I magine that you’re looking for a needle in a haystack, but you have no idea what a needle is. All you have is the name, “needle,” and a hypothesis that it’s sharp. Now imagine that there’s more than one needle—that they’re actually surrounding you, outnumbering the hay in your haystack. You know they’re all around, but you still can’t find them.
“Dark matter is strange,” Ben Brubaker says. “We can tell it’s there, but it doesn’t give off light at any frequency.” Brubaker is a PhD student in the Yale Physics department, studying under Steve Lamoreaux, an atomic physicist best known for his demonstration of the Casimir Effect—a phenomenon in which closely spaced parallel plates are driven together by so-called “quantum fluctuations”—after many years of solitary work.
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The space in which they pursue their project—referred to on the lab’s website as the Axion Dark Matter eXperiment at High Frequency, or ADMX-HF—sits past a door that warns passersby they’re approaching a strong magnetic field. Inside, it’s bracingly cold, even on an unseasonably warm autumn day, and there are no windows. But there are blinking screens, brightly colored wires and a steep staircase that leads to an underground level. There, the primary machine sits impassively, waiting to resume its task, next time with a broader range of axion parameters. Since Brubaker and Lamoreaux are in the midst of refining their process, the magnet has been removed and the delicate inner hardware revealed.
Brubaker and Lamoreaux are part of a small team searching for subatomic particles called dark matter. But even that’s too imprecise. They’re actually searching for one hypothetical particle, called an axion—which, charmingly, got its name from 1970s soap commercials and which, “if it exists, could constitute dark matter,” Brubaker says. And, just to split atoms for a moment, they’re not searching for just any old axion. They’re searching for a particular mass of axion, and if they find it, they’ll be able to answer one of the most pressing mysteries in physics.
The concept of dark matter emerged from the realization that, as Brubaker puts it, “There’s much more mass in the universe… than there is any right to be if you estimate mass based on what we can see.” Since everything made of atoms emits light and dark matter doesn’t, the natural hypothesis is that the latter is made up of “a totally new fundamental particle that inhabits most of the universe.”
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To find it, Brubaker and Lamoreaux have constructed a white cylindrical machine with brassy innards meant to make the invisible visible. It consists of three main parts: a magnet, an ultra-sensitive detector and a cooling system. “It has an enormous magnetic field—very similar to the kind of magnet you would stick your head in for an MRI,” Brubaker says, “and if dark matter is made of axions, then when an axion passes through a magnetic field, it has a very small probability of turning into a microwave photon,” which can then be detected.
But how do you find the photon you’re looking for amid an endless stream of other photons? Temperature. The entire experiment is kept extremely cold to reduce the “noise” of other photons. “A hundredth of a degree above absolute zero,” to be exact. The chilly atmosphere of the surrounding lab seems tropical in comparison. At this low temperature, the detector can register the tiny excess power created by axion conversion at a level of 10^-23 Watts—that’s a hundred thousandth of a billionth of a billionth of a Watt.
Currently, the machine is down for hardware upgrades, and while Brubaker discusses their experiment, Lamoreaux is downstairs with the apparatus, working on a way to make it even colder for their next run.
The first step of the experiment, which has taken five years to complete, has proven that the axion, if it exists, does not subscribe to the parameters they were testing. But Brubaker isn’t frustrated. “The particle’s all around us, and we just have to be sensitive enough to detect it, which means you can do this with a small team—just a few people in a University lab,” he says. “And for an experimental physicist, that means you can understand the details of the experiment very well.”
Dark matter isn’t “out there” in the way that black holes and many other mysteries of our universe are. It’s a domestic particle. It’s here, with us always, passing through you as you read this. So it would be nice to know what it is, and what it means. “There’s something else… that plays an enormous role in the history of the universe and could point us towards a more complete description of nature,” Brubaker says. “You never really know what kind of surprises are going to come out of fundamental physics research.”
Dark Matter Research at Yale’s Wright Laboratory
266 Whitney Ave, New Haven (map)
Wright Laboratory | Steve Lamoreaux Research Lab
Written and photographed by Sorrel Westbrook.
