What is the Cosmological Constant?

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Speaker 1: Daniel, what happens if you have a great new physics theory? I mean just really beautiful, gorgeous, perfect explains almost everything. This sounds great so far, but I knew it was a butt coming. But it's wrong about one thing. Well, is it like a little thing? Yeah, just a little thing called the whole universe? All right? Well, is it like just a little bit wrong? It's wrong by about the size of the whole universe. Doesn't sound like such a great theory. But you know there's always a fix. Oh yeah, what's that? Well, engineers would love it. We just add a fudge factor. And here's how safety factors not fudge factors. But that's it. Really. Just put a big number in it and you can fix it. Step one, put in a big number. Step two, give it a fancy sounding name. Hi. I'm Orge I'm a cartoonists and the creator of PhD comics. Hi. I'm Daniel Whiteson. I'm a particle physicist, and I have never fixed a theory with a fudge factor, and not yet, Daniel, how about a podcast? Have you faced the podcast? I've never fudged the physics on this podcast, but I've also never come up with my own theory of the universe. Have you had fudge while you were recording this podcast? My theory is that fudge is the basic element of the universe because it brings joy, and in the end, what's life about other than beauty and joy and in chocolate obviously, But welcome to our podcast Daniel and jrge Explained the Universe, a production of I Heart Radio, in which we compare the universe to various snack foods, delicious and dark and dense sometimes but with all the stuff that's happening out there in this crazy world. We want to take you on a tour of the grandest, deepest, most amazing but yet strangely accessible questions of the universe. Right, we want to take your mind and have it go on a trip out into the far reaches of the cosmos and to think about what it is that we're all doing here, and how did this crazy universe come to be and why is it the way it is. That's right, because the universe belongs to all of us, and wondering and being curious about the universe is as old as being human. And we think that everybody should understand what scientists are thinking about, what the deepest questions are and what scientists are pretty clueless about and only pretend to think they understand anything about. Physicists fudge things. Sometimes that's right, and not little questions, and not by a little bit. Sometimes we need a really really massive fudge, really big bowl of fudge. Hey, you know on a bad day that sometimes that's all that makes you feel like, that's pretty good about it? Right now? Yeah, I wouldn't mind swimming in a swimming pool full of fudge. All right, we'll wipe that mental image, folks and replace it with questions about the universe, so to be on the program. We'll be talking about what such fudge fact about the universe that physicists have come up with. And this comes up a lot in discussions about the entire universe and the theories that underlied, like general relativity and dark energy. That's right, and this is one of my favorite topics in physics because it's a topic where we are absolutely sure that we are in the beginning days of understanding. Like if you go back and read in history about people thinking about the nature of reality and our things made out of atoms or made out of fire and water, it feels like man, they had some pretty crazy ideas back then. They had no idea what they were doing, right, While there are fields of physics where we are also just starting out having all sorts of crazy ideas, which physicists in ten fifty or a hundred years will look back and snortal act. Yeah, and this one's particularly interesting because it all sort of comes down to a number. Would you say it's the biggest number in physics. It's definitely the wrongest number in physics, the wrongest and the biggest. Man. One of the weird things about this number is why it's so small. We think it should be a lot bigger, and it turns out to be kind of small, and we don't understand that. I see it's a small number numerically, but I'm saying, like, in terms of significance, it's a huge number. It's a little number with big significant the biggest slice of the fudge pie of the universe. To be on the program, we'll be talking about what is the cosmological constant? All right? So this was a question that was sent to us by someone from Belgium. So this is Pascal asking what is the cosmological constant? Hi, Danielle and Hockett. I have a nagging question about the cosmological constant. I understand that Anstein introduced the cosmological constant in the field equation because he thought that this would make the universe static, but in fact, the presence of the cosmological constant in the field equation actually shows that the universe is expanding. So that's why he said that this was the biggest mixtake of his life, which, by the way, shows one more time how brilliant it was. Even when he was making you mistake, it turns out that it was right. So my question is, how does the presence of the cosmological constant in the fit equations show that the universe is expanding? And more deeply, where did this cosmological constant come from? Who quoten quote invented it? Thank you so much for your podcasts and cheers from Belgium. All right, cheers, Pascal. Thanks for sending in that question, and I think it's awesome that it's a question that's nagging up, a question that next you also, Daniel doesn't keep you open, Oh my gosh, the history and future fate of the universe totally keeps me up at night. I mean, that's like the biggest question in physics. You know, literally literally the biggest question in physics. Are we living in the space that's going to be crunched? Are we exploding out into the heat death of the universe? What is the shape, the size and nature the dynamics of the universe, like thought of as a whole object. It's it's incredible that humans can even consider things so vast in our tiny little minds and sort of comes down to one number almost, it seems to come down to one number, a number we had to insert into the equations to explain what we see. And you know, the reason I love this topic is because not only do we have fresh new ideas for how to explain what we see, but our understanding of what we're seeing has also changed. You know, a hundred years ago, we thought there was just one galaxy in the universe, and then we discovered their other galaxies and they're zooming away from us. And then we discovered, oh my gosh, the things are expanding even faster and faster. So like, only twenty years ago did we figure out that there was this weird thing called dark energy tearing our universe apart. And now we're struggling to explain it. So, yeah, it's a big knack. It's dark energy, just fudge. Maybe something to think about. Fudge energy would have been a energy energy, the quantum fudge energy. The number is called the cosmological constant. And so as usual, we were wondering how many people out there and know what this term means and where it came from. So as usual, Daniel went out and asked people on the street what is the cosmological constant? And before you listen to these answers, think about it for a second. If someone asked you what it is, would you know what to say. Here's what people had to say. I have no idea what it is. The idea that there's one constant that explains all the others, so we don't have to have like forty two to explain all the different little stuff. I think, So I have no clue. Does that I mean it has something to do with light? Maybe I don't know that's a cosmological constant, so I would say it's something to do with the creation of life or um. The long those line is probably like a number like Dealer's constant or something. Some some mathematical things it's some sort of scale factor. Uh. I guess it's the best way to describe it. No, if you had to guess like movement, something like that, something that's more fixed and something that throughout time they've seen constantly. There heard of it, but I can't remember right now. I believe that refers to Einstein's whoopsie and which had to add a factor to an equation to account for either the repulsion or attraction that would actually make the evolution of the universe's topology. I guess you must say um stable or not stable. I know I'm getting that little right. It's also synonymous these days with dark matter, I think, or the effect of dark matter. You guess, something to do with how the universe expense. Okay, something about the shape of the cosmos. I'm not sure, all right, some pretty good answers out there. Yeah, some people are pretty close, and then some other people sort of grasping at, you know, broad things, because it's it sounds broad and consequential, right, cosmologicalsmologically, Yeah, it's not like it's not like the local neighborhood constant or sofa my sofa constant. You know, it's like it's it's going for the it's going for the fences, cosmological cost, it's a dramatic name. What do you think about the name? You approve, Well, let me see what it is. You know it is? It is it cosmological and insignificance. I think you'll find that it is. My guess is that it's not even a constant there, Like you guys got even that part of the name wrong. That's a good guess. And you know, it's a kind of thing where you think it's a constant, You call it a constant, then you discover hopes it's changing, and you still call it a constant. The only thing that's constant is the name. The only thing that isn't changing about it. But it is sort of a pretty big topic, and it all sort of originated with Einstein, right, This is something Einstein came up with kind of by accident. So tell us about the history. And this is something you have to understand the history of it. And Pascal's question really goes to that you have to understand sort of where Einstein's mind was when he was trying to explain the universe. And you're right, it began with Einstein, but really it was Einstein building on what Newton did. This was like in nineteen fifteen around right, Yeah, this is the early nineteen hundreds, and Einstein was trying to understand the universe and its shape and how and how gravity works because he had gotten these ideas from Newton that everybody else had that gravity is something where two objects with mass pull on each other. And he didn't like this idea, and he tried to come up with a more general idea for what gravity might be, and he reimagined gravity completely, right. His idea of gravity was not that gravity is like a force or two objects pull on each other, but that it's sort of the effect of mass on space itself. So space is no longer just like a backdrop. It's not like an emptiness on which things happen. It's a dynamical part of the universe. Meaning you put mass into space, space changes, right, And so he imagined gravity as a bending of space. Any local density of energy will bend space around it, changing the shape of the universe. And this idea sort of came up from the equations, right, Like if you sort of look at the equations of gravity and things moving because of gravity, you can sort of look at the equations into ways as a as a force or as a as a kind of a bending of space. Right. It's not like he suddenly came up with this idea. Well. I think it had a complex history and it required him to merge some ideas or mathematics that had recently been developed. But I think it's a pretty big conceptual shift to say gravity is not just a force between two objects, like electromagnetism, but it's something conceptually very different. It's a changing of the shape of space itself. I think that's sort of mind bending, the way you know, the mind bending to think about space and bending. Right. And so he came up with this idea and it worked really well for lots of things that he was able to recover Newton's theory from it. He showed that thinking about gravity in this way gave the same predictions that Newton gave. Right. It didn't mean apples should fall differently from trees, right, because Newton's theory sort of worked, right, It's been tested a lot of ways and even explained the motion of the planets mostly right. And so it's important when you come up with like a deeper theory that it still explains all the stuff that Newton had gotten right. Right in einsience theory, the apple doesn't fall from the tree. It just sort of rides down own the space time, or it sits in the same spacetime. Yeah, it's surfs, right, it's surfs on space. But the motion is the same. Right, Einstein doesn't predict that you'd see anything different from when an apple falls. But then it did make small differences in predictions for like how mercury moved. Really, yeah, that's the procession of mercury. And so he proved that his idea was right and the Newton's idea was wrong. But then he took the idea even bigger. He said, all right, if we think about this, what does that mean for the whole universe? Right? Can I understand what that means for like everything? He also swung for the fences. Yeah, he went cosmologically saying, hey, it predicts his apple. Let's go for the universe. And you only have to think about it for a moment to realize, Well, if the Sun bends space or the Earth moves around it, right, that means that mass and energy is bending space sort of towards itself. Then what's going to happen when you have a lot of masks, like a universe sized blob of mass. Well, it's going to cause things to contract, right, it's going to cause things to contract. What do you mean, like it under its own weight. Yeah, the gravity of all the stuff in the universe should pull all the stuff together. Right. If you're Einstein, you think, okay, I have an empty universe. Space is flat. Then I add galaxies and stars and gas and dust. What should happen, Well, space will bend in a way to pull all that stuff eventually together. And so in Einstein's universe, originally all that stuff should compact, should fall into itself, and eventually create you know, like a huge black hole. But do you need Einstein's gravity formulation that way? Can what a Newton also predicted, everything would just pull on itself and class Oh yeah, that's a great question. Right now. In Newton's universe, you don't necessarily get a collapse. I mean, you have gravity and it's pulling stuff together. But in Newton's universe, space is flat, and so it's possible for stuff to be arranged in a way that's sort of stable in static like the way that our planets orbit the Sun and don't collapse the way our galaxy doesn't collapse because it's spinning. And in Newton's time, remember they only knew about our galaxy, that know about other galaxies out there, so even this concept of the larger universe was not around. But for Einstein, space can bend, and so even if things are in stable orbits like they are here, they would still eventually collapse. In fact, Einstein's calculations were done assuming that everything was smoothly distributed, So even in the universe where gravity would all cancel out like that, even in that scenario he predicted that everything would collapse. So in Newton's universe things could be arranged stable so they don't collapse, or Einstein, without the cosmological constant, predicted everything would eventually collapse. But that's a problem, right, This prediction, this consequence of his theory or consequence of gravity, that the universe should be like falling in on itself, is not what Einstein thought was happening at the time, because back then, if you looked out into the sky, things look pretty static, right, nothing that nothing looks like it's trunching together. Yeah, back in niften or so, people thought the universe was static, that the stars are just hanging there in space and there was no rel of motion, and things were just sort of fixed. They've been that way forever, they would be that way forever. Things look pretty peaceful. Yeah, And so when Einstein came up with this theory and it predicted that the universe should be falling in and itself, he thought, oh, there must be something wrong, something must be wrong with the universe or with his equations. Well, he didn't doubt that the universe was static. He tried to fudge his equations. He says, all right, well, if the universe is not collapsing in itself, then I need something to prevent it from collapse, something to push in the other direction to keep its static, to balance. Because if you apply his theory to the universe or just really it doesn't have to be the universe, right, it had just any collection of mass back at least in the way that they thought space and mass was like back then. Then that's sort of inevitable, right, if you have gravity, everything's gonna come crunching down together. So he's like, wait, that's not happening. So therefore I'm going to fudge my equation. Yeah, he fudged it. He said, all right, so what I need is something to balance gravity. So he has this equation which predicts the basically the velocity how things will move through space based on the matter and energy density. And he just added another number with a minus sign to to balance it out, to balance it out, to make it match the idea of a universe that's not collapsing. Yeah, he said, if there's some effect on gravity from mass and energy, what if there's something else which is pushing back something else which provides a counterbalancing influence so that there is no overall gravity and so and so this is his famous fudge factor, right, And did he call it the cosmological concept or was that name given to it afterwards? He called it the cosmological concept. He named it capital lambda, and he chose this minus sign. And there's no explanation for It's not like it comes from anything. It's not like there's a bottoms of physics reason why it should exist. It was really just added to try to describe the universe that he was seeing interesting, all right, And so this number has been described as sinds biggest blunder. And so let's get into whether or not it was a blunder or not and what that means. But first let's take a quick break. All right, Daniel, did Einstein commit a blunder or not when he introduced the cosmological constant in his equations? What do you think? I think it totally is a blunder, because well, it didn't even really solve his problem. Like the problem he had was that gravity was pulling in and he needed something to be sort of pushing out. But the way he described it, it was a very delicate balance, like he needed this number to be exactly the right thing so that the effect or gravity from mass would be balanced by the effect of gravity from this weird cosmological constant. But it doesn't work unless they're exactly balanced. But I guess why do you call it a blunder? I mean, I just think he's just being a good scient doesn't be like, oh, I need something. I'm trying to a word with these equations to make them fit when I'm observing. Therefore, I'm going to add this. It's not like he maybe thought something wrong, did he know? But my complaint is that it doesn't even really work, Like if you actually had a universe like that, then it wouldn't be static because any little extra pocket of mass that was over dense, like you know, a solar system whatever, would start this runaway effect because it's not stable, like an extra pocket of mass very quickly generates extra gravity and overcomes this cosmological constant. And so while he wouldn't have like everything drawing into the center, there would be lots of little collapses. Oh, I see, his theory doesn't even really predict a static universe. I see you're saying, putting it into the same equations that he had before made a balance. But it's like a super precarious and technically it only works if matters totally evenly distributed through the universe and there's no extra little spots of extra density, and if there are, then those very rapidly coalesced. In collection doesn't know what happened. The galaxies are in galaxies and planets really just like small concentrations with mass, and so he's not describing what's happening, right, He's trying to describe what he thought was happening, which is a stable universe. But his description doesn't even lead to a stable universe. You mean the whole equations wrong, not just that constant. Yeah, I don't think the equation is he put it together describes the static universe that he was trying to describe, all right, So how did they know it was a blunder? Well, I think it's the blunder because it doesn't even describe the universe he thought he was describing. But then it turns out that the universe is different from what he thought, that the universe is not static, right, that the universe he was trying to describe suddenly shifted from under his feet, right, because we now know that the universe is expanding, right, that's right. Later on in the nineties, they discovered that galaxies are actually moving apart from each other, that's right. Hubble, building on work of various other people, discovered that there are other galaxies out there and they're really far away, and they're moving away from us faster and faster. So he discovered that the universe not static, that it's expanding. And so this would have blew up Einstein's idea because he had worked carefully to add this number to his equations to describe a static universe, and then it turns out, oops, the universe not well, his problem was that he called it a constant. Right if he had called it not, or is it that they even did, the whole math equation is wrong. I know. The problem is not that he called it a constant that we can talk about later about whether we think it's varying in time. The problem is that he put this number in to fudge his equation to describe a static universe, which is not our universe. Okay, so we we don't live in a static universe. Therefore any equation that assumes that is wrong. That's right. And so then Einstein abandoned the cosmological constant, and he never actually said it was his greatest blunder. But after that he was definitely not a fan of it. You know, he thought it was He was not well motivated, and you sort of putting it in by hand, and it doesn't come from anything. It doesn't really make sense. I see. Well, he was pretty cool about it. Then he didn't try to like hang onto it. And this party is a little bit confusing because you might think, well, Einstein put the cosmological constant in to prevent the universe from collapsing in his model, but then he discovers the universes expanding? How does he get rid of the cosmological constant? Right, just put another number in it, a plus number. Well, the cosmological constant already was pushing in that direction, right, the cosmological constant. He had kept the universe from collapsing. It was a positive repulsive force. Did you just make that number bigger and will explain expansion? Right? And so down the road, in order to explain expansion, accelerating expansion, we're gonna have to make that number bigger. But what Einstein did was get rid of it, right, not make it bigger, but he just made it zero. He's like, oh, this is wrong, and that seems confusing, right, because then there are two things to keep in mind here at once, the expansion, which is like a velocity, and then the change in expansion, which is like an acceleration. Just like in your car, you have a certain velocity and then the engine or breaks gives you accelerating aation to change that velocity. Now, the cosmological constant is more like the engine. It gives acceleration to the expansion, either positive or negative. Now, Einstein had originally assumed that the expansion velocity was zero, that we lived in a static universe, and so he set the cosmological constant to zero to also gave no acceleration. So what Hubble discovered is that the expansion velocity was positive. Hubble didn't measure the acceleration. He couldn't, so Einstein at that point knew that his no expansion, no acceleration description was wrong. Now, when Einstein tossed out the cosmological constant, it gave him a universe with negative acceleration because gravity was collapsing it, but it could still have positive expansion velocity at that moment. It's sort of like driving at high speeds at the same time as hitting the brakes to slow you down. So no cosmological constant means negative acceleration, which would eventually turn the universe's expansion around into a collapse. But Einstein was more giving up on the whole idea using the cosmological constant to get balanced and get zero acceleration and zero velocity. So the cosmological constant um tells you how how fast the expansion is changing. Yeah, okay, And so by making it zero than Einstein thought that he was saying, okay, it's expanding, but it's not accelerating, it's not getting faster and fast. So Einstein's vision, I think was the universe is expanding right now, but I'm gonna get rid of the cosmological constant, which means that expansion is decreasing. And so in the future Einstein thought expansion would slow down, stop and eventually universe would still collapse. Can't this Einstein guy get anything right? I mean, but that he was kind of wrong about that too, right, because later on, more recently, we discovered that the universe is expanding faster and faster and faster. That's right, Hubble was right, the universe is expanding, and the question was is that expansion slowing down quickly or is that expansion slowing down slowly? And we went out to measure it, and this covered that neither of those are true. Right, That the expansion is accelerating, that it's going faster and faster every year, right, And we figured this out by watching supernova's explode, which is let us understand how far away things are and how fast they're moving away from us. And we reconstructed this sort of history of the speed the things are moving away from us, and that told us that things are moving away from us faster and faster every year. And so not only is hubble saw is the universe expanding, but that expansion is getting faster every year. Right. We We've had podcast episodes about this, about the the idea that the universe is kind of exploding. Yeah, the universe is sort of being torn apart, and it's going through puberty or something. The most precise way to think about it, I think, is that space is expanding, right, We're creating new space between us and other galaxies. Right. And a very common question from listeners is, if space is being created between us and other galaxies, why isn't it being created between us and the Sun, or between me and you, or between in his banana, and and it is. It's just that we're getting pulled together by gravity, that's right. It is. It's being created equally everywhere. That's why it's a cosmological constant. It's constant in space. Everywhere in space is being stretched the same way. But as you say, the Earth is holding you onto it, and the Sun is holding us by its gravity, and our galaxy is holding itself together even even like the air inside of your mouth. Right now, is literally expanding, is literally expanding. Yeah, everyone's brain is literally exploding right now, not just because of us, that's right. And we call this dark energy, right, but it's just physics shorthand for we have no clue what's going on. This is, you know, something we observe. We see that the universe is expanding, and this is something we only discovered years ago. It's mind blowing to realize that before that we were ignorant of this really basic fact about our own EXAs well. So I guess my question now is, then, is dark energy related to the cosmological constant? You're sort of making it sound like it's the same thing. Like what Einstein was missing in his equation was the idea of dark energy and that maybe this constant is related to it or or is it totally separate. It's related to it, and you know, the idea is you see something out there in the universe, something you don't understand, which is like the universe is expanding and that expansion is accelerating. That's dark energy, just the observation that the expansion is accelerating. No cosmological constant idea involved. Yet there's several possible explanations for dark energy, one of which is the cosmological constant. Right, how do you describe it? You want physics equations that describe it so you can understand it, so you can predict it. So you need to somehow describe it. And so one way to describe that is to take Einstein's field equations, which are awesome, and put the cosmological constant back in, back in. So he put it back in. He had taken it out, and now everyone is saying, no, no, wait, don't take it out. It actually helps us understand what's what's happening. That's right, and you need to put it back in and put it back in larger than he did. Right. He put it back in to try to balance the universe on a knife edge to keep it static, and then he pulled it out again. He's like, oh, the universe is not static. I'll just let it collapse in the future. Now we gotta put it back in and crank it up so that it's accelerating the expansion to the un Everyone's like, more fudge, Put more fudge in. Don't put it in the fridge, just pour the whole thing in. That's right. He put in some fudge. Then he took the fudge out, and now we've doubled the fudge. That's nice double fudge. It's a double fudged universe. Maybe ein Steins Blunder was just picking the wrong ice cream flavor. You never know. Alright, let's get into whether or not this cosmological fudge constant is real and what that means for the fate of the universe. But first let's take a quick break. All right, we're talking about the cosmological sin and we're talking about how it's something that Einstein put in, then took out, and then people put back in because it explains how the universe can be expanding faster and faster. So it's kind of a real thing because we're seeing it. But Daniel explain to us what it actually is and like physically what it means, and and how does it explain how the universe is expanding. Yeah, so nobody knows the answer to any of those questions, so we could just end the podcast, right, Well, then, thank you very much, we'll end the podcast. It's a fascinating question and it's something physicists or thinking about a lot, and it's worth understanding what physicists do not yet understand. And the first thing to know sort of the mechanics of it, like how did he put it in? Well, the the equations for john relativity are very complicated, but you can solve them in some sort of simplifying assumptions and you get like two equations, one that gives you the expansion of the universe, the other that gives you the acceleration. And if you look at those equations you can google them later, you see that there's a term there for mass and energy and that has one effect, and he just literally put in a number with an opposite sign to balance it. And so it's something Einstein's description of mathematically would be something which has the opposite gravitational effect of mass in it, and you have to put it in a certain sort of solution of the equation. Yeah, you have to put it into the equations in a certain place, because it's not in like equals semc squared. That's not where it is. It's somewhere else in the equation. That's right, that's not the that equal s mc squared is not part of Einstein's field equations for general relativity, And so it goes into those field equations, and and this is what we do in physics. We're like, all right, this model, these equations describe what we see. Then what does that mean? Right? The next step is interpretation, like why is it like this and not something else? What does that tell us about the universe that we need this number here? Okay? So yeah, he people agree he put it in the right place, but they don't agree that it's actually a constant. Is it? Well, we don't know. And the way you can interpret it sort of physically is to think about it like maybe it's the energy of empty space, right, because if space itself has some energy inherent in it, then it could have this effects. Right, So we're like searching for a physical explanation and this could be totally wrong, right, This could be like, you know, maybe the universe is made out of air, fire and water. Could be that level of idea which peoples scots. But we're just groping around in the dark here, and and this is what we came up with. What you came up with was that space is not space, and emptiness is not empty. Noess, there's actually something in not an empty space. There's something in empty space, and it's important that this gets something really big, right if you think of it as the energy of empty space, not as something in space. Then as the universe expands, As space expands, you get more space, you get more of this stuff. Right, Because say you have like a cube of space and it has two hydrogen molecules in it, and then it expands, right, Well, you still only have two hydrogen molecules in it. So the density of stuff in the universe is decreased, so the gravitational effect of that stuff has decreased, but the cosmological constant, the energy of empty space, is constant. So you get twice as much space, you have twice as much of this mysterious dark energy. It kind of sounds like magic, Like you're like the you know, like the total energy in the universe. You're just it just bubbles up from like an infinite fountain. Yeah, it's pretty weird. And gradually it's sort of takes over, Like as the universe expands, you get more dark energy, and so the fraction of the energy of the universe that's in dark energy just grows and grows and grows and grows, and eventually it's going to be totally dominant. Does that mean that the energy of the universe is not being concerned. Well, that's a whole other question. It's a great question. It's pretty complicated. I think we should dive into that and a whole other podcast. But the brief answer is that the energy the universe might just be zero. So where's all this new energy coming from. It's a lot of negative energy in the universe that's bound up in gravitational interactions, and so this new energy can be balanced by negative energy of the gravitational interaction. That's uh, oh I see when you create something, Oh I see, Like if you're creating space between you and me, there's energy being created by the space, but we're also sort of storing it in the gravitational potential. Energy between negative energy in our gravitational potential, because you need to add energy to free us. Like if you have Daniel and Jorge orbiting each other, we're bound together gravitationally. Then in order to make a free Daniel and a free Johe, you need to add energy to the system to pull it apart. Yeah, so that means that that has negative energy. But it's weird that the universe kind of wants that it wants to free you, Daniel, why why didn't want what doesn't it wanted to come to me? I don't know. I don't know why the universe wants what it wants, But it's it's weird to think about dark energy because it feels like a strange coincidence, Like we are living at a time when right now dark energy is about seventy percent of the universe. We know eventually it's going to take over, So why is it that we happen to live at this time when like matter is thirty scent and dark energy matter and radiation and all that stuff ist and dark energy is sevent It feels like sort of a weird balance. Really why? I mean like if we were if the human race had come up a billion years ago, we might be asking the same question, like, oh, why is it six But if you look at the history of the universe over a trillion years, only the very first blip is going to have any sort of balance between matter and dark energy. Most of it will be dominated by dark energy. So even before us, you know, the dark energy is the future, not the past, I guess. I mean, like we're wondering why it is the way it is like that now, But if we had been born a billion years before, wouldn't it also be odd? It would also be odd. Yeah, it's weird to find two things in balance that won't stay in balance. Right. We don't think that there's anything that's keeping dark energy in balance with these other forces. Eventually it will take over, and so it's just sort of weird to be alive in a moment when it hasn't yet taken over because most of the history of the universe. In the future it will be in charge, but in the past there's less or more less less because the universe is getting more and more diluted, and so dark energy is growing in important Okay, all right, so these are all related to each other. The cosmological constant, the energy of empty space, and dark energy. Are these all different names for the same thing? Or I guess help me understand why we have three names for it. Yeah, there's sort of three layers of ideas there, and there's one more layer we should be into. The dark energy is the description of the accelerating expansion in the universe that's like experimental something is out there doing this, as we call it dark energy. The cosmological constant is an attempt to describe dark energy using gravity, say well, maybe it's just a feature of gravity, right, Oh, it could not be. It could not be, could be something totally different. We could not need a cosmological constant. And there's something that's probably different going on. Really, Oh I see, I get it all right, Yeah, yeah, there are other explanations for dark energy that don't involve the cosmological constant. So the cosmological constant could still be zero, like Einstein said, it coulds zero out here. See, you guys were calling him a blunderer, and you don't even know. I'm gonna I'm gonna go switch you over to t mind Stein here and say maybe I'm gonna keep with him. I think that's bananas. And the cosmological constants an attempt to describe that, right, And then we go and say, well, how can we explain the cosmological constant? If it exists, if it's real, if it's there, what could be creating it? This energy of empty space is an attempt to calculate what the cosmological constant should be. Oh, I see, it's a theory. It's a hypothesis built on a hypothesis of a hypothesis, and because maybe it would work like if you if you then sat down and said, all right, what is the energy of empty space? And can I calculate it? And if I get the right number, if I get the number that actually measuring out there in the universe, that suggests that I'm right right, Okay. So they sat down and they said, all right, how much energy do we expect there to be an empty space? And you can calculate this because we know that there are quantum fields out there in empty space, like the Higgs field, which is not a zero. When the Higgs field is at its lowest level, it's not at zero. And we talked about this in another podcast. What would happen if the Higgs field collapse down to zero and destroy the universe. So we're we're lucky, We're happy that the Higgs field is not at zero. But then if you add up all the energy you think is stored in the Higgs field and various other fields, you get a number, and you compare that number to the number that we measure for the cosmological constant, and they're different. I see. So this idea that there's energy everywhere is not unusual. You're saying that all of the quantum fields have energy in them, and you're saying that they actually have too much energy. Yeah, the number you get is too big by a factor of ten to the one hundred and twenty. Maybe Higgs is fudging it too, you know, Higgs flavored fudge what that means? But could it be awesome? Maybe like a field that we don't know about. Is that possible to or like thinking like you know, maybe these fields are leaking or something. Yeah, exactly. People say, well, maybe there's another field there we haven't discovered, and it happens to cancel all the other ones to give us a really tiny number. And that's weird, right, Like, it's weird if these two things balance each other to a hundred and twenty decimal places to give us the number the reasure, let's call it the fudge field, the fudge field. And so that's not very satisfying, right, And then other people say, well, who cares about those other fields? It doesn't even have to be a field, doesn't even have to be the energy of empty space. It can just be a basic number of the universe, like maybe it's just a parameter of the universe like a remainder or just like a speed of light, you know, or the planks constant. You know. Maybe there's just a number and it's part of the universe. Yeah, yeah, exactly. And people don't like that answer either, because then well why this number and not any other number? And to answer that you have to go multiverse, which is also unsatisfying. I feel like we're stagging crazy hypothetical ideas one and top of the other. How deep does this go, Daniel? This is about as deep as it goes. Once you get to the anthropic principle and the multiverse, you really can't go deeper into the scientific bologna. You gotta throw your heads up and be like, that's just the way it is. Folks. Well you're drowning and scientific bologna at that point. So we're out of fudge. That's it. We filled the pool with fudge and we're in the deep end. Now, Well, what is this anthropic principle? I think it means that things are just the way they are, and we think it's weird only because we happen to exist. Yeah. It says when you have a random number, you can't explain. It says, well, maybe there's an infinite number of universes, and each one has a different random number, and only in the universes where that random number happens to be what it is, so that you can't have intelligent life? Do you have intelligent life asking why is that number? What I see? There are other universes where this cosmological constant is different, but there's nobody around to ask the question. Yeah, if on those other universes the cosmological constant was some crazy big number and the universe just like exploded in the first bill a second and no interesting structure formed, and you didn't get you know, awesome podcasts asking about the nature of the universe, or maybe there are universes where you know that there are the two guys having a podcast. They're wondering, I wonder why pie is seven point six. They must live in a different geometrical space then, But yeah, and I find that answer totally unsatisfying because it's kind of like saying there is no answer, stop asking, And that's not who I am. You know, I'm always asking questions. I always want to dig deeper. I just want to know why. You're like, I'm sure Einstein was wrong. I know it. I'm pretty sure Einstein was wrong. I have to go on team not Einstein. Oh I see anti Einstein. Oh man. I mean I'm pro Eenstein in general, but in this one, I don't think you guys right? All right, well, I think that clears it up a lot for me. How all these things are related. Um, so let me try to recap then. So we know the universe is expanding, and we call that dark energy. We know the universe expanding, and its expansion is accelerated, right, It's getting faster and faster, and we don't know what it is in any of our equations. We just call it dark energy, and so we have a theory about what it could be, and maybe it's due to gravity, and so that's where the cosmological constant comes in. And then we don't have a good explanation for the cosmological constants, so we just poured a lot of fudge in it and then call it. Call it the energy of not energy. And that's right, the fudge of empty space. All right? Well, um, and I think it's been pretty interesting that to think about these huge questions about the universe, you know, and how how ay we don't know what's going on and be how you know, even people like Einstein are sort of grasping it strong sometimes. That's right, And we made a little bit of fun of science here for having silly ideas. But you know, this is how real science gets done. When you're on the forefront of human ignorance, you try crazy stuff and you say, well, maybe it's something like this. Can we make this work? Can we make that work? Because you know, the universe is ridiculous, and so no ridiculous ideas should be discarded because it might be correct, it might be accurate, it might describe our ridiculous reality. This is the best we can do, folks. It's a process, right, you want to join in the fun, Go study physics, that's right. If you've ever done any writing, you know the rough draft is always pretty roub. And that's where we are now. All right, Well, thank you very much to Pascal for asking this question, and we hope that helps you sleep a little bit better at night. That's right, And remember that the biggest questions in the universe, about the biggest universe out there are still unsolved, which means you might be the person to figure them out. Thanks for joining us. See you next time before you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us on Facebook, Twitter, and Instagram at Daniel and Jorge That's one Word, or email us at Feedback at Daniel and Jorge dot com. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of I Heart Ready More podcast for my Heart Radio. Visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H