DARK MATTER & THE DINOSAUR
New theory challenges our notions on the origins of humanity
Dark matter inspires ma n y strange theories, but until n- ow few have in volved giant lizards and the origins of humanity.
If physicist Lisa Randall’s theory is correct, however, there is a clear link between d- ark matter, the great un known majority of universal stuff, and the extinction of the dinosaurs, which cleared the path for the rise of mammals, including that special species, Homo sapiens.
Roughly, her idea is that the rotation of a vast disc of dark matter through our solar system dislodged an asteroid from a weak and distant orbit, and sent it hurtling toward Earth, where it landed on Me-x ico’s Car-ibbean coast 66 mil lion years ago, kicking up so much debris that sunlight was blocked out around the world.
Randall, a Ha- rvard theoretical physicist who gave the inaugural Fields York lecture o-n the physics and mathematics of the universe at York University in Toronto this week, is no tinfoil-hatted crank.
For example, Sean Tulin, the York physicist who hosted the talk, called her a “rock star in physics,” the first tenured female theoretical physicist at Harvard, Princeton and MIT, who has also appeared on The Daily Show and written an opera, Hypermusic Prologue: A Projective Opera in Seven Planes.
But it was this dinosaur theory she explained for the gathered crowd of physicists, in more technical terms than she does in her new book, Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe.
Dark matter, discovered by the pioneering American physicist Vera Rubin who noticed discrepancies in the speed of galaxy rotation, is the biggest blank space on the map of modern physics. It is o-bviously out there in the uni verse, in quantities far greater than normal matter, because the effect of its gravity is easy t- o see. In our cosmic vicin ity, for example, dark matter seems to be arranged in a vast disc that cuts across the Milky Way Galaxy. But gravity is its only signature; it does not i- nteract with light or, seem ingly, any other force.
None of this should be too surprising to a physicist, Randall said. “Why should everything be made of atoms?” she said. But the trickier question is what is it made of ? Short of a general assumption that it is made of some kind of particle, n-o one has any idea, not with standing a wide array of efforts to detect it either directly, as in the SNOLA of northern Ont-ario, which looks for the signa ture of dark matter as it passes through the Ear-th, or indirect ly in particle colliders, where dark matter might break down into normal particles.
It was while discussing these scientific investigations with Paul Dav-ies, a physicist at Ari zona State, that Randall started imagining how she might link dark matter and dinosaurs.
A key aspect of her theory is the creation of discs. Mo-st galaxies look roughly like discs, spinning on a single plane around a centre of mass. The reason for this, simply put, is cooling.
Galaxies look the way they do because they were once huge spinning clouds of hot gas that cooled over millions of years. As they cooled, their a- ngular momentum, or spin ning, stayed more or less the same, and so the cooling gas collapsed into a spinning disc, often with spiral arms. Our Milky Way Galaxy is a classic example.
So if dark matter is arranged in a disc, as it seems to be in the Milky Way, it is probably cooling. And in the world of normal matter, things cool by radiating energy. A disc of dark m-atter, then, is likely to also re quire some kind of dissipating energy, which Randall calls, poetically, “dark light.”
None of this rises beyond the realm of theory, but Ran-dall de scribed various ways that this disc-formation concept should g-ive rise to “observational con sequences,” or things that can actually be measured.
The Oort cloud is a region of icy bodies way out on the d-istant edges of the solar sys tem, just barely held in place by the gravity of the sun.
Randall’s theory is that, as the galaxy spins, the dark matter disc “bobs up and down through the plane of the Mi- lky Way,” creating some thing like a gravitational tide. If this tide disturbs the Oort Cloud enough, it can set off a cascade, tipping an object from stable orbit to terrestrial collision course.
A simulation she showed suggested this should happen about every 35 million years, and so she has been looking f-or a regular pattern of extinctions due to asteroid impacts but as yet has not been able to draw a firm conclusion.
As she wrote in a research paper in 2014 with Matthew Reece, which first proposed the idea: “Although statistical e- vidence is not overwhelm ing, possible support for an approximately ( 35- million year) periodicity in the crater record on Earth could indicate a nonrandom underlying enhancement of meteorite impacts at regular intervals.”
In layman’s terms, that means dark matter might have killed the dinosaurs, and thus set the ecological stage for humanity.