Hunting the Wild Neutrino
Steve Mirsky: Welcome to the Scientific American Podcast Science Talk, posted on May 23rd, 2014. I’m Steve Mirsky. On this episode –
Ray Jayawardhana: They are connected to such a wide range of phenomenon from the subatomic to the cosmic that they could tell us a lot about the nature of matter, about what triggers exploding stars, to what the universe might have been like, the conditions within seconds after the big bang.
Steve Mirsky: That’s Ray Jayawardhana. He’s a professor in observational astrophysics at the University of Toronto. He’s also an award-winning writer, and his latest book is called Neutrino Hunters: The Thrilling Chase for Ghostly Particle to Unlock the Secrets of the Universe. He was in New York recently and dropped by Scientific American. So I’m reading your book. I’m at about Chapter 3, and I said, “Hey, this book sort of reminds me of Microbe Hunters.”
Ray Jayawardhana: Oh, yeah?
Steve Mirsky: And I look at the title, and – so did Microbe Hunters inspire you?
Ray Jayawardhana: Actually, no.
Steve Mirsky: It didn’t?
Ray Jayawardhana: I haven’t read that one.
Steve Mirsky: It’s a classic in biology in medical, the history of medical research. What’s great about your book is if you’re interested in current science, it’s fascinating, but I have a really strong interest in the history of science also, and it’s all in there, too. So just tell us what a neutrino is. I think a lot of people would like to start right there.
Ray Jayawardhana: Well it’s just a type of elementary particle, like an electron or a quark. It’s just quite different from others. Well for one thing, it’s the most common type of matter of article in the universe. So other than particles of light we call photons, it’s the next most common type of particle that exists.
Steve Mirsky: Tell me – I know it’s in the book – like how many neutrinos are passing through our bodies right now.
Ray Jayawardhana: Trillions every second.
Steve Mirsky: Trillions every second.
Ray Jayawardhana: Every second. Some of them are coming from the nuclear furnace of the sun. That’s where they’re produced, and they stream right out of the sun, come all the way through space, and pass through our bodies and pass right through the earth in most cases back into space.
Steve Mirsky: What is it you liken it to? Or somebody did like a bullet passing through fog.
Ray Jayawardhana: Yeah, bullet cutting through fog because they hardly ever interact, which is why they’re so hard to pin down and so difficult to study.
Steve Mirsky: If they don’t hit a nucleus, you’re not going to know about them.
Ray Jayawardhana: Yes, and that challenge is pretty small because they only feel what we call the weak force, the weak interaction force. That means that they are very – I call them pathologically shy. They really have a strong reluctance to mingle with other particles, which makes them antisocial and difficult to pin down, but they are connected to such a wide range of phenomenon from the subatomic to the cosmic that they could tell us a lot about many different things, many different mysteries about the nature of matter, about what triggers exploding stars, to what’s going on in the heart of the sun, to what the universe might have been like, the conditions within seconds after the big bang.
So they really cut through this wide swath in terms of the phenomenon that neutrinos have connections to. What’s more, even the neutrinos being produced in the interior of the earth because some radioactive material is in there, and that’s producing heat that’s heating the interior of our planet. The radioactive decay also produces neutrinos. We call them geo-neutrinos, neutrinos produced by the earth, and just in the last decade, scientists have detected these geo-neutrinos. So they might even allow us to understand the makeup of our own planet.
Steve Mirsky: That’s geo-neutrinos, like geothermal energy.
Ray Jayawardhana: Exactly, yeah.
Steve Mirsky: So the history of the termination of the existence and then capture of neutrinos is like a history of really big names in 20th century physics.
Ray Jayawardhana: Indeed, and some very colorful characters that I write about in the book, including some physicists who you might not have heard of, like Ettore Majorana, an Italian physicist who was this reclusive genius, really struggled with many things in his life, and disappeared without a trace at age 32. We still don’t know for sure what happened to him.
Steve Mirsky: It’s not clear. He might have jumped overboard, or he might have gone to a monastery. Nobody knows what happened to him.
Ray Jayawardhana: Exactly. There’s a lot of speculation about what happened to him, whether he jumped off a boat between Sicily and Naples, whether he might have absconded to South America, whether he got taken by the mob. There’s all kinds of stories swelling around his disappearance, so much so that people in Italy for a while were reporting Majorana sightings like Elvis sightings in America.
Steve Mirsky: And his contribution again -
Ray Jayawardhana: His contribution was to raise the question whether neutrinos and their antimatter twins behaved in identical ways or not.
Steve Mirsky: They could be the same particle except for the spin.
Ray Jayawardhana: Exactly, but do they interact with matter in identical ways or not. It’s in some ways a simple but profound idea, but it’s only now that physicists are getting to the point where they can experimentally start to test that question, to test his hypothesis, and to answer that question, and it could have very grand ramifications in terms of could neutrinos have helped the universe become dominated by matter. Because right after the big bang, there might have been equal amounts – there should have been equal amounts of matter and antimatter, and yet, today’s universe is dominated by matter. How did that asymmetry come about? That’s a very deep and difficult question, and neutrinos, the nature and the characteristics and the behavior of neutrinos, might give us some really valuable insights to get at that difficult question.
So that’s one reason that Myrana’s involvement in neutrino physics is quite important.
Steve Mirsky: One of the great things about the history of neutrino physics is how wrong some of the really big guys were, like Dirac and Hans Bethe.
Ray Jayawardhana: Indeed. Well initially, people justifiably enough thought, “How could we ever detect this particle experimentally?”
Steve Mirsky: Was it Pauli who said, “I may have proposed a particle that can’t be detected.”
Ray Jayawardhana: Indeed, Pauli —
Steve Mirsky: He was really embarrassed about having to put that forth.
Ray Jayawardhana: Exactly. I mean he took this at the time radical step of proposing the existence of a whole new particle. And remember, back then, there were only two matter particles were known. Only the electron and the proton. Not even the neutron had been identified yet when Pauli suggested the idea of a neutrino. So it was a radical step. It was to solve a growing crisis in physics, but he himself soon came to question his wisdom and wonder whether, “What have I done? I’ve proposed a particle that couldn’t be detected.”
And in fact, he bet a case of champagne that it would never be detected, and it took 25 years for physicists to finally have experimental detection of neutrinos in the early to mid 1950s.
Steve Mirsky: And detection is different from capture.
Ray Jayawardhana: We can’t really capture them because they zip right by at nearly the speed of light. So there’s no capture in the sense of putting it in a bottle. Can’t quite do that. But you can capture it. You can measure it hitting something, and then that interaction -
Steve Mirsky: Its effect.
Ray Jayawardhana: Exactly. And because they interact so rarely, you need an incredibly large volume for your detector. So whether it’s a large vat of water or dry cleaning fluid, or in the case of the latest and the biggest of neutrino detectors called ice cube, which is literally a cubic kilometer of ice at the south pole deep under the surface, that’s being dotted with these 5,000 sensors, they drill down with holes into the ice and lower the cables with these optical sensors mounted on them, and they’re buried forever now. It’s almost like launching a mission into space.
You’re not going to go back and dig them out. They’re buried deep down in the ice, but they register the flashes of light that emitted when neutrinos interact with an atom and produces a new particle called a muon as the moon—muon travels through the ice, that’s what lights it up. But it tells you when neutrino has arrived. It also tells you the direction from which it came, and it tells you something about the energy of the neutrino. So I don’t know if you followed in the news that the ice cube collaboration reported the detection of some 28 neutrinos coming from well beyond our solar system, probably well beyond our galaxy because they’re sort of the – basically, the second batch of cosmic neutrinos ever detected. The only other time we had seen neutrinos from beyond our solar system was from supernova 1987A. So this is only the second time.
It’s a big deal. It’s sort of the fledgling start of a new branch of astronomy, the neutrino astronomy. If you think about it, it took them about two years to detect these 28 neutrinos, to register them. That means you’re registering about one neutrino a month with a cubic kilometer sized detector. It just gives you some sense of how hard it is to trap them, to nail them down. So so far, they don’t have the numbers, the statistics to even tell us for sure what the sources of these really high-energy neutrinos are, but hopefully over the next few years, that’ll start to be clearer.
Steve Mirsky: And it’s the fact that they have much higher energies than other neutrinos that we know about that lets us know that they’re from a cosmic origin, probably some supernova somewhere.
Ray Jayawardhana: It is a clue that most likely, these high energy neutrinos come either from jets of particles that are accelerated by super massive black holes at the hearts of galaxies, or from really gigantic stars that explode at the end of their lives that also produce a phenomenon we call gamma ray bursts, which also might accelerate particles to very high speeds and energies. So either way, I think these cosmic neutrinos are going to give us really interesting insights about some of the most wylent corners of the universe.
Steve Mirsky: We have neutrinos coming from the sun all the time, but those are not at these incredibly high levels of energy.
Ray Jayawardhana: Indeed.
Steve Mirsky: That’s how we can discriminate among the different neutrinos.
Ray Jayawardhana: Indeed, and they’re also neutrinos produced in the upper atmosphere of the earth when cosmic rays, these energy particles, collide with atoms in the earth’s own atmosphere. You also get atmospheric neutrinos produced. They’re literally everywhere. They’re coming from underneath your feet, they’re raining down from space, they’re being produced in our own atmosphere, there’s no escape. But luckily, they don’t do much harm. They don’t do any harm, and they don’t leave much trace.
Steve Mirsky: So ice cube is the biggest neutrino detector on the planet right now. But there are a handful of others all over the world.
Ray Jayawardhana: Absolutely, and it’s one of the reasons that I wrote the book at this time is because neutrino physics is getting very exciting. There’s many more experiments than there have ever been, and you can kind of divide the experiments into three different types. One is detecting neutrinos – natural neutrinos coming from space from the sun, from exploding stars. Then there are neutrinos detectors which are measuring neutrino beams produced in accelerators. So for example, at Fermi Lab Chicago, they produced a neutrino beam which travels through the earth and is detected in a mine in Minnesota. Right?
And then there’s a third kind of neutrino detection, which is to use neutrinos that are byproduct of nuclear power plants. So you take your detector and stick it near, you know, whether there’s a nuclear power plant because a byproduct of that process is to produce neutrinos, and there are a number of those kinds of neutrino detectors as well. For example, in Diabe, in the South China Sea – in China, and also in France in a village called Shoe in France where there’s a nuclear power plant, neutrino physicists have set up their detector. So you know, naturally occurring neutrinos, byproducts of nuclear plants, and then specifically created neutrinos to be able to study them, are all being chased and hunted down by these physicists to solve the mysteries associated with them.
Steve Mirsky: And you talk about how it’s possible that because neutrinos are an inevitable byproduct of nuclear reactions, they could be used to figure out if somebody is running nuclear facilities on the sly.
Ray Jayawardhana: Exactly. It’s certainly – so neutrinos have gone from this sort of esoteric strange particles, which they still are, to people starting to think about some practical uses for them. And one of the more seriously investigated ideas is the possibility because they are a byproduct of nuclear reactors and bomb explosions and anything that involves that kind of process, that you might be able to use the fact that these neutrinos can’t really be held back. They’re going to escape. It’s not like you can stop them by surrounding the facility with thick walls or anything like that.
Steve Mirsky: They go right through.
Ray Jayawardhana: They go through any of that. So people are investing seriously, and there are some designs and perhaps one prototype for trying to use it as a way of monitoring nuclear reactor activity so that international monitors could have a new tool in their hands.
Steve Mirsky: The wildest thing you talk about is stock traders wanting to use it for communication so that they can send the information directly through the earth and get a millisecond advantage over the people who have to go around the earth with photonic -
Ray Jayawardhana: They’re looking for an extremely fast buck.
Steve Mirsky: Right. Extremely fast buck. What’s your day-to-day relationship with neutrinos?
Ray Jayawardhana: Not a lot except that I have to let them go through my body. My own research as an astrophysicist has to do with looking for and characterizing planets that orbit other stars. Like we call expo-planets, which is also a booming field, and that’s what my last book, Strange New Worlds, was about. Because that’s another very exciting area of science, and it’s a lot of fun to be a part of an endeavor that feels a little bit like the wild west where you’re making discoveries every other day, at least once a week. It’s a lot of fun. But neutrinos caught my eye as a perfect topic for a book because of the signs of neutrinos is really interesting and intriguing and fascinating, but also the colorful cast of characters involved throughout history, and also even now, the magnificent arsenal of neutrino trapping devices that have been built to study these elusive particles.
It’s quite a nice combination of very fascinating and interweaved story.
Steve Mirsky: Yeah, you’ve got direct. You go – Pauli is a major player.
Ray Jayawardhana: You’ve got Fermi.
Steve Mirsky: Fermi, Bruno Pontecorvo.
Ray Jayawardhana: Indeed.
Steve Mirsky: Really interesting guy that a lot of people probably don’t know as well as the other ones.
Ray Jayawardhana: Absolutely. So he was the guy that in the thick of the cold war tensions in 1951, you know, fled with his family to Russia and caused quite an international ruckus. Made headlines around the world because there was a lot of speculation and fear, frankly, that he might have been a Russian spy or he might have taken nuclear secrets behind the iron curtain. So there were all these very interesting characters who were fascinated by neutrinos, working on neutrinos, but also had really interesting, in some cases dramatic, life stories.
Steve Mirsky: Hans Beta had a funny quip. He had published something that turned out to be incorrect.
Ray Jayawardhana: Yeah, and he said, “You shouldn’t believe everything you read in the papers.”
Steve Mirsky: Right, in the papers. In his papers. So the bottom line for all this research is to try to really nail down a grand unified theory. Right?
Ray Jayawardhana: Well it is to understand whether what we call the standard model of physics, which accounts very well for most of the world we see around us, is that sufficient, or do we need to go beyond that in search of new physics? And because the original formulation of the standard model assigned a mass of zero to neutrinos, and now they’ve turned out to have some mass – it’s miniscule mass, but they do have – they’re not massless, is experimental evidence that maybe the standard model isn’t quite enough, and we might need to go beyond it. And that’s one of the sort of elements that tease physicists and fascinated them in terms of why study neutrinos. But there are many different reasons for studying neutrinos from the cosmic to the subatomic, and the prospect of finding new physics is among the most exciting for the physicists.
Steve Mirsky: Yeah, we always hear that hydrogen is the most abundant element in the universe, but how many neutrinos are there for every hydrogen proton?
Ray Jayawardhana: You got me. I don’t know that off the top of my head.
Steve Mirsky: You have a number in the book for every atom in the universe, so I forget what it is. It’s early on. I’ll find it in here and help the audience out after we’re—
Ray Jayawardhana: That gives you a sense of, yeah, how abundant they are. I think it was – yeah, I know where it is. I think it’s oreamas coat, I think he said.
Steve Mirsky: Yeah, it’s – why don’t we just say it’s gabillions, and I’ll nail that down.
Ray Jayawardhana: Okay.
Steve Mirsky: It’s a really fun read, and again, if you’re like me, if you like science but also the history of science, then you really can’t have more fun than reading this book. Thanks so much for coming in and being with us today.
Ray Jayawardhana: Thank you for having me.
Steve Mirsky: I’m afraid gabillions was a bit of an overestimate. From Page 9 of Neutrino Hunters, quote, “According to Hisashi Moriyama of the University of Tokyo and the University of California Berkeley, there are a billion neutrinos for every atom in the universe,” end quote. Not gabillions. I regret the lack of total recall. Also, I want to read you a paragraph from Page 125 on neutrinos and supernovas. Alex Friedland of Los Alamos National Laboratory in New Mexico explained that a supernova is in essence a, quote, neutrino bomb, end quote, since the explosion releases a truly staggering number, some ten to the 58, or ten billion trillion trillion trillion trillion of these particles.
Even as astronomical numbers go, that is an astoundingly big one. In fact, the energy emitted in the form of neutrinos within a few seconds is a few hundred times what the sun emits in the form of photons over its entire lifetime of nearly ten billion years. What’s more, during the supernova explosion, 99 percent of the precursor stars’ gravitational binding energy goes into neutrinos of all flavors while barely half a percent appears as a visible light. So there’s another example of just how mind boggling all this stuff is.
Well that’s it for this episode. Get your science news at our Web site, www.ScientificAmerican.com, where you can check out the collection of Scientific American e-books. The latest volumes in the series are titled Tomorrow’s Medicine, that’s one, and then Allergies, Asthma, and the Common Cold. That’s the other one. $4.99 each. They’re at Books.ScientificAmerican.com/SA-Ebooks, or just go to our homepage and look for books on the right side on the top. And follow us on Twitter where you’ll get a Tweet whenever a new item hits the Web site. Our Twitter name is @SciAm. For Scientific American Science Talk, I’m Steve Mirsky. Thanks for clicking on us.
[End of Audio]