Admittedly, my first reaction to the title of this book was that it must be some kind of joke. It sounded, well, loony. But Lisa Randall is a brilliant, world-famous, very influential theoretical physicist and I am…none of the above, so my initial reaction was, at best, probably uninformed. Sadly, I got lost a few times when reading this, especially when the discussion turned to particle physics (see above about what Lisa Randall is and I am not), but I think I caught the main thread of her proposal. I’ll try to summarize:
In order for the universe to behave the way it does, something that isn’t ordinary, visible matter (like stars and such) must be exerting a gravitational influence. It’s uncertain if this something reacts with anything else (like electromagnetism), but if it does, it’s not obvious. By consensus, this unknown something is called dark matter, but no one really knows what it is. Professor Randall discusses some of the possibilities, few of which I can honestly say I fully understand. Her conjecture, based on what little data that exists, is that the dark matter may not be all one type of unknown something. Different dark matter parts may interact with other parts in ways not entirely unlike how protons and electrons of normal matter interact. Dark matter of this nature could, theoretically, form a disk that is contiguous with the plane of galaxy and exert significant gravitational influences on normal matter (like the Sun and our own lovely planet).
So where do dinosaurs come in?
Impact craters on Earth suggest that there may be some periodicity (30-35 million years) to when really big things fall out of the sky and rearrange the landscape. (This is not yet firmly established.)
Such impacts probably are not asteroids that normally hang out between Mars and Jupiter but are, instead, large comets. (Also not certain.) These comets could originate in the Oort cloud (which probably does exist, although we have no firm observational evidence).
As the Solar System travels around the disk of the galaxy, it not only goes round and round but also up and down. This takes it through the galactic plane and the hypothesized dark matter disk, possibly every 30-some million years (although this is uncertain). When it does pass through, though, the dark matter could nudge objects from their stable orbits in the Oort cloud and send them inward toward the sun and Earth. Some of those could actually hit us, and one such might be the prime suspect for whatever caused that big crater off the Yucatan peninsula and took out the dinosaurs 66 million years ago.
So you see, it’s not loony. It’s actually quite informative, although it is highly speculative. There are a lot of unknowns here, but some may be known better soon, and the theory will stand or fall based on the evidence. That’s science.