WEBVTT - What Is String Theory? 0:00:06.600 --> 0:00:08.840 One thing that I really love about physics is that 0:00:08.960 --> 0:00:12.720 sometimes the laws of physics don't just work, they're actually pretty. 0:00:12.800 --> 0:00:15.560 What do you mean physics can be pretty? You know? 0:00:15.560 --> 0:00:18.439 I thought physics and science was like a hard hitting 0:00:18.480 --> 0:00:22.560 objective thing, you know, human endeavor. Absolutely, we got big tasks. 0:00:22.600 --> 0:00:24.720 We want to understand the universe and makes sense of it. 0:00:24.800 --> 0:00:27.040 But sometimes we come up with an idea, something that 0:00:27.120 --> 0:00:30.680 just looks beautiful, something which is has an innate elegance 0:00:30.720 --> 0:00:33.120 to it. You mean, like you'd see a theory walking 0:00:33.159 --> 0:00:35.199 down the road and you'd be like, oh, man, that 0:00:35.200 --> 0:00:38.440 that theory hasn't going on. Yeah, there's some sexy the 0:00:38.479 --> 0:00:41.159 curves in that theory. You mean like graphs though, right, 0:00:41.280 --> 0:00:44.800 Like that that kind of occurs, right, that graph is 0:00:44.800 --> 0:00:48.159 a nice curve to look those peaks. And one of 0:00:48.159 --> 0:00:50.239 the most controversial theories of all time, one of the 0:00:50.240 --> 0:00:53.040 ones that gets people up in arms, is also one 0:00:53.080 --> 0:00:57.360 that's probably survived because it's so beautiful. An alogot isn't 0:00:57.360 --> 0:01:00.560 the theory of attraction. No, it's a theory that was 0:01:00.600 --> 0:01:04.320 once described as a piece of twenty first century physics 0:01:04.319 --> 0:01:08.160 that had fallen by accident into the twentieth century. So 0:01:08.200 --> 0:01:29.040 it's a future Babe, future baby exactly. Hi. I'm Orge, 0:01:29.080 --> 0:01:32.200 I'm a cartoonist and I'm Daniel. I'm a particle physicist, 0:01:32.360 --> 0:01:34.039 and we are the authors of the book We Have 0:01:34.200 --> 0:01:37.200 No Idea, which talks about all the things we don't 0:01:37.240 --> 0:01:39.959 know about the universe and how we might hope to 0:01:40.080 --> 0:01:43.000 one day understand them. Yeah. So, welcome to our podcast. 0:01:43.440 --> 0:01:46.200 Daniel and Jorge explained the universe, in which we take 0:01:46.319 --> 0:01:49.680 everything and anything in the universe and try to explain 0:01:49.720 --> 0:01:51.000 it to you in a way that makes sense and 0:01:51.080 --> 0:01:54.040 hopefully makes you laugh to be on the program. We're 0:01:54.080 --> 0:02:01.960 going to talk about, Oh, string the that's right, string theory. 0:02:02.200 --> 0:02:04.520 And this is a question that we've been getting from listeners. 0:02:04.600 --> 0:02:07.560 We ask people, please send in your request for topics, 0:02:07.680 --> 0:02:10.120 and maybe more than fifty percent of the request work. 0:02:10.160 --> 0:02:12.760 Can you explain string theory? What is stringth theory? Talk 0:02:12.800 --> 0:02:16.600 about string theory more than yeah, and it's fascinating. It's 0:02:16.600 --> 0:02:19.000 because string theory really is a part of sort of 0:02:19.040 --> 0:02:21.560 cultural zite guys. It's like an idea that people know 0:02:21.720 --> 0:02:24.000 exists even if they don't understand it. It's a big 0:02:24.040 --> 0:02:26.000 part of that show The Big Bang Theory, right, like 0:02:26.040 --> 0:02:29.800 the people in that show there they supposedly study string theory. 0:02:29.919 --> 0:02:33.400 I don't know. I don't watch that show me neither, 0:02:33.520 --> 0:02:37.760 but that's what I've been told. Your cultural advice expert 0:02:37.800 --> 0:02:40.800 has told you that this is a culturally relevant thing. Well, yeah, 0:02:40.800 --> 0:02:42.640 it's it's something people have heard about. Well have you 0:02:42.680 --> 0:02:44.960 heard about string theory before you started spending your time 0:02:45.000 --> 0:02:48.040 talking to physicists? Know, yeah, I've heard about it. You know. 0:02:48.600 --> 0:02:51.080 It's one of these things that you hear a lot about. 0:02:51.120 --> 0:02:53.839 It's these like crazy theory about the universe, but it's 0:02:53.880 --> 0:02:56.560 really and you know, you hear certain things about it, like, oh, 0:02:56.600 --> 0:02:59.760 everything is made out of strings, but you don't really 0:03:00.080 --> 0:03:01.680 kind of know what it is and what does it 0:03:01.720 --> 0:03:04.240 mean for things to be strings. You're a very visual person. 0:03:04.320 --> 0:03:05.640 What image do you get in your head if I 0:03:05.639 --> 0:03:07.920 tell you everything is made out of strings? Do you 0:03:07.919 --> 0:03:10.519 get like a universe an idea of like a universe 0:03:10.520 --> 0:03:12.800 where everything is crocheted out of yarn? Or how does 0:03:12.840 --> 0:03:14.519 it work? In your head? I would to just ask 0:03:14.560 --> 0:03:19.040 what are those strings made out of? Right? Right? Of course? 0:03:19.040 --> 0:03:21.040 So you are a physicist at hard right, because every 0:03:21.080 --> 0:03:24.399 question just leads to the next question. That's right, beautiful physicists, 0:03:24.400 --> 0:03:30.320 a hard supermodel on the outside. No comment. Um, but 0:03:30.400 --> 0:03:32.560 I thought it was an interesting question to tackle because 0:03:32.560 --> 0:03:34.720 it's something everybody has heard about, but very few people 0:03:34.880 --> 0:03:37.400 actually understand. I think that's why people wanted us to 0:03:37.560 --> 0:03:39.960 talk about, is saying, can you make this not just 0:03:40.040 --> 0:03:42.240 something we have heard this phrase, but something where we 0:03:42.280 --> 0:03:44.520 can know what it means and gets an insight into 0:03:44.520 --> 0:03:47.240 why people are spending their time doing it. Right. Yeah, So, 0:03:47.280 --> 0:03:50.200 as usual, we went out into the street and ask 0:03:50.600 --> 0:03:53.560 do you know what strength theory is? Yeah? So before 0:03:53.600 --> 0:03:55.720 you hear these answers, think for a moment, could you 0:03:55.840 --> 0:03:58.160 define strength theory? Do you know what it is and 0:03:58.240 --> 0:04:01.080 why it's persisted for so long. Here's what people who 0:04:01.120 --> 0:04:04.320 I asked had to say. Um, No, I have no 0:04:04.400 --> 0:04:07.839 idea what that is. No, I do not. I've heard 0:04:07.840 --> 0:04:10.560 of it. My only way of Big Bang theory Okay, 0:04:11.320 --> 0:04:15.760 I don't know. I'm sorry. The connectedness of Adams and 0:04:15.920 --> 0:04:23.159 sub atomic particles Okay, it's something that Sheldon worked on. Yes, Okay, 0:04:23.160 --> 0:04:25.120 So first of all, it's kind of interesting because you 0:04:25.279 --> 0:04:28.520 normally you go out into your university campus to ask people, 0:04:28.560 --> 0:04:30.880 but this time you went somewhere different. Yeah, that's right. 0:04:30.920 --> 0:04:33.119 You see, Irvine was closed for a holiday, so instead 0:04:33.160 --> 0:04:35.440 I went to the mall here in Irvine, the Spectrum, 0:04:35.440 --> 0:04:38.640 and I asked a bunch of random strangers, um questions 0:04:38.640 --> 0:04:41.320 about science. And again I was struck by how many 0:04:41.360 --> 0:04:43.640 people were willing to answer my questions. I thought people 0:04:43.680 --> 0:04:47.000 would say, who are you? Go away security security? Right? 0:04:47.040 --> 0:04:50.520 Maybe they sense a certain beauty about you, Daniel, You're like, 0:04:50.560 --> 0:04:54.360 who is this beautiful specimen of a person? Know? Who is? 0:04:55.000 --> 0:04:57.960 Apparently I just don't look very threatening, you know. Um, 0:04:58.000 --> 0:04:59.480 I look like I could could get knocked to a 0:04:59.480 --> 0:05:03.360 religious a passing breeze or something. Um. So everybody was 0:05:03.400 --> 0:05:05.640 willing to engage, which was awesome, and people had some 0:05:05.640 --> 0:05:08.680 pretty fun ideas, and everybody had heard of it. Nobody 0:05:08.680 --> 0:05:12.119 had said hell what, and your other speculation was correct. 0:05:12.160 --> 0:05:14.760 Some people had heard of strength theory specifically because of 0:05:14.800 --> 0:05:18.040 the Big Bang theory. So thank you Big Bang Theory. 0:05:18.480 --> 0:05:21.120 You've mined all of this juice from nerd culture and 0:05:21.160 --> 0:05:24.320 you have actually communicated something to the public. And congratulations. 0:05:24.320 --> 0:05:26.599 Nobody understands what string theory is, but they do understand 0:05:26.640 --> 0:05:29.119 that it is a theory. Well, I think that show 0:05:29.360 --> 0:05:31.960 doesn't even try to explain it, right, They almost use 0:05:32.040 --> 0:05:35.120 it for the opposite effect, Like, let's depict our characterist, 0:05:35.160 --> 0:05:40.120 this impenetrable, unrelatable genius that speaks gobbling Google, so we'll 0:05:40.160 --> 0:05:42.920 just having to talk about strength theory and that nobody 0:05:43.040 --> 0:05:45.240 and nobody's going to understand that. So it's it's likely. 0:05:45.720 --> 0:05:49.560 So you're saying string theory represents the impenetrability of physics. 0:05:50.560 --> 0:05:52.840 I think it's more important to explain these things to 0:05:52.920 --> 0:05:55.440 people rather than just toss these words around and try 0:05:55.480 --> 0:05:57.840 to intimidate people. So yeah, I think that's what I mean. 0:05:57.880 --> 0:06:01.080 It's like they use it to intimidate people about physics, Yeah, 0:06:01.120 --> 0:06:03.800 when physics is nothing but warm and cuddly and just 0:06:03.839 --> 0:06:06.159 wants to explain the universe to you. Man, there's nothing 0:06:06.200 --> 0:06:10.279 intimidating about physics, right. It's about revealing secrets and giving 0:06:10.360 --> 0:06:13.920 understanding and insight and appreciating beauty. And that's the thing 0:06:13.960 --> 0:06:17.080 about string theory is it doesn't just potentially explain a 0:06:17.080 --> 0:06:20.159 lot of things. It also offers some elegance, some gorgeousness, 0:06:20.160 --> 0:06:23.239 like a peak into what nature is doing underneath. Because 0:06:23.279 --> 0:06:25.520 you know, you can have ugly theories and you can 0:06:25.560 --> 0:06:28.680 have elegant theories, you know, and you might ask the difference, 0:06:28.680 --> 0:06:30.400 like how what is the difference? Well, I can ask 0:06:30.440 --> 0:06:32.680 you the same question about art, right, Like I look 0:06:32.680 --> 0:06:34.680 at the Kendinsky and I say, hey, that's beautiful, and 0:06:34.720 --> 0:06:37.160 somebody else says whatever, I could do that in an afternoon. 0:06:37.160 --> 0:06:40.680 It's garbage. It's subjective, right, you can't. It's like the 0:06:40.720 --> 0:06:42.760 whole question of what is beauty is something that's very 0:06:42.800 --> 0:06:46.920 difficult to nail down. So you shouldn't judge a painting 0:06:46.960 --> 0:06:51.360 by the same metric you used to judge of physics theory. Um. 0:06:51.440 --> 0:06:54.080 And you know, two physicists can disagree about what theory 0:06:54.160 --> 0:06:56.839 is pretty and what theories ugly. So it's it's totally subjective. 0:06:56.880 --> 0:07:00.159 It's not an objective fish like a you know, I 0:07:00.200 --> 0:07:04.159 like this kind of theory. I like that kind of theory. Yeah, 0:07:04.360 --> 0:07:06.120 Like you know, I like theories with handcuffs in the 0:07:06.120 --> 0:07:09.640 midstet of strings, right, like my handcuff theory of the universe. 0:07:09.760 --> 0:07:17.960 That's where that's where you're going theories or yeah, okay, 0:07:18.000 --> 0:07:21.520 So let's break it down for people. What is string theory? Right? 0:07:21.600 --> 0:07:24.720 So string theory is basically is the idea that the 0:07:24.800 --> 0:07:27.640 smallest elements of matter with things that things are made 0:07:27.680 --> 0:07:31.920 out of are not points, not particles, but instead their lines, 0:07:32.320 --> 0:07:41.120 their strings, strings of what strings of basic universe stuff? Right, So, 0:07:41.240 --> 0:07:43.920 like the electron is is not like a little ball, 0:07:44.200 --> 0:07:46.080 and we know it's like a quantum object, which is 0:07:46.080 --> 0:07:48.480 like a point with some kind of probability. But you're 0:07:48.480 --> 0:07:51.040 saying if you zoom in even more, maybe you would 0:07:51.040 --> 0:07:53.120 see a little squiggle there. Yeah, And the sort of 0:07:53.120 --> 0:07:56.480 two ideas there. One is what is the most basic element? 0:07:56.520 --> 0:07:59.000 And the second is is their most basic element? So 0:07:59.040 --> 0:08:01.600 this assumes there is a most basic element. You know 0:08:01.640 --> 0:08:03.520 that you you look at something next to you, pick 0:08:03.560 --> 0:08:05.480 up in the nearest object you have, you know, maybe 0:08:05.520 --> 0:08:08.200 it's an apple, maybe it's a platypus, maybe it's a 0:08:08.280 --> 0:08:10.560 you know, I don't know what, and and think about 0:08:10.600 --> 0:08:12.320 what it's made out of. It's made of molecules, right, 0:08:12.400 --> 0:08:15.440 Tear those apart, you get atoms. Tear those atoms apart, 0:08:15.480 --> 0:08:17.800 you get protons and neutron's electrons. Tear those apart, you 0:08:17.800 --> 0:08:20.640 get quarks. Right, and you could keep going and eventually 0:08:20.760 --> 0:08:23.240 you get two smaller and smaller particles. Right. The question 0:08:23.320 --> 0:08:26.800 is do you ever get to the smallest particle. Right, 0:08:27.040 --> 0:08:29.240 that's one question. Is there a smallest thing? And we 0:08:29.360 --> 0:08:31.280 covered that in a whole podcast, but here we're just 0:08:31.320 --> 0:08:33.880 gonna assume that there is. Right, at some point, you 0:08:33.880 --> 0:08:36.120 get down the most basic thing where you're not allowed 0:08:36.160 --> 0:08:37.920 to ask what it's made out of because it's made 0:08:37.920 --> 0:08:40.719 out of the most basic universe stuff. It's like the 0:08:40.800 --> 0:08:44.559 one circle on a lego set. It's like, you can't 0:08:44.600 --> 0:08:48.520 get any smaller than that. That's right, it's the unit exactly, 0:08:48.880 --> 0:08:51.319 And that's you might feel like that, that's frustrating. Why 0:08:51.320 --> 0:08:53.120 can't I ask what it's made out of? You know? 0:08:53.200 --> 0:08:56.000 But it's also not frustrating because it would be the answer. 0:08:56.040 --> 0:08:58.360 I mean, if you actually got there and you said, look, 0:08:58.559 --> 0:09:00.360 everything in the universe is made out of this one 0:09:00.480 --> 0:09:03.319 basic thing. That's a deep insight, right, that's what we're 0:09:03.360 --> 0:09:06.000 going for. That's the day we wish for that we 0:09:06.160 --> 0:09:09.280 peel back a layer of reality and see everything is 0:09:09.280 --> 0:09:11.120 made out of this thing, because then you can ask 0:09:11.320 --> 0:09:13.880 why this thing? What does that mean? Oh? I see? 0:09:13.960 --> 0:09:17.800 So string theory is saying that everything electrons course, eventually, 0:09:17.800 --> 0:09:20.360 if you break them down, you'll get to this one 0:09:20.440 --> 0:09:22.920 type of string. That's right. We think of things being 0:09:22.960 --> 0:09:25.120 made of particles, We think of them as tiny dots 0:09:25.640 --> 0:09:28.880 right in space. But string theory says they're not dots, 0:09:28.960 --> 0:09:32.960 their lines okay, and they're they're these loops and wiggles 0:09:33.120 --> 0:09:36.480 instead of being dots. And then everything is made out 0:09:36.480 --> 0:09:38.679 of these strings. And you might ask, well, how can 0:09:38.720 --> 0:09:42.000 you get different kinds of particles, for example, out of 0:09:42.240 --> 0:09:46.000 one kind of string? Right, And the idea there is 0:09:46.040 --> 0:09:49.320 that the strings can vibrate, the strings can wiggle, right, 0:09:49.400 --> 0:09:51.960 the reverberations in the string just like you know a 0:09:52.000 --> 0:09:54.760 rubber band or a string. Is it like an actual vibration, 0:09:54.840 --> 0:09:56.880 like it goes up and down or is it just 0:09:56.920 --> 0:10:00.199 like the different shapes you can make with a string. Oh, 0:10:00.200 --> 0:10:03.240 I see No, it's actual motion of the string. Yeah, 0:10:03.480 --> 0:10:06.600 And so it's different, different vibrational modes. So they get 0:10:06.600 --> 0:10:09.040 excited and they can get into this state or that state. 0:10:09.559 --> 0:10:14.600 As the string vibrates in different ways, it makes different particles. 0:10:14.640 --> 0:10:17.559 So some tiny particle calling it's an electron, for example, 0:10:18.000 --> 0:10:21.080 is actually a string vibrating this way, and a cork 0:10:21.200 --> 0:10:23.440 is a string vibrating the other way. And the neutrinos 0:10:23.480 --> 0:10:26.120 a string vibrating a third way, so the same thing 0:10:26.520 --> 0:10:30.640 with different vibrations can appear as different particles. Okay, so 0:10:30.679 --> 0:10:33.439 it's not like different strings and a guitar. That's not 0:10:33.440 --> 0:10:36.719 what we're talking about. We're talking about one string. It's 0:10:36.760 --> 0:10:39.640 like a one string guitar and just the different ways 0:10:39.679 --> 0:10:42.600 in which it can vibrate that gives rise to all 0:10:42.640 --> 0:10:45.320 the different stuff we see in the universe exactly. And 0:10:45.400 --> 0:10:47.840 like a guitar, you can pluck the string differently and 0:10:47.880 --> 0:10:50.839 you can get different notes, right, you can if based 0:10:50.880 --> 0:10:53.000 on how fast it's vibrating and you know where you 0:10:53.080 --> 0:10:54.640 put your finger in the end, you can get different 0:10:54.640 --> 0:10:57.040 notes out of the same string. And it's key here, 0:10:57.080 --> 0:10:59.840 that's one string, right, it's a single string. Because we're 0:11:00.000 --> 0:11:02.760 to explain everything in the universe in terms of one object. 0:11:03.280 --> 0:11:04.920 So we're trying to explain how you get all this 0:11:05.040 --> 0:11:07.560 complexity in terms of one thing. And that's the answer 0:11:07.880 --> 0:11:11.520 from string theory is that the string has different modes 0:11:11.520 --> 0:11:14.160 to it to drink, can do different things. And you know, 0:11:14.200 --> 0:11:16.920 you might think that's sort of weird, Like I expect 0:11:17.240 --> 0:11:19.280 stuff if it's all made of the same thing, to 0:11:19.360 --> 0:11:22.000 be the same thing, right, Like if everything is made 0:11:22.040 --> 0:11:24.319 of the same stuff. Why is this red and that blue? 0:11:24.400 --> 0:11:27.520 And this tastes delicious and this tastes terrible, right, And 0:11:27.600 --> 0:11:30.640 it comes from the way it's vibrating. It's kind of 0:11:30.679 --> 0:11:32.559 like maybe light. You know, a light is just made 0:11:32.559 --> 0:11:35.320 out of one thing, photons, but depending on the frequency, 0:11:35.400 --> 0:11:39.040 then it's different colors. Yeah, exactly. And the way things 0:11:39.120 --> 0:11:41.240 move and vibrany can totally affect the way they we 0:11:41.400 --> 0:11:44.000 perceive them. You know, think about for example, water, right, 0:11:44.559 --> 0:11:47.079 water is made out of water molecules, but so is ice, 0:11:47.360 --> 0:11:49.320 and so is steam. Right, They're made out of the 0:11:49.400 --> 0:11:52.559 same thing, but we feel them, we experience them very 0:11:52.600 --> 0:11:55.600 differently because of the way they're moving, right, steam and 0:11:55.679 --> 0:11:59.240 liquid water. How the water particles moving more than an ice, right, 0:11:59.280 --> 0:12:01.680 And so it's the most into those particles that generates 0:12:01.679 --> 0:12:05.400 the macroscopic qualities that we used to define it. So 0:12:05.440 --> 0:12:07.640 the things we used to define the electron and things 0:12:07.640 --> 0:12:10.040 we used to define a quirk actually come just from 0:12:10.080 --> 0:12:13.720 the vibrations of these strings. Again according to this theory. Okay, 0:12:13.800 --> 0:12:16.320 so so then, but then my question is still, what 0:12:16.400 --> 0:12:19.920 are these strings made? Is it just like made out 0:12:19.920 --> 0:12:21.880 of universe I told you? Or hey, you're not let 0:12:21.960 --> 0:12:23.880 to ask once we get down to the lowest level, 0:12:24.320 --> 0:12:27.880 no more questions. No, but you know what I mean, 0:12:27.920 --> 0:12:30.200 like is it like a like a physical string or 0:12:30.280 --> 0:12:32.360 just like a mathematical string? Do you know what I mean? 0:12:32.400 --> 0:12:36.960 Like is prepare for philosophical detour here, like what's actually 0:12:37.080 --> 0:12:42.520 vibrating like universe stuff? Yeah? Yeah, Well, because I still 0:12:42.520 --> 0:12:45.320 look in the end, all physics theories are just models. Right, 0:12:45.320 --> 0:12:48.040 you gonna ask the question is this really happening or 0:12:48.120 --> 0:12:50.640 is this just a mathematical model? In my head, I 0:12:50.760 --> 0:12:54.600 used to do calculations and predict the results of experiments. Boom. 0:12:54.679 --> 0:12:57.360 That is a big philosophical question, right, and there's no 0:12:57.400 --> 0:13:00.240 way to answer that. So we think of these things 0:13:00.280 --> 0:13:03.560 as models in our head reflect reality. Okay, you know 0:13:03.640 --> 0:13:05.400 the top cork doesn't exist or not? Or is it 0:13:05.480 --> 0:13:08.120 is a calculation a model in my head? We could 0:13:08.440 --> 0:13:10.079 you know, smoke banana peels and talk about that for 0:13:10.160 --> 0:13:12.920 a long time without making any progress. So this model 0:13:12.960 --> 0:13:16.600 is just asking me to imagine that the most fundamental 0:13:16.600 --> 0:13:18.959 thing at the universe are these little strings. They can 0:13:19.040 --> 0:13:21.640 vibrate in different ways, but then these trains can move 0:13:21.679 --> 0:13:24.640 around and they can't be cut into pieces. Right, you 0:13:24.679 --> 0:13:27.160 can't get anything smaller than a string. It's the most 0:13:27.200 --> 0:13:29.960 basic unit. Like, there's something about the stuff of the 0:13:30.040 --> 0:13:33.560 universe that is just you can't vibrate or do things 0:13:33.559 --> 0:13:36.520 shorter than these little strings. Yeah, exactly. Or thinking about 0:13:36.520 --> 0:13:38.000 it from the other direction, you know, how do you 0:13:38.000 --> 0:13:40.679 make a universe? Well, you start with a huge pile 0:13:40.720 --> 0:13:43.600 of tiny strings, and then the way those strings interact 0:13:43.640 --> 0:13:46.040 gives you all sorts of interesting structure. But that's what 0:13:46.120 --> 0:13:49.280 you start from, right, that's the universe's initial condition is 0:13:49.320 --> 0:13:51.400 like a huge pile of strings. And these trains can 0:13:51.440 --> 0:13:54.400 move around space. Yeah, they move and they interact with 0:13:54.440 --> 0:13:56.959 each other, right, and that's where all interesting stuff. But 0:13:57.080 --> 0:13:59.400 are these related to the quantum fields? How does that 0:13:59.440 --> 0:14:02.599 really fields? Yeah? So everything we'd be built out of 0:14:02.640 --> 0:14:05.760 these strings, including all the particles and all the forces. 0:14:05.960 --> 0:14:09.000 And that's actually why string theory is so popular because 0:14:09.040 --> 0:14:12.080 string theory, we think, can explain some of the mysteries 0:14:12.080 --> 0:14:14.320 of quantum fields and some of the mysteries of how 0:14:14.360 --> 0:14:16.439 to bring gravity into the fold and describe it in 0:14:16.520 --> 0:14:18.559 terms of a quantum field. So the short answer to 0:14:18.600 --> 0:14:21.440 your question is, all the quantum fields arise from these 0:14:21.440 --> 0:14:26.360 string interactions. All these fields, all these particles just come 0:14:26.400 --> 0:14:29.800 from this one string guitar being plugged the different frequencies. 0:14:30.920 --> 0:14:34.080 That's right. So while you're imagining a single string guitar 0:14:34.080 --> 0:14:49.760 of the universe, let's take a quick break. All right. So, um, 0:14:49.800 --> 0:14:53.360 that's that's a crazy concept to ask people to digest. 0:14:53.400 --> 0:14:56.440 But let's assume that that's the theory. Um, why who 0:14:56.480 --> 0:14:58.400 came up with this and why do we think it's 0:14:58.400 --> 0:15:01.040 a good theory about the universe? Yes, the string theories 0:15:01.040 --> 0:15:02.720 had a lot of people contribute to it. It's sort 0:15:02.720 --> 0:15:04.800 of an old theory that started out trying to explain 0:15:04.840 --> 0:15:07.280 something else and then was tossed aside when it didn't work, 0:15:07.320 --> 0:15:10.320 and it was later picked up again, um and reused 0:15:10.600 --> 0:15:14.560 two as a theory of everything. And this sort of 0:15:14.640 --> 0:15:18.040 idea of string theory is to take a different approach 0:15:18.080 --> 0:15:20.360 to solving this question of what is the universe made 0:15:20.360 --> 0:15:24.000 out of? As an experimentalist, my approaches take something concrete, 0:15:24.200 --> 0:15:26.920 break it into pieces, gets smaller and smaller and smaller. 0:15:27.120 --> 0:15:29.560 You know, as you discover new stuff, you're revealing secrets 0:15:29.560 --> 0:15:31.720 to the universe, and just keep going until you get 0:15:31.720 --> 0:15:34.880 to the smallest bit. Sort of via top down approach, right, 0:15:35.400 --> 0:15:37.600 This idea is different. This is sort of a bottom up. 0:15:37.680 --> 0:15:40.400 They say, let's just start at the very bottom. Let's 0:15:40.440 --> 0:15:43.160 go to the most basic element and try to explain 0:15:43.200 --> 0:15:46.120 the universe from the start. You know, if a hypothesize 0:15:46.280 --> 0:15:48.440 the universe has made of strings, can we put them 0:15:48.480 --> 0:15:51.280 together in a way that explains the universe and describes 0:15:51.360 --> 0:15:53.720 everything we see around us? But I guess how did 0:15:53.920 --> 0:15:57.440 someone even think of using strings? How do you make 0:15:57.480 --> 0:15:59.640 a lot of things out of one thing? And a 0:15:59.640 --> 0:16:02.520 little ring that vibrates different ways is one way to 0:16:02.920 --> 0:16:04.960 get a lot of things out of one simple thing? 0:16:05.040 --> 0:16:06.840 Is that kind of the origins of it? Yeah, exactly, 0:16:06.840 --> 0:16:11.520 you should imagine. Physicists are basically random, terrible idea generators, 0:16:12.240 --> 0:16:14.680 and most of those just don't work. So at some 0:16:14.720 --> 0:16:17.400 point somebody's like fed up with thinking about the universe 0:16:17.400 --> 0:16:19.360 in terms of particles, and they're like, well, what if 0:16:19.360 --> 0:16:21.120 they're not you know, what if they're not dots, Let's 0:16:21.160 --> 0:16:23.680 just try it with lines. Does that work? You know? 0:16:23.760 --> 0:16:26.720 And basically every idea that you can imagine, somebody has 0:16:26.760 --> 0:16:28.680 tried to make that work as a theory and everything, 0:16:28.680 --> 0:16:31.360 and usually given up after about two seconds because the 0:16:31.360 --> 0:16:34.040 theory of everything based out of little puppies or whatever 0:16:34.400 --> 0:16:36.720 doesn't work. It's very hard to make that put together. 0:16:36.800 --> 0:16:38.480 But like they maybe they say, what if there's just 0:16:38.560 --> 0:16:41.520 one particle that makes up everything, how would you how 0:16:41.520 --> 0:16:43.600 would you explain how this one particle can turn into 0:16:43.600 --> 0:16:46.280 other things? And so that's kind of difficult maybe, But 0:16:46.360 --> 0:16:49.560 a string, you can imagine it vibrating or moving in 0:16:49.600 --> 0:16:53.440 different ways to give rise to different particles, right, yeah, exactly. 0:16:53.480 --> 0:16:55.160 And people were playing with it and like, what can 0:16:55.200 --> 0:16:57.040 we do with this? And they try, like I said, 0:16:57.040 --> 0:16:59.360 they try to use it to solve other problems. Specifically, 0:16:59.400 --> 0:17:02.160 they try to under stand the strong nuclear force using strings, 0:17:02.520 --> 0:17:04.879 and it didn't work. And then later somebody else said, Hi, 0:17:04.920 --> 0:17:07.600 I heard about this idea of strings. I wonder if 0:17:07.600 --> 0:17:09.640 I can use that to solve this other problem, which 0:17:09.680 --> 0:17:12.600 is why can't we get gravity to play well with 0:17:12.640 --> 0:17:15.440 the other forces. You know, if you want to understand 0:17:15.520 --> 0:17:17.440 the way the universe works, you have to try to 0:17:17.480 --> 0:17:19.920 explain everything in terms of one theory, right, to bring 0:17:19.920 --> 0:17:22.359 it all together into a single explanation, because that's a 0:17:22.359 --> 0:17:24.600 big problem right now in physics, right, Like it's like 0:17:24.880 --> 0:17:28.040 marrying quantum physics with gravity. That's right. It's a marriage 0:17:28.040 --> 0:17:30.920 we've been trying to arrange forever, but the two participants 0:17:31.119 --> 0:17:33.520 just do not want to do not want to play 0:17:33.520 --> 0:17:37.159 along exactly. They don't pressure. Yeah, So we have these 0:17:37.160 --> 0:17:40.760 sort of two towering achievements of physics. On one hand, 0:17:40.840 --> 0:17:43.760 quantum mechanics, right, a revelation about a hundred years old. 0:17:43.760 --> 0:17:46.560 It tells us that the universe is very different from 0:17:46.600 --> 0:17:49.080 the way we thought it was, that there's uncertainty, that 0:17:49.119 --> 0:17:52.760 there's fuzziness, a limited amount of knowledge we can actually 0:17:52.920 --> 0:17:56.199 obtain about the universe. And it's most specifically that the 0:17:56.280 --> 0:17:59.600 universe is quantized, it's broken up into discreete little chunks. 0:18:00.640 --> 0:18:03.639 And on the other hand, we have gravity and general relativity, 0:18:03.920 --> 0:18:07.760 which is an incredibly successful theory that describes the motion 0:18:07.800 --> 0:18:10.920 of planets around stars and black holes and all sorts 0:18:10.920 --> 0:18:13.560 of crazy stuff and time dilation in the way space 0:18:13.600 --> 0:18:17.000 and time are connected, all this incredible stuff. But it 0:18:17.080 --> 0:18:20.440 assumes the universe is not quantum mechanical, right. It assumes 0:18:20.480 --> 0:18:23.879 that that energy can be subdivided into arbitrarily small bits, 0:18:24.040 --> 0:18:26.480 and you can have an infinite number of locations and 0:18:26.520 --> 0:18:29.680 an infinite amount of information. Right, And so the two 0:18:29.720 --> 0:18:32.320 theories are not consistent, and most of the time they're 0:18:32.320 --> 0:18:35.480 talking about different stuff so they don't overlap. Sometimes, like 0:18:35.480 --> 0:18:37.640 when you're talking about a black hole, then the two 0:18:37.680 --> 0:18:40.159 give you very different stories. Okay, so, how is strength 0:18:40.200 --> 0:18:44.919 theory able to marry gravity and quantum mechanics? Right, So 0:18:44.960 --> 0:18:48.080 that is exactly the right question. How does string theory 0:18:48.119 --> 0:18:51.520 allow us to bring together quantum mechanics and gravity? Well 0:18:51.600 --> 0:18:53.879 to understand that, you really have to understand why we 0:18:54.040 --> 0:18:57.080 failed without string theory. And the problem is that when 0:18:57.119 --> 0:18:59.920 you bring together quantum mechanics and gravity, you get lots 0:18:59.920 --> 0:19:03.320 of infinities. Right. A theory doesn't work when it can't 0:19:03.359 --> 0:19:05.840 predict the results of experiments. So if you ask a 0:19:05.880 --> 0:19:08.720 theory what happens when I smash two particles together, it 0:19:08.720 --> 0:19:12.280 should give you a reasonable answer. If the answer is infinity, 0:19:12.400 --> 0:19:14.879 or you know, nothing will happen or something, then it 0:19:14.920 --> 0:19:17.120 doesn't make any sense. It has to give physical answers, 0:19:17.119 --> 0:19:19.800 and infinity is not a physical answer. The problem is 0:19:19.800 --> 0:19:23.080 when you try to bring gravity into quantum mechanics, you 0:19:23.160 --> 0:19:26.520 get lots of these infinities. And the infinities come because 0:19:26.520 --> 0:19:29.240 of the point particles, because you're trying to treat these 0:19:29.280 --> 0:19:32.000 objects as if they're just dots in space, and that 0:19:32.119 --> 0:19:34.000 leads to lots of craziness. You know, how do you 0:19:34.040 --> 0:19:36.159 have mass in a tiny little dot in space that 0:19:36.200 --> 0:19:39.359 has infinite density? Right now? We have lots of other 0:19:39.480 --> 0:19:43.480 theories that do play well with quantum mechanics. Electromagnetism, for example, 0:19:43.800 --> 0:19:46.439 very happily married with quantum mechanics. And the reason that 0:19:46.520 --> 0:19:49.320 works is that we have tricks to hide those infinities. 0:19:49.400 --> 0:19:51.959 We can bundle up those infinities that that pop up 0:19:52.160 --> 0:19:54.280 in the from the point particles in various other ways 0:19:54.320 --> 0:19:58.320 mathematical tricks. Those tricks don't work for gravity because gravity 0:19:58.359 --> 0:20:00.879 is very different from the other forces. The strength of 0:20:00.880 --> 0:20:03.720 the force grows with the energy of the object, right, 0:20:04.080 --> 0:20:06.600 So in this case, when an object has more and 0:20:06.640 --> 0:20:09.720 more energy, it feels more and more gravity, right because 0:20:09.720 --> 0:20:12.480 gravity is proportional amount of energy in an object. So 0:20:12.560 --> 0:20:15.320