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Speaker 1: People might disagree about what kind of art they like.

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Speaker 1: In fact, pretty much everybody does. But we all know

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Speaker 1: what it means when we say that something is beautiful.

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Speaker 1: It means that we appreciate it, that it moves us,

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Speaker 1: that it strikes us, that we see an elegance in it.

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Speaker 1: But what does it mean if you say a theory

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Speaker 1: of physics or a little bit of math is beautiful?

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Speaker 1: How can math be gorgeous? How can physics be elegant?

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Speaker 1: What does that really mean? Well, string theory is the

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Speaker 1: theory of physics that's most often described as a bit

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Speaker 1: of twenty first century gorgeous physics that fell into our laps.

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Speaker 1: What does that really mean? What is so beautiful about

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Speaker 1: string theory? And just because something is beautiful, does that

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Speaker 1: tell us whether it's more likely to describe our universe

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Speaker 1: to actually be right? That's the question we're going to

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Speaker 1: be asking today on the podcast What's so beautiful about

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Speaker 1: string theory? Welcome to Daniel and Kelly's Extraordinary Universe.

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Speaker 2: Hello, I'm Kelly Wiener Smith, and I know nothing about

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Speaker 2: string theory. In fact, sometimes my eyes crossed and I

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Speaker 2: just blankly stare at the wall. When the conversation comes up,

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Speaker 2: But today I'm gonna understand it.

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Speaker 1: Hi. I'm Daniel Whitson. I'm a particle physicist, which might

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Speaker 1: make it sound like I should know string theory, but

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Speaker 1: actually it means I just smashed particles together without understanding

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Speaker 1: the nature of the universe.

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Speaker 2: Oh all right, Well, so I've got a question for you.

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Speaker 2: I listened to your beautiful opening about what does it

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Speaker 2: mean to have a gorgeous equation? So my question for

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Speaker 2: you is, what is the most beautiful equation?

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Speaker 1: The most beautiful equation? Oh my gosh. To me, the

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Speaker 1: most beautiful equation is actually not in physics. It's in math.

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Speaker 1: Oiler's identity. It says E to the IPI plus one

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Speaker 1: equals zero, And I just think it's incredible because it

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Speaker 1: combines like a bunch of different stuff. You have E,

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Speaker 1: pie zero, one and I all together, and it's so compact,

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Speaker 1: and it's just so much encoded into it. It's like

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Speaker 1: so dense with useful information. It tells you about how

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Speaker 1: you can think about signs and cosigns in terms of

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Speaker 1: complex numbers. To me, it's just fascinating to have so

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Speaker 1: much information packed so tightly and so beautifully into a

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Speaker 1: single equation.

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Speaker 3: Awesome, A fine choice.

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Speaker 1: But I also have to say that in grad school,

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Speaker 1: the moment I discovered I was not going to be

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Speaker 1: a theoretical physicist was when I was sitting next to

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Speaker 1: my office mate and I realized that he did his

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Speaker 1: homework just like I did, but he did it two

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Speaker 1: or three times in different fonts because he got really

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Speaker 1: excited about like writing these equations. He's like, Oh, I'm

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Speaker 1: all writing in italics, or I can write these symbols

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Speaker 1: another way. And I realize, like, wow, this kid really

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Speaker 1: jams out about like writing down the equations. It's something

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Speaker 1: about being a theoretical physicist that I just didn't have.

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Speaker 1: I was like happy to be done with it once.

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Speaker 2: Yeah, I gotta be honest, that doesn't strike me as

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Speaker 2: super efficient. I'm going to do the same thing three times,

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Speaker 2: but I'm glad that he's super into it.

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Speaker 1: Yeah, but there's something about the equations and the formalisms

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Speaker 1: and the expressions and even the fonts. The way you're

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Speaker 1: writing these mathematical symbols, then you've got to be excited

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Speaker 1: about if you're going to work in the nitty gritty

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Speaker 1: of figuring these things out. Because being a theoretical physicist

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Speaker 1: is a lot about writing equations on paper, So if

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Speaker 1: you don't like that, then probably shouldn't be one.

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Speaker 3: Yeah, fair enough.

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Speaker 2: Well, today we're talking about a theory that is regularly

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Speaker 2: described as beautiful, and I'll tell you by the end

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Speaker 2: of the episode, I'm moderately convinced that string theory is beautiful,

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Speaker 2: maybe even more than moderately convinced. But I think we

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Speaker 2: should see what our audience thinks about out what's so

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Speaker 2: beautiful about string theory? Is this something that people know already?

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Speaker 1: That's right. I reached out to our listeners to ask

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Speaker 1: them what do they think is beautiful about string theory.

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Speaker 1: If you'd like to contribute your voice for future episodes,

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Speaker 1: please write to us two questions at Danielankelly dot org.

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Speaker 1: We will sign you up. Also send us questions about anything.

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Speaker 1: I got a recent question about somebody's dating life which

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Speaker 1: I totally couldn't answer, but I enjoyed reading anyway, so

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Speaker 1: feel free to write to us.

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Speaker 3: You should have sent that to me.

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Speaker 2: I was on Dan Savage's podcast, and I feel like

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Speaker 2: that makes me a relationship expert, so you can just

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Speaker 2: send those to me.

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Speaker 4: I've got it covered.

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Speaker 1: Okay, there, you go, folks, We are self proclaimed experts

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Speaker 1: in anything, So think about it for a minute. What

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Speaker 1: do you think is beautiful about string theory? Here's what

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Speaker 1: some listeners had to say. I don't think the universe

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Speaker 1: would be so elegant to be a dangled, naughty strandfield.

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Speaker 4: Mess unifies general relativeivity and quantum mechanics. Physicists love elegance

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Speaker 4: and symmetry. It may also provide a new baseline of

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Speaker 4: what's the tiniest thing, And then we.

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Speaker 1: Get to ask the question is that it? Or is

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Speaker 1: there something beyond that? The amount of money that Brian

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Speaker 1: Green was able to make by taking advantage of popularizing it,

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Speaker 1: we're able to mathematically explain why gravity is so weak

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Speaker 1: compared to the other forces.

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Speaker 5: So nusks, Dodd, what is string theory? The dad says,

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Speaker 5: why you ask such difficult questions? Ask me something easier.

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Speaker 5: So the sun says, okay, why does mum get so angry?

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Speaker 4: Ah?

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Speaker 5: Well, string theory is a theoretical framework.

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Speaker 6: It's a kind of symmetrical beauty.

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Speaker 1: The beauty to me is that we keep searching for

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Speaker 1: the boundaries that would have to be the g string.

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Speaker 7: Nothing's beautiful best string theory except that confusion is beautiful.

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Speaker 7: People want to try to bring everything thing all together

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Speaker 7: into one unified theory that explains everything. I think that's

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Speaker 7: what makes it beautiful.

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Speaker 6: And they look like worms string theory in all the theories

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Speaker 6: that try to bridge this gap really show the spirit

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Speaker 6: of scientists and researchers and physicists everywhere to keep on trucking.

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Speaker 3: The totality of its failure in the same way that

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Speaker 3: a lot of other unfalsifiable and self sealing things are

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Speaker 3: in life that we.

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Speaker 1: Love that the maths of it all is quite elegant.

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Speaker 8: What I like about the idea of it is that

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Speaker 8: rather than trying to think of the universe in discrete particles,

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Speaker 8: kind of just thinking about it in like pulses of energy.

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Speaker 4: I cool it confusing.

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Speaker 2: Well, Daniel, it looks like we're teaching the controversy today

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Speaker 2: because our.

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Speaker 3: Answers range from I don't think there's anything.

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Speaker 2: Beautiful about it to you know, it's pleasing esthetically, And

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Speaker 2: there was a good range of answers, what do you

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Speaker 2: think is it beautiful?

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Speaker 1: I think it's fascinating to apply this subjective standard to

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Speaker 1: something which is supposed to be objective. Right, we're talking

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Speaker 1: about like the answer to the question of how the

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Speaker 1: universe runs itself, the machinery of the cosmos. Why do

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Speaker 1: we care about whether it's beautiful? Why should beauty be

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Speaker 1: a guide? Like if we have two theories, should we

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Speaker 1: pick the one that's more beautiful and follow that because

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Speaker 1: we think it's more likely. I think it's this sort

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Speaker 1: of like bias we have that we think nature should

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Speaker 1: be beautiful because we mostly look around and we're like, oh, yeah,

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Speaker 1: the world is pretty. I wonder if aliens evolving on

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Speaker 1: an ugly planet, one that they find like if kind

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Speaker 1: of yucky, would tend to be biased towards yucky theories

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Speaker 1: of physics because their life is pretty yucky. Or maybe

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Speaker 1: everybody of alves to think that their planet is beautiful

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Speaker 1: and everybody tends towards beauty. I don't know. To me,

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Speaker 1: it's a deep sort of philosophical question of what is

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Speaker 1: beauty anyway, and why do we appreciate it in our

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Speaker 1: world and why do we look for it in our physics?

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Speaker 2: All right, So first an observation in my experience, it

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Speaker 2: seems to me that when people say, oh, this equation

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Speaker 2: is beautiful, what it usually means is it makes their

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Speaker 2: life easier. It explains a lot of things. And maybe

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Speaker 2: this is human laziness is the wrong answer, because most

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Speaker 2: of the people working on these equations or anything but lazy.

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Speaker 2: But like, oh, it's nice. It explains a lot of things.

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Speaker 2: I don't have to worry about that stuff. So you

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Speaker 2: did seem earlier to think that Euler's equation was beautiful,

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Speaker 2: but now you seem to be a little bit more

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Speaker 2: critical of people saying talking about equations that describe the

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Speaker 2: universe as beautiful.

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Speaker 3: Do you feel like there's some difference there.

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Speaker 1: No, I can see beauty and I can appreciate it. It's

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Speaker 1: like when you see a piece of machinery and there's

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Speaker 1: only a few moving parts, but it can do something

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Speaker 1: really complex, or you look at a piece of code

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Speaker 1: and you're like, wow, that is so simple and yet powerful.

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Speaker 1: You can appreciate the beauty of that. I just don't

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Speaker 1: know why the universe has to work that way, Like

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Speaker 1: the universe could be a total mess. We could discover

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Speaker 1: the way it works, be like, actually, I have some

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Speaker 1: notes this could have been done better, you know, like

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Speaker 1: more documentation please. So I can definitely appreciate beauty when

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Speaker 1: I see it, and I think I can even capture what

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Speaker 1: he's beautiful about something. I just don't know why we

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Speaker 1: expect the universe to be beautiful. I mean, I hope

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Speaker 1: that it is, but we'll see.

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Speaker 2: I mean, I think the universe is beautiful, like the

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Speaker 2: sunsets are beautiful, the biodiversity is beautiful. But it certainly

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Speaker 2: seems to me that anytime we try to explain what's happening,

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Speaker 2: there's nothing beautiful in this.

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Speaker 3: But maybe that's just the.

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Speaker 2: Biologist working on ecological models, where we're like, this is

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Speaker 2: a mess, and cells are a mess, and everything's a mess,

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Speaker 2: but we're all just muddling forward.

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Speaker 1: And let's not even get into chemistry because that's a disaster.

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Speaker 3: Now, we weren't going to get in a chemistry Daniel,

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Speaker 3: that's not what we do.

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Speaker 1: That's right, exactly. But neither of us are also string theorists.

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Speaker 1: And so I reached out to somebody I know online,

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Speaker 1: Thomas Van Reed, who is a string theorist and writes

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Speaker 1: about this stuff. And I've seen him on social media

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Speaker 1: venting gently about how string theory is not well understood

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Speaker 1: and mis explained and misunderstood by the general public. So

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Speaker 1: I invited him to come on the podcast and tell

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Speaker 1: us all about it.

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Speaker 3: Let's jump right in.

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Speaker 1: So then is my great pleasure to welcome to the

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Speaker 1: podcast Professor Thomas van Reid. He's a theoretical physicist at

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Speaker 1: the Institute for Theoretical Physics at ku LEEUFN. Some of

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Speaker 1: his recent work include papers called the Stability of axion,

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Speaker 1: saxyon wormholes, and the quantum theory of gravitation, Effective field theories,

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Speaker 1: and strings yesterday and today. So I thought he'd be

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Speaker 1: a good person to talk to about string theory and

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Speaker 1: its alleged elegance. Thomas, thank you very much for joining us.

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Speaker 4: It's my pleasure to be here.

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Speaker 1: So my first question for you is, what is this

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Speaker 1: big problem that everybody's trying to solve. We hear a

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Speaker 1: lot in popular science about how we have general relativity

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Speaker 1: and we have quantum mechanics and these two theories don't

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Speaker 1: work well together, and we need some theory of quantum gravity.

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Speaker 1: Why do we need a theory of quantum gravity? What

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Speaker 1: is this big issue? Why can't we just have gr

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Speaker 1: and quantum mechanics and be happy with those.

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Speaker 4: So in everyday life, gravity is a classical force and

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Speaker 4: there's no problem in understanding gravity. Sometimes it's a bit complicated,

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Speaker 4: especially you know when you're looking at say, black hole mergers,

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Speaker 4: you need full blown relativity. But it's still a classical theory.

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Speaker 4: You can put it on a computer, you can do

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Speaker 4: advanced calculations and you can understand what's going on.

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Speaker 1: And what do you mean when you say a classical theory?

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Speaker 1: What does classical mean? It sounds like a technical word

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Speaker 1: you're using.

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Speaker 4: Classical can mean two things. In physics, it's very confusing.

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Speaker 4: So classical can mean that you do newtont mechanics and

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Speaker 4: you don't do relativity. Relativity is a correction to Newton mechanics,

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Speaker 4: and the correction takes into account that the speed of

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Speaker 4: light is finite. So physics theories are always corrected by

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Speaker 4: some numbers. And you can think of the difference between

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Speaker 4: relativity and Newton mechanics to be that one theory is

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Speaker 4: corrected by the other by numbers which go like one

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Speaker 4: added by the speed of light, which is a very

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Speaker 4: tiny number. So that's the first sense of classical. I

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Speaker 4: actually meant the second sense of classical, and that's where

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Speaker 4: you say I take say it doesn't matter whether it's

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Speaker 4: a Newtonian or a relativistic theory, but I add quantum mechanics.

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Speaker 4: They're in quantum mechanics. We also have a small number

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Speaker 4: called Plank's constant, right, So very informally speaking, you could

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Speaker 4: say that quantum mechanics correct classical mechanics by terms in

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Speaker 4: equations that are powers of this small number.

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Speaker 1: So classical is a fuzzy word that basically means old fashioned,

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Speaker 1: the same way like you might call classical music Mozart,

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Speaker 1: but the kind of music I like to listen to

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Speaker 1: is called classic rock on the radio, even though it's

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Speaker 1: not that old. And so you're talking about two different

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Speaker 1: senses in which physics has evolved from Newton to Einstein,

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Speaker 1: and then from Einstein to like Schrodinger and Heisenberg and stuff.

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Speaker 1: And so in this sense, when you say a classical

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Speaker 1: theory physics, you mean without quantum mechanics.

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Speaker 3: And you know, some of that must is pretty old.

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Speaker 3: By that man, we are getting a little bit old,

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Speaker 3: I'm sorry.

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Speaker 1: And for the record, notes are totally rocks.

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Speaker 2: Ok Okay, no, I'm not disagreeing there. So the biologist

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Speaker 2: who's trying to keep up with the physicists here, all right,

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Speaker 2: So it sounded to me like you were saying, quantum

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Speaker 2: mechanics and general relativity can be reconciled if you just.

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Speaker 3: Divide by the right terms.

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Speaker 2: I was under the impression that they describe completely different

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Speaker 2: phenomena and kind of don't work together at all.

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Speaker 4: It's too quick to say that they can easily be combined,

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Speaker 4: but it's also too quick to say that they cannot

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Speaker 4: be combined. So, first of all, indeed, are there regimes

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Speaker 4: of interest where the two theories should be combined. Because

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Speaker 4: usually gravity we think of very large things. Gravity is

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Speaker 4: so weak that in order to see it you need

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Speaker 4: to have large objects, massive objects. You know, the Earth

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Speaker 4: is pretty big, and I can still lift my glass

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Speaker 4: of water from my table, meaning that, you know, the

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Speaker 4: electromagnetic forces in my body are stronger than the gravity

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Speaker 4: of the full Earth. So gravity is weak and things

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Speaker 4: need to be big to be able to see it.

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Speaker 4: There's another option, if things are dense enough, you know,

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Speaker 4: imagine taking the Earth and compressing it into the size

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Speaker 4: of my water cup, Okay, and then even compressing it

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Speaker 4: more so, then of course I will get into a

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Speaker 4: regime where you say, well, you know, it becomes very small,

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Speaker 4: and then the theory of econom mechanics becomes important. Yet

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Speaker 4: also gravity becomes strong. And you can ask do we

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Speaker 4: know of such regimes? And we do. I would say

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Speaker 4: it's the most important regime for all of physics. It's

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Speaker 4: the early universe. So if we go back in time

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Speaker 4: and we look with our telescopes, so looking with the

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Speaker 4: telescope means that you look back into the you look

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Speaker 4: into the past, you see that the universe was denser.

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Speaker 4: And if we just follow our classical equations, it actually

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Speaker 4: tells us that the density will go to infinity, which

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Speaker 4: is of course not true, but it isn't in the

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Speaker 4: cation that in the very early universe, you know, everything

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Speaker 4: was very tiny, so quantum mechanics was absolutely important and

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Speaker 4: gravity was huge, so we need a theory of quantum gravity.

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Speaker 4: One other example that we have already measured are black holes.

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Speaker 4: Some black holes have always been a sort of a

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Speaker 4: theoretical invention, but they're not anymore. We have seen them.

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Speaker 4: They're out there, okay. And what you sometimes wrongly hear

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Speaker 4: when people you know, talk about signs in a for

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Speaker 4: the for the bigger public, they would tell you that

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Speaker 4: black holes, for sure are objects were Quantum gravity is

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Speaker 4: important because gravity is strong near a black hole. That's

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Speaker 4: actually not entirely correct. If you look at a big

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Speaker 4: black hole, for instance, a black hole in the in

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Speaker 4: the middle of our galaxy, the gravitational parts that the

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Speaker 4: horizon of that black hole is big, but it's not

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Speaker 4: ridiculously big, okay, And the bigger a black hole, the

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Speaker 4: weaker gravity is at the horizon of a black holes.

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Speaker 1: It's kind of entry intuitive a bit is that because

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Speaker 1: you're further from the.

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Speaker 4: Center exactly, and it's also because the density of the

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Speaker 4: black hole goes down as the black hole grows like

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Speaker 4: the black hole. I think, if I'm not mistaken, you

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Speaker 4: can always fact check this. But I think the black

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Speaker 4: hole in the center of our galaxy as a density

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Speaker 4: compared to water. So it's wrong to say that for

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Speaker 4: sure quantum mechanics will be important near the horizon of

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Speaker 4: a black hole. But what we are pretty convinced of

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Speaker 4: is that if you would jump in a black hole,

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Speaker 4: we don't know what's there. But it cannot be classical

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Speaker 4: physics anymore because at some point the classical equations tell

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Speaker 4: you rubbish. They tell you things which are impossible, so

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Speaker 4: we know the classical theory has to break down. So

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Speaker 4: the assumption is that just as in the early universe,

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Speaker 4: in the very center of a black hole, there's also

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Speaker 4: quantum mechanics and gravity at play at the same time.

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Speaker 1: So I want to get back to what you said

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Speaker 1: about things breaking down, but in a minute. First, I

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Speaker 1: want to focus on this question of quantum mechanics and

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Speaker 1: gravity at play at the same time. So you told

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Speaker 1: us earlier that general relativity, or we can call it gravity,

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Speaker 1: describes usually big things, and quantum mechanics usually describe small things.

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Speaker 1: And now you're saying that at the beginning of the

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Speaker 1: universe and inside black holes, we think both of those

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Speaker 1: are relevant. And that's why we need a unified theory,

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Speaker 1: because we need some way to describe that and to

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Speaker 1: disagree to conflict. Why is there a conflict and their predictions.

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Speaker 1: Couldn't it just be that they make the same prediction

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Speaker 1: for what happens in that scenario. Couldn't it just be beautiful,

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Speaker 1: a fortunate harmony among the theories.

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Speaker 4: How what's the quickest way to explain? So let me

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Speaker 4: give you an example that I hope more people know,

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Speaker 4: maybe even from high school or first year of university. Say, okay,

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Speaker 4: think of an electric field. So you have a charge particle,

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Speaker 4: and a charge particle is surrounded by an electric field

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Speaker 4: that it sources itself. So when you look at it classically,

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Speaker 4: and when you think of a particle classically, it means

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Speaker 4: that a particle is a point. And maybe if people

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Speaker 4: remember this still, there was this formula that it said

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Speaker 4: that the strength of this electric field went like a

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Speaker 4: negative power of the distance from the particle. Say, you know,

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Speaker 4: take it's one over our squared. That's actually that the force.

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Speaker 4: Then you find that this force becomes infinitely big as

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Speaker 4: you approach the particle. Okay, it's the same for the energy.

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Speaker 4: The total energy carried by that particle would be infinite.

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Speaker 4: And we know that can that cannot be correct. And

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Speaker 4: then we have learned later on one hundred years ago,

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Speaker 4: when people understood the quantum theory of charged particles, there

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Speaker 4: was nothing going infinite. Things were just super well behaved,

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Speaker 4: numbers were finite. Nothing weird was happening. And gravity is

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Speaker 4: that sounds completely analogous, right. Even the formula for the

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Speaker 4: force of gravity is almost the same as a formula

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Speaker 4: for the Kulan force. Both can give you infinities. And

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Speaker 4: for the cool on force, we learned that that infinity

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Speaker 4: is gone when you treat it quantum mechanically.

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Speaker 2: Both general relativity and quantum mechanics at some point start

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Speaker 2: giving you infinities that make no sense when you push

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Speaker 2: them to their extremes.

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Speaker 4: So quantum mechanics doesn't give you infinities, but the classical

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Speaker 4: theory does, so relativity does. Yeah. So then the question is,

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Speaker 4: if you treat relativity in a quantum mechanical way, would

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Speaker 4: you get sensible numbers? And do you Well, that's a

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Speaker 4: good question, so yeah, to be able to answer it,

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Speaker 4: I should I should tell you this is the theory

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Speaker 4: that of quantum gravity. And to say that something is

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Speaker 4: the theory of quantum gravity, I mean you can write

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Speaker 4: down a theory which is extremely hard, but imagine you

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Speaker 4: succeed and people succeeded. You don't know whether it's the

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Speaker 4: only option, right, so you need to Normally you test

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Speaker 4: the theory. And the problem is that to go out

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Speaker 4: and test it requires you to look for these, you know,

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Speaker 4: places where gravity is so strong, and I guess none

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Speaker 4: of us wants to jump in a black hole. You could,

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Speaker 4: but you know, you could test it, but unfortunately you

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Speaker 4: would not be able to tell anymore to anybody else

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Speaker 4: because you cannot escape from the black hole. Right, So

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Speaker 4: nature is playing a very mean trick on us. It

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Speaker 4: seems that humanity, in order to test the theory of

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Speaker 4: quantum bravity, it is forced to do something that kills you.

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Speaker 4: You know, this actually goes under the name of censorship,

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Speaker 4: cosmic censorship. It's actually something quite serious in the physics community.

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Speaker 4: Gravity works such that you could actually just see quantum bravity. Unfortunately,

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Speaker 4: there's always what we call a cosmic horizon preventing you

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Speaker 4: to see it. Either it's the horizon of a black hole,

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Speaker 4: or you have to go back in time. But if

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Speaker 4: you take your telescope, it's actually impossible to directly look

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Speaker 4: at the Big Bang. So that's kind of mean. Otherwise

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Speaker 4: you could just observe it.

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Speaker 3: Yeah, it's frustrating.

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Speaker 4: Religious, I would say God is playing you know, is

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Speaker 4: an evil person, so to speak.

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Speaker 1: Yeah, I also believe in cause free speech. I think

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Speaker 1: the universe should be free to tell us how it works.

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Speaker 1: And I'm bummed about all this censorship. Okay, I have

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Speaker 1: a lot more questions, but first let's take a quick

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Speaker 1: break and let our brains rest a moment. Okay, we're

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Speaker 1: back and we are talking to Thomas Van Riet, a

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Speaker 1: self proclaimed string theorist, about how strength theory works and

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Speaker 1: why it's so pretty. So let's go back to this

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Speaker 1: question of infinities. You said just a moment ago that

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Speaker 1: it's hard, and we hear this a lot. Quantum gravity

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Speaker 1: is hard. It's the hardest problem. And you're telling us

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Speaker 1: that we have general relativity, which works beautifully outside of

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Speaker 1: event horizons, and after some critical density in the universe.

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Speaker 1: We have quantum mechanics, which works beautifully and very effectively

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Speaker 1: for very small things and very high energies. Why is

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Speaker 1: it hard to bring these two things together? What is

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Speaker 1: the challenge? I mean, We've made a quantum version of electromagnetism,

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Speaker 1: We've made a quantum version of the nuclear forces. Like,

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Speaker 1: why is it so hard to take gravity and make

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Speaker 1: it quantum?

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Speaker 4: It is hard for two reasons. Maybe they're more, but

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Speaker 4: there are two that are very sort of prominent. So

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Speaker 4: one of them technically goes under the name that the

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Speaker 4: theory of gravity is non renormalizable. We can come back

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Speaker 4: to that it has to do with infinities of sorts.

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Speaker 4: But actually we have some experience with non renormalizable theories

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Speaker 4: in the past and resolve them. But still it usually

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Speaker 4: means bad.

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Speaker 1: It's tough.

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Speaker 4: That's already what it tells you. The second thing is

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Speaker 4: that gravity, at the same time is a theory or

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Speaker 4: a classical theory of space and time, a theory of

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Speaker 4: the background. Okay, so in quantum mechanics, the way the

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Speaker 4: loss of quantum mechanics are formulated is that you assume

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Speaker 4: that this background is fixed. What does it mean in

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Speaker 4: practice is that you have two For instance, in let

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Speaker 4: me try to give a good example that doesn't sound

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Speaker 4: too abstract. In quantum mechanics, you use the notion of

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Speaker 4: two points in space time, whether they're what we call

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Speaker 4: costly connected, whether they can talk to each other, whether

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Speaker 4: you know you can send a lightweight from one point

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Speaker 4: to the other.

437
00:23:24,160 --> 00:23:25,600
Speaker 1: You're talking about light counes.

438
00:23:25,800 --> 00:23:31,600
Speaker 4: Exactly, but somewhere maybe less technical. Imagine that right now

439
00:23:31,600 --> 00:23:34,720
Speaker 4: there are people I don't know, ten kilometers away from us.

440
00:23:35,040 --> 00:23:37,080
Speaker 4: If we want to communicate with them, we cannot do

441
00:23:37,119 --> 00:23:39,359
Speaker 4: it right now. We can do it in a you know,

442
00:23:40,440 --> 00:23:42,200
Speaker 4: a little bit of time, the little time it takes

443
00:23:42,200 --> 00:23:44,480
Speaker 4: to send the light way. But so the two points

444
00:23:44,480 --> 00:23:47,280
Speaker 4: that are us here right now, and then people a

445
00:23:47,280 --> 00:23:51,560
Speaker 4: little bit away, we are what you call disconnected. But

446
00:23:51,640 --> 00:23:53,760
Speaker 4: imagine now that you have a theory of space and

447
00:23:53,840 --> 00:23:57,080
Speaker 4: time where space and time are globally that's what relativity

448
00:23:57,119 --> 00:24:00,840
Speaker 4: tells you. Then maybe that that whole notion changes, right

449
00:24:01,119 --> 00:24:03,520
Speaker 4: as a quantum mechanics is telling you that things fluck

450
00:24:03,560 --> 00:24:05,960
Speaker 4: to it. Things are very wobbly at a small scale.

451
00:24:06,440 --> 00:24:09,720
Speaker 4: They're so lobbly that maybe you know in your equations

452
00:24:09,720 --> 00:24:12,800
Speaker 4: what you thought are disconnected points, maybe they're not disconnected

453
00:24:12,840 --> 00:24:16,359
Speaker 4: anymore because you're wobbling your background that is telling you

454
00:24:16,400 --> 00:24:19,959
Speaker 4: that it's connected or not, And that's what makes it

455
00:24:20,359 --> 00:24:21,040
Speaker 4: kind of annoying.

456
00:24:21,320 --> 00:24:23,919
Speaker 2: Daniel, is this going back to our map analogy that

457
00:24:23,960 --> 00:24:25,840
Speaker 2: we keep bringing up on the show or is this

458
00:24:26,200 --> 00:24:26,840
Speaker 2: something different?

459
00:24:26,840 --> 00:24:30,160
Speaker 1: This is the same, Yeah, that's exactly right. In GR,

460
00:24:30,359 --> 00:24:33,119
Speaker 1: we have the concept of distances which are not fixed, right,

461
00:24:33,119 --> 00:24:36,439
Speaker 1: which can change. Whereas you're saying, in quantum mechanics, this

462
00:24:36,520 --> 00:24:39,960
Speaker 1: is essentially the background. So quantum mechanics is assuming that

463
00:24:40,000 --> 00:24:42,840
Speaker 1: there's a stage on which everything is happening, and GR

464
00:24:42,960 --> 00:24:44,880
Speaker 1: is like the theory of that stage, and it's changing

465
00:24:45,000 --> 00:24:48,480
Speaker 1: underneath it. But what I don't understand is why that

466
00:24:48,520 --> 00:24:51,679
Speaker 1: makes it hard, Like can't we do quantum mechanics on

467
00:24:51,800 --> 00:24:55,040
Speaker 1: curved space? You know, you can think about your fields

468
00:24:55,160 --> 00:24:57,800
Speaker 1: and my quantum mechanical view of space time is like, yeah,

469
00:24:57,840 --> 00:24:59,760
Speaker 1: you have this backdrop and you put fields on top

470
00:24:59,800 --> 00:25:01,399
Speaker 1: of it, and then you do the physics of the

471
00:25:01,440 --> 00:25:04,200
Speaker 1: fields and stuff is propagating. Is it hard to do

472
00:25:04,240 --> 00:25:07,760
Speaker 1: that quantum mechanical field theory in a curved space time?

473
00:25:08,080 --> 00:25:10,040
Speaker 1: Having people been able to do that? What's so hard

474
00:25:10,040 --> 00:25:10,480
Speaker 1: about that?

475
00:25:10,800 --> 00:25:15,080
Speaker 4: Very good? So indeed, relativity can curve space time, and

476
00:25:15,119 --> 00:25:17,760
Speaker 4: then you need to formulate quantum mechanics on curved space.

477
00:25:18,840 --> 00:25:21,800
Speaker 4: That is not easy, but that people have done for sure.

478
00:25:22,320 --> 00:25:24,840
Speaker 4: One example why that is not so easy is that

479
00:25:25,160 --> 00:25:27,320
Speaker 4: quantum mechanics tells you there has to be a global

480
00:25:27,359 --> 00:25:31,600
Speaker 4: time direction. Things move forward or backward in time. On

481
00:25:31,640 --> 00:25:35,919
Speaker 4: a curved space time, what you thought was time can

482
00:25:35,960 --> 00:25:38,639
Speaker 4: actually at some point become space or vice versa. And

483
00:25:38,680 --> 00:25:42,040
Speaker 4: a famous example is a black hole. Imagine you approach

484
00:25:42,080 --> 00:25:45,159
Speaker 4: a black hole, you jump through the horizon. What do

485
00:25:45,240 --> 00:25:48,240
Speaker 4: you know is that you have to move forward to

486
00:25:48,320 --> 00:25:51,960
Speaker 4: the singularity. But you see that means that that spatial

487
00:25:52,000 --> 00:25:54,600
Speaker 4: that action became time because what is time for us?

488
00:25:55,119 --> 00:25:59,359
Speaker 4: Time is the only dimension in which we cannot stop

489
00:25:59,440 --> 00:26:02,879
Speaker 4: moving forward. I can decide now to sit on my chair,

490
00:26:03,560 --> 00:26:06,439
Speaker 4: but I cannot decide to move backward in time or

491
00:26:06,800 --> 00:26:08,919
Speaker 4: be still in time. I always have to move forward.

492
00:26:09,440 --> 00:26:11,800
Speaker 4: So the fact that once you pass the black hole horizon,

493
00:26:12,560 --> 00:26:16,399
Speaker 4: you're moving forward in time, forward towards similarity me is

494
00:26:16,400 --> 00:26:20,760
Speaker 4: that that forward direction became time, and time became actually

495
00:26:20,760 --> 00:26:24,560
Speaker 4: a spatial direction. So for quantum mechanics, for shredding equation,

496
00:26:24,600 --> 00:26:27,600
Speaker 4: that's pretty annoying, but we learned how to deal with it,

497
00:26:29,000 --> 00:26:31,719
Speaker 4: and dealing with it gives you this amazing phenomenon, like

498
00:26:32,280 --> 00:26:36,200
Speaker 4: talking evaporation of black hoves. But what I said about

499
00:26:36,240 --> 00:26:40,280
Speaker 4: quantum gravity is still something different because in quantum gravity,

500
00:26:40,480 --> 00:26:44,240
Speaker 4: it's that curve background that is it self fluctuating under

501
00:26:44,240 --> 00:26:48,760
Speaker 4: the confluctuations. Right, So there's no problem doing quantum mechanics

502
00:26:49,200 --> 00:26:51,359
Speaker 4: on a curve background. It's just a bit more complicated

503
00:26:51,400 --> 00:26:54,399
Speaker 4: because of the problem I told you. But now the

504
00:26:54,440 --> 00:26:58,159
Speaker 4: background itself should become dynamically in equalum theory, so that

505
00:26:58,200 --> 00:27:02,400
Speaker 4: your standard sharting equation is not well formulated to deal

506
00:27:02,520 --> 00:27:05,600
Speaker 4: with the fact that the background itself is the thing

507
00:27:06,640 --> 00:27:08,280
Speaker 4: that is part of the theory.

508
00:27:08,560 --> 00:27:11,720
Speaker 1: I see. So you can do quantum mechanics on flat space,

509
00:27:12,040 --> 00:27:15,200
Speaker 1: that's easy. You can do quantum mechanics when space gets curved.

510
00:27:15,320 --> 00:27:17,840
Speaker 1: That's a little bit more technical, but people with big

511
00:27:17,880 --> 00:27:20,680
Speaker 1: brains to figure that out. But having the space itself

512
00:27:20,720 --> 00:27:22,840
Speaker 1: respond to the quantum mechanics, to have it all be

513
00:27:22,960 --> 00:27:26,040
Speaker 1: dynamical and link together and be harmonious, to have this

514
00:27:26,160 --> 00:27:29,080
Speaker 1: back and forth where energy is telling space how to

515
00:27:29,119 --> 00:27:31,679
Speaker 1: bend and space is telling matter how to move, that

516
00:27:31,880 --> 00:27:34,280
Speaker 1: is too technical for people to have figured out, or

517
00:27:34,359 --> 00:27:35,320
Speaker 1: that's the challenge.

518
00:27:35,680 --> 00:27:37,719
Speaker 4: That's a challenge ship absolutely.

519
00:27:38,119 --> 00:27:40,240
Speaker 1: And this I think also connects to the other comments

520
00:27:40,240 --> 00:27:42,920
Speaker 1: you made about renormalizable theories, which I think is worth

521
00:27:42,960 --> 00:27:45,080
Speaker 1: digging into for a minute because it connects to the

522
00:27:45,119 --> 00:27:47,960
Speaker 1: example you talked about a moment ago about an electron

523
00:27:48,040 --> 00:27:53,040
Speaker 1: having apparently infinite charge or apparently infinite energy. Right. If

524
00:27:53,040 --> 00:27:54,919
Speaker 1: you take an electrons charge and you look at it

525
00:27:54,920 --> 00:27:57,520
Speaker 1: from a distance, it appears to have charge of negative one. Right,

526
00:27:57,560 --> 00:27:59,560
Speaker 1: But as you say, an electron is surrounded by its

527
00:27:59,600 --> 00:28:02,760
Speaker 1: feel and that field you can think of as a

528
00:28:02,800 --> 00:28:06,440
Speaker 1: cloud of potential particles. And so if you actually think

529
00:28:06,480 --> 00:28:09,679
Speaker 1: about what the charge of the electron is that we measure.

530
00:28:09,920 --> 00:28:12,560
Speaker 1: It's the charge of the electrons surrounded by the cloud, right,

531
00:28:12,600 --> 00:28:15,639
Speaker 1: And as you penetrate deeper into the cloud, you measure

532
00:28:15,680 --> 00:28:18,360
Speaker 1: a more and more negative charge. And then that charge

533
00:28:18,480 --> 00:28:20,040
Speaker 1: if you get all the way through the cloud to

534
00:28:20,080 --> 00:28:23,320
Speaker 1: the electron, the charge apparently becomes negative infinity, which is

535
00:28:23,400 --> 00:28:26,720
Speaker 1: crazy and bonkers and unphysical. And so you were talking

536
00:28:26,800 --> 00:28:29,960
Speaker 1: earlier about renormalizable theories and how we've managed to patch

537
00:28:30,000 --> 00:28:32,120
Speaker 1: this up with quantum mechanics. Can you say a few

538
00:28:32,160 --> 00:28:34,280
Speaker 1: words about what it means to renormalize the theory? How

539
00:28:34,280 --> 00:28:36,080
Speaker 1: do you get rid of an infinity in the theory?

540
00:28:36,119 --> 00:28:38,120
Speaker 1: How do you solve that kind of problem where you're like,

541
00:28:38,160 --> 00:28:41,520
Speaker 1: hold on a second, electrons can't have negative infinity charge?

542
00:28:41,800 --> 00:28:43,920
Speaker 1: How do you solve that? What is renormalizablainy I just.

543
00:28:43,920 --> 00:28:46,080
Speaker 2: Clarify real quick so that the biologist and me wants

544
00:28:46,120 --> 00:28:48,880
Speaker 2: to confirm. So when you guys say you're getting infinities,

545
00:28:49,040 --> 00:28:50,800
Speaker 2: that's just a fancy way of saying we're wrong.

546
00:28:51,040 --> 00:28:53,840
Speaker 3: Like it's just this is not working, right, Okay, got

547
00:28:53,880 --> 00:28:54,440
Speaker 3: it all right?

548
00:28:54,480 --> 00:28:54,600
Speaker 1: Yes?

549
00:28:55,240 --> 00:28:58,800
Speaker 4: Absolutely absolutely. To be honest, I think to explain to

550
00:28:58,880 --> 00:29:02,160
Speaker 4: normalizability that the story of the infiniti This is what

551
00:29:02,320 --> 00:29:05,960
Speaker 4: usually is told. Is I think leading people astray. It's

552
00:29:06,040 --> 00:29:08,120
Speaker 4: not the right way of explaining it. May I try

553
00:29:08,160 --> 00:29:11,080
Speaker 4: to explain it differently, but please go ahead of It's okay. Yeah,

554
00:29:11,400 --> 00:29:14,120
Speaker 4: maybe it's good to go back to. You know what

555
00:29:14,200 --> 00:29:17,280
Speaker 4: Newton got famous for, you know his theory, and what

556
00:29:17,360 --> 00:29:20,120
Speaker 4: is his theory saying? Maybe people remember that. You know,

557
00:29:20,840 --> 00:29:23,680
Speaker 4: there's an equation that he got famous for, which is

558
00:29:23,720 --> 00:29:27,400
Speaker 4: called ethical en times a, which is essentially telling you

559
00:29:27,400 --> 00:29:32,160
Speaker 4: that a force on a particle equals the mass of

560
00:29:32,200 --> 00:29:36,960
Speaker 4: the particle times the acceleration that the particle is undergoing

561
00:29:36,960 --> 00:29:40,480
Speaker 4: because of the force. So you can ask yourself, is

562
00:29:40,520 --> 00:29:42,959
Speaker 4: this really a lot? A lot of physics? Means that

563
00:29:43,000 --> 00:29:45,720
Speaker 4: you suddenly there are three things you know and you

564
00:29:45,760 --> 00:29:48,520
Speaker 4: actually found a connection between them. I would say, isn't

565
00:29:48,520 --> 00:29:53,440
Speaker 4: this a definition? The Newton just defined the workforce by

566
00:29:53,520 --> 00:29:56,520
Speaker 4: saying it's en times a. It looks like that. But

567
00:29:56,680 --> 00:29:59,440
Speaker 4: there's another famous example that you know in high school

568
00:29:59,440 --> 00:30:02,560
Speaker 4: you learned Olmslow and usually you call it you say

569
00:30:02,600 --> 00:30:08,800
Speaker 4: that resistance is voltage divided by current. See, that's not

570
00:30:08,880 --> 00:30:12,560
Speaker 4: a lot. That's the definition of resistance. There's no information

571
00:30:12,640 --> 00:30:17,000
Speaker 4: in that equation, but a definition on was successful because

572
00:30:17,040 --> 00:30:21,520
Speaker 4: he said this R is a constant. That's that's the law.

573
00:30:22,240 --> 00:30:24,240
Speaker 4: R is a concept, and then it becomes something with

574
00:30:24,400 --> 00:30:28,720
Speaker 4: predictive power. Namely, I measure the voltage over a resistant

575
00:30:29,240 --> 00:30:31,240
Speaker 4: over a resistance, and then I know the current that

576
00:30:31,320 --> 00:30:34,480
Speaker 4: goes through it. But that's only because my real equation

577
00:30:34,560 --> 00:30:36,800
Speaker 4: is art equal the concept. So what's the equation of newtant?

578
00:30:37,640 --> 00:30:41,200
Speaker 4: Newton's idea was only successful because he essentially wanted to

579
00:30:41,240 --> 00:30:44,920
Speaker 4: tell us this F is universal. Imagine the way an

580
00:30:44,920 --> 00:30:48,080
Speaker 4: apple falls under this F whether how it falls in

581
00:30:48,560 --> 00:30:52,560
Speaker 4: Cambridge or in China, it will be the same formula.

582
00:30:53,240 --> 00:30:55,000
Speaker 4: So that means that once you have the formula for

583
00:30:55,080 --> 00:30:57,240
Speaker 4: the F and you say it's true all over the universe,

584
00:30:58,200 --> 00:31:02,320
Speaker 4: it becomes very strong the prediction. So Newton and his

585
00:31:02,480 --> 00:31:05,959
Speaker 4: program was having a lot of predictive power by you know,

586
00:31:06,080 --> 00:31:08,640
Speaker 4: moving around in the universe. He found something true all

587
00:31:08,680 --> 00:31:12,080
Speaker 4: over the universe. Okay, so this is the same with normalizability.

588
00:31:12,880 --> 00:31:16,000
Speaker 4: So instead of moving around from the left to the right, up, down,

589
00:31:16,040 --> 00:31:20,840
Speaker 4: whatever future past, renormalizability has to do with zooming in

590
00:31:20,960 --> 00:31:23,440
Speaker 4: and zooming out. If I have an equation and I

591
00:31:23,480 --> 00:31:27,000
Speaker 4: want you to have predictive power. It has to tell

592
00:31:27,040 --> 00:31:29,440
Speaker 4: me what also happens when I zoom in or I

593
00:31:29,520 --> 00:31:32,240
Speaker 4: zoom out. Okay, zoom, let us think of zooming in.

594
00:31:32,280 --> 00:31:34,080
Speaker 4: That's what really the problem lies. It means that I

595
00:31:34,480 --> 00:31:38,880
Speaker 4: go to very small length skills. I want a theory

596
00:31:39,040 --> 00:31:41,920
Speaker 4: which gives me a single equation with all the constants

597
00:31:41,960 --> 00:31:43,760
Speaker 4: known and measured, so I can tell you what happens

598
00:31:43,800 --> 00:31:46,880
Speaker 4: at small distance skills when I zoom in. A non

599
00:31:46,960 --> 00:31:49,760
Speaker 4: renormalizable theory, it doesn't give you infinities. People should stop

600
00:31:49,760 --> 00:31:52,520
Speaker 4: saying that they give you completely finite numbers after some

601
00:31:52,600 --> 00:31:55,320
Speaker 4: mathematical trickery. But what it does is that the more

602
00:31:55,360 --> 00:31:59,240
Speaker 4: you zoom in each time, the equation gains another constant

603
00:31:59,640 --> 00:32:01,560
Speaker 4: that we know the value, and we have to go

604
00:32:01,600 --> 00:32:04,360
Speaker 4: out in nature nature and measure it. Right. So imagine

605
00:32:04,400 --> 00:32:07,560
Speaker 4: you want to somebody asking me, okay, Thomas, what happens

606
00:32:07,560 --> 00:32:11,760
Speaker 4: in a gravitational field at you know, a micrometer. I say,

607
00:32:11,760 --> 00:32:13,720
Speaker 4: oh my god, I have to you know already maybe

608
00:32:13,720 --> 00:32:18,480
Speaker 4: correct Neutant's law for quantum gravity. And I say, yeah,

609
00:32:18,480 --> 00:32:20,640
Speaker 4: there's an extra constant in the equation. It's not you know,

610
00:32:20,640 --> 00:32:23,560
Speaker 4: the force is not one over our square. There's maybe

611
00:32:23,560 --> 00:32:26,680
Speaker 4: one over our cube, but it's not one. It will

612
00:32:26,720 --> 00:32:29,320
Speaker 4: be some number multiplying the equation. Okay, I go out

613
00:32:29,320 --> 00:32:31,440
Speaker 4: in nature and measure it. Good. I have the number,

614
00:32:31,760 --> 00:32:34,400
Speaker 4: and as somebody wants to go ten times smaller or

615
00:32:34,400 --> 00:32:37,840
Speaker 4: twenty times smaller, suddenly a term which goes like one

616
00:32:38,080 --> 00:32:40,840
Speaker 4: R to the power for becomes important. You need to

617
00:32:40,840 --> 00:32:42,600
Speaker 4: know the coefficient of the term. I again have to

618
00:32:42,640 --> 00:32:45,280
Speaker 4: do a measure. So you see I don't have predictive power.

619
00:32:46,320 --> 00:32:49,160
Speaker 4: That's the definition of a non revisable theory. It means

620
00:32:49,160 --> 00:32:51,440
Speaker 4: that you know, the smaller you get, the more constant

621
00:32:51,440 --> 00:32:56,440
Speaker 4: theory has to be more precise, but it cannot predict

622
00:32:56,480 --> 00:33:01,240
Speaker 4: what the constants are, whereas renormalizable theory it says, hey,

623
00:33:01,280 --> 00:33:03,240
Speaker 4: I don't need any new constant guys. I mean, I

624
00:33:03,280 --> 00:33:05,800
Speaker 4: can tell you with the computation on what you know,

625
00:33:05,960 --> 00:33:09,720
Speaker 4: how the theory behaves at the smallest length skills. So unfortunately,

626
00:33:09,760 --> 00:33:13,600
Speaker 4: the way historically this came about, and that's where the

627
00:33:13,640 --> 00:33:16,200
Speaker 4: word nenormalizable comes from, is that you know, we were

628
00:33:16,200 --> 00:33:19,160
Speaker 4: getting infinities and then we found we always say a

629
00:33:19,160 --> 00:33:21,680
Speaker 4: mathematical treat but in fact it's a physics treat to

630
00:33:21,760 --> 00:33:24,960
Speaker 4: get rid of them. But you see, that's that's not

631
00:33:25,000 --> 00:33:27,440
Speaker 4: the essential part. The essential part is whether the theory

632
00:33:27,480 --> 00:33:30,600
Speaker 4: is predictive, whether there's only a few constants that you

633
00:33:30,640 --> 00:33:32,720
Speaker 4: can get out, go out and measure, or whether you

634
00:33:32,760 --> 00:33:35,160
Speaker 4: need an infinite amount of consonts if I want to

635
00:33:35,200 --> 00:33:38,920
Speaker 4: get infinitely small. And so if we take Einstein's theory

636
00:33:38,960 --> 00:33:43,520
Speaker 4: classical theory of gravity, we apply our usual techniques of

637
00:33:43,640 --> 00:33:49,560
Speaker 4: quantum theory, we find that it's non renormalizable, not meaning

638
00:33:49,560 --> 00:33:51,640
Speaker 4: that it gives you infinities. This is actually, I think

639
00:33:51,640 --> 00:33:55,400
Speaker 4: a bad explanation. It gives you too many consonants that

640
00:33:55,600 --> 00:33:57,680
Speaker 4: we don't know what they are, and we will have

641
00:33:57,760 --> 00:33:58,200
Speaker 4: to measure.

642
00:33:58,400 --> 00:34:01,120
Speaker 1: I see. So a renormalizable theory, you can say I

643
00:34:01,120 --> 00:34:04,040
Speaker 1: don't really know what's going on inside the electron. Maybe

644
00:34:04,040 --> 00:34:06,240
Speaker 1: there's other particles, maybe not, But I can measure the

645
00:34:06,360 --> 00:34:08,480
Speaker 1: charge and I can move on, and I can say

646
00:34:08,480 --> 00:34:10,840
Speaker 1: it's all wrapped up in this number. They'll charge it

647
00:34:10,880 --> 00:34:13,080
Speaker 1: the electron. And as long as I can make a

648
00:34:13,160 --> 00:34:15,319
Speaker 1: finite number of measurements, like I don't have to measure

649
00:34:15,360 --> 00:34:17,560
Speaker 1: an infant number of properties in the electron, then I

650
00:34:17,560 --> 00:34:19,680
Speaker 1: have a theory. I can use because that can make

651
00:34:19,680 --> 00:34:22,160
Speaker 1: a finite number of measurements in a finite amount of time.

652
00:34:22,680 --> 00:34:25,280
Speaker 1: So a non renormalizable theory, you're saying, is one where

653
00:34:25,520 --> 00:34:28,840
Speaker 1: you can't ever capture all those details in a single

654
00:34:28,920 --> 00:34:31,560
Speaker 1: number or two numbers, or even a finite number of numbers.

655
00:34:31,719 --> 00:34:34,279
Speaker 1: You'd need to measure an infinite number of parameters to

656
00:34:34,320 --> 00:34:37,400
Speaker 1: have a theory that you can actually use to make calculations.

657
00:34:37,840 --> 00:34:40,480
Speaker 1: But you said a minute ago that we have other

658
00:34:40,600 --> 00:34:43,920
Speaker 1: non renormalizable theories. I think, for example, quantum chromodynamics, it's

659
00:34:43,960 --> 00:34:46,440
Speaker 1: non renormalizable, and we've made that work. I mean, I

660
00:34:46,480 --> 00:34:48,400
Speaker 1: know it's a headache, but we've made it work. What

661
00:34:48,560 --> 00:34:51,600
Speaker 1: is it about gravity that's so special that we can't

662
00:34:51,680 --> 00:34:55,960
Speaker 1: use our non renormalizable fancy clever tricks to get quantum

663
00:34:55,960 --> 00:34:56,759
Speaker 1: gravity to work?

664
00:34:57,040 --> 00:35:01,960
Speaker 4: Right, So you're saying humanity has dealt normalizable theories, made

665
00:35:01,960 --> 00:35:04,040
Speaker 4: them to work, and I can tell you what the

666
00:35:04,080 --> 00:35:07,279
Speaker 4: problem is. So I guess don't forget that before we

667
00:35:07,360 --> 00:35:10,239
Speaker 4: already said that gravity had two problems for it to

668
00:35:10,280 --> 00:35:14,880
Speaker 4: be hard to quantize. Non rymalizability was one of them.

669
00:35:15,040 --> 00:35:17,440
Speaker 4: So there's still the other one. So that's part of

670
00:35:17,480 --> 00:35:20,640
Speaker 4: my answer, But it's still I believe it's very different.

671
00:35:20,680 --> 00:35:22,560
Speaker 4: Like the other part of my answer will be the following.

672
00:35:23,280 --> 00:35:26,799
Speaker 4: Usually what happens in physics. Actually, every instance we have

673
00:35:26,800 --> 00:35:30,040
Speaker 4: seen so far where the theory was non renormalizable, we

674
00:35:30,120 --> 00:35:33,919
Speaker 4: actually cured it by realizing that we didn't have all

675
00:35:34,360 --> 00:35:39,400
Speaker 4: what we usually call degrees of freedom. Okay, so what

676
00:35:39,440 --> 00:35:41,840
Speaker 4: does that mean? So I assume it I go to

677
00:35:41,880 --> 00:35:46,600
Speaker 4: small distances, and I always assume that. You know, if

678
00:35:46,600 --> 00:35:48,800
Speaker 4: I have the theory of the electron, there's only the electron.

679
00:35:48,920 --> 00:35:55,240
Speaker 4: Say well, maybe they're very massive particles out there which

680
00:35:55,280 --> 00:35:58,239
Speaker 4: require a lot of energy to be created. In physics,

681
00:35:58,640 --> 00:36:01,440
Speaker 4: having a lot of energy is the same as going

682
00:36:01,440 --> 00:36:05,880
Speaker 4: to very small distances. So all non renormalizable theories we

683
00:36:05,960 --> 00:36:11,480
Speaker 4: have encountered were always made renormalizable by realizing that we

684
00:36:11,520 --> 00:36:15,560
Speaker 4: didn't take into account fluctuation fields particles that were just

685
00:36:15,680 --> 00:36:17,759
Speaker 4: very massive so that we didn't measure them yet.

686
00:36:17,840 --> 00:36:18,399
Speaker 3: That's real quick.

687
00:36:18,400 --> 00:36:20,520
Speaker 2: Saying you needed more degrees of freedom means there was

688
00:36:20,560 --> 00:36:22,719
Speaker 2: something else that wasn't included in the equation that needed

689
00:36:22,719 --> 00:36:22,960
Speaker 2: to be.

690
00:36:22,880 --> 00:36:27,000
Speaker 4: The exactly absolutely absolutely, And then you see, oh this

691
00:36:27,080 --> 00:36:30,520
Speaker 4: is nice, my theory becomes mathematically normalizable. But then actually

692
00:36:30,520 --> 00:36:33,920
Speaker 4: we went out in nichere we found technologies to increase

693
00:36:33,920 --> 00:36:35,879
Speaker 4: our energy in our experiment, and then we saw those

694
00:36:35,880 --> 00:36:39,040
Speaker 4: particles that we predicted mathematically because we wanted the theory

695
00:36:39,120 --> 00:36:43,760
Speaker 4: to prenormalizable. Okay, I think that's extremely beautiful. Like you

696
00:36:43,760 --> 00:36:46,480
Speaker 4: you do something on mathematical clouds, it predicts new particles

697
00:36:46,480 --> 00:36:49,480
Speaker 4: for it to work out, and there you measure them. Okay.

698
00:36:50,120 --> 00:36:52,839
Speaker 4: And here's the funny thing with gravity. What string theories

699
00:36:52,880 --> 00:36:54,560
Speaker 4: will typically tell you. What I think more and more

700
00:36:54,560 --> 00:36:57,960
Speaker 4: people are leaning towards it, is that if you want

701
00:36:57,960 --> 00:37:00,600
Speaker 4: to make gravity normalizable, it looks like you the infinite

702
00:37:00,640 --> 00:37:04,240
Speaker 4: amount of particles with ever increasing energy. And that sounds

703
00:37:04,239 --> 00:37:06,239
Speaker 4: super bad when you say that first, because you're like,

704
00:37:06,280 --> 00:37:09,640
Speaker 4: oh my god, infinite amount of particles to solve your problem.

705
00:37:09,760 --> 00:37:13,360
Speaker 4: It's like measuring an infinite number of concepts. You're not

706
00:37:13,440 --> 00:37:15,600
Speaker 4: better off. Okay, So of course now I'm going to

707
00:37:15,880 --> 00:37:18,840
Speaker 4: sell string theory here. No, what is so beautiful is

708
00:37:18,840 --> 00:37:21,719
Speaker 4: that it's infinite tower of particles groups together in the

709
00:37:21,800 --> 00:37:23,840
Speaker 4: motion of a string. It just meant that what we

710
00:37:23,840 --> 00:37:26,600
Speaker 4: thought were particles, no, it was just a single object.

711
00:37:26,880 --> 00:37:29,040
Speaker 4: There's no tower. It's just a string that can vibrate

712
00:37:29,080 --> 00:37:31,960
Speaker 4: in different ways. So there's a lot of structure in

713
00:37:32,000 --> 00:37:34,720
Speaker 4: that infant amount of particles that you need to invoke

714
00:37:34,880 --> 00:37:37,920
Speaker 4: together innormalizable theory. Yeah, otherwise it looks very bad, like

715
00:37:38,480 --> 00:37:41,560
Speaker 4: every time you take in a new particle you find

716
00:37:41,560 --> 00:37:44,120
Speaker 4: that renormalizability still requires a new one, and you think,

717
00:37:44,160 --> 00:37:46,640
Speaker 4: oh my god, you guys are just you know, in

718
00:37:46,640 --> 00:37:49,560
Speaker 4: an never ending street of problems. No, we see that

719
00:37:49,600 --> 00:37:52,600
Speaker 4: every single particle we have to add as exactly properties

720
00:37:52,600 --> 00:37:54,440
Speaker 4: that we could have predicted from the previous one. So

721
00:37:54,440 --> 00:37:57,160
Speaker 4: there's a beautiful structure, and what looks like an infinite

722
00:37:57,160 --> 00:38:01,160
Speaker 4: tower of particles just becomes a single stringing object with

723
00:38:01,320 --> 00:38:04,719
Speaker 4: almost no constant associated to it.

724
00:38:04,760 --> 00:38:07,759
Speaker 1: So there, you just said the word beautiful. What is

725
00:38:07,840 --> 00:38:10,480
Speaker 1: beautiful about that? Is it? Because wow, this is a

726
00:38:10,480 --> 00:38:12,600
Speaker 1: hard problem, and now have a solution. Is it like

727
00:38:12,640 --> 00:38:15,960
Speaker 1: my headache is gone? Or is there something objectively beautiful

728
00:38:15,960 --> 00:38:17,560
Speaker 1: about this particular solution?

729
00:38:17,800 --> 00:38:19,880
Speaker 2: Can I go back to a real quick question and

730
00:38:20,040 --> 00:38:21,600
Speaker 2: then can we move to beauty because I don't want

731
00:38:21,640 --> 00:38:23,640
Speaker 2: to miss my chance to understand this because I'm actually

732
00:38:23,640 --> 00:38:24,400
Speaker 2: really following everything.

733
00:38:24,400 --> 00:38:24,920
Speaker 3: I'm excited.

734
00:38:25,200 --> 00:38:28,160
Speaker 2: Okay, So instead of needing to measure an infinite number

735
00:38:28,320 --> 00:38:32,600
Speaker 2: of constants? Can we measure that string? Do we know

736
00:38:32,600 --> 00:38:34,760
Speaker 2: how to measure the string? Does that make our situation

737
00:38:34,800 --> 00:38:35,279
Speaker 2: any better?

738
00:38:35,360 --> 00:38:38,040
Speaker 4: I'm going to be honest in practice. No, but this

739
00:38:38,120 --> 00:38:41,680
Speaker 4: week we could have predicted you in advance. Okay, So

740
00:38:41,800 --> 00:38:43,840
Speaker 4: this has nothing to do with string theory. I just

741
00:38:43,880 --> 00:38:47,840
Speaker 4: told you that the regime ware gravity and quantum mechanics

742
00:38:47,880 --> 00:38:50,480
Speaker 4: are relevant. Is either we have to jump through a

743
00:38:50,480 --> 00:38:54,120
Speaker 4: black hole, which is not nice as an experience, or

744
00:38:54,239 --> 00:38:56,040
Speaker 4: we somehow have to be able to move back in

745
00:38:56,120 --> 00:39:00,239
Speaker 4: time to the Big Bang, or people are able to

746
00:39:00,320 --> 00:39:04,520
Speaker 4: build you know, galaxy sized accelerated. That is a true

747
00:39:04,520 --> 00:39:08,040
Speaker 4: statement independent of what the theory of quantum gravity is.

748
00:39:09,080 --> 00:39:11,880
Speaker 4: It just you know, you predict what is the energy

749
00:39:11,880 --> 00:39:15,120
Speaker 4: density needed to see those effects. Of course, one can

750
00:39:15,200 --> 00:39:20,040
Speaker 4: be lucky and some effects of the highest energy densities

751
00:39:20,120 --> 00:39:23,000
Speaker 4: or the smallest lendsciales can trickle you know how they

752
00:39:23,000 --> 00:39:24,920
Speaker 4: say trickle down? Is it correct English? I don't know,

753
00:39:24,960 --> 00:39:28,560
Speaker 4: but can leave an imprint on larger distances and smaller energies.

754
00:39:28,600 --> 00:39:31,680
Speaker 4: Is if it's something that we're looking into, we are hoping,

755
00:39:31,800 --> 00:39:33,600
Speaker 4: you know, I'm praying, but we don't know for sure,

756
00:39:33,800 --> 00:39:35,880
Speaker 4: So I hope that explains a bit, yeah, and not

757
00:39:36,040 --> 00:39:39,120
Speaker 4: to the beauty. It's I like the questions that I'm

758
00:39:39,320 --> 00:39:42,040
Speaker 4: trying to find an analogy. Okay, so imagine I don't

759
00:39:42,040 --> 00:39:45,520
Speaker 4: know whether this reminds you of the word beauty, but

760
00:39:45,840 --> 00:39:48,279
Speaker 4: imagine you have a super complicated puzzive in front of you.

761
00:39:49,320 --> 00:39:51,640
Speaker 4: I don't know, one billion pieces and you just don't

762
00:39:51,640 --> 00:39:54,839
Speaker 4: know how to put them together, and suddenly you find

763
00:39:54,880 --> 00:39:59,520
Speaker 4: two connecting and because you see two pieces that connect,

764
00:40:00,080 --> 00:40:02,880
Speaker 4: you suddenly see the third piece lying there, and the

765
00:40:03,000 --> 00:40:06,360
Speaker 4: more you put them together, suddenly it's just one structure

766
00:40:06,560 --> 00:40:09,600
Speaker 4: that is like extremely simple. Okay. It's like imagine if

767
00:40:09,600 --> 00:40:13,319
Speaker 4: a blackboard full of equations and you cannot solve them,

768
00:40:13,560 --> 00:40:16,040
Speaker 4: and suddenly you realize that your equation was too complicate,

769
00:40:16,120 --> 00:40:19,359
Speaker 4: that terms are dropping against each other, and you keep

770
00:40:19,360 --> 00:40:22,520
Speaker 4: on canceling terms, and suddenly you have an equation left

771
00:40:22,560 --> 00:40:25,480
Speaker 4: which is just one centimeter insights. You're like, oh my god,

772
00:40:25,520 --> 00:40:27,799
Speaker 4: this is you know, this is amazing. That's the kind

773
00:40:27,840 --> 00:40:31,720
Speaker 4: of beauty we're talking about that we think that renormalizing

774
00:40:32,120 --> 00:40:36,279
Speaker 4: gravity is a nightmare. It gives you ugly theories. And

775
00:40:36,320 --> 00:40:39,360
Speaker 4: then the first thing we try, which you know, just

776
00:40:39,400 --> 00:40:42,960
Speaker 4: on mathematical grounds, and we get something that is in

777
00:40:43,080 --> 00:40:46,640
Speaker 4: terms of the length of equations, is even smaller than

778
00:40:46,719 --> 00:40:51,080
Speaker 4: any equation that we have had in the past. And

779
00:40:51,120 --> 00:40:54,000
Speaker 4: that is what I think why so many people like it.

780
00:40:54,840 --> 00:40:57,040
Speaker 4: And then the confusing part is that it's not because

781
00:40:57,120 --> 00:40:59,960
Speaker 4: the size of the equation is small that it's easy

782
00:41:00,080 --> 00:41:04,160
Speaker 4: to solve. It just means that it's very elegant, okay,

783
00:41:04,160 --> 00:41:06,640
Speaker 4: in the sense that, for instance, there maybe elegance is

784
00:41:06,640 --> 00:41:10,560
Speaker 4: better than beauty. The elegant thing of string theory is

785
00:41:10,600 --> 00:41:12,120
Speaker 4: that they're no constants in the.

786
00:41:12,000 --> 00:41:13,920
Speaker 1: Theory, no numbers at all.

787
00:41:14,320 --> 00:41:19,719
Speaker 4: No numbers at all exactly. Any other theory non physics

788
00:41:19,880 --> 00:41:21,799
Speaker 4: has to have a lot of numbers that you go

789
00:41:21,880 --> 00:41:25,600
Speaker 4: out and measure. String theory doesn't have a number. Actually

790
00:41:25,640 --> 00:41:29,080
Speaker 4: it only is one. It's the size of the string

791
00:41:29,239 --> 00:41:30,120
Speaker 4: as variables.

792
00:41:30,120 --> 00:41:31,400
Speaker 3: But no constants.

793
00:41:31,600 --> 00:41:34,319
Speaker 2: Is that I'm having trouble imagining an equation with no

794
00:41:34,400 --> 00:41:36,280
Speaker 2: numbers that's exactly correct.

795
00:41:36,360 --> 00:41:39,160
Speaker 1: So it's like ex equals why not ex equals two

796
00:41:39,160 --> 00:41:40,360
Speaker 1: point seven four times?

797
00:41:40,360 --> 00:41:42,680
Speaker 4: Why right? Where I didn't know the two point seven

798
00:41:42,719 --> 00:41:44,200
Speaker 4: I had to go out and measure it, all.

799
00:41:44,160 --> 00:41:46,120
Speaker 2: Right, So I'm excited because this is the most that

800
00:41:46,160 --> 00:41:47,959
Speaker 2: I've understood string theory in my.

801
00:41:47,880 --> 00:41:50,200
Speaker 3: Life so far, but I could still use the brake.

802
00:41:50,480 --> 00:41:52,520
Speaker 2: So let's go ahead, get some more coffee, a little

803
00:41:52,560 --> 00:41:54,759
Speaker 2: bit more brain fuel, and we will be right back

804
00:41:54,840 --> 00:42:16,040
Speaker 2: to talk more about string theory. All right, we are

805
00:42:16,080 --> 00:42:19,480
Speaker 2: back with Thomas Van Reed. Let's jump back into string theory.

806
00:42:19,880 --> 00:42:23,520
Speaker 2: So string theory we've discussed that it can help when

807
00:42:23,560 --> 00:42:26,280
Speaker 2: you're in those really tiny little situations where you'd usually

808
00:42:26,320 --> 00:42:27,080
Speaker 2: have to get a lot.

809
00:42:27,000 --> 00:42:28,600
Speaker 3: More calculate, a lot more constant.

810
00:42:29,160 --> 00:42:32,000
Speaker 2: Does it also work if you zoom out or is

811
00:42:32,040 --> 00:42:34,160
Speaker 2: it just a theory for when you're super zoomed in?

812
00:42:34,400 --> 00:42:36,919
Speaker 4: This is an excellent question. So that's where it gets hard.

813
00:42:37,840 --> 00:42:42,040
Speaker 4: Surprisingly Okay, So when you zoom out in physics, it

814
00:42:42,160 --> 00:42:45,840
Speaker 4: means okay, large distance also means low energy. And what

815
00:42:46,040 --> 00:42:50,040
Speaker 4: is the hardest part of working with high energy theories

816
00:42:50,080 --> 00:42:53,440
Speaker 4: like string theory, is to understand if I take the

817
00:42:53,440 --> 00:42:55,720
Speaker 4: theory and I run into low energies like the energy

818
00:42:55,760 --> 00:42:58,720
Speaker 4: densities that we like, have you know in your office, okay,

819
00:42:59,160 --> 00:43:02,000
Speaker 4: then it's not you, and so it becomes very difficult

820
00:43:02,440 --> 00:43:05,319
Speaker 4: to understand. So how would the world look like on

821
00:43:05,360 --> 00:43:10,359
Speaker 4: this low density or large distances? I mean, string theory

822
00:43:10,360 --> 00:43:13,880
Speaker 4: predicts a completely unique world. At small distances you see little,

823
00:43:13,880 --> 00:43:16,560
Speaker 4: you know, vibrating strings behaving in a certain way. But

824
00:43:16,600 --> 00:43:18,839
Speaker 4: then if you do mine it, it's not obvious what's

825
00:43:18,880 --> 00:43:20,879
Speaker 4: going to happen. Okay, this is why we always say

826
00:43:20,880 --> 00:43:23,040
Speaker 4: we have trouble or we are not sure whether we

827
00:43:23,080 --> 00:43:26,120
Speaker 4: can reproduce the large the universe as we typically know.

828
00:43:27,560 --> 00:43:29,520
Speaker 4: But this is not a problem of string theory. This

829
00:43:29,640 --> 00:43:33,799
Speaker 4: is effect of all high energy theories. And maybe I

830
00:43:33,840 --> 00:43:37,880
Speaker 4: can give an analogy. Okay, so imagine that you have

831
00:43:37,960 --> 00:43:44,920
Speaker 4: a rocky landscape, hills, mountains, whatever, very very complicated, many valleys,

832
00:43:45,560 --> 00:43:48,520
Speaker 4: and you have a football. But the football has a

833
00:43:48,560 --> 00:43:52,319
Speaker 4: lot of energy, you know, so then it's like up

834
00:43:52,360 --> 00:43:55,040
Speaker 4: there up the tops of the mountains, right because it

835
00:43:55,200 --> 00:43:57,560
Speaker 4: just says lots of alosity. It's moving through those valleys

836
00:43:57,600 --> 00:44:01,040
Speaker 4: and it's just all the way up. But then you

837
00:44:01,080 --> 00:44:03,840
Speaker 4: know the restriction and the velocity is going down. Well,

838
00:44:04,120 --> 00:44:07,160
Speaker 4: if I have many values, I don't know where the

839
00:44:07,200 --> 00:44:09,280
Speaker 4: ball is going to roll down and where the value

840
00:44:09,280 --> 00:44:12,000
Speaker 4: is that it's going to end. That's the problem we have. Well,

841
00:44:12,040 --> 00:44:13,840
Speaker 4: I don't think it's a problem with theory, it's just

842
00:44:14,120 --> 00:44:16,960
Speaker 4: it's typical. Actually, even the standard model has this property

843
00:44:17,000 --> 00:44:18,759
Speaker 4: that this difficulty.

844
00:44:18,880 --> 00:44:21,399
Speaker 1: That's a great explanation. Thank you. Can you circle back

845
00:44:21,400 --> 00:44:25,040
Speaker 1: and help us understand more specifically how string theory solves

846
00:44:25,320 --> 00:44:28,719
Speaker 1: these problems of quantum gravity. You talked about how howing

847
00:44:29,080 --> 00:44:32,360
Speaker 1: string replaces the infinite number of parameters you might have

848
00:44:32,400 --> 00:44:35,280
Speaker 1: to measure how does it solve the problem of quantum

849
00:44:35,280 --> 00:44:39,680
Speaker 1: mechanics and general relativity working together on this dynamic space time.

850
00:44:40,000 --> 00:44:42,560
Speaker 4: So first, I think it's very important to have a disclaimer.

851
00:44:43,440 --> 00:44:45,800
Speaker 4: We don't have the full theory, right, so whether it

852
00:44:45,880 --> 00:44:48,319
Speaker 4: solves all problems that we know quantum gravity we do

853
00:44:48,360 --> 00:44:50,239
Speaker 4: not know. I have to be honest on this. I

854
00:44:50,280 --> 00:44:53,680
Speaker 4: would say that from a mathematical point of view, the

855
00:44:53,719 --> 00:44:57,800
Speaker 4: way it solves this is by not quantizing gravity. That's

856
00:44:58,040 --> 00:45:00,319
Speaker 4: very strange to say what it is. That's why string

857
00:45:00,400 --> 00:45:03,640
Speaker 4: theory did so quantizing. When we use the word quantizing,

858
00:45:03,680 --> 00:45:07,000
Speaker 4: it means that we take our classical theory it has

859
00:45:07,040 --> 00:45:11,040
Speaker 4: a certain amount of variables like electromagnetism has the electric

860
00:45:11,120 --> 00:45:15,480
Speaker 4: field and has the electron field, and always said that's quantizing.

861
00:45:15,960 --> 00:45:19,600
Speaker 4: Let's make it quantum mechanical. So you could say, well,

862
00:45:19,680 --> 00:45:23,480
Speaker 4: relativity is what we call the metric field. That's a

863
00:45:23,520 --> 00:45:27,880
Speaker 4: field that describes how space and time curve. Okay, and

864
00:45:27,960 --> 00:45:30,440
Speaker 4: that's what people usually do. They say, Oh, we learned

865
00:45:31,000 --> 00:45:33,920
Speaker 4: in history of quantized series. We take that classical what

866
00:45:34,040 --> 00:45:36,680
Speaker 4: we call field and we turn it into a quantom

867
00:45:36,719 --> 00:45:37,560
Speaker 4: mechanical field.

868
00:45:37,640 --> 00:45:39,239
Speaker 1: But how do you do that? How do you quantize

869
00:45:39,239 --> 00:45:41,399
Speaker 1: the theory? You don't just like tap your magic wand

870
00:45:41,440 --> 00:45:43,320
Speaker 1: down and say and now you're quantum mechanical.

871
00:45:43,880 --> 00:45:46,640
Speaker 4: Oh my god, this is tough. So mathematically you would

872
00:45:46,680 --> 00:45:49,319
Speaker 4: say it turned a field into an operator, but that

873
00:45:49,400 --> 00:45:52,400
Speaker 4: probably means a little two people listening, here's an attempt.

874
00:45:52,400 --> 00:45:55,719
Speaker 4: I'm not sure it's even good. Quantum mechanics tells you

875
00:45:55,800 --> 00:45:59,839
Speaker 4: that things there are only probabilities, right, what you thought

876
00:46:00,000 --> 00:46:02,959
Speaker 4: as a particle. We sometly say it so a way,

877
00:46:03,640 --> 00:46:06,000
Speaker 4: it's not a very good word. What we have in

878
00:46:06,040 --> 00:46:10,120
Speaker 4: said is a probability distribution of where the party consulute.

879
00:46:11,200 --> 00:46:17,360
Speaker 4: So objects are turned into probability distributions. That's quantizing a theory.

880
00:46:17,600 --> 00:46:21,319
Speaker 4: And then there's a certain equation for the probability distribution.

881
00:46:23,160 --> 00:46:25,279
Speaker 4: But more mathematically, it means that you take a field

882
00:46:25,320 --> 00:46:26,680
Speaker 4: and you make it into an operator.

883
00:46:26,880 --> 00:46:28,799
Speaker 1: No, that's a great way to think about it. A

884
00:46:28,880 --> 00:46:32,920
Speaker 1: classical theory says that everything is specified and there is

885
00:46:33,000 --> 00:46:35,560
Speaker 1: infinite information even if you don't have it, whereas a

886
00:46:35,640 --> 00:46:39,560
Speaker 1: quantum theory leaves some uncertainty and says, well, this isn't determined.

887
00:46:39,600 --> 00:46:41,520
Speaker 1: Maybe the electron is here, maybe the electron is there.

888
00:46:41,520 --> 00:46:43,840
Speaker 1: Maybe the field is this value, maybe it has that value.

889
00:46:44,040 --> 00:46:45,719
Speaker 1: And for those of you playing along at home, an

890
00:46:45,760 --> 00:46:49,160
Speaker 1: operator here is making a measurement. It's like applying something

891
00:46:49,239 --> 00:46:52,359
Speaker 1: to it and getting a result out. And so that's

892
00:46:52,360 --> 00:46:55,160
Speaker 1: a crucial element of quant mechanics. Okay, so now we're

893
00:46:55,160 --> 00:46:58,680
Speaker 1: going to try to quantize space time and you say,

894
00:46:58,719 --> 00:47:01,040
Speaker 1: we can think of the metric as a field. The

895
00:47:01,120 --> 00:47:03,279
Speaker 1: metric is like how much curvature there is at every

896
00:47:03,280 --> 00:47:05,520
Speaker 1: point in space. So if we think of like the

897
00:47:05,560 --> 00:47:07,960
Speaker 1: curvature and space as a field, why is it hard

898
00:47:07,960 --> 00:47:10,000
Speaker 1: to quantize that. Why can't we think of that as like, well,

899
00:47:10,080 --> 00:47:12,400
Speaker 1: maybe the curvature is this value, maybe the curvature is

900
00:47:12,400 --> 00:47:15,160
Speaker 1: that value. Why can't we just think of that probabilistically.

901
00:47:15,400 --> 00:47:17,840
Speaker 4: That was the problem of the problems we talked about before.

902
00:47:17,960 --> 00:47:21,279
Speaker 4: Then you run into the problem of non renormalizability. If

903
00:47:21,320 --> 00:47:23,600
Speaker 4: you do it that way, or you're run into the

904
00:47:23,640 --> 00:47:26,680
Speaker 4: problem that you know, it's a background itself that has

905
00:47:26,719 --> 00:47:30,800
Speaker 4: to become a probability. So the formalism of Qunlem mechanics

906
00:47:30,800 --> 00:47:33,200
Speaker 4: gets very confusing at that point. And as I said,

907
00:47:33,600 --> 00:47:37,320
Speaker 4: we already knew that a theory that is non renormalizable

908
00:47:37,360 --> 00:47:39,800
Speaker 4: means that you're not having the right degrees of freedom,

909
00:47:40,080 --> 00:47:43,920
Speaker 4: you're missing information. So the way string theory went about

910
00:47:44,080 --> 00:47:48,120
Speaker 4: is people that discovered it. We're not trying to quantize gravity.

911
00:47:48,160 --> 00:47:50,600
Speaker 4: Let's let's be clear on this. Okay. They wanted to

912
00:47:50,640 --> 00:47:54,000
Speaker 4: solve another puzzle, and for some reason, which is a

913
00:47:54,000 --> 00:47:58,000
Speaker 4: long story by itself, they were interested into string like

914
00:47:58,040 --> 00:48:02,000
Speaker 4: objects and how they move and how strings move quantum mechanically.

915
00:48:02,880 --> 00:48:06,759
Speaker 4: So they do their computation and they suddenly see that

916
00:48:07,480 --> 00:48:10,520
Speaker 4: the string can fluctuate in what we mathematically call a

917
00:48:10,560 --> 00:48:13,279
Speaker 4: spin to field. If you don't know what a spin

918
00:48:13,320 --> 00:48:15,560
Speaker 4: to field is, it's just a fancy way of saying

919
00:48:16,360 --> 00:48:20,120
Speaker 4: it describes what I call the metric field. They just says,

920
00:48:20,200 --> 00:48:22,480
Speaker 4: but that's strange. There's no space and time, and yet

921
00:48:22,680 --> 00:48:25,919
Speaker 4: they found the structure, which is what they knew from relativity.

922
00:48:26,160 --> 00:48:28,880
Speaker 4: And then they started to look into it deeper, and

923
00:48:28,920 --> 00:48:32,400
Speaker 4: they wanted to understand the equations that that metric field obeyed,

924
00:48:33,280 --> 00:48:36,040
Speaker 4: and they were completely surprised that, you know, they didn't

925
00:48:36,040 --> 00:48:40,040
Speaker 4: ask for it. They found Insten's equations. So this is

926
00:48:40,400 --> 00:48:42,000
Speaker 4: also what I call absolute beauty.

927
00:48:42,920 --> 00:48:43,240
Speaker 1: Okay.

928
00:48:43,320 --> 00:48:46,280
Speaker 4: Other approaches to quantographty they said, let me take insent

929
00:48:46,360 --> 00:48:50,239
Speaker 4: equations for true, just have them. I said, also just

930
00:48:50,280 --> 00:48:52,160
Speaker 4: dropped them down. I said, I didn't know why these are

931
00:48:52,160 --> 00:48:55,400
Speaker 4: my equations. Okay, he didn't derive them. And so the

932
00:48:55,480 --> 00:48:58,040
Speaker 4: other approaches to quanto gravity say, let me take those

933
00:48:58,040 --> 00:49:01,640
Speaker 4: equations that you know, quantitize them. String theories did something else.

934
00:49:01,680 --> 00:49:04,920
Speaker 4: They were looking at strings vibrating for a completely different reason.

935
00:49:05,040 --> 00:49:08,600
Speaker 4: They not only recover Einstein's equations, the classical ones they predict,

936
00:49:08,640 --> 00:49:11,960
Speaker 4: they literally predict them, but they immediately have them quanta mechanically,

937
00:49:12,920 --> 00:49:15,200
Speaker 4: and it meant that they needed they have all these

938
00:49:15,200 --> 00:49:18,000
Speaker 4: possible vibrations of the string. It's just one vibration that

939
00:49:18,040 --> 00:49:21,280
Speaker 4: gives you this metric field, but the string can vibrate

940
00:49:21,320 --> 00:49:24,120
Speaker 4: in so many other ways. And then suddenly it gave

941
00:49:24,200 --> 00:49:27,480
Speaker 4: them other things. They knew, for instance, all the forces

942
00:49:27,560 --> 00:49:30,120
Speaker 4: in nature. They come in two kinds. Okay, there's gravity.

943
00:49:30,280 --> 00:49:32,319
Speaker 4: This is a separate guy. It's is described by this

944
00:49:32,719 --> 00:49:36,880
Speaker 4: metric field. And the other forces are with a manematical

945
00:49:36,960 --> 00:49:41,040
Speaker 4: term are gauge forces, young meals forces. Electromagnetism is an

946
00:49:41,040 --> 00:49:43,400
Speaker 4: example of it, okay. And the two other are the

947
00:49:43,480 --> 00:49:46,560
Speaker 4: nuclear forces, and they are all described by one equation

948
00:49:46,640 --> 00:49:49,400
Speaker 4: which is called the Young Mules equation, and a special

949
00:49:49,520 --> 00:49:52,279
Speaker 4: kind of young music equations that maybe people listening who

950
00:49:52,320 --> 00:49:55,200
Speaker 4: had a little bit of a scientific, you know, education

951
00:49:55,360 --> 00:49:57,640
Speaker 4: remember are what we call the maximal equations, which are

952
00:49:57,680 --> 00:50:01,239
Speaker 4: the equations of electric and magnetic fields. But this is

953
00:50:01,280 --> 00:50:03,560
Speaker 4: part of a general mathematical equation which is called the

954
00:50:03,600 --> 00:50:07,480
Speaker 4: young music question, which also mathematicians study for completely different reasons.

955
00:50:07,480 --> 00:50:09,600
Speaker 4: But guess what they were looking at the other modes

956
00:50:09,640 --> 00:50:12,399
Speaker 4: of vibration of the street, and without asking for it,

957
00:50:13,080 --> 00:50:15,520
Speaker 4: the young music quations appeared, and at that point people

958
00:50:15,600 --> 00:50:18,160
Speaker 4: were like, my god, this is insane. Okay, So this

959
00:50:18,200 --> 00:50:20,839
Speaker 4: is where all the hype came from, all right, from

960
00:50:20,880 --> 00:50:23,840
Speaker 4: string theory, like the excitement of people all came from this.

961
00:50:24,760 --> 00:50:27,440
Speaker 4: Not only do we you know, we get the classical

962
00:50:27,480 --> 00:50:29,640
Speaker 4: theories we didn't ask for that we've gotten. So you

963
00:50:29,680 --> 00:50:31,320
Speaker 4: get all advance, so to speak.

964
00:50:31,520 --> 00:50:34,040
Speaker 1: So I'm getting a sense from you that the elegance

965
00:50:34,400 --> 00:50:38,200
Speaker 1: of string theory comes from the sort of discovery that

966
00:50:38,239 --> 00:50:41,879
Speaker 1: it answers questions simply, and sometimes it answers questions we

967
00:50:41,880 --> 00:50:45,000
Speaker 1: weren't trying to answer. In that sense, it feels more

968
00:50:45,160 --> 00:50:49,200
Speaker 1: like you're accidentally revealing a big chunk of truth rather

969
00:50:49,239 --> 00:50:53,440
Speaker 1: than you're like laboriously putting together an over complicated answer

970
00:50:53,680 --> 00:50:56,160
Speaker 1: that's just an invention in your mind. Is that the

971
00:50:56,200 --> 00:50:59,240
Speaker 1: feeling here that we've like uncovered a vein of reality.

972
00:50:59,520 --> 00:51:01,920
Speaker 4: Absolutely, And I think that's for all of science. Like

973
00:51:02,040 --> 00:51:07,400
Speaker 4: I can imagine in biology, when you understood like gene

974
00:51:07,400 --> 00:51:12,440
Speaker 4: structure and I suddenly realize how things work. It becomes

975
00:51:12,480 --> 00:51:16,000
Speaker 4: so simple, Like I think the same evolution happened in biology.

976
00:51:16,040 --> 00:51:18,759
Speaker 4: You have all this phenomena. At some point we learned

977
00:51:18,760 --> 00:51:22,239
Speaker 4: about to sell and the smaller organisms, and all of

978
00:51:22,239 --> 00:51:26,479
Speaker 4: these phenomena suddenly can be explained in a more microscopic way.

979
00:51:26,800 --> 00:51:29,960
Speaker 4: So the theory becomes simpler. It became maybe I'm simplifying.

980
00:51:30,000 --> 00:51:32,240
Speaker 4: I mean, I'm not the expert here, but I would

981
00:51:32,239 --> 00:51:35,120
Speaker 4: say biology at some point became the theory of the cell,

982
00:51:35,480 --> 00:51:37,360
Speaker 4: which is so much smaller and so much in a

983
00:51:37,400 --> 00:51:38,160
Speaker 4: way simpler.

984
00:51:38,360 --> 00:51:41,200
Speaker 1: So is it then about the theory itself or is

985
00:51:41,239 --> 00:51:44,160
Speaker 1: it about the insights the theory gives you about how

986
00:51:44,200 --> 00:51:46,239
Speaker 1: the universe works, or just the place where we are

987
00:51:46,320 --> 00:51:49,080
Speaker 1: where we're like wollw We're frustrated by these problems for decades,

988
00:51:49,120 --> 00:51:51,920
Speaker 1: and now finally the headache has gone away. I mean,

989
00:51:51,920 --> 00:51:54,000
Speaker 1: can you look at the theory itself and say, this

990
00:51:54,080 --> 00:51:56,399
Speaker 1: theory is beautiful? Is there a chance that we could

991
00:51:56,440 --> 00:51:59,600
Speaker 1: have revealed the theory which feels truthful? But then you're like, actually,

992
00:51:59,640 --> 00:52:01,239
Speaker 1: I don't like it. It's kind of ugly.

993
00:52:01,440 --> 00:52:05,239
Speaker 4: Right. I guess different versions of beauty were felt at

994
00:52:05,239 --> 00:52:08,759
Speaker 4: different stages, right, So the people first making these discoveries

995
00:52:09,600 --> 00:52:13,239
Speaker 4: of seeing einscience equations and so on, when you read

996
00:52:13,400 --> 00:52:17,359
Speaker 4: their biographies, they really are like they talk about it

997
00:52:17,360 --> 00:52:20,480
Speaker 4: extremely emotional, like they could be crying because they saw

998
00:52:20,520 --> 00:52:24,080
Speaker 4: that part of beauty. But my generation came later, so

999
00:52:24,239 --> 00:52:26,359
Speaker 4: we kind of you say, you got used to it,

1000
00:52:26,520 --> 00:52:28,520
Speaker 4: you don't feel that beauty on it. The thing that

1001
00:52:28,560 --> 00:52:31,000
Speaker 4: strikes me is that when you first learn about Newton's

1002
00:52:31,040 --> 00:52:34,080
Speaker 4: second law, I don't think none of us feels what

1003
00:52:34,120 --> 00:52:37,800
Speaker 4: Newton felt at the time, and I think we are

1004
00:52:37,920 --> 00:52:41,479
Speaker 4: underestimating the emotions because one other things that I didn't

1005
00:52:41,480 --> 00:52:44,239
Speaker 4: tell you what Newton's second ploy is. It tells you

1006
00:52:44,239 --> 00:52:48,760
Speaker 4: about what we call the deterministic view of nature. Newton

1007
00:52:48,840 --> 00:52:51,239
Speaker 4: realized that this equation was telling you that, you know,

1008
00:52:51,480 --> 00:52:54,120
Speaker 4: I'm sitting on my chair and later on I will

1009
00:52:54,120 --> 00:52:56,839
Speaker 4: walk away. But according to Newton's equation, I don't have

1010
00:52:56,880 --> 00:52:59,640
Speaker 4: the choice. I have no freedom. There's no freedom of

1011
00:52:59,760 --> 00:53:01,040
Speaker 4: you know, there's no free will.

1012
00:53:01,200 --> 00:53:03,800
Speaker 3: Do the philosophers know you all have solved that problem.

1013
00:53:04,239 --> 00:53:07,600
Speaker 4: No, it's the classical theory, right, So, but physics is deterministic,

1014
00:53:07,680 --> 00:53:10,520
Speaker 4: so the according to physics. I think we should emphasize this.

1015
00:53:10,640 --> 00:53:13,359
Speaker 4: There is no free will in physics. Anybody that tells

1016
00:53:13,440 --> 00:53:16,520
Speaker 4: you that there is is wrong physics. As I don't

1017
00:53:16,520 --> 00:53:18,719
Speaker 4: say we have solved it. But there is no free

1018
00:53:18,760 --> 00:53:21,839
Speaker 4: will in physics, absolutely not. Free will is completely in

1019
00:53:21,920 --> 00:53:25,040
Speaker 4: contradiction with physics. Not the illusion of free will, but

1020
00:53:25,040 --> 00:53:27,239
Speaker 4: free will. But it's no way, there's no room in

1021
00:53:27,280 --> 00:53:30,080
Speaker 4: physics for free will, not in the usual notion of

1022
00:53:30,120 --> 00:53:31,960
Speaker 4: the word free will. Any I want to say that

1023
00:53:32,000 --> 00:53:34,759
Speaker 4: the beauty that we feel or now the students you know,

1024
00:53:34,800 --> 00:53:38,520
Speaker 4: which are younger than me. There are different versions of beauty.

1025
00:53:38,560 --> 00:53:40,799
Speaker 4: It's more where you start applying the theory. I can

1026
00:53:40,840 --> 00:53:42,560
Speaker 4: give you one example of a thing that I found

1027
00:53:42,600 --> 00:53:46,040
Speaker 4: beautiful is like you have equations with singularities, like these

1028
00:53:46,040 --> 00:53:49,239
Speaker 4: infinities we talked about, and string theory can do calculations

1029
00:53:49,280 --> 00:53:51,040
Speaker 4: and you see there's no infinity, And then you learn

1030
00:53:51,120 --> 00:53:54,440
Speaker 4: how string theory tells you that there's no infinity, and

1031
00:53:54,480 --> 00:53:56,680
Speaker 4: it does it in a very creative and funny way.

1032
00:53:56,800 --> 00:53:59,680
Speaker 4: There's often a picture like you can even see it literally,

1033
00:53:59,800 --> 00:54:02,680
Speaker 4: it's not an equation, it's not formal us. You can

1034
00:54:02,719 --> 00:54:04,280
Speaker 4: just see it, and that's kind of beautiful.

1035
00:54:04,400 --> 00:54:06,239
Speaker 2: Too bad the listeners can't see your face because you

1036
00:54:06,239 --> 00:54:08,080
Speaker 2: have the biggest grin on that You've had the whole

1037
00:54:08,080 --> 00:54:09,799
Speaker 2: interview explaining how beautiful it is.

1038
00:54:09,840 --> 00:54:11,600
Speaker 3: Like you're clearly getting a total kick out of this.

1039
00:54:11,760 --> 00:54:13,200
Speaker 3: It's it's awesome.

1040
00:54:13,320 --> 00:54:14,920
Speaker 1: I think it is really hard to put yourself in

1041
00:54:14,960 --> 00:54:19,080
Speaker 1: the minds of earlier generations to appreciate how big some

1042
00:54:19,160 --> 00:54:22,240
Speaker 1: of those steps forward were. Like, it seems pretty basic

1043
00:54:22,280 --> 00:54:25,520
Speaker 1: what Aristotle accomplished. You like, things fall down. I could

1044
00:54:25,560 --> 00:54:28,280
Speaker 1: have said that, but you know, to systematize the world

1045
00:54:28,320 --> 00:54:30,480
Speaker 1: at all. What was a big step forward. I think

1046
00:54:30,480 --> 00:54:33,319
Speaker 1: you're right that it's underappreciated. So what is it that

1047
00:54:33,360 --> 00:54:35,960
Speaker 1: we're underappreciating now in terms of strength theory. I mean,

1048
00:54:35,960 --> 00:54:38,040
Speaker 1: there's a lot of popular writing about strength theory, a

1049
00:54:38,080 --> 00:54:40,440
Speaker 1: lot of popular conceptions about it. But from somebody on

1050
00:54:40,480 --> 00:54:43,080
Speaker 1: the inside, what do you feel like is most often

1051
00:54:43,120 --> 00:54:46,560
Speaker 1: misunderstood or misrepresented about the nature of strength theory.

1052
00:54:47,000 --> 00:54:49,359
Speaker 4: I have to be careful, careful not to become too

1053
00:54:49,440 --> 00:54:53,399
Speaker 4: sort of drawn into the sociological discussion, but I feel

1054
00:54:53,440 --> 00:54:58,480
Speaker 4: I cannot not say it so string theory, say, thirty

1055
00:54:58,719 --> 00:55:03,960
Speaker 4: twenty years ago, when it's people discussed it in science outreach,

1056
00:55:04,200 --> 00:55:08,200
Speaker 4: it was only the one, okay, And now it's the opposite,

1057
00:55:08,320 --> 00:55:10,880
Speaker 4: And I think that the opposite went so far that

1058
00:55:10,960 --> 00:55:13,760
Speaker 4: it's completely misrepresenting the field.

1059
00:55:14,080 --> 00:55:16,480
Speaker 1: When you say the opposite, you mean like people being

1060
00:55:16,520 --> 00:55:20,200
Speaker 1: critical of string theory because it hasn't yet predicted some

1061
00:55:20,239 --> 00:55:21,440
Speaker 1: experiment and been proven.

1062
00:55:21,440 --> 00:55:25,319
Speaker 4: Writers is exactly, this is an example exactly. So they

1063
00:55:25,360 --> 00:55:27,400
Speaker 4: will tell you this, and then of course you have

1064
00:55:27,480 --> 00:55:29,560
Speaker 4: to tell them, because they don't tell you this, that

1065
00:55:29,600 --> 00:55:33,120
Speaker 4: this is true for any theory of quantogravity and We

1066
00:55:33,160 --> 00:55:35,160
Speaker 4: knew this in advance. We knew this before we started

1067
00:55:35,160 --> 00:55:37,759
Speaker 4: working on string theory with absolute certainty that if you

1068
00:55:37,760 --> 00:55:40,560
Speaker 4: have access to the smallest Lend skills, you can falcify

1069
00:55:40,600 --> 00:55:43,120
Speaker 4: a theory one from the other. Okay, string theory from

1070
00:55:43,120 --> 00:55:46,319
Speaker 4: the other examples. What is completely not obvious is that

1071
00:55:46,360 --> 00:55:50,560
Speaker 4: some of these high energy small distance effects have an

1072
00:55:50,560 --> 00:55:54,799
Speaker 4: imprint at larger distances. At a moment, we don't know,

1073
00:55:54,920 --> 00:55:57,480
Speaker 4: and we're actually looking into it. And this program has

1074
00:55:57,520 --> 00:55:59,560
Speaker 4: a name. I think it's super exciting. It's called the

1075
00:55:59,600 --> 00:56:03,239
Speaker 4: Swamp program, and it's where we try to look into

1076
00:56:03,239 --> 00:56:05,120
Speaker 4: that question. But at the moment we do not know.

1077
00:56:06,160 --> 00:56:10,560
Speaker 4: But as any other supposed alternative to string hearing is

1078
00:56:10,560 --> 00:56:13,000
Speaker 4: not even there at that stage where they can even

1079
00:56:13,040 --> 00:56:17,160
Speaker 4: ask this question, does my theory predict something at a

1080
00:56:17,280 --> 00:56:19,920
Speaker 4: bigger length scale, because normally you don't expect it to

1081
00:56:19,920 --> 00:56:23,759
Speaker 4: be the case? Right, So can I get away of

1082
00:56:23,920 --> 00:56:26,160
Speaker 4: not sending a student into a black hole to learn

1083
00:56:26,200 --> 00:56:28,040
Speaker 4: about pornography? We don't know.

1084
00:56:28,360 --> 00:56:30,640
Speaker 2: I mean, master students are expendable. You could send like

1085
00:56:30,680 --> 00:56:31,560
Speaker 2: four or five of them.

1086
00:56:32,560 --> 00:56:35,719
Speaker 4: Unfortunately they can't explains what they're what they're seeing, right,

1087
00:56:35,800 --> 00:56:39,000
Speaker 4: so they couldn't explain it. That's that's a Otherwise I would,

1088
00:56:39,040 --> 00:56:41,200
Speaker 4: you know, be interested in maybe jumping into a black

1089
00:56:41,239 --> 00:56:43,799
Speaker 4: hole just to see because if you jump into a

1090
00:56:43,800 --> 00:56:45,400
Speaker 4: big black hole, actually it doesn't need to be a

1091
00:56:45,400 --> 00:56:48,960
Speaker 4: painful experience. You can pass the horizon without you know,

1092
00:56:49,000 --> 00:56:52,720
Speaker 4: feeling it too much, and then you could actually see

1093
00:56:53,400 --> 00:56:54,320
Speaker 4: a singularity.

1094
00:56:54,560 --> 00:56:54,719
Speaker 1: You know.

1095
00:56:54,800 --> 00:56:57,120
Speaker 4: Interstellary is a little bit about this, right, you jump

1096
00:56:57,160 --> 00:57:00,880
Speaker 4: into a black hole. There's a movie about it. But yeah,

1097
00:57:00,920 --> 00:57:03,480
Speaker 4: so I think is my frustration that there is a

1098
00:57:03,520 --> 00:57:06,160
Speaker 4: back correction to the original hype. But the back correction

1099
00:57:06,960 --> 00:57:12,560
Speaker 4: especially you know now on social media, but also i'd

1100
00:57:12,560 --> 00:57:15,200
Speaker 4: say conventional science outreach. To give an example, I saw

1101
00:57:15,320 --> 00:57:18,000
Speaker 4: my children that at an age where they get interested

1102
00:57:18,040 --> 00:57:20,959
Speaker 4: in science and they start googling things. So I see

1103
00:57:20,960 --> 00:57:24,840
Speaker 4: their first hit on Google when they ask a question

1104
00:57:24,880 --> 00:57:27,640
Speaker 4: which is about fundamental physics, and the first hit that

1105
00:57:27,720 --> 00:57:31,480
Speaker 4: they have is criticism on stream. There it became so

1106
00:57:31,720 --> 00:57:34,320
Speaker 4: mainstream that this is the first thing you see, and

1107
00:57:34,360 --> 00:57:35,640
Speaker 4: that's not healthy anymore.

1108
00:57:35,760 --> 00:57:38,520
Speaker 1: Okay, So just to make sure I understand, you're saying

1109
00:57:38,560 --> 00:57:41,240
Speaker 1: it's fair to criticize string theory and say you haven't

1110
00:57:41,240 --> 00:57:44,680
Speaker 1: made a prediction, which can be verified, But all the

1111
00:57:44,680 --> 00:57:47,920
Speaker 1: theories of quantum gravity also had that issue that we

1112
00:57:47,960 --> 00:57:50,240
Speaker 1: can't go inside a black hole, And many theories of

1113
00:57:50,280 --> 00:57:53,200
Speaker 1: quantum gravity haven't even come together and coalesced and enough

1114
00:57:53,240 --> 00:57:56,080
Speaker 1: detail to make any predictions, not to mention ones that

1115
00:57:56,200 --> 00:57:58,280
Speaker 1: can be tested. So then let me wrap up by

1116
00:57:58,240 --> 00:58:01,560
Speaker 1: asking you a last question, which is about the truth

1117
00:58:01,560 --> 00:58:04,080
Speaker 1: of strength theory. I mean, you're excited about string theory

1118
00:58:04,080 --> 00:58:06,520
Speaker 1: because you think it's simple and it feels like a

1119
00:58:06,640 --> 00:58:09,880
Speaker 1: compelling potential answer to the question of like what really

1120
00:58:09,920 --> 00:58:12,800
Speaker 1: happening in the universe. So do you think, for example,

1121
00:58:13,160 --> 00:58:16,600
Speaker 1: in some hypothetical scenario where aliens arrive on Earth and

1122
00:58:16,640 --> 00:58:19,880
Speaker 1: they're very advanced scientifically, and we can figure out how

1123
00:58:19,920 --> 00:58:21,800
Speaker 1: to communicate with them, et cetera, et cetera, what do

1124
00:58:21,800 --> 00:58:25,240
Speaker 1: you think are the chances that alien physicists are doing

1125
00:58:25,280 --> 00:58:28,600
Speaker 1: string theory that they have also stumbled upon this explanation.

1126
00:58:28,800 --> 00:58:30,720
Speaker 2: Daniel always has to get aliens into the show at

1127
00:58:30,800 --> 00:58:32,880
Speaker 2: least once, and so here we go.

1128
00:58:34,160 --> 00:58:38,880
Speaker 4: We all owe aliens. Actually, Okay, I don't know whether

1129
00:58:38,960 --> 00:58:41,840
Speaker 4: my answer is of any meaning, but I would say

1130
00:58:41,880 --> 00:58:44,040
Speaker 4: they will discover string theory. I actually don't even doubt it.

1131
00:58:44,120 --> 00:58:49,160
Speaker 4: I'm one hundred percent convinced. And as to the question before,

1132
00:58:49,520 --> 00:58:54,160
Speaker 4: people tell you that a theory without predictions is not science,

1133
00:58:55,400 --> 00:58:58,640
Speaker 4: and I think we have to really step away from this.

1134
00:58:59,440 --> 00:59:04,240
Speaker 4: So in science are two things. They're observables and they're computables,

1135
00:59:05,120 --> 00:59:08,640
Speaker 4: especially in theoretical sciences, and what a theory has to

1136
00:59:08,680 --> 00:59:11,360
Speaker 4: get right are the computables. For instance, if I have

1137
00:59:11,400 --> 00:59:14,280
Speaker 4: a theory that can explain phenomena at large distances, but

1138
00:59:14,320 --> 00:59:17,080
Speaker 4: I look at small distances and the theory tells me

1139
00:59:17,120 --> 00:59:19,600
Speaker 4: that I can go back in time and kill my

1140
00:59:19,920 --> 00:59:23,520
Speaker 4: mother before I was born. I know that theory is nonsense,

1141
00:59:24,440 --> 00:59:27,720
Speaker 4: but I cannot make an experimental verification. But the theory

1142
00:59:27,760 --> 00:59:33,280
Speaker 4: is just nonsense. It's not logical. And the thing that

1143
00:59:33,320 --> 00:59:36,360
Speaker 4: people that the audience and you know, the greater public

1144
00:59:36,480 --> 00:59:41,080
Speaker 4: needs to understand, quantum gravity is so extremely constraining in

1145
00:59:41,200 --> 00:59:45,960
Speaker 4: terms of just logical consistency that you almost uniquely arrive

1146
00:59:46,000 --> 00:59:49,920
Speaker 4: at an answer. And that's where this is true science. Okay,

1147
00:59:49,960 --> 00:59:53,000
Speaker 4: despite not having access at a moment to an experiment

1148
00:59:53,040 --> 00:59:57,240
Speaker 4: to test it, you almost uniquely are pushed into a

1149
00:59:57,280 --> 01:00:01,000
Speaker 4: direction to solve this problem of non remortalizing. Now I'm

1150
01:00:01,000 --> 01:00:03,520
Speaker 4: selling it too much, But I hope you're understanding what

1151
01:00:03,560 --> 01:00:04,560
Speaker 4: I'm trying to say.

1152
01:00:04,800 --> 01:00:06,600
Speaker 2: I've read a couple of books on strength theory and

1153
01:00:06,680 --> 01:00:10,200
Speaker 2: never understood them, but I've totally understood our conversation today.

1154
01:00:10,240 --> 01:00:11,720
Speaker 3: So I'm this has been awesome.

1155
01:00:11,800 --> 01:00:13,720
Speaker 4: Happy to hear that it's awesome.

1156
01:00:14,720 --> 01:00:17,000
Speaker 1: And if aliens arrive and they don't do strength theory,

1157
01:00:17,080 --> 01:00:18,720
Speaker 1: maybe they can listen to this episode to get a

1158
01:00:18,720 --> 01:00:24,640
Speaker 1: primer on how strength theory works. Exactly, exactly, wonderful. Well,

1159
01:00:24,640 --> 01:00:26,080
Speaker 1: thank you very much for coming on the show and

1160
01:00:26,080 --> 01:00:28,520
Speaker 1: talking to us about the hard problem of quantum gravity

1161
01:00:28,560 --> 01:00:31,600
Speaker 1: and how string theory might be the solution. Thanks very much.

1162
01:00:31,760 --> 01:00:33,840
Speaker 4: It us a lot of fun. Thank you so much.

1163
01:00:41,800 --> 01:00:45,320
Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio.

1164
01:00:45,560 --> 01:00:48,080
Speaker 3: We would love to hear from you, We really would.

1165
01:00:48,240 --> 01:00:51,000
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1166
01:00:51,200 --> 01:00:52,880
Speaker 1: Extraordinary Universe.

1167
01:00:53,000 --> 01:00:55,960
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1168
01:00:55,960 --> 01:00:59,400
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1169
01:00:59,200 --> 01:01:02,880
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1170
01:01:02,960 --> 01:01:06,000
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1171
01:01:05,800 --> 01:01:07,520
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1172
01:01:07,600 --> 01:01:11,400
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1173
01:01:11,480 --> 01:01:12,360
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1174
01:01:12,440 --> 01:01:15,360
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1175
01:01:15,480 --> 01:01:17,040
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