Daniel and Jorge Explain the UniverseDaniel and Jorge talk about whether the Universe would make sense without antimatter.
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Hey, Daniel, are you glad our universe has antimatter?
Hmmm No, I'm definitely pro our universe, So I guess I'm not anti antimatter.
That means your pro matter. But I guess the question would you miss antimatter if we didn't have it?
I mean, I like things the way they are, so if we lost antimatter, the universe would be pretty different and maybe worse.
But what if it's better?
Or maybe it couldn't exist without antimatter and it would disappear in a puff of mathematical contradictions.
Okay, then I would be anti antimatter. I would not be pro antimatter.
I'm just saying it matters.
Hi, I'm boring my cartoonist and the creator of PhD comics.
Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I love all the kinds of matter out there, the matter and the antimatter and the pro matter.
What about the meh matter? Not pro, not anti, It's just kind of.
There, you know. I will admit that there are some particles I think are exciting particles. I'm like, yeah, that's just a mess about.
Your favorite kind of matter is chocolate matter.
It's certainly better than vanilla matter.
Carp matter. But anyways, Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we dig deep into all kinds of matter out there that matters. We talk about the things that make you up. We talk about the things that make nothing up, and things that seem to exist for which we do not yet understand. The whole universe is like a jigsaw puzzle with lots of weirdly shaped pieces, and our goal is to find all those pieces fit them together to tell the whole story of our universe. And on this podcast we like to do that and try to explain all of it to you.
That's right. It is a vast and complicated universe, full of all kinds of crazy and interesting kinds of matter and energy and concepts and mathematics that we like to explore as human beings and ask questions about and then explain it to you, or at least ask you the question, what's the matter with you?
We study all of these particles, we try to understand them, and sometimes we even taste them to see if they're delicious. But I wasn't joking when I said that some of the particles out there are a little crazier and harder to think about than others. I mean, there are so many particles discovered in the era of the particle Zoo that we almost ran out of silly Greek letters to use to name all of them.
Oh boy, what happens when you run out of Greek letters?
Then you start using Hebrew letters. Okay, like the Gimmel particle on the aleph particle. H interesting, but We've discovered so many weird masons and baryons that we had to use some of those weird Greek letters that nobody even really knows how to write down.
I guess we have done a pretty good job of kind of looking out into the universe and basically taling up all the different kinds of matter, all the different kinds of particles that can't exist out there, because there are a lot. As you're saying, there are.
A lot, And it's sort of a two step process to understand the universe. Like number one, just look out and see what's there. Gather together all the puzzle pieces. Number two, try to click them together to tell the whole story. Are there pieces missing? Do they fit together into a puzzle or is it just a weird, disjointed pile of confusion.
Yeah, And I guess the history of it is that we used to think that we knew what the building blocks of the universe was, right. We thought the elements of the periodic table were like the basic lego pieces of the universe, but actually those turned to be made of other things. And then those some of those things turned to be made of other things.
That's right. We revealed this sort of hierarchical structure of matter, things made of smaller things made of smaller things, but the path to understand them in the history of science was not so straightforward. We sort of like drilled down and then got wider and weirder, and then drilled down again and got wider and weirder. For example, when we wanted to understand the nucleus, when we wanted to understand protons and neutrons and what's inside them, we'd build bigger atom smashers and higher energy colliders, but we didn't immediately find out what was inside the proton. Instead, first we discovered all sorts of weird other kinds of particles that don't exist inside the atom chaons and pions and rowe particles and omega particles and all sorts of other Greek letters I don't even know how to pronounce. Things got weird before they got clearer.
Yeah, no, I understand. It's all Greek to me.
In the same way that we want to understand what's inside the quarks that make up the proton, but first we found more quarks along the way. Instead of figuring out what's inside the upcork and the down cork, we found the charm and the strange, and the top and the bottom. So the universe gives us a big pile of clues before it reveals its deepest secrets.
Yeah, it is a weird universe full of surprises. And one of the weirdest things about matter in the universe is that it seems to have an opposite to it. There seems to be a lot of antimatter in the universe.
Every particle out there seems to have its weird twin. And we don't know if this is a detour in our path to finally understanding what is the fundamental nature of matter, or if it's a crucial side quest to get a clue that will help us unlock the deepest mystery. We don't know if and the matter is necessary, We don't know what role it plays. We don't really know what clue it's got us about the nature of the universe.
And so to the other podcast, we'll be asking the question why do we have anti particles? Feel like that's a weird double negative question, like why don't we have particles? Or why do we have anti particles? What's the correct grammar here or is it in Greek? I think why do we have anti particles? Is the deep question? You know, every time we see something in the universe, we wonder like, hmmm, did it have to be this way? Is this necessary? Is this a clue as to the fundamental nature of the universe or just sort of like a random accident. Well, so, as usual, we were wondering how many people out there had thought about this question or have any ideas about why we have anti particles.
So thank you very much to everybody who answers these questions for this fund segment of our podcast. If you would like to play along next time, please don't be shy. Write to me two questions at Danielandjorge dot com.
So think about it for a second. Why do you think we have anti particles? Here's the people had to say.
In general, antiparticles exist because particles exist and there's some sort of balance that was broken at the Big Bang.
I don't know, but the universe seems to like symmetry, and somehow antiparticles have to exist for some kind of symmetry to be to be fulfilled. But I don't know. It's kind of crazy.
I think anti particles exist for the same reason you don't get monopole magnets.
But I've got clue, so we'll say with me, well, maybe not.
I feel like you need the antiparticles like cancel it out, because you can't have like something from nothing. You need to have something and then the opposite of it, so that like overall nothing has changed.
Anti particles are probably like the ying and yang for every particle that has to exist an anti particle in order to balance the forces in the universe, similar to matter and antimatter.
I think the reason why antiparticles exist is because everything in nature and physics seems to be balanced. So if you sum up everything, it comes off like zero. But yeah, for everything that exists, there needs to be an anti thing. Somemoi like King and John.
All right, some very philosophical answers here, some of them kind of zen.
Yeah, there's a lot of philosophy in these questions, you know, wondering whether the universe could have multiple explanations or just one explanation, or whether it has any explanation at all, whether it makes sense, and whether it's sensible to human minds. All that stuff is tied up in this quest to understand the universe.
Do you think maybe there are anti particle scientists out there and or cartoonists. We're wondering why do we have particles? What is this weird stuff?
I don't know, but humans are capable of developing science as well as anti science. More recently, I'm.
Just antiphysics, I like all the other sciences.
Are you antiphysics or are you anti physicists?
I'm anti answering that question, and that's an answer to that position there. Well, let's dig into it, Daniel Water, Anti particles Is it like antimatter exactly?
Anti particles are what make up anti matter. So matter is the stuff that we find around us, that you were made of, that I am made out of. Everything you have ever eaten is made out of particles that we call matter particles. So you and I are made out of protons, neutrons, and electrons, and those protons and neutrons are made up of quarks. Antimatter is made up of anti particles, so you could have, for example, anti hydrogen is made of an anti proton and an anti electron, where the anti proton is then made of anti quarks. So there's a close connection, of course between anti matter and anti particles.
I see. So particles are the little things that we're all made out of, and some of them have anti versions of them. Do all particles have antiversions or only some of them? Like do the force particles have anti force particles?
Great question, sort of yes and no. All the particles have anti particles, but some of them are their own anti particles, so I'm not sure if that counts as having an antiparticle. So, for example, the electron has an antiparticle the positron, and the muon has an antiparticle the anti muon, and the quarks have antiparticles the anti quarks. Those are different particles, or you could think of them as two parts of the same pair, but they are distinct states. But then particles, like you said the force carrying particles like the photon. The photon is its own anti particle, and so you might also say it doesn't have an anti particle, But I'd like to think about it as one particle playing two roles.
What about some of the other force particles, do they have anti versions?
Well, there are two W bosons and they are each other's antiparticles. So you have the W plus and the W minus for example, So those two force particles are each other's anti particles, which is why we have two of them. The z boson is its own antiparticle, and the gluon is actually eight gluons, all of different colors, and some of them are each other's antiparticles. So you can have like a red anti green gluon which is the antiparticle to the anti red green gluon. It that's really colorful with gluons.
M Well, I feel bad for those particles that are their own anti versions of themselves. It's like they're their own worst enemies.
Or maybe they're lonely, right, one is the loneliest number.
After all, this should hang out together.
Some people confuse anti matter with dark matter, and there's lots of mysteries in particle physics, right, lots of things that we don't understand about the universe. But those are two separate mysteries. Dark matter is the invisible matter that's out there in the universe that we know is holding galaxies together and shaping the whole development of the large scale structure of the universe. We don't know what it is, and if it's made of particles, that's a different idea from antimatter. Antimatter is a real thing that we can make, that we can study. We've seen it in our detectors. We know for sure that it exists and it's made of antiparticles.
Well, I guess maybe the question now is how do you make antimatter? Can you make it or does it exist in nature? Or is it just a matter of like flipping the sign on some quantum property of regular particles.
So sort of all of the above. Antimatter isn't very common. The universe is almost entirely made of matter, meaning it's made of particles instead of anti particles. But sometimes antimatter is produced, though it doesn't last very long because it runs into normal particles and annihilates. But for example, the discovery of antimatter, which led to the nineteen thirty three Nobel Prize, was from naturally produced antimatter. So a positron the opposite particle to an electron produced in cosmic rays, meaning high energy collisions of particles from space hitting the upper atmosphere and creating antimatter which then showered down to the surface of the Earth.
So when was this When was the first time we saw antimatter?
So it was first observed in the late nineteen twenties. It was predicted by Paul Durack, the quantum physicist, who saw the mathematical need for them in his equations and he said, Hm, my equations predict there should be electrons and should also be another particle with the opposite charge as the electrons. So he predicted it, and then Carl Anderson saw it. We have a whole fun podcast episode about the discovery of antimatter and the twists and turns and the egos involved. It's a really fun story. Check that out. We've known about it for almost one hundred years now.
It sort of involves cloud chambers, right, which is something you can usually find in most science museums.
Yeah, early particle physics didn't have fancy digital electronics and the complicated detectors we have now. They had to use techniques to observe the paths of these particles with the technology they had. And one thing you can do to illuminate what particles are flying through the air around you is to create clouds of water vapor. If you have air that's super saturated with water, meaning it actually has more water in it than it likes to have, then it's very easy to knock that water out of the air, and a passing charge particle will do just that and will create a string of droplets in the air. You can actually create cloud chambers at home. Check out lots of YouTube videos for how to do this. You can build one in your garage. You can see them at science museums and so you can see high energy particles streaming through the air around you, muons and all sorts of stuff. Carl Anderson proved that a fraction of these are actually anti matter particles, and he did that by showing how they curve differently in magnetic fields, because magnetic fields will change the path of a charge particle depending on the charge. A positive charge will bend it one way, a negative charge will bend it the other way. So he saw particles that had the same mass as electrons, but bend in the other direction.
Like a positively charged electron. Is that basically what an anti electron is, Just an electron with a charge flip.
Yeah, that's what anti particles are. They're just like their particle counterparts, but they have the option charges, So the opposite electric charge, the opposite weak charges, and the opposite color charges. So in the case of the electron, it's basically a positively charged electron.
Right, because I guess an electron doesn't have the weak charge and it doesn't have the strong charge.
Right, electrons do have the week charge. Actually, remember, the weak force is actually unified with electromagnetism into one force we call electro week. And electrons can interact via the weak force. They can emit w's for example, that's how beta decay happens. So electrons interact with the weak force. In fact, every particle we've ever seen interacts with a weak force, which is fascinating because the other forces are not so democratic, Like the strong force only interacts with quarks and not at all with electrons or neutrinos, and electromagnetism doesn't interact with neutrinos. But we've never found a particle that doesn't have any kind of weak charge. Every particle out there so far we discovered interacts with the weak force.
Wait, what's the name of the week charge? If you have a week charge, what is that call?
Well, there's actually two different week charns. One of them is called weak isospin and the other one is called weak hypercharge. But you can combine them actually to make electromagnetic charge. So there's two different charges for the electro weak force, but one of them is really from electromagnetism.
I'll pretend I totally understood that. But I guess when you're trying to make an anti electron, which one do you flip? Do you flip the electromagnetic charge like the you know plus and mind is that we're all familiar with, or do you flip one of these other sub charges? And if you do do I mean there are several versions of an anti electron.
Now you flip all the charges. So there's only one version of a positron, and it has a positive electric charge. It also has both of its weak charges flipped.
But what if you flip one and not the other one?
You can't do that, man, don't do that.
I'll tell you why not to do. Tell you why I can't do it. Then I can see you whether or not I can't. I will do it.
It's not me, man, it's the laws of the universe. No, we do not see particles where only one charge is flipped and the other one is not or why not? Yeah, that's a very cool question. Imagining particles that are particles into one force and anti particles according to another force. Remember, we recently answered a question about whether it even matters whether you're calling something matter or antimatter, and turns out that's totally an arbitrary distinction. So it doesn't really matter if one force considers a particle matter and the other one considers a particle the anti matter. But the forces do have to be consistent, and in the case of the weak force and electromagnetism, for example, they are tightly linked, so you can't just flip one and not the other. The charges of the two forces really are connected by the structure of the theory.
I think what you're what you're saying is this matter antimatter distinction is really kind of arbitrary, kind of right, Like it's not a clear cut like maybe there are shades of gray or shades of antiness.
Yeah, we definitely don't claim to understand everything there is to know about antimatter. But I think you're right a lot of this comes down to just like what do you call matter and what do you call antimatter. Crucial idea is that there are these symmetries that you can flip these charges and the equations still work. That the universe can do both of these things, and so it does in some cases. We have like multiple ways to categorize what is matter and what is antimatter.
Well, I think the thing that most people probably remember about antimatter, and that maybe is relevant here, is that like a matter particle and its antimatter particle, if they touch, then they annihilate. They become pure energy, right, We've talked about that before they explode. That's one of the things about antimatter.
Particles and their antiparticles can annihilate into a force particle. So for example, an electron and a positron can come together to make a photon, or a z boson and a quark and an anti quark can come together to make a gluon, and the opposite can happen. Also, a photon can turn into a matter antimatter pair, or a z boson can decay into a muon and its antiparticle.
But then I guess if antiinus is kind of a relative or there's a grey area there, or how does that affect the annihilation? Like if I take a quark and an antiquark, but I flip some of the other de signs, do they still annihilate.
They can annihilate if there is a particle that carries their combined charges. So for example, an electron and a positron can annihilate because in total they have zero electric charge and the photon has zero electric charge. That's why an electron cannot annihilate with another electron, because then you'd have to have a particle with a minus two charge in order to conserve electric charge. So the same thing goes for the other charges.
So like if I have a green cork and an anti green cork, but a given different you know, regular charges, what's gonna happen? Are they going to annihilate or repel each other? Or what I'm just trying to get at, like what it means to be antimatter? Is it depending on this annihilation thing or is it kind of random.
It's a little bit more complicated for the color charge because gluons themselves are colored. You know, the photons don't have any charge for example, right, so it's simple plus and minus annihilate to zero charge photons. In the case of gluons, gluons do carry color. In fact, they carry two colors, which is even more confusing. So for example, a red anti green quark can combine to make red anti green gluon. The glue on itself carries two of those colors, but the gluons don't carry electric charge, so this can only happen for quarks that have opposite electric charges that can balance out to zero electric charge. So one way to think about how to pair particles and antiparticles is whether they can annihilate into these force particles.
I see, so maybe one particle can have multiple anti versions of itself.
There are definitely multiple different versions of quarks that an individual quark can annihilate with to create a gluon because there are so many different kinds of gluons, though they always have to have opposite electric charges because the gluons don't have electric charge. So yeah, it gets really complicated when you're talking about the color charges because there's multiple different color charges and the gluons carry them themselves, and so the whole thing is a big mess.
Is that how you in every physics paper, YadA YadA, YadA, YadA, And it's all a big thing.
It's a big mess, and it's a glorious and we're still working to try to figure it out. Yeah.
Cool, Well, I guess the big question is, so, why do we have anti particles at all? Why do they exist in the universe? And so let's dig into that question and some of the other open questions about antimatter. But first let's stick a quick break.
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All right, we're talking about antimatter antiparticles and why do we need them at all? Which sounds like a very insensitive question.
Well, it's sort of the deepest question we ask When we see something in the universe. We ask, like, why is it this way and not some other way? Does it have to be this way? Is the universe parsimonious? Like it only contains things that have to happen, Or is it sort of like baroque that has all sorts of flourishes that it doesn't really need and it's just sort of beautiful. We tend to think of the universe as parsimonious. We try to take every piece that we find and fit it into the puzzle to explain why the universe works this way.
Well, I guess one of the reasons we as we talked about last time, that we call some things matter and something's antimatter, is that we mostly see matter out there in the universe, at least as far as we know. Our planet, our Solar System, our galaxy is made out of regular matter. And there's a big mystery about why there isn't as much antimatter in the universe. But maybe one question that you can ask is, like, is matter and antimatter made at the same rate in the universe? Like if you run a particle collision experiment and you create some energy and some particles spill out to matter, particles get made as much as antimatter particles.
It depends a little bit on what you start from. I mean, if you start from particles of matter, then you're going to get more matter particles than antimatter particles. If you start from antimatter particles, then you're going to get more antimatter. And we actually ran a whole collider that smashed matter versus antimatter. Now is the collider outside Chicago, the tebatron collided protons with anti protons, and so there we got even splits of matter and antimatter. Whereas the collider at Cerne, the Large Hadron Collider, smashes protons with protons because antimatter was such a big headache to produce for the other collider, And so there we get more matter produced than antimatter because we're starting from matter. But most of these processes are symmetric.
Right.
If you just have a big pile of photons and you wait for them to decay, they will produce an equal number of positrons and electrons.
I see. So I guess the big mystery is that it sounds kind of like the universe is able to make equal amounts of both kinds of matter, but what we see in the universe is mostly only one kind of matter.
Yeah, we suspect that the very early universe, matter and antimatter were created at the same rates that as the universe cooled down from the frothing pile of quantum fields and things got cold and isolated enough that you could call things particles. That the particles and anti particles existed at basically the same level. Then there was a huge amount of annihilation, as you can imagine, and most of the matter and antimatter went away and turned into radiation. But a little bit more matter is left over than antimatter, and we don't understand the source of that discrepancy, even though it's the reason why we have matter galaxies and matter, stars and matter, people and matter chocolate and not antimatter. The universe seems to have some preference for matter over antimatter.
Which makes me ask the question, is anti chocolate vanilla or white chocolate or is it a case of having multiple antiversities?
I hope so, because neither of those things should be categorized with chocolate chocolate.
You just anti everything.
That's I'm just anti calling things chocolate that aren't chocolate. Even calling them anti chocolate somehow groups them together in a chocolate category where they don't belong.
What about vegan chocolate, not chocolate.
No, totally chocolate it comes from the cocoa bean.
Yeah, absolutely, all right, Well, the big question is why does it exist at all? Why do we have antimatter? Like is it something that the equations of the universe requires or is it just something that seems to happen. That's the big question, right.
That's the question, and the short answer is we don't know. But what's really fascinating is that without antimatter, some of our basic theories of physics don't work very well together. Like we have relativity and we have quantum mechanics, both things that we think make sense in the universe, but when we try to bring them together, we get some conflicts. And it turns out that antimatter resolves those conflicts and lets us bring special relativity and quantum mechanics together into one theory.
I thought those two things didn't like each other.
So we have two different theories of relativity, special relativity, which tells us about what happens when things move really really fast near the speed of light, and then general relativity, which tells us how space bends in the presence of mass. General relativity and quantum mechanics we do not know how to combine into a theory of quantum gravity. That's something for a future physicist maybe one of our listeners to figure out. But special relativity and quantum mechanics we do know how to combine, and we've had that for many, many decades. So that's basically relativistic quantum mechanics, and that is something that we know how to do thinking about quantum particles and moving near the speed of light, and we do that all the time in our particle colliders, right, happens all the time that we have high speed particles. So relativistic quantum mechanics we can do. Bend space, curved space. Quantum mechanics we don't know how to do.
Interesting. Okay, so you're saying somehow antimatter and antiparticles somehow make quantum mechanics and special relativity work together. What does that mean?
So it all has to do with preserving causality, and special relativity makes it really hard to think about causality, to think about the order that things happen in the universe, because it forces us to think about the order of events in a very different way than like Newton thought about things and the way that we intuitively think about things. You probably think about the universe happening as if there's like a giant clock and the whole universe like ticks forward and then the next thing happens, and the universe ticks forward and the next thing happens. But you can think of the whole universe as having like one clock, so you can tell like one story about what happened in the universe. Special relativity tells us that that's not actually true, that there's lots of different clocks in the universe, and how fast they tick depends on where you are and how fast they're moving relative to you, So you can actually tell lots of different stories about what happened in the universe, even stories that conflict with each other, that contradict each other about the order in which events happen.
Yeah, I know. We've talked about this before and include it in our book. It's kind of this idea that if two people run a race, you think that whoever wins would be clear, but it sort of depends on how fast they're moving and how fast the judges moving, or how fast you're moving as an observer.
Right, Imagine two people are running a race, but instead of running alongside each other on a track the way people typically do. Imagine them starting in the same place but running opposite directions. This makes it easier to think about because they end up far apart from each other. If you're standing at the starting line and you're not moving relative to the starting line, imagine these two runners run at the same speed relative to you. You call it a tie. But if somebody else is flying along in a spaceship alongside one of these runners, they see the two runners moving at different speeds relative to them, and moving clocks run slow, which means they see one of these runners in slow motion relative to the other one, so they'll think one of the runners wins the race and the other one is slower. But another judge going the opposite direction sees this same thing, but flipped He sees the first runner's clock running slow, so he thinks the second runner wins the race. So who you think wins the race depends on the speed you're going relative to the runners. Like people can honestly disagree about the order of events. Did the first runner reach the finish line first or did the second runner reach the finish line first. This is not a case of like people being confused or mistaken or getting things wrong. It means that there are multiple true stories about what happened in the universe that conflict with each other.
Well, there's sort of one story, right, It's just when you transform it between points of views, the order of events changes.
Yeah. That sounds to me like multiple stories. But you're right that we can link them together. Special relativity tells us how to predict what any observer will see. And what special relativity says is that different observers will see the order in different events. The laws of physics are consistent from frame to frame, and they predict the observers tell different stories. Yeah, so you can think about that as like one coherent understanding.
Yeah, that's what I mean. It's like it's not like there's two realities or that nobody can ever figure this out. It's more like, you know, everyone has to agree on which observer they're measuring the race by.
Right, that's right. It means that the order of events is not universal, right, that it's dependent on the observer.
Well, or it is universal, as you said, it changes depending on what you ask.
Yeah, it depends on the observer. Right, It's not something everybody agrees on will happen from their point of view. Right, different points of view will see a different order of events. And that's very confusing when you think about causality, because you think, like you know, there should be an order two events, Like you can't finish the race before you start it, you can't receive a message before you send it, you can't die before you're born. There are some things in the universe where there's a causal link between them, right, and so they have to happen in a certain order.
All right, Well, what does that mean for causality and antimatter?
Then well, you might think that this makes the universe nonsense because if different people can see events order different ways, does not just break causality. Does that mean you can eat an apple before it's grown. Does that mean you can get a message before it's sent? To this kind of stuff, Well, special relativity has some protection built in for that, right, It says this can only happen for things that are really, really far apart, things that are so far apart that light can't pass between them. We call these spacelike events instead of timelike events. And so you can reorder events that are really really far apart because they're already not causally connected. If two things are so far apart that light couldn't pass between them, then there's no way for them to have a causal connection. You can't like send a message from one to the other. And so things that are already causally not connected. Those things you can reorder by traveling at some crazy speed. Things that are causally connected, like if you turn on a flashlight and then the beam arrives somewhere else, there's enough time for light to get from one to the other. You can't reorder those events just by going faster or slower.
All right, So then how does that figure into antimatter?
So these events that you can't reorder, those are things we call inside our light cone. Light cone are things that we can affect in our future, and there's things that affected us from the past. So that special relativity, and it has this nice causal connection for things inside your light cone. Things outside your light cone, they can get reordered by things going faster or slow. Quantum mechanics, however, doesn't naturally obey this rule. Quantum mechanics has weird limitations on how much you can know about objects, momentums, and velocities, so For example, you measure a particle really, really specifically, the heisenbergen certainty principle tells you you can't know anything about its velocity how fast it's going. So, in principle, quantum mechanics allows things to go faster than the speed of light. That allows particles to move from one place to another outside the light cone because they could be going faster than the speed of light. Quantum mechanics doesn't have the speed of light built into it, naturally, it allows particles to violate this speed limit. Whoa, whoa, whoa whoa.
Uh on, then they think quantum mechanics can break the speed of light. That sounds a little bit too much, Daniel, I think you mean maybe, like our math allows it to, but we don't know if in reality it can go faster than light.
Doing If you just start from sort of low speed quantum mechanics, the original quantum mechanics that was developed right, non relativistic quantum mechanics for slow moving particles, then that theory with the Heisenberg uncertainty principle doesn't respect the speed limit of the universe. It's only when you try to bring quantum mechanics and special relativity together to make a theory of relativistic high speed particles that you have to answer this question like, uh, oh, what happens if particles that quantum mechanics predicts can go faster than the speed of light? What does special relativity say about that? So it's you know, in trying to bring the mathematics in harmony with the universe, that we run into this problem. We're like, hold on a second. Quantum mechanics has this problem with causality, allows things to move outside your light cone. What's going on and between you bring these two things together, that antiparticles save the day and allow you to bring quantum mechanics and special relativity together in a way that makes perfect sense.
I think maybe what you mean is that antimatter says physicism because their original theory made no sense.
Yeah, you cannot bring quantum mechanics and special relativity together without anti particles.
Right, It's like the limitations of the theory would allow things to move faster than light, but probably in reality they don't.
That's right. We think special relativity is the law of the universe. Nothing moves faster than light. Original old school quant mechanics has this problem that allows things to move faster than the speed of light, potentially breaking causality. And you're right, we don't think that happens in reality, So we need to patch up the theory. And it turns out that we need antimatter in order to do that.
All right, Well, let's dig into how antimatter saves the day. It's sort of like a plot twist. The villain actually turns out to be the good guy. So let's dig into that, and what does it mean about our understanding of matter, antimatter and all kinds of matter in the universe. But first, let's take another quick break.
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All right, we're talking about antimatter antiparticles. Why do we have them? Why do we need them? It turns out that they're useful in making our theories work, which is not really I guess an answer to the question, is it.
Well, it's sort of an answer to the question. You know, it says that the universe needs this to be consistent, or our theories need this in order to be consistent. Description of the universe.
Okay, So then you were saying that it somehow helps reconcile special relativity and quantum mechanics. How does it do that?
So let's think about how quantum mechanics breaks causality. Right. Imagine you have like a particle that you emit right here at this moment, and quantum mechanics predicts that it has a probability to end up like in Andromeda ten seconds from now. That would break causality because it'd be outside your light cone. It would be like getting to Andromeda faster than the speed of light. Nothing that we do right now should be able to affect Andromeda until millions of years into the future, because Andromeda is millions of light years away.
I think you're saying, the quantum mechanics, we have a description of a particle here, and because there's uncertainty about where it can be, there's a certain probability that in the next second it can be right where it is now, or it can be a meter away or two meters away, And there's a very very very small possibility that in the next two seconds, according to the quantum mechanics, it can then be in Andromeda. That's kind of how you would describe it.
Yeah, exactly if you have a lot of uncertainty on its momentum because you've narrowed down its position super duper well, and Heisenbergen certainty principle tells you you can't know both things at the same time. So if you know the position really really well, you don't know the momentum, and therefore there's a possibility that it has some crazy high momentum would be faster than the speed of light, getting it to Andromeda in just ten seconds instead of the millions of years it should take. And this would be a problem for causality because those two events are space Like, it's outside of our light cone, which means that somebody flying by in a spaceship could see them happen. In the other order, could see this particle arrive in Andromeda before it leaves our galaxy, which is nonsense. Right, So anything that moves faster than the speed of light breaks causality. That's one reason why we don't think things can move faster than the speed of light, because it would allow you to reorder events that are causally linked. Right, so make the universe nonsense.
Well, it sort of sounds like quantum mechanics just breaks causality anyways, right, doesn't the quantum mechanics say that particles can just pop out of nowhere without any cause? So like quantum mechanics says that a particle can suddenly disappear here and appear in Andromeda. Why not?
Now, I wouldn't say that quantum mechanics necessarily breaks causality. It makes a different description of the universe. It makes the universe probabilistic instead of deterministic. You know, it says weird things can happen, like a photon can turn into an electron and a positron, or it could do something else. It says that the laws of the universe only predict what might happen instead of what does actually happen. But there is still causality. Like in quantum mechanics, the wave function right now is determined by the wave function in the past. Right the wave function itself doesn't specify exactly what will happen, only the probabilities. But the wave function is still determined by the past wave function, so there should still be logic in quantum mechanics.
I guess that's weird because if you're saying that anything might happen.
I would say anything might happen. You know, quantum mechanics. This is the probability for things to happen. Some things are impossible even in quantum mechanics, Like you can't violate conservation of electric charge, right, Electrons have no probability to turn into positrons directly because I would violate conservation of electric charge, which is built into our quantum mechanical theories.
But haven't we talked about how like according to quantum mechanics, a pink elephant could certainly appear out of nowhere, outside of the Earth's orbit right in space.
Yeah, that's not impossible. That doesn't break any of the rules.
But then we have no cause, would it.
Well, the cause would be that there's a distribution of probabilities for what those particles in the vacuum could do. They could sit there and do nothing. They could create one electron, they could create ten electrons, they could create forty two trillion electrons. They could create a Boltzmann brain, they could create a pink elephant. Those things are probabilities. What does our universe choose one particular probability and not another? What does it choose one that's like really unlikely, like a pink elephant in space, and not another that's more likely that we don't understand. That's like a deep question in quantum philosophy, whether all of them happen at once in different universes, Whether the universe collapses these wave functions to choose one, whether it even is truly random. That is definitely not something we know. But I wouldn't say there's no cause. There's still like a distribution of probabilities for what might happen.
Well, let's get back to the antimatter particle. How does that antimatter particle fit into this scenario.
Then, So it turns out if you do these calculations, and you calculate, like, okay, what's the probability for my particle to appear in and Roma in ten seconds from now now, and you include antimatter, then those probabilities vanish. Because the probability for you to see a particle go to Andrama in ten seconds, there's another probability for a particle to go from Andromeda to here in ten seconds, for an antimatter particle to come the opposite direction, And because matter and antimatter have all the opposite properties, those two things quantum mechanically cancel each other out. So the antimatter nonsense cancels out the matter nonsense to make no nonsense. Whoa, whoa, wha.
Wait, we had the scenario of having one particle here that suddenly appears in Andromeda in ten seconds. You're saying, there's a different scenario in which an anti particle, the exact antiparticle of my particle is where my particle would appear. That one disappears and appears where my current particle is at the same time, and somehow that cancels it out, But what are the chances that there's an antiparticle exactly where my my particle would go.
Well, all of this stuff is very unlikely. But when you do a quantum mechanical calculation, you sum over all the possibilities, and these equations are wave equations, so you can get like constructive interference and destructive interference and things where the probabilities cancel out, those things just don't happen. Like in the double slit experiment, you see interference places where lots of particles and places with no particles, the places where no particles land, and the interference on the screen is because there's been destructive interference among the probabilities. So when the probabilities cancel out, those things just don't happen in the universe. And so the probability for a particle to break special relativity and appear in Andromeda is canceled out by the probability for an anti particle to do the opposite.
Well, I guess what does it mean to cancel out the probability? That means that it's never going to happen.
It means that it's never going to happen. And so if you bring quantum mechanics and special relativity together, and you include anti particles, then it all clicks together perfectly and you get no violations of causality.
Wit.
Wait, the wouldn't that also cancel all movements, like even a meter distance?
Yeah, great question. It doesn't happen for things inside the light cone because things inside the light cone everybody agrees on the order, whereas things outside the light cone you can reorder them. So, for example, if I say, well, look, my particle left here and ended up in and rama in ten seconds, that's outside my light cone. So somebody else flying by in a spaceship might see them happen in the opposite order. Right. Seeing it happen in the opposite order is like seeing a particle go backwards in time, which is equivalent to the anti matter particle. Right. So both probabilities exist, the particle and anti particle version, because you can reorder them because they are outside your light cone. Things inside your light cone you can't reorder them. Their order is fixed. Only things outside the light cone where you could reorder them, where somebody could see it as a particle and the other person could see it as an anti particle. Only those things cancel out.
It feels a little convenient, like maybe saying like, oh, my theory breaks down after this limit. Let's just come up with something totally different that makes sort it only applies outside of this limit where my thing breaks.
Yeah. Well, it's sort of convenient and sort of spooky, right. It's sort of like if you didn't know anti particles existed, and you were trying to bring quantum mechanics and relativity together into relativistic quantum mechanics, you be like, huh, this is a problem. This could be solved if, for example, there were the existence of antimatter hmm, and then you went out in the universe and you found it, you'd be like, wow, that was pretty cool. Here it sort of works the opposite direction. We're like, no antimatter exists, and we can use it to help bring these two theories together. It is very convenient, but that's sort of like a glorious moment when you're like, oh wow, look these things. They sort of need to exist for the universe to be self consistent.
Now, you said something earlier that was kind of interesting. You said, anti particles kind of go back in time. What does that mean?
Well, mathematically, you can look at a particle moving forwards in time, and it's equivalent to an antimatter particle moving backwards in time. And you can sort of see that in this example we're talking about, where like, my particle goes from here to Andromeda, and it does it faster than the speed of light. Right. If it does it faster than the speed of light, that means that somebody else going by in a spaceship they could see it happen in the opposite order. They could see it arrive in Andromeda before it leaves my house in the Milky Way, right, which means that it's started in Andromeda. The first event is in Andromeda. So I could say, look, this is a particle going forwards in time faster than the speed of light. Somebody else could say, no, it goes the other direction. They could say, no, it's going from your future to your past. But I see it as an antimatter particle, because they could reorder the events, and so they see it going from Andromeda to the Milky Way, and they see it moving as an antimatter particle.
But I guess maybe in order to measure my particle here and there, don't I need to measure the particle, wouldn't they collapse the wave function and make this all kind of not really applicable.
You would need to collapse the wave function absolutely, and of course it wouldn't really happen. Right, That probability is actually zero. You can't collapse the way function and make this happen. What we're talking about really is just a partial probability. There's another part to that calculation, the antimatter part that cancels it out. So you can't actually do this right. You can't see a particle appear in Andromeda in ten seconds. It would take millions of years to get there, and the probability for that to happen is canceled out by the anti matter version. So that's why it just doesn't happen.
Is this sort of like one of those virtual particle scenarios where like just a matter of fact that something else can happen, actually in a way happens, canceling out other effects that are happening.
Yeah, you can think about this the way other quantum mechanical weirdness happens, where like particles can interfere with themselves. Right again, like in the double slit experiment. If you don't know which slit the particle went through, has a probability to go through both, and those probabilities can actually interfere with themselves, so single particle interferes with itself. This is sort of the same deal. Like this single particle that goes from here to Andromeda, you could also be seen as an antimatter particle going the other direction, and those two probabilities cancel, which is why it never actually happens.
All right, well, then what is the I guess main takeaway is it that quantum mechanics does work with special activity, and it's because antimatter particles exist or are a possibility in the universe.
That's exactly right. You need antimatter to bring quantum mechanics and special relativity together and not break causality. If we think the universe is causal, meaning that like there's a logical flow to things that the past influences the future and not the deep past, then you need antimatter in order to have special relativity and quantum mechanics. We just don't know how to do it without antimatter.
Cool. All right, Well, you've commissed me. I'm pro antimatter or I'm not anti antimatter.
Does that mean that you're pro anti vanilla, which means you're willing to try some chocolate.
I am pro anything with the word vanilla in it, all right.
I'm part of the Vanilla eradication project. How do you feel?
Right?
Oh my god? And that is how this podcast got canceled, Daniel. Thank you. It's been a nice run. We're done.
No, I love vanilla. Vanilla is wonderful.
We've gone the way of Scott Adams and Dilbert.
I'm not a flavorist, Okay, I'm definitely pro vanilla.
I'm just more flavorists, Daniel.
I need to go for some flavor sensitivity training.
It sounds like, thank you, maybe you should examine those anti FeAs, all right.
Well, between this and the next episode, I will do a deep dive into my own internal flavor preferences.
There you go, examine your own anti matter, all right. Well, another interesting bit of how we're trying to figure out how the universe works, and how sometimes it's interesting how our theoris of the universe actually kind of turn out to be true, which is kind of surprising, right.
It is surprising sometimes that crazy little human brains can come up with mathematical stories that do seem to describe the universe, even in ways we didn't anticipate.
All right, well, thanks for joining us. We hope you enjoyed that. See you next time.
Hey everyone, I want to take a moment and share a personal message with you. When I record these podcasts, there's no live audience here and so I have no idea really how they're going to be received. So I love hearing that they have an impact on people's lives, maybe inspiring you to think about the universe, or talk to your kids about physics, or even just keep your brain going on long drive or a boring shift at work. That's what gives me the energy to keep making these to put them out twice a week without fail for five years now. So it really heartens me to hear from you. But I realize that you all don't get to know each other as much to hear about these experiences. So I want to share a little bit with you, including an example that made me smile and one that frankly brought some tears to my eyes. First, a happy one. Someone writes in and says, I don't have a question but a compliment. Just wanted to let both of you know that I greatly appreciate the way you explaining physics. As a person who has no science background and barely passed college algebra, it's refreshing to hear people explain things without talking down to the listener. That's wonderful and it's exactly what we're trying to do, make physics more accessible to everybody without dumbing it down at all. But some of the messages we get are a little bit harder to hear. A woman wrote in that her brother is a listener and an ultrarunner, but that at thirty nine he had a massive stroke and faces a long recovery. She writes that quote each night he makes sure his phone is charged and loaded with enough Daniel and Jorgey to get him through the night. It's without drama that I say that your show is one of his lifelines right now. You guys are his intellectual support above all, on behalf of our family. I want to thank you for your podcast and being a comfort to him in this season. Wow, it's hard to overstate how deeply that touches me, and I want to send him our encouragement on his road to recovery. I'm so glad that we can be there to help in this small way. And I want to say thank you to everyone out there, those of you who are listening and writing back or just enjoying silently. You're all the reason that I do this. Thanks for listening, and remember that Daniel and Jorge explain the Universe is a production of iHeartRadio. For more podcasts from iHeart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases many farms you anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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