Lisa Randall is telling me she may have a clue to the next great mystery in cosmology.
We are having lunch in a restaurant at the Charles Hotel, not far from Harvard where she teaches theoretical physics, with specialties in particle physics, string theory, mathematics, astrophysics and cosmology. Randall, a slender woman, now 50, reminds one of a younger Joan Didion— light-years of consciousness behind her eyes.
She is a star professor of the stars, a cosmological celebrity, and only in part because she is the first female theoretical physicist tenured at Harvard . It was really her conjecture in the late ’90s about string theory’s “extra dimensions” that gained her prominence in the field. She garnered more attention for her explication of the Higgs boson quest, and for her subsequent writings attempting to explain to the rest of us what she does and how exciting it is to do it, most recently Knocking on Heaven’s Door.
And now she thinks she and her Harvard physics colleagues have found something new. What she is excited about is “dark matter,” which—along with “dark energy”—makes up the vast majority of the known universe. The current estimate is that 70 percent of the universe is dark energy and 26 percent dark matter. Which adds up to 96 percent. Meaning that what we see and know adds up to a measly 4 percent.
Four percent! The invisible 96 percent apparently keeps the universe in gravitational equilibrium, preventing it from collapsing on itself or dissipating into virtual nothingness. But we know almost nothing else about it. The problem has been that the dark stuff doesn’t seem to interact with the 4 percent we know in such a way that gives us a clue to its nature.
But Randall believes she may have found a clue. In fact, the day before we met she delivered a talk at an American Association for the Advancement of Science conference in Boston in which she announced that she may have found evidence of the interaction of dark matter with our matter. A potentially sensational development for cosmologists just now setting out into the uncharted vastness of the dark matter universe.
It started, she tells me, because “there was a signal that I wanted to understand.”
“A signal from outer space?” I asked her.
“A signal from a satellite that could see into the center of a galaxy.” Far, far away, near the heart of the Milky Way, two infinitesimally small dark matter particles could have collided and “annihilated” each other. But instead of leaving no trace, signals of the annihilation traveled across the vastness of space to be detected by the Earth-orbiting Fermi satellite. If those signals are validated, Randall says, they might be evidence of dark matter interactions—perhaps the first legible fingerprints of dark matter to be picked up in our humble 4 percent realm.
“I know full well that the signal may be spurious,” she says, but what’s important “is the process of trying to make a model that predicts it. I was considering a model where there were interactions for the dark matter and then realized that actually this is a whole other scenario that’s interesting in its own right, and in fact works better and could lead to a cooling off of a component of dark matter, which would make it collapse into the disk the way baryons do.”