Science Friday - The Nobel winner searching for deep-space neutrinos in Antarctica

Episode Date: October 7, 2026

It’s Nobel Prize week, and this year's prize in physics went to Francis Halzen “for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin.” The IceCube is a massive neutrino detector that covers a cubic kilometer of Antarctic ice, and looks for high-energy neutrinos coming from deep space. In 2013, Ira spoke with physicist Francis Halzen about the decision to build the IceCube at the South Pole and the challenges of constructing a map of the cosmos with neutrinos.Guest:Dr. Francis Halzen is a professor of physics at the University of Wisconsin–Madison and the 2026 recipient of the Nobel Prize in physics.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Follow our show on Instagram, TikTok, Facebook, and Bluesky @scifri and sign up for our newsletters. Got a science question that’s keeping you up at night? Call us: 877-472-4374 Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

Hey, it's Flora and you're listening to Science Friday. This week is Nobel Prize Week, and this year's prize in physics went to researcher Francis Halson, quote, for decisive contributions to the Ice Cube neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin. But way before all that excitement, back in 2013, Ira traveled to Madison, Wisconsin, and talked with Dr. Halston about his work. And I think you'll enjoy the conversation. Here's Ira. Astronomers and astrophysicists have traditionally for centuries looked upwards to the sky to learn more about the universe. We've launched telescopes into space. We have sent probes beyond our solar system to study dark matter, colliding galaxies, how the planets formed.

But there is a group of scientists that is turning its eyes downward, and I mean way down. They have built a telescope. a mile deep into the ice at the south pole. Wow, what if you have to fix that? The frozen observatory is appropriately named Ice Cube, and it's not looking for your typical star stuff, but the elusive neutrino. What are neutrinos?

Why build a telescope a mile deep in the Antarctic ice? Well, here is a man with all the answers. Francis Halzin is the Hildale and Gregory Bright Professor in the Physics Department, University of Wisconsin-Madison. and welcome to Science Friday. What are neutrinos and why are we so interested in them? Well, I think your introduction was to the point.

I mean, when we know of another way to look at the sky and at the universe, you know, we've never been able to resist it. And this was probably the hardest way to do it, and that made it a challenge. And so neutrinos, you can think of just another way, another form of light. And we discovered them in the 1956. And as they have no electric charge, they make beams just like light beams.

And so we knew we could look at the sky with them. The only problem is that we collect light with our eyes and with a mirror. Neutrinos come as elementary particles, and we know how to detect elementary particles. The only problem is that to actually look at the sky in an effective way, you had to build a kilometer cube detector. And this had never been done before. And so we took us about since the idea to now, it took just half a century. Just half a century.

Just half a century. Why do you build it a mile down beneath the ice, where it's absolutely dark, right? Well, as I said, it's a particle detector. If we build it on the surface, in fact, it's not impossible, but it would be much more complicated because the surface of the Earth is bombarded by cosmic rays. Incredible numbers. And you would have to find these neutrinos in this reign of cosmic rays and would be very challenging.

If you go a mile deep, then you have to only find one neutrino, in a million events that impersonate a neutrino. So your background is much lower. Most of the radiation that can impersonate the neutrino is shielded. And of course, the best way to shield the radiation that impersonates neutrinos is to detect them through the Earth. So our favorite way to look at the universe at the South Pole is to look at the sky above Madison. Oh, it's focused at Madison? the other end, the other end of the telescope,

looks at Madison from the South Pole? That's our favorite direction. Well, and you've come to the right place there. Nutrinos are really tiny, aren't they? They go through just about everything, don't they? They are just like light. And they almost travel at the speed of light. They have a small mass, but that's relevant in this talk.

And so they are identical, except they go through work. Oh, except they go through wall. Yes. Well, light's not going through the wall, but the neutrino-like light, but is dissimilar that it can go through the wall. Yes, and they go through the earth, and they go through our detector. They go through everything. They go through everything. And it's only occasionally that you can catch one, and that's why you have to build this big device.

So you eliminate all the interference from the other particles, you hope you get to see a few neutrinos. Because they go through everything and they occasionally go through your device. That's about it. And what is so special about them that we go through all this trouble to try to catch them? What do we want to know about them that we don't know? Well, that's a different question. In fact, I'm a particle physicist. I don't know any astronomy.

I learned very little, but I'm a particle physicist. And of course, my interest in this and of most of the, my colleagues who built this detector was a challenge at building a particle detector. In fact, after we spent 20 years on it, it came quite as a shock when it was finished, that we actually had to do something with it. You never expected to finish it. In fact, I hope that the science is as exciting as building this thing. So what, you'll go ahead.

So as a particle physicist, you like to study the particle. Well, yes. In fact, we have a big international collaboration, and about one-third of my colleagues are only interested in the neutrinos themselves. They don't care where they come from in the sky. Someone else's problem. Yes, exactly. And these neutrinos have about a thousand times the energy of any neutrino we have ever produced with an accelerator. So they may, they, so this is a number. a whole other aspect.

It's another flavor of neutrinos. In other words, the ones you build in the accelerators are just puny compared to the ones you can detect coming from outer space. Exactly. And in fact, neutrinos were very mysterious for a while, didn't they? There are a lot of different kinds of neutrinos. Yeah. And so that's the particle physics side of this. And they oscillate and do all kind of interesting things.

And so if you look at particles in a different energy range, you usually discover something new about them. And that's, of course, what we are after also. You know, they talk about all this dark energy and things that inhabit. Most of the universe is made out of this dark energy. Could it be neutrinos? No. Okay, we've eliminated.

Actually, this was an excellent idea that died about 20 years ago. I know, I'm always up there on the Times with the latest thinking. On the other hand, you know, you must have by now the idea that we just build this thing because nobody had built it before. And when you build something that nobody is built before, you usually discover something. And so it's basically a shot in the dark. But one aspect that's not a shot in the dark, which is related to your question, is that I'm now going to tell you what another third of my colleagues are doing.

the last third is actually looking at the sky. But one of the goals of this experiment, and in fact that's why we got our first meager funding 20 years ago, was because it could see dark matter. Oh, because you, ah, so when in under the we're going to find the dark matter stuff. And we're still looking like everybody else. Of course, dark matter exists. You know, that's real as the...

Yeah. The table. You just can't. You can't see it, though. We just don't know what it is. It holds those galaxies together. So we have found the hardest way of seeing it. That is, dark matter over time, as it interacts gravitationally, has been trapped in the sun.

And so the sun is actually a reservoir of dark matter. Okay. And so the dark matter in the sun is concentrated in the center. and when the dark matter particles collide, they make stuff that we know, and some of this stuff will decay neutrinos. So we are looking for neutrinos coming from the center of the sun that are made by dark matter, and that would be our way to, A, detected, and then B, maybe learn something new about it. How long does it take a neutrino to get from the center of the sun to the outside of the sun into?

It comes immediately. A photon we see, light we see from the sun, has spent like a hundred million years working its way out. It's a hundred million years for light to get from the center of the sun out? It's something like that. It's a very long time. And a neutrino just, boom, pops out. It comes at the speed of light. Wow.

No wonder you want to study this stuff. This is very mysterious. How many kinds of neutrinos are there? There are three types. Three types. Yes. And so, but we take any type. You'll get whatever.

You build it, the neutrinos will come. You must know that the neutrinos we are really interested in for any of the subjects I have mentioned up to now come about at a rate of 10 to 100 a year. That's it. Yes, so we know them all by name. You each neutrino, you've named all the neutrinos you've discovered. Give me a couple of names.

No, come on. We named them after. Sesame Street characters. So you have a big bird and you have a... Yeah, so after we ran the detector for a year, we looked at what we had, and so we found two really interesting events, and we called them Bert and Ernie.

Wow. Who else? And we find the more energetic one, you know what it will be called. Cookie Monster? No, big bird. Big bird. What, it got Cookie Monster in there, too?

Already been used. Yeah? No, I've lost track, actually. But it's not funny because, you know, our block of eyes in the South Pole has more than 5,000 light sensors in them. And they also have each a name. And you would think you would number them one to 5,000. It's much easier when you work with a system like that. Occasionally, we want to say it was, you know, sensor number 5,000.

120. It's much easier to remember them. We know them by name, and it's the same for our neutrinos. So this is Bernie over here, and it's Gilda there, and it looks like Leo's not picking up anything. Yeah. So you actually, you anthropomorphize, I guess, or whatever the... Yeah, so it are two of our postdoc who named them, and they promise me that they don't spend more than one hour a week on it. Unnamed it. Yes. This is fascinating. It's fascinating about the atrinos. Thank you very much. Thank you very much, Dr. Halson, for taking a have to be with us today.

It's more than you've ever wanted. Now we can, can we name them, we name the neutrinas ourselves if we get new ones? Can you have a contest? We'll talk about it. We'll arrange. We'll arrange. Okay. Francis Housen is the Hildale, Gregory Bright Professor, and the Physics Department

at the University of Madison in Wisconsin. That interview was recorded in 2013 and was produced by the one and only 11th. Lexa Lim. And one last thing, it's Ceplepod Week, of course, and you can celebrate with a game. SciFry teamed up with Grand Gamers Guild on an escape room card game all about the one and only chambered nautilus. Every purchase supports Science Friday, play, learn, and support SciFrii all at the same time. Go to science Friday.com slash cephalopod Week. Thank you for listening. Happy Nobel Week to those who celebrate. We will see you tomorrow. I'm Flor Lichten.