Dark matter - Lisa Randall’s Guide to the Galaxy

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.”

At this point, where “the baryons collapse into the disk,” I am totally lost, but “the important thing,” she continues, “is that it’s just a scenario that oddly enough no one has considered. People thought about dark matter interacting—but having all the dark matter interacting. And [in this model] it’s very constrained.” It’s an infinitesimal piece of the 96 percent deigning to interact with our poor, pitiful 4 percent.

The reporter in me suddenly feels this could be a huge scoop, a cosmic scoop—just yesterday the curtain may have been lifted on much of the 96 percent of the universe we have been clueless about. But the math program dropout in me despairs at truly understanding what she’s telling me. Fortunately, she shows me a copy of her notes for her AAAS talk, titled “What Is Dark Matter?” Although it leaves many things obscure to me, it gives a great sense of her voice when speaking to her peers—careful but sometimes exuberant.

Here are a few samples:

—It’s not dark—it’s effectively transparent!
—Hopes to see it based on it being a little opaque.
—Talk today...alternatives to standard WIMP paradigm. 

WIMP, Randall tells me, stands for “Weakly Interactive Massive Particles,” the dominant paradigm about dark matter to this point.

—Why should everything be like our matter?
—What is mysterious is that energy stored in dark matter and ordinary matter is so similar.
—Experimental Lampposts: LHC. 

(The LHC is the Large Hadron Collider, the multibillion-dollar particle accelerator on the Swiss border that found evidence of a Higgs particle—or “something more elaborate,” as she says in the new preface to Heaven’s Door, since she believes there are some ambiguities in the evidence that the Big Discovery actually was a Higgs particle. The LHC is in the shop now, so to speak, getting retrofitted to produce even more astoundingly energized collisions of particles, which, she told me, might discover more anomalies that indicate something about dark matter.

—Waiting for higher energies, more intensity.
(Aren’t we all?)
—Don’t know yet if this lamppost in the right region.
(Meaning not Switzerland but super-subatomic infinitesimality.)
Now here’s her signal:
—Dark matter particle hits another dark matter particle and annihilates.
—Annihilation produces Standard Model [already discovered 4 percent type] particles.
—Not dark!

After that there’s a page headed, in nearly inch-high letters:

—This changes everything!

She concludes with these wry lines:

—I know what everyone wants to know is when will we see dark matter.
—Answer could be sooner—or later—than we think!

It seems fairly certain that when it happens, if it happens anytime soon, Lisa Randall will be among the first to know.
(Recent reports emerging since our talk hint at other possible dark matter observations, but Randall believes her partial interaction scenario is still salient.)

Although Randall’s work takes her thoughts into outer space, it is a question about another dimension, inner space, that she gives the most elaborate answer to during our lunch. The subject comes up near the end, as she is spearing forkfuls of my blueberry cobbler. I ask her about human consciousness—the dark matter within us—namely whether she has thought about the mind/brain question: Is the mind the product of the brain, all our thoughts neurochemically determined (as the “materialists” say), or is the mind not a slave of the physical brain, somehow capable of free will (as the “dualists” believe)? Or can we never answer that question? The philosopher Colin McGinn calls himself a “Mysterian” as an homage to the ’60s one-hit wonder band (“96 Tears”) Question Mark & The Mysterians because he thinks our consciousness may never be capable of comprehending the mystery of its own nature.

Randall seems to take McGinn’s argument as a challenge:..

Read more: http://www.smithsonianmag.com/science-nature/Lisa-Randalls-Guide-to-the-Galaxy-208338141.html?c=y&story=fullstory