Latest / Daniel and Kelly’s Extraordinary Universe / What Is String Theory?
Transcript
- 0:06Speaker 1: One thing that I really love about physics is that
- 0:08Speaker 1: sometimes the laws of physics don't just work, they're actually pretty.
- 0:12Speaker 1: What do you mean physics can be pretty? You know?
- 0:15Speaker 1: I thought physics and science was like a hard hitting
- 0:18Speaker 1: objective thing, you know, human endeavor. Absolutely, we got big tasks.
- 0:22Speaker 1: We want to understand the universe and makes sense of it.
- 0:24Speaker 1: But sometimes we come up with an idea, something that
- 0:27Speaker 1: just looks beautiful, something which is has an innate elegance
- 0:30Speaker 1: to it. You mean, like you'd see a theory walking
- 0:33Speaker 1: down the road and you'd be like, oh, man, that
- 0:35Speaker 1: that theory hasn't going on. Yeah, there's some sexy the
- 0:38Speaker 1: curves in that theory. You mean like graphs though, right,
- 0:41Speaker 1: Like that that kind of occurs, right, that graph is
- 0:44Speaker 1: a nice curve to look those peaks. And one of
- 0:48Speaker 1: the most controversial theories of all time, one of the
- 0:50Speaker 1: ones that gets people up in arms, is also one
- 0:53Speaker 1: that's probably survived because it's so beautiful. An alogot isn't
- 0:57Speaker 1: the theory of attraction. No, it's a theory that was
- 1:00Speaker 1: once described as a piece of twenty first century physics
- 1:04Speaker 1: that had fallen by accident into the twentieth century. So
- 1:08Speaker 1: it's a future Babe, future baby exactly. Hi. I'm Orge,
- 1:29Speaker 1: I'm a cartoonist and I'm Daniel. I'm a particle physicist,
- 1:32Speaker 1: and we are the authors of the book We Have
- 1:34Speaker 1: No Idea, which talks about all the things we don't
- 1:37Speaker 1: know about the universe and how we might hope to
- 1:40Speaker 1: one day understand them. Yeah. So, welcome to our podcast.
- 1:43Speaker 1: Daniel and Jorge explained the universe, in which we take
- 1:46Speaker 1: everything and anything in the universe and try to explain
- 1:49Speaker 1: it to you in a way that makes sense and
- 1:51Speaker 1: hopefully makes you laugh to be on the program. We're
- 1:54Speaker 1: going to talk about, Oh, string the that's right, string theory.
- 2:02Speaker 1: And this is a question that we've been getting from listeners.
- 2:04Speaker 1: We ask people, please send in your request for topics,
- 2:07Speaker 1: and maybe more than fifty percent of the request work.
- 2:10Speaker 1: Can you explain string theory? What is stringth theory? Talk
- 2:12Speaker 1: about string theory more than yeah, and it's fascinating. It's
- 2:16Speaker 1: because string theory really is a part of sort of
- 2:19Speaker 1: cultural zite guys. It's like an idea that people know
- 2:21Speaker 1: exists even if they don't understand it. It's a big
- 2:24Speaker 1: part of that show The Big Bang Theory, right, like
- 2:26Speaker 1: the people in that show there they supposedly study string theory.
- 2:29Speaker 1: I don't know. I don't watch that show me neither,
- 2:33Speaker 1: but that's what I've been told. Your cultural advice expert
- 2:37Speaker 1: has told you that this is a culturally relevant thing. Well, yeah,
- 2:40Speaker 1: it's it's something people have heard about. Well have you
- 2:42Speaker 1: heard about string theory before you started spending your time
- 2:45Speaker 1: talking to physicists? Know, yeah, I've heard about it. You know.
- 2:48Speaker 1: It's one of these things that you hear a lot about.
- 2:51Speaker 1: It's these like crazy theory about the universe, but it's
- 2:53Speaker 1: really and you know, you hear certain things about it, like, oh,
- 2:56Speaker 1: everything is made out of strings, but you don't really
- 3:00Speaker 1: kind of know what it is and what does it
- 3:01Speaker 1: mean for things to be strings. You're a very visual person.
- 3:04Speaker 1: What image do you get in your head if I
- 3:05Speaker 1: tell you everything is made out of strings? Do you
- 3:07Speaker 1: get like a universe an idea of like a universe
- 3:10Speaker 1: where everything is crocheted out of yarn? Or how does
- 3:12Speaker 1: it work? In your head? I would to just ask
- 3:14Speaker 1: what are those strings made out of? Right? Right? Of course?
- 3:19Speaker 1: So you are a physicist at hard right, because every
- 3:21Speaker 1: question just leads to the next question. That's right, beautiful physicists,
- 3:24Speaker 1: a hard supermodel on the outside. No comment. Um, but
- 3:30Speaker 1: I thought it was an interesting question to tackle because
- 3:32Speaker 1: it's something everybody has heard about, but very few people
- 3:34Speaker 1: actually understand. I think that's why people wanted us to
- 3:37Speaker 1: talk about, is saying, can you make this not just
- 3:40Speaker 1: something we have heard this phrase, but something where we
- 3:42Speaker 1: can know what it means and gets an insight into
- 3:44Speaker 1: why people are spending their time doing it. Right. Yeah, So,
- 3:47Speaker 1: as usual, we went out into the street and ask
- 3:50Speaker 1: do you know what strength theory is? Yeah? So before
- 3:53Speaker 1: you hear these answers, think for a moment, could you
- 3:55Speaker 1: define strength theory? Do you know what it is and
- 3:58Speaker 1: why it's persisted for so long. Here's what people who
- 4:01Speaker 1: I asked had to say. Um, No, I have no
- 4:04Speaker 1: idea what that is. No, I do not. I've heard
- 4:07Speaker 1: of it. My only way of Big Bang theory Okay,
- 4:11Speaker 1: I don't know. I'm sorry. The connectedness of Adams and
- 4:15Speaker 1: sub atomic particles Okay, it's something that Sheldon worked on. Yes, Okay,
- 4:23Speaker 1: So first of all, it's kind of interesting because you
- 4:25Speaker 1: normally you go out into your university campus to ask people,
- 4:28Speaker 1: but this time you went somewhere different. Yeah, that's right.
- 4:30Speaker 1: You see, Irvine was closed for a holiday, so instead
- 4:33Speaker 1: I went to the mall here in Irvine, the Spectrum,
- 4:35Speaker 1: and I asked a bunch of random strangers, um questions
- 4:38Speaker 1: about science. And again I was struck by how many
- 4:41Speaker 1: people were willing to answer my questions. I thought people
- 4:43Speaker 1: would say, who are you? Go away security security? Right?
- 4:47Speaker 1: Maybe they sense a certain beauty about you, Daniel, You're like,
- 4:50Speaker 1: who is this beautiful specimen of a person? Know? Who is?
- 4:55Speaker 1: Apparently I just don't look very threatening, you know. Um,
- 4:58Speaker 1: I look like I could could get knocked to a
- 4:59Speaker 1: religious a passing breeze or something. Um. So everybody was
- 5:03Speaker 1: willing to engage, which was awesome, and people had some
- 5:05Speaker 1: pretty fun ideas, and everybody had heard of it. Nobody
- 5:08Speaker 1: had said hell what, and your other speculation was correct.
- 5:12Speaker 1: Some people had heard of strength theory specifically because of
- 5:14Speaker 1: the Big Bang theory. So thank you Big Bang Theory.
- 5:18Speaker 1: You've mined all of this juice from nerd culture and
- 5:21Speaker 1: you have actually communicated something to the public. And congratulations.
- 5:24Speaker 1: Nobody understands what string theory is, but they do understand
- 5:26Speaker 1: that it is a theory. Well, I think that show
- 5:29Speaker 1: doesn't even try to explain it, right, They almost use
- 5:32Speaker 1: it for the opposite effect, Like, let's depict our characterist,
- 5:35Speaker 1: this impenetrable, unrelatable genius that speaks gobbling Google, so we'll
- 5:40Speaker 1: just having to talk about strength theory and that nobody
- 5:43Speaker 1: and nobody's going to understand that. So it's it's likely.
- 5:45Speaker 1: So you're saying string theory represents the impenetrability of physics.
- 5:50Speaker 1: I think it's more important to explain these things to
- 5:52Speaker 1: people rather than just toss these words around and try
- 5:55Speaker 1: to intimidate people. So yeah, I think that's what I mean.
- 5:57Speaker 1: It's like they use it to intimidate people about physics, Yeah,
- 6:01Speaker 1: when physics is nothing but warm and cuddly and just
- 6:03Speaker 1: wants to explain the universe to you. Man, there's nothing
- 6:06Speaker 1: intimidating about physics, right. It's about revealing secrets and giving
- 6:10Speaker 1: understanding and insight and appreciating beauty. And that's the thing
- 6:13Speaker 1: about string theory is it doesn't just potentially explain a
- 6:17Speaker 1: lot of things. It also offers some elegance, some gorgeousness,
- 6:20Speaker 1: like a peak into what nature is doing underneath. Because
- 6:23Speaker 1: you know, you can have ugly theories and you can
- 6:25Speaker 1: have elegant theories, you know, and you might ask the difference,
- 6:28Speaker 1: like how what is the difference? Well, I can ask
- 6:30Speaker 1: you the same question about art, right, Like I look
- 6:32Speaker 1: at the Kendinsky and I say, hey, that's beautiful, and
- 6:34Speaker 1: somebody else says whatever, I could do that in an afternoon.
- 6:37Speaker 1: It's garbage. It's subjective, right, you can't. It's like the
- 6:40Speaker 1: whole question of what is beauty is something that's very
- 6:42Speaker 1: difficult to nail down. So you shouldn't judge a painting
- 6:46Speaker 1: by the same metric you used to judge of physics theory. Um.
- 6:51Speaker 1: And you know, two physicists can disagree about what theory
- 6:54Speaker 1: is pretty and what theories ugly. So it's it's totally subjective.
- 6:56Speaker 1: It's not an objective fish like a you know, I
- 7:00Speaker 1: like this kind of theory. I like that kind of theory. Yeah,
- 7:04Speaker 1: Like you know, I like theories with handcuffs in the
- 7:06Speaker 1: midstet of strings, right, like my handcuff theory of the universe.
- 7:09Speaker 1: That's where that's where you're going theories or yeah, okay,
- 7:18Speaker 1: So let's break it down for people. What is string theory? Right?
- 7:21Speaker 1: So string theory is basically is the idea that the
- 7:24Speaker 1: smallest elements of matter with things that things are made
- 7:27Speaker 1: out of are not points, not particles, but instead their lines,
- 7:32Speaker 1: their strings, strings of what strings of basic universe stuff? Right, So,
- 7:41Speaker 1: like the electron is is not like a little ball,
- 7:44Speaker 1: and we know it's like a quantum object, which is
- 7:46Speaker 1: like a point with some kind of probability. But you're
- 7:48Speaker 1: saying if you zoom in even more, maybe you would
- 7:51Speaker 1: see a little squiggle there. Yeah, And the sort of
- 7:53Speaker 1: two ideas there. One is what is the most basic element?
- 7:56Speaker 1: And the second is is their most basic element? So
- 7:59Speaker 1: this assumes there is a most basic element. You know
- 8:01Speaker 1: that you you look at something next to you, pick
- 8:03Speaker 1: up in the nearest object you have, you know, maybe
- 8:05Speaker 1: it's an apple, maybe it's a platypus, maybe it's a
- 8:08Speaker 1: you know, I don't know what, and and think about
- 8:10Speaker 1: what it's made out of. It's made of molecules, right,
- 8:12Speaker 1: Tear those apart, you get atoms. Tear those atoms apart,
- 8:15Speaker 1: you get protons and neutron's electrons. Tear those apart, you
- 8:17Speaker 1: get quarks. Right, and you could keep going and eventually
- 8:20Speaker 1: you get two smaller and smaller particles. Right. The question
- 8:23Speaker 1: is do you ever get to the smallest particle. Right,
- 8:27Speaker 1: that's one question. Is there a smallest thing? And we
- 8:29Speaker 1: covered that in a whole podcast, but here we're just
- 8:31Speaker 1: gonna assume that there is. Right, at some point, you
- 8:33Speaker 1: get down the most basic thing where you're not allowed
- 8:36Speaker 1: to ask what it's made out of because it's made
- 8:37Speaker 1: out of the most basic universe stuff. It's like the
- 8:40Speaker 1: one circle on a lego set. It's like, you can't
- 8:44Speaker 1: get any smaller than that. That's right, it's the unit exactly,
- 8:48Speaker 1: And that's you might feel like that, that's frustrating. Why
- 8:51Speaker 1: can't I ask what it's made out of? You know?
- 8:53Speaker 1: But it's also not frustrating because it would be the answer.
- 8:56Speaker 1: I mean, if you actually got there and you said, look,
- 8:58Speaker 1: everything in the universe is made out of this one
- 9:00Speaker 1: basic thing. That's a deep insight, right, that's what we're
- 9:03Speaker 1: going for. That's the day we wish for that we
- 9:06Speaker 1: peel back a layer of reality and see everything is
- 9:09Speaker 1: made out of this thing, because then you can ask
- 9:11Speaker 1: why this thing? What does that mean? Oh? I see?
- 9:13Speaker 1: So string theory is saying that everything electrons course, eventually,
- 9:17Speaker 1: if you break them down, you'll get to this one
- 9:20Speaker 1: type of string. That's right. We think of things being
- 9:22Speaker 1: made of particles, We think of them as tiny dots
- 9:25Speaker 1: right in space. But string theory says they're not dots,
- 9:28Speaker 1: their lines okay, and they're they're these loops and wiggles
- 9:33Speaker 1: instead of being dots. And then everything is made out
- 9:36Speaker 1: of these strings. And you might ask, well, how can
- 9:38Speaker 1: you get different kinds of particles, for example, out of
- 9:42Speaker 1: one kind of string? Right, And the idea there is
- 9:46Speaker 1: that the strings can vibrate, the strings can wiggle, right,
- 9:49Speaker 1: the reverberations in the string just like you know a
- 9:52Speaker 1: rubber band or a string. Is it like an actual vibration,
- 9:54Speaker 1: like it goes up and down or is it just
- 9:56Speaker 1: like the different shapes you can make with a string. Oh,
- 10:00Speaker 1: I see No, it's actual motion of the string. Yeah,
- 10:03Speaker 1: And so it's different, different vibrational modes. So they get
- 10:06Speaker 1: excited and they can get into this state or that state.
- 10:09Speaker 1: As the string vibrates in different ways, it makes different particles.
- 10:14Speaker 1: So some tiny particle calling it's an electron, for example,
- 10:18Speaker 1: is actually a string vibrating this way, and a cork
- 10:21Speaker 1: is a string vibrating the other way. And the neutrinos
- 10:23Speaker 1: a string vibrating a third way, so the same thing
- 10:26Speaker 1: with different vibrations can appear as different particles. Okay, so
- 10:30Speaker 1: it's not like different strings and a guitar. That's not
- 10:33Speaker 1: what we're talking about. We're talking about one string. It's
- 10:36Speaker 1: like a one string guitar and just the different ways
- 10:39Speaker 1: in which it can vibrate that gives rise to all
- 10:42Speaker 1: the different stuff we see in the universe exactly. And
- 10:45Speaker 1: like a guitar, you can pluck the string differently and
- 10:47Speaker 1: you can get different notes, right, you can if based
- 10:50Speaker 1: on how fast it's vibrating and you know where you
- 10:53Speaker 1: put your finger in the end, you can get different
- 10:54Speaker 1: notes out of the same string. And it's key here,
- 10:57Speaker 1: that's one string, right, it's a single string. Because we're
- 11:00Speaker 1: to explain everything in the universe in terms of one object.
- 11:03Speaker 1: So we're trying to explain how you get all this
- 11:05Speaker 1: complexity in terms of one thing. And that's the answer
- 11:07Speaker 1: from string theory is that the string has different modes
- 11:11Speaker 1: to it to drink, can do different things. And you know,
- 11:14Speaker 1: you might think that's sort of weird, Like I expect
- 11:17Speaker 1: stuff if it's all made of the same thing, to
- 11:19Speaker 1: be the same thing, right, Like if everything is made
- 11:22Speaker 1: of the same stuff. Why is this red and that blue?
- 11:24Speaker 1: And this tastes delicious and this tastes terrible, right, And
- 11:27Speaker 1: it comes from the way it's vibrating. It's kind of
- 11:30Speaker 1: like maybe light. You know, a light is just made
- 11:32Speaker 1: out of one thing, photons, but depending on the frequency,
- 11:35Speaker 1: then it's different colors. Yeah, exactly. And the way things
- 11:39Speaker 1: move and vibrany can totally affect the way they we
- 11:41Speaker 1: perceive them. You know, think about for example, water, right,
- 11:44Speaker 1: water is made out of water molecules, but so is ice,
- 11:47Speaker 1: and so is steam. Right, They're made out of the
- 11:49Speaker 1: same thing, but we feel them, we experience them very
- 11:52Speaker 1: differently because of the way they're moving, right, steam and
- 11:55Speaker 1: liquid water. How the water particles moving more than an ice, right,
- 11:59Speaker 1: And so it's the most into those particles that generates
- 12:01Speaker 1: the macroscopic qualities that we used to define it. So
- 12:05Speaker 1: the things we used to define the electron and things
- 12:07Speaker 1: we used to define a quirk actually come just from
- 12:10Speaker 1: the vibrations of these strings. Again according to this theory. Okay,
- 12:13Speaker 1: so so then, but then my question is still, what
- 12:16Speaker 1: are these strings made? Is it just like made out
- 12:19Speaker 1: of universe I told you? Or hey, you're not let
- 12:21Speaker 1: to ask once we get down to the lowest level,
- 12:24Speaker 1: no more questions. No, but you know what I mean,
- 12:27Speaker 1: like is it like a like a physical string or
- 12:30Speaker 1: just like a mathematical string? Do you know what I mean?
- 12:32Speaker 1: Like is prepare for philosophical detour here, like what's actually
- 12:37Speaker 1: vibrating like universe stuff? Yeah? Yeah, Well, because I still
- 12:42Speaker 1: look in the end, all physics theories are just models. Right,
- 12:45Speaker 1: you gonna ask the question is this really happening or
- 12:48Speaker 1: is this just a mathematical model? In my head, I
- 12:50Speaker 1: used to do calculations and predict the results of experiments. Boom.
- 12:54Speaker 1: That is a big philosophical question, right, and there's no
- 12:57Speaker 1: way to answer that. So we think of these things
- 13:00Speaker 1: as models in our head reflect reality. Okay, you know
- 13:03Speaker 1: the top cork doesn't exist or not? Or is it
- 13:05Speaker 1: is a calculation a model in my head? We could
- 13:08Speaker 1: you know, smoke banana peels and talk about that for
- 13:10Speaker 1: a long time without making any progress. So this model
- 13:12Speaker 1: is just asking me to imagine that the most fundamental
- 13:16Speaker 1: thing at the universe are these little strings. They can
- 13:19Speaker 1: vibrate in different ways, but then these trains can move
- 13:21Speaker 1: around and they can't be cut into pieces. Right, you
- 13:24Speaker 1: can't get anything smaller than a string. It's the most
- 13:27Speaker 1: basic unit. Like, there's something about the stuff of the
- 13:30Speaker 1: universe that is just you can't vibrate or do things
- 13:33Speaker 1: shorter than these little strings. Yeah, exactly. Or thinking about
- 13:36Speaker 1: it from the other direction, you know, how do you
- 13:38Speaker 1: make a universe? Well, you start with a huge pile
- 13:40Speaker 1: of tiny strings, and then the way those strings interact
- 13:43Speaker 1: gives you all sorts of interesting structure. But that's what
- 13:46Speaker 1: you start from, right, that's the universe's initial condition is
- 13:49Speaker 1: like a huge pile of strings. And these trains can
- 13:51Speaker 1: move around space. Yeah, they move and they interact with
- 13:54Speaker 1: each other, right, and that's where all interesting stuff. But
- 13:57Speaker 1: are these related to the quantum fields? How does that
- 13:59Speaker 1: really fields? Yeah? So everything we'd be built out of
- 14:02Speaker 1: these strings, including all the particles and all the forces.
- 14:05Speaker 1: And that's actually why string theory is so popular because
- 14:09Speaker 1: string theory, we think, can explain some of the mysteries
- 14:12Speaker 1: of quantum fields and some of the mysteries of how
- 14:14Speaker 1: to bring gravity into the fold and describe it in
- 14:16Speaker 1: terms of a quantum field. So the short answer to
- 14:18Speaker 1: your question is, all the quantum fields arise from these
- 14:21Speaker 1: string interactions. All these fields, all these particles just come
- 14:26Speaker 1: from this one string guitar being plugged the different frequencies.
- 14:30Speaker 1: That's right. So while you're imagining a single string guitar
- 14:34Speaker 1: of the universe, let's take a quick break. All right. So, um,
- 14:49Speaker 1: that's that's a crazy concept to ask people to digest.
- 14:53Speaker 1: But let's assume that that's the theory. Um, why who
- 14:56Speaker 1: came up with this and why do we think it's
- 14:58Speaker 1: a good theory about the universe? Yes, the string theories
- 15:01Speaker 1: had a lot of people contribute to it. It's sort
- 15:02Speaker 1: of an old theory that started out trying to explain
- 15:04Speaker 1: something else and then was tossed aside when it didn't work,
- 15:07Speaker 1: and it was later picked up again, um and reused
- 15:10Speaker 1: two as a theory of everything. And this sort of
- 15:14Speaker 1: idea of string theory is to take a different approach
- 15:18Speaker 1: to solving this question of what is the universe made
- 15:20Speaker 1: out of? As an experimentalist, my approaches take something concrete,
- 15:24Speaker 1: break it into pieces, gets smaller and smaller and smaller.
- 15:27Speaker 1: You know, as you discover new stuff, you're revealing secrets
- 15:29Speaker 1: to the universe, and just keep going until you get
- 15:31Speaker 1: to the smallest bit. Sort of via top down approach, right,
- 15:35Speaker 1: This idea is different. This is sort of a bottom up.
- 15:37Speaker 1: They say, let's just start at the very bottom. Let's
- 15:40Speaker 1: go to the most basic element and try to explain
- 15:43Speaker 1: the universe from the start. You know, if a hypothesize
- 15:46Speaker 1: the universe has made of strings, can we put them
- 15:48Speaker 1: together in a way that explains the universe and describes
- 15:51Speaker 1: everything we see around us? But I guess how did
- 15:53Speaker 1: someone even think of using strings? How do you make
- 15:57Speaker 1: a lot of things out of one thing? And a
- 15:59Speaker 1: little ring that vibrates different ways is one way to
- 16:02Speaker 1: get a lot of things out of one simple thing?
- 16:05Speaker 1: Is that kind of the origins of it? Yeah, exactly,
- 16:06Speaker 1: you should imagine. Physicists are basically random, terrible idea generators,
- 16:12Speaker 1: and most of those just don't work. So at some
- 16:14Speaker 1: point somebody's like fed up with thinking about the universe
- 16:17Speaker 1: in terms of particles, and they're like, well, what if
- 16:19Speaker 1: they're not you know, what if they're not dots, Let's
- 16:21Speaker 1: just try it with lines. Does that work? You know?
- 16:23Speaker 1: And basically every idea that you can imagine, somebody has
- 16:26Speaker 1: tried to make that work as a theory and everything,
- 16:28Speaker 1: and usually given up after about two seconds because the
- 16:31Speaker 1: theory of everything based out of little puppies or whatever
- 16:34Speaker 1: doesn't work. It's very hard to make that put together.
- 16:36Speaker 1: But like they maybe they say, what if there's just
- 16:38Speaker 1: one particle that makes up everything, how would you how
- 16:41Speaker 1: would you explain how this one particle can turn into
- 16:43Speaker 1: other things? And so that's kind of difficult maybe, But
- 16:46Speaker 1: a string, you can imagine it vibrating or moving in
- 16:49Speaker 1: different ways to give rise to different particles, right, yeah, exactly.
- 16:53Speaker 1: And people were playing with it and like, what can
- 16:55Speaker 1: we do with this? And they try, like I said,
- 16:57Speaker 1: they try to use it to solve other problems. Specifically,
- 16:59Speaker 1: they try to under stand the strong nuclear force using strings,
- 17:02Speaker 1: and it didn't work. And then later somebody else said, Hi,
- 17:04Speaker 1: I heard about this idea of strings. I wonder if
- 17:07Speaker 1: I can use that to solve this other problem, which
- 17:09Speaker 1: is why can't we get gravity to play well with
- 17:12Speaker 1: the other forces. You know, if you want to understand
- 17:15Speaker 1: the way the universe works, you have to try to
- 17:17Speaker 1: explain everything in terms of one theory, right, to bring
- 17:19Speaker 1: it all together into a single explanation, because that's a
- 17:22Speaker 1: big problem right now in physics, right, Like it's like
- 17:24Speaker 1: marrying quantum physics with gravity. That's right. It's a marriage
- 17:28Speaker 1: we've been trying to arrange forever, but the two participants
- 17:31Speaker 1: just do not want to do not want to play
- 17:33Speaker 1: along exactly. They don't pressure. Yeah, So we have these
- 17:37Speaker 1: sort of two towering achievements of physics. On one hand,
- 17:40Speaker 1: quantum mechanics, right, a revelation about a hundred years old.
- 17:43Speaker 1: It tells us that the universe is very different from
- 17:46Speaker 1: the way we thought it was, that there's uncertainty, that
- 17:49Speaker 1: there's fuzziness, a limited amount of knowledge we can actually
- 17:52Speaker 1: obtain about the universe. And it's most specifically that the
- 17:56Speaker 1: universe is quantized, it's broken up into discreete little chunks.
- 18:00Speaker 1: And on the other hand, we have gravity and general relativity,
- 18:03Speaker 1: which is an incredibly successful theory that describes the motion
- 18:07Speaker 1: of planets around stars and black holes and all sorts
- 18:10Speaker 1: of crazy stuff and time dilation in the way space
- 18:13Speaker 1: and time are connected, all this incredible stuff. But it
- 18:17Speaker 1: assumes the universe is not quantum mechanical, right. It assumes
- 18:20Speaker 1: that that energy can be subdivided into arbitrarily small bits,
- 18:24Speaker 1: and you can have an infinite number of locations and
- 18:26Speaker 1: an infinite amount of information. Right, And so the two
- 18:29Speaker 1: theories are not consistent, and most of the time they're
- 18:32Speaker 1: talking about different stuff so they don't overlap. Sometimes, like
- 18:35Speaker 1: when you're talking about a black hole, then the two
- 18:37Speaker 1: give you very different stories. Okay, so, how is strength
- 18:40Speaker 1: theory able to marry gravity and quantum mechanics? Right, So
- 18:44Speaker 1: that is exactly the right question. How does string theory
- 18:48Speaker 1: allow us to bring together quantum mechanics and gravity? Well
- 18:51Speaker 1: to understand that, you really have to understand why we
- 18:54Speaker 1: failed without string theory. And the problem is that when
- 18:57Speaker 1: you bring together quantum mechanics and gravity, you get lots
- 18:59Speaker 1: of infinities. Right. A theory doesn't work when it can't
- 19:03Speaker 1: predict the results of experiments. So if you ask a
- 19:05Speaker 1: theory what happens when I smash two particles together, it
- 19:08Speaker 1: should give you a reasonable answer. If the answer is infinity,
- 19:12Speaker 1: or you know, nothing will happen or something, then it
- 19:14Speaker 1: doesn't make any sense. It has to give physical answers,
- 19:17Speaker 1: and infinity is not a physical answer. The problem is
- 19:19Speaker 1: when you try to bring gravity into quantum mechanics, you
- 19:23Speaker 1: get lots of these infinities. And the infinities come because
- 19:26Speaker 1: of the point particles, because you're trying to treat these
- 19:29Speaker 1: objects as if they're just dots in space, and that
- 19:32Speaker 1: leads to lots of craziness. You know, how do you
- 19:34Speaker 1: have mass in a tiny little dot in space that
- 19:36Speaker 1: has infinite density? Right now? We have lots of other
- 19:39Speaker 1: theories that do play well with quantum mechanics. Electromagnetism, for example,
- 19:43Speaker 1: very happily married with quantum mechanics. And the reason that
- 19:46Speaker 1: works is that we have tricks to hide those infinities.
- 19:49Speaker 1: We can bundle up those infinities that that pop up
- 19:52Speaker 1: in the from the point particles in various other ways
- 19:54Speaker 1: mathematical tricks. Those tricks don't work for gravity because gravity
- 19:58Speaker 1: is very different from the other forces. The strength of
- 20:00Speaker 1: the force grows with the energy of the object, right,
- 20:04Speaker 1: So in this case, when an object has more and
- 20:06Speaker 1: more energy, it feels more and more gravity, right because
- 20:09Speaker 1: gravity is proportional amount of energy in an object. So
- 20:12Speaker 1: the typical tricks we use to hide those infinities under
- 20:15Speaker 1: the rug that works for quantum electrodynamics doesn't work for
- 20:19Speaker 1: gravity when we try to do quantum gravity. So how
- 20:22Speaker 1: does string theory to solve that problem? Simple? It just
- 20:25Speaker 1: says there are no points. It says at the smallest scale,
- 20:28Speaker 1: you don't have to worry about dealing with gravity a
- 20:31Speaker 1: tiny points because there are none because that it's smallest scale.
- 20:34Speaker 1: The universe is not made of points but strings, and
- 20:37Speaker 1: so it's a nice way to sort of circumvent that problem.
- 20:39Speaker 1: And that's why string theory can bring together quantum mechanics
- 20:43Speaker 1: and gravity so nicely. And I got people excited, and
- 20:45Speaker 1: that's where the beauty was. People were like, wow, and
- 20:48Speaker 1: it's beautiful. There's like these strings floating around. You get
- 20:51Speaker 1: these membranes and its It seemed really cool to people.
- 20:56Speaker 1: So you said something interesting, which was that people thought
- 20:59Speaker 1: that dringth theory was beautiful and elegance. So can you
- 21:02Speaker 1: try to explain like why people thought that, Like is
- 21:04Speaker 1: it simple or is it just it's so open ended
- 21:09Speaker 1: or it just seems to be working or it doesn't
- 21:11Speaker 1: fall into the ugliness of other theories. I think people
- 21:14Speaker 1: just have fun working with it, you know. I think
- 21:16Speaker 1: it's I think it stimulates people's imaginations can have fun,
- 21:20Speaker 1: and physicists can have fun. Yeah, and you know, when
- 21:23Speaker 1: you do string theory, you write down these diagrams, and
- 21:26Speaker 1: instead of these diagrams being lines with swils, that diagrams
- 21:29Speaker 1: are like loops, and they have sheets to and to
- 21:32Speaker 1: connect them, you know, membranes, and you get to think
- 21:35Speaker 1: about these high dimensional surfaces and people have a lot
- 21:38Speaker 1: of fun with them, and it's been so invigorating for
- 21:41Speaker 1: physicists that's actually led to a lot of good results
- 21:45Speaker 1: just in mathematics, Like mathematicians have learned about things from
- 21:49Speaker 1: the things that physicists have done while exploring its string theory,
- 21:53Speaker 1: and so it's it's stimulated. The whole field of mathematics
- 21:55Speaker 1: and mathematics is about the beauty and interconnectedness of numbers.
- 21:59Speaker 1: They don't care if it actually just scribes anything in
- 22:00Speaker 1: the real world, right, It's about these abstract ideas and
- 22:03Speaker 1: how they come together. And one of the lead physicists
- 22:06Speaker 1: who works on string theories name is Ed Witten. He
- 22:08Speaker 1: won what's basically the Nobel Prize for math, which is
- 22:11Speaker 1: the Field Medal, which is even harder to win than
- 22:13Speaker 1: the Nobel Prize because they only give it every two years,
- 22:16Speaker 1: and he's a physicist, and he won the top prize
- 22:18Speaker 1: in mathematics for advances in string theory, which tells you that,
- 22:22Speaker 1: like there's a huge amount of mathematical machinery that's been
- 22:26Speaker 1: invented here. And these folks they love it like it's
- 22:29Speaker 1: a it's fascination for them. It's a there's a deep
- 22:32Speaker 1: pleasure in manipulating these equations and in thinking about it. Oh,
- 22:35Speaker 1: usually it's the other way around, Like usually you guys
- 22:38Speaker 1: have to come over the theory and convince mathematicians that
- 22:42Speaker 1: this is something fundamental here. It seems to be coming
- 22:45Speaker 1: from the other way. It's like, here's something that even
- 22:47Speaker 1: mathematicians I think might be fundamental about the universe. Well,
- 22:51Speaker 1: I don't know if mathematicians think it's fundamental about the universe.
- 22:53Speaker 1: They just think it helps solve interesting problems. They're like, oh,
- 22:56Speaker 1: this is a cool tool. It can solve some problems
- 22:58Speaker 1: in math, or it gives us a new way to
- 23:00Speaker 1: think about mathematical problems. You know, And anytime you get
- 23:03Speaker 1: a new tool, it's fascinating. And you imagine, for example,
- 23:05Speaker 1: you're an artist and somebody invents a new musical instrument
- 23:08Speaker 1: and you're like, oh, cool, what can I use this for.
- 23:10Speaker 1: I can invent a new kind of music. I can
- 23:12Speaker 1: have a new kind of rhythm or a new kind
- 23:14Speaker 1: of song. Or in the same way, you create a
- 23:16Speaker 1: new physics theory, a new basic object you get to
- 23:18Speaker 1: play with. It's exciting. He gives you things to play
- 23:21Speaker 1: with and ideas to try. And so like this is
- 23:24Speaker 1: a said, hey, look I have a one string guitar,
- 23:28Speaker 1: and were like, whoa, I can play the whole universe
- 23:32Speaker 1: on that thing. But you know, string theory has a
- 23:35Speaker 1: lot of people who love it and adherence and a
- 23:37Speaker 1: lot of people in departments who are working on it.
- 23:39Speaker 1: But there are also a lot of people who don't
- 23:41Speaker 1: like string theory. It's got sort of a backlash as well.
- 23:43Speaker 1: Any you know, you've made it as a physics theory
- 23:46Speaker 1: when you have haters, right, physics haters physics. All right,
- 23:51Speaker 1: let's get into it, but first let's take a quick break.
- 24:06Speaker 1: Al Right, So, strength theory has its haters, people who
- 24:09Speaker 1: don't think it's all that or who think it might
- 24:11Speaker 1: be wrong, or maybe it's not all that beautiful. So
- 24:14Speaker 1: what are some of the arguments against string theory. Yes,
- 24:17Speaker 1: so I would say there's really two categories of attacks
- 24:20Speaker 1: people make against string theory. One is there's just too
- 24:24Speaker 1: many of them, and the other is that we can't
- 24:26Speaker 1: test it. Too many stringth theories, too many string theories.
- 24:30Speaker 1: It's not a singular concept, you know, stringth theory, it's
- 24:35Speaker 1: actually string theories. I remember loctrology, string theories, string theories.
- 24:45Speaker 1: There are a lot of There are a lot of
- 24:46Speaker 1: these things. There's lots of ways that you can put
- 24:47Speaker 1: it together, lots of different ways you can shape the string,
- 24:50Speaker 1: and lots of ways you can have them interact with
- 24:52Speaker 1: each other. And um, you know we were saying earlier,
- 24:55Speaker 1: you'd like a simple theory. You'd like to make your
- 24:57Speaker 1: choices for how you build the theory, not the arbitrary
- 25:00Speaker 1: will be forced by the mathematical construction, you know, like
- 25:03Speaker 1: why is there a three here? It's the only way
- 25:04Speaker 1: that it works. So we have a theory where there
- 25:07Speaker 1: are lots of ways it could work. Then you have
- 25:09Speaker 1: a question like which way do we choose? And that's
- 25:11Speaker 1: the problem with string theory. There's lots of ways to
- 25:14Speaker 1: build one. They all have the same basic idea, right,
- 25:17Speaker 1: which is the universe made out of little strings and
- 25:19Speaker 1: everything comes out of the way vibrates. But you're saying,
- 25:22Speaker 1: there's a lot of options after that basic concept, like
- 25:25Speaker 1: how do they how do these strings interact or what
- 25:29Speaker 1: do they sound like? Or exactly? Um, and the reason
- 25:33Speaker 1: is that you can't make string theory work in four dimensions. Right,
- 25:36Speaker 1: Our universe that we experience has four dimensions, is three
- 25:40Speaker 1: dimensions of motion x, y z and then one dimension
- 25:43Speaker 1: of time, So we live in four dimensions. But strings,
- 25:46Speaker 1: for they get them, to get them to have these
- 25:47Speaker 1: mathmatical properties that we want to unify quantum mechanics and gravity,
- 25:51Speaker 1: they have to operate in more dimensions for the math
- 25:53Speaker 1: works like the dimension in which they're vibrating kind of thing,
- 25:58Speaker 1: and then are four just the ones where it's moving
- 26:00Speaker 1: around it. In some theories, yes, they vibrate in those
- 26:03Speaker 1: other dimensions, and that changes how we see them in
- 26:05Speaker 1: these dimensions. But there's a lot of different kinds of
- 26:07Speaker 1: string theory, and so that's not a general statement. And
- 26:10Speaker 1: some of them are eleven dimensional theories and some of
- 26:12Speaker 1: them are twenty six dimensional theories. Right, And so the
- 26:15Speaker 1: ideas these strings are vibrating these other dimensions, but we
- 26:18Speaker 1: don't see those other dimensions, like I don't I can't
- 26:21Speaker 1: move in twenty six dimensions. How can you say that
- 26:24Speaker 1: your theory, which has twenty six dimensions explains my four
- 26:27Speaker 1: dimensional universe. So to answer that, to solve that problem.
- 26:31Speaker 1: They have to roll up those other dimensions and tuck
- 26:33Speaker 1: them away and make them small, to make them like hidden,
- 26:36Speaker 1: kind of like too small to the experience in our
- 26:39Speaker 1: everyday lives. Yeah, which is why you don't see them
- 26:41Speaker 1: or experience them or see them in physics experiments. And
- 26:44Speaker 1: there's lots of different ways to do that, because twenty
- 26:47Speaker 1: six dimensions a lot of freedom, and so you can
- 26:49Speaker 1: organize that in lots of different ways, and there's you
- 26:51Speaker 1: can make choices, and you have to make choices. How
- 26:54Speaker 1: do you take this twenty six dimensional theory boil it
- 26:56Speaker 1: down to four dimensions. Turns out there's like ten to
- 26:59Speaker 1: the five hundred different ways to organize that, which is
- 27:02Speaker 1: a lot of different choices, different flavors of stringth theory,
- 27:05Speaker 1: or different choices you can make different flavors. You went
- 27:08Speaker 1: to the ice cream shop for string theory, and they
- 27:10Speaker 1: have ten to the five hundred different flavors. And if
- 27:13Speaker 1: you want a sample of each one, you're not even
- 27:15Speaker 1: going to order. You're gonna be full before you leave.
- 27:17Speaker 1: Ten to the five. Thing about what that number is?
- 27:20Speaker 1: Right for scale, there's like ten to the ninety particles
- 27:23Speaker 1: in the universe, So it's the problem in strength theories
- 27:26Speaker 1: said all of these strength theories would work. Is that
- 27:30Speaker 1: kind of the problem yes, um, yeah, And that thing
- 27:32Speaker 1: that gets into the second criticism, which is, you know,
- 27:35Speaker 1: can we test string theory. We can only see the
- 27:37Speaker 1: universe down to a certain scale so far. I mean
- 27:39Speaker 1: we use large the large Hadron collider, and we smash
- 27:41Speaker 1: particles together, we get down to distances of like ten
- 27:44Speaker 1: to the minus twenty meters, right, really really small distances.
- 27:49Speaker 1: So all the string theories, the ten of the five
- 27:51Speaker 1: hundred string theories, they all can explain things that happened
- 27:54Speaker 1: that we've seen so far, all of them right. To
- 27:56Speaker 1: distinguish between them, we need to look much deeper. Oh
- 27:59Speaker 1: I see. So like mathematically there's a whole bunch of
- 28:02Speaker 1: possible ones, but experimentally we can't test which one is
- 28:06Speaker 1: right exactly. And that's the problem because strings, if they exist,
- 28:11Speaker 1: we think they're about ten to the minus thirty five
- 28:14Speaker 1: meters in size, which is super duper tiny. And maybe
- 28:17Speaker 1: you're thinking, I don't know, we can see down to
- 28:19Speaker 1: ten to the minus twenty meters. How much smaller is
- 28:22Speaker 1: tend of the minus thirty five they're basically it's just
- 28:25Speaker 1: tiny it's much much smaller. It's ten to the fifteen
- 28:29Speaker 1: times smaller, right, And to give you a sense of scale,
- 28:31Speaker 1: like the solar system is about ten to the fifteen
- 28:34Speaker 1: meters across. It's a big difference, you know, if you
- 28:37Speaker 1: could see only solar system size stuff, where if you
- 28:39Speaker 1: could see like one meter size stuff. So strings are
- 28:43Speaker 1: really really tiny, which is why we're not anywhere close
- 28:46Speaker 1: to seeing them. Doesn't the theory have also ways in
- 28:49Speaker 1: which it kind of builds up to our world? It does,
- 28:51Speaker 1: but you can't distinguish between those theories. Um, they all
- 28:54Speaker 1: predict the same thing, and they're also competing theories. You know,
- 28:57Speaker 1: there's a theory of quantum loops you not strings, but loops, right,
- 29:01Speaker 1: that also explains quantum gravity. And we can't distinguish between
- 29:05Speaker 1: the various string theories and this theory of quantum loops
- 29:08Speaker 1: because we can't see small enough yet, right. And so
- 29:11Speaker 1: it's a criticism of this whole bottom up approach. Right, Yeah, cool,
- 29:14Speaker 1: you started at the bottom, but you haven't built up
- 29:17Speaker 1: far enough for us to test your theory. Is this
- 29:19Speaker 1: just mathematical masturbation or you're actually doing something useful? Right?
- 29:24Speaker 1: So sometimes people argue like, Okay, string theories nice, but
- 29:27Speaker 1: it's not physics, it's math because it can't be tested.
- 29:30Speaker 1: But that's but then that's what they need to do.
- 29:33Speaker 1: They need to build up their math to sort of
- 29:35Speaker 1: our scale in our world. But you're saying that's really difficult. Absolutely,
- 29:39Speaker 1: it's difficult because they've got a long ways to go.
- 29:41Speaker 1: They have to go from ten to the minus thirty
- 29:43Speaker 1: five up to ten to the minus twenty. It's a
- 29:46Speaker 1: tall mountain to climb. And they've been working on it
- 29:49Speaker 1: for twenty years. And you know, like with any theory
- 29:51Speaker 1: that had um fanfare and and excitement around it twenty
- 29:54Speaker 1: years ago, Um, they're gonna be people who say, oh,
- 29:57Speaker 1: you failed if you haven't succeeded yet, right, and so
- 30:00Speaker 1: people who just sort of impatient. Are we ever going
- 30:01Speaker 1: to get there? Is string theory ever going to provide
- 30:04Speaker 1: something we can actually test or these guys just gonna
- 30:06Speaker 1: be twiddling around on chalkboards for the next two years.
- 30:08Speaker 1: But I think the problem is maybe it seems kind
- 30:11Speaker 1: of random that you would think that the universe is
- 30:14Speaker 1: made out of little strings, and that you would just
- 30:18Speaker 1: come up with this concept out of the blue and say, hey,
- 30:20Speaker 1: let's dedicate twenty thirty years of a lot of people's
- 30:22Speaker 1: time to investigating this idea. You know what, it was
- 30:26Speaker 1: totally random. They just opened the dictionary and picked a
- 30:29Speaker 1: random or and said, let's make it into this theory
- 30:31Speaker 1: out of ice cream. No, as I said before, it's
- 30:37Speaker 1: a bit random, but it works. You know, mathematically, hangs together,
- 30:40Speaker 1: and a lot of theories don't. You can't build a
- 30:42Speaker 1: theory of the universe out of ice cream or out
- 30:45Speaker 1: of puppies triangles. You couldn't make it work. Oh man,
- 30:49Speaker 1: we never thought that. I that's what I mean. Have
- 30:51Speaker 1: you thought about all the possible shapes stick figures. I'll
- 30:54Speaker 1: be right back. Hold on, I'm gonna try and invent
- 30:56Speaker 1: trying the theory right now. I'll get back to you.
- 30:58Speaker 1: Stigure theory. Why not the x K C D theory
- 31:01Speaker 1: of the universe? How could we c string theory? Well,
- 31:07Speaker 1: one thing is you could build a super duper collider
- 31:10Speaker 1: the size of the solar system and and see things.
- 31:12Speaker 1: That's small, but that's the gazillion dollar solution. The other
- 31:15Speaker 1: things you could try to be really clever and find
- 31:18Speaker 1: some unique prediction of string theory that we could see
- 31:21Speaker 1: in our experiments. Something which would only be true if
- 31:25Speaker 1: strings were happening at the lowest level, right, Because in
- 31:28Speaker 1: physics we don't always need to see things directly in
- 31:30Speaker 1: order to prove that they exist or believe that they exist.
- 31:33Speaker 1: You can kind of infer information or Yeah, a lot
- 31:37Speaker 1: of our stuff is a lot of indirect information pointing
- 31:40Speaker 1: in the same place. Right, Like, when you solve a murder,
- 31:42Speaker 1: you don't need to see the murder on video to
- 31:45Speaker 1: prove that somebody did it. You know, you have evidence
- 31:47Speaker 1: from blood spatter and from DNA and from you know,
- 31:49Speaker 1: other circumstantial evidence builds a solid case. It was Mr
- 31:54Speaker 1: Green with the string in the dining room solved. That's right,
- 32:01Speaker 1: We we have solved the mystery. Today on the podcast,
- 32:05Speaker 1: all Right, what do you think the future holds for
- 32:07Speaker 1: a string theory? Do you think it's it's promising or
- 32:10Speaker 1: are people starting to lose faith? I think it's gonna
- 32:13Speaker 1: oscillate back and forth. I think people will lose faith
- 32:15Speaker 1: for a while. It's gonna vibe rate exactly, it's gonna
- 32:18Speaker 1: wiggle and jiggle, it's gonna lose. You know, it's popular
- 32:21Speaker 1: right now and for a while. Everybody who's aplanning grad
- 32:24Speaker 1: school and physics wanted to do string theory because they
- 32:26Speaker 1: heard about Brian Green's book and they heard about a
- 32:28Speaker 1: big bank theory and it was popular. And then there's
- 32:30Speaker 1: a bit of a backlash now, so fewer people are
- 32:32Speaker 1: getting excited about string theory, fewer physics departments are hiring
- 32:35Speaker 1: strength theorists. But it's a promising candidate, and we don't
- 32:39Speaker 1: have that many promising candidates for the theory of everything.
- 32:42Speaker 1: So it'll stick around and people will come up with
- 32:45Speaker 1: great ideas and then everybody get excited again, like, oh
- 32:47Speaker 1: my gosh, look this guy came up with a cool
- 32:49Speaker 1: way to make stringth theory. Do this new thing. So
- 32:52Speaker 1: we will go back and forth. Um, I don't know
- 32:54Speaker 1: if we'll every be able to test it as a
- 32:55Speaker 1: theory that we will require a real moment of insight
- 32:59Speaker 1: to how to find some unique property of string theory
- 33:02Speaker 1: that we can see. Well, I personally hope you guys
- 33:04Speaker 1: figure it out and you know, stop stringing us along.
- 33:10Speaker 1: You don't like that we're just in our offices, you know,
- 33:12Speaker 1: drawing things on the chalkboard, going that's right. I thought
- 33:18Speaker 1: if anybody a cartoonists would appreciate, you know, enjoying the
- 33:21Speaker 1: beauty of diagrams and uh, you know, doodles and stuff
- 33:24Speaker 1: like that, because that's in the end what we're doing.
- 33:26Speaker 1: We're like trying to do the universe into into understanding.
- 33:29Speaker 1: We'll remember, I'm a musician, not a cartoonist. Oh I
- 33:33Speaker 1: forgot that. Yes, um, maybe you could sing something, go ahead, Yeah,
- 33:38Speaker 1: I think us sing us to your theory of the
- 33:39Speaker 1: universe materia. I'm on the edge of my scene. You'll
- 33:44Speaker 1: be running away from your seat if you hear me singing.
- 33:47Speaker 1: But alright, cool, that's a really great overview of the
- 33:50Speaker 1: string theory, right, That's that's part of this quest to
- 33:53Speaker 1: kind of find out what the universe is actually made
- 33:55Speaker 1: of at the deepest level. Yeah. Absolutely, And so thanks
- 33:59Speaker 1: everybody listening, and I hope that we've explained to you
- 34:01Speaker 1: finally what is string theory? Keep plugging way. If you
- 34:13Speaker 1: still have a question after listening to all these explanations,
- 34:16Speaker 1: please drop us a line. We'd love to hear from you.
- 34:19Speaker 1: You can find us at Facebook, Twitter, and Instagram at
- 34:22Speaker 1: Daniel and Jorge that's one word, or email us at
- 34:25Speaker 1: Feedback at Daniel and Jorge dot com.