In the end, it has turned out to be a very grown-up quest. To answer the central question, we must learn the science of the entire universe: its origins in the big bang, the structure and origins of the solar system, the geology of our planet, the nature of biological evolution, the perils of extinction – and, of course, the biggest mystery in cosmology – dark matter. As Randall puts it, “the physics of elementary particles, the physics of the cosmos, and the biology of life itself all connect – not in some New-Age sense, but in remarkable ways that are well worth understanding”.

Randall’s writing is as laid back and unfussy as ever. If you appreciated her clear, straightforward style in Warped Passages and Knocking on Heaven’s Door, you won’t be disappointed by Dark Matter and the Dinosaurs.

In fact, she seems to have pared down the flourishes to a minimum. We occasionally see glimpses of her life – her “very messy office” or an intriguing conversation with a taxi driver – but for the most part this is a straightforward primer: an introduction to each of the arguments that makes up her thesis, all tied together with an honest look at the plausibility of the whole. Maybe there’ll be no deep impact in the end, but it’s certainly worth the journey.

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