Neutrinos are strange little things. This tiny, enigmatic particle with no charge exists in virtually every corner of the universe, but without powerfully sensitive, sophisticated instruments, physicists would have no way of knowing they exist. In fact, trillions are passing through you every second.
Physicists devise all sorts of ways to coax neutrinos into the detection range. But IceCube—which celebrates its 20th anniversary this year—stands out in particular for its unique setup: 5,160 digital sensors latched onto a gigantic Antarctic glacier. Recently, the IceCube Collaboration set the most stringent upper limits on a key statistic for ultra-high-energy neutrinos, often found inside cosmic rays. It’s also slated to receive some major technological updates later this year, which will make the detector—already one of the largest neutrino experiments on Earth—even larger and stronger than ever.
Gizmodo reached out to Carlos Argüelles-Delgado, an astrophysicist at Harvard University and a neutrino expert who’s been with IceCube since 2011, when the experiment began its physical operations in Antarctica. We spoke to Argüelles-Delgado about why IceCube is, well, in Antarctica, some highlights from the experiment’s 20-year run, and what we can expect from the forthcoming IceCube-Gen2. The following conversation has been lightly edited for grammar and clarity.
Gayoung Lee, Gizmodo: Let’s begin with the elephant in the room. Why did physicists decide Antarctica was a good place to find neutrinos?
Argüelles-Delgado: Yeah. You have a combination of two very difficult problems. You’re looking for something that’s very rare that produces very small signals, relatively speaking. You want an environment that is very controlled and can produce a large signal at a small background.
The IceCube project—kind of a crazy project if you think about it—the idea is we’re going to take a glacier about 2.5 kilometers [1.5 miles] tall, which is one of the most transparent mediums that exists on the planet. We’re going to deploy these very sensitive light sensors [called digital optical modules] that can detect single light particles known as photons. And so, you have this array of light detectors covering 1 cubic kilometer [0.24 cubic miles] of essentially pitch-dark space. When a neutrino comes from outer space, it can eventually interact with something in the ice and make light, and that’s what we see.
Gizmodo: It’s really difficult to understand what neutrinos actually are. They sound like something churned by particle physicists, but at other times they’re discussed in the context of experiments like IceCube, which searches for neutrinos from space. What exactly are neutrinos? Why does it feel like they appear in every niche of physics?
Argüelles-Delgado: That’s a good question. One reason that neutrinos appear in very different contexts—from particle physics to cosmology or astrophysics—is because neutrinos are fundamental particles. They are particles that cannot be split into smaller pieces, like the electrons. Like we use electrons in laboratories, we also use electrons in detecting physical phenomena.
Neutrinos are special because we have open questions about their behaviors and properties [and] about the universe in the highest energy regime, where we observe cosmic rays. So, observing neutrinos in a new setting on a new energy scale is always very exciting. When you try to understand something with a mystery, you look at it from every angle. When there’s a new angle, you then ask, “Is that what we expected to see? Is that not what we expected to see?”
Gizmodo: In the spirit of attempting new angles to solve mysteries, what sets IceCube apart from other neutrino detectors?
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