At Long Last, The Higgs Particle... Maybe

This week physicists announced the discovery of the long-sought-after Higgs boson—or at least something that looks a lot like it. Theoretical physicist Sean Carroll explains why the tiny particle is so fundamental to our understanding of the universe, and why it took 50 years to find it.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY; I'm Ira Flatow. It's the moment physicists had been waiting for for decades, the discovery of the elusive Higgs boson or at least a particle that looks a lot like it. Some have compared the news to the splitting of the atom or discovering the structure of DNA.

But I know some of you are out there saying big deal. How does this strange thing, how does this change anything, basic science discoveries, especially of invisible things? So what? Well, maybe my next guest can change your mind. He was so excited, he had to get on a plane and make a pilgrimage to CERN in Geneva to hear the news, and he's here to tell us what this discovery could mean for the future of physics, and, who knows, our entire understanding of the universe.

Sean Carroll is a theoretical physicist at Cal Tech and author of the forthcoming book "The Particle at the End of the Universe," and it's about the search for the Higgs. He joins us from Cal Tech. Welcome back.

SEAN CARROLL: Thanks, Ira, good to be here.

FLATOW: Do you have to change the ending of your book?

CARROLL: I have to change much of my book yes, that's right, but it's in a very good way. We're all extremely excited. This is a rare event, and it's a great pleasure to be part of it.

FLATOW: Is it for sure that they have found the Higgs?

CARROLL: No, it's for sure that they have found a particle. It's for sure that this particle is Higgs-like, it does things that the Higgs boson was meant to do in some ways. It's not at all sure yet that it is the same as the simple vanilla Higgs of the standard model of particle physics.

In fact, we're all hoping that it's not. It'll be much more interesting to find something even more complicated.

FLATOW: Tell us about this vanilla Higgs. What is it for? How does it fit into our theory of the universe?

CARROLL: Well, the basic story is one of mass. Different elementary particles have different properties. There's only, you know, a handful of elementary particles that we're all made of, and each one has a specific electric charge, a specific interaction with a strong nuclear force and with gravity and also a certain mass.

And it turns out that if you look at the theories of physics that we have, that was such a success, they have so much symmetry built into them that there's an implication, namely that all of the particles they describe should be massless, should have exactly zero mass.

And that implication is patently false. So you need to do something about it. And in 1964, the year The Beatles came to America, a handful of physicists figured out a way to fix that problem, by introducing a new field into nature, a field who breaks the symmetry that is built into particle physics and by breaking that symmetry allows all the other particles to get mass.

That field is the Higgs field, and the vibrations in that field give us the Higgs boson.

FLATOW: So the experiments at CERN were able to sort of ring that field, shock the field, and out pops a Higgs?

CARROLL: That's exactly right, and in fact, that's how you make all particles in particle physics. The photon, the particle of light, is a wave in the electromagnetic field. And even things that we really think of as particles, not fields, like the electron or the up quark, these are still fields. This is just the lesson of 20th-century physics is that the world is described by quantum field theory.

So it's the Higgs field that is doing the work, giving mass to all the other particles, but it's the Higgs boson which is a vibration in that field that lets us tell the Higgs field is there.

FLATOW: So could you ring the gravitational field and have a gravity thing pop out?

CARROLL: Absolutely. I mean, at Cal Tech, we're very interested in trying to do that, and the thing is that gravity is such a weak force that you're never going to detect an individual graviton, a particle of gravity. What you could do is detect the combination of a gajillion(ph) gravitons that makes up a gravitational wave, and that's an ongoing project, looking for gravitational radiation from astrophysical sources.

FLATOW: That's an interesting project. Let's talk a little bit more about how the Higgs fits into the whole picture of the universe because one of the things - and someone tweeted us and asked on our Facebook page: If the Higgs has a field, and also the field can produce a Higgs particle, where does the energy come to make these things? Where does it come from to make the field or to make the particle?

CARROLL: Well, it's not cheap, that energy. I mean, that's why we built the Large Hadron Collider. We have a 27-kilometer ring that accelerates protons to enormous energies. They're moving at 99.9999 percent of the speed of light. And so these protons have, you know, a thousand times the energy they would have if they were just sitting still, and then they smack into each other. That's where the energy comes from.

And the whole point of a particle accelerator, a collider, is to get as much energy as you can into as small a volume as you can, and you do that by smashing these protons together, and then watching what comes out. And occasionally, what comes out is a Higgs, and that Higgs quickly decays into other particles, and that's what we detect.

FLATOW: But what is keeping the energy field around us, and it's permeating all of us, the Higgs field, correct?

CARROLL: Yeah, that's very...

FLATOW: What is keeping that working?

CARROLL: That's a great question. It turns out that the Higgs is unique among all the fields we know in that it would cost energy to keep the Higgs field at zero. It actually doesn't cost any energy at all to have it take on some non-zero value in empty space.

So when you're moving through the room, if you were flying through interstellar space, you'd be moving through Higgs field, and if you wanted to move that Higgs field back to zero, it would cost an enormous amount of energy to do that.

FLATOW: I guess, you know, in trying to think of it, taking a mental picture of it, we know that if I have a radio transmitter, and I put out radio waves, the transmitter is supplying energy to the radio waves to keep the field going. So what's supplying energy to the field in nature, the Higgs field, to keep it going?

CARROLL: Well, think about, you know, a pendulum, and a pendulum, the lowest-energy thing it can do is just to be hanging straight down, not doing anything, right? But now imagine you have an upside-down pendulum. Now - you know, so it wants to hang up, but it costs energy to lift it up and have it be hanging exactly vertically. The low-energy state of an upside-down pendulum is to be at rest, either to the left or to the right.

So the Higgs field is like an upside-down pendulum. It wants to be at some non-zero value. That's the least energy you could imagine putting into it.

FLATOW: Now, we always hear about the Higgs, we hear about the Higgs particle, but as we're talking, there could be different kinds of Higgs particles, correct? There may be other ones besides this basic one.

CARROLL: That's absolutely true, and that's going to be, you know, an ongoing project. This is not the end of the story. This is the beginning of 20 or 30 years of hard work ahead of us. If you believe in super-symmetry, which is a speculative theory moving forward, there's a very definite prediction you get from that theory, which is that there should be five Higgs bosons. So it could be we've only found 20 percent of the Higgs conglomerate.

FLATOW: There should be five of them. Do they do the same as this Higgs?

CARROLL: They do different things. There's one Higgs that is kind of giving mass to half the particles. Another one is giving mass to the other half, and a few are just flying around doing their own thing.

FLATOW: Now you...

(LAUGHTER)

FLATOW: A very interesting way of putting it. Now you said that - and I've heard this many times from physicists, that they were sort of disappointed that they found it. They'd rather have something more exotic or continue the search.

CARROLL: You know, we've only found - we've only just found it, and even in the data we already have, there are hints that are, I would say, more than just wishful thinking, strong hints that it is not the simple vanilla, standard model Higgs boson, that it is doing something a little bit different. And if so, that's a direct implication that there are more particles out there waiting for us to discover them.

FLATOW: So it may not be as simple as - you have to surf through the data a little bit more?

CARROLL: Yeah, and you need to collect more of the data. So the biggest part of the signal that we got was from the Higgs boson decaying into two photons. But photons don't have mass, which means the Higgs doesn't interact with them directly, it only interacts indirectly, by creating some other virtual particles and then having those virtual particles decay into photons.

So the interesting thing is that we got twice as many events of two photons as you would have expected if it were just the vanilla, standard-model Higgs. And that could be because there's hidden particles, hidden virtual particles that we don't yet have catalogued in the standard model that are helping increase the number of Higgs decays into two photons. And if that's true, then a new era has really just begun.

FLATOW: Of trying to figure out what those new particles are.

CARROLL: Absolutely. I mean, could they be involved with dark matter? Could they be hints of super-symmetry or of something even more exotic?

FLATOW: So dark - this is where we might find out what dark matter is made out of?

CARROLL: Yeah, one of the great things about the Higgs boson is that it likes interacting with other particles. The interactions might be very faint, but it's pretty shameless in terms of all the different particles it will interact with, especially once they have mass.

So the Higgs boson can interact with dark matter very easily. So we're hoping to look at its decays. Is there some sign that maybe it's decaying into things we can't see? Can we use it to help figure out how to detect dark matter in an underground laboratory? This is one of the most exciting implications of this new discovery.

FLATOW: So where do you go from here directly with new experiments?

CARROLL: Well, the simplest thing is that they already have extended this run of the Large Hadron Collider. They were planning on shutting it down in the fall, shutting it down for two years to upgrade the machine. And now they said, well, we can't possibly just shut it down, this is too exciting. So they're going to run it for an extra two or three months just to collect more data right now.

And going beyond that, you know, we would love to build a follow-up particle accelerator, one that, you know, once we now know that we've discovered something new, we can fine-tune the design of the next-generation machine to really learn what we can from this new particle.

FLATOW: You know, I remember 20 years ago on SCIENCE FRIDAY sitting here talking with physicists who wanted the supercollider in Texas to be built. Would it have discovered the Higgs before CERN?

CARROLL: Yes, it would very easily have started running around the year 2000 or so, it depends on, you know, construction delays, and the superconducting supercollider would actually have been at higher energy than the LHC was. So who knows what we would have discovered by now. But, you know, it's an expensive game, and it's our job as scientists to really communicate as clearly as we can the reasons why this is fundamental and exciting.

FLATOW: Is this sort of a poke in the eye to American science in that we did not build the supercollider, and it was discovered in Europe?

CARROLL: You know, my friend Lisa Randall(ph), who's been on the show, talked to Bill Clinton after he had no longer been president, once he was a former president, and he said one of his biggest regrets as president was not pushing harder to build the superconducting supercollider.

Going forward, it's going to be an international project one way or the other. No one country can do it anymore. So the next collider might be built in Japan or China. We don't know, but I'm just hoping that the United States steps up to the plate and plays at least an important role in whatever we do going to the next step.

FLATOW: All right, we're going to take a break, come back and talk lots more with Sean Carroll, author of the upcoming book - maybe he's going to push it out a little faster...

CARROLL: Yes.

(LAUGHTER)

FLATOW: "The Particle at the End of the Universe," our number 1-800-989-8255. You can tweet us @scifri, @-S-C-I-F-R-I. He's a physicist at California Institute of Technology in Pasadena. You can also tweet us @scifri, @-S-C-I-F-R-I, and go to our Facebook, where we have all kinds of - we have a Higgs boson joke. A Higgs boson walks into a bar. Give us a punch line. We'll be right back after this break. Stay with us.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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FLATOW: This is SCIENCE FRIDAY; I'm Ira Flatow. We're talking this hour about the discovery of the Higgs of Higgs-like, Higgsy, pick whatever description you like, boson. Sean Carroll is a theoretical physicist at the California Institute of Technology in Pasadena.

Sean, what would you call the other Higgs. If there are a lot of different ones, there's a Higgs-1, -2, -5, what would you - what do you call them?

CARROLL: Well, that's a great question. There were six different people that contributed to the original proposal of the Higgs boson. So maybe we could name five of them, give five of them particles named after themselves. But I think, you know, yeah, we're going to call it Higgs-1, Higgs-2, the pseudo-scaler Higgs, the charged Higgs and so forth.

FLATOW: Let's see if we can get some questions here in, because lots of people would like to talk about it. 1-800-989-8255. Let's go to Gary(ph) in Washington, D.C. Hi, Gary.

GARY: Good afternoon. There's a Buddhist principle that says that all material things are compounded. So what are the most fundamental things that we know of, and what fundamental things, those relatively fundamental things are the Higgs boson composed of? He spoke about photons, and I wonder what are those composed of.

FLATOW: OK, good questions. Is there anything inside a Higgs boson?

CARROLL: That is a good question, and, you know, the short answer is always we don't know yet. There are certainly theories that say that the Higgs boson could be what we call a composite, there could be other particles of which it is made. And there are very fun theories that go under names like Technicolor.

But we don't know, we have no evidence right now that the Higgs is anything other than simple, that it's perfectly fundamental right now, but definitely moving forward we're going to be looking as hard as we can for any evidence that it's something more complex. That would be great.

FLATOW: 1-800-989-8255. People are talking about it. Let's go to Warren(ph) in San Anselmo, California. Hi, Warren.

WARREN: Hi.

FLATOW: Hi there.

WARREN: How are you?

FLATOW: Fine, how are you? Go ahead.

WARREN: Good. My question is: With the particle collider, do they shoot a stream of protons, or how do they manage to grab just two if that's the case? It's so infinitesimally small.

FLATOW: Yeah, how do they make sure they hit each other?

CARROLL: Yeah, that's a good question. We have - you know, there's - it's not just two protons. No, in fact you have literally billions of protons moving through the LHC at any one time, half of them moving clockwise and half of them moving counterclockwise in separate pipes. And then we bring them together inside a few specific machines called the detectors.

And when they bring into collision, you have sort of one bunch of protons passes through another bunch of protons, and fireworks go off inside the detector, and you get dozens of collisions at any one moment. And then very dedicated and hardworking experimental physicists and their computer expert friends work to disentangle the individual events from all of these fireworks going off.

FLATOW: I'm glad you talked about those experimentalists who have to actually make the device that you guys predict is going to find something.

CARROLL: Yeah, yeah, no, they are the heroes of this game right now.

(LAUGHTER)

CARROLL: And in case it's not absolutely clear, I'm on the radio right now, but the people who deserve the credit for this are the people who built the LHC, built the detectors and the experimentalists who actually analyze the data, thousands of them in many different countries working for 40 years now to make this happen.

FLATOW: Because isn't - you know, there are two kinds of physicists. I, you know, I put them in the crude groups, the experimentalists and the theoretical physicists who make the predictions. And isn't it rare that an actual prediction made by a theoretical physicist is actually found by an experimental physicist, that you predict something, and you find it?

CARROLL: I like to think it's not that rare. Certainly it depends on the quality of your theory. It's much more often the case that a theorist makes a prediction, and the experimentalists prove them wrong. But, you know, when you're on the right track, you know, Einstein came up with general relativity, but no one believed it until the prediction he made for light being deflected by the sun was verified several years later.

And that's when all the excitement took off. So physics is a very experimentally-based science. Until we get the data, the evidence for something, we can't be sure it's there.

FLATOW: Is that the last time that was proven?

CARROLL: Oh no, it happens all the time. I mean, particle physics, the low-hanging fruit has been picked, and it's become harder and harder to get to the high energies that we need to discover new particles. But the reason that's true is because our theory has been so good that the particles we predict, like the W-boson, the Z-boson, the Tau-Lepton, the Bottom quark, these are all things that were predicted and then we found them, and it's a little bit less exciting.

FLATOW: Here's a tweet that came in from Alan Zephyr(ph), who says: What implications does the Higgs have for string theory, brain theory, things like that?

CARROLL: We don't know yet. It doesn't necessarily have any. It certainly narrows down the possibilities, which is crucially important when you want to move forward. It could be that string theory is not right, and the Higgs boson is nevertheless still there.

What we're hoping is that by studying the properties of the Higgs now that we've found it, we'll get a little bit more clues about other particles, and that will help us decide that if string theory is the right story what kind of string theory is responsible.

FLATOW: Is this - does this kill super-symmetry then?

CARROLL: Oh no, certainly not. It's a little bit of a tension because super-symmetry would have been happier if the Higgs had been a little bit lighter, but if the Higgs had been a little bit heavier, then super-symmetry would be very unhappy. Right now, super-symmetry is just a little bit grumpy.

We're certainly still looking for super-symmetry. It's a great theory, and it might help us explain dark matter, as well as other things that we've observed in nature.

FLATOW: Now most of the particles have sort of an anti-particle associated with them, correct? Is there an anti-Higgs?

CARROLL: There's not an anti-Higgs. It depends on the particle. Sometimes particles are essentially their own anti-particle. Like the photon doesn't have a separate anti-particle, and neither does the Higgs.

FLATOW: Here's a Twitter, a tweet that came in: Why do you think - Martin Barossman(ph) writes - why do you think Higgs bosons only attract and do not repel?

CARROLL: Well, different kinds of bosons have different kinds of forces associated with them. That's what bosons do: They push and pull on us. And it ultimately comes down to what spin they have. Different elementary particles have a fundamental property called their spin, and the graviton, for example, is a spin-two particle, and it only attracts things together.

The photon, which is a spin-one particle, can attract or repel, depending on what's going on. The Higgs boson just attracts things together. But that force is so weak, it's not really what the Higgs boson is all about.

FLATOW: Let's go to Walter(ph) in Summerville, Mass. Hi, Walter. Hi, welcome to SCIENCE FRIDAY. Are you there? I guess he dropped off. He asked a question that lots of people want to know, that you get asked all the time I'm sure, is: Are there any practical applications of this discovery?

CARROLL: Yeah, the professional physicist will soon be flying about in Higgs boson-powered jetpacks, but it might take a few more years for that to trickle down to the wider public.

(LAUGHTER)

CARROLL: No actually, the Higgs boson is more or less useless for technology in the near term. It decays very quickly. It doesn't hang around. You make one, and then in one zepto-second, it turns into other kinds of particles. That's one thousandth of a billionth of a billionth of a second. So you're not going to make a better smartphone or refrigerator using the Higgs boson.

But who knows, 50 years from now, 100 years from now, we might have very clever ideas. That's what happened with a little thing called electricity.

FLATOW: Of course it's been very difficult to unite the four forces. The three forces of nature have been united except for gravity as a quantum idea with the other four - the other three forces. Will the discovery of the Higgs do anything to unite gravity or to talk about general relativity or relativity at all?

CARROLL: Yeah, it doesn't have a direct effect. If bringing gravity into the fold of the forces that we understand on the base of quantum mechanics is a ten-step process, then maybe this is step number one. It doesn't immediately tell us anything about how gravity works.

The Higgs boson does help understand mass, and mass is one of the sources of gravity, but it's not the gravitational aspects of mass that the Higgs is responsible for. It's really just the fact that when you push on something, it resists your pushing. That's the kind of mass that the Higgs boson really takes care of.

FLATOW: And before we go, we've got about a minute left, how does the Higgs work to give something mass?

CARROLL: In a minute, yes. That's great. The Higgs fills empty space. It breaks a symmetry, the deep-down symmetry of nature that is - cannot be explained in a minute, but it's basically a symmetry between left-handed - leftward-spinning, counterclockwise particles and rightward-spinning clockwise particles.

So by hiding this symmetry, the Higgs makes the world look a little bit like it's through a funhouse mirror, makes it look a little bit different. And one of the effects of that is that particles slow down and gain mass when they move through the Higgs field that exists in empty space.

FLATOW: It's like walking through molasses or something.

CARROLL: It's a lot like that. You know, you're surrounded like a fish in water. The Higgs boson is everywhere.

FLATOW: OK, Sean, thank you very much for taking time to talk with us today. When - any new publication date for your book?

CARROLL: It was going to be January, it will now be in the fall.

(LAUGHTER)

FLATOW: Good call. Sean Carroll is a theoretical physicist at the California Institute of Technology in Pasadena, author of the forthcoming book "The Particle at the End of the Universe," which is all about the search for the Higgs particle. Thanks again for joining us today. Good luck to you.

CARROLL: Thanks, Ira.

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