Humans, cars and planets are made of molecules. And molecules are made of atoms. Atoms are made of protons, neutrons and electrons. What are they made of? This is the standard model of particle physics, which explains how everything is put together and the forces that mediate all those particles.
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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 392, the standard model. 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?
Pamela Gay: I’m doing well, how are you doing Frasier?
Frasier Cain: Great. I would like to remind everybody that we actually record Astronomy Cast as a live show, so if you enjoy Astronomy Cast and you feel like, “Man, I wish I could hear Frasier and Pamela chat before they start recording the show and make a lot of mistakes with their audio and try to set things up and mess their intros, that would be cool. And also I’d love to stick around and chat with them and suggest topics and have some of my questions and have them answer it live and interact,” then you can also do that. So we stick around after we record the show and answer questions for half an hour. So every Astronomy Cast is actually an hour long but you as a podcast listener only get half of it. So you can join us live on YouTube, we post literally everywhere. We post in our twitter feed, we post it on Universe Today, so if you want to join us live, we do that every Monday at 12:00 p.m. Pacific time.
Pamela Gay: Except for today, which is Tuesday.
Frasier Cain: Except for today. We do often change the date. So just a reminder that if you want to join us live, we would love to have you join us and say hi and give us some questions and we’d love to answer them.
Pamela Gay: 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: So physicists have finally come to realize how everything is mostly connected, how electro-magnetism, the strong and weak nuclear forces, are really just aspects of the same thing, what all the particles are and how they interact. This is known as the standard model, and it’s the theory that gives us our best understanding of the underlying laws of nature, except for gravity. Don’t worry about gravity. Pay no attention to the gravity. Pamela, so the standard model. When you introduce the standard model in your classes, how do you sort of typically bring that up?
Pamela Gay: See I’m lucky, I teach the intro to physics classes, and so I don’t have to go there. It makes it quite simple. In my universe there are electrons and protons and neutrons and we avoid everything else other than the photons.
Frasier Cain: And they’re just little solar systems with little atoms zipping around in little circles?
Pamela Gay: Not quite, because I do address the fact that electron orbitals are not these perfect little ellipses like planetary orbitals, but rather are clouds of probability of this is where an electron should be. But yeah, we get to have it much more simplistic at the introductory level, which is really Newton’s physics with a little bit of Einstein thrown in, but none of this quantum mechanics.
Frasier Cain: But when you fill in for the physics teacher who is handling, for example, the standard model, do you start by just telling everybody in the class that their whole life is a lie, that everything they thought was true was not true, that what they think is matter, you know, and what they think is photons and what they think, it’s all connected in ways they can barely even imagine?
Pamela Gay: No, because that would be mean, and the reality is that the standard model doesn’t break any of our basic understandings of physics. The standard model is out there as basically a framework that you can plug all of the known particles into and, conveniently enough, it doesn’t require anything we haven’t discovered, and while there are a few things that should exist that don’t seem to fit into the existing standard model very well, like dark matter.
Frasier Cain: Gravity.
Pamela Gay: Well yes, gravity is sitting off to the side going, “Hello, I’m something else.” But for the most part, the standard model is that good, solid framework for putting together literally all the little bits and pieces of our universe within one conceptual understanding. And there’s something highly pleasing about it, because it’s this beautifully symmetric diagrammed out theory where you have different generations of particles of increasing mass and decreasing stability as you go and there’s symmetry where you have the electron and the electron neutrino and the muon neutrino. And all of these symmetries and all of these ways that seem to beautifully mirror across the different ways of having charge, of having color, of having all the different characteristics of particles, it’s just pleasing. It’s a pleasing theory.
Frasier Cain: I can just imagine what it must have been like when scientists as they were doing the math and realized that you could sort of pull out pieces and replace them and it all started to come together into one big mathematical formula, and that you’re just looking at the different objects in different ways. So what is, then, the standard model? What is your definition when you explain it to people?
Pamela Gay: Well the standard model, most simplistically, is the way that we organize the standard particles that make up our universe. It’s how we look at the way up and down quarks add up to make electrons that have their partner, the electron neutrino, and they also work together to build the proton, and so out of these two quarks. We’re able to get at all the stable things that make up our everyday interactions that you have charm and strange that add up to build the muon, and then you have the muon neutrino. Sorry, up and down do not build the electron, they build the proton, but they’re part of the family with the electron, and charm and strange are part of the family with the muon. And we just have these beautiful symmetries as we go through, and then you end up with bosons as well that are another set of partner particles, and these are the ones that carry the force that hold together these particles in all of these different ways. And it’s literally just a framework and we plug the things into the framework and the math works out and the displeasing part of it is while it’s like a puzzle that comes beautifully packaged that you dump it out on the table and you put everything together and it fits, just like there’s absolutely no reason that one puzzle should have The Hobbit on it and another puzzle should have the Mona Lisa, there’s absolutely no reason that this particular puzzle should shape out our universe.
It is filled with a bazillion, by which I mean a few dozen, constants that are just kind of, “The universe said this is what the constant should be.”
Frasier Cain: Alpha is this.
Pamela Gay: Yeah, so there’s a whole lot of, “The universe simply says this is what it should be,” that we can’t mathematically explain and that makes a lot of people really uncomfortable. They want there to be an underlying these masses must have these values because of this underlying physics and these things must have these constants because of this underlying physics, and the standard model is like, “Nope, I’m good.”
Frasier Cain: Right. Here’s the part where you multiply everything by 1.0296418, because. That’s the math. So then let’s go top down. So let’s look at, like we know that houses and trees and cars and stuff are made of molecules, and the molecules are made of atoms. And the atoms are made of?
Pamela Gay: They are made up of things called leptons. So this is where we have electrons are the stable ones that show up in atoms, and outside of the atom we also find muons and tau particles that crop up, and these are all part of that lepton family. And mediating a lot of these interactions are their partner neutrinos, the electron, muon, and tau neutrinos. So that’s that first order of stable particles.
Frasier Cain: Right, so when I think of, we think of the proton and the neutron in the nucleus and we think of the electrons in this probability shell around the – now you can’t break the electron down any further, right?
Pamela Gay: No.
Frasier Cain: It’s a fundamental particle. Okay.
Pamela Gay: No, the electron, the muon, and the tau particle are just fine where they are, and so are their matching neutrinos.
Frasier Cain: Right, and so you’ve got the, in the center of the atom, you’ve got that nucleus, you’ve got the protons and the neutrons in whatever configuration, and those can then be made up of, they’re made up of smaller particles, right?
Pamela Gay: Yes, those are made up of the quarks, and in particular, everything, again, with the symmetry of all the stable stuff, falls into the first generation of particles, those protons and neutrons are both made up of the up and down quarks. So we have up and down quarks make up the protons and the neutrons, and then in that same first generation, we have the electrons that orbit that nucleus made of protons and neutrons, and mediating the interactions we have the electron neutrino, and its anti-particle, the anti-electron neutrino.
Frasier Cain: Now when you say mediating those interactions, what does that mean?
Pamela Gay: Well, so for instance we have the decay process by which a neutron, if you try and leave it out on a shelf all by itself, it will decide, “I would rather be a proton and an electron.”
Frasier Cain: Because who wouldn’t?
Pamela Gay: Exactly, exactly. Everyone wants to be excited with charge, and a neutron is just not excited with charge. So the process by which it changes its identity from being not neutron to being a proton and an electron, you have to conserve all of the little bits, and part of conserving all of the little bits is you have an anti-electron neutrino that goes off and is taking care of things that otherwise wouldn’t be properly conserved.
Frasier Cain: And so are these, I mean when I think about these particles I kind of imagine them, they are the thing that carry, that provide these interactions, but you imagine them kind of zipping back and forth and, you know, how are they actually doing this, or do we not even know?
Pamela Gay: So the quarks are held together depending on what it is that’s being built, they’re being held together in groups of three or two or we think five now, like we think there might be some penta-quarks out there. And they’re held together, in some cases, with what are called gluons, and so inside the atom we have those protons and neutrons are held together with gluons, and so we talk about the gluon boson and we did an entire show on forces in bosons. The gluons are gluing the quarks together to form these particles.
Frasier Cain: Now is there anything that we know of that’s even more fundamental? Do we know if there’s anything that makes up quarks?
Pamela Gay: No, and in fact quarks should be, unless our theory is totally fubared, quarks should be the fundamental particle.
Frasier Cain: And so there’s nothing that makes up quarks?
Pamela Gay: Well energy.
Frasier Cain: Unless you’re a string theorist, and then you think it’s vibrating strings, but we’re not going to go there. Okay so then how do the forces, right, so those are the particles, how do the forces play into this, the strong force, the weak force, and electromagnetism?
Pamela Gay: Well it depends on exactly what the particle is. So the gluons, this is the boson that is basically holding together the quarks, and so this is part of the strong force, and the way we look at it is this is one of the stronger forces, thus called the strong force. That was a bad unintended pun that came out there. And so quarks are held together with gluons, it’s a strong force, it’s mediated by the boson when you start looking at the mathematics. Then you have the electrons and the protons, most of the time, are just acting like happy little charged particles. This is how electronics works, this is how we deal with a lot of things in everyday chemical reactions and all of these electromagnetic forces are said to be mediated by the photon, which is another type of boson that we also talk about as being light. So those are really the two big ones that I think we worry about on a day to day basis. We also have the electromagnetic force, this is where we start looking at the W and Z bosons that are mediating that. Again, we did an entire show on this.
Frasier Cain: Yeah, on photons.
Pamela Gay: Yeah, so there’s a lot of little particles but everything lines up so that we have the weak force mediated by the W and Z bosons, the electromagnetic force mediated by the photon, the strong force is mediated by the gluon. Where things go sideways, as you already mentioned, is with gravity, and a particle that currently sits outside of the standard model and may or may not exist is the graviton. So we have a word, but it hasn’t been observed and, like I said, it sits outside of this standard model that we put together.
Frasier Cain: Quantum mechanics describes, with tremendous accuracy, the movement interactions of all of these particles, but when you try to bring in gravity, if you tried to take gravity and you tried to take some of the math that works just perfect for quantum mechanics and use that in gravity, what happens?
Pamela Gay: Well, we just don’t have a theory.
Frasier Cain: You get infinities or something don’t you?
Pamela Gay: Well it’s sort of like saying it’s the color six. It’s, if you don’t have –
Frasier Cain: You can’t get there from here.
Pamela Gay: Yeah, exactly, or the sum of two and two is blue. There may be a theory for that, but we haven’t found it yet.
Frasier Cain: Right. So, now what about antimatter? How does antimatter play into the standard model?
Pamela Gay: It’s the complimentary particles, where everything was formed with symmetry, although due to asymmetries and how things decayed in the early universe, we did end up with mostly what we refer to as regular matter instead of antimatter. Regular matter and antimatter, they both have positive masses. It’s the exact same mass generally. But you end up with other differences. So the positron, which is the antimatter particle of the electron, has the opposite charge. So some of the characteristics of antimatter particles get flipped, and because of this flipping, when the matter and antimatter particles meet it tends to be rather explosive. Now this isn’t to say that every time antimatter hits regular matter you’re going to get an explosion because there are plenty of antimatter particles flying through you right now. It has to be the right type of interaction. So a positron and an electron that meet are going to annihilate one another and become a happy little burst of energy, or an unhappy burst of energy.
But that antimatter neutrino that’s flying through your body right now, your body doesn’t care.
Frasier Cain: So, we know that the matter and antimatter, all of the different forces today, all of the particles, they’re all separate and discreet things, they interact with each other but they’re their own thing, but I think the part that’s kind of most amazing to me is how cosmologists have gone back in time right to moments, with their math, right to moments before the big bang and really started to figure out how these elements, or how these different forces, came together in a more fundamental way. And when you’re right at the edge, moments after the big bang, we didn’t have the separation that we do today.
Pamela Gay: Right, and as near as theorists can tell, as the energy within a volume increases, the way the forces act starts to become more and more unified. As the energy goes up, the first thing that you see happens is the electromagnetic and the weak force become the single electro weak force.
Frasier Cain: The electro weak force.
Pamela Gay: It’s a thing.
Frasier Cain: And you can take the math for electromagnetism and kind of plug it in to the weak force and make one set of math that describes that when it’s in a locked in state.
Pamela Gay: A better way to look at it is as the energy density goes up and up and up, the way these two forces work becomes the same thing.
Frasier Cain: Right, I see. Okay.
Pamela Gay: So it’s not that you’re plugging one into the other, it’s that within the limits of the way the universe was in the first moments, both the forces are acting the exact same way and they become the same force.
Frasier Cain: And I guess why did they separate is a weird, but I mean –
Pamela Gay: Well that then becomes as the energy density goes down their behaviors differ, and we can think of this in a lot of different ways. It’s a mathematical limit. So when we use Newtonian gravity, it describes everyday life perfectly well and it doesn’t have all of those extra bits and pieces that relativity has. But if we used the relativistic equations to describe everyday life, those terms are so tiny that we get the exact same results. Now the electromagnetic and the weak forces do have different ways of existing in the low-energy regime, but as you get to higher and higher energies, it’s just the equations tend towards the exact same place.
Frasier Cain: Right, okay, okay, and so then the same thing happens with the strong force.
Pamela Gay: So at an even higher energy density at an even earlier point in the very beginning of the universe, the strong force then merges in with the electro weak force. And if you keep going back, if you keep going to higher and higher energy densities as you get to earlier earlier times in that tiniest fraction of a second after the big bang, gravity should merge in as well. Now there we’re still working on the math.
Frasier Cain: Right, and that is still, that sort of leads into my next questions which is what are the big unknowns in the standard model right now? I mean we just, and by we I mean they and by they I mean Nobel prize winning physicists, just added the Higgs boson which is sort of one of the final big pieces of the standard model. So what is still left to discover?
Pamela Gay: The way you’re describing it makes it seem like we’ve known about the standard model for a bazillion years and the Higgs boson is just something that came out of left field, and the reality is that the standard model is something that’s largely been worked on since World War II. This is largely new physics that required particle accelerator colliders to do the experiments to help us understand, “Well, there’s a whole lot more than just the proton, electron, and neutron to this universe we live in.” And in the wild heyday of coming up with all of these particle physics theories, the Higgs boson was theorized very early on. A lot of this work took place in the ‘60s and ‘70s. Now the problem was that while all six flavors of quarks had been predicted for decades and the Higgs boson had been predicted for decades, in order to create the high density of energy in one point that would allow these higher mass particles to spontaneously come into existence out of the energy, we had to build massive super-colliders. And it’s only been with the Tevatron at Fermi and Large Hadron Collider at CERN that we’ve finally been able to generate the needed energies to have these particles spontaneously come into existence out of the energy.
So Higgs is a new, fabulous measurement of something that the standard model had been predicting since before either of us were born.
Frasier Cain: Right, but I guess if that particle hadn’t been found, it would have meant there was something seriously wrong with the standard model itself, but by finding it, it really makes the standard model even more almost bullet proof at this point, but yet there are still other places, right, where it goes.
Pamela Gay: And so where the standard model leaves us going, “Well huh,” is dark matter. So there’s a particle called the axion that isn’t required by the standard model, but fits within the schema of the standard model that might help us solve the dark matter problem. It could account for 85 percent of the dark matter out there. So the standard model doesn’t leave us high and dry with dark matter, but there’s a lot of other ways of theorizing dark matter that require entirely new additions to the standard model, so you have super symmetry which ends up with each particle being just one of a giant family of particles. Dark energy also really doesn’t fit within anything. Dark energy is kind of that reality that makes everyone scratch their heads hard enough that sometimes their brains really are going to fall out, because we don’t know how to get there from here.
Frasier Cain: Right. So it’s not just gravity anymore that cause these problems for the standard model, there’s, as you said, there’s the dark matter, there’s the dark energy. Dark matter maybe fits within but that’s still, it’s like they have to keep pushing, again, we did a whole episode on super symmetry, and in fact we actually did two episodes on super symmetry. We did one and then threw it out because we weren’t happy with how well we were explaining it, and then we did a whole other episode. So when you listen to our super symmetry episode, that’s actually our second take on the entire episode. We literally got 95 percent of the way through and said, “You know what? This is just garbage. Let’s take another crack at it.”
Pamela Gay: I think in all the 400 ish episodes, we’ve only done that three times.
Frasier Cain: Yeah, and that was earlier on, and I remember that as the one, but anyway, so, we did a whole episode on super symmetry and it really is like the Higgs boson, if I remember right, the Higgs boson is like the bottom of the ladder, and super symmetry is this whole new ladder and the rungs just go, but they’re just going to take higher and higher energy to get anywhere near them to confirm dark matter.
Pamela Gay: And it starts to feel like a ladder that was built by Escher.
Frasier Cain: What do you mean by that?
Pamela Gay: So Escher paintings, where things fit together in all sorts of strange branching ways, super symmetry starts to feel like you go up one ladder and find yourself at the side of a different ladder in a different dimension.
Frasier Cain: Right. And it’s got to be frustrating for the particle physicists, or maybe it’s exciting I guess, because at this point the standard model is so complete and so, as you said, you know, you take all the puzzle pieces, you throw them on the table, you put it all together and you’re like, “Look at that, it’s like a perfect circle. It all works great,” and then you’re like, “But what about the dark matter? Where does that go? It doesn’t even fit in, and gravity is like some kind of goo. How does that come together?”
Pamela Gay: Well, so like I said, the graviton doesn’t break the standard model, it’s just not something we’ve been able to observe, and the axion maybe an answer to dark matter and it doesn’t break standard model, it’s just not required. The real issue that I think we come down to with the standard model is there’s a lot of people that just are like, “This must be wrong,” and the reason that, and wrong in the sense that Kepler’s theories of planetary motions described everything perfectly, but they had no underlying physics, and a lot of people are uncomfortable with the standard model because it has all of these constants in it that are just sort of measured and not predicted or anything else. So people really want that beautiful, elegant, underlying theory that says, “Well, we have all of these constants because of this thing, and these are all derived from this resonance,” and standard model just is. It just is. And as an observer, I’m good with that. I’m good with having a universe that is sometimes, at the most simple level, just built that way and needs a constant now and then.
But it does leave people looking for that underlying, perfect, singular unifying theory very uncomfortable.
Frasier Cain: Right, but if there were no mysteries, they would be bored, right? So I think it’s the searching for it is, I think, what keeps them entertained, not necessarily finding it. I’m sure that’s exciting, but you want to have another mystery around the corner, and fortunately the universe has no shortage of mysteries around the corner.
Pamela Gay: That’s entirely true, and while the standard model may be the Kepler’s theory of planetary motions of the particle physics world with no underlying, “Well because this,” just like Kepler’s theories were beautiful in describing how planets moved, until you got to Mercury and required relativity, the standard model works, and that’s a starting point. That’s a starting point to being able to build and do and eventually understand. So we’ll hopefully get there.
Frasier Cain: Right, and if I guess what’s next? What is the sort of cutting edge research or the theoretical work being done? Like if there were some buzz words, I mean people have heard string theory, but that’s only just one. What are some other kind of terminologies and stuff that people might have heard where people are trying to sort of search for – I guess the Einstein, the relativity’s version compared against Newtonian motion, what is the sort of next class of theory that people are trying to explore?
Pamela Gay: I think that super symmetry is really the place where people are trying to figure out is this theory real? And this, again, gets back to the building the bigger detector, because if we can get to higher and higher energies, we start to be able to produce some of the lower massed super symmetric particles that are still just out of reach of what we can do, and there’s been some tantalizing hints that maybe we’re starting to get, but the data is still really noisy. It’s like trying to watch a channel you don’t legally get on cable television. You sometimes get hints that there is a signal there, but most of the time you just get static. So we need to get to those higher energies to start to prove with meaningful signal whether or not this additional suite of particles exists. If it does, that starts to get us at an underlying theory, but it’s still a start and we’re still missing gravity, so the standard model continues to be, even with super symmetry, a theory of mostly everything but not yet everything.
Frasier Cain: Awesome. All right, well thanks Pamela. 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 firstname.lastname@example.org, 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: 33 minutes