All fundamental particles are either fermions or bosons. Last week we talked about quarks, which are fermions. This week we’ll talk about bosons, including the famous Higgs boson, recently confirmed by the Large Hadron Collider.
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Dr. Pamela Gay: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Frasier Cain: Astronomy Cast episode 394, bosons. Welcome to Astronomy Cast, our weekly fact-based journey through the cosmos. We help you understand not only what we know, but how we know what we know. My name is Frasier Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, professor at Southern Illinois University, Everettsville, and the director of Cosmo Quest. Hey Pamela, how are you doing?
Dr. Pamela Gay: I’m doing well, how are you doing Frasier?
Frasier Cain: Doing great. We just recorded a whole new batch of videos with some great topics so if people haven’t already they should go and subscribe to the Universe Today channel over on YouTube. I’ll let you figure out how to find it. Yeah, what’s happening over there?
Dr. Pamela Gay: It goes. It’s moving into the holiday season. It is, when we’re recording this, the Monday before Thanksgiving. When you are probably getting this in the podcast feed, it is the Monday after US Thanksgiving, which is that internet shopping Monday, and so if you are one of those people that pay attention to that sort of insanity, and even if you’re not, I’d encourage you go check out astrogear.spreadshirt.com. We have Cosmo Quest and Astronomy Cast, and other random astronomy based shirts, mugs, things like that. If you’re watching live, I’m wearing my Ceres, the other former planet, which is my team Ceres shirt, so yeah, go get some astronomy stuff to inflict on everyone you love for this holiday season, whichever holiday it is that you may be choosing to celebrate or avoid.
Frasier Cain: Smooth product placement, Pamela.
Dr. Pamela Gay: I had to try. This episode of Astronomy Cast is brought to you by 8th Light Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember that’s www.8thlight.com. Drop them a note. 8th Light, software is their craft. Astronomy Cast is proudly sponsored by cleancoders.com. Training videos with personality for software professionals.
Frasier Cain: All right, all fundamental particles are either fermions or bosons. Last week we talked about quarks, which are fermions. This week we’ll talk about bosons, including the famous Higgs boson, recently confirmed by the Large Hadron Collider. Okay, so I barely understood last week, and I think this week is just going to really confuse me. But at least I think we can classify, as I mentioned, we can classify everything into fermions or bosons, fermions, quarks, I’m good, everything else, bosons, what’s a boson?
Dr. Pamela Gay: A boson is, by definition, a particle that has an integer spin, so they have a spin of zero, one, two, 10,000, that’s still an integer, we haven’t found any with that spin, but if we did it would be a boson. So to recap from last week, we talked about fermions last week, which can add up to different things, but they all have spin that is a multiple of one half, so one half, three halves, five halves, and fermions generally come in two species. There are the leptons, which are individual particles that we can encounter in real life, so there’s things like electrons, muons, which are unstable, tau particles which are unstable, but they exist, and then there’s the, refusing to interact with anything, neutrinos. These are also leptons, so you have the electron neutrino, the tau neutrino, the muon neutrino. So those are all fermions, those are all spin exactly one half. Then we have the quarks. Now the difference between the leptons is leptons are spin one half, and they have a charge of zero or minus one, and their particles have a charge of plus one. Quarks, to be weirdo freaks, have an electric charge of either two thirds or minus one third, and if it’s the anti-particle, just flip that inside out.
So yeah, weirdo charge.
Frasier Cain: Right, the charge makes almost sense to me just because we’ve done enough chemistry knowing how charges of particles come together and turn into atoms, and it makes sense that if you add two thirds and you minus one third and minus another one third then you have a neutral charge, and then if you add two thirds and then add more thirds you get a positive charge, so I think it all makes sense. But when you talk about spin, what does that mean?
Dr. Pamela Gay: It’s just an adjective that we applied to some weird quantum thing and the reason it matters is if spin is one half, and it’s not actually spinning, it’s just a word someone came up with. It’s not actually spinning, but if it has a spin, useless adjective used for historical reasons, if it has a spin ½, then poly-exclusion principle applies and these are things that insist that nothing like them can share an energy level. So these are your diva particles. If you have an energy level in an atom, that energy level can only have one spin up, and then it can also have one spin down, because those are two different things and the poly-exclusion principle says you can only have one of each of these things.
Frasier Cain: So it is not that the particle itself is spinning at any rate, it is –
Dr. Pamela Gay: It’s just an adjective to go with it.
Frasier Cain: But the point being and the poly-exclusion, principle is really important because that’s what stops necessarily them, you can’t have two particles that have the same spin in the same spot, right?
Dr. Pamela Gay: Exactly. So bosons have a spin of zero, one, two, in all practical uses that we find them, they have spins of zero, minus one, or plus one. So these integer spins, they don’t have any of these diva like characteristics to them. In fact, in bose-einstein condensates, if you lower the temperature of a conglomerate of bosons enough, all the bosons are going to try and plow themselves into a single energy level, and this is where you get really weird physics going on.
Frasier Cain: And so they’re almost doing the opposite of the poly-exclusion principle, they’re trying to get themselves into this aligned state, right?
Dr. Pamela Gay: Exactly. It’s like, “Can I be the lowest energy level? Why yes, we can all be the lowest energy level.”
Frasier Cain: Let’s all do it together. And we actually did a whole show on bose-einstein condensates, which are this strange situations that these bosons get into. But okay, so we’ve talked a bit about its fundamental kind of characteristics, about its spin, but why are these things important? Where do we find them? How do they make up? We talk about all the different particles and how the nucleus of the atom is the neutrons and the protons, so where do the bosons come in?
Dr. Pamela Gay: So the bosons come in by literally saying, “We are going to organize all of you,” and they tell everything what to do by being the force carriers.
Frasier Cain: Force carriers, okay. And so what kinds of forces are we talking about?
Dr. Pamela Gay: All the forces. They’re non-discriminatory, although they do form unions. So, you have all of the photons are like, “And we shall be the ones who mediate the electromagnetic force,” and if you have two things that are repelling each other because they have the same charge, or they’re attracting each other because they have opposite charges, or you have things that are magnetically attracting and repulsing each other. That’s all because there’s photons in there mediating that force, communicating the force between the two things that are either attracting one another or repelling one another.
Frasier Cain: Okay, so what about the strong nuclear force and the weak nuclear force? Is that bosons mediating that as well?
Dr. Pamela Gay: It is bosons all the way down. So, with the strong force, here you’re starting to look at what are called gluons, and we generally just kind of lump them all together and say “gluons,” but in reality there’s eight different gluons, and this is because, again, don’t get excited, we just used a word, it has no real good meaning, we refer to the quarks as having colors.
Frasier Cain: Oh no.
Dr. Pamela Gay: So to make things worse, we go through and start calling them things like blue and red and stuff like that. Just go with it. Just go with it. So these eight different types of gluons are there gluing the quarks together.
Frasier Cain: Right. And so I think the thing with gravity, of course, is they’ve been searching for the boson version of gravity, which would be the graviton.
Dr. Pamela Gay: Exactly. So where things get different between these different things is our photon, it actually has zero mass, which is why it can get the speed of light. That’s very exciting. And the photons conveniently have absolutely no charge, otherwise our universe would be kind of a mess, because moving charge creates magnetic and electric fields, and just imagine if all the photons were creating fields. That would be really bad. So luckily photons are out there with zero mass, zero charge, conducting the electromagnetic force. Photons are the reason your refrigerator magnets stick to your refrigerator.
Frasier Cain: So a photon is a boson that we are familiar with.
Dr. Pamela Gay: Yes. Then we also have the gluons which are conducting, mediating if you will, the strong force. They are the ones that are gluing the different kinds of quarks together, and we also refer to the way the protons stick together inside of the atom as residual color force, and so the gluons are actually just holding that whole nucleus together with that residual color force.
Frasier Cain: So I wonder how that kind of works when I think about photons, when something generates a photon, a photon moves across space, strikes my eye, you know, creates an electric current in my brain, that is the force being mediated across that distance, right?
Dr. Pamela Gay: Not quite. So this is where it gets really confusing.
Frasier Cain: Oh good, I’m glad it starts getting confusing now. Let it begin.
Dr. Pamela Gay: So I have to admit, what I tweeted in preparation for this show was, “Oh dear god, particle physics hurts.” So we experience photons on a regular basis because they’re generated by lots of different things. They’re being generated by chemical reactions in glow sticks. They’re being generated when you add electricity to gasses and it excites certain photons. All sorts of different processes generate photons, including some nuclear decay processes. And these free range photons that may eventually end up hitting our eye in a meaningful way that leads to us perceiving something, these free range photons aren’t necessarily the ones that are carrying around force. What it turns out is that refrigerator magnet that you have stuck to your refrigerator; there are what are called virtual photons going back and forth between the refrigerator and the magnet carrying all of that force around with them. And we don’t actually get to see those as light, just to be confusing.
Frasier Cain: Great, no, that makes complete sense. But they, I mean I guess these virtual photons, they move at the speed of light which is sort of, and magnetism moves at the speed of light.
Dr. Pamela Gay: Yes.
Frasier Cain: Okay great. So then how does a particle accelerator, like the Large Hadron Collider, pull some of these particles apart so you can actually say, “Ah, there is one of these bosons?”
Dr. Pamela Gay: So what’s interesting is in the colliders, it’s not pulling things apart in order to reveal these things, what its actually doing is its revealing them by creating a large blob of energy, actually a very small blob of energy, and that energy condenses out into mass. So, when you take a particle accelerator and, quite often, you will accelerate two different particles in opposite direction and smash them into each other or smash a stream of particles into a stationary target, you’re smashing things together in either case, and in the smash, you’re taking all of the kinetic energy that the accelerator has given to that particle. So we have taken, we’ve translated electricity into creating electromagnets. Those electromagnets have been done work, they’ve moved and accelerated those particles that are being accelerated whether they be positrons, electrons, protons, whatever, and then all of that kinetic energy plus the mass, so E=MC squared, gets smashed into a small region and all of that energy gets liberated and then has the chance to recombine into whatever it is that enough energy was confined to produce.
Frasier Cain: Right, however the math holds out. If I dumped a pile of Lego pieces in front of you and said, “Build whatever you can with these pieces.”
Dr. Pamela Gay: Exactly.
Frasier Cain: That is the collision of those particles, they smashed all of the energy put into them, you get an amount of mass equal to that total energy, and then however, like let’s build a Higgs Boson, we’ve got a little left over, let’s build a couple of photons, and maybe a neutron, because that’s what we’ve got, and then they’ll decay. Right?
Dr. Pamela Gay: So with the gluon, for instance and I’m looking these numbers up so I don’t screw it up. So a gluon itself has a mass that is actually zero. It is a mass zero particle, but it does have this energy and that energy, we’re able to see how it interacts with stuff. So it’s not like we are actually detecting gluons directly. We’re seeing how it all fits together, how they’re delaying and expanding different reactions. Now we luckily can start to directly detect, or at least via their decay particles, the next kind of boson which we haven’t discussed yet, which is the W and the Z bosons.
Frasier Cain: Then let us begin.
Dr. Pamela Gay: So what force are we missing?
Frasier Cain: Hold on, we talked about the strong nuclear force, so is it the weak nuclear force?
Dr. Pamela Gay: It is the weak nuclear force. So the weak nuclear force is the force that allows quarks to change identities. So, for instance, we know experimentally that a neutron left alone on a shelf is not going to stay a neutron. It is going to decay into other things. It is going to decay, the proton that gets left over is what we notice the most, but as well as the proton we have an electron go flying off and we have an anti-neutrino flying off, and this is because the electro weak force allows, via the W bosons, an up type quark to exchange with a down type quark.
Frasier Cain: Okay.
Dr. Pamela Gay: Still with me?
Frasier Cain: Yeah.
Dr. Pamela Gay: Okay, so these W bosons, which do this awesome thing we need, they are able to decay into things that we can track in accelerators. So for instance, we’ve seen positrons and electron neutrinos, this is an up quark and an anti-down quark, are another type of reaction that goes into this, and we also have a charm quark and an anti-down quark, if I’m reading these equations correctly, is another way that these can also be spotted. So you have these different combinations. There’s another combination that is a muon and a muon neutrino, or you could have an up and a strange, or anti-strange quark. There’s all of these different combinations, but they add up in specific ways where we can balance out all of the qualities, all of those color qualities, all of those spin qualities, all of those different things, and we know, “Hey, all of these things add up to the same kind of critter we’re not directly detecting,” and that critter we’ve named the W boson.
Frasier Cain: And the Higgs boson sort of falls from this, right?
Dr. Pamela Gay: Sort of.
Frasier Cain: I mean I know the W and the Zed boson were only discovered fairly recently, only in the last couple of –
Dr. Pamela Gay: Yeah, they were discovered in the ‘80s.
Frasier Cain: And so these were some of the last pieces to come together to really hold together the standard model, except for the Higgs boson.
Dr. Pamela Gay: And what’s cool is the Z boson actually gets its name from having zero electric charge, for Z is for zero, and because Stephen Weinberg said that it was the last particle needed for the standard model.
Frasier Cain: And the Ws are for the weak force.
Dr. Pamela Gay: Ws are for the weak force, and the Ws, the reason we’re saying plural, is because there’s one with a negative electric charge and one with a positive electric charge, and this is really just the particle and anti-particle, but we see them both, we refer to them to the W minus and W plus. I don’t know why, that’s just what we do. Sort of like we have electrons and positrons.
Frasier Cain: I wonder if like a particle physicist wants to just go and just re-structure the whole thing just to make it a lot more straightforward, to make quarks have charge one or negative one, to come up with new terms instead of spin and not give them colors, you know, to really like, I don’t know, like the periodic table of elements. When that was put together, it really made a lot more sense, and I think somebody needs to come back around and take a crack at re-doing particle physics entirely. So if anyone wants this job, I have a Nobel prize for you.
Dr. Pamela Gay: Well no, no, you’re just asking people to rename things, so now you sound like the French council on words. No, it’s really just a matter of in struggling to try and make it linguistically possible to talk about all of these complex particles and all of their various attributes, people grabbed at words that, well; describe normal three dimensional object, and normal three dimensional objects spin, so let’s say that electrons have spin up and spin down, and normal everyday objects have color. So, let’s just call the quarks’ weird thing that they do color force, or color charge, and the theories we have all work perfectly well, there’s just linguistic weirdnesses to them, and a lot of linguistic weirdnesses are just historical leftover echoes that electron and positron turned out to be a particle, anti-particle group, and we just ended up with the two names instead of saying the anti-electron. It’s history.
Frasier Cain: Yeah, but won’t Weinberg feel embarrassed if they find other particles after the Zed boson.
Dr. Pamela Gay: Well, and he was one of the ones that was involved in super symmetry, so if super symmetry becomes true, which is next week, then he will be the one to blame for all of the excess stupidly named particles that are in our future.
Frasier Cain: Because there’s like a whole, I mean super symmetry as a name is a whole set of particles matching all the particles that we know about way off into super symmetry and so you’re going to need to invent whole new letters.
Dr. Pamela Gay: Yes. It’s like going from normal chess to three-dimensional chess.
Frasier Cain: Right. So I mentioned briefly, where does the Higgs fit into the rest of these bosons?
Dr. Pamela Gay: So this is where we start getting into additional strange words. So when we talk about the W and Z bosons, we often call them intermediate vector bosons. I don’t know who gave them this word. Again, more adjectives, but what comes out of them being these intermediate vector bosons is they have mass. Then we have the gluon, which does not have mass, and it’s also called a gauge boson. So you have this massless, chargeless thing, versus this has mass, either does or doesn’t have charge thing, and then with the Higgs boson, you now have a scaler boson. So we have a scaler boson, a gauge boson, and an intermediate vecton boson family. The Higgs is the scaler, and the Higgs is hanging out there with a whole lot of mass and no charge whatsoever, which is again good, because gravity is kind of everywhere. The Higgs boson was needed to figure out how the heck things ended up having mass, and the explanation is that the Higgs bosons, just like your photons are going back and forth on your refrigerator holding your refrigerator magnet to the refrigerator, the Higgs bosons are going around not coupling things to the earth, not coupling anything to anything really, but what they’re doing is they’re coupling everything to this background scaler field, the Higgs field, and it’s in this coupling that the Higgs bosons are responsible for things having mass, responsible for things having the characteristics of inertia and momentum.
And the more strongly things couple with the Higgs boson, the more Higgs bosons are partnered up with something, the more mass it has, the more inertia it has, the more momentum it has as a function of how fast it’s going.
Frasier Cain: And so when you have a lot of mass, then you have a lot of Higgs bosons at the same time?
Dr. Pamela Gay: Yes, you are well loved by the Higgs bosons, yes.
Frasier Cain: Right, and when you are moving quickly –
Dr. Pamela Gay: Still just as coupled to those Higgs bosons.
Frasier Cain: But making them angry?
Dr. Pamela Gay: Well no, the Higgs bosons really don’t care. All they care about is thou shalt have momentum and inertia, and giving that to you. The way to think about it is, and this is not my own analogy, this is one that I read many many years ago, and I wish I remember what magazine it was in. I want to say it was Scientific American but I could be wrong. The initial analogy I read is it’s like a rock star with a posse. As they try and move through the room, the bigger the posse, the more people are going to turn and look at them and the harder it is going to be for them to move in general because they have to move this whole posse with them. If you have someone who is not famous and has no posse, they just move through the room. There’s nothing slowing their ability to get going.
Frasier Cain: Right, low mass.
Dr. Pamela Gay: Low inertia as well, and so the bigger your posse, the more Higgs bosons you have attached to you, the harder it is for you to get moving. Now once you’re moving, you’re cool. It’s that whole an object in motion stays in motion, an object at rest stays at rest thing. It’s the getting from the moving to the not moving, or from the not moving to the moving, where the Higgs boson really matters.
Frasier Cain: Right, okay. And so are there any sort of bosons, apart from going into the super symmetry, and I guess the graviton, right? Is the missing boson at this point.
Dr. Pamela Gay: Yeah, it’s kind of the one that doesn’t even end up on the chart except occasionally as an asterix. If the graviton does exist, and we don’t know if it does, and that’s kind of messy to think about, if the graviton does exist, it doesn’t have mass, doesn’t have charge, doesn’t have spin – well, it could have a spin one, but it doesn’t have charge, and it doesn’t have mass, and it’s out there communicating gravity the way the photon is communicating the electromagnetic force where it travels over vast distances. And it’s flying around everywhere. But we don’t know how to detect it, we don’t know if it’s required. It doesn’t necessarily seem to be required, and this makes people highly uncomfortable. And this is where you start having to think perhaps too hard, and this is one of those 4:00 a.m. semi-drunk conversations that people get into where where Einstein often encouraged people to think of gravity as the shape of space, where gravity actually distorts space, but that’s not a particle physics phenomenon.
So are we looking at two totally different paradigms or not? And this is where it’s best just not to think about it too hard unless you’re a theorist chasing down that Nobel prize, in which case don’t have more than two collaborators.
Frasier Cain: Right, and anyone who does turn up the graviton, Nobel prize.
Dr. Pamela Gay: Exactly. Again, only work in collaborations of three or fewer.
Frasier Cain: Yeah, and most of the papers coming out of the Large Hadron Collider are in the hundreds of collaborators, so it’s going to be tough. All right, so let’s see if I have this wrapped around my head. Are you ready?
Dr. Pamela Gay: No, but go ahead.
Frasier Cain: Okay, so the bosons are the particles that mediate the various fundamental forces, and so the one that we’re most familiar with, the one that’s associated with electromagnetism, is the photon. There are also, with the strong nuclear force, we’ve got the gluons, and with the weak nuclear force, we’ve got the W and the Z, bosons. These are the ones that mediate the weak nuclear force. There is no boson yet for gravity, which if it could would allow us to finally merge all of the forces together into one beautiful, put the universe on a t-shirt, theory, but that doesn’t exist and that would be the graviton, and the Higgs boson is the fundamental force that mediates mass as we understand it. How’d I do?
Dr. Pamela Gay: Yes, well it’s not really a force. Well, other than you tried to call mass a force which other than that you did great.
Frasier Cain: It is the particle that mediates mass.
Dr. Pamela Gay: Yes.
Frasier Cain: All right, so there you go everybody, so now, and just to summarize from last week, the leptons, they are the fundamental particles that create photons, neutrons, things like that, as well as the neutrinos and all of their anti-matter equivalents, and then we’ve got the bosons, that create all the particles that mediate the fundamental forces. So next week, what’s left? We said all of the things on the one hand and all of the things on the other hand, so what’s left?
Dr. Pamela Gay: What’s left is why we still have the Large Hadron Collider and the Fermi accelerator being added to and build upon, and this is trying to figure out what the heck is dark matter and how do we explain dark energy? And what are the theories beyond the standard model that people are grasping at with these instrumentation packages?
Frasier Cain: Is it possible that we only understand half, and that now with super symmetry there’s a whole other half to figure out?
Dr. Pamela Gay: It’s way bigger than half. It’s way bigger than half. It hurts.
Frasier Cain: All right, well then I think I look forward to things getting even more complicated next week.
Dr. Pamela Gay: Excellent.
Frasier Cain: Thanks Pamela.
Dr. Pamela Gay: Thank you.
Frasier Cain: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Frasier Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at email@example.com, tweet us at astronomycast, like us on Facebook or circle us on Google+. We record our show live on Google+ every Monday at 12:00 p.m. Pacific, 3:00 p.m. Eastern, or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org. If you enjoy Astronomy Cast, why not give us a donation? It helps us pay for bandwidth, transcripts, and show notes. Just click the donate link on the website. All donations are tax deductible for US residents. You can support the show for free too. Write a review, or recommend us to your friends. Every little bit helps. Click “Support the show” on our website to see some suggestions. To subscribe to this show, point your podcatching software at astronomycast.com/podcast.xml or subscribe directly from iTunes. Our music is provided by Travis Serle, and the show is edited by Preston Gibson.
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Duration: 32 minutes