Did dark matter kill the dinosaurs, and does it even exist?

Physics professor and author Lisa Randall. Picture: 'Rose Lincoln/Harvard Staff
Physics professor and author Lisa Randall. Picture: 'Rose Lincoln/Harvard Staff
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This engaging summary of cosmology and quantum physics could be the work of a genius or a crackpot

Dark Matter And The Dinosaurs by Lisa Randall | Bodley Head, £25

WHILE there is a great deal to admire in this book, its eye-grabbing title is not one of them. Being neither a palaeontologist nor a particle physicist, I can only report rather than review Lisa Randall’s hypothesis. It comes down to five big ifs. If dark matter is able to interact with itself rather than purely gravitationally, and if it then forms into a dark matter disk spliced through our galaxy, and if the solar system passes through it cyclically and its effects dislodge a comet-shower from the Oort Cloud, and if any of them then hits Earth, then if mass extinctions are a regular phenomenon rather than random or from various causes, the culprit is five ifs ago. A putative dark matter disk did for the non-putative and definitely extinct dinosaurs, if, if, if, if and if.

Along the way to a theory both tenuous and intriguing, Randall does provide a very clear summary of contemporary thinking about cosmology, the development of the Earth and the current state of quantum physics. She writes wittily and keeps the reader apprised of those who disagree with her thinking, in a generous and unpartisan fashion. That her theories might be confirmed or denied in the near future – mostly through the GAIA satellite’s research – is commendably left on the table. Such equanimity is a virtue in any contemporary science work intended for a wide readership. It is also fairly bold to produce a book which within five years might be either prescient or completely misguided.

One key concern throughout is the importance of nomenclature. Dark matter, for example, is not dark. Nor is it evil or malign. As Randall states, it would be more accurate to refer to it as transparent matter – the fact that the stuff is invisible is just one reason why it is so aggravatingly hard to find. Likewise she is precise in differentiating between meteors, meteoroids and meteorites (as well as their difference from asteroids and comets). Although science progresses, with one theory or paradigm superseding the previous one, language accretes, carrying its own history.

Some of the most interesting parts of the book are the digressions on how the language evolves: so although meteorology technically refers to the study of the weather rather than meteors, its etymology links back to older schema where aqueous meteors were rain and snow, aerial meteors were winds, luminous meteors were rainbows and aurora, and igneous meteors were what we call meteors, as well as lightning. Sometimes the naming of proposed phenomena is almost comical: in discussing other possible celestial bodies that might trigger comet showers, Randall looks at discredited theories for the grandiosely named “Nemesis” (a companion star to our Sun) and the eerie “Planet X”.

Given this precision, it is irksome that sometimes Randall slips into shorthand definitions. For example, she summarises the principle of Occam’s Razor as “the simplest explanation is the best (and most likely)”. That’s not precisely what William of Ockham wrote (and it’s difficult to find his most famous saying in his extant works). Instead, his contention was that “plurality must not be posited without necessity”. There are times where there is a necessity for “plurality” – for example, Newton’s mechanics may be simpler than Einstein’s Theory of General Relativity, but Newton’s equations do not accurately predict the precession of the perihelion of Mercury, while Einstein’s do. In terms of prose style, though mostly eloquent and lucid, there is a preponderance of split infinitives. I realise they are now a common Americanism, sanctioned by the opening voiceover in Star Trek, but to British ears they can begin to greatly grate.

Randall is good at providing clever, easy-to-grasp metaphors and images for scientific concepts that are subtle and difficult. If dark matter is so elusive, how do we know it is there at all? Randall compares this to the presence of a celebrity on a busy street. You might not personally see George Clooney, but you can see the crowds and flash-bulbs around him. Similarly, she uses neat comparisons to social media to show how a single interconnected web can still have areas that are unconnected and discrete. She is smart on “ordinary matter chauvinism”. Since it is the stuff that makes up the Earth and the scientists on it, there is a tendency to concentrate on it. As she points out, there are ten times more bacterial cells living inside us than human cells in our bodies, but they don’t feature much in definitions of what it means to be human. She turns this chauvinism on its head: given how complicated ordinary matter is, why shouldn’t dark matter be equally complex? Hard to argue against, much more difficult to prove.

This is the kind of book where the journey is more engaging than the destination. As a guide to a number of fields in contemporary science it is eminently readable and always interesting. Whether it turns out to be crackpot or genius, time will tell.