Daniel and Jorge Explain the UniverseDaniel answers Listener Questions about black holes, antimatter stars and why the Universe exists!
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When you look up at the majesty of the night sky, when you marvel at the intricate beauty of our microscopic, quantum world, sometimes you just can't help but wonder where does it all come from? Why does our universe exist at all? Who or what is responsible for all of this crazy, beautiful, bonkers universe. That's the biggest hope and the biggest challenge for physics, not the small question of why are we here, but the much bigger, deeper.
Question of why is there a here at all? Hi, I'm Daniel, I'm a particle of physicist, and welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio. On this podcast, we talk about everything in the universe, the stuff that's really big and vast and hard to understand, and the stuff that's super small and tiny and mind bogglingly weird. We talk about all of it, and we explain it to you in a way that we hope actually makes sense. It leaves you with the feeling that you have grappled with a small piece of the world and one that you could import part of the universe into your brain, that you can make a little model inside your head of what's going on out there in the universe, and that it can work. It can help you understand how the universe works, think about what it's doing, and make predictions about what it might mean. The goal of this podcast is not just for you to hear a bunch of fancy science sounding words and come away feeling like you were in the presence of science, but to invite you to include you in the process of science, because science is a human endeavor, is by the people of the people, and for the people, and you are the people. You're the people we are doing science for. It's not just for a bunch of folks in white lab coats and crazy hair. Is for everybody, because humanity wonders about the universe, and humanity deserves answers about the universe. And that's why humanity has decided to spend a non trivial amount of money paying for science. And that's why I think it's important that US scientists come back and talk to people and explain to them what we have learned, what it means, and connect back with that inherent curiosity that, in the end, is what's responsible for driving this entire wonderful, crazy, frustrating, exhilarating project of unraveling the mysteries of the universe. Normally, I'm joined by my co host, Jorge cham a cartoonist and roboticist, and we joke about bananas as he asks me crazy questions. But he's not available today. So I am taking the opportunity to catch up on questions from you instead. That's right. Our loyal listeners often send us questions things that they think about, that they are wondering about. They have imported a little bit of the universe into their minds, and one piece of it doesn't quite make sense. And so I encourage everybody out there who has a question about the universe, something they are wondering about, something they would like to hear understood, to write to us. Send us your questions either on Twitter at Daniel and Jorge or via email to questions at Danielandthjorge dot com. We write back to everybody. We answer every email. You will get your question answered. And sometimes the questions are interesting enough or fun enough that I want to answer them here on the podcast because I think other people might want to hear the answers to these questions. I think that probably a lot of people are wondering about those particular questions, and so on today's episode will be answering listener questions. I love all of our episodes, from the science fiction universe to the extreme universe to the everyday physics, but maybe closest to my heart are these questions that come from you, from the listeners who are wondering about the world, Because, as I said earlier, questions really are at the heart of science. Science doesn't move forward without people, individual folks asking questions about the universe and wanting to know the answer. Think about that graduate student or that physicist or that biologist out there devoting her life to answering one particular question about the way microbes work, or about the way rings form about a planet. It's because that person has a deep curiosity about that one question and needs to know the answer. So that's one of the joys of life, is figuring out who you are and what you want out of it, and what questions you want answered about the universe. So please don't hesitate. Send me your questions. I'd love to encourage them and to help give you a few answers. And particularly i'd like to encourage our listeners from Africa and from South America. We get questions from all over the world. But I was looking at the demographics recently and realizing that there's a group of people out there who've been a little more silent than the other folks. So if you're a listener in Africa or in South America. Please take my special encouragement to write to us with your questions. We want to hear from you and we want to help you understand the universe. All right, So let's get to the first listener question. This one comes to us from a very young listener him.
My names Megan.
I'm nine years old. I heard my damn on the show, and I want to ask you a couple of questions. So number one, halean does it take to get to a black hole? At number two, why are the stars round? Thank you for answering my question.
Bye, Well, thank you Meggan for sharing your questions. I think she overheard her dad. I want to answer questions for future topics. So thanks very much Meghan's dad for letting Meghan send in her questions and for encouraging science and curiosity in the next generation. So Meghan asks us two questions. First, how long does it take to get to a black hole? And why are stars around? Well, my first thought is like, why does Megan want to go visit a black hole? And is that a good idea? I mean, I certainly want to go visit a black hole. I want to go see what's inside them and maybe learn something deep about the nature of the universe and help unravel the secrets of quantum gravity. But you know, I'm not nine years old, and so I think it's up to Meghan's dad to decide whether or not he should lend Meghan the keys to the spaceship for this particular field trip. So how long does it take to get to a black hole? Say you wanted to get into a spaceship and go to visit one. Well, you know, there are two kinds of black holes out there in the universe that we've discovered. There are the ones at the centers of galaxies, super massive black holes with masses like millions of times the mass of our sun. Those are spectacular and very interesting, but also really far away and hugely dangerous because they are as the centers of galaxies where the radiation is intense and the X rays just from the black hole's accretion disk itself would be really intense, and then just the center of the galaxy is a pretty crazy spot. So there is another kind of black hole which I think would be much more reasonable to visit, and these are stellar black holes, the ones that result from a star aging and no longer having fusion pressure to push back against gravity, trying to squeeze it down and eventually just giving up the ghost and becoming a black hole. And so the one that's nearest to us is actually only about eleven hundred and twenty light years from the Sun. It's called qv telescope. If you want to put that into your space navigation system, and you might ask, well, how long does it take to get to s something that's eleven hundred light years away? Well, you know, if you traveled at the speed of light, of course, it would take eleven hundred years, which seems like a really long time, and it is. But there's a bit of a relativistic wrinkle we'll dig into there in a minute. But we, of course can't travel at the speed of light unless you develop some technology to like scan your body and convert it into photons and beam yourself somewhere else. But then you'd need some technology on the other side to receive those photons and reconstruct your body. So a more realistic way to go and visit a black hole is to build a spaceship that's actually capable of such flight. Now, there are two main limits to doing such a thing. One is acceleration. To get up to that speed, you have to speed up, and the human body has some pretty tough limits on how fast we can accelerate. If you try to accelerate more than five or ten g's, your insides will get liquefied, and so for comfortable travel over long periods, you really don't want acceleration much more than one G. So let's do the calculation. Say you have spaceship that could accelerate at one G. You would actually get up to pretty close to the speed of light within just a couple of years, so most of the trip would be spent pretty close to the speed of light. So if you have to travel one thousand, one hundred and twenty light years, it would only take you one thousand, one hundred and twenty two years. Now, the other problem with this scenario, of course, is the fuel. To accelerate, you need fuel, and fuel makes your ship heavier, which means you need more fuel to accelerate it. So you have this rocket equation problem, sometimes known as the toothpick problem, because accelerating something even as small as a toothpick up to very high velocities would require an enormous quantity of fuel. And so, for example, if Megan's ship was ten tons, which is really pretty small for a spaceship, it would require something like thirteen million tons of fuel for this kind of trip, and so basically the ship would be all fuel, and most of that fuel is there to help push the rest of the fuel. So this is why we talk about things like black hole power drives and other kinds of things. Of course, it'd be kind of silly to have a black hole power drive to go visit a black hole. If you have a black hole power drive, that means either you can capture or make your own black holes anyway. But the relativistic wrinkle is actually quite interesting because while from Earth's point of view, it takes one one hundred and twenty two years before you reach that black hole. So that's like Megan's dad's clock. If he had a telescope and he was keeping an eye on Meghan during her trip, he would see her clock running very slowly, according to him, very very slowly, so that by the time she reaches the black hole, she would only have experienced thirteen point seven years, so she would only be twenty two years old by the time she reached the black hole. Now, of course, for everybody back on Earth, more than a thousand years would have passed. And if she actually wants to turn around and come back to Earth, that's a whole other relativistic wrinkle. When she turns around special relative, it gets really complicated because that's another kind of acceleration, and that gets us into the twin paradox, which we can talk about another time on the podcast. So, Meghan, the answer is, it would take you more than a thousand years to reach a black hole, but from your point of view, it would only feel like about fourteen years. So fac to that into your decision about whether or not to build your spaceship and go visits black hole. But if you go and you do discover secrets of the universe and quantum gravity, please send me an email now. Megan's second question was why are things around? Like why are the stars round? Which is related to another really interesting question, you know, like why are planets around? Why is most of the stuff in the universe round? And the answer is gravity. A little bit counterintuitive, but gravity, even though it's the weakest force we know about, is the dominant force when it comes to the structure of astronomical stuff, the shape of the Earth, the shape of the Sun. All this kind of stuff is round because of gravity. And think about it pretty simply. Gravity pulls stuff down, right, So if you have the Earth with anything sticking up on it, eventually that's going to get knocked down, maybe wind or water, even if you don't have any atmosphere or water on the surface. Any kind of process eventually is going to settle into a lower energy state. And for gravity, the simplest configuration a lowest energy state is a sphere. So anything that's big enough to have its own gravity is eventually going to be round. That's why small things are not necessarily round, like asteroids and meteors are sometimes weird shapes because they don't have the gravity to pull themselves together into a round object. Whereas things as big as the Earth or even the Moon or definitely the Sun. Gravity does its thing and pulls anything that sticks out a little bit down until eventually you get a sphere. But of course, not everything out there in the sky is a sphere, right, I mean, our Solar system is not a sphere. It's like a flat disk, and our galaxy is not a sphere. It's also a flat disk. So why is it that those things are not round, And that's because they have something which can actually overcome gravity, and that's spin, that's rotation. The Solar system is spinning. The Earth is spinning around the Sun. That's why it doesn't fall in due to the Sun's gravity because it has enough velocity to stay in orbit. And the same thing with the Sun. The Sun is spinning around the center of the galaxy, which is why the Sun and all the other stars don't just fall into the black hole at the center of the galaxy. And that's why black holes have an accretion disk around them, because that rotation keeps stuff from falling in. So you have a couple forces here at play. Mostly you have gravity dominating for things like the size the Moon and up to the Sun. But then if things are spinning fast enough, they will turn into a disk. Like if you took the Earth and you spun it faster, it would turn into a disk. In fact, the Earth itself is not exactly round because it's spinning. Distance from the surface to the center of the Earth is actually greater at the equator because the Earth is spinning, and if you spun the Earth even faster, it would eventually turn into a pancake, and the same with the Sun. So everything out there is balancing a bunch of different forces. Mostly you don't see the effect of electromagnetism or the weak nuclear force, or even the strong force on the shapes of astronomical objects because they're mostly balanced out. The Earth doesn't have an overall positive charge. The Sun doesn't have an overall negative charge. If it did, that force would be so strong, it's so much more powerful than gravity that you would get these streams of basically currents until things did get balanced out. But gravity can't get balanced out. There is no opposite charge to gravity. There's no negative mass that can create anti gravity to balance out gravity. Gravity is always there, It always has to be contended with. It has to wait until everything else gets sorted out and neutralized before it basically gets to take the field and dominant. But eventually gravity takes over. And that's why gravity is the dominant force for the universe, and that's why the Sun and the Earth are round, all right, Megan, thanks very much for those wonderful questions. I want to get to so more less inner questions. But first let's take a quick break with big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price you thought you were paying magically skyrockets. With mint Mobile, You'll never have to worry about gotcha's ever again. When mint Mobile says fifteen dollars a month for a three month plan, they really mean it. I've used mint Mobile and the call quality is always so crisp and so clear. I can recommend it to you. So say bye bye to your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. 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Hello Daniel and Jorge, So I have been wondering for some time about anti matter stars. We know matter is everywhere in the universe and anti matter just doesn't exist in quantities that are big enough for anything like this. But if there was an anti matter star, or if there is a one in the whole universe, how could we tell it's an anti matter star? How would it be different? It would shine like a normal star or would it? Thank you?
All right? Super fun question? I love this kind of question, like, how do we know what we know? Is it possible for this weird, crazy scenario life thought of in my mind to be our reality? And that's a very important kind of thought process, and that's basically what physicists are doing. We're always wondering, all right, here's what we know. What is that consistent with? Is there a way I could imagine the universe to be different and still look the same way? Are we being fooled by our preconceptions? So it's this kind of creative, out of the box thinking that's really vital in science. So let's dig into it first. Let's just remind ourselves, like what is antimatter? What do we know about it? The existence of anti particles is one of the most incredible and beautiful symmetries for me. In the universe. Every particle that we know of, every fermion, electrons and quarks and neutrinos, and all of these particles have a partner particle. There's like this symmetry where you reflect all these particles and boom, they all have an exact opposite. So the electron, for example, has the positron, which is a positively charged version of the electron, and the muon, which is naturally negatively charged, also has a positively charged version. Each of the quarks, like the upcork and the downcrk, have an anti up anti down. This is stuff that you hear about in science fiction, but it's actually real. It's out there in the universe. It's a kind of thing that can exist. And when we do particle physics, we're often exploring two different questions. One is can this stuff exist? Like what's out there theoretically on nature's menu, which if you made the right conditions, could exist in the universe, And then like, is there any of it? How do you actually make it? Can we created? Which is a totally separate question. But antimatter is something that's in the universe, and frankly, we don't know why. Why does every particle have this mirror version of itself? Why does that exist? It tells us something deep about the nature of the universe that every particle seems to come in pairs. Maybe it means that we shouldn't even think about the particles as in pairs. Maybe the fundamental object is the pair, not the particle, right, Because if everything comes as part of a unit, then maybe that unit is the thing that's part of the universe. This is kind of the deep fundamental theoretical questions. You can spend a lot of time smoking banana peels and thinking about And we do a lot of experiments to try to understand antimatter. We make it it cerned, but we can't make a whole lot. You have to smash protons and do a big block of matter, and some little bits of antimatter come out sometimes and we can collect it and do experiments about it. And one really interesting question we have about antimatter is it actually an exact copy? Is it really the same thing as matter but with the charges reversed? Are anti electrons really just the exact opposite of electron? And one way to think about that, and this is I think the direction of this question about antimatter stars is does antimatter behave the same way as matter? Like can you make big complicated things out of antimatter the same way you can out of matter? And we've done these kinds of experiments so far. We've made things like anti hydrogen, which is an anti proton with an anti electron in orbit around it, and we've studied it and we've asked like, well, does it look like hydrogen? Does it radiate energy the same way? Does it follow the same physical laws? And so far the experiment suggests that it does. We've never detected any difference between the way antimatter works and the way that matter works. So it seems like a perfect symmetry. And yet there's a big mystery there because we know it can't be a perfect symmetry. How do we know that, Well, the universe is mostly made of matter, right, I'm made of matter, You're made of matter. The Sun is made out of matter, The Solar System is made out of matter. If matter and antimatter are basically symmetric and the universe treats them exactly the same way, why is there more matter than there is antimatter? This is one of the deepest questions in physics. We just don't know the answer. You know, we imagine that when the universe began that things were symmetric, because it's hard to imagine anything else. If you imagine the universe started out with more matter than anti matter, you're just sort of like presupposing the answer to the question and introducing a new question. If the answer to the question, why does the universe have more matter than antimatter is just well it started that way. Then you can just ask why did it start that way? So it's more interesting to start from the assumption that the universe began with equal amounts of matter and antimatter. But now we don't have as much matter. So what happened to it? Well, we know what happens when matter and antimatter meet each other. They annihilate. What does that mean? And from a particle physics point of view, it's not magic. It just means that, like when an electron meets a positron, they can turn into a photon. They turn their matter into energy. Right, this is e equals mc squared. Matter is really just a form of energy, and so you can turn that matter into energy and they can annihilate into a photon, or they can annihilate into a z boson. Quarks can meet anti quarks and turn into photons. They can also turn into gluons. So all these kinds of matter can annihilate and turn into energy, which can then do whatever energy wants to do. So, if there was an equal amount of matter and antimatter in the early universe, you would expect it would eventually meet and annihilate itself, and we would have a universe just filled with photons and gluons and z bosons and stuff like that, but we don't. We still have matter left over, and so people wonder, like, is there some process in the universe which preferentially turns antimatter into matter, so that we ended up with a little bit more matter and then the rest of it annihilated and we had some leftover, which is just matter, which is what we are, which is what created the entire universe that we are living in. So that's the idea, but we've never explained that. We don't have an understanding of how that happens. There are a few processes and particle physics we found which seem to prefer creating matter to antimatter. And these things are like CP violating processes and B and K masons, and you can listen to our podcast episode about CP violation if you want to hear more or about that. But these are not big enough to explain the asymmetry. They account for a tiny fraction of the asymmetry. You need a much more dramatic way to turn antimatter into matter to explain the universe that we see, so we don't understand it. And this suggests to us that there is some asymmetry between matter and antimatter. There really is some reason why the universe prefers matter to antimatter, and we want to know what that is, right, We want to know why because that seems like a deep truth about the universe. But then there's another possibility, the other possibilities. Hold on a second, and this is the question that was asked, really is how do we know there isn't more antimatter out there? Are we just assuming that all the stars out there are made of matter? What if they were made out of antimatter?
Right?
The question is wonderful because you're exactly right. An antimatter star would look a lot like a matter of star. If antimatter can do things like make anti hydrogen, then why can't anti hydrogen anti fuse into anti helium. If it did, it would produce photons just like the matter version of that process. So mostly you're right that antimatter stars would look like normal stars. And so when you're looking out in the sky, it is possible that some of those stars might be antimatter stars, but it's not exactly the same, because stars don't just produce photons. Obviously, they produce lots and lots of photons. As you're out there sunning your face on a nice winter morning, it doesn't really matter if those photons came from a star or an antimatter star, because the photon is a boson, it doesn't have an antimatter version of itself, and so it could come from an antimatter star. But stars make other things too. You're familiar with the solar wind, for example, the solar wind is a stream of particles that come out of the Sun when fusion happens. In the crazy chaos of a star. You don't just make light, You make neutrinos, you make electrons, you spew off protons, and so that's solar wind. Can tell us something about what kind of star it is, because an antimatter star would make antisolar wind, right, it would preferentially produce antiprotons and positrons and anti neutrinos and all sorts of other crazy stuff. All right, but these stars are still really far away, right, how would we know if those stars we're making this antimatter solar wind well inside our solar system? We're pretty sure everything's made of matter, right, we don't think that one of the planets is made out of antimatter. And then we have two ways of figuring out whether other stars might be made out of antimatter. One is just to look at cosmic rays. Cosmic rays, some of them come from the Sun, but a big proportion of them don't come from the Sun. They come from the other stars in our galaxy. And so this like galaxy solar wind, is an accumulation of all the solar wind from other stars, and that contains a lot of particles, and some of them are antiparticles. Right, there are positrons and the there are anti protons in that wind. Cosmic rays sometimes are antiparticles, but we don't think that comes from anti stars. We have an explanation for how you can make anti particles, like pretty simply photons sometimes split into positrons and electrons, and so we have an idea and we can explain even how to make anti protons in solar wind. So basically, the cosmic rays that we see here on Earth or in our telescopes up in space are totally consistent with the stars in our galaxy being made out of matter and not antimatter. If there was antimatter, then we would see heavier stuff. We would see like anti iron or anti uranium or anti oxygen, stuff like that. We see heavy versions of those elements in cosmic rays. It's a tricky topic. We don't have precise measurements, but we don't see any anti heavy elements in cosmic rays, so we don't think that there are anti stars sort of in our galaxy. Now cast your mind a little further, right, How do we know that Andromeda, for example? Is it made entirely out of anti stars? Are we measuring the solar wind from that galaxy? That's a lot harder to do, though. We do get particles from Andromeda, of course, But more generally, we have another technique for figuring out if there are like big antimatter patches to the rest of the universe, and that's by thinking about where the matter and antimatter patches might cross. Like if our galaxy was made of matter and Andromeda was made of antimatter, then the antimatter particles from Andromeda would be hitting the matter particles from our galaxy somewhere in between. And what would happen while they would annihilate, and you would see this like surface that was creating photons and other kinds of particles add a particular energy because you'd expect, for example, when an electron annihilates with a positron, it turns into a photon that mostly has the energy of twice the mass of the electron. So there's this characteristic flash of light that happens when antimatter and matter annihilate. And we can look to see sort of at the boundary between our two galaxies if that's being created, and we don't see it. And this is a very powerful way to look deep into the universe and see, like are there surfaces, there are there boundaries between matter and antimatter regions of the universe, And so we haven't explored the entire universe this way. We've looked out past our galaxy cluster and between other galaxy clusters, and we've never seen any evidence of like massive annihilation of matter and antimatter into photons, which is what you would expect to see again at one of these sort of like boundaries between a matter region and an antimatter region of the galaxy. So we haven't ever detected that. Now that doesn't mean, we can rule it out entirely in the entire universe, right there could be a portion of the universe that's so distant that we just can't probe it yet with these methods. Absolutely, we've looked sort of like the ten Megaparsex scale. We know that our large neighborhood doesn't have any significant antimatter in it. That doesn't mean that there isn't antimatter in the rest of the universe. So yes, absolutely, there could be an antimatter galaxy out there somewhere super far away and we just haven't seen it yet, or evidence of its cosmic rays annihilating with the cosmic rays from a matter galaxy. It's certainly possible, and that would be sort of a beautiful explanation to this mystery of antimatter. If it turns out that the universe actually is symmetric to matter in antimatter, If there are matter patches of the universe and antimatter patches of the universe, and that they're in balance somehow, then of course you have to wonder like, well, why did this become a matter patch and why did that become an antimatter patch. But you can imagine such things being answered by quantum mechanical randomness in the formation of structure and all sorts of fun stuff like that. But in the meanwhile, we're digging into the question of whether there are larger asymmetries between matter and antimatter. If, as we suspect, the universe is mostly matter, then we try to understand what that means, because we think that that's going to tell us something about like why there is matter at all, why we're not just living in a universe filled with photons. So if it's true that the universe is mostly matter, then we should be grateful that there's an asymmetry, because that is in fact why we are here. All right, wonderful question. Thanks very much for sending that in. I want to answer one more question, but first let's take another break. When you pop a piece of cheese into your mouth, or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are us. Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty 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. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the bomb, and irrigates the crops. How is US Dairy tackling greenhouse gases? 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Okay, we're back and we're talking about the nature of the universe, symmetries and black holes. And now we have a fun question from listeners that's maybe one of the deepest questions in physics and philosophy.
Hi, Daniel and Jorge. I know this often gets lumped into the realm of philosophy, but is there a physics explanation of why there is anything rather than nothing in the universe? Why does any of this exist? What may have tr triggered any of the matter, energy and forces we observe? Thanks James Cronister.
Thank you James for not being afraid to ask the biggest and deepest questions and the questions that overlap with philosophy. I don't think that's a negative thing to be lumped in with philosophy. I think it's wonderful. I think it means our questions are relevant. You know, philosophy tells us what our questions mean and why they're interesting, and why we want an answer to them, and how to think about them. And so I think that all of the deepest questions in physics have philosophical implications. That's why they're exciting. You know, if you knew exactly how the universe was created, for example, from a physics point of view, that would definitely have philosophical implications. So I think the most fun questions in physics are the ones that also get philosophers excited. And you're right, there's been a lot of philosophical discussion back to the ancient Greeks about why is there something rather than nothing? And it's a really fun question to think about. And first I think you should think about, like, what do we mean by nothing? What is the opposite idea that we're considering. On one hand, we have the universe and us, and there's definitely something here. What is the alternative that we're wondering about. What is the thing that we're trying to rule out? What is the nature of nothing?
You know?
And let's knock down first some very simple ideas about what nothing might be. From a physics point of view. It's not just like not having this stuff, not having these stars and these galaxies and these particles, right, It's something deeper. It's something about the possibility of things being in the universe. But the nature of existence itself, it's a pretty weird thing to consider, you know, a universe with nothing or not a universe. You couldn't ever, like do an experiment to prove that nothing exists, because of course your experiment is a thing, and so it can't really prove it. And so that's why this is a fun sort of philosophical question. But what I still think that we can make progress on if we think about what physics has told us about the nature of the universe and the nature of nothing. By nothing, do we mean, for example, just space, but with no matter in it, like, delete the stars, delete the galaxies, delete the planets, delete all the stuff that's out there in the universe. Is that what we would consider to be nothing? Well, I think it's an interesting question, like why doesn't that universe exist rather than ours? But I think the question goes deeper, right because I think in that question you would still ask, well, why is there space? Why is there a universe for things to be? And even if there don't happen to be anythings in it right now, that universe still has the possibility of things. And more specifically, we know that physics tells us that even space is not really empty a bowl. There's no such thing really as empty space. If you somehow remove all the matter in space and make as good a vacuum as you can, then there's still a thing there, and that's space. Because space has inside of it quanti fields, and those quantum fields we know are always buzzing with energy. Despite your best effort to reduce the energy of that space, quantum fields can't go down to zero energy. It's a fundamental property of quantum fields that their lowest state is not add zero energy. And in our universe at least there's one field, the Higgs Boson field, which is totally rife with energy. It's stuck, it's at this weird minimum that has a lot of energy in it. And so there's a lot of energy in even what we think about as empty space. And some people who think about the nature of the universe and why is there something rather than nothing take this as the answer. They say, well, there has to be something because space is filled with quantum fields, and those fields have energy and so boom, Therefore there has to be something. I don't really find that answer to be satisfactory, because it really just suggests another question, which is, you know, well, why do those quantum fields even exist? And I like the way that a philosopher, David Albert put about it. He says, quote, the fact that some arrangements of fields happen to correspond to the existence of particles and some don't is not a whit more mysterious than the fact that some of the possible arrangements of my fingers happen to correspond to the existence of a fist and some don't. Really, he's saying that it's not really that interesting to think about. Why are the fields sometimes making a planet and why are the fields sometimes making empty space? The question really is why are the fields right? Why do we have fields at all? Why do we have space even that has the possibility for fields? And this is the deep question I think that physics should answer, and this is sort of where physics is. We know that space is out there, We know that every bit of space is filled with quantum fields, and those quantum fields have energy, and so from that starting point we can ask the question, what does physics have to say about the nature of nothing and why there is anything? Because remember, the goal of physics is to try to grapple with the universe to make sense of it, and I think an important part of making sense of the universe is just understanding why it exists. You know, we want to understand that if the universe exists, it should be because it has to exist or because it cannot not exist. The nature of physics is to get the simplest possible explanation for the universe as we see it. You know, we use OCAM's razor, and we remove anything from our explanation that's not necessary. We want to boil it down to the smallest, simplest description. That doesn't mean we want to boil it down to nothing, right, That's why I think about the question in this way. Is the simplest thing something or is the simplest thing nothing? It might be that nothing is sort of incoherent. You know, what do we even mean by nothing? So from that point of view, if we understood the simplest, deepest nature of the universe, we might be able to point to it and say, oh, look, this is the simplest possible thing. It's even simpler than nothing. So that might be why the universe has to exist. So we're jumping ahead of ours those a little bit and digging into the implications of the answer. But first, let's talk a little bit more about what quantum physics and general relativity tell us about the nature of space and what that says about why it exists. So, of course we have two different voices in this story. We have the voice of quantum mechanics and the voice of general relativity, which tell us two very different stories about the nature of space and give us two very different answers about why the universe should or shouldn't exist. So let's start with quantum mechanics. Quantum mechanics treat space and time very very differently. Quantum mechanics says space is the place where quantum fields are. Every point in space is just a place where a quantum field has a value over here, the electron field has one value. Over there, the electron field has another value. That's all a quantum field is. It's just a point in space with a value in it. Sometimes that values a vector, sometimes it's a number, sometimes it's more complicated. Whatever, it's just a point in space. But time is separate. Time is how those fields evolve. And the most famous equation in quantum mechanics the Shorting equation. That's what that equation is about. It tells you if you have a quantum wave function or graduate that to a quantum field. It tells you how that changes with time. And the most important thing about the Shorten Air equation is that it says that quantum information is never lost. Like a quantum wave function changes as time goes on. Maybe a photon spreads out, or maybe it interacts with the wall or something happens, but the information is not lost. According to quantum mechanics and the shorter Air equation. Everything about the past is encoded in the present. This means that you can reconstruct what happened in the past just by looking at the information about the arrangement of quantum particles now. And the really fascinating thing about this is that it says that this works backwards and forwards. Right, the shortening equation can tell you how your wave functions will change as the future goes on. It won't tell you where the actual outcomes of experiments are, right, that depends on this whole measurement problem that we're not going to dig into today. But it tells you how the probabilities evolve and how they have evolved in the past. What that means is that quantum mechanics says the universe should basically be eternal because quantum information can't be destroyed, which means if it exists now, it always has to exist and it can't have not existed in the past. So from the point of view of quantum mechanics, the universe has to have always existed. There can't be a point in the timeline of the universe where it doesn't exist if it does exist today, So it sort of requires this like consistency as a function of time. Now, the mystery is that general relativity tells us a different story. Right. General relativity tells us that space and time are very very closely connected. It prefers a tightly bundled space and time with the two react together to the presence, for example, of mass in the universe. And general relativity is what help helps us understand the fact that the universe is expanding. It's not just that we have a universe, and not just like why is there something? Why is there every year more of that something than there was before? Right, the universe is expanding, it's growing, and when we think about the nature of that space, right, it tells us that space can be created. What's happening now between us and other galaxies is the stretching of space, the creation of new space. That means that space isn't eternal. It's being made right now by some process that we do not understand, and that tells us a different story about the nature of space, This basic fundamental thing that we're struggling to understand why it has to exist. Maybe it doesn't have to exist because there's some process that can make it, which means maybe the opposite is true. As well. And in fact, because we don't understand the mechanism of this creation of space, it suggests that the mechanism might be reversible. And there's still this possibility that dark energy will up and it will halt the accelerating expansion of the universe and turn things around and bring it all back and crunch it back together to make a new singularity, the time symmetric version of the Big Bang right pull together down into a big crunch. And this would involve not just the compactification of space, but the destruction of space, the shrinking of distances between things, exactly the same way that dark energy right now is expanding the distances between things by creating new space. This would involve the compactification. This would involve the destruction of space, the shrinking of distances between things, not just moving things through space, but actually destroying the space between them. That's pretty hard to think about, but it gives you a clue about like what's fundamental to the universe. Now. The problem is, we don't really believe that either of these theories are correct. We look at general relativity and we look at the history of the universe and we say it doesn't really make sense for the universe to always have existed. The quantum mechanical view that the universe can't have had a beginning because the information in the wave function of the universe can't be destroyed doesn't seem quite right. It doesn't job with our observation to the universe does seem to have had a beginning. It seems to only have been fourteen billion years old. On the other hand, if we retreat to the corner of general relativity, we say, hmm, some problems with this theory also. First of all, it ignores the obvious quantum mechanical nature of our universe. All of our particle physics experiments and investigations in the last one hundred of years have revealed that the fabric of reality is quantum mechanical, and general relativity ignores that. But more importantly, when we look back at the very beginning of the universe and try to understand, like, well, if the universe is being created, what is the beginning of that process, general relativity leaves us with a question mark that singularity, the moment of infinite density that begins our universe. In the general relativistic story, does it make any sense infinite curvature and infinite density is not something we think is physically true. We don't think it's a historical, actual accounting of events. It's a failure of general relativity. It's when the theory breaks down and can no longer give us a sensible answer. So what does physics tell us about why there is something rather than nothing? It tells us that we have a lot of work to do before we understand what is the thing that we are trying to explain. If we want to understand why there is something rather than nothing, we need physics to lead us closer to understanding what that thing is. Because when we know what that thing is, then we can ask interesting and fascinating questions about why it should exist and what it would be like for it to not exist. But we don't even know the fundamental nature of the universe. We need that unification of quantum mechanics and general relativity into some theory of quantum gravity so that we can look at it and we can say, okay, the basic element of the universe is a For example, why do strings have to exist? Would it be simpler to not have them? There are some people who think really interesting and fascinating thoughts sort of about that future without actually knowing what that future is. For example, one of my favorite books is Our Mathematical Reality by Max Tegmark, and he makes a fascinating argument which I don't actually believe, but I think it's super fun. He says essentially that because our universe can be described mathematically, therefore it is a mathematical construct, and that's why it exists. In his mind, you have to imagine, like every set of mathematical laws that do hold together and make a consistent universe, that universe exists because the mathematics works. I'm not sure I can take that last step that every mathematical self consistent universe that you can write down on paper actually does exist out there. It seems like you would have more really really simple universes than like vastly complex universes like ours, and that you also have to imagine, like what is the mathematical substrate on which all of these like meta universes are running on. But it's a really fun question, so I hope that answers your question. Basically, doesn't yet know what the thing is in something, so we can't really answer the question, why is there something rather than nothing. Thank you everybody who's sent in all your super fun questions. Keep thinking deeply about the nature of the universe and how quantum particles work, and please keep sending us your questions. They are the light of our day. We will answer all of your emails, trust me, or interact with us on Twitter if that's what you prefer. So please keep thinking deeply about the universe and keep asking questions. Tune in next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeartRadio, visit the iHeartRadio app Apple Podcasts 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. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. 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