Lisa Randall: Dark Matter and the Dinosaurs

By Shawn Radcliffe

Star Trails over Green Lake by Dan Barr

Dark matter is already known to be everywhere. But in her new book, Dark Matter and the Dinosaurs, Harvard cosmologist Lisa Randall proposes that this mysterious substance also played a role in the demise of the dinosaurs on Earth.

Although dark matter—which accounts for 85 percent of the universe—is always assumed to be ‘dark’, Randall says that it would be better described as transparent. Matter that is truly ‘dark’ would, in fact, absorb light. Dark matter doesn’t interact with light at all—or people, for that matter—although it does interact with gravity.

“People are trying to devise very clever ways to look for very subtle, small effects, but so far as we know, the dark matter is not interacting with us a whole lot,”  said Randall in an interview on On Being. “It’s interacting via gravity, but gravity is actually a very weak force at a fundamental level. That’s why you need large amounts of dark matter to observe its effects.”

There is a lot of evidence suggesting that dark matter is spread out in the galaxy, forming a diffuse spherical halo. However, Randall and her colleagues propose that some of the dark matter might radiate energy and cool down in the same way as ordinary matter. This would allow it to concentrate along the mid-plane of the galaxy.

This concentrated area of dark matter would have consequences that could be observed. It would also affect our solar system as it orbits the galaxy with a slight up and down wobble to its movement. As the solar system passes through the area of denser dark matter, the gravitational effect would be strong enough to dislodge comets from the spherical Oort Cloud that surrounds the solar system.

“Our proposal is that every 30 or 35 million years, there’s this extra tidal force that dislodges comets from the Oort Cloud,” said Randall, “and explains the periodicity of large comet hits.”

This could explain the comet that struck the Earth 66 million years ago, leading to the death of 70 percent of the plants and animals on the planet, including the dinosaurs.

Randall’s idea, though, is far from settled. More evidence is needed to show the periodic nature of Earth impacts, something that can be determined by identifying craters of those impacts. Additional three-dimensional mapping of the galaxy may also provide clues as to the existence of a disk of dark matter along the mid-plane.

However, while erasing some of the mysterious nature of dark matter, Randall also highlighted one of the other outcomes of the cosmic event that led to the extinction of the dinosaurs—the rise of humans as a species.

“Extinctions destroy life,” writes Randall, “but they also reset the conditions for life’s evolution.”

“The future enters us in this way in order to be transformed in us, long before it happens.” ~ Rainer Maria Rilke