Listener Questions 39: gravitons, antimatter and unified forces!

00:00:08
Speaker 1: Hey, Daniel, how's our podcast inbox looking like? These days?

00:00:12
Speaker 2: Always filled with such great questions from curious minds, young and old, sober and less than sober. Why do we get drunk called on the podcast? No more like ideas inspired by banana peels?

00:00:26
Speaker 1: No, I see drunk with curiosity about this amazing universe? Is that what you mean? Smoking in the fumes of scientific knowledge, becoming one with the universe, high on ideas about the cosmos? Put any good ideas in there? Any interesting questions or sparks that might inform your research?

00:00:47
Speaker 2: Hmm, Yes and no. No, in that I haven't exactly been mailed any promising theories of everything yet.

00:00:54
Speaker 1: But yes, in which way.

00:00:55
Speaker 2: Well, some listeners actually have useful skills and have volunteered to help out with my recent projects. I recently published a paper together with a listener about neutron stars.

00:01:04
Speaker 1: What did you pay them?

00:01:09
Speaker 2: I paid them in knowledge about the universe?

00:01:11
Speaker 3: Man?

00:01:13
Speaker 1: Is that a yes?

00:01:14
Speaker 4: And I no?

00:01:14
Speaker 1: Also, well, so we're not only disseminating signs, we're making signs here with our listeners.

00:01:21
Speaker 2: Yeah, depending on your definition of we, you.

00:01:24
Speaker 1: Mean, like, I don't count I'm getting paid. I'm a part of it.

00:01:27
Speaker 2: Well, when you and I published a paper about neutron stars, then you can get some credit.

00:01:31
Speaker 1: We have published a couple of books to say I definitely took the credit for that. But I guess that fits the professor model. They do all the work, you get the credit.

00:01:40
Speaker 2: Everybody gets a deep puff of knowledge about the universe.

00:01:43
Speaker 1: Well, I guess you can pay them in munchies later.

00:01:45
Speaker 2: Dorito's and ding Dong's moving signs forward.

00:02:03
Speaker 1: Hi am Warham and cartoonists and the creator of PhD comics.

00:02:06
Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I make sure all of my researchers are.

00:02:12
Speaker 1: Paid in money or pats in the back.

00:02:15
Speaker 2: No, in money. I don't believe in unpaid internships, so everybody who participates and does some research definitely gets paid.

00:02:23
Speaker 1: Do you believe in summer undergrads underpaid internships?

00:02:29
Speaker 2: No, we provide funding for summer undergrads. Otherwise people who aren't independently wealthy couldn't afford to do research.

00:02:37
Speaker 1: Grad students a little underpaid. Wasn't there a big strike by grad students at the u SEE schools?

00:02:41
Speaker 2: There there was a massive strike by grad students and postdocs, and as a result, we are upping all of their salaries by a big chunk. So congrats on your successful unionization and activism.

00:02:52
Speaker 1: Which means you were underpaid them before.

00:02:54
Speaker 2: I think we're still underpaying them. I think we should pay them more absolutely.

00:03:00
Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.

00:03:05
Speaker 2: In which we try to pay it forward to the next generation of curious humans who want to understand the universe. All of science is driven forward just by people wondering and thinking and exploring the nature of the universe, and that's exactly what we do here on this podcast. We dive deep into the things that make us wonder, that make us curious, that make us ask questions about why the universe is this way and not some other way, and we do our best to answer those questions, or at least to introduce you to our current state of ignorance.

00:03:36
Speaker 1: It's right because ignorance and asking questions is how science starts and how science keeps going. Every time you answer question turnside, you feel ignorant about the next question, which you have to ask in order to try to get the answers.

00:03:48
Speaker 2: For like every four year old, we have discovered the power of the infinite Why why this? Why that? Well, why that other thing? We don't know if science is an infinite series of questions or if one day we will the answer which satisfies all of our curiosity. But until that day we can keep asking questions. And not just those of us getting paid to do science, but everybody out there asks questions and wonders about the universe and tries to figure it out. It's part of just living your life as a human being, building a model of the world around you and trying to figure out how to survive it.

00:04:21
Speaker 1: Do you think the universe gets annoyed at some point of humans asking so many pesky questions? You know, like the typical parent. At some point you want to be a good, supportive parent. But at some point it's like, because.

00:04:33
Speaker 2: I don't know, there's a lot of different ways you can go there, Like maybe the universe is set up as a mystery for us, you know. I was a guest on a podcast recently called The Universe is a video game which operates on the premise that not only is the universe a simulation, it's actively designed to be a video game, and we are basically playing it.

00:04:49
Speaker 1: Wait, like, the universe is an escape room, but if you escape the universe, where do you escape too?

00:04:54
Speaker 2: I don't know if it's an escape room, but there might be like a boss figure at some point you have to fight in the end to win the fi the knowledge of the universe.

00:05:01
Speaker 3: Mm.

00:05:02
Speaker 1: And then does it restart again basically as most Vida games do.

00:05:06
Speaker 2: I don't know, but I'd love to figure out the cheat code for the universe and like fast forward to the last level. That would be pretty fun.

00:05:12
Speaker 1: WHOA Like if you if you jump up, up, down, down, left, right, forward, backwards, do you somehow unlock some superpower?

00:05:21
Speaker 3: Mm hmm.

00:05:21
Speaker 2: But you know, there is one way in which science sort of is like a video game, except that we get to save the game. You know, when we start to understand the universe, we don't have to start from scratch the way you might when you load up a first video game. You get to start from where the last people figure it out. We are standing on the shoulders of so many giants who have understood so many things about the universe that we get to ask questions they may never even have considered.

00:05:45
Speaker 1: I feel like maybe you haven't played a Vita game since Atari. You know you can save games now, right, you can be able to do this since the Game Boy.

00:05:54
Speaker 2: I think it has been a while since I've played a classic video game. Actually, right now, I'm playing one suggested to me by a listener. It's called The Witness. You walk around an island and solve all sorts of fun geometric puzzles.

00:06:04
Speaker 1: But anyways, questions are how we move things forward, and questions is what we talk about here on the podcast, and sometimes those questions come from listeners.

00:06:13
Speaker 2: That's right. We don't just want you to be a passive participant falling asleep as we chat about the universe. We want to stimulate your curiosity. We want you to hear what we're saying, but try to fit it together in your own head so that it makes sense to you. And in that process, there might be some things that don't quite click together or that bump with other things that we told you or that you already knew. And doing physics is a process of trying to reconcile those conflicts of understanding how it can all click together into one understanding. So if you have questions about what you've heard or something else you read online, or things you're wondering about the universe banana pel inspired or not, Please write to us two questions at Danielandhorge dot com. We really mean it. We love your questions and we will respond to everybody.

00:06:57
Speaker 1: And if you make it to the next level, you get to fight dead as the final boss. Is how it works?

00:07:02
Speaker 2: Do you get to work with me on our research paper?

00:07:06
Speaker 1: Why is you they get to fight me as the final boss?

00:07:08
Speaker 2: Or maybe the universe is a game, but it's not one of those fighting or competitive games. Maybe it's one of those cooperative games.

00:07:14
Speaker 1: You know, you mean, like a like a giant citizen science project.

00:07:17
Speaker 2: Yeah, exactly.

00:07:19
Speaker 1: Wait are you saying a kademi is not competitive at all?

00:07:23
Speaker 2: Oh boy, there's a lot to dig into.

00:07:24
Speaker 1: There, don't they offer a giant price whoever discovers things first.

00:07:30
Speaker 2: It is competitive at many levels, of course, but in the end we are one community trying to unravel the nature of the universe. You do have to dangle a literal gold medal in front of some people to get them to work harder, but the goal in the end is cooperative. We do just want to understand the nature of this reality.

00:07:47
Speaker 1: Yeah, I guess you do share what you learn unless you're doing it for a company.

00:07:51
Speaker 2: I guess exactly. And so we ask questions. You ask questions, and we try to answer your questions. But sometimes people write in a really fun question that I think other people might want to hear the end to, or it just takes me a little bit of time to dig into, and so those questions get promoted to questions we talk about here on the podcast.

00:08:07
Speaker 1: Ooh, do you provide like a nice little sound effects like thing level up? Your question has leveled up plus one experience?

00:08:17
Speaker 2: I haven't yet, but I will now in the future. A great idea.

00:08:20
Speaker 1: Yeah, there you go, plus one PhD.

00:08:23
Speaker 2: Maybe I'll just sample your voice from what you just said and send that to them.

00:08:26
Speaker 1: Oh yeah, sure, I guess. I'm sure people want to listen to me more more every day. But today on the podcast, will he tackling listener questions number thirty nine? Ooh, what happens when we get to listener questions forty two? Are we going to reveal the final answer?

00:08:48
Speaker 2: We're gonna reveal the final question of everything in the universe?

00:08:52
Speaker 1: The wait The final question is forty two question mark.

00:08:55
Speaker 2: Nobody knows what the question is, right, that's the whole game. Figuring out what the question is really is a big part of science. I love that book for that reason. It's ridiculous, but it's also kind of.

00:09:05
Speaker 1: Deep, right right, Well, what if I just ask the question that comes after the answer forty two, like forty two or why forty two?

00:09:14
Speaker 2: What's forty one plus one?

00:09:16
Speaker 1: That's an answer, I guess, or that's a question exactly.

00:09:19
Speaker 2: This is like the Jeopardy version of science.

00:09:21
Speaker 1: But today we're answering questions from listeners, and we have three great ones here about gravitons, antime, matter, and the four forces and how they relate to quantum physics. So let's jump right in. Our first question is from Andres's a question about the Higgs boson.

00:09:40
Speaker 5: Hi, Daniel J.

00:09:40
Speaker 3: Jorge.

00:09:41
Speaker 5: This is Andres, and here's my question. Is the Higgs boson potentially the elusive graviton? On one hand, we have gravity as the only fundamental force without a known gouge boson, and on the other we have the Higgs boson, the boson that is not linked to a fundamental force. This is particularly intriguing given the relationship between and gravity and the fact that the Higgs field is associated with delivering master particles. Would be great to hear your thoughts on this topic. Thanks and congratulations for the success of the podcast. In the books by.

00:10:12
Speaker 1: All Right, awesome question for Andrez. We should just give them the Nobel Prize. You figured it.

00:10:16
Speaker 2: Out, ding, ding Ding. You have leveled up on dress.

00:10:20
Speaker 1: Oh, I think when you get the Nobel Prize, that's that's like the game over isn't unless unless you get to fight the ghost of Alfred Noble as the final boss.

00:10:28
Speaker 2: Well, it can't be the end of the game because some people have multiple Nobel Prizes, so you can just keep playing and keep winning.

00:10:33
Speaker 1: But don't you just play the same game? Kind of like the science doesn't get harder, does it? Once he's solved? Once you get the Nobel Prize.

00:10:41
Speaker 2: You can't just turn in the same paper and get another Nobel Prize and say, hey, this one earned me a Nobel Prize. Last time. You got to find something new. So yeah, you got to play the same game again but find a new solution.

00:10:51
Speaker 1: Well, it's still the same game. Kind of. There's some hope for winning multiple those but anyways, Andres has an interesting question. He's wondering the higgs boson is related to the graviton, because, as he said, the higgs boson is and the graviton seem related, but nobody seems to be maybe putting them in the same sentence as much.

00:11:11
Speaker 2: Yeah, it's a really fun question because Andres is doing exactly what we suggest it, which is like trying to click pieces together. If gravity doesn't have a gauge boson and the higgs boson doesn't have a force, why can't we click those things together to make a single idea? And there's a great history of that kind of thing in physics, you know, clicking together electricity and magnetism to make electromagnetism, where each one has a missing bit that compliments the other. And even the higgs boson is an example of that, people clicking the weak force together with electromagnetism and noticing, ooh, there's a hole left over where a new particle sits. So Andres's idea is in the spirit of a great tradition. In this case, they don't quite fit together in the way that he's hoping.

00:11:52
Speaker 1: Well, you just boiled the answer, should we, you know, try to dig into it? A little bit. Let's dig into it. So I guess a lot of people might not be familiar with the Higgs boson and the gravit bond, So let's break each one of them down, one at a time.

00:12:04
Speaker 2: What is the Higgs boson? So the Higgs boson is a particle, and it's a particle associated with a field that fills all of space. We call it the Higgs field. And like in the case of every particle, the particle is an excitation of that field. The field is just like a set of numbers through all of space. Every point in space has a number associated with it, and if at some point in space that number gets high, it gets excited. It's like a lot of energy there. We can call that a Higgs boson. But the exciting thing about the Higgs field is what it does to other particles. It interacts with the other particles. So other particles like electrons or top quarks that are oscillations in their own fields, as they move through space, they interact with the Higgs field, and the interaction changes how they move. So a electron flies through space differently because it's interacting with the Higgs boson, and the interaction there is very different from any other kind of interaction. Doesn't just like change the momentum of the electron the way a photon might. The higgson does something a little bit different. It makes the electron move as if it had mass. So we say the Higgs boson gives mass to particles, that's what we mean. We mean the particles move through the universe interacting with their Higgs field, and then interaction changes the way they move so that it looks as if they actually had mass. But really their mass comes from this interaction.

00:13:20
Speaker 1: So when you say like it interacts as if it has mass. For example, like the electron is just cruising along at a constant velocity, that means that it doesn't interact with the Higgs field, right, because something that is in motion, the mass tends to stay in motion, right, So for example that in that interaction nothing happens.

00:13:38
Speaker 2: Well, the true electron before it interacts with the Higgs field doesn't have any mass. The electron on its own would be massless. Like if you turned off the Higgs field in the universe, the electron would be massless. And so an electron flying through space with constant velocity that requires the Higgs boson, because otherwise it would be moving at the speed of light.

00:13:56
Speaker 1: But I guess once it gets a velocity it then it stays in that velocity.

00:14:00
Speaker 2: That's right, and that's inertia, right, we call this inertial mass. It's the property of objects to move in a straight line and to not accelerate unless a force acts on them.

00:14:09
Speaker 1: So then you're saying the interaction of the electron with the Higgs field is that it somehow the Higgs field pushes it along and keeps it going at a certain velocity.

00:14:16
Speaker 2: Or what what it does is it changes how that particle reacts to a push, Like because it has mass, it reacts differently to a force. You know, force equals mass times acceleration. So you have a particle with a lot of mass, you apply a force, it's not going to accelerate very much. If you have a particle with very very low mass, you apply that same force, it will accelerate much much more. So, the mass delivered by the Higgs boson changes how those particles will respond to a push. So if the electron had more mass, if it interacted more strongly with the Higgs field, then it wouldn't get as much acceleration for the same force. That's really what inertial mass is.

00:14:51
Speaker 1: So it sort of affects motions and pushing and pulling, but there's no force involved. I guess at least another fundamental forces are involved.

00:14:59
Speaker 2: Yeah, that's a bit of a feel plosophical point. And Dress says that the Higgs boson doesn't have a force associated with it. And you know, the Higgs boson is a boson, and the other bosons that we've talked about, like the photon, the W, the Z, the gluon, they're all associated with a force associated with electromagnetism or the weak force or the strong force. And so you can ask, like, does the Higgs boson have a force? And we don't often say that it does, but we don't really have a great reason for saying that. I mean, the Higgs boson does transfer momentum and kinetic energy the same way other bosons do. The reason we don't say it's the mediator of a force is that it's not the mediator of like a fundamental force the way electromagnetism and the weak force and the strong force are those are fundamental in a slightly different way than a force that you would associate with the Higgs boson.

00:15:46
Speaker 1: Is okay, So then the Higgs boson is a boson, but it doesn't have a force associated with it. It just kind of interacts with particles in order to give them the effect of inertia. All right, Now, let's dig into the graviton. What is the graviton or does it even exist?

00:16:01
Speaker 2: Yeah, so the graviton is a hypothetical particle. We don't know if gravity is a classical theory, meaning that it ignores quantum mechanics, or if it's a quantum theory, meaning that it respects the rules of quantum mechanics, the uncertainty, the fact that things have to be discretized. You know, you can have like one photon or seven photons, but not three point one two photons. These kinds of rules, those quantum rules apply to all of the other forces, electromagnetism, strong force, the weak force, even the Higgs field. These are all quantum theories, but gravity, so far, our theory of it is general relativity, which is not a quantum theory. But there are versions of gravitational theories that try to make it into a quantum force, to say maybe gravity isn't the curvature of space time like Einstein described. Maybe it's a quantum force like the other forces like the strong force and electroweak, et cetera. And if that's the case, it would have a boson. That boson would be called the graviton. But that's hypothetical because we haven't yet seen the graviton. Nobody's observed that it's out there that exists in our universe. It's just like, if gravity is a quantum force, there should be a boson, and this is the name of it.

00:17:11
Speaker 1: Is that necessarily true though, Like you know, it sounds like you can have a boson without a force. Can you have a force without a boson, or something like a force or that gives you the effect of a force without actually having a boson.

00:17:23
Speaker 2: It's a great question. You can't. I mean, what a force really is is the transmission of energy through a field, and that's going to come in the form of a ripple, and we can call that ripple a particle. Also, all these forces that we're talking about, these are called gauge forces, and they exist to protect some symmetry in the universe. We have a whole episode on this really interesting mathematical principle called local gauge invariance, which requires that this weird number through all of space is preserved and the forces exist in order to preserve that. So like the photon exists to preserve this symmetry in electromagnetism, and the other bosons existent that symmetry. So if we build gravity in the same way, if we make a quantum theory of gravity and require the same sort of gauge invariance that we do for the other fields, then it would have a graviton to sort of mediate that momentum and preserve the local gauge symmetry. There are other theories of quantum gravity that don't have a graviton, but they don't treat the force as a quantum theory like efforts to quantize space itself. Like loop, quantum gravity doesn't necessarily have a graviton, but theories that make gravity to a quantum force they do have a graviton.

00:18:30
Speaker 1: Oh I see, So a graviton is the particle that would transmit the gravitational quantum force, but it's maybe not necessary in order to marry quantum physics and gravity. In general relativity, you don't need the graviton necessarily.

00:18:43
Speaker 2: That's right. In some theories of quantum gravity, you have a graviton, but again it's just theoretical, like we haven't ever seen the graviton because gravity is so weak, right, gravity is so much weaker than the other forces. It's very, very difficult to observe the graviton. It would require an enormous particle accelerator.

00:18:59
Speaker 1: All right, well, now let's dig into Andres's real question, which is, could the Higgs boson be the graviton with it all make it click together and win a noble price or two. So let's dig into that, but first let's take a quick break. All right, we're answering listener questions here today, and our first question came from Andres, who asked, is the Higgs boson the graviton? Which is a really tantalizing question, And so we talked about what the Higgs boson is and what the graviton is or could be, and so now the question is are they the same? And it sort of sounds like maybe the answer is no, because we talked about how the Higgs boson is about inertial mass, but the graviton is about gravity, and those two things are not necessarily the same.

00:19:50
Speaker 2: Yeah, it's tempting to group them together in your mind because they both do seem to be related to mass, but that doesn't mean that they actually play the same role. Right, So, as you say, the Higgs boson gives you inertial mass, but it's actually not the only source of inertial mass. It doesn't have a monopoly on giving mass to things. Remember that mass is just a measure of how much internal stored energy there is in something, and that energy can come from interactions with the Higgs field, but it can also come in other ways. It can come from other fields. Like the proton is made of quarks, and those quarks have very very small masses, but the proton is really massive. Most of the mass of the proton doesn't come from the mass of the quarks that make it up, but from the energy in the strong force that binds those quarks together, and so it's mostly that stored energy. So the Higgs boson does have a relationship with mass, but not a monopoly on it. There are other ways to get mass, so mass is sort of independent from the Higgs mechanism itself.

00:20:49
Speaker 1: How do the other kinds of masses get inertia, then we have no idea.

00:20:53
Speaker 2: Right, yeah, exactly. We say that the Higgs field interacts with these particles and so it sort of stores internal energy. Why internal stored energy leads to inertia is sort of a deeper mystery, right, And you alluded to it earlier when you talked about the difference between inertial mass and gravitational mass. And in Newton's time that was a mystery. We had the inertial mass, which was m in f equals ma that told us how things responded to pushes, and then we had the gravitational mass in his gravitational formula. And according to Newton, these are two different concepts, and it was sort of miraculous that everything seemed to have the same inertial and gravitational mass. Einstein tells us that those two things are the same concept, and that's basically his whole theory of gravity, that acceleration due to gravity really is inertial motion, and there is no gravitational force, there is no gravitational mass. There's just the inertial mass, and things move through space because space is curved and all that good stuff. So general relativity sort of unifies those two concepts.

00:21:50
Speaker 1: So then why couldn't the graviton be the Higgs because the graviton is about gravity and not inertial mass.

00:21:55
Speaker 2: Yeah, exactly, the graviton doesn't give inertial mass to objects. You know, the graviton in this case would sort of like bend space. Sort of weird. You have a quantum theory with emitted particles, and then those particles themselves are responsible for curving space, so you have like quantum field theory on curved space, but that can affect massless particles. So for example, gravity has effect on massless particles like photons. Gravity bend space, right in Einstein's theory of relativity, masses bend space. I mean, even in a quantum version of gravity, you would have to bend space with these gravitons and photons moving through that bend space will curve, and so there's no involvement of the Higgs boson there at all. There's no inertial mass on these objects, and yet they still do move through curved space. So gravity does things that the Higgs boson can't do.

00:22:43
Speaker 1: All right, So then I guess the answer is that it's not the same thing gravity and inertia. So then the Higgs boson can't be the graviton or is that still possible.

00:22:51
Speaker 2: No, it's not still possible. I mean there is a close connection between gravity and inertia and general relativity. But you can again have gravitational effects on objects with no MA, and you can have mass even if there wasn't gravity. Like an electron flying through totally empty space, as you said earlier, is still going to have inertia even if it doesn't feel the gravity of anything. So these really are separate concepts and require separate particles.

00:23:15
Speaker 1: It is pretty fascinating to think that quantum mechanics, like this huge theory that we have totally disregards or doesn't take gravity into account, like gravity as far as quantum mechanics knows, gravity doesn't exist, right.

00:23:27
Speaker 2: Yeah, that's right. Our quantum field theory that describes these other forces can't really grapple with gravity. I mean, we can do quantum field theory in curved space. If you have a reason why space is curved, you can do those calculations. But we don't know how to make gravity into a quantum theory. Like we have this idea of a graviton, but when you do the calculations and quantum theory, everything blows up and you get nonsense answers. So we don't know how, like mathematically, how to build a quantum theory of gravity. Yet it's a huge open area of research.

00:23:54
Speaker 1: All right, So then the answer under this is not really Unfortunately game over for you. You have to start over. Can you at least send them another quarter or something?

00:24:02
Speaker 2: Yeah, you get three more lives undress.

00:24:08
Speaker 1: That's moore than most of us get. I guess my last question is you know, if you beat the Higgs boson, do you then get to the final boss on?

00:24:17
Speaker 2: Nice? I can't believe you didn't see that coming.

00:24:21
Speaker 1: All right, well, let's get to our next question, and this one comes from Richard, and it's about matter and antimatter.

00:24:27
Speaker 4: I have a question regarding how particles are assigned to the matter versus antimatter categories. In popular science, matter and antimatter are defined as opposites with the same properties but opposite charges. But that does not indicate how to determine which of a pair of opposites is matter and which is antimatter. For a single particle, the distinction is arbitrary, but not for a group. If the categories of matter or antimatter have some relational meaning between the particles. For instance, suppose tomorrow we discovered two new particles X and Y, which are identified as matter antimatter pairs. How would physicists decide which of these particles is categorized with the other matter particles and which are to be categorized as antimatter. I've heard you speak about the asymmetry of the week fourth with respect to how it interacts with left or right handed particles differently from matter than antimatter. So would this be the determining factor? What if a particle did not interact with the weak force? Is there something more basic in the standard model which determines this. A related question is whether or not there is any flexibility in the way we categorize the currently known particles. For instance, can we flip the quarks matter antimatter categories so an adam would consists of a quote unquote antimatter nucleus and a matter set of electrons Or would this lead to a complication in other Standard model rules which would seem less elegant and simple.

00:25:50
Speaker 1: All right, awesome question from Richard. I feel like he wrote out a whole thesis here for us. Does he get an automatic Noble Prize?

00:25:57
Speaker 2: Maybe he gets the anti Nobel Prize for sending an answer instead of a question.

00:26:01
Speaker 1: Ooh, I want an anti Nobel prize. What do I anti have to do?

00:26:05
Speaker 2: I don't know. But when you get it, don't let it touch your Nobel Prize.

00:26:08
Speaker 1: I think we're safe from that because I don't have one. But it's an interesting question about matter and antimatter, I guess basically his question is why do we call some things matter and something's antimatter? Like how do we know if you find a new particle whether you should call it a matter particle or an antimatter particle.

00:26:27
Speaker 2: Yeah, it's a great question. I love this. He's wondering, like how we built these ideas and how much freedom is there really? And are these choices arbitrary or are they required by some other sort of mathematical structure. Great question.

00:26:39
Speaker 1: Cool, So let's dig into it, Daniel, what is antimatter?

00:26:42
Speaker 2: So it turns out that for every kind of particle that we know about electron, a core, commuon, there's another kind of particle that can exist in the universe that's very, very similar to that particle. Except that it has the opposite quantum numbers. So if you have a particle with negative one charge, it's anti particle has positive oid charge. And if it's a particle with red color for the strong force, there's another version of it with anti red color, for example. So all the quantum numbers of the particle, the charges, for example, associate with each of the forces, so charge, weak, hypercharge, strong color are flipped for the anti matter particle. And so this is something that the universe can do. It's like a feature of the universe, but it's not something that exists very often, like the stuff that we see around us is all made of matter. I'm made of matter, you're made of matter. But this is something the universe has the capacity for, even if it doesn't exist very often in reality.

00:27:40
Speaker 1: Now, are those the only quantum numbers, because is in like spin quantum number. You can flip that and not get antimatter, right.

00:27:46
Speaker 2: That's right. But an electron can have like positive or negative spin, so it's not like an inherent property of the electron to be positive or negative, and positrons, the anti particle of the electron can also have positive or negative spin, and the kind of spin they can have is the same. Like both of them are spin one half particles, meaning they're fermions. So that's not different between matter and antimatter. The spin structure is the same.

00:28:09
Speaker 1: Okay, I guess I'm just saying, like the difference between matter and antimatter is if you flip some of the quantum numbers, specifically I guess the ones that you would call charge, right, like electrical charge in terms of the forces.

00:28:21
Speaker 2: Yes, exactly, you flip the charges of the particle.

00:28:24
Speaker 1: Which are sort of the numbers associated with forces.

00:28:27
Speaker 2: Right exactly. And interestingly, you don't flip the mass, Like the positron doesn't have negative mass, and you might think it would if gravity was also a quantum force and you thought of mass as like the charge in a gravitational force, but you don't, and gravity we don't know if it's a quantum force. But anyway, positron and an electron have the same.

00:28:47
Speaker 1: Mass, although it is possible, right, I mean, theoretically it is possible for something to have negative mass, right kind of like the theories don't prevent it, which has never seen it.

00:28:57
Speaker 2: Well, we don't fundamentally understand what mass is. As we said, Earth and there are some theories of negative mass particles, though that raises all sorts of other complicated issues, But we did a whole podcast about that, so people who are curious about negative mass particles dig into that. But in our universe, we've never seen any negative mass particles, and the antimatter particles we have seen all do have positive mass, though we don't actually know what the gravitational force is on antimatter. We recently did a podcast episode about that, whether antimatter falls up or down, it might have positive mass but repulsive gravity. That would be fascinating, all right.

00:29:33
Speaker 1: But in general, if you have a particle and you flip all of its charges to charge the hypercharge and the color, then you get the anti matter version of that particle. That's kind of the rule, or that's kind of what the anti matter is exactly.

00:29:48
Speaker 2: And it's part of this beautiful trend in the universe that we have these symmetries, Like the universe doesn't just have like, oh, here's a kind of particle, there's a kind of particle. It seems to like to reflect each kind of particle in multiple ways, Like the electron has the muon version of it, it also has the antimatter version of it. So there's these weird reflections of each particle. It can exist in multiple ways, which might be like hints about what's going on inside these particles. Why there are these symmetries. We just don't really understand it.

00:30:18
Speaker 1: A little bit like how the proton is a plus one charge and the neutron has a zero charge, But it's all because of the quarts inside of them and how they're arranged exactly.

00:30:28
Speaker 2: It might be that positrons and electrons are actually built out of the same bits, just organized in different ways, and organize them in another way and you get a muon. We just don't know what's inside these particles, but it's a big screaming clue that there's some interesting internal structure that we haven't yet discovered. But right now all we can do is sort of look at it, categorize it, describe it. We haven't been able to explain these phenomena at all all.

00:30:49
Speaker 1: Right, So, now, if I have an electron and I flip its charge, I get the positron, which is the antimatter version of the electron. But if I have another particle that has hypercharge and I flip that charge, and that becomes the anti matter particle version of that particle. Right, But some charges have like three charges, So how do you flip those?

00:31:06
Speaker 2: Yeah, great question. Well, you know the color, there are three options. There are red, green, and blue, but there's also anti red, anti blue, and anti green. So you can take a red quark and flip it to an anti red quark.

00:31:19
Speaker 1: So really there's six colors in terms of charge. Right, because plus and minus for the electron counts as two kinds of charges. It sounds like color you can have them six kinds of charges.

00:31:30
Speaker 2: Yeah, I suppose that's true. Makes you wonder what anti blue looks like. Maybe it's anti bluetiful.

00:31:35
Speaker 1: Well, that's a colorful analogy.

00:31:37
Speaker 2: I got a whole rainbow of analogies over you're here.

00:31:39
Speaker 1: Well, at least it's not adult or a gray theory there. It's no gray area there, right, So then I guess Richard's question is like, how do you know something is matter or you should be calling it antimatter? Like he said, if you discover a new particle and it has you know, plus this or minus a, how do you know whether you should call it matter or anti matter?

00:32:00
Speaker 2: Yeah, it's a great question. And to dig into it, we have to think about like the differences between matter and antimatter, like what is the difference? Why do both of them exist? Is it really totally symmetric? And we know, of course, the answer is that it's not totally symmetric. I mean, I'm made of matter. You're made of matter. The Earth and the Solar System and the galaxy are made of matter. There's little bits of antimatter created here and there in collisions, but mostly we're made of matter, and the universe as a whole seems to be made of matter instead of antimatter. So that tells you right off the bat that they can't be symmetric because it's an imbalance. There's a lot more matter than antimatter, so there's got to be some difference between matter and antimatter, and that's not something that we understand, Like there are a few processes out there that seem to prefer making matter instead of antimatter, but we still can't explain how you could have started the universe in a symmetric state of equal amounts of matter and antimatter and ended up with only matter left over, Like we just don't understand that. So there is some imbalance between the two, but we still don't understand it. And the short answer to your question is that matter is what we call the stuff that's around you know, the things that we find around us. Electrons we call them matter because they're here, and positrons we call them antimatter because they're not.

00:33:12
Speaker 1: So theoretically, as far as we know, there is a symmetry. There's no difference between matter and antimatter. You're saying, like, experimentally, from what we can see out there, there's just a whole bunch more of what we call matter than there is of what we call antimatter.

00:33:26
Speaker 2: Yeah, that's almost true. To be more precise, theoretically, there is a small difference, Like in the Standard model, there are a few processes we call them CP violation that break the symmetry between matter and antimatter, but they're really really small effects. They can't explain the large difference we see experimentally. So experimentally we see a large difference. Theoretically we expect a very small difference and that we can't explain.

00:33:48
Speaker 1: So then really you're saying, what we call matter and not antimatter is kind of what we see. The most of out there in the universe.

00:33:55
Speaker 2: Yeah, exactly, And it could be that there are galaxies out there of antimatter, really really far away, beyond our ability to probe. There could be whole galaxies made out of antimatter, and they would also emit photons and shine at us. Some of the galaxies seen by the James Webspace Telescope might be made of antimatter, and aliens in those galaxies would call their antimatter matter because it's what they're made out of. So it's really just sort of like a relative arbitrary label.

00:34:22
Speaker 1: Whoa like, we could be the antimatter versions, right, or like maybe we are the villains, We're the evil plants.

00:34:29
Speaker 2: Yeah, we have some cool techniques to figure out if distant things are made of matter or antimatter. Basically, we look for regions in between our island of matter and any potential island of antimatter where the particles radiated by those galaxies would slam into each other and cause bright flashes. We haven't seen any of those, which convinces us that the neighborhood at least isn't made of antimatter. But this is a limit to how far out we can look so there might be islands of antimatter out there, just sort of beyond where we've seen.

00:34:58
Speaker 1: I think that's the name of a new Netflix reality show, Antimatter Island.

00:35:03
Speaker 2: Every week somebody gets annihilated.

00:35:07
Speaker 1: Or at least ridiculed in public. Well, then, I guess Richard's question is, like, if you find a new particle out there, like a totally new particle, not relate to any of the ones that we know or see around, how do you know whether you should call it a matter particle or an antimatter particle.

00:35:22
Speaker 2: Yeah, And the answer is that it's arbitrary. It doesn't really matter, you know, Like what we call matter is just one side of the coin, and what we call antimatter is just the other side. It doesn't really have any importance. Like, we could all decide to call the muon antimatter and to its antiparticle matter, right, We could do that and it wouldn't create any problems theoretically, it wouldn't change the way we do any calculations, doesn't really affect anything. It's just the name we give things. We like to be consistent, so we look for patterns. We say, well, the electron, we start by calling that matter. The muon will call that matter also because has the same charges as the elect and so the tow also, right, and we'll say the proton is matter, and so the quarks. It's made out of our matter. But we could have made other choices. We could say, oh, the quarks are antimatter, right, that could be cool. We wouldn't create any problems. But the quarks, you know, they have the same weak charges as the electron, So we'd like to say that those things are matter, just sort of like out of consistency. But it's not a strong requirement, doesn't really change anything. So for example, if we discover dark matter and there are two versions of it where one is the anti particle of the other, Richard's question is a great one. Which one do we call matter? In some sense it would be totally arbitrary, But if there's like a lot more of one of them and a lot less of the other, we probably call it the dominant one.

00:36:39
Speaker 1: Matter interesting, all right, So then that's the answer for Richard. You know, it's kind of arbitrary what we call matter and antimatter. We go with matter for the stuff we're made out of, and the stuff that looks like the stuff we're made out of, right, And if we alread discover a new particle, we would just have to I guess, either flip a coin or see which one is more popular. I guess we'll go by popularity.

00:37:01
Speaker 2: That what you're saying, Yeah, it doesn't really matter in the end, And there's a possibility, of course, So we also discover a new particle and it doesn't have an anti particle. We think there might be versions of matter out there that are called Mayorana particles. Check out our podcast episode about that that are their own anti particles, and neutrinos might even be mairana particles. They might not be anti neutrinos, so we might not have to make that decision.

00:37:25
Speaker 1: All right, I guess it's a very democratic endeavor science. Whoever gets the most votes gets to decide what they're called.

00:37:32
Speaker 2: Whatever happens, I'm sure we'll argue about it all rights.

00:37:35
Speaker 1: To get to our last question of the day, it's an interesting question about the four forces and how they unify with quantum mechanics. So let's dig into that. But first let's take another quick break. All right, we're talking about listener questions here, questions from listeners and their amazing curiosity. Our last question comes from Ryan, who is a question about unifying the four fundamental forces?

00:38:10
Speaker 3: Hi, Daniel, and Jorge. I'm a big fear of the show. I started listening in high school and now I'm a college student. I wrote this question in a while ago, but your response email went in the spam and I finally saw it now, So now finally ask the question why does it matter that the four fundamental forces of physics, the like strong force, weak force, electromagnetic and gravity are unified? And then kind of similar to that, why is does classical mechanics need to be unified with quantum mechanics That we know they all work in their own realms, so why do they have to be unified?

00:38:50
Speaker 1: All right? Awesome question from Ryan, who is a longtime listener. I was kind of glad he said he's in college because if he said he was in grad school, it'd be like, what are we that old?

00:38:59
Speaker 2: We're not old enough to have earned a PhD. Almost though everybody's been listening that long has a PhD in Internet physics.

00:39:05
Speaker 1: Yeah, or we others people who get their PhDs in like two or three years. It's totally possible, right, Yeah, absolutely, that's true. I hope we've been out there guiding some folks through their PhDs. All right, Well, Ryan's question is kind of an interesting one, but kind of a philosophical or a subtle one. I think he wants to know, like, why are you trying to unify the four forces of nature? Or why are you trying to unify classical mechanics or like general relativity with quantum mechanics. Can you just let them be their own thing? And maybe we're in a universe where they don't have to be unified, or they don't want to be unified, or you know, we should just think of them as separate things. I think that's his question, right. I think you're right, And I love the audacity of this question. You're like, aren't all y'all wasting your time? What's the whole point of.

00:39:48
Speaker 2: This big project of physics to try to explain the whole universe?

00:39:52
Speaker 1: Well? I don't know if you said that, but it does sound like you're sensitive about that.

00:39:56
Speaker 3: No.

00:39:56
Speaker 2: I love that because it takes sometimes young people showing up up and looking at what us senior folks have done and scratching their heads and going is this the right direction? Or did you guys make a basic wrong assumption like on step one. That's how we can make really great progress because some of us are sort of stuck in certain ways of thinking. So I love these sort of basic naive questions about the whole project of science.

00:40:18
Speaker 1: Cool. Well, his question is why bother, Daniel, why are you trying to find a theory of everything? Couldn't we just have a four nice theories of everything and be happy with that? Or maybe that's just how the universe is, that it has four separate rules that it's stuck too.

00:40:34
Speaker 2: Well, he's right to question, because philosophically, the universe doesn't necessarily have to have a single theory of everything. I mean, that would be pretty weird to have like several different theories that seem to be based on different principles and operate under different rules. But we don't have any guarantee that the universe has a single theory of everything. We recently had a philosopher on the podcast to talk about this exact topic and philosophy, it's called disunity, the idea that you can't combine all the theories of physics into one, that there might be just like different regimes in different realms where different laws apply. That would be weird, though, because you've got to ask, like what happens in between, you know, the boundaries between the two laws or where they kind of overlap. That's where the questions are. But you know, we don't know for sure. Nobody's promised us that physics can be boiled down to a T shirt.

00:41:23
Speaker 1: Sounds like the answer to Ryan's question then, is that we don't need to unify classical mechanics and quantum mechanics. You're just doing it to be annoying, to be that annoying kid who keeps asking why why do they need to be unified? Why not? I'm still getting paid.

00:41:37
Speaker 2: We're not just doing it to be annoying. We're doing it for a few pretty good reasons. One is that philosophically, it makes a lot more sense to have a single theory of the universe. I mean, something is happening out there in the universe, and we imagine that that something is following some rules, and those rules should be like self consistent. And if you have multiple rules, then you got to sometimes wonder, like, well, which rule applies? You know, It's like if mom and dad have different rules a boy dessert and then they're both home for dinner. Like whose rule applies? Do you get ice cream after dinner or not? You know, the universe has to make decisions, right, things have to happen or not happen, and so there's no room for things to clash. That's sort of philosophical answer.

00:42:18
Speaker 1: Is that necessarily true? Though, canny? You have two fundamental rules about the universe that don't clash, Like, you know, Dad can say you can't have dessert on Monday, Wednesday, and Friday, but mom says you can't have dessert Tuesday, Thursday and on weekends, and that kind of works out. No, it actually doesn't work out for the kid because then they can't have dessert.

00:42:36
Speaker 2: If you had rules that were exclusive, that had separate regimes that never conflicted, then sure. And the fascinating thing is that that's almost true for Ryan's suggestion about classical mechanics and quantum mechanics, Like classical mechanics and general relativity specifically mostly deals with really really big stuff. Gravity is so weak that basically it's only relevant for things like bigger than a baseball or or a planet or a galaxy. And quantum mechanics mostly applies to the very very small stuff, right. Its effects basically wash out or average out for anything that's big enough for gravity to play a role. That's one reason why it's been hard to unify them because they rarely talk about the same thing. They're mostly non overlapping, except of course, where it gets really interesting. Inside a black hole, for example, things are super duper small, so quantum mechanics is important, and super duper massive, so gravity is important. So what happens inside a black hole? Right? What happens when mom and dad disagree about the dessert you're going to get. In the case of quantum mechanics and general relativity, they're not completely exclusive. They do have to agree on what happens inside a black hole.

00:43:42
Speaker 1: Yeah, they do have to agree, but we don't know that they disagree, right, Like, we just don't know what happens inside of a black hole. I think you said earlier that you can have quantum mechanics on curve space, and so maybe what if gravity's used to think the curve space and quantum mechanics just sits on top of that, and maybe inside of a black hole they find a way to agree about who eats deserved on Sundays.

00:44:03
Speaker 2: But if they agree, then you're unifying them, right, You're bringing them together to make the same prediction. You're showing that they're fundamentally the same theory. They make the same prediction inside a black hole.

00:44:14
Speaker 1: Or I guess not that they maybe not that they agree, but that they don't disagree.

00:44:18
Speaker 2: I guess, yeah, well, right now they do disagree, right. General relativity predicts singularities and quantum mechanics says nuh uh no, deserve for you. So they definitely disagree right now, which means we need to modify one of them to make them agree.

00:44:31
Speaker 1: Do they disagree? I wonder? I mean, like, you know, general relativity says that a singularity is possible, right, but what if it's just not possible because quantum mechanics doesn't allow particles to have singularities.

00:44:45
Speaker 2: Yeah, that's one solution is to just carve out that region and say general relativity doesn't apply here. The rules of generalativity apply outside of ent horizons and not inside of horizons. It creates event horizons, but then inside of it it doesn't work, and in fact, the of general relativity are kind of nonsense. Inside of event horizon, a singularity we don't think is a physical prediction, and so you could just carve out general relativity and say outside this dotted line, it applies. Inside that dotted line it doesn't, and quantum mechanics rules there. I think that's less satisfying than finding a way to unify them, but it might be the way the universe works. We do not have a guarantee that everything is unified into a complete, single theory. On the other hand, we have a lot of historical trends in that direction, like unity seems to be the rule of the universe. We've had a lot of success finding ways to click together other phenomena to simplifier explanations of the universe down from more forces to fewer forces.

00:45:40
Speaker 1: Right, Like you mentioned earlier, electricity and magnetism were combining to electromagnetism and electromagtism, and the week four we're combining to electroweak force. Could you merge electroweak force with the strong force to get the electromediocre force.

00:45:56
Speaker 2: It is a really fun question about what would happen to the names there, because you notice that when electromagnetism and the weak force got merged, magnetism got dropped It's like that middle partner that when the law firms merge, it just got removed from the name, right, it's just electro week. And so when we merge electroweek with a strong force, what's going to get dropped? I don't know if it becomes electro strong or something else. But anyway, we haven't been able to do that yet. Those are called grand unified theories. They exclude gravity. Just adding the strong force together with electricweek would be a grand unified theory, and we haven't able to do that. But we do have some interesting hints. If we think about what happens at very very high energies, there's this fascinating clue that suggests that we might be able to unify the forces.

00:46:40
Speaker 1: But I guess Ryan's question is more like, why do they have to be unified? Like couldn't I mean, you're calling them already fundamental forces. Why can't we just live in a universe where there's the electroweak force and the strong force at the same time. Those two don't conflict, do they?

00:46:54
Speaker 2: Those two do non conflict, And yeah, we could, I think just esthetically, we prefer simpler explanations, right, That's the reason we started this project. That's the reason we discovered that electricity and magnetism were actually just one thing, not two separate things, because we were looking for unity for simplicity. So I think it's just philosophical. We prefer those kinds of explanations, so we search for them. We hope to find a simple explanation for the universe, but we're not guaranteed that it will be simple or that it will be unified. It just has to be self consistent, and it either comes by unifying them or by drawing dotted lines and saying, y'all have to play in different sandboxes.

00:47:29
Speaker 1: And I guess to answer Ryan's question, like, philosophically, we could just leave it at that, right, Like we could just say, well, the electroweak force is separate than the strong force. There just two different things doing their own things. We could just leave it at that, right, But then all of your physicists would have nothing to do.

00:47:45
Speaker 2: Kind of Yeah, we could stop asking questions and stop being curious and stop looking for patterns and simplicity. But it's gotten us pretty far so far, so I think it's a worthwhile effort. I'm going to keep looking for patterns and looking for ways to click these puzzle pieces together in two simpler ideas that explain the universe. And again we do have some really tantalizing hints. You know, as you crank up the energy of all these things, the strength of the forces change, right, the force of the weak force and the electromagnetism and the strong force. The power these forces changes with the energy you use in the interaction, and it seems like as you crank up the energy, those strengths sort of converge, like the strong force gets weaker and the other forces get stronger, and they seem to be sort of growing towards a single value, which suggests that maybe they actually are a part of the same force, but we haven't figured that out yet.

00:48:35
Speaker 1: It sounds to me like maybe the real answer to Ryan's question is why are we trying to unify the forces. The answer is because we don't know that they're not unified, right.

00:48:43
Speaker 2: That's right, and we have lots of examples of successfully unifying them in the past, so let's keep.

00:48:48
Speaker 1: Going, right. It's like you're trying to basically find the answer, positive or negative, whether or not they can be unified, because that's kind of what science does, is you come up with a question and you can have to answer it right, even if it annoys the universe.

00:49:01
Speaker 2: Or even if the answer annoys us. If we discover that the explanation for everything requires like a bunch of different ideas with dotted lines drawn between them, that won't be so satisfying. But hey, it will be the.

00:49:12
Speaker 1: Truth at least until the sequel game comes out, now with more forces, now with the ability to save your progress. All right, well, thank you to all of our listeners for sending in their question, and especially thanks to the three whose question we answered here today. Thanks for your curiosity.

00:49:28
Speaker 2: Thank you everybody, and please don't be shy. If you have a question about how the universe works, or doesn't work or shouldn't work, please write to us to questions at Danielandjorge dot com.

00:49:39
Speaker 1: We hope you enjoyed that. See you next time.

00:49:49
Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple podcast, or wherever you listen to your favorite shows.