What is membrane theory?

00:00:07
Speaker 1: Hey, Daniel, have you guys figured out what's inside a black hole? Yet?

00:00:12
Speaker 2: Unfortunately not? Still pretty confused.

00:00:14
Speaker 1: Okay, it sounds like you guys need to go back to the drawing board get some new ideas.

00:00:20
Speaker 2: I know, but like from where the smartest people on the planet have been stuck in this question for literally decades.

00:00:26
Speaker 1: See that is where you are going wrong. You are looking to the smart people. If you need wacky, crazy ideas, you need to ask the wacky crazy people like me.

00:00:39
Speaker 2: You're saying we should go to the insane asylum and ask people what they think is inside a black hole.

00:00:43
Speaker 1: I think that they could come up with some good ideas. They might be insane enough in the membrane to figure it out.

00:00:51
Speaker 2: Insane in the brain. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And if you didn't get my Cypress Hill reference, you're officially young.

00:01:16
Speaker 1: I am Katie. I am not a physicist. I like animals, though, and I like the universe. And I got that reference.

00:01:26
Speaker 2: Because you're insane in the membrane.

00:01:28
Speaker 1: Exactly, just the membrane, though the rest of me is perfectly.

00:01:32
Speaker 2: Sane and welcome to the podcast Daniel and Jorge Explain the Universe, in which we do our best to bring this insane universe into your brain. We try to make it all make sense, from the tiniest little quantum particles to the hugest swirling accretion disks surrounding super massive black holes. We have this hunch that maybe the universe is understandable, that it's a big mathematical puzzle that we can of eventually figure it out if we put all of our brains and membranes together. And our goal on this podcast is to explain all of it to you.

00:02:08
Speaker 1: Now, that's another song, super Massive black Hole. I think muse soundtrack to that really sort of indie movie called Twilight.

00:02:19
Speaker 2: Are you sure that wasn't part of the hip hop wars in the nineties, super Massive black Hole?

00:02:24
Speaker 1: I couldn't say. In the nineties, I was not cool enough to know.

00:02:29
Speaker 2: Well, you know, maybe there are some secrets in music that can help us crack the mysteries of the universe, because you know, some people say the universe is musical and there's a connection between music and mathematics, right, So maybe we have been looking in the wrong places.

00:02:44
Speaker 1: Yeah, Like I've heard this in terms of string theory, where strings aren't you know, they're not like violin strings, But it's something about some like either vibration or pattern. Honestly, I do not understand it, but you know, well, I think that is interesting that there is the idea that a lot of the mysteries of the universe could be about certain frequencies or patterns, which is also what is the major components of music.

00:03:16
Speaker 2: Exactly, Although if you listen to Terrence Howard on Joe Rogan, it's all frequencies.

00:03:20
Speaker 1: Man, is all frequencies?

00:03:22
Speaker 2: Man?

00:03:22
Speaker 1: Why am I not on Joe Rogan? See, I just can say that too.

00:03:27
Speaker 2: I can because you believe that one times one equals one, and Terrence Howard proves that it equals to And that's why you're just not mathematically qualified to be.

00:03:38
Speaker 1: I just can't think outside of the box enough to not do mauth good exactly.

00:03:43
Speaker 2: But we are fascinated by the mysteries of the universe. We do think that there are mathematical solutions to them. Maybe they are encoded in the sonatas of Mozart. Maybe the engineers are right that it's all vibrations all the way down. But we hope that there is an explanation. And one of the biggest things and we need an explanation for is how to think about the universe on the smallest scales. What happens when things get really, really dense and really really tiny. One of the biggest puzzles in modern physics is how to put together the two pillars of our understanding of the universe, relativity and quantum mechanics. We've been banging our heads against this for almost one hundred years, basically since we've had relativity and quantum mechanics and realize that they are fundamentally incompatible at the smallest scale. And we've been trying to figure this out. And today on the podcast, we'll be exploring yet another attempt to unify relativity and quantum mechanics. So on the podcast today we'll be answering the question what is membrane theory?

00:04:49
Speaker 1: Okay, as a biology nerd, I'm pretty sure I can answer this. A membrane is a semi permeable barrier, So I solved it. Congratulations to me.

00:05:04
Speaker 2: What about the audio barrier between us and the listeners the ideas from our brains and that their brains have we permeated a membrane.

00:05:12
Speaker 1: I yes, why not. I don't know enough about audio engineering to say no or philosophy, so I'm gonna say yes. We're like salt ions through the airwaves, permeating the membrane, so hopefully you can reach homeostasis.

00:05:32
Speaker 2: So I'm not surprised that when you heard this phrase you thought of cellular membranes divisions between solutions. You want to keep osmosis from, like moving all these bits of salt over here, or using fats to keep that over there. But it's not just in biology that we have membranes. It turns out that they are fundamental concept in theories of quantum gravity. But before we dig into that, I was curious what everybody else out there thought when they heard membrane theory. As usual, I asked our cadre of volunteers to speculate on the question without the opportunity to use Google. So, if you would like to join this group of volunteers in the future, please don't be shy. Write me to questions at Danielandjorge dot com. We all want to hear what you have to say. In the meantime, check out these answers from listeners. What do you think membrane theory is here's what people had to say. That's the first time I'm hearing golfit.

00:06:27
Speaker 3: But if I had to guess membranes, the function of the membranes are to pass on stuff in one direction and other stuff not in the other direction. So maybe we're talking about it's a mechanism about particle coexistence through a wall of things something like that.

00:06:45
Speaker 4: Just to guess, what comes to mind for me on that one is that it's something that you use to separate things, like in a fuel cell car, you know, you separate components and you make energy. Maybe it's like a desalination thing where you take salt.

00:06:57
Speaker 2: Out of water.

00:06:58
Speaker 4: So maybe there's some membrane here in the universe that's doing.

00:07:01
Speaker 2: That in space.

00:07:03
Speaker 5: I'm guessing membrane theory has to do with the outside of a cell. Maybe how the membrane, you know, protects the core of the cell and how it stays intact.

00:07:16
Speaker 2: I think it has to do with string theory. There are strings that vibrate in there one dimension, and I think a membrane is a something similar that can have more than one dimension.

00:07:26
Speaker 1: See, I'm I'm definitely with the theory that everything is a cell. If you look at the universe, it's just a giant body for some kind of huge animal. You know, it makes sense, right, you're saying the universe is alive. Yeah, it's a big maybe a giant cat. I don't know. Have you ever looked at like a black cat? Right, It's it kind of has that sort of quantum mechanics and general relativity paradox. Right, it's like a fluid, it's a solid. It's sweet and loving, and then it bites you. So yeah, I think the universe could be a giant cat. And when you get down to the tiniest components there cells, and yeah, it's been solved.

00:08:11
Speaker 2: You're welcome and we're done, Thank you very much. Physics is over. Katie wins all of the Nobel prices. Heay, Well, we're definitely hearing from listeners the connection to biology, which makes a lot of sense, and the idea of having two dimensional surfaces or even connections to string theory. So there's a lot of good stuff in here that we're going to dig into and explain in this episode. But a plus to all the listeners.

00:08:37
Speaker 1: I mean, I would assume that, yes, it's probably not like a cellular membrane. But if we're talking about a membrane, I would guess it is some kind of barrier through which certain physics transactions can occur. But that would be my guess.

00:08:56
Speaker 2: Is this whole podcast a physics transaction? We are taking your time and exchanging it for knowledge, is like a physics transaction.

00:09:03
Speaker 1: You know what? That's pretty good. I think I'm wondering about the exchange rate, though, because that's that's the real issue.

00:09:10
Speaker 2: Yeah, I think we're too high on the jokes permit it and too low and the physics permitted so far. Let's try to flip that right now.

00:09:16
Speaker 1: All right, well, okay, let me have it. Like, what's going on with this membrane theory?

00:09:21
Speaker 2: So membrane theory is an attempt to crack the puzzle of quantum gravity. So let's start with that. What is the puzzle of quantum gravity? Why do we want to crack it? What is the issue? Why are all the smart people on the planet thinking they need to go into the insane this islum if they can't figure this out? The basic issue is we have two ways to describe the universe. There's general relativity, which tells us about space and time and energy, and the expansion of the universe describes a lot of the big stuff. It tells us how gravity works and how the universe is expanding, and how far away galaxies are getting red shifted and all that good stuff. And then we have quantum mechanics, which describes the really small stuff, the little part of goals light and all this kind of quantum fields and sort of our understanding of microscopic matter. And the issue is that we don't know how to make these two things play well together.

00:10:11
Speaker 1: They don't play nice because I've actually, i think I've been on the show a couple times when we talked about this conundrum, and so it seems like, you know, when you have these mathematical theories that describe each of them, it works within it. So the general relativity math works within general relativity. It seems really nice and neat and good. Same thing for quantum mechanics. But then when you try to cross the beams the math beams, suddenly it doesn't work. Like if you're trying to use general relativity math to describe what you know is observed in experiments happening on sort of the quantum level, or vice versa. It no longer works. Is that more or less?

00:10:53
Speaker 2: Yeah? I love crossing the math beams. That's awesome. I want a t shirt that says I'm crossing the math beams. But yeah, that's basic the idea. And remember that what we're doing in physics is trying to build a mental model that describes the universe easy. Those mental models are always imperfect. They're always incomplete, they're always simplifications. Even if you're talking about like the flight of a baseball, right, how does a baseball fly across the field? Well, I'm going to use a parabola in Newton's equations, but I can't do the calculation very easily. I have had to include air resistance, so I decide I'm not including that because it's probably not important, and really, to answer my question of whether the guy's going to catch it, air resistance doesn't matter. I'm not going to include effects of humidity and the siazillion things I could include in my model to make it a very accurate description of the universe that I don't need to to answer my question. And so the models that we build to answer questions about the universe are always incomplete, they are always approximations, but they're still very very useful. And that's the issue with quantum mechanics and general relativity is that they are two different approximate descriptions of the universe that make different approximations, different foundations assumptions that go into building those models that are incompatible, and they let us describe different parts of the universe, as you say, very very well. So if I want to talk about how two electrons scatter off of each other, I can use quantum mechanics and talk about how they interact and the virtual particles they exchange or the fields that ripple between them, and it all works out amazingly well. And that can ignore what general relativity would do in that situation because it's irrelevant. It's like the wind resistance or the humidity on the baseball. It doesn't affect the calculations, so I can ignore it. Or if I want to say, hey, how do galaxies form and how do they swirl around each other? I can use general relativity to answer those questions, and that can ignore the quantum effects because who cares what one electron does in Andromeda doesn't affect whether our galaxy is going to crash into that galaxy, general relativity dominates. The amazing thing is that in every situation in our universe you can use either quantum mechanics to explain it or general relativity and ignore the other one. A perfect divorced couple that have separated their lives and never have to interact. You know, there are no argument at McDonald's about who's taking the kid. Yeah, they're co parenting the universe. And so you might think, all right, great, what's the problem, right co parents can live in harmony without ever talking to each other. Well, there's two problems. One is that's really unsatisfying, right, Like, we want one explanation for the universe. We don't want two different explanations. We don't want a Russiaman universe where both parents tell very very different stories about what's going on. Right.

00:13:34
Speaker 1: I get that.

00:13:36
Speaker 2: We think that there is one story about the universe. There's something that's happening, and that there are rules that are being followed, and we want to know what they are. We want our best approximation of them. So it's deeply unsatisfying to have two different, incompatible theories of the universe. And also, there are moments in the universe a very few places. In times when you can't ignore one ar or the other, you need things like the heart of a black hole a singularity. In general, relativity is incompatible with quantum mechanics, which says you've got to have some fuzziness or the Big Bang or the very early universe when things were really, really hot and dense. You need the rules of quantum mechanics to describe those particles. But you can't ignore gravity because things are so hot and so dense. So we desperately want to find a way to bring these two together. But as you say, the math beings don't cross, right.

00:14:27
Speaker 1: I mean, it's like, as physicists you now kind of have to play as a couple's therapist, where you have these two theories that are essentially speaking different languages and they cannot come to an agreement, and they can be perfectly functional on their own, but then when they come together, they are unable to communicate. And the Yeah, I mean, it seems like resolving that difference between the two theories, like resolving why they don't work with each other, would actually reveal some big things that we just fundamentally have not understood yet about the universe.

00:15:06
Speaker 5: M M.

00:15:06
Speaker 2: You know, I've heard anecdotally about couples that don't actually speak the same language, you know, where they have like literally now yet they've fallen in love. That's actually true, they have some other love language.

00:15:18
Speaker 1: Hi language interpretive there.

00:15:21
Speaker 2: Love at first sight, right, doesn't love it first word?

00:15:24
Speaker 1: Yeah.

00:15:24
Speaker 2: Anyway, you're right that quantum mechanics in general relativity don't get along, and one of the reasons is that they are built on very different assumptions. Like general relativity says the universe is smooth, it's continuous, it's precise, there's an infinite number of locations. It says that you can divide space an infinite number of times, like relativity agrees with Zeno's paradox, right that between you and a candy store, there's always a distance that you can cut in half. Space from the point of view of general relativity is something that's smooth and continuous and you always have a very specific location, whereas quantum mechanics says not. Nothing is actually smooth and continuous. There are not infinite number of locations between any two points. Things are discrete and chunky. A beam of light is actually made up of little pieces of light, little packets of light. Everything in the universe is discrete, and it's also imprecise. None of these little packets have a precise location that have probabilities. So you see the foundations of these two theories are very very different. They start from two very different places, and so weaving them together has a lot of challenges. People have been trying to make theories of quantum gravity to say, hey, let's take gravity and try to describe it in the language of quantum mechanics. For example, think of it like a quantum field that are exchanging virtual particles. They even have a name for these particles, it would be the graviton. But when you sit down and try to do those calculations, gravity is different from the other quantum forces because it couples to itself. Everything that has energy has gravity, and so if you emit a graviton, it also feels gravity, and it emits gravitons, which emit more gravitons. You can infinite number of gravitons, and then you start to get nonsense answers. So as you say, the math beams don't cross.

00:17:06
Speaker 1: So in terms of gravitons, is that something that has ever been able to be studying the same way that you can study protons or is it just sort of a byproduct of this seems like this could be a thing based on the math that we have theorized about.

00:17:23
Speaker 2: Yeah, gravitons are purely theoretical, and they're not even coherently theoretical. Theories that have gravitons in them just don't work their problems with them, and so it's not just that we haven't seen them. We don't even understand how they would work if they did exist. And there also would be really really hard to spot, Like if you're thinking about gravitational waves from rotating black holes, for example, those are not gravitons. Those are ripples in space and time. They are like a beam of light. Gravitons would be like taking that beam of light and breaking it up into photons. So you take that gravitational wave and now break it up into tiny little gravitons. But even gravitational waves are really hard to see. Gravitons would be much much tinier, well beyond our capability. But also mathematically they just don't work. If you try to do calculations with gravitons, you get weird answers like what's the probability that this electron is going to go left? Oh, one hundred and forty percent? What that doesn't make any sense, right, And so that's telling you that fundamentally there is a problem with the mathematics that you need to go deeper and start from something else, change one of your assumptions in order to make a working theory of quantum gravity.

00:18:31
Speaker 1: I mean this kind of reminds me in biology of how like the history of biology and medicine, where we would start to understand things like we would start to understand how certain medications work, or you know, understand things like, you know, a man and a woman make a baby and the like, there seems to be these germinal cells responsible. But then we didn't have the ability to get tiny enough inside the human body where we couldn't see like proteins, we couldn't see, you know, maybe we at some point could see cells, but we couldn't see DNA. So there were so many strange and interesting theories that kept circling around trying to get closer and closer to the truth. Like there were really funny ones like imagining that there's just like a tiny person inside of a sperm cell and then that grew into a baby. But essentially it's like we were able to make scientific observations, but without the ability to get small enough in terms of like we didn't have electron microscopes, we didn't have the technology or understanding to study DNA, these theories could not kind of you know, interweave until we got to that point. And that kind of seems like where, you know, sort of like what's happening with the universe. Like we're able to, you know, make all of these really interesting scientific observations and they're not necessarily wrong, but there is some fundamental aspect that it's not necessarily that it's too small to see, but it's something that we can't see yet or something that is really hard to observe that might help tie these things together exactly.

00:20:09
Speaker 2: And because it's a question mark, it's deeply unsatisfying to not have figured it out. We suspect that when we do figure it out, it'll be something new, something fascinating, something that tells us about the basic nature of the universe. Because it's telling us that Gr's description of the universe is wrong. Space is not just some bendable manifold and the quantum mechanics description of the universe is wrong in some important way. That's what I love about physics, because it's not just I have a model in my head that is predicting the universe. You can then look at that model and ask questions about it that are philosophical and like, huh, why does the universe work this way? Or you can look at it and say, oh, that's why time flows forwards and there's only one dimension of it in three dimensions of space. If you have that fundamental theory of the universe, we hope that those kind of answers can come from it deep insights about the very nature of reality. And for people who think like, oh, that's so weird and abstract, I mean, that's like the context of our whole lives, you know, our entire existence. Understanding the basic nature of reality of space and time and matter and energy like that is the stage of our life, the context of our existence. The stakes could literally not be higher.

00:21:19
Speaker 1: I mean it's interesting because I'm really curious about things like animal and human behavior, understanding them and understanding things like perception and you know, but those kinds of questions I don't see as too fundamentally different from the questions that physicists are answering, because in a way, you know, our perception of things are sort of like behaviors and stuff. That is how we're able to perceive the universe. And so these kinds of questions of understanding. Of course, the methodologies are very different, and what we find are going to be very different with these two questions, but it's that's still that kind of desire to understand what are we and where are we? How do we function, and how do we function in relation to our environment? And you know, of course the universe being the largest environment that we can think of in which we are. But you know what, we should probably take a quick break while I really ponder an egg and the membrane of an egg and try to think about whether this is something that could describe the universe. All right, so we are back. I've been staring at this egg for five minutes. Daniels can attest to that, and you know, I think maybe the universe could be an egg with yellow stuff on the inside. What do you think?

00:22:53
Speaker 2: I love your egg theory of the universe. I want to see the math behind it before I really commit to.

00:22:58
Speaker 1: It one plus one equals too or wait, one time is one equals too? I accidentally did I'm so bad at math. I was trying to make a joke where I did it bath and I did it correctly.

00:23:11
Speaker 2: Oops. Oops, oops.

00:23:13
Speaker 1: So, Daniel, I really want to get deeper into these ideas because we've talked about how these things don't seem to add up, and these attempts to make things to add up have in some sense, I don't want to say failed, but they haven't reached the finish line yet. So like gravitons don't make sense yet, are there is there anything promising where we are seeing some revelations that may help us get closer to why there is this fundamental miscommunication between general relativity and quantum mechanics.

00:23:46
Speaker 2: So there definitely has been some progress. Nobody's totally figured it out, but some of the smartest folks on the planet have some ideas. And before we get into membrane theory, you need to take a step back and understand where it came from, which is from string theory.

00:24:01
Speaker 1: Okay, I'm excited because I remember I remember watching I Think like a PBS nova thing and they tried to explain string theory, and it just confused me more than I think, you know, like if you just said, like, imagine what string theory is, I'd probably be less confused at that point until after watching this documentary. I'm not I don't want to be mean to PBS, but I don't think they really explained it very well because it was like they're like these vibrating strings like on a violin, and it's like, I don't know that that makes a lot of sense, and I'm confused. You mean, there's tiny violins everywhere. What's going on? Are the world's smallest violins making up the universe? So I do want to understand better.

00:24:44
Speaker 2: All right, let's see if we can do better than Brian Green on PBS. The idea is to avoid some of the mathematical problems that come when you try to cross the beam. Those infinities. A lot of those infinities come from the basic assumption that things are points, that particles are time need dots because those have infinities in them. There's infinite densities and the zero volume, et cetera. So instead of having points, string theory says, what if everything is a line, so a point is like zero dimensions, right, it doesn't go in any way. But a string is one dimension. It's like, well, let's have it have some extent, and having it have a length means it's not infinitely dense anymore. There's like a fundamental length to it, and that avoids some of the infinities in the calculations. Is like a minimum size to stuff, and that's the length of a string. And so these strings would be the fundamental bits of the universe. Essentially the universe is strings. But these strings can do things. They can wiggle, right, just like strings in our world, like a violin string.

00:25:42
Speaker 1: Can or or a guitar string if you prefer that.

00:25:48
Speaker 2: But we can't see those wiggles directly. And so what we see is something really zoomed out, like the string wiggles. This way, it looks like an electron. When you zoom way out with string wiggles that way, it looks like a muon the string. Another way it looks like a quark. So the idea is not that the electrons and the quarks are made of tinier particles the way that like the atom is made of smaller particles, but that you get something fundamentally different. Right, we need something fundamentally different to solve this puzzle of quantum gravity. We need a new idea, and so we say that these particles are instead made of vibrating strings, and they just look like different particles because we're too zoomed out to see the details.

00:26:26
Speaker 1: I guess for me, the question is like, I understand the difference between a point and a line in terms of dimensionality, but in terms of like a line of what? Like That's where I get caught up, because I, you know, usually it's so hard to think about the fundamental like unit of something because maybe this is just biology brain, but everything has a smaller thing in it, right, Like You've got a mouse and the mouse has tissues, and the tissues have cells. Cells have proteins, and the proteins have molecules, and the molecules have atoms, and the atoms have quarks, et cetera, et cetera. I might have skipped a few steps, but you get the idea, which is that I'm always thinking, like, what, what do you mean like a string of what? A line of what?

00:27:14
Speaker 5: So?

00:27:14
Speaker 1: How has that resolved? Like what is? Because I'm assuming it is not like a literal strand of you know, like in biology, like a strand of protein. Like if you're like, there's a string of something, I'm thinking like, oh, is it proteins? Like you know, is it lipids? What's it made out of? So in in physics, like what is this line?

00:27:32
Speaker 2: Yeah, it's a great question, and I understand what you're saying. You're imagining string in your mind. And you know, if you're thinking about like a line of frosting on a cake, you're thinking that squeezed out of some tube and the line of frosting is made out of that frosting, and therefore the frosting is the basic universe stuff, not the line of it. And so you're wondering, like, well, what's that string made out of? What is string stuff? And the answer is we don't know. And you're right that the pattern is that stuff has made a smaller stuff, which has made a smaller stuff, which is made of smaller stuff. And so far we've never seen anything that is just itself that is not made of something.

00:28:06
Speaker 1: That's the truth, You're absolutely right.

00:28:09
Speaker 2: But we have this hunch, We have this hunch that maybe it is that maybe there's a bottom to the explanations of the universe. We don't know, And there are philosophers out there who argue that it could be infinitely regressive, right, that you just could keep going forever and ever and ever, and there is no foundational firmament to the universe. Everything is made of something smaller.

00:28:29
Speaker 1: I hate it either way, Daniel, like either explanation. It feels uncomfortable somehow, right, Like if the explanation is like there is the smallest unit and it's a line that wiggles, I'm like really. And then if you're like no, but then the line that wiggles, can you can infinitely get smaller and smaller and smaller, And then still that It's like, really, it's so hard, And I feel like maybe the reason it's so difficult is that our human brains are geared towards a certain type of understanding of things based on what our evolutionary needs are in terms of something has a start point and endpoint, or something is made out of something else and time goes from point A to point B. When someone who is not a physicist is trying to think about these things, I think about stuff that is probably not very relevant to it, Like when I think of I don't know, you keep talking about wiggly lines, and I just think about al dente spaghetti and that's not what it is and it can't be. But it's so hard to think of. Okay, there's a basic unit that can't get any smaller, but it's not made out of anything, and that, you know, it just kind of breaks my brain. I cannot conceive of that.

00:29:44
Speaker 2: Well, let me put it in another way, which is maybe easier to sit with in your brain, which is, we don't know whether strings, if they exist, are the fundamental basis of the universe, or if they're made of something smaller. You can put it that way, right, And we can put it that way because we actually don't have to know. This is one of the beautiful things about physics is that we can do calculations at various scales, ignoring the internal details, not having to know them. Like when we did that calculation of the baseball flying across the field, we didn't have to keep track of all the electrons and even the air resistance on all those details to mostly get the right answer. You can do physics at lots of different scales. So even if the universe infinitely is made of smaller stuff, or if there is some fundamental chunk to it, we can still do physics about it without even knowing the answer. So thanks to the universe for being understandable at lots of levels even before we figured out quantum gravity. You can imagine another scenario where in order to do any calculation you had to understand all the little bits inside of it. You had to figure out the fundamentals of quantum gravity before you could make chicken soup. Right, But fortunately in our universe you can throw baseballs and make chicken soup and play violins without understanding all the details, so we can make progress. We can say, well, maybe electrons are made of strings without knowing whether those strings are also made of something else, and still have some insight into this layer of the universe, without knowing if there are more layers beyond it.

00:31:07
Speaker 1: So we've got possible strings that we don't know exactly if they exist. But it's a line that can wiggle in the way in which it wiggles forms some kind of different thing, which I can kind of accept at this point. Is that sort of it? In terms of string theories, it seems like there would probably be a lot more complexity involved.

00:31:30
Speaker 2: Yeah, there is more complexity. The mathematics of those strings is very cool. At first, when people were working it out, they were only able to use strings to describe some kinds of particles, particles that we call bosons, which are photons and the W and the Z and the higgs and the gluons. These are all the bosons, the force carrying particles. So the original string theory could only describe bosons. And then people worked on it and found new ways for those strings to wiggle, so they could also describe fermions, and that's called super string theory. Super as a reference to this other idea, supersymmetry, which connects fermions and bosons. Check out our whole episode about that. But so then people developed super string theory, and then there was this sort of revolution in the nineteen eighties when people got really excited about it. They call it the first super string revolution. And that's when people realize, Wow, this string theory is not just a cool mathematical model. It can describe all the kinds of particles in our universe. And also it seems like a very promising theory of quantum gravity. They were able to avoid some of the infinities of earlier attempts the problems with gravitons by describing things in terms of strings. So it was a very exciting time. A lot of people worked on it, and the problem was that they had lots of different ideas. So there's not like one string theory or one way to do string theory. People figured out a bunch of different kinds of string theories, like you can have strings that are always open, like they're just lines, or strings that are closed which means they're loops, or you can have a theory with strings sometimes are open and sometimes are closed, or different kinds of ways to solve super gravity. And so at the end of the eighties there was sort of a confusion because there were like five different types of string theory that were all seemed very very different and all kind of worked, and people weren't sure sort of where to go from there.

00:33:13
Speaker 1: Right. I mean, that seems kind of tricky because it's almost like you're sort of filling in the gaps, right with these different theories, and you can it seems like they were able to come up with different sort of math or different theories that did fill that gap in different ways, and so I don't know how you would pick which one works if they all sort of can on average kind of like fix that gap.

00:33:39
Speaker 2: And that's very unsatisfying, right, because we think the universe is following a set of laws. We think there is one set of laws, and so then if you find like two explanations for the universe that both work, you're like, well, which one is really happening?

00:33:52
Speaker 1: Right?

00:33:53
Speaker 2: You know, is a deep philosophical question.

00:33:55
Speaker 1: Could there actually be something where on this level there could be multiple sets of rules that all work at the same time.

00:34:03
Speaker 2: Yeah, philosophers think it's possible that there are multiple explanations for the universe, multiple theories that predict the universe and describe it and explain what's happening, but have fundamentally different stories about sort of what's going on behind the curtain. We don't know if that's possible, but there's a group of philosophers who think it might be. And boy, I hope they're wrong because that would be very frustrating. In the stupid strink community also was hoping they were wrong. And we're trying to figure out this puzzle, and one way to try to figure it out is to see are there connections between these different theories. Can we show that actually these theories are really the same thing dressed up in different clothing, Like are we really just telling the same story using different words or using different symbols. It harkens back to like the nineteen twenties when people were developing quantum mechanics, for example, and you had Schroeninger he had his wave equation of quantum mechanics, and you had Heisenberg, he had his matrix formulation of quantum mechanics, and those two guys did not like each other. In fact, they hated each other, and they also disliked each other's ideas, like Heisenberg really didn't like Schrodinger's wave equation. You thought it made quantum mechanics like too visual, it gave you a mental image when in stage you just focus on the math of the matrices. And everybody else hated Heisenberg's matrices because nobody could understand what they meant. And then a few decades later John von Neumann showed actually they're the same. They make the same calculations. You can convert one into the other, and so they're just like two different ways to write the same thing, the way that like algebra and geometry are fundamentally the same. You want to solve a system of equations like two lines, you can either draw them on a piece of paper and see when they cross, or you can do a bunch of algebra and solve for it. In the end, those feel like two different kinds of math, but they really are revealing the same thing or the same relationship between concepts. So people were wondering, can we do that first dring theory? Can we show that these different string theories They're called type one, type two A, type two B, so.

00:36:03
Speaker 1: Thirty two sounds like a disease.

00:36:05
Speaker 2: And E eight x E eight. These are crazy names, I know, terrible, terrible names. Will be deeply offended.

00:36:12
Speaker 1: I have type one string theory.

00:36:17
Speaker 2: I'm so sorry, kame. There's a group for that. So people were wondering, is it possible these actually are different mathematical expressions for the same phenomena. And it was a hard problem. But there are smart people out there, and this guy, Ed Witten, maybe one of the smartest dudes ever. He's at the Institute for Advanced Studies near Princeton, and he was playing with these strings. Remember, the strings don't just exist in our three dimensions of space, the math works best if space has nine dimensions. So these strings are one dimensional lines through nine dimensional space, our three dimensions, and then six more dimensions that we can't sense or perceive or really experience in any way, but the strings need them in order to make their math wiggle correctly.

00:37:03
Speaker 1: Hmm, yeah, no, I mean I think this is it's always a wild time trying to think about other dimensions, because we could probably explain other dimensions with math, but to try to conceptualize them, I don't know if that's even possible with our brains, given that our brains are three dimensional brains and function in a sort of three dimensional way. So without your neurons being able to span into the other six dimensions, that seems difficult.

00:37:34
Speaker 2: It is very difficult. You're right, We intuitively think in three dimensions. It's very hard to think in additional dimensions. It's even hard to think in fewer dimensions. Like if you try to imagine a two D sheet or one D line, you're imagining it in three D space. You put that sheet into three D space, or that line in three D space. Or if I tell you imagine a zero dimensional dot, you think of a point and you sketch it out into some three D space, because that's the natural playground of our mind. So if you can't go down the dimension, there's no hope angling up a dimension. It's really very difficult.

00:38:08
Speaker 1: I almost passed out once trying to think about like nothing, like going you know, sort of the zero dimension thing, trying to think about nothing. And I felt very weird to try to think about that for too long. It felt like my brain was kind of leaving my body. Maybe I was just sleepy. I don't know. But yeah. There's also that book Flat Landers, where it tries to, in an artistic way, represent how difficult it is to bridge the gap between a two D existence and a three D existence. But you know, fundamentally, even that book is describing it as a visual experience where having vision requires three dimensions. It seems so yeah, and.

00:38:48
Speaker 2: So making progress on this requires super smart dudes to do superstring theory. And so Edwinten was thinking about these nine dimensional strings, and so those theories are ten dimensional because it's nine facial dimensions and one time dimension. He was thinking about these nine dimensional strings, and he was inspired by this leap from zero dimensional points to one dimensional lines. Strings and he was wondering, should we take it a step further. Instead of thinking about these things as one D strings in nine dimensional spaces, maybe they're actually two dimensional objects membranes, right, sheets in higher dimensional space. And so these would be like two D sheets in ten dimensional space, which looks like one dimensional objects strings if you only look at them in nine dimensions. So the idea is he invents this extra dimension, this eleventh dimension or a tenth dimension of space, and extends the strings into that space to make them into membranes.

00:39:48
Speaker 1: So more like a sheets theory.

00:39:50
Speaker 2: Yeah, exactly, from strings to.

00:39:52
Speaker 1: Sheets sponsored by sheets the convenience store and gas station.

00:39:58
Speaker 2: So the exciting thing is that Witten thought that if you worked with membranes instead of strings, you could explain all these different string theories. That these five string theories were actually just five different ways to look at the same sheet. So you roll it up this way, it looks like one. You roll it up another way it looks like another. You look at it from this perspective, it looks like a different string theory. But these five string theories that people were playing with and confused about were actually just like extreme examples of one membrane theory, and this this famous talkie gives at University of Southern California in ninety five where he points this out and he makes this connection, and he has this diagram on the slide which is just like all five theories and it just like draws lines between them.

00:40:44
Speaker 1: Is it like a corkboard was the eldest shoveled?

00:40:48
Speaker 2: It's exactly like that. Yeah, it's not very compelling as a diagram, and even his explanation is somewhat lacking. You know, he doesn't have all the math. He has sort of like this leap of intuition. He has some hints that these things do connect to each other. It's like a new direction forward. And it's sort of like the way Fineman worked. You know, Fineman developed QED and he didn't work out all the math came later when like Schwinger worked through all the details to prove that Fineman's leaps of intuition were correct. Witness sort of similar. He's like sees these connections in his brain. He knows that it can work, even if he hasn't like actually sat down and worked through it all. And so this one talk in ninety five inspired what they called the Second super string Revolution and led to like hundreds and hundreds of papers of people working on membranes. The interesting thing is that Witten himself wasn't actually sure that membranes who were going to work. He was like, hmm, it might be membranes, it might not be memoranes. I'm not sure. He knew that these things were connected, but he didn't want to actually call his theory membrane theory, so he just called it M theory, and he wrote in his paper quote, we will non committally call it the M theory, leaving to the future the revelation of M to membranes, Like people really worked through the math and showed that these things were two D objects or actually ten D objects, then we could call it membrane theory. But until then, let's just keep it M theory in case it turns out to be like mouse theory or mama theory or something else.

00:42:15
Speaker 1: Yeah. No, I mean I like that your hedge in your bets. I also like this guy kind of sounds like there's this I forgot his name, but I think he is like a quote unquote neurosurgeon who kept claiming that he could do like head transplants, and his demonstration was a bunch of dried spaghetti and a banana to show how you could basically like connect all of the arteries and spinal cord and everything. I think maybe the banana was supposed to be the spinal cord. Anyways, it was like a spaghetti banana demonstration, which did not inspire confidence. So, of course, I think with the physics, when you go out on a branch in terms of physics, it's maybe less risky than trusting someone who says they can do a head transplant.

00:43:06
Speaker 2: Yeah, so I think Edwinten. I wouldn't trust him to do a head transplant. But I'm glad that he's around and he's helping us figure out the mysteries of quantum gravity. And it's really cool that he was able to show that these theories are related to each other. You know, there are these funny dualities they find where they show that this theory is mathematically equivalent to that theory. You know, like this theory if you make it really strong, looks like that theory if you make it really weak. It's fascinating to show that the theories, even though they have again very different of mathematical foundations. They really are exploring the same concepts because the symbolism, the notation we use is really just a way to describe the abstract ideas. And so even if you use different notations and different symbols, if you can show that the ideas are equivalent, then you really have made a connection between them. And it's a relief also to think, like, well, maybe there is a connection, because then we don't have to pick one of the theory. We don't have to have a reason to choose one. We can just say, oh, they're all just special cases of one unifying idea. And in the end, that's what physics is trying to do, is come up with some unifying, simplifying explanation for everything we see out there in the universe.

00:44:14
Speaker 1: I mean, I find it really appealing not having to make a decision between like really hard choices. That sounds great. Sign me up for physics. Let's take a really quick break, and then when we get back, let's talk more about membrane theory and how it could tie everything up in a nice little bow. All right, So I was a little bit glib about tying everything up in a nice little bow. I know that is the desire of physics, and yet it seems pretty tricky to do that.

00:44:58
Speaker 2: It is pretty tricky, but along the way, we can entertain ourselves by amusing notation and making up really weird phrases and names for things. So physics, as everybody knows, is very good at using inappropriate and confusing words to describe things. And so physicists have taken this phrase membrane and tried to generalize it to any dimensional surface. So, like, you know, a membrane is like a two D surface. You can imagine like a sheet or like a cell wall. It's two dimensions, right, And so physicists don't call that a membrane. They call that a two brain, okay, so that they can call a string a one brain, or like the point a zero brain. You're a zero brain, yeah, exactly. Well, even worse is the general phrase for it. If you have a surface in P dimensions, you call it a P brain.

00:45:52
Speaker 1: That's what I call my dog all the time. I'm like, look at you, old pepe brain.

00:45:56
Speaker 2: Yeah, well you didn't realize you're actually giving it a vast You're connecting it to the fundamental theory of the universe. Maybe cookie can reveal something true about reality.

00:46:06
Speaker 1: I look into her eyes, I see these deep pools of knowledge. But then it turns out she just had to burn.

00:46:14
Speaker 2: Cookie, had too many cookies.

00:46:15
Speaker 1: It sounds like, yeah, exactly. So now I'm confused because I kind of got the idea of the membrane being like, it's not a point, it's not a line. It's like a plane, but not necessarily a flat plane, one that could be sort of wrapped around different dimensions. So I kind of get that. Now we're sort of this terminology of zero brain being a point, one brain being a string, two brain being a two D surface. What is the point of having brain in there? Like as a term? Like what and I don't mean this like in a mean way, just like what purpose is that serving in terms of helping with the research or the explanation.

00:47:02
Speaker 2: Yeah, it's a good question. Maybe physicists just like saying brain because it doesn't sound smart, sounds like they're talking about their brains. But physicists like to think about different versions of ideas, not to be limited by our experience of the universe, you know, where we have one dimensional objects and two dimensional objects and three dimensional objects. They'd like to generalize it and to be opened to other dimensions and other scales, and so for example, Edwinton's first idea was maybe the way to do this is to use two dimensional sheets, which is fascinating to think, like, Okay, the universe isn't made of points of stuff or even lines of stuff, but maybe like sheets of stuff. It would be pretty weird if the universe was made of two dimensional things the fundamental nature of it, the basic building block where sheets, that would be weird. But recently people have been making some progress in an alternative version of m theory in which the brains are five dimensionals, so they use five brains, meaning that like you still work in a theory where there are ten spatial dimensions in one time dimension, but the fundamental building blocks of the universe are not sheets. There five dimensional objects, which is pretty hard to think about and impossible to visualize with our three brains.

00:48:16
Speaker 1: Yeah, that's an interesting thing because usually the intuitive direction of units right of stuff or like building blocks of stuff is like you go from simple to more complex, right, so like you'd start out with you know, zero dimensions than one dimensions than two dimensions and three dimensions than four dimensions, et cetera. Right, and then like as you get to the smaller building blocks, the kind of intuitive way is like the smaller the building block, the fewer the dimensions. Right. But I think it is really interesting the idea that the smallest building block could be something that is actually operates among you know, more dimensions than say, we did as human consciousness. Is because that seems, I don't know, for some reason, that makes more sense to me than like the smallest unit being like a point, even though I cannot there is no way I can even begin to conceive of five dimensions without sounding like I'm high on Joe Rogan, I.

00:49:25
Speaker 2: Think you're right though, and I think the lesson there is the universe is filled with surprises. You know. We set up this question with we have a puzzle about the fundamental nature of reality. Is a quantum mechanical? Is it general relativistic? Is this something new and weird and different? And we don't have an answer yet, But this line of investigation building strings into membranes into p brains is suggesting that we've been thinking about it wrong in terms of tiny little objects that actually at the foundation of the universe, the basic level of reality, the intellectual firmament that we can finally reach built out of complex objects, objects with five dimensions to them, or even two dimensions. And that's the kind of revelation we're looking for, you know, that's exactly the hope that the math points us to structures that tell us something about what's actually happening out there in reality. And in a way, that's a surprise, because I don't expect our intuition to correctly guess how the universe works. I expect it to be a surprise. It would be quite disappointing if the universe was a certain way and we were like, oh, yeah, that makes sense. Instead, I want that moment where we're like, oh, wow, the universe actually works in this weird way, how could that possibly be? And then it requires like a reworking off your mental model to incorporate that, But that brings you more in aligned with the way the universe actually works. And that's kind of the whole goal of science, right, is to align our brains with the workings of the universe, not just our silly, clueless, primitive guesses about how the universe might work.

00:50:55
Speaker 1: So if it was up to me, I would just hazard a guess that the universe is man, little worms, man, just tile worms.

00:51:04
Speaker 2: I see. So that's your worm brain theory of the universe.

00:51:06
Speaker 1: My brain theory.

00:51:09
Speaker 2: You and RFKU.

00:51:10
Speaker 1: Yeah, I should run for president and me and my worms know how.

00:51:15
Speaker 2: To run this chuntry Vice President Terrence Howard, all right, well, thanks for coming along on this crazy mental journey down into the fundamental nature of the universe to think about weird quantum objects, also obeying the rules of gravity and revealing that the universe is made out of building blocks that we do not yet understand, but they might require one brain's two brains or p dimensional pea brains.

00:51:42
Speaker 1: Thank you for helping me understand that the universe is not made out of tiny violence. That really helps.

00:51:49
Speaker 2: It's only possible because your brain is not a banana. All right, Thanks very much everybody, and tune in next time for more science and curiosity. Come find us on social media where we answer questions and post videos. We're on Twitter, Discorg, Instant, and now TikTok. 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.