“The universe presents me with a problem,” says Lindley Winslow PhD ’08, “and my job is to design the experiment that can address it.”
Sounds straightforward enough—except that Winslow, MIT’s Jerrold R. Zacharias Career Development Assistant Professor of Physics, is tackling one of the biggest problems our universe has to offer. Once and for all, she and her team want to detect dark matter.
There’s regular matter, of course—the stuff that makes up everything from sweaters to iced tea to air (i.e., solids, liquids, and gases). And then there’s dark matter, which accounts for just over a quarter of the mass in our universe… but no one’s ever seen it or touched it (that’s why physicists call it “dark”). We know it has to be out there because its gravitational influence would explain why galaxies and stars move and orbit the way they do. That is to say, the evidence that dark matter is real is only indirect; we’re able to observe its influence on the matter we can see.
Numerous physicists are working to prove dark matter’s existence, using a wide range of methods. For example, Nobel laureate Samuel C. C. Ting, MIT’s Thomas Dudley Cabot Professor of Physics, heads up a team analyzing cosmic rays captured by a large particle detector mounted on the International Space Station.
Taking a much different tack, Winslow’s experiment to directly detect the dark stuff involves creating a remarkable magnet here on Earth. The brainchild of MIT theoretical physicists Ben Safdi and Jesse Thaler and Princeton’s Yonatan Kahn PhD ’15, the magnet will be built by coiling hundreds of loops of metal wire into the shape of a doughnut that’s several inches across. Winslow will then place it in a special refrigerator, dial down the temperature to near absolute zero, and run a current through the doughnut.
With this arrangement, you’d expect a magnetic field within the doughnut only; “you should have zero magnetic field,” explains Winslow, “in the doughnut hole.”
Which means that if—and this is a big if—Winslow and her colleagues are able to measure a magnetic field in that hole, something else must be creating it. The job facing her team, which also includes MIT professors Janet Conrad, Joseph Formaggio, and Kerstin Perez, would then be to prove the “something else” is due to dark matter. The experiment, which goes by the acronym ABRACADABRA (seriously), is no simple feat. The design challenge most worrying Winslow is how to keep her doughnut perfectly still. “How do we isolate this magnet,” she asks, “from things like construction of the new building next door? These are very precise experiments where small vibrations can lead to effects that you don’t expect.”
Winslow says the process behind making a magnet to such exacting specifications relies on trying something smart, and then, when it fails (which it inevitably will), looking to see what went wrong, revising it, and trying something smarter. “We’ll build version one, and we’ll have to iterate that design again and again.” But Winslow admits that sometimes you hit a roadblock you just can’t maneuver around, which means “you have to completely scrap the design you’re working on and try a different approach.”
With the setup so delicate, the reasons for failure so abundant, and her dark target so elusive, Winslow’s experiment is no slam-dunk. But there are likely to be big payoffs along the way. For instance, by making “one of the strongest and most precisely known magnetic fields ever built,” Winslow expects the project could improve MRI technology. Of course, she’s not in this for the MRIs. Rather, Lindley Winslow is in this to cast the bright light—of a magnet pulsing with current, of iterative trial-and-error design, of sheer human ingenuity—on dark matter, that invisible something.