Daniel and Jorge Explain the UniverseCould the 3D entire Universe be a projection from a 2D surface somewhere?
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Hey, Daniel, how many dimensions do you have?
Oh? More than I'd like these days?
Too many late night snacks from the fourth Dimension.
Yeah, or from the fridge dimension.
Actually, yeah, that's like its own mini universe of.
Deliciousness where I'm both a master and the slave.
But aside from how many cookies are involved, how do you know you're a three dimensional bee?
I mean I don't know. The world seems to be three dimensions.
Yeah, but so does the stuff on my TV. But that's just like how your brain perceives it.
All Right. Well, then if I'm just like in a two dimensional matrix, does that mean I can eat as many snacks as I want.
Well, technically yes, if you're in a two D world, you can eat all the to these snacks you want and gain zero weight.
I'll be right back.
Hi.
I am Hoe. I'm a cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I enjoy any dimension snack.
Really, even a one dimensional snack. I guess spaghetti is a one dimensional snack technically, especially the spaggattini or the angel hair.
Yeah, exactly. I don't discriminate. I'm not a dimensionist. I see all dimensions as equal.
So welcome for our podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we take apart the universe into its various dimensions, the ones that are understood and the ones that remain puzzling. We take your mind on the journey into all of those dimensions, trying to understand what we do know about the universe and what we don't. We range from the smallest of questions about the smallest of things and their color and shape and whether they spin, all the way out to the biggest and deepest and broadest of questions about the nature of a human context in this crazy and beautiful cosmos.
Because it is a pretty wild universe, and we like to take you up and the down, on the front and the back, and the left and the right, and the good and the bad jokes as well. That's right, there's a lot to explore in the universe, That's what I'm saying.
We span the entire dimension of humor all the way from puns to dad jokes. Is there anything else?
Aren't this on the same axis or the same you know point? Is there such a thing as a non silly dead one?
My teenagers say that any joke I make is a dad joke.
Oh, I see you have no death according to them.
That's right. It's all one dimension and there's.
Sense of humor. Seems to be one dimensional too, because you're pretty funny, Daniel for a physicists, I guess that's a two dimensional compliment.
Right, projected onto the surface of physicists, you look pretty funny.
But yeah, we like to explore all the big questions about the universe. What's real and possibly what's not real in this universe because this universe seem to have a lot of surprises in store for us.
That's right, We as an intelligent species have been digging into the question of the nature of reality, What is actually out there and is it different from what we perceive. We would like to know something true, something universal about the universe, not just what humans think it might be, but something we could like compare notes with aliens about.
Right, But what if the aliens are since they're in the same universe, what if they're just as fooled as we are by this crazy kind of tricks through universe we live in.
I believe in the wisdom of the crowds. You know, if you average over infinite intelligent races. Somebody out there has got to figure out what the universe is actually like. I don't like the idea that we've all been fooled in just the same way.
And you know that from the Internet. I guess it's a good test bet for that idea.
Yeah.
Absolutely, On the internet you can find every possible opinion with evidence, without evidence, it doesn't really matter.
You can find all the dimensions there.
You certainly can. But our goal on this podcast and as a species is to unravel the fundamental nature of the universe, to see it for what it is, and to ask the most basic questions about what it's like and its structure and its shape.
Yeah, and sometimes these questions sort of make you uncomfortable, maybe, uh Daniel as a physicist, because you know, we're sort of questioning how real is real or how real are the things that physicists think are real.
That doesn't make me uncomfortable. That makes me excited. When we are on the verge of like revealing that the universe is totally different from the way that we thought it was, that we're all just you know, projections on the wall of Plato's cave. That's exciting because it means we're going to learn something we're going to emerge from like some shroud of ignorance and actually understand something deep and true about the universe, even if it upends everything we thought we knew and changes the entire context of our existence. That's sort of the goal of physics.
Maybe I'm just projecting here, Daniel does it makes me a little bit uncomfortable to think that everything I know is to be real is not actually real.
Well, I'm pretty sure that's true.
Well, today we're going to be asking one one sort of version of this question, is the universe real? And it has to do with sort of like the dimensionality of the universe and how many dimensions it actually has, and is it different than the number of dimensions we feel and see and touch and can feel ourselves in.
That's right, And we're going to use the word dimension here, and we don't mean, you know, like the alternate dimension where everything is made out of marshmallows, or where aliens escape to as sort of a parallel universe. You see that a lot in science fiction. What we mean by dimension here really is the mathematical description of it, meaning just like a direction of possible emotion. And I've always found it fascinating that our universe has three dimensions or seems to have three dimensions, because you've got to wonder, like why three three is such a weird number.
Yeah, So to be on the program, we'll be asking the question is the universe a hologram? Oh, Daniel, are you sure we can't just talk about the marshmallow dimension where all the aliens are? That sounds like a pretty good podcast topic.
Are the aliens made of marshmallows in that dimension or that? Do they just eat marshmallows?
I don't know. You tell me you're the one projecting this image into my brain.
Maybe they go hunting for marshmallows.
So the question is is the universe a hologram? Now this is a pretty interesting question. Are you saying, like the whole universe where we live in is a hologram? Like an illusion? Kind of?
Yeah, that's sort of the idea that maybe the universe doesn't actually have three dimensions. Maybe it's actually just the projection in our minds or in our experience of what's actually a two dimensional universe that sort of like feels like three dimensions that we can experience as if it was three dimensions. Sort of like a hologram, although you know, it makes the universe sound like a cheap trick.
Like one of those baseball cards or those little tinfoil things you put on dollar bills.
Yeah, like by yourself on ninety nine cent universe sounds like a bargain. But I love these kinds of questions because they go to the very core of the nature of reality. You know, if we are wrong about the number of dimensions of space, what else are we wrong about? Maybe everything? And that might make some people uncomfortable, but it makes me excited because it means that there might be crazy, mind blowing revelations about the very nature of reality around the corner.
Yeah, so this is a pretty tricky question. Is a universe a hologram? And so, as usual, we were curious how many people out there had thought about this question or have an opinion on this question. So Daniel went out there into the Internet to ask people is our universe a hologram?
So thank you people of the Internet for participating. And if you are a person of the Internet and you'd like to volunteer to answer random questions, please It's very easy and fun and just takes a few minutes. Right to us two questions at Danielandjorge dot com.
So think about it for a second. Do you think the universe you live in is nothing but an illusha a hologram. Here's what people had to say.
Show doesn't seem like it a holograph, as I understand it is just a trick of light.
I don't know what hollo means.
I'm part of the universe, and I feel like I have substance, And even if that's just a trick of my brain and I am just an image, how can a light based image create self awareness? So I'm guessing no, I could be somebody else's dream.
Yeah, I think no, No, I don't know why. It sounds like somebody gave up and said, well, it's a holograph, man, and that's it. It's a holograph. But well, even if it's a holograph, who made it?
Why?
And who's paying for it?
I'm not paying for that.
I would say no, because a three D display of lights so photons which are massless, and as far as I can see stuff around me and myself, we have mass. So I find it very hard to imagine that the universe is a holograph.
Of course, of course, the universe is a holograph. No, I'm not sure if the universe is a holograph or not. I have heard some theory that maybe the universe is it's a two dimensional image projected onto three dimensional space or something like that. I have heard this theory, but it's been a long time and I don't quite remember how it goes.
Well, Technically, a holograph, I think, is a written something that someone has written in their own hands. So maybe the universe is a holograph if you call God the writer of the manuscript.
Not sure there.
Maybe from our perspective on Earth, the universe actually is the holograph. For example, it bends and refracts and reflects light in many different directions depending on where you are in it a.
Lot of the holographic principle. I can't remember exactly what that is, but I think it might be related to the Maldicina conjecture, which says that, well, assuming the universe is ad is, in other words, it has negative curvature, then everything in the universe, all the information that is important in the universe, can be represented on the surface of a boundary surrounding the entire universe.
All right, Some pretty confident answers here. Some people were like, of course, some people were like, no, I don't think so. Some people said sounds very technical.
Yeah exactly. And I also like the ones that focus on the death and nition of a hologram or a holograph.
Mm or those two things different. A holograph and a hologram.
Yeah, confusingly, the two things have almost nothing in common. Like, a hologram is what we're talking about. It's a trick of light that it gives the impression of a three D volume from a two D surface. You know, this is the kind of thing you'll see on a baseball card or on a dollar bill, et cetera. A holograph is actually just like an essay written by one person in their own handwriting what I know. And then holography is the study of holograms, not the study of holographs. And the holographic principle that we're going to be talking about today that the universe might be a hologram. It's not the hologrammic principle, it's the holographic principle.
Oh man. That's before we even get to English units, right, because then you have to talk about the Holo pounds and the Holo ounces, and then eventually you have to talk about the hollow deck, which you know, then we get into real nerd territory exactly.
This entire podcast has been nothing but an exercise for the holodeck. None of this has been real.
Your whole life, we're all just you know, Ais in your little cosplay here, Daniel.
No, I thought I was in your Holodeck experience. I thought you were the real thought.
I thought you were what you were both with Ais.
Somebody over here better be real otherwise this whole thing is a bad joke.
It's holograms all the way down.
That's the real hologramic principle.
So yeah, it seems to have a lot of definitions, and so I guess let's get down to business and let's lay it down for people, like, what is the one that we're talking about today. We're talking about holograms, right, and I guess what does that mean?
That's right, we're talking about holograms, which is part of this idea of a holographic principle that the universe might be a hologram. And so again, what we mean by a hologram is the projection of two dimensional surface into a three dimensional space, And that sounds fancy and mathematical, but really what we mean is something that looks like it has lume, like it's three dimensions x, y and z, but really there's only enough information for X and y that you can take all the information in a volume and somehow encode it on a flat surface. And you might be familiar with one of these things. It's something you can look at, like at a sheet of paper. As you change your angle, the image changes, just as if you were looking at something that had three dimensions.
So we think it has three dimensions, but really it's we're just looking at a two D surface, which means that all of that sort of three D information is sort of encoded or you know, written down in that two D piece of paper somehow.
Exactly, because a three D object, when you look at it, you only ever see a two D slice, right, you see one side of it, or you see another side of it, or you see another side of it. So a three D object has all of those two D slices somehow encoded into it, right, And so a hologram is a two D surface with all that three D information encoded into it somehow so that when you look at it from different angles you see the right two decize, so your brain is like, oh, that's a three D object, just sort of like in Star Wars when Princess Leah is projected out of R two D two. Right, it's not just she's on a screen. It looks like she's there. And they have these all over Star Wars all the time, though they're like confusingly low tech, right, they're always like weird and flickery. Anyway, Princess Leah says, you know, help me, Obi one, you're my only hope, and that's a hologram because it looks like she's sort of taking up physical volume rather than just printed onto.
A screen, right, and right now you're my only hope, Daniel, Because I'm a little bit confused here because it gets tricky, right, because you're talking about Princess Leab and so she's been projected into that three D world, but we're looking at it on a flat screen, and then we're looking at it through two eyeballs, which also kind of take two D pictures. So are we talking about the sort of illusion of death or are we talking about things having actual depth encoded in a two D surface.
We're talking about having enough information to describe a volume, but encoded on a two D surface. So hologram is when you can describe something using only two dimensions, but it has enough information to describe the full three D volume. And that's not always possible, right, It's not always possible to describe a three D object in terms of a two D surface. It depends on what you can do with that two D surface, Like how do we make holograms? How do you have those like baseball cards where it looks like the players moving as you turn it. They do that by adding information to the two D surface, Like they have these little ridges on the surface, so that when you look at the image, you're seeing like a different part of those ridges, and they have like different images on different parts of those ridges. So they've done something to encode, to add information to the two D surface so that you have the whole three D thing actually printed down there on two D.
Right, because they sort of like fool your eyeballs into thinking it's three D, right, Like if they give one image to one eyeball and they give another image to the other eyeball, and somehow you think it's three D, but really it's all on a two D surface, except that on that surface they sort of cleverly print thing so that it somehow delivers different information to each eye.
Yeah, and different information to each eye gives you the illusion of depth. But also I think it's crucial that as your head turns in relation to the two D surface, you see a very different image. Like if you just have a picture printed on a flat piece of paper, then as your head turns you're seeing the same picture. You're seeing it from a different angle, but you're seeing the same actual information in a hologram. As your head turns and you're looking at the two D surface from a different angle, you're actually getting a different image. The image you're seeing is changing in just the same way it would if it were a three D object and you could like look behind it or look over its shoulder or something. You're revealing more information. That's the experience that makes your mind think it's a three D object.
Now, how did those work? Really quickly?
They do?
They code like the image and from every possible angle or is there something more to like? You know, how they use lasers and stuff like and special materials to sort of encode that through D information.
There's a lot of different ways to do it. None of them are perfect. We can't do a complete, perfect hologram yet in our universe, you know, like those baseball cards, they have a little bit of an angle there. It's obviously not a three D object. That's done by having these little ridges so that when you look at it from a different angle, you actually see a different image, sort of like those billboards that change as you drive by them, because there's actually like a bunch of different pictures printed at different angles. And the more clever ones, the more impressive ones, use interference tricks. They send multiple beams of light from every point on the surface, and then where you are you get a different kind of interference from those different beams, and that's what creates the sort of illusion of three D. The dependence on your angle comes from the interference effects.
All right, pretty cool, And then I guess the question is, how could our universe be a hologram? Are you saying that we're like maybe be printed on a surface somewhere with the ridges, or do you think maybe we're you know, what we think is the our three D universe is actually printed on a surface somewhere, or maybe there are everything's one surface. Is that what you're saying.
Yeah, that's the idea that maybe our universe can be described the three dimensions of our universe of space and time and gravity can be described by information you could put onto a two D surface. And so then that begs the question, like, well, if our universe feels like it's three D but it is equivalent to a two D universe, what's the real universe? Is the real universe two dimensions with some weird extra bits encoded onto that two dimensions? Or is it actually three dimensions? You know, which one is like physically fundamentally the true universe and which one is like mathematical equivalents.
Well, I guess the question here would be if we're actually like a three D universe printed on a two D surface, then like who which which of the dimensions is fake? Do you know what I mean? Like it's up and down face and somehow it's encoded in the left and right, front and back or how would that even? Like what do you do with the extra dimension or what does this come from?
Yeah, that's a great question. Well, you know, out in the depths of space, of course, every direction is the same. You can just pick a direction and it's just as good as any other direction. So it's not like up and down or left or right or back and forth really have any meaning in terms of the universe. So on that two D surface, it's not like two of our space dimensions exist and the other one is just deleted. It's some other kind of space. So like, take our three dimensions X, Y, and Z. They map to two weird dimensions on that surface, called them I don't know A and B, but they're not like physical space dimensions the way we think about them. And then there's something else going on on that surface that lets you like encode Z, that lets you take that third dimension and make sure that that information is not lost.
But I guess if that information is there basically be another dimension or are you saying that it's somehow encoded through some trick by the first two dimensions.
No, it's basically there, and so the information is fundamentally equivalent, but it's like a different sort of structure. Like we're talking about mapping our universe, which has three dimensions and gravity and all this kind of stuff into like an abstract space something which is like where we talk about quantum field theory on that space, and we talk about the relationships between points on that two dimensional surface, and so that has effectively three dimensions because it's two dimensions plus some other weird piece of information in the quantum field. There really are two different sort of visions of the universe. One is you have three dimensional space and gravity and everything moves along, and the other is that you have a two dimensional space. But then on that space is this quantum field which is capable of encoding a third dimension.
All right, sounds a bit technical, so let's dig into the details of that. But first let's take a quick break.
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All right, we're wondering if the universe is all it seems to be, or whether it's kind of inflated in a way, whether it's fulling us into thinking that it has three dimensions, but really you're saying it could have two dimensions plus like a little pocket value or field that tells you that gives you that third extra feeling of a third dimension.
Yeah, and you know, all of this goes into trying to understand what is the nature of space itself, Like what is this thing we call space? And I think that's really interesting and like historically to think about how the ancient thinkers thought about space, you know, Newton and Descartes and those folks just thought about space is like the backdrop of the universe. It was absolute, it was fundamental. Obviously you had to have space, and everywhere in the universe has to have space. And more recently we've learned that space does weird things. It bends, it wiggles, it shakes, that it expands, it does all these crazy things. And now we're not even sure what space is. We talked about it on a podcast episode recently, whether it's possible to even have parts of the universe that don't have space in them, you know, a universe without space. So part of this just goes to like trying to understand what is the nature of this space, what are the rules of it? Is it really three dimensions where all those three dimensions are equivalent, or is it actually two dimensions with one extra tricky dimension that's making us feel like it's three dimensions. And that's why these are I think our deep and important questions.
It's like, maybe we think we're in you know, X, y and Z space, you know, front, back, top, down, left, right, but really we're actually in like AB space, and each point in AB space has a little special C value that maybe some of those three things combined give us the feeling of X, Y and Z, but really it's just A and B with a little extracy.
Yeah, and that all motion, all actual physical motion, only occurs along that surface, right, that A and B value.
All right, So let's get into why we would think that. It sounds like a pretty crazy idea. I mean, if I think about it, I'm pretty certain we are in three D space. You know, I can move up and down, left and right, front and back, and I can things when I touch them, they feel like they're three dimensional? Why would we think it's not.
For a long time we did think it was three D space, and that felt pretty settled that there are ideas about how the universe might have more dimensions, you know, eleven or twenty six. But this particular idea that the universe might be two D instead of five more dimensions came from the craziest thing in the universe. And so, of course it came from studying black holes. And you know how on the Extreme Universe series, I'm always saying, like, we look at the extremes of the universe because it shows us what's possible. It breaks the rules, it stretches them. That's exactly what happened here. People were looking at black holes and trying to understand, like, what is on the inside of a black hole? What's it like in there? And some people have this crazy idea, maybe it's not like anything. Maybe there is no inside to a black hole. Maybe all there is to the black hole is the event horizon. Maybe black holes are actually just two dimensions.
Yeah, we've had episodes about what happens when you go inside of a black hole and what they are and I think it is that like when something sort of goes towards a black hole, because of the way it bends bace and time, it never actually goes in right like, it basically stops at the surface forever.
In a way, it depends on who you ask, which is the tricky bit. So if you are watching something fall into a black hole, then as it gets closer and closer to the black hole, space is curved more and more, and then there's more and more gravitational time dilation, which is an effect where time slows down where space is curved, and so the closer you get to the black hole, the more time slows down, and so you never actually reach it. You have to wait for time equals infinity to see something actually fall into a black hole. That's if you're the person on the outside watching, right If you're the person jumping into the black hole, then you don't experience any of that. And just like in relativity, your experience of time depends on who you are, where you are, and how fast you're going. And so in this case, you just fall right in, you pass through the event horizon, you head towards the singularity, and so people are wondering, like, what's going on. How can everything be smeared on the outside of the black hole and also be inside the black hole? How is that possible?
You're saying it depends on who you ask, right, Like, to us on the outside and far from a black hopefully things gets mirrored on the surface of the black hole, the event horizon. But you're saying to the person falling in, they just fall right in, but at time infinity.
For us, Yeah, that's exactly right. We see them fall in only a time equals infinity. But they see themselves fall in, you know, very normally and very naturally. And these two things contradict each other, and so often in relativity you have people having different accounts of the same situation and both being correct. And that's possible in scenarios where there's like no causal link between the events, they have a timelike relationship, for example. But here it's hard to understand, you know, how the black hole actually accumulates stuff, whether there are actually are things inside the black hole. And it goes to this question of like the black hole information. Right, we talked about how if you put something into a black hole, then its information is inside the black hole, Like you throw a banana in there. Where does its energy go, where does its entropy go? Where does its quantum information go? And people are trying to understand, like what happens when these black holes evaporate? Is everything actually on the surface of the black hole and so it never really fell in, and so it's information wasn't lost or was it inside the black hole? Actually, and when the black hole evaporates, its information is somehow lost. So it's important whether it's actually gone inside the black hole or not.
Then can you still slip on the banana do if it's on the surface of the black hole?
That's really the important question. I mean, that's what this whole thing well. I mean, if you're going to do a cartoon on the surface of a black hole, you want to make it physically accurate, right, And every cartoon's got to have somebody slipping on a banana. And so I appreciate your desire here to do physically accurate black hole surface cartoons.
Thank you comedy, Yeah, and then you laugh about it at the end of time. No, But I think what you're saying is that there's this kind of paradox, right, like we think things splat on the surface, but some according to the people going in, they go inside. And so there's this kind of idea that maybe you know, once you go inside, you're just like on a to the surface of the black hole.
Yeah, that was sort of the start of the puzzle, like how do you reconcile these two things? They seem like fundamentally very different things. And Hawking and this other guy, Beckenstein, we're working on this and trying to understand, like where's the information in a black hole? How does it actually work? And they were working on this one day and they were calculating how much information can be encoded inside a black hole. That were working on these calculations of black hole entropy, thinking about black holes as like thermodynamic objects with temperatures that radiate and all this stuff. And one day they arrived at this equation, and this equation told them that the amount of information inside a black hole doesn't depend on the volume of the black hole. It depends on the area of the surface of the black hole. So like it doesn't depend on the radius cube, it depends on the radius squared. And that's kind of interesting, that's the suggestion. It says, like hmm, the maximum information you can store in a black hole depends on the area of its surface, not on its volume. That suggests that maybe actually these are just two dimensional objects.
Like a black hole is just a two dimensional object. But we see it grow, right, don't we see it growth? Doesn't that mean that it has volume to it?
It could be a two dimensional object embedded in our three D world, right, Like the surface of a sphere technically is a two D object. It's embedded in a three dimensional universe. It has a radius, it can move around in three dimensions, but it's actually a two D object. Like an infinitely thin sheet of paper would also be a two D object.
So that's where this idea of a holographic universe hologrammic hologramhic.
Holographic principle of a holographic universe, meaning the universe is a hologram.
So you're saying that the black hole could be a two dimensional object in our three D world. So how do we go from there to the whole universe is just two D?
Oh, we didn't yet. First we're trying to understand the interior of a black hole, and the first step was to think, well, maybe the interior of the black hole is a hologram, right, maybe there is no interior. So if you are that person that fell into the black hole and you think you're on the inside of the black hole, you're actually not. You're actually still on the surface. But the whole surface of the black hole has enough information to encode what feels like a three D internal volume. So first, before we go to the whole universe, people thought maybe the two D surface of a black hole is a hologram that projects the three D interior.
So then what happens is the black hole grows. The whole inside stays on the surface, but it grows with the black hole.
Oh man, you can't think about that. You can't change the parameters. This only works for a single thing falling into a black hole. It gets much more complicated as soon as you add like something else to a black hole. You know, for example, if you throw a banana into a black hole, then in principle, it never actually enters the event horizon. It's smeared across the surface forever, right, And that's what we're talking about. Now. If somebody behind you throws in an apple, everything changes because that apple will now change the shape of the event horizon. The event horizon will actually grow out to meet that apple as the apple falls in, and it will absorb the banana. So it's a totally different scenario if you're now like tossing in multiple things into the black hole, not even something we're capable of thinking about carefully.
But that is what's happening right now in the universe, right Like black holes are constantly sucking stuff in, things are constantly fallen into, and they're constantly growing. So why would we think that that's what's going on.
Then yes, that is definitely what's happening in the universe. And we see black holes actually growing, and so we don't know what's going on there. If you're the banana and you're like smeared across the black hole surface, and then somebody else throws in an apple and it increases the size of the event horizon, it increases the surface area, and now that surface area in theory should be capable of describing a larger internal volume. There is nothing actually inside the black hole in this picture. Inside the black hole, there's no space, there's nothing. There isn't anything in there that's not three D space that you can move around in there's just this weird surface that has mathematically encoded onto it enough information to describe a three D space. So the banana in the apple feel like they're in a normal three D space inside the black hole, but they're still smeared across the edge of it, all right.
So then thinking about black holes and what happens at the surface is what sort of led us to this idea of a universe as a hologram, Like, are you saying that we're a universe imprinted on the surface of a black hole, or are you saying that this Just thinking about black holes led us to think, like, oh, maybe the whole thing is imprinted somewhere else.
Yes, exactly. This idea from black holes led us to think more carefully about the relationships between three D spaces and two D spaces. And there was a bunch of guys working on string theory, and string theory is really really difficult. It's really hard to do any sort of calculation in string theory, and sometimes when a problem is too difficult, you look for like a mathematical trick to make it easier. There's this idea that you have a three dimensional universe encoded on a two dimensional space, and some folks realize that if you did that with string theory, it might solve some mathematical problems, like if it's too difficult to do a calculation in two dimensions, well what if it's actually a three dimensional universe, then you can do the calculation there. And so people were playing around with that and realizing, oh, you can play the same game, not just with the black hole, but with string theory, and so maybe you can describe the entire three dimensional universe that has strings in it as a two dimensional service and that would make some calculations easier to do, and other calculations actually harder to do. But they sort of projected this whole idea onto the universe. And you know, that's a really fun moment in science when you're like, build a tool over here, and you're like, oh, this is cool. This solves this problem, and then you turn around you're like, hold on a second, maybe I could do this to everything, you.
Know, maybe I can make it two thirds easier, so I have to do as much mad.
Yeah, And so there was this really big important result by a guy at the Institute for Advanced Studies in Princeton where that collection of smart folks over there called ADSCFT, which you can google if you're interested in more details about it, or maybe we'll do a podcast episode about that. But it gave us this vision that maybe the entire universe can be described in terms of being a three D illusion of a two dimensional surface somewhere.
All right, Well, I have two questions for this three three dimensional problem. I guess the first one is where did the third dimension go?
Like?
How is it being encoded in this to the surface? And two, could we ever tell the difference that whether or not we are in a hologram or not. So let's get into these questions. But first, let's take another quick break.
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All right, I know here's my favorite question in these episodes. What does it all mean? Man? Like, if we're actually if our three D universe is actually imprinted on a two D surface somewhere, Like where did the third dimension go? Is it just an illusion? Is it actually there? You mentioned like maybe it's encoded in some quantum fields. Can you talk more about that? Like how does how would that encode a whole dimension?
Yeah? So think about space, right, you think about space's emptiness, but we actually know that space isn't just empty that everywhere in the universe. Space has these things in that we call quantum fields. And what is a quantum field, Well, it's just like a number at every point in space. So for example, you know, there's the electromagnetic field, and anywhere you go in the universe you can ask what's the strength of the electrome magicstic field? Here? What's the strength of it over there? It's something that has like a value at every point in space. And the em field is actually more complicated because there's more than just a value. It has like multiple values for every point in space. But that doesn't matter. So this is something which is sort of like added to space. You know. It's like if instead of just having a city with an address where you have a house at every location. Now inside that house you have a number like how much is that house worth? Right, So that's like another piece of information at every point in space. It's encoded into this quantum field.
But there's lots of quantum fields. Though you're saying this like extra information is encoded in all the fields, or like there's one quantum field for basically the Z direction.
Yes, there's a special quantum field, because if you just have a quantum field, it can have like arbitrary random values and that doesn't give you like a dimension. Instead, if you have a special quantum field that follows certain rules, these are called conformal field theories. If you have aquantum field which looks the same if you zoom in really really close or if you zoom out really really far, if it tends to follow the same rules, but things that are zoomed in really really close don't interact very well with things that are zoomed out really really far, then the mathematical structure of that quantum field theory has some symmetries to it which allow things to behave exactly as if there was a third dimension. Like if things that are zoomed in really really small don't interact with things that are like really zoomed out in this quantum field theory, then it's sort of like things passing by each other in that other dimension. And you know, if there's a scale that you can like zoom in and zoom out, then it's sort of like there's another direction there in this quantum field. And so this is like a way to encode something into the quantum field by adding a bunch of rules for how it behaves, and those rules essentially make it as if it was exactly like a dimension.
Kind of feel like maybe you're trying to pull a fast one on you. You're here, Daniel, I am one hundred percent. I feel like you're trying to paint an illusion here. I feel like maybe you're saying that there maybe are three dimensions, but one of them you don't want to call it a dimension, do you know what I mean? Like, maybe it feels like maybe it's just like a technicality about the naming of it. But if it acts and looks like a dimension, why not just call it a dimension.
I got nothing against calling it a dimension, but it is different from the other two.
Right.
And our program here, not just on this podcast, but as humans trying to scratch out the nature of the universe, is to figure out the nature of the universe. And so if it turns out that two the dimensions are different from the third dimension, then that's quite interesting. And so we'd be fascinated to discover, for example, that our universe was actually one dimensions with like two weird projected dimensions instead of being three dimensions, or if we were like, you know, a three dimensional surface in a four dimensional space. I think I would definitely want to know that. You know, it doesn't change how you live your life necessarily or whether you should buy insurance, Yes, definitely by insurance, but it changes, I think, our concept of the nature of reality. So I definitely want to know. Even if mathematically the two things are totally equivalent, physically, it means that one of these dimensions is not the same as the other two.
Right, But is it not the same in that fundamental of a way, or is it just different in a sort of like notation mathematically way.
No, I think it's fundamentally different, because that would mean that space itself is two dimensions. And remember one of our goals here is to understand the nature of space, and so space itself is two dimensions. But then it has these properties, you know, these properties which allow to do things that three dimensional space would do. Then that's different from living in three dimensional space.
Yeah, I feel like you're trying to pull a Pluto here on the up and down dimension or something. It's technically a dimensionoid, not a dimension. It's a dwarf dimension.
Yeah, exactly. But you know, some of these calculations, these string theory calculations, are harder to do in a certain number of dimensions, and they make more sense in fewer or in more dimensions. And so if the sort of fundamental theory of everything turns out to only work in two dimensions and not in three, that also sort of tells you something about the nature of the universe itself. You know, the universe prefers the two dimensional description. I mean, in theory, you could describe the universe in terms of any number of dimensions you want, But we're looking for the most compact, the simplest, the most natural description that we hope reveals not just the way we are thinking about things, but the actual structure of the physical universe outside our minds.
And I guess it also sort of depends on what you define as space, right, Like space, If you define space as only the two dimensions you like, then yeah, there's it's only a two D space. But if you maybe define spaces these two dimensions plus this extra you know, value of the quantum field, then you know, maybe that is what space is quote unquotem.
That's definitely what our experience of space is, right, Either space is naturally three dimensional or it's two dimensions with this x st wiggle room in it that allows us to experience it as if it was three dimensions. I mean, it sounds to me like your question is sort of like saying, isn't a hologram actually a three D object? Like, well, no, it's not really there, you know, like it really is just a two D surface. A baseball card isn't actually three dimensions? And you might say, well, it doesn't look any different if you couldn't actually tell, what would it matter? Well, it matters to me because I want to know the truth. Man, What does it all mean?
All right? Well, let's get into the last question here, which is, how would we even tell if we are in a two D or three D universe? Right, Like, if the difference is so small or subtle or kind of sort of like you know, complex, will we ever be able to, you know, devise an experiment to tell us whether we are two D or three D.
Well, we're not sure, but there are some folks out there who have some really fun ideas for figuring out if we actually live on a two D surface. And the idea is that a two D surface with a projection and if three D surface would actually be different because there would be different quantum fluctuations, Like we're talking about a quantum field generating this third dimension, right, and so we would definitely be sensitive to like the way these fields fluctuate, and quantum fields fluctuate differently in two dimensions and in three dimensions. We had a whole fun podcast episode about the nature of two D objects. You should go check that out. But things move differently in two dimensions and in three dimensions, and so they fluctuate differently, and so we can see like quantum fluctuations from the very very beginning of the universe. Quantum fluctuations you normally think of like oh, this electron went left instead of right, and nobody really cares and nobody can ever see them. But in the very beginning of the universe, those fluctuations dictated like how things happened, and they got blown up into real measurable effects. So if there was a two D world, we would see different quantum fluctuations than in a three D world, and we might be able to see hints of that in remnants of the early universe.
Oh, I see, because when the universe was born, you're saying, at the Big Bang, you know it thinks were so compact and hot and small and dance that quantum fluctuations were a big deal. And so as the universe blew up, if there was actually only two dimensions, then we would see something funny going on right now in sort of the universe around us.
And because this bonus dimension is responsible for making the third dimension and affecting how gravity works in this three dimensional world, we should be able to see it in gravitational wave detectors. Basically, the bottom line is that if we live in a two dimensional world with a funny bonus dimension, we should be able to see a weird sort of like noise in gravitational wave detectors that you wouldn't otherwise see. This noise would be like an extra fuzz or a unique kind of fuzz that comes from the two D surface instead of being in a three D world.
But I think you're saying You're not saying that there's like one dimension that's fake. You're saying that, you know what I mean, It's not like Z is fake. It's more like X, Y and Z actually mapped to AB in a little bit, and something bonus called C. You want to see black gravitational waves, for example, you would see some weird mathematical or some weird dependency on the gravitational waves.
Yeah, exactly. The idea is if all the three dimensions are not the same, if two of them are actual dimensions and one of them is just a bonus, then there are different rules for those dimensions, and when it comes to things like quantum mechanics and so, they have different impacts on things like gravitational waves. And we should be able to see if there's like two dimensions of noise in the gravitational waves or three dimensions of quantum noise in the gravitational waves. That was the idea. At least. There's this guy from me, that Craig Hogan, who said in two thousand and eight that he had a prediction for what he thought these gravitational wave detectors should see if we actually lived in a holographic universe, if we lived in a two D world projected into three D by our minds, then we should see this extra fuzz in these experiments from these gravitational wave detectors. So that was his prediction in two thousand and eight.
So we've actually seeing gravitational waves now with the Lego experiments, and so have we seen this noise? Is there evidence for a holographic universe?
So there was sort of in a moment of excitement because he sent his prediction. He's like, here's what you should see. You should see this kind of fuzz if you look at your data. And then they sent Tom back some data and it looked just like the fuzz he predicted, And so for a moment people were like, what a hold on a second, did Hogan just prove that we live in a hologram But then it turns out that you know, he might have seen that plot already he might have known in advanced the kind of noise that they were seeing. What it might have been a postdiction and not a prediction, right. And you know, these gravitational wave detectors are very tricky and have a lot of noise in them, and the whole game is getting them to be quiet and noise free so you can see gravitational wave. So it's not that impressive to like find noise in a gravitational wave detector.
It's almost like the noise is the illusion, right, Like you can project anything you want into that noise if you do the theory right exactly.
And so people did some other calculations and they realized that, oh, even if he's right that you can see it in this way, then the size of the noise he predicts is much much smaller than anything we're seeing. So so far, we don't have any evidence that we're living in a holographic universe or that the universe is a hologram, But there are clever people out there thinking about ways to sort of probe this and looking for clues around the edges of stuff to see if we're just living on a baseball card.
Well, I hope it's a valuable one, not one of those common cards.
It's got a baseball player slipping on a banana near a black hole.
But you only think he's slipping exactly sleeping.
What you have to wait till the end of time to see him actually slip on the banana.
All right, Well, I guess once again the answer is stay tuned. We think it's possible. Well, we know it's possible we could be into the sort of universe, But I guess we don't have the instruments right now to tell the difference, or we don't know the right way to tell the difference.
Even that's right, people are still thinking about it and coming up with ways to predict it. And there are folks out there thinking about clever experiments that might be sensitive to the nature of space. Is it really two plus one dimensions or is it three dimensions? We don't even know. But maybe in the future somebody will unravel this. Somebody will figure out that it only makes sense for it to be two plus one, or one of these listeners out there will come up with a really awesome experiment to probe the very nature of space and time.
And in the meantime, I guess you should watch out for those three dse next because you are still three dimension as far as everyone else.
That's right. Just toss them in the black hole and watch for infinity as they very slowly fall in.
It's the long term diet. There you go. All right, Well, we hope you enjoyed that and it didn't know what flattened your mind, Daniel, I.
Hope it doesn't change the nature of your experience in this universe, because that third dimension is for any fun. I like being able to step over puddles rather than having to walk through them or go around them. So let's all savor and enjoy that third dimension at least while we know it's real.
Well, we hope you enjoyed that. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
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