Tuesday, January 12, 2016 by Greg White
Why do we exist? The answer depends on who you ask, really. Those with strong religious inclinations believe humans are the end goal of a divine plan, whereas atheistic materialists believe people are a biological accident. According to a radical new hypothesis purported by theoretical physicist Lisa Randall, however, dark matter could shed light on this age-old question.
Randall is a physics professor at Harvard University. She has written several popular science books, including Warped Passages: Unraveling the Mysteries of the Universe’s Hidden Dimension. Her studies focus on theoretical particle physics and cosmology.
In her latest book, Dark Matter and the Dinosaurs, Randall suggests that the extinction of the dinosaurs, which was necessary for the emergence of humans, has roots tethered to dark matter – an invisible, mysterious type of matter that comprises 85 percent of all matter in the known universe.(1)
Paleontologists agree that approximately 66 million years ago, a giant comet collided with Earth, which led to the extinction of the dinosaurs. The catastrophe wiped out an estimated 75 percent of species. Nevertheless, the extinction event enabled small primates to flower, which eventually became bipedal creatures with swollen brains.
But, what caused a massive comet to collide with the Earth? Was it divine order or the stroke of chance? Randall doesn’t deal with black and white dichotomies. She proposes that a dense disc of dark matter concentrated at the center of the Milky Way could be responsible for the wave of extinctions that sandblasted Earth.
Physicists are still in the dark about the real nature of dark matter. General relativists suggest the mystery of dark matter can be dissolved with a complete theory of gravity, particle physicists suggest dark matter is an unaccounted particle, while string theorists suggest dark matter is a manifestation of gravity in a parallel universe.
Although physicists have yet to solve the mystery of dark matter, it has been directly detected by gravitational lensing. It is usually concentrated in large hallows around galaxies. However, Randall believes there could be a large, dense, disc of dark matter located in our own galaxy.
If there really is a disc of dark matter in the Milky Way, then it should exert a gravitational pull on neighboring objects, including our solar system. But the solar system isn’t always near the dark matter disc, which is where Randall’s theory gets interesting.
As the solar system revolves around the center of the Milky Way, it oscillates up and down through the plane of the galaxy. Astronomers estimate that it takes 32 million years for the solar system to pass through this plane, which means if there is a disc of dark matter, we pass through it at the same rate.(2)
According to Randall’s hypothesis, each time we pass through the dark matter disc, it exerts a gravitational pull on a blizzard of comets located at the outskirts of the solar system known as the Oort Cloud. Consequently, these comets are projected towards the solar system, where they collide with planets, like the one that killed the dinosaurs 66 million years ago. In other words, extinction events aren’t sporadic under Randall’s hypothesis, but are a predictable consequence of dark matter.
It’s impossible to run the clock backwards to see if this is really the case. However, if a disc of dark matter was discovered lurking within the Milky Way, it would add significant weight to Randall’s hypothesis. In her final comments, Randall writes:
“In some global sense, we are all descendants of Chicxulub [the town where the dinosaur-killing meteor impacted]. It’s a part of our history that we should want to understand. If true, the additional wrinkle presented in this book would mean that not only was dark matter responsible for irrevocably changing our world, but also that some of it played a crucial role in allowing our existence.”(2)