Researchers say that they've discovered a new subatomic particle - one that appears to contain four quarks bound together. Physicist Sean M. Carroll describes the significance of the find, and talks about the ongoing effort in physics to explain why the universe is the way it is.
Copyright NPR. View this article on npr.org.
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I'm Ira Flatow. This week, researchers reported that they think they've spotted the tell-tale signs of a previously undiscovered, subatomic particle. This one was unusual because it appeared to be made of four quarks bound together, an arrangement they have never seen before. And they're not sure exactly how that arrangement might work.
Yes, it's that mysterious world of particle physics we like to talk about. So even with the discovery of the Higgs boson, there's a lot more to be learned about the building blocks of our universe, not to mention the weird stuff like dark matter and dark energy.
Joining me now to help us sort through all this weirdness is Sean Carroll. He's author of "The Particle at the End of the Universe" and a senior research associate in physics at the Caltech in Pasadena. Welcome back to SCIENCE FRIDAY, Sean.
DR. SEAN CARROLL: Hi, Ira.
FLATOW: This is mysterious, this thing, four quarks. Why? What's four? What's so different about that?
CARROLL: Well, the difference is just that's not what we usually see. The great thing about quarks is that they're never out there by themselves. They're never isolated. We only see quarks in combinations, and this is called confinement. You know, the quarks are confined in the bigger collections of things. But the actual combinations we see tend to be made either out of one quark and one anti-quark, which we call mesons or three quarks, which we called baryons like the proton and the neutron. Four quarks hanging out together to make a particle is not something we've seen before.
FLATOW: Do we have a name for it?
CARROLL: Yeah, the Zc-339, something ridiculous and scientific and boring like that.
FLATOW: But somebody will - now, is this for sure? Do we have to keep testing it to see if thing really exists?
CARROLL: You know, it's not for sure, but it seems pretty solid. The thing is that we say this is a particle, but to be honest, these particles don't hang around. They decay very, very quickly. And so really, what you're seeing is some temporary arrangement, you know, some fluid social grouping of quarks to get together and chat for a little while, but then they go their separate ways.
FLATOW: Tell the uninitiated what a quark is.
CARROLL: Well, you know, way back in the early 20th century, we figured out what the atom is. The atom has electrons going around on the outside, and inside, there's a nucleus. And later, we realize that the nucleus is made of protons and neutrons. Protons are these big, heavy particles of positive charge. Neutrons are big, heavy neutral particles thus the name. And then it wasn't until the '60s that people realized that the proton and neutron weren't elementary particles themselves. They were combinations of even smaller particles call quarks. This is an idea that people had.
Murray Gell-Mann here at Caltech and George Zweig pointed this out independently. But people are very, very skeptical of the idea because Gell-Mann and Zweig said, OK, if you imagine that protons and neutrons are made of quarks, we can explain all these stuff. But it looks like you'll never see a quark all by itself. And this was very contrary to how particle physics worked back in the day. You would, you know, smash things together and you'd make new particles.
But it turns out that we can actually look inside the proton and the neutron by firing high-energy particles at them. And we see that the inside of a proton is not, you know, a dense point-like thing. It's a floppy thing with many particles inside, and that's evidence that quarks are truly there.
FLATOW: Mm-hmm. Well, we had, you know, the James Joyce "Finnegans Wake" poem "Three quarks for Muster Mark". Now we have four quarks for...
CARROLL: Yeah. That was - Gell-Mann's idea was that this is a good name for them because they came in groups of three. And yes, so in principle, there can be five quarks. There was an excitement a couple of years ago about a pentaquark state that would have five quarks in it. And you know, six quarks is easy. Just take a neutron and a proton and stick them together, and you've got, you know, heavy hydrogen. That's six quarks right there.
So the reason why this is important is because even though we know, we think we know, the basic rules of quarks and gluons and the strong interactions, it's very, very difficult to go from that basic knowledge to explicit, predictive, quantitative things that you can measure. The strong interactions are strong. They're difficult to understand. So we need to collect data and find new things to realize how this stuff that is most of you and me actually works.
FLATOW: Do we need new science to take the four quarks?
CARROLL: That would be the most awesome possible result. But it seems unlikely, you know, there's no reason to think yet that we can't explain the four-quark state in terms of quantum chromodynamics, the theory that we have - that we know and love came to be in the early 1970s. But whenever you find something like this, you study it and you test its properties and you test them against your expectations...
CARROLL: ...from the theory you have, and you hope that they don't fit. If they don't fit, that means there's new physics there which is the world after.
FLATOW: Yeah, you never, you know, there are all those scientists who did not want to find anything when they turn on a - the CERN Collider that they were hoping not to find the Higgs boson 'cause that would make it more exciting than finding...
CARROLL: Well, it's more interesting. It pushes you. You know, we don't make progress by confirming our theories. We make progress by overturning our theories. That's the great thing about science.
CARROLL: If you want to win the Nobel Prize, you don't prove Einstein was right. You prove Einstein was wrong, somehow.
FLATOW: 1-800-989-8255, if you'd like to talk about particle physics. And of course, the first thing I always think of when I hear about new particles and strange things that are happening, I think about the other really strange things that are around us like the dark energy and dark matter strangeness. Would this answer anything about what the dark energy is made out of or any of the dark matter?
CARROLL: It doesn't have anything directly to do with that. But it's an indication of the kinds of things that the Large Hadron Collider is capable of. You know, there's a lot of excitement when the LHC found the Higgs boson. But that's just step one. You know, we were hoping that there's many more steps. Right now, the LHC is turned off as they're, you know, tightening the screws and upgrading things, supercharging the machine, and it's going to come back...
CARROLL: ...in 2015 with higher energies, and we're hoping to be surprised, right and left.
FLATOW: Now, I saw this - there was a new theory going around this week, to understand dark matter. I saw an article on it. Supposedly about a simple theory which means simple - only makes half my hair hurt.
FLATOW: But something about anapoles and things like that which, I thought, was that different from a magnetic monopole? I mean, it was hard to explain. Can you explain that a little for us, what this - what was happening?
CARROLL: Yeah. It's a clever idea. And I'm not sure if it's right or not or it will stand up to further scrutiny. But when we talk about dark matter, what we really want is for the dark matter to not be completely dark. That is to say, we would like to be able to detect the dark matter, either to make it at the LHC or to detect ambient dark matter particles in laboratories deep underground. And in order for that to happen there has to be some interaction between the dark matter and the ordinary matter that we know and love. The favorite kind of interaction is actually through exchanging Higgs bosons. That's why finding the Higgs boson is so important to our search for dark matter.
But the anapole dark matter idea says, you know what, it could be good old ordinary electromagnetism that could cause the interaction. And ordinarily, you just scoff at that. You say, that can't possibly be right because we would have noticed it a long time ago. If the dark matter were electrically charged, it wouldn't be dark even a little bit.
CARROLL: And what these guys have figured out is a way to give a particular kind of electromagnetic field that is actually very, very hard to notice. It's not charged. It's like a little kind of curly magnet that you really need to be very, very careful to ever find. So it's almost a little bit embarrassing that, you know, we didn't think of this sooner. You know, we - the dark matter has been there for a long time and we've been thinking about different ways it could interact for a long time. It's a great reminder that without actual data, the theories are never finished. We always have...
CARROLL: ...new ideas to come up with.
FLATOW: We have to seek Sheldon Cooper on these problems, if he can come up with it.
CARROLL: It might be beneath his notice.
CARROLL: But, yeah, I think he'd be good.
FLATOW: But I kept thinking - 'cause I've never heard the term, I mean, anapole before, is that different from a monopole?
CARROLL: Yeah. You're not alone in never having heard of the...
CARROLL: ...term anapole before. I don't remember ever hearing it myself.
FLATOW: Well, I feel a lot better.
CARROLL: They possibly made it up. I'm not quite sure.
FLATOW: They made it up.
CARROLL: You know, we're familiar with monopole, dipole, et cetera.
CARROLL: This is to say, a monopole is just a charge. Something that's sitting there and the lines of force just radiate out from it in all directions straight in straight lines, right? That's the field around an electric charge.
CARROLL: We don't think that there are, in nature, magnetic monopoles. At least we haven't found any yet. There are theoretical predictions they could exist. We haven't found an individual magnetic charge. That will be like finding a North Pole of a magnet without ever having a South Pole...
CARROLL: ...attached to it. Magnets come in dipoles. They have North and South Poles. And so this anapole idea is a new way of twisting around the electric and magnetic fields so they don't go off to infinity at all. They're just sort of curled around in a little tube-like configuration around the particle.
FLATOW: Yeah, I saw a picture of it. They said, the feel doesn't go outside of the Taurus, you know?
CARROLL: That's right.
CARROLL: Yeah. So like a little donut particle. So Homer Simpson will be very happy, if not, Sheldon Cooper.
FLATOW: I don't know. We can tell Sheldon he needs to work on it. OK, let's go to the phones. Let's go to Jamie(ph) in Morris, Michigan. Hi, Jamie.
JAMIE: Yeah, how you doing?
FLATOW: Hi, there. What...
JAMIE: I was wondering if he can explain exactly how small these are in relation to maybe the size of an atom? Like...
FLATOW: How big is a quark compared to an atom?
CARROLL: They're very small.
JAMIE: In layman's term.
FLATOW: In layman...
FLATOW: They're very, very small.
CARROLL: They're very small. So, you know, these are actually very difficult questions to answer because when you talk about elementary particles, you're in a - you're talking about things were quantum mechanics can't be ignored anymore. You know, when you talk about you and me and talk about how tall we are or how much mass we have, you can ignore the fact that the world is truly quantum mechanical and treat us as classical objects. But if you talk about an electron or a quark, there's no such luck. So from one way of thinking, an electron has zero size. It's a point-like particle. And what we mean by that is that if it weren't for quantum mechanics the electron would have zero size.
The quantum mechanics smears out that electron. And the reason why you and I have the size we do is because the atoms that we're made of have electrons in them that take up space in the atoms due to the rules of quantum mechanics. And there's this weird thing where the heavier a particle is, the less space it takes up. So something like the Higgs boson or quarks actually are smaller from the quantum mechanical point of view than something like an electron, which is relatively light.
FLATOW: There goes my hair. If I might try to translate that a little bit, that means that being an electron, it could be in different places than one spot so it's - when you look at it, it's sort of like the blur in that point.
CARROLL: Well, you know, we might as well - since this is the sophisticated truth-loving SCIENCE FRIDAY audience...
CARROLL: ...we might as well tell the truth.
CARROLL: ...which is that there is no such thing as where the electron is. You know, we sometimes talk casually, informally, incorrectly about quantum mechanics as saying you don't know exactly where the electron is but the truth is there isn't any such thing as where the electron is. There is a quantum state that tells you where you might see it if you were to look for it. And that's what smeared out over the size of the atom.
FLATOW: There you go. I'm talking with Sean Carroll, author of "The Particle at the End of Universe" on SCIENCE FRIDAY from NPR. I'm Ira Flatow talking about one of my favorite topics, which is all of this spooky stuff because we get to get really geeky, which is kind of fun.
FLATOW: Anyway, speaking of geeky, we're going to go to the phones and go to Joe in Toledo. He's going to get really geeky on us. Right, Joe?
JOE: I'm going to try.
JOE: A few years back, a surfer mathematician came up with this theory that was suppose to explain everything. And I was wondering, part of that theory was he predicted some particles that hadn't existed yet or hadn't been found yet. And I wonder if this was one of those particles. If it match up with that theory?
CARROLL: Yeah. So, you know, I hate to be that guy, but the truth is that most unified theories of everything that are proposed by amateur physicists don't turn out to fit the data when it comes right down to it.
So Garrett Lisi, who is, you know, a good guy, an amateur physicist, proposed a theory just at the theoretical level. It didn't really quite work as well as he suggested.
And there's a lot that is involved in going from a good mathematical geometric idea to the down and dirty predictions that we contest in our particle accelerators. It's not just math, there's physics involved.
And so the answer is no. I don't think that this particular theory is helped by this new particle being discovered, because this particle isn't quite well with good old fashioned standard model of particle physics. It's not new in the sense of brand new particles. It's a new grouping of the old particles.
FLATOW: Uh-huh. Just as a little bit of sidetrack today, Sean, and I just want to remark that the world of physics lost one of its big thinkers this week, Kenneth Wilson...
FLATOW: ...Nobel Prize on phase transitions. Tell us about him and why he was so important?
CARROLL: Yeah. You know, he doesn't get the public recognition. He was actually a shy kind of guy who hid away from the public and didn't write that much. But he's a Nobel Prize winner who's, you know, contribution to physics are up there with people like Stephen Hawking or Richard Feynman.
CARROLL: He was really the guy who understood quantum field theory for the first time in the 1960s and '70s. And, you know, before then we had these infinities and we figured out little tricks to get rid of the infinities.
And there was Wilson who understood that the infinities came from a place, processes at really high energies in really short distances, that we didn't even have any right to trust quantum field theory in the first place. We don't know what's going on at these incredibly tiny distances, but that's OK.
You can write down what Wilson called effective field theories that tell you what happens in experiments at low energy at accessible things and that, sort of, bundle up all the high energy phenomena in measurable quantities. So finally, quantum field theory makes sense, and we are all Wilsonians now as my colleague John Preskill put it.
FLATOW: And was he not later involved in science education reform effort?
CARROLL: Yeah. He was a very remarkable guy, not only did he helped figure out what quantum field theory is and he helped invent what we call lattice quantum field theory. He was a pioneer in using computers to do quantum field theory and to do physics more generally.
And then, later in life, he became a very strong advocate for physics education. He moved from Cornell to Ohio State and tried to improve how we teach physics to people. So, you know, deserves the accolades that he gets.
FLATOW: Getting back to our four-quark particle, when will we have a name for this thing besides - come on?
CARROLL: We will never have a name for this thing.
FLATOW: Is that right?
CARROLL: Well, you know, how many things like this we discovered? Not...
FLATOW: I don't know.
CARROLL: ...not with four particles, but, you know, with three or two quarks inside. There are hundreds of such things. We can't give them - that we've run out with Greek letters a long time ago.
Willis Lamb, who, you know, won the Nobel Prize, at his Nobel Prize acceptance speech he said, you know, it used to be if you discovered a new particle you won the Nobel Prize. These days if you discovered new particle, you should get a $10,000 fine, because there are just different ways to take all the quarks and put them together in different combinations.
So, you know, I think the - the Z sub C3390 or whatever it is called, it's perfectly appropriate humble name for this wonderful thing even if - as we hope, we learn a lot from studying it.
FLATOW: All right. And that's where we'll leave it. Thank you very, Sean, for taking time to be with us today. That was great.
CARROLL: Sure. My pleasure.
FLATOW: Sean Carroll, author of "The Particle at the End of Universe" published last year and a senior research associate in physics at the California Institute of Technology in Pasadena. Transcript provided by NPR, Copyright NPR.