The Nobel winner searching for deep-space neutrinos in Antarctica

In 2013, Frances Halzen spoke with Ira about the IceCube Neutrino Observatory. This week, Halzen won the Nobel Prize.

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  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 Halsin, 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. Halsin about his work. And I think you'll enjoy the conversation. Here's Ira.

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  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.

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  What are neutrinos? Why build a telescope a mile deep in the Antarctic ice? Well, here's a man with all the answers. Francis Halsin is the Hildale and Gregory Bright Professor in Physics Department, University of Wisconsin at Madison. Welcome to Science Friday.

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  Glad to be here.

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  Why, what are neutrinos, and why are we so interested in them?

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  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 of just another way, another form of light. And we discovered them in 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.

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  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 it took us about, since the idea to now, it took just half a century.

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  Just half a century?

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  Just half a century.

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  Yeah. Why do you build it a mile down beneath the ice, where it's absolutely dark, right?

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  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 with incredible numbers. And you would have to find these neutrinos in this rain 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.

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  Most of the radiation that can impersonate a 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.

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  Oh, it's focused at Madison?

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  Yeah.

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  The other end, the other end of the telescope looks at Madison from the South Pole?

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  That's our favorite direction.

• 4:19Speaker 02

  Well, and you've come to the right place there.

• 4:22Speaker 03

  Yes.

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  Neutrinos are really tiny, aren't they? They go through just about everything, don't they?

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  Well, they are just like light.

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  Yeah.

• 4:31Speaker 03

  And they almost travel at the speed of light. They have a small mass, but that's irrelevant in this talk. And so they are identical, except they go through walls.

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  Oh, except they go through walls?

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  Yes.

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  Well, like we know, doesn't go, light's not going through the wall, but the neutrino liked light, but is this similar that it can go through the wall?

• 4:51Speaker 03

  Yes, and they go through the Earth, and they go through our detector.

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  They go through everything just about.

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  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.

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  Huh. So you eliminate all the interference from the other particles, you hope you get to see a few neutrinos.

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  Yes.

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  Because they go through everything, and they may occasionally go through your device.

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  That's about it.

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  And what is so special about them that we want, we go through all this trouble to try to catch them? What don't we know, what do we want to know about them that we don't know?

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  Well, that's a different question. In fact, we, 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 my colleagues who built this detector, was it 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.

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  And you never expected the finisher, huh?

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  And in fact, I hope that the science is as exciting as building this thing.

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  So what, you go ahead. So as a particle physicist, you like to study the particle?

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  Well, yes. In fact, in fact, the one, we have a big international collaboration, and about one-third of my colleagues are only interested in the neutrinos themselves.

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  Right.

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  They don't care where they come from in the sky.

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  Someone else's problem.

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  Yes, exactly. And these neutrinos have about 1,000 times the energy of any neutrino we have ever produced with an accelerator. And so they may, so this is a whole other aspect.

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  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, you can detect coming from outer space.

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  Exactly.

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  And in fact, neutrinos were very mysterious for a while, didn't they? There are a lot of different kinds of neutrinos.

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  Yeah. And so, so that's the particle physics side of this, and they oscillate and do all kinds 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.

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  You know, they talk about all this, this dark energy and things that inhabit, most of the, most of the universe is made out of this dark energy. Could they be, could it be neutrinos?

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  No.

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  Okay, we've eliminated.

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  Actually, this was an excellent idea that died about 20 years ago.

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  I know, I'm always up there on the times with the latest thinking, yes.

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  On the other hand, you know, you must have by now have the idea that we just built this thing because nobody had built it before. And when you build something that nobody's 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.

• 8:23Speaker 02

  Oh, because you, ah, so you went in under the, we're going to find the dark matter stuff.

• 8:28Speaker 03

  That's right. And we are still looking, like everybody, like everybody else. Of course, dark matter exists. It's, you know, it's real as the, the table.

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  But you just can't, you just can't see it, though.

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  We just don't know what it is.

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  It holds those galaxies together.

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  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.

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  Okay.

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  And so the dark matter in the sun is concentrated in the center. And when this, 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, detect it, and then B, maybe learn something new about it.

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  How long does it take a neutrino to get from the center of the sun to the outside of the sun interior?

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  It comes immediately.

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  Immediately.

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  A photon we see, light we see from the sun, has spent like 100 million years working its way out.

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  It's 100 million years for a light to get from the center of the sun out?

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  It's something like that. It's a very long time.

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  And a neutrino just, boom, pops out.

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  Comes at the speed of light.

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  Wow. No wonder you want to study this stuff. This is very mysterious. How many kinds of neutrinos are there?

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  There are three types.

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  Three types?

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  Yes. And so, but we take any type.

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  You'll go, whatever, you build it, the neutrinos will come, is what you're saying.

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  You must know that the neutrinos we are really interested in for any of these subjects I have mentioned up to now, come about at a rate of 10 to 100 a year.

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  That's it?

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  Yes, so we know them all by name.

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  You each neutrino, you've named all the neutrinos you've discovered. Give me a couple of names.

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  No, we named them after system history characters.

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  So you have a big bird and you have a...

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  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 Bird and Ernie.

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  Wow. Who else?

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  And we find a more energetic one, you know what it will be called?

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  Cookie Monster?

• 10:59Speaker 03

  No, Big Bird.

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  Big Bird. What, it got Cookie Monster in there too?

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  In fact, it's already been used.

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  Yeah?

• 11:05Speaker 03

  No, I've lost track, actually. But it's not funny because, you know, our block of ice 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, 1 to 5,000. It's much easier when you work with a system like that. Occasionally, you want to say it was, you know, sensor number 5,120. It's much easier to remember them. We know them by name and it's the same for our neutrinos.

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  So this is a Bernie over here and it's Gilda there and it looks like Leo's not picking up anything, that sort of thing. So you actually, you anthropomorphize, I guess, or whatever the...

• 11:53Speaker 03

  Yeah, so we got two of our post-docs who named them and they promised me that they don't spend more than one hour a week on it.

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  On naming it?

• 12:02Speaker 03

  Yes.

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  This is fascinating. It's fascinating about their neutrinos. Thank you very much. Thank you very much, Dr. Housen, for taking the time to be with us today.

• 12:11Speaker 03

  Pleasure.

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  More than you've ever wanted. And now we can, can we name them, we name the neutrinos ourselves if we get new ones? Can you have a contest? We'll talk about it.

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  We'll arrange.

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  We'll arrange. Okay, we'll have a Francis Housen is the Hildale Gregory Bright Professor in the Physics Department at the University of Madison in Wisconsin.

• 12:36Speaker 01

  That interview was recorded in 2013 and was produced by the one and only Alexa Limb. And one last thing, it's Cephalopod Week, of course, and you can celebrate with a game. Sci-Fri 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 Sci-Fri all at the same time. Go to sciencefriday.com/cephalopodweek. Thank you for listening. Happy Nobel Week to those who celebrate. We will see you tomorrow. I'm Flora Lichtman.