Does anti-matter feel anti-gravity?

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Speaker 1: Hey, Jorgey, do you have your antimatter snack yet? I had a banana as usual. It's anti slip. Does that count? No? But you do know that bananas give off antimatter radiation, don't you wait? What that's bananas? Isn't that dangerous. It's so little that it doesn't really matter. That's why you're so matter of fact about it. That's why it annihilated my taste for bananas. Well, the important thing is that it annihilates your hunger. That's the whole point of eating food, is the antimatter of hunger. Hi am or Handy, cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at U C Irvine. And it really has been years since I had a banana. Years. Oh my gosh, I feel sorry for you. Why are you depriving yourself and one of life's simplest pleasures. Although I recently convinced my daughter to start eating bananas, so now we have bananas around the house. Oh my goodness. Wait, why are you recommending it to your daughter but not having any yourself. You know, it's a very personal question, person to person, I mean you brought it up, and I'm just asking a fallow up question. I just mean that it's subjective. You know, one person can love bananas, another person can hate them. To slippery slope, some people find them appealing. Welcome to a podcast Daniel and Jorge Explained the Universe, a production of Our Heart Radio in which we try to explain our subjective, our personal experience of the universe the way that it seems to us. All this data that we gather with our eyeballs, biological and technological, the things that we see out there in the universe, we want to understand all of them. We want the whole universe to be a story that makes sense to the human brain. This is part of course, the long journey of science and trying to wrap up the mysteries of the cosmos into something we understand. And our goal on this podcast is to take you on that journey and explain all of it to you. Yeah, because it is a very mysterious universe, full of amazing things that are happening in it, and a lot of things that we don't understand, even things that we take for granted on an everyday basis. Yeah, there are so many basic questions about the universe that we do not have answers to, which means that for you young folks listening, you future scientists, there are plenty of discoveries left to be made, lots and lots of open questions for you to explore. These are big questions about the universe, about our very existence, of why we're here and how it is that we are here because there is a lot of the things in the universe that matter, and also a lot of things that antimatter, like bananas. I wasn't joking that bananas produced antimatter. That's a real thing. Oh yeah, But is an antimatter dangerous? Like if you touch antimatter, you explode anti matter. When it hits real matter, it will annihilate into photons. But bananas contain potassium, which is unstable. It undergoes radioactive decay, emitting positrons, which are anti electrons, and when those do hit your body, they will annihilate and create a tiny little flash of light. But it's such a tiny amount of antimatter that it doesn't really matter. Well, that's why I eat bananas, because you know, it makes me glow, makes me feel lighter too. There isn't potassium in everything. I mean, it's all around us too, right, It's not just bananas that have potassium. That's right. It's not just bananas that have potassium. And it's all sorts of other things that also radioactively decay. So it's actually anti matter sort of all around us all the time. It's also showering down on us from the atmosphere because of cosmic ray impacts. Yeah, there are all kinds of amazing things showering us at the moment right now and enveloping us, and and for a lot of those things, we still have big questions about them, even big things like gravity. Anti matter is fascinating. It appears in science fiction, but it's also some thing that's real. It's one of these interesting hints that the universe is more complex than just the stuff that we are made out of, that the universe is capable of doing many more things than can just be found out of the particles that we are made of. There are all sorts of other weird possible particles out there, and they all give us hints about what the underlying rules are governing the universe itself. And you're right, because ant matter is so rare. There are basic questions we have about its properties, Yeah, including something as basic as gravity, gravity, which you know we kind of depend on every day of our lives to stay on planet Earth. Without gravity, we'd all be floating out there in space. That's not something I ever worry about, but maybe I should start to do. We need to like look at the gravity prediction every day as well as the weather prediction. Well, I know it's a heavy burden to be carrying around worrying about gravity, but it seems to be pretty reliable. Right. We ever noticed any change in your gravity? I mean, I don't want to enquire about your weight or anything like that. That's also personal information. That definitely explains it. Right, It's not that I'm getting heavier and heavier. It's at the gravity of the Earth itself is increasing. Sounds like you have an amazing experiment in at hand here, But it does raise a lot of interesting questions about gravity and antimatter, specifically whether or not they are the same for everything in the universe. That's right, antimatter seems to be like the opposite of matter in so many interesting ways, and so people also wonder whether or not antimatter falls down or whether it might possibly fall up, like does antimatter fail upwards? So today on the program we'll be tackling the question does antimatter feel anti gravity? Interesting? Now, are you saying it might feel anti gravity or it has anti feelings against gravity? We should invite it onto the podcast to ask it what its emotional response is to gravity. But I think today we're focusing on a more physics question, which is just like, when gravity does this thing, where does antimatter go? Doesn't like run away from gravity? Is that what you mean? Because antimatter is the opposite of matter in so many interesting ways, Yet we also really don't understand how gravity works for fundamental particles. We think about gravity in terms of like boulders or basketballs, or baseballs, or even little bits of sand, But once we get down to the quantum level, those particles do things that baseball's, basketballs and bits of sand can't do, and we don't really know how to apply gravity to those situations, which opens up all sorts of questions like maybe it does the opposite of what it does for normal matter. Do you think antimatter minds that we call it antimatter? Like maybe it just has a different opinion about the universe. You know, maybe it's just pro something else. Yeah, I think in the antimatter galaxies that might be out there in deep space. On their podcast, they're probably calling us the antimatter yeah. Or maybe there's a third opinion, you know, why does it have to be so adversarial these politics of physics? Stop the polarization of physics exactly, it's all just matter. Yeah, it's not helping our society for sure. Well, as usual, we were wondering how many people have thought about anti matter and whether it feels gravity, or whether it feels anti gravity, or whether anti feels gravity. So thanks very much to everybody who participates in this segment of the podcast. If you would like to try answering the question of the day, please feel free to write in. We'll set you up and you can hear your voice on the podcast. Think about it for a second. Do you think antimatter falls down or up? Here's what people had to say, pravity, because anti gravity might be things pushing each other apart. What do you think gravity or anti gravity? I feel like anti matter still has mass. It doesn't have like anti mass, so I don't think it feels anti gravity. Do we know if there's anti gravity? Is their uncle gravity? I think that antimatter feel gravity in the same way that normal matter feels gravity, and anti gravity, I think is we don't know if that even exists. Well, if I remember your lessons on anti matter, it should feel gravity because any matter is just regular matter with opposite chart. I know that matter feels gravity because of the bending of spacetime towards something with mass. I don't really know what anti matter is and whether it exists in another field or spatial field than mass. But I suppose in the field that anti matter exists, maybe there's the bending of that field, which would be called anti gravity, So I'd say it does feel anti gravity. Alright, a lot of very pro and anti pocisitions on this question. My emotions go up and down as I was listening to those things. I like how people were anti knowing an answer. What happens when knowledge collides with anti knowledge. You probably get the current state of affairs right now in the world. You get a physics podcast about the mysteries of the universe. But it is an interesting question whether antimatter feels anti gravity, because I guess antimatter feels natively about a lot of things. Yeah, antimatter is one of my favorite ideas in physics because it shows you that our matter isn't the only kind of matter that can be out there. There's like the opposite of our kind of matter. Though, like what exactly opposite means is a bit of a question philosophically, Right, Well, I guess maybe start with the basics what is matter for of all? Because I know there are matter particles and there are force particles, right, I think the basic idea is that the universe is filled with quantum fields, and some of these are matter quantum fields. Right. Yeah, what we call matter is what you and I are made out of. We call it matter because it's the first thing we discovered, and so we sort of named it the normal stuff. And you and I are made of these particles electrons and protons and neutrons, which are of course made up of core works inside them. And as you say, they are all bound together by forces, the electromagnetic force, the weak nuclear force, the strong force, which all use particles to communicate with each other. So there's like the photon for the electromagnetic force and the gluon for the strong nuclear force. And so you and I are like this big complicated mesh of particles all weaving themselves together to make me and you. Right, and we are made out of the basic three kinds of matter particles, right, electrons, and one type of forks, and another type of cork. And wait, a third type of cork. Right, three courts? How many quarks are there? There are six quarks that we have discovered, the up cork and the down cork. Those two are the ones that we find mostly in the proton and the neutron, although there is a little bit of other kinds of quirks sometimes appearing in the proton and neutron, but for the most part, it's up quarks and down corks make protons and neutrons, and you add electrons to complete the atom. Right, So we're made out of those kinds of icles, and most of most of the stuff in the universe is made out of those three particles, right, Like the planets, the stars, the comments out there, the asteroids, the whole galaxies are basically those three kinds of particles. Right. Yeah, we think that our entire solar system, our entire galaxy, our cluster of galaxy is all made out of this same kind of basic stuff that these basic building blocks can be put together in lots of different ways to make stars and lava and weasels and peanut butter and all the stuff that we know in the universe. And that's why we call it matter. And on a semantic note, I would include also the force particles, you know, the gluons and the photons and things that tie them together to really make them who we are. So we're not just like a loose pile of particles as constituting matter in this case. I know, sometimes particle physicists distinguished between matter particles and force particles, but when we're talking about matter and versus antimatter, I think it makes more sense to just lump it all together as matter. Okay, shifting definitions here of basic things like matter and force. I guess we're all a little bit das to that. But also that's the stuff that we're made out of. But there's also other stuff in the universe in this category of matter, right, there's like heavier electrons and heavier courts. Yes, there are other versions of these particles. This is one of the really fascinating things about particle physics is that the particles we know, the electron, the upcork, and the down cork have these reflections. That's what I meant earlier about the sort of philosophical definition of opposite. Because with the particles we know, there are several versions of them. So even before we talk about antimatter, as you said, there are heavier versions of these particles, so they're sort of reflected in this one dimension along mass. So there's like a heavier version of the electron it's called a muon, and a heavier version of the up cork it's called a charm cork. And then there's a second reflection, right, So there's the muan and then the towel is the upcork, the charm cork, and then the top cork. So each of these basic particles of matter that we know, there's two more versions of each of them. So it's this weird reflection of the kinds of matter that we're familiar with along the mass access they're heavier versions of each of these. Well, not all the particles, right, the force particles don't have heavier cousins, do they. Yeah, that's right. Only the fermions have these heavier cousins. We're not aware of any heavier version of the photon or the z boson. Okay, but there is something called antimatter particles, which is like if you take all of those particles you mentioned, the ones we're made out of their heavier cousins. And also in some ways, if you also take the force particles and numpit amount in, there's a whole other version of all of those particles that are called antimatter. That's exactly right. So all these particles that were aware of, there's another way they're reflected, not just like there's a heavier version of them, but now there's like this opposite version of them where we take all the charges, for example, and we flip them, so the electron has charged minus one. There's another version of the electron, which we call the antimatter version of the electron. Sometimes we call it a positron, which has charged plus one. So it's reflected in this like different direction. And that's true also for the muan and for the up cork, and for the down cork and the top cork. All these particles have their antimatter versions. So the antimatter versions are when you flip their charges, which is related to the kind of force they feel, right, Like electrons feel the electromagnetic force, which means they have a charge, and that's what you flip to get the anti electron exactly. And we're talking here just about the electric charge, which is a label that we put on particles that feel the electromagnetic force. And a minus charge means one thing, and a positive charge means something else. And we know, for example that like positive negative charges will pull on each other and similar charges will repel each other. So that's a label we put on particles to describe how they react to electromagnetic fields. And so an electron an apostitron are the same, except they react oppositely to these fields. The same electromagnetic field which pushes an electron up will push a positron down, so it has the same mass as an electron, but the opposite electric charge. Right. And then other particles like the corks, they don't feel the electromagnetic force, right, so they don't have electrical charge. Right. Corks do have electromagnetic charge, but they're really weird. They're like plus two thirds or minus one third, so they definitely feel electromagnetic fields. You just don't typically think of them as doing so because they also have a charge for a much more powerful force, a strong nuclear force. So they have the electric charge and they also have this color charge for the strong nuclear force. Okay, so of course feel the color charge and also the electric charge. Now, then is an anti cork something that has both of those things flipped or just one of those things flipped. Both of those things get flipped for an antiquark exactly. And I guess that's true for all the other particles. But what about the force particles. That's also true for their antimatter versions, So that's really interesting. It actually depends on the force particle. So for example, the W boson that actually carries electric charge, it's like there's a positive version and a negative version, and one is the anti particle of the other. So the antiparticle of the W plus is the W minus. Okay. Yeah. And then there's some interesting things about certain particles that are their own antiparticle, like photons, right, that's right. For photons, there is no other particle to serve as the antiparticle. They are their own antiparticle, which is sort of weird. But the way we think about in particle physics is like you take a particle, you apply the antiparticle operator to it, and say, what do you get? If you start with an electron and you apply the antimatter particle operator to it, you get a positron. You start with the photon and you apply this operator to it, you just get the photon back and sort of like symmetric. So the photon serves as its own antiparticle. Because I guess, does the photon have a charge. Photon does not have an electric charge, right, the photon does not feel electromagnetic fields. If a photon is flying through space and this electric field there does not bend the path of the photon. If you don't have anything to flip, then you can't have an antimatter because is that kind of generally the rule. That's generally the rule, and that holds also for example, for gluons. Luonto the particle that transmit the strong nuclear force, and they do carry color, they carry this charge, and so you can't have anti gluons. You can take a gluon and make the anti version of it as the opposite color. All right, So that's matter and antimatter. But one thing, I guess all matters seems to have in common, whether or not it feels certain forces or not. Is that everybody seems to feel gravity? Right, Well, we're not exactly sure about what happens with antimatter and gravity, but there is something we think that isn't flipped, which is the mass. Like an electron we think has the same mass as a positron, it's not like that mass then goes negative. That suggests they probably have a similar relationship to gravity as the original particle, but we just aren't sure. Well, yeah, I guess that's what I was trying to get at, which is that a lot of most of these particles, the matter particles, have mass, right, that's one thing we know about them, and almost in a way, that's kind of what makes the matter part Yeah, all the fermions definitely do have mass. Even the new trinos have mass, even though they have a really tiny little bit of it, and all of them get mass, we think from the same process, which is interacting with the Higgs boson, And to interact with the Higgs boson you have to have an antimatter particle. Also, the Higgs boson requires particles to interact like in pairs. It couldn't give the electron mass if the positron didn't exist, for example, right, All right, well then, I guess you know, we know that all of these matter particles feel gravity, right because we feel gravity, and all of the things on Earth feel gravity. And we know that the stars and the planets out there, and the galaxies and the galaxy clusters all feel gravity and they're mostly made out of matter stuff. And so the question that is, does antimatter also feel gravity or does it feel something else, maybe the opposite of gravity. And so let's get into that weighty question. But first let's take a quick break. All right, we're anti talking about not feeling anti gravity or is this a pro gravity podcast? I'm definitely pro gravity. I don't want it to pick up and move somewhere else, like I'd like for it to stay pretty much where it is. I'm relying on it every day. Oh really, I guess I'm more morally flexible when it comes to gravity. I mean, if I could, like, you know, ignore it for a little bit, that'd be pretty cool to fly around, wouldn't that be great? It would be nice to be able to manipulate gravity, right If we had ways to create like anti gravity somehow, it'd be easier to move your bed across the room, or to ship stuff across the world, or to launch stuff into outer space. That would be pretty awesome. We forget other stuff. How about ourselves, we could all be flying around. Finally, you get that flying car exactly right. It could be an anti car. Well, that's one of the exciting things about all of these open questions is that once you understand the way the universe works, you might discover something really surprising that's could give you a handle for creating all sorts of new crazy technologies. Yeah. I mean, we've been waiting for these anti gravity flying cars for for years. We're still waiting, Daniel, what's the hold? Well, you know, antime matter is not easy to study. It's sort of all around us in very very tiny amounts. It's made when cosmic rays hit the atmosphere. Part of the shower of particles that comes down to the surface is antimatter. There's like muans and anti muans as well, but it doesn't last very long because it smashes into stuff and annihilates, and it just doesn't seem to be very much of it in the universe, which is one of the big mysteries. Right. We talked a lot about how matter and antimatter are symmetric. It's all the same, just with the flipped number. You might wonder like, well, why isn't there more antimatter in the universe. Why is the universe matter and not anti matter? What's the difference in the end. Yeah, we have a whole episode on that, and I think we also have a whole episode on the annihilation of matter and antimatter. Right. When a matter particle like an electron hits it's antimatter version a positron, they like disappear and turn into pure energy, right, Yeah, they can turn into a photon, they can turn into a z boson, And you're right, they do disappear, right. It's not like what comes out as a rearrangement of the bits inside the electron and the positron. This really is alchemy that we're talking about. You're transforming the energy from one quantum field the electron of depositron field, then into a photon field, and then into something else. That photon can turn into corks or into w's or into something else entirely. It really is pretty awesome. This annihilation is like a conduit for transforming matter into something else. And it's funny that you mentioned that it's all around us, right, I mean, well, technically it is all around us, because if there's an electron quantum field all around this, there's also an anti electron quantum field all around this too. Right. Is it a separate field or is it the same field as the electron? Oh, good question, It is its own field. There's another field there for the anti electron. We tend to comple them together sometimes in the calculations, although it gets complicated because there's like left handed versions of them and right handed versions of them, and the weak force treats those differently. Dig into our episode about the weak force and symmetry to understand that more in detail. But the short answer is, yes, we are surrounded by quantum fields for antiparticles. Even if there aren't actually antiparticles around us. Their fields are there, like parking spots are there even if no cars are in them. Yeah, there's negativity all around us these days, it seems. But as we're saying, what's interesting about antimatter is that it's like regular matter, but it has certain of its properties flipped, like the charge of the electromagnetic force and charge and also it's a color and things like that. And so one thing that regular matter particles we know have is something called mass, Like it's a little it's a property of regular matter particles, and that's the thing that gives it, you know, inertia, and it makes it feel gravity. Right, it's kind of a measure of how much it feels gravity or how hard it is to push or pull. Yeah, mass is one of these amazing things that seems so simple. We think we understand it. You have an intuitive stance of what mass is, but when you dig into it theoretically, it turns out to be kind of complicated. As you say this, two different ideas of mass there. One is inertial mass, which is like, when you push on something, how much does it move? And that's the mass that appears in Newton's equation F equals M A. Basically, it relates F how hard you're pushing on something to A how fast it accelerates when you push on it. And Newton tells us that the relationship between those two quantities is mass. That's sort of what inertial mass is. Something with more inertial mass takes a larger force to get the same acceleration. Something with almost no inertial mass. You can accelerate pretty easily with a very small force. That's conceptionally different from this other concept of mass, gravitational mass. That's the mass that appears, and like the gravitational force equation g mm over are squared that tells you, like how strong gravitational forces between two objects, right, and so, regular particles have this property that we call mass. I mean we've called it before in this podcast. Like it's almost like a label or it's almost like a charge for the force of gravity, right, Like the electric charge is kind of like it's a measure how much it feels electromagnetic force. Mass is kind of like the measure of how much it feels gravity and inertiap Right, It's almost like it's like a little property of matter. Yeah, it's like a little property of matter and you shouldn't think of it. It's like how much stuff the electron has, or how much stuff the top cork has. In our theory, these are all point particles. I have no volume. This is just like a property of the particle. If you're comfortable assigning like quantum labels to things, like this thing has a positive charge, and you don't have to like figure out a physical place for that charge to live. You should try to do the same thing with the mass of the particle. Like the particle just has this mass. You don't have to like have room to put enough stuff into the top cork to make heavy. It just sort of is that massive. There's another interesting level to dig into there, which is like, is this mass actually a property of the particle itself or is it a property of the interaction of that particle with fields, Because we think that like in a universe without a Higgs field, all these matter particles, the top cork, the electron, they would be massless, they would fly around like photons. It's only because the Higgs field is there that these particles have a mass. So sort of like a cloud of Higgs bosons surrounding every particle changing the way it moves so that it looks like as if it had mass. So if you want to zoom out, you can just think, I'm just gonna put a label on these particles. You want to zoom in, you could think about, like, well, this particle is sort of like a virtual cloud of Higgs bosons around it that are changing it, and I'm just going to label the whole cloud is having this mass. Do you think of it as a kind of a label like you said that particles just have just like electric charge, And so the question is if antimatter is just regular matter with some of the charges flipped, does it also flip the label of mass, like does it also flip how it feels gravity or how it feels inertia? Right, that's the main question we're asking today. Yeah, and it really comes down to this basic question about what is gravity anyway? Is gravity a force the way the other forces are, you know, the electromagnetic force and the strong force, who have all their charges flipped for antimatter. If you think about it that way, then gravity is just another force and the charge for it is mass, as you say, And then it would make sense. It would be like sementric It would follow the pattern if also mass was flipped for antimatter. Or is gravity not a force? If gravity is something else? And we've been thinking about it as a force because we just don't see the curvature of space and time, and so we've created this fictitious force to explain the effect of the bending of space time on the motion of particles and If that's the case, it would make sense for space time to treat everything inside of it the same way. Antimatter and matter particles are both just little bundles of energy and his energy that bends that space, and so then it would make sense for matter and antimatter to all have the same relationship with gravity instead of the opposite relationship. So this question about whether antimatter feels gravity or anti gravity is also kind of a question about like what is gravity anyway? But I guess the main picture of trying to pain is that you know, like if an electron has a negative charge, the negative electric charge, and it weighs, you know, point zero zero zero zero zero something kilograms, doesn't anti electron not just have positive electric charge, but does it also maybe way negative through a point zero zeros there zero something kilograms? And what would that mean for the anti electron? Yeah, that would be super fascinating, right, And because we have two different concepts of mass, we have to think about them sort of individually. Like if a positron had negative inertial mass, what would that mean? It would mean that if you push on it in one direction, it would accelerate the other direction, right, Remember force equals mass times acceleration. These are vectors, So if mass is negative, that means that acceleration of force are pointing in different directions. So you like give it a shove to the left and it moves to the right. That's what having negative inertial mass would mean. That's like really counterintuitive. Negative gravitational mass would be different. It would allow for gravitational repulsion. Gravity attracts things that both have positive mass. But if two particles, one with positive gravitational mass and one with negative gravitational mass meat, they might repel each other, which would be really interesting because that's not something we've ever seen. Gravitational repulsion. Yeah, super fascinating. And so let's maybe talk more about each of these scenarios one at a time. And so, first of all, let's say that antimatter doesn't just flip the charges electrical charges of the forces in regular matter particles, but let's say it also flips its inertial mass, so it has anti inertia. I guess is the idea, And like you said, it's kind of kind of intuitive where you try to push something but it actually moves towards you. That would be weird, right, That would be very weird instead of counter through everything we've understood and everything we've experienced in the universe, that would be a very strange experience for us to shove somebody and then have them slam into you. But I guess maybe it does make sense if you just think about it as it being antimatter, and where you think you're pushing it, you're actually pulling it because it feels you're pushing force the opposite way, So it's almost like you're just pulling on something, right, Like an electron attracts a positively charged particle, right, so it doesn't push it when it gets near it, it actually pulls it. So couldn't that just be the same for anti mass? It could be, although it's a bit more general than that. We're talking about. Any force applied to a positron would then move it in the opposite direction of that force, whether it's a gravitational force or electromagnetic force, or the weak force, which positrons also feel. It's a little bit deeper than just saying electromagnetism can attract and repel, so what's the big deal. Now it's applied to every force on this positron, it would be pretty strange. Yeah, but I mean if you think about it, like an electron repels another electron, right, because they have both have negative charge. Now, if you have an electron and a positron, they would normally attract each other because they have opposite charges. But then if it has negative inertial mass, then it actually maybe flips that force and it does repel. Yeah. I think what happens there is even weirder because the positron is repelled from the electron, but the electron is still attracted to the positron, right, It's still attracted to that positive charge, and so they sort of like chase each other. Like the positron gets pushed away from the electron, but the electron gets pulled along with the positron, So you get this sort of like weird runaway effect. Yeah. I guess when that is kind of a way to prove that antimatter doesn't have anti inertial mass is that, you know, if you have an electron, it gets attracted to an anti electron, which means that it doesn't have anti inertia. Yeah, anti inertia would be really weird. Negative inertial mass particles would behave very strangely, and this is something we would have seen because we do see positrons in the world. We see them in cosmic rays, we can bend them with magnets. We don't see them doing this sort of weird behavior of being pushed in the opposite direction of the force. So negative inertial mass is not something anybody really considers seriously. When it comes to antimatter. It would be really bizarre. We haven't seen it, but I wonder if it's possible, Like could you have maybe a third version of an electron, not just a positron, with something that has its opposite charge, but also has negative inertia, which would act just like another electron to an electron, Like you would think it was an electron, but really it's an antimatter electron with a flip inertial mass. Yeah, negative mass electron. It's certainly possible that there are other reflect actions of the particles that we're not aware of. Our we're not limited to just matter and antimatter or heavier versions. You know, there are theories about like supersymmetric versions of each of these particles, and so it's totally possible to come up with another idea like a particle that it's just like the electron, but with negative inertial mass, and say maybe it could exist in the universe. Then you have to answer questions like, well, why was made in the Big Bang? Where are these? If they do exist, why haven't we seen them? And if you haven't seen them, they have to come up with an explanation for why they don't seem to appear in our universe. But it doesn't mean that it couldn't possibly exist in the universe. But I guess you're saying that the antimatter that we have seen so far, like the anti electrons that we've seen, seem to have regular inertial mass. Yeah, and this is not so challenging to observe because we can apply pretty powerful forces like electromagnetic forces to antimatter particles, which are rare but not impossible to make into manipulated and we can see their behavior. So, for example, the discovery of antimatter was seeing a positron moved through a magnetic field and bending in a way that an electron doesn't. So we're pretty sure that antimatter has inertial mass the same way that normal matter does. All right, Well, now let's tackle this idea of having anti gravitational mass. Now, is there such a thing as gravitational mass? I thought gravity wasn't really a force, It was really kind of a bending of space. This idea has some interesting history. Newton considered these things separate. He said, things have inertial mass and they have gravitational mass. These are different ideas. If you're on an empty space where there's no gravity, and objects still had inertia, right, and the force of gravity, the mass that appears in there didn't necessarily have to be the same as the mass in F equals m A. People measured it, and they always found these two things to be the same. The mass that appears in those equations were the same, and so people thought, well, that's weird, what a crazy coincidence of these things really are separate concepts and yet always managed to be exactly the same. So that was sort of an unexplained mystery for a long time. Einstein, when he developed his theory of relativity, he said, well, let's just assume that these things are the same. He baked that in to his theory of relativity. That's not a proof that they are, that's just an assumption of the foundation of general relativity. He said that gravity and inertia are basically the same thing. Okay, and so then what does that mean for having negative gravitational mass or anti gravitational mass. Well, it means that general relativity makes a very strong prediction that anything with energy bends space the same way. And so we think that antimatter probably feels gravity the same way that matter does. So Einstein and general relativity say antimatterer should feel gravity, it shouldn't feel anti gravity, and that's a strong prediction from general relativity. Well, that's a strong you're saying assumption about general relativity, right, But it is it possible for something to have negative gravitational mass, so that if I throw it at a black hole, it's actually going to run away from the black hole and not towards the black hole. I mean, it's possible in the sense that like anything is possible in the universe, and we don't know if general relativity accurately describes everything in the universe, and specifically, we don't know how to apply general relativity to particles. So it's possible that antimatter breaks general relativity and that quantum gravity allows for other weird forces on antimatter particles like anti gravity. But if you just say we believe in general relativity, then it's not possible for antimatter to have anti gravity. I see, So if something could have negative gravitational mass, it would mean Einstein was wrong, or that general grotivity needs to be maybe expanded. Doesn't necessarily mean it's wrong, or would you just need to like add something to Einstein's theory. Well, that's an interesting philosophical question. I mean, we're pretty sure that Einstein is wrong, not in the sense that any of his predictions have been proven wrong, but we don't know how to extend his theory to quantum particles. It definitely needs some sort of adaptation, and that might mean that it needs to be like tossed out and completely replaced with the theory of quantum gravity. That's a completely different picture of how space gets bent using like quantum gravitons. Or it might be that we take Einstein's theory and we quantize it that we like say, space itself is made of quantum bits that are woven together, and general relativity emerges from that. We really don't know whether we need to build on top of Einstein's theory or whether we need to like re examine the very foundations of it. But we do know that can't work in the quantum realm, so it needs some sort of update. It might be that we discovered failing only when we see inside black holes, or it might be that we discovered failing when we examine the gravitational properties of antimatter. Well, I guess I'm not quite sure what you're saying. Are you saying that? Okay? So eince science theory assumes that gravitational mass and inertial mass are the same, which means that you can't have negative rotational mass anti gravitational mass, or that you still could or like, if you have negative inertial math anti inertial mass, then that would also mean you have anti gravity irrotational mass. Einstein's theory says you can't have negative gravitational mass, that that just can't happen because of the equip into principle. But we don't know that that's true, right, We don't know what the universe actually does. So if we discover antimatter with negative gravitational mass, that means general relativity is wrong in some important way. But maybe wouldn't that just mean that it has negative inertial mass. Like, if something has a negative inertial in them mass, then in in Einstein's formulation, they would also have negative gravitational mass. Yeah, that's a really cool thought. You're right that general relativity just requires that they have the same inertial and gravitational mass, which I suppose would allow for them to both be negative. But again, we haven't seen particles with negative inertial mass. So the antimatter we know and we are familiar with doesn't have negative inertial mass, so then general relativity would predict that it also has positive gravitational mass M. So it's then it is possible to have a particle out there that if you throw at a black hole, it's going to run away from the black hole. But if it has both negative and gravitational mass, it would have the opposite force on it, and then that worse would push it in the opposite direction, and two opposites resulted in going the same way. WHOA, So it would still go towards the black hole. It would still go towards the black hole, Yes, because they would cancel each other out. Yeah, exactly. Black hole's force would technically be away from it, and that would result in a particle moving towards it. So double bonkers unless um, somehow Einstein's theory is wrong and they're sort of not the same thing, right exactly, the possibility that Einstein is wrong and that antimatter particles have positive inertial mass and negative gravitational mass. All right, well, it seems like, um, it is possible maybe to have anti gravity from being an antimatter particle, to have an anti inertial or anti gravitational mass seems possible. But I guess then the question is does it actually happen? What are some experiments we've done to try to find the answer to this question. So let's get into that, But first let's take another quick break. All right, we are feeling a lot of anti emotions here talking about antimatter, anti gravity, anti mass, anti everything. It's a very contrary episode. We're going up, we're going down. We're going anti up and anti down all at the same time. Can you go anti anti? Those would be your double negative mass particles, right, be anti anti attracted to a black hole? What would you call the antimatter version of your parents, sister, your anti anti These are tough questions we're asking today, assuming people are still listening or the left in an anti huff. All right, we're talking about whether or not antimatter feels anti gravity, which is kind of turned out to be a pretty complicated question because, first of all, you have to think about whether antimatter has anti inertia mass or anti gravitational mass, and whether or not if they're the same thing according to Einstein, or maybe they're not. I don't know. I don't know. I feel like from all this theoretical discussion, it seems like you're saying that it's not possible to have anti gravity. I think it's very unlikely that antimatter has anti gravity just because general relativity is so successful. The YadA YadA YadA, dot dot dot. On the other hand, why do we do experiments. We don't do experiments just to like yawn and check the boxes off of theoretical predictions. We do experiments because we want to explore the universe. We want to find crazy, shocking things that we can't explain that let us pull the rug out of everything we thought we knew and build up new ideas about the universe. So this is definitely something we should check. We should go and see whether antimatter follows our expectations or anti follows them. I think I see what you're saying. You're saying you're anti anti gravity, but you're pro the government giving you more money to run experiments. Is that kind of what I'm sensing here. I it's a little um contradictory position here. I think it's just exciting to go out and ask basic questions, like, hey, does antimatter of f all up or down? And it's incredible to me that almost a hundred years after we've discovered anti matter, we still don't really know the answer to that. Like, experimentally, it turned out to be surprisingly tricky to do experiments with antimatter, right, And specifically, you're talking about measuring I guess, the gravity of a particle, right, I mean, you can measure the gravity of a planet, of a person, of a banana, but it's hard to kind of talk about the gravity of tiny little particles because they feel very little gravity. It's hard to even measure the gravity of a banana. Like you can measure the weight of a banana, you put it on a scale, but there you're measuring the gravity of the Earth. Right. The Earth is pulling on the banana. If you have two bananas in the room next to you, it's pretty hard to measure their attraction between themselves because gravity is so weak. It's like ten to the thirty times as weak as electromagnetism, So it's something we typically ignore. Right, you have two bananas on your table, you don't expect to see them like creep towards each other if you leave them alone. But they would in space, Right, that's the idea. If you were floating out there in space and you have two bananas, eventually they would become a bi banana. Banana na na. Yeah. But even doing that experiment in space would be hard because the gravity is so weak that it might get swamped by other stuff like the solar wind would probably blow on those bananas, pushing on them harder than the force of gravity between the bananas. Or if the bananas have like a little bit of residual positive and negative charge, like you rubbed one on your pants accidentally and giving it some static electricity, then those forces, even a few electrons on the surface of each one, would be more powerful than gravity. So gravity is super hard to measure for small things because it's so weak, it's swamped by everything else. It's like trying to listen to a whisper during a really loud concert. But I guess if you said the experiment the right way and make sure everything doesn't have a charge, the two bananas would come together eventually, because that is what happens out there in space, right, That's how planets get formed and asteroids and the sun. Right. Yeah, we think that's the basic process for forming all of the structure in the universe. And we've done some really pretty awesome virtuoso experiments measuring the gravity of like little things, things about the size of a centimeter and involves isolating them from everything else and seeing very very small motion, which people observe by like attaching a mirror to the object and shining a laser on the mirror and seeing the laser spot like move a tiny little bit so that you see that the object has moved. These are really super precise experiments, very very difficult to do, but still there. With macroscopic objects, we're talking about like things the size of a millimeter or centimeter, not individual particles, so we can measure the mass of tiny, regular matter of things. But I guess it's hard to do it with antimatter, right, because that's really the question we're asking today is like, if you have something made out of or a whole bunch of antimatter in one spot, would it feel anti gravity? That's the experiment. That's also hard to do it because it's hard to put together a lot of antimatter. It is. We can make antimatter at CERN, for example, we smash matter into targets and the whole spray of stuff comes out, including some antimatter, and we can filter it out and do experiments with it, and we do that kind of thing. But we make like pico grams of antimatter every year it's CERN. So you want to make like a bananas amount of antimatter, it would cost zillions of dollars and take years and years and years. So instead of making really big objects out of antimatter, we try to do really precision experiments with much smaller amounts of antimatter. Also, would be super dangerous to come to make like a even a piece size or raisin size amount of antimatter, because then if it touches regular matter, it's it's going to destroy the Earth basically, right, It's one of the most efficient ways to release the energy inside matter, which is a huge amount, right equals mc squared. C is a really big number. The speed of light C squared is a really big number. Is squared. So as you say, like a raisin's worth of antimatter combined with the reason but have as much energy is like a nuclear detonation. So yes, if you are making antimatter in your kitchen, be very careful. Yeah, we're very anti that kitchen. A recipe there, But I think what you're saying is that you can make antimatter in your colliders and certain, but you haven't made enough to really do gravitational experiments to see whether antimatter feels anti gravity. We actually have done a few experiments with antimatter that do ask this question about the effects of gravity on these particles, but they're very, very difficult to do and not as sensitive as we'd like yet. What I mean, so you did the experiments but didn't reach a conclusion or what couldn't get the data. So they've done the experiments. They take anti protons and they combine them with anti electrons to make anti hydrogen. And the reason they do that is you need neutral antimatter. You don't want any electric or magnetic fields affecting your antimatter. You want to measure only the gravitational force on these objects. So they make neutral anti hydrogen, which is super awesome anyway, because then they can do things like study the spectral properties of it and see if anti hydrogen behaves the same way as hydrogen, which this whole other really fascinating field of science to try to figure out what is the difference between matter and antimatter. But because they have a collection of these anti hydrogen atoms, they can also see like what happens when they float there, Like do they drift down or do they drift up? Well, I guess, first of all, how do you hold a bunch of anti hydrogen? So you create this I guess by bringing together anti electrons and anti protons, and then they make answer hydrogen and then you get a little cloud of anti hygen. What do you do with that? Do you keep it inside of a bottle? It's really challenging to contain. You're absolutely right. What we do is we keep it in a magnetic bottle. It doesn't work very well. A magnetic bottle is good at holding charged particles. Because magnetic fields bend the path of charged particles. So, for example, the beams and the large hadron collider are kept moving in a circle because of very powerful magnets or plasma, and a fusion reactor is kept in a magnetic bottle to keep it from escaping because it's filled with charge particles. It doesn't work very well all on neutral particles, but even anti hydrogen has a magnetic moment because the spins the particles, they do feel magnetic fields a little bit, so we can keep them in like a very very bad magnetic bottle, and it works best if those anti hydrogen atoms are slow, if they're cold, they're not like flying around with high velocity, then this very weak bottle tends to contain them. But that's a challenge because making anti hydrogen that's moving slowly is hard because you have to combine the positrons and the anti protons which come in in beams, so you have to have like slow beams, like gases of these things like merge together. The whole thing is experimentally very tricky. Yeah, it sounds pretty hard, but they have done this kind of and what did they find. Did they find that it falls at the bottom of this bad bottle, or does it flow it up to the top of the bad bottle. So there's a very cool experiment at CERN. It's called the Alpha experiment, which stands for anti hydrogen laser physics apparatus. Is a terrible acronym or really awesome experiment. And they do not see anti matter falling upwards very fast. I mean, some of these hydrogen atoms do float up and some of them do float down. And because the difficulty of measuring gravity, it's not a very precise measurement. What they can do is they can say that anti hydrogen doesn't have a negative gravitational mass of sixty five times the inertial mass. So if anti hydrogen had a negative gravitational mass of like a hundred or a million times the inertial mass, they would have seen it because they would have flown upwards really fast. They don't see them flying upwards really fast, so they can say if it does have a negative gravitational mass, it's not that big. So it's like very imprecise. So far, if they had a lot more anti hydrogen or more time, they can make more precise measurements. They could sort of narrow this down statistically, all they can do right now is like rule out a really crazy result where anti hydrogen has a negative gravitational mass that's also much bigger in magnitude in the inertial mass. But could it have a varying different gravitational mass in magnitude than than it's inertial mass. I mean, we're exploring the bonkers universe theory out here, so maybe right. And this is also sort of like just the way that they can express their results. Even if the theoretical options are well, it either has a positive gravitational mass or negative one times the inertial mass. We can't tell the difference between those two. Experimentally, all we can do is tell the difference between negative sixty five and positive one. So we can rule out negative sixty five, we can't yet rule out negative one. M I see. So they done the experiment and they don't have a clear result, but it's not an anti result either. It's not. And they're just getting started, right, and so they're going to make more anti hydrogen and they're gonna do more precise experiments. There are other experiments coming online at CERN to measure this in other ways and so in the next few years we hope to get more precise measurements of the gravitational properties of antimatter. All right, Besides cern are there other experiment is that we've done or are going to do to measure the gravity of antimatter. These kind of particle physics experiments are really the most direct way to probe this. You can also do other sort of thought experiments to think about the effects of antimatter. For example, like the protons that are inside me and you, we talked earlier about how they have quarks inside them, Well, they also have antimatter inside them. Like the gluons that are inside the protons, they sometimes turn into cork anti cork pairs like very briefly before going back to being a gluon the way like a photon will turn into a particle antiparticle pair briefly and go back to being a photon. So that means that like you and I are partially made of anti matter. If antimatter had anti gravity in some weird way, then we would see the effect of that on protons. And we don't see any weird behavior of protons. They don't seem to have any sort of like deviation between their inertial and gravitational mass. So that's a strong hint that antimatter probably has normal. Yeah, we all have a little bit of negativity inside of us, a little bit of a contrarian inside of us. But I think you're saying that we all are made a little bit of antimatter and it doesn't seem to be affecting the regular matter. But at the same time, it's a very tiny amount, isn't Isn't it like super duper negligible the amount of antimatter inside of us? Yeah, so it would be pretty negligible. All right. Well, maybe to wrap up here, I think we've sort of maybe a little bit debunked the idea of anti gravity for antimatter particles. I mean, theoretically, it seems like it's not really possible, or I mean it's possible, but we would mean we would see a very different universe. And also these experiments that you describe kind of rule it out as well. So if that's true, then if you can't have anti gravity, what does that mean about our theories of the universe. I think I agree mostly with what you say, but I always hold out a little bit of hope for the crazy result. You know, even if the theory very strongly says that can't happen, that just makes me more excited to go and discover it that way, because it means undermining that whole theory and starting from scratch, and to me, those are the most exciting moments in science. So I think you're right that the theory very strongly suggests that antimatter doesn't have anti gravity, But that still makes me hopeful. Wait, what makes you hopeful that maybe one of these experiments will get a shocking result and discover antimatter fluting up in a gravitational field and give us a clue about the next direction we should take for gravity, for understanding whether it is a quantum field or whether space itself is quantized, and how to get to quantum gravity. All right, well, I think what you're trying to say is keep giving you money to run these experiments just to make sure that the universe is not actually crazy. I'd say, we never know where the next surprise, where the great big learning moment about the universe, will come, and so it makes a lot of sense to go out there and do careful experiments and see if the universe is the way we expect or not? Where is to the anti way we expect? All right, we'll stay tuned, as I guess we keep exploring this idea of antimatter and what gravity actually is. I guess it's hard to prove that there's such a thing as anti gravity if we don't actually kind of know what gravity is. That's a good point. We anti know gravity, right like, It's still kind of up for the babe whether general relativity, which is Einstein's theory, is right or not, and how it matches up with quantum mechanics. It's one of the deepest questions at the heart of modern physics, how to unify these two pillars of our understanding of the universe. All right, well, I guess we'll keep waiting for news from the fringes of physics. We'll keep funding those experiments. You mean it's above my pay grade? All right? Well, we hope you enjoyed that or anti enjoyed that. Thanks for joining us, See you next time. Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast from My Heart Radio, visit the I Heart Radio app Apple podcasts or wherever you listen to your favorite shows. No.