WEBVTT - Why is quantum gravity so hard?

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<v Speaker 1>Hey, Daniel, how smart do you have to be to

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<v Speaker 1>be a physicist?

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<v Speaker 2>You know, it's not actually about being smart. It's more

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<v Speaker 2>about thinking that these kind of particular challenges are really fun.

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<v Speaker 1>So if you like having fun, you shouldn't be a physicist.

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<v Speaker 1>What do you mean?

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<v Speaker 2>I mean, you know, science is a very personal thing,

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<v Speaker 2>so some people might think doing integrals is really boring,

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<v Speaker 2>and somebody else might do them to relax.

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<v Speaker 1>Well, are you saying math can be relaxing.

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<v Speaker 2>It can be relaxing, and it can also be exciting.

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<v Speaker 1>You know.

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<v Speaker 2>Sometimes you're like bush whacking through the math and you

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<v Speaker 2>make amazing discoveries and you don't even have to risk

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<v Speaker 2>your life to jaguars.

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<v Speaker 1>Well you do have to worry about paper cuts, right.

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<v Speaker 2>Yeah, you know. I think there's a reason they didn't

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<v Speaker 2>make Indiana Jones a physicist.

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<v Speaker 1>Yeah. I don't think physicists could pull off the Indiana

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<v Speaker 1>Jones hat.

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<v Speaker 2>And we all have daddy issues.

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<v Speaker 1>Hi. I'm Jorge make, cartoonist and the author of Oliver's

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<v Speaker 1>Great Big Universe.

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<v Speaker 2>Hi, I'm Daniel. I'm a particle physicist and a professor

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<v Speaker 2>at UC Irvine, and I always wanted to have physics

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<v Speaker 2>adventures ooh.

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<v Speaker 1>Like real adventures, like in your couch, like, oh no,

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<v Speaker 1>I spilled my coffee.

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<v Speaker 2>I don't think you have to risk your life and

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<v Speaker 2>like get into a spaceship or even become an astronaut

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<v Speaker 2>to have physics adventures. You know, you can explore the

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<v Speaker 2>universe in your mind, make amazing discoveries, and feel like

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<v Speaker 2>you are connecting yourself to the universe.

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<v Speaker 1>I guess technically aren't like real adventures physical adventures. But

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<v Speaker 1>I guess maybe you don't want physical adventures, want physics adventures.

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<v Speaker 2>Yeah, exactly, physics versus.

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<v Speaker 1>Physical phone You don't want to make any physical exertions

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<v Speaker 1>or efforts, just like the mental kind.

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<v Speaker 2>Yeah, but you know, sometimes thinking really hard can make sweat.

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<v Speaker 2>I've definitely perspired while doing intergrals before.

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<v Speaker 1>M I see, have you ever wiped out doing integrals?

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<v Speaker 2>I've never injured myself doing math, that's for sure.

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<v Speaker 1>Well, I guess some people headaches. I guess that's sort

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<v Speaker 1>of cow injury.

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<v Speaker 2>Exactly. Migraines are a hazard of doing physics.

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<v Speaker 1>Yeah, no, I find math very relaxing, actually puts me

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<v Speaker 1>right to sleep. In fact, you should make an a

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<v Speaker 1>f for like a sleep relaxation app. And now we're

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<v Speaker 1>going to do integrals people do like the all time.

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<v Speaker 1>There you go, that's very ASMR and you will be

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<v Speaker 1>subliminally learning math.

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<v Speaker 2>The billion dollar idea right here.

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<v Speaker 1>Yeah, I can finally quit this podcast job. But anyways,

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<v Speaker 1>welcome to our podcast Daniel and Jorge Explain the Universe,

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<v Speaker 1>a production of iHeartRadio.

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<v Speaker 2>In which we do our best to make the complexities

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<v Speaker 2>and the challenges of physics accessible to you and to everybody,

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<v Speaker 2>because we think that the whole point of physics is

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<v Speaker 2>to understand the universe, and not just by a select

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<v Speaker 2>few group of people who can understand nineteen dimensional string

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<v Speaker 2>theory integrals, but by everybody. Because the end science is

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<v Speaker 2>a bunch of stories, mathematical or intuitive or in English,

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<v Speaker 2>and we want to tell those stories to you.

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<v Speaker 1>That's right. We take you through the adventures of science,

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<v Speaker 1>the wipeouts, the close calls, and the headaches of trying

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<v Speaker 1>to find out how the universe works and what are

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<v Speaker 1>place in it is.

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<v Speaker 2>Sometimes these integrals are more annoying than mosquito bites, though

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<v Speaker 2>never as dangerous as jaguars.

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<v Speaker 1>I don't think anything is this annoying is mosquitobiites. Jaguars

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<v Speaker 1>are pretty pesky too. Have you ever seen a jaguar

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<v Speaker 1>in the wild in the wild? Uh no, no, thankfully not.

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<v Speaker 1>Or do you mean like a car the car? I

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<v Speaker 1>think plenty of jaguars around here in South Pasady.

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<v Speaker 2>That's true, and those drivers can be pretty dangerous.

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<v Speaker 1>Yeah, yeah, and annoying like mosquitos.

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<v Speaker 2>You just want to swat all the jaguar drivers.

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<v Speaker 1>No, no, that's a you can get arrested for that

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<v Speaker 1>kind of thing. Yeah, exactly, Well, let me insult them

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<v Speaker 1>on a podcast.

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<v Speaker 2>When you make a billion dollars on your sleep math

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<v Speaker 2>app that you can buy yourself a jaguar and you

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<v Speaker 2>can be the same one.

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<v Speaker 1>I can buy several jaguars and a mosquito repellent.

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<v Speaker 2>Well, I was just wondering, because I know you grew

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<v Speaker 2>up in Panama, if you'd ever seen a jaguar or

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<v Speaker 2>maybe just jaguar sized mosquitoes.

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<v Speaker 1>Oh, I see, I see. That's your your perception of

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<v Speaker 1>how I grew up. I grew up in the hut,

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<v Speaker 1>in the jungle, barefoot, with my little pet jaguar next

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<v Speaker 1>to me. Exactly. I think people will live.

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<v Speaker 2>No, I'm asking paint us the picture.

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<v Speaker 1>I've seen a lot of coyotes around here in the wild. Yes, yeah,

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<v Speaker 1>those are pretty dangerous too. I guess if you're the

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<v Speaker 1>if you're small, you're a small baby or something.

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<v Speaker 2>In our neighborhood, everybody with a small dog puts these

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<v Speaker 2>spiky vests on them so the coyotes can't just snatch

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<v Speaker 2>them up and have a snack.

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<v Speaker 1>Wait, what you turn your dog into a weapon? What

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<v Speaker 1>do you mean is like spy? How dangerous are these spikes?

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<v Speaker 2>They're pretty big because there's a whole epidemic of coyotes

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<v Speaker 2>jumping into people's backyards and like grabbing these little dogs.

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<v Speaker 1>Oh wow, maybe just not keep your dog out at night.

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<v Speaker 1>Don't turn it into dangerous weapon. Like what if the

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<v Speaker 1>dog runs at a little kid or something wearing this

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<v Speaker 1>killer jacket.

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<v Speaker 2>Yeah, these coyotes are pretty brazen. It's not just that night.

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<v Speaker 2>During the full daylight, they will hop in people's backyards

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<v Speaker 2>and make off with their little shit.

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<v Speaker 1>Sues M. Sounds like me. You just just make the

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<v Speaker 1>coyotes your pets, and then that's also the problem, doesn't it. Well, last,

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<v Speaker 1>then you get a problem of jaguars coming in here

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<v Speaker 1>and eating your coyotes.

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<v Speaker 2>And somehow we have to connect all of this back

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<v Speaker 2>to physics.

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<v Speaker 1>Yeah, no, there's a physics zero of sizes right right, yes, sizes. Yes.

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<v Speaker 2>Some problems are hard, like how to protect your little

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<v Speaker 2>pet from neighborhood coyotes, and other problems are hard, like

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<v Speaker 2>how do you figure out the mathematics of the universe?

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<v Speaker 1>It's all connected, yeah, because I guess. Figuring out the

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<v Speaker 1>math of the universe has been one of the goals

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<v Speaker 1>of physics, to understand what's underlying everything that we see

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<v Speaker 1>around us, and all of the mechanics and the motion

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<v Speaker 1>and the energy that is swirling around us, what is

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<v Speaker 1>at the core of the universe.

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<v Speaker 2>Physics has two great theories, two incredible ideas that have

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<v Speaker 2>been very very successful, quantum mechanics and general relativity. But

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<v Speaker 2>bringing them together into an idea of quantum gravity has

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<v Speaker 2>been a challenge that has stood for over a century.

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<v Speaker 2>The greatest minds in physics have tried to take a

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<v Speaker 2>bite out of it, but it seems to be protected

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<v Speaker 2>by a spiky vest that's right.

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<v Speaker 1>It's been one of the hardest problems to solve in

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<v Speaker 1>physics for the last one hundred years, which makes you

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<v Speaker 1>wonder why is it so hard? What's taking so long

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<v Speaker 1>to solve this fundamental problem in physics.

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<v Speaker 2>It's because us physicists haven't just gotten off our couch

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<v Speaker 2>and bush whacked our way into the mathematical jungle.

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<v Speaker 1>Yeah. Yeah, I think that's the problem, Daniel. You need

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<v Speaker 1>to get off your couch an experiment with real gravity,

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<v Speaker 1>not just like imaginary gravity.

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<v Speaker 2>I'm waiting for my Indiana Jones hat to come. You

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<v Speaker 2>can't do it without the right cand of hat. You

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<v Speaker 2>have to be prepared.

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<v Speaker 1>Oh that's right, Yeah, that's right. You don't want to

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<v Speaker 1>get sunburned. It's not like there are other ways to

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<v Speaker 1>protect yourselves from the UV rays.

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<v Speaker 2>I mean, I want to understand the universe, but I'm

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<v Speaker 2>not willing to make physical sacrifices.

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<v Speaker 1>Do you also need a whip? Also?

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<v Speaker 2>I want to whip those integrals into shape for sure.

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<v Speaker 1>Yeah, there you go, crack them into shape. But anyway,

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<v Speaker 1>to be on the podcast, we'll be tackling the question

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<v Speaker 1>why is quantum gravity so hard?

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<v Speaker 3>Now?

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<v Speaker 1>Is this like hard like difficult or hard like tough?

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<v Speaker 2>If your floors are made of quantum gravity and you

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<v Speaker 2>drop your glass, man, is it gonna shatter? Yeah?

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<v Speaker 1>But how is it going to fall without gravity? Quantum mechanics,

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<v Speaker 1>I answered everything, it's gonna fall and not fall. No.

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<v Speaker 2>I love that physics has a name for this theory

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<v Speaker 2>quantum gravity, but it's just kind of like a placeholder.

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<v Speaker 2>We don't know what it is, or how it works,

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<v Speaker 2>or what the mathematics of it are. People argue about

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<v Speaker 2>different approaches. We already have a name for it, but

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<v Speaker 2>we haven't even figured it out yet.

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<v Speaker 1>Sounds unbrand for how physicists name thinks. Well, anyways, we're wondering,

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<v Speaker 1>as usual, how many people out there had thought about

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<v Speaker 1>this question of why quantum gravity is so hard? As usual,

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<v Speaker 1>Daniel went out there and God answers from real people.

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<v Speaker 2>Thank you to all the real people and definitely not

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<v Speaker 2>made up had GPT inspired bots who answered this question.

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<v Speaker 2>If you are a real person and you'd like to

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<v Speaker 2>answer future questions, please write to me two questions at

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<v Speaker 2>Danielandjorge dot com.

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<v Speaker 1>So think about it for a second. Why do you

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<v Speaker 1>think quantum gravity is so hard to solve? Here's what

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<v Speaker 1>people had to say.

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<v Speaker 3>I know that.

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<v Speaker 4>Quantic mechanic is very good explaining things that happen in

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<v Speaker 4>very smallst scale, and gravity is not very strong and

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<v Speaker 4>small as scale.

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<v Speaker 1>I don't know.

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<v Speaker 4>I think that's the reason, but I don't really I

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<v Speaker 4>don't really know.

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<v Speaker 1>I honestly don't have an intelligent answer for that. But

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<v Speaker 1>I will say this, if Albert Einstein was afraid of it,

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<v Speaker 1>that I am too.

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<v Speaker 4>It's hard because we are trying to apply our comparatively

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<v Speaker 4>super massive vantage point to these tiny particles in the

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<v Speaker 4>quantum realm that probably don't even know the difference.

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<v Speaker 2>They probably don't even know that gravity is a force.

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<v Speaker 2>Did you mean real people as opposed to chat GPT

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<v Speaker 2>or real people as opposed to physicists. I'm just now

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<v Speaker 2>realizing that was a jab.

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<v Speaker 1>I mean, like not paid actors. Okay, although maybe you

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<v Speaker 1>should include a chatgypt answer every every time we do this. Interesting. Yeah,

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<v Speaker 1>that's right now. What does chat GPT say about quantum

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<v Speaker 1>gravity being so hard?

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<v Speaker 2>Chatchipt says quantum gravity is consider challenging because it involves

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<v Speaker 2>the attempt to reconcile two fundamental theories of physics, quantum

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<v Speaker 2>mechanics and general relativity. Each of these has been incredibly

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<v Speaker 2>successful in its own but it becomes problematic when combined.

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<v Speaker 1>Whoa it just did the podcast for us? Done? AI

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<v Speaker 1>did replace? In our job? Does a chat GPT have

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<v Speaker 1>like a like a voice out. Can you have it

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<v Speaker 1>read the answer?

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<v Speaker 2>I think the free version that I have access to

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<v Speaker 2>you can't do images or voices. So no, you cannot

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<v Speaker 2>be replaced by chat jipt just yet.

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<v Speaker 1>Oh right, you still need us to read the answer

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<v Speaker 1>chat GPT gives out. I see.

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<v Speaker 2>Also, I would never rely on chat CHEPT. I asked

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<v Speaker 2>some hard physics questions sometimes and it just makes up balogney. Oh.

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<v Speaker 1>I think the news here is that you're asking chat

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<v Speaker 1>GPT for answers.

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<v Speaker 2>Yeah, I like everybody else, I was curious when it

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<v Speaker 2>came out, what you like to talk to the average

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<v Speaker 2>of the internet wisdom and follies, And the answer is

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<v Speaker 2>it's not very reliable.

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<v Speaker 1>Well, technically, neither are we, Daniel. I don't think we're

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<v Speaker 1>gonna have a hard answer here today.

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<v Speaker 2>No, but we're not going to make stuff up.

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<v Speaker 1>Well, So let's dig into this question. Why is quantum

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<v Speaker 1>gravity so hard? Why is it so difficult? Why has

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<v Speaker 1>it puzzled physicists for over one hundred years? So let's

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<v Speaker 1>start with the basics, Daniel, what is quantum gravity?

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<v Speaker 2>So chatchapt got this bit right. Quant gravity is an

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<v Speaker 2>attempt to bring together are two great theories of physics.

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<v Speaker 2>Quantum mechanics that describes things like electromagnetism and how particles

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<v Speaker 2>work and gives us a probabilistic picture of the universe,

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<v Speaker 2>and general relativity that described space and time and gravity

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<v Speaker 2>and explains things like the expansion of the universe and

0:12:21.480 --> 0:12:25.440
<v Speaker 2>how things move through space and time. And both of

0:12:25.440 --> 0:12:28.760
<v Speaker 2>these work really really well in their own regime. Quantum

0:12:28.800 --> 0:12:32.080
<v Speaker 2>mechanics for the small stuff, general relativity for the big stuff.

0:12:32.480 --> 0:12:34.920
<v Speaker 2>Quantum gravity is an attempt to have a single consistent

0:12:34.960 --> 0:12:36.960
<v Speaker 2>theory that works for all the stuff.

0:12:37.280 --> 0:12:41.079
<v Speaker 1>And these were developed independently, sort of right like, while

0:12:41.240 --> 0:12:44.840
<v Speaker 1>Einstein was coming up with general relativity, other people were

0:12:44.880 --> 0:12:47.720
<v Speaker 1>thinking about things at the smallest level and why they

0:12:47.800 --> 0:12:51.080
<v Speaker 1>were it quantized right exactly.

0:12:51.120 --> 0:12:54.800
<v Speaker 2>They were developed independently, though, around the same time, and

0:12:54.840 --> 0:12:57.960
<v Speaker 2>both were actually sparked by Einstein. Quantum mechanics really got

0:12:58.000 --> 0:13:02.520
<v Speaker 2>its kickoff from Einstein's realism that the photoelectric effect, what

0:13:02.600 --> 0:13:04.920
<v Speaker 2>happens when you shine a bright light at a piece

0:13:04.920 --> 0:13:07.320
<v Speaker 2>of metal, can only be explained by the fact that

0:13:07.320 --> 0:13:10.480
<v Speaker 2>photons were little packets. They were quantized. They weren't just

0:13:10.559 --> 0:13:14.240
<v Speaker 2>continuous beams of energy because what you saw was as

0:13:14.280 --> 0:13:16.840
<v Speaker 2>you turned up the energy of that beam of light,

0:13:16.920 --> 0:13:20.560
<v Speaker 2>you didn't get electrons with more energy boiling off. You

0:13:20.640 --> 0:13:24.040
<v Speaker 2>got more electrons because each one just gets one servant,

0:13:24.160 --> 0:13:27.080
<v Speaker 2>one photon. That was explained by saying the beam of

0:13:27.120 --> 0:13:30.079
<v Speaker 2>light had more photons in it, not just a brighter beam.

0:13:30.600 --> 0:13:33.480
<v Speaker 2>So Einstein kicked off quantum mechanics around the turn of

0:13:33.520 --> 0:13:36.280
<v Speaker 2>the century, and at the same time he developed his

0:13:36.400 --> 0:13:40.560
<v Speaker 2>theory of special relativity and general relativity that explained the

0:13:40.600 --> 0:13:43.520
<v Speaker 2>apparent force of gravity. And these two have been in

0:13:43.600 --> 0:13:46.760
<v Speaker 2>parallel development over the last hundred years, but nobody's been

0:13:46.800 --> 0:13:49.760
<v Speaker 2>able to bring them together into one picture of how

0:13:49.760 --> 0:13:50.920
<v Speaker 2>the universe works.

0:13:51.559 --> 0:13:53.280
<v Speaker 1>I guess maybe the question is why do you want

0:13:53.320 --> 0:13:55.360
<v Speaker 1>to bring them together? Like, if you have one that

0:13:55.400 --> 0:13:58.160
<v Speaker 1>works really well for some things and the other one

0:13:58.200 --> 0:14:01.800
<v Speaker 1>works well for other things, what's the need to unify them?

0:14:01.880 --> 0:14:02.800
<v Speaker 2>Yeah, it's a fair question.

0:14:02.840 --> 0:14:03.040
<v Speaker 1>You know.

0:14:03.120 --> 0:14:05.280
<v Speaker 2>Sometimes in life we have things that are separate, Like

0:14:05.559 --> 0:14:07.480
<v Speaker 2>you got one group of friends and another group of friends,

0:14:07.480 --> 0:14:11.400
<v Speaker 2>you bring them together, it's awkward. You don't do it again, right, Yeah,

0:14:11.600 --> 0:14:15.040
<v Speaker 2>they're usually a bad idea, And I guess in this

0:14:15.120 --> 0:14:17.400
<v Speaker 2>case there are two answers. One is philosophical and the

0:14:17.440 --> 0:14:21.040
<v Speaker 2>other really is experimental. Philosophically, we just think that the

0:14:21.120 --> 0:14:24.760
<v Speaker 2>universe probably does have a single set of laws. You know,

0:14:24.800 --> 0:14:28.680
<v Speaker 2>there should be one explanation for why something happens. You know,

0:14:28.720 --> 0:14:31.160
<v Speaker 2>the same way like when a computer program runs, it's

0:14:31.240 --> 0:14:33.320
<v Speaker 2>running with one source code. It's not like there's two

0:14:33.360 --> 0:14:36.920
<v Speaker 2>codes there battling it out. There should be one explanation.

0:14:37.560 --> 0:14:39.800
<v Speaker 2>And this is just sort of like a philosophical preference.

0:14:39.880 --> 0:14:42.880
<v Speaker 2>It would be nice if the universe had a single,

0:14:43.040 --> 0:14:46.200
<v Speaker 2>unified theory. It would sort of make sense to our brains.

0:14:46.200 --> 0:14:47.960
<v Speaker 2>That doesn't mean it has to happen. It's just sort

0:14:48.000 --> 0:14:49.800
<v Speaker 2>of like a philosophical preference.

0:14:51.400 --> 0:14:55.040
<v Speaker 1>Well, maybe explain to folks how they're separate. So, for example,

0:14:55.200 --> 0:14:59.680
<v Speaker 1>quantum mechanics works to describe what exactly, like the motion

0:15:00.520 --> 0:15:04.840
<v Speaker 1>or of little tiny particles or their interactions, or what

0:15:04.960 --> 0:15:06.760
<v Speaker 1>exactly does quantum mechanics do.

0:15:07.440 --> 0:15:11.480
<v Speaker 2>Quantum mechanics describes everything about tiny little particles, their motion,

0:15:11.680 --> 0:15:15.160
<v Speaker 2>their interactions, what's going to happen, what's not going to happen.

0:15:15.680 --> 0:15:18.680
<v Speaker 2>If you have, for example, two electrons and they're interacting

0:15:18.680 --> 0:15:21.600
<v Speaker 2>with each other, quantum mechanics tells you what's going to happen.

0:15:21.840 --> 0:15:24.120
<v Speaker 2>You make two electron beams, you shoot them at each other.

0:15:24.400 --> 0:15:27.360
<v Speaker 2>Quantum mechanics tells you the probabilities of what will come

0:15:27.400 --> 0:15:30.560
<v Speaker 2>out of those collisions, or if you replace an electron

0:15:30.560 --> 0:15:32.240
<v Speaker 2>with a muon, or you put in a quark or

0:15:32.280 --> 0:15:35.080
<v Speaker 2>a proton or whatever. Quantum mechanics is the rules of

0:15:35.120 --> 0:15:38.880
<v Speaker 2>all of those interactions, and the standard model of particle

0:15:38.920 --> 0:15:41.280
<v Speaker 2>physics what we talk about on this podcast all the

0:15:41.320 --> 0:15:44.960
<v Speaker 2>time that has been super successful in explaining the structure

0:15:45.000 --> 0:15:48.040
<v Speaker 2>of matter deep down inside the atom and why everything's

0:15:48.080 --> 0:15:51.240
<v Speaker 2>bound together and how that all works. That's all quantum mechanics.

0:15:51.240 --> 0:15:55.000
<v Speaker 2>It's all fundamentally quantum mechanics. Every little bit of it

0:15:55.080 --> 0:15:58.320
<v Speaker 2>is quantum mechanical, and it's quantum mechanical because it paints

0:15:58.320 --> 0:16:01.240
<v Speaker 2>this picture of how the universe works that's very different

0:16:01.240 --> 0:16:04.120
<v Speaker 2>from the way that our universe seems to work, the

0:16:04.160 --> 0:16:07.200
<v Speaker 2>one on our level you know about baseballs and planets

0:16:07.200 --> 0:16:10.600
<v Speaker 2>and basketballs, where things have like smooth paths. It tells

0:16:10.680 --> 0:16:13.600
<v Speaker 2>us that fundamentally the universe follows very different rules. That

0:16:13.720 --> 0:16:18.280
<v Speaker 2>quantum objects, tiny little bits, only have probabilities to go places.

0:16:18.280 --> 0:16:20.160
<v Speaker 2>They don't have smooth.

0:16:19.840 --> 0:16:22.240
<v Speaker 1>Paths, right, thinks are kind of fuzzy down at the

0:16:22.280 --> 0:16:25.680
<v Speaker 1>microscopic level. What does general relativity do exactly?

0:16:25.840 --> 0:16:30.600
<v Speaker 2>So general relativity explains space and time and gravity, So

0:16:30.640 --> 0:16:33.320
<v Speaker 2>it says that what Newton described as a force of

0:16:33.360 --> 0:16:37.720
<v Speaker 2>gravity is actually just objects moving through curved space. Newton

0:16:37.720 --> 0:16:40.680
<v Speaker 2>imagined space was absolute as this backdrop of the universe,

0:16:41.080 --> 0:16:43.760
<v Speaker 2>and then things with mass had a force between them.

0:16:44.040 --> 0:16:44.240
<v Speaker 1>You know.

0:16:44.280 --> 0:16:47.080
<v Speaker 2>He famously explained that apple dropping and also the Moon

0:16:47.280 --> 0:16:51.080
<v Speaker 2>orbiting the Earth unified in his law of gravity as

0:16:51.080 --> 0:16:54.480
<v Speaker 2>an attraction between mass. But Einstein tells us that that's

0:16:54.520 --> 0:16:57.640
<v Speaker 2>not the case. General relativity tells us that actually things

0:16:57.680 --> 0:17:00.920
<v Speaker 2>are just moving through the curvature of space. Space itself

0:17:00.960 --> 0:17:04.280
<v Speaker 2>is curved when mass is nearby, and that changes the

0:17:04.440 --> 0:17:08.399
<v Speaker 2>natural inertial path of objects. Objects will move in what

0:17:08.480 --> 0:17:11.200
<v Speaker 2>looks like curves even without accelerating.

0:17:11.480 --> 0:17:14.800
<v Speaker 1>And space gets spent by gravity, right or gravity is

0:17:14.840 --> 0:17:15.800
<v Speaker 1>the bending of space.

0:17:15.880 --> 0:17:20.000
<v Speaker 2>Right, base gets spent by energy in a very complex way. Essentially,

0:17:20.040 --> 0:17:22.480
<v Speaker 2>mass is a kind of energy, so it helps bend space,

0:17:22.640 --> 0:17:24.800
<v Speaker 2>but it's not the only way you can bend space.

0:17:25.200 --> 0:17:27.280
<v Speaker 2>And gravity is sort of a fuzzy term. Now, it's like,

0:17:27.320 --> 0:17:30.080
<v Speaker 2>are you referring to the Newtonian force, which isn't really

0:17:30.119 --> 0:17:32.720
<v Speaker 2>part of our picture anymore, or you're talking about the

0:17:32.720 --> 0:17:35.560
<v Speaker 2>whole theory of general relativity as an explanation for it.

0:17:35.880 --> 0:17:38.800
<v Speaker 2>But you know, what we describe as gravity things seeming

0:17:38.800 --> 0:17:42.119
<v Speaker 2>to fall down, is explained by Einstein, is things just

0:17:42.200 --> 0:17:44.360
<v Speaker 2>following the curvature of space.

0:17:44.400 --> 0:17:48.640
<v Speaker 1>Which which gets a curved because of the presence of energy. Right,

0:17:48.680 --> 0:17:51.440
<v Speaker 1>that's the basic and that effect. Basically you can sort

0:17:51.440 --> 0:17:53.920
<v Speaker 1>of lump it into the idea of gravity.

0:17:54.320 --> 0:17:57.120
<v Speaker 2>Yeah, exactly. And we had a whole podcast digging deep

0:17:57.160 --> 0:18:00.240
<v Speaker 2>into like why gravity isn't the force and how if

0:18:00.280 --> 0:18:02.440
<v Speaker 2>you're moving along with the curture of space time you

0:18:02.480 --> 0:18:05.719
<v Speaker 2>don't feel any acceleration even if other people see you,

0:18:05.800 --> 0:18:08.560
<v Speaker 2>like moving in circles or moving towards the center of

0:18:08.640 --> 0:18:11.280
<v Speaker 2>the Earth, all that kind of stuff. It's a really

0:18:11.280 --> 0:18:14.320
<v Speaker 2>fascinating different way to think about how the universe works.

0:18:14.320 --> 0:18:17.399
<v Speaker 2>It tells a very different story from Newton's, but it

0:18:17.440 --> 0:18:19.840
<v Speaker 2>mostly describes really really big stuff because you need a

0:18:19.840 --> 0:18:23.080
<v Speaker 2>lot of mass to curve space, and that curvature is

0:18:23.160 --> 0:18:25.359
<v Speaker 2>kind of gentle, so the effect of that curvature is

0:18:25.400 --> 0:18:28.640
<v Speaker 2>hard to measure, especially compared to these quantum forces, which

0:18:28.640 --> 0:18:31.600
<v Speaker 2>are extraordinarily powerful in comparison.

0:18:32.040 --> 0:18:34.639
<v Speaker 1>All right, so now maybe paint us a picture of

0:18:34.760 --> 0:18:38.760
<v Speaker 1>how they are not unified, Like can I just have

0:18:38.880 --> 0:18:43.280
<v Speaker 1>some quantum particles interacting in a gravitational field? Or can

0:18:43.359 --> 0:18:46.120
<v Speaker 1>I just have the path of a quantum particle bent

0:18:46.320 --> 0:18:49.600
<v Speaker 1>by the bending of space and time. What doesn't these

0:18:49.600 --> 0:18:52.560
<v Speaker 1>two things do together? Like, what are scenarios in which

0:18:52.640 --> 0:18:53.520
<v Speaker 1>they exclude each other?

0:18:53.680 --> 0:18:55.280
<v Speaker 2>Yeah? Great, And so this is sort of like number

0:18:55.320 --> 0:18:58.439
<v Speaker 2>two reason why we want to unify them, because in

0:18:58.480 --> 0:19:01.840
<v Speaker 2>some situations they disc Like we talked earlier about having

0:19:01.840 --> 0:19:04.560
<v Speaker 2>separate theories of the universe, Maybe that's cool, but it's

0:19:04.600 --> 0:19:07.040
<v Speaker 2>not cool if they're talking about the same phenomenon. If

0:19:07.040 --> 0:19:10.040
<v Speaker 2>you're asking them the question what happens here? Most of

0:19:10.080 --> 0:19:12.160
<v Speaker 2>the time you can keep them separate because for tiny,

0:19:12.160 --> 0:19:15.080
<v Speaker 2>little particles you can ignore gravity. Gravity is very very

0:19:15.119 --> 0:19:18.119
<v Speaker 2>weak for little particles, and for really big stuff, quantum

0:19:18.119 --> 0:19:20.399
<v Speaker 2>effects mostly average out. You don't need to know quantum

0:19:20.440 --> 0:19:23.119
<v Speaker 2>mechanics to predict the path of a baseball. But in

0:19:23.160 --> 0:19:27.359
<v Speaker 2>some scenarios they do disagree, things like what happens inside

0:19:27.400 --> 0:19:30.240
<v Speaker 2>a black hole. That's a scenario where you have really

0:19:30.280 --> 0:19:34.160
<v Speaker 2>powerful gravity so gravity can no longer be ignored. And

0:19:34.400 --> 0:19:37.240
<v Speaker 2>things are very very small because we think that things

0:19:37.280 --> 0:19:40.600
<v Speaker 2>are super compressed inside a black hole, so quantum effects

0:19:40.720 --> 0:19:45.720
<v Speaker 2>are important. So super duper massive, very very tiny objects,

0:19:46.000 --> 0:19:49.760
<v Speaker 2>quantum mechanics and general relativity disagree about what happens there,

0:19:50.240 --> 0:19:52.960
<v Speaker 2>and so the universe can't have a contradiction. Two theories

0:19:52.960 --> 0:19:55.160
<v Speaker 2>tell different stories. They can't both be right.

0:19:55.480 --> 0:19:57.600
<v Speaker 1>But I guess I mean, in like an everyday scenario,

0:19:57.720 --> 0:20:00.639
<v Speaker 1>do they work together? Sort of like a man imagining

0:20:00.720 --> 0:20:04.520
<v Speaker 1>say a microscopic particle, like an electron out there in

0:20:04.560 --> 0:20:07.679
<v Speaker 1>the near Earth orbit and it's floating out there in

0:20:07.680 --> 0:20:10.520
<v Speaker 1>space close to the Earth. Does it get pulled by gravity?

0:20:10.840 --> 0:20:12.919
<v Speaker 1>Is it going to fall down to Earth? Is there

0:20:12.960 --> 0:20:15.840
<v Speaker 1>a problem with me trying to use quantum mechanics to

0:20:16.080 --> 0:20:17.400
<v Speaker 1>model how it falls to Earth?

0:20:17.840 --> 0:20:20.119
<v Speaker 2>Yeah, so you might think, can't we just test quantum

0:20:20.200 --> 0:20:23.160
<v Speaker 2>gravity and figure out what the answer is, which one's

0:20:23.240 --> 0:20:26.560
<v Speaker 2>right by looking at the gravity of a tiny quantum particle, Right,

0:20:26.640 --> 0:20:28.840
<v Speaker 2>So that's what you're asking. What happens for the Earth's

0:20:28.880 --> 0:20:30.359
<v Speaker 2>gravity on an electron?

0:20:30.560 --> 0:20:32.320
<v Speaker 1>Yeah? Like, do the two theories break down or do

0:20:32.400 --> 0:20:35.840
<v Speaker 1>they agree on their normal conditions that are not inside

0:20:35.880 --> 0:20:36.480
<v Speaker 1>of a black hole.

0:20:36.560 --> 0:20:38.919
<v Speaker 2>So the two do not agree about what happens to

0:20:38.960 --> 0:20:41.679
<v Speaker 2>an electron in the Earth's gravitational field.

0:20:41.840 --> 0:20:42.359
<v Speaker 1>They don't.

0:20:42.680 --> 0:20:45.320
<v Speaker 2>They don't, but they're not both relevant at the same time.

0:20:45.400 --> 0:20:47.520
<v Speaker 2>It's a little tricky, and the issue is how do

0:20:47.560 --> 0:20:50.920
<v Speaker 2>you calculate the gravitational field of the electron, or even

0:20:50.920 --> 0:20:54.200
<v Speaker 2>the gravitational force on the electron, or the effective curve

0:20:54.280 --> 0:20:57.200
<v Speaker 2>space however you want to say it, because that depends

0:20:57.240 --> 0:21:01.520
<v Speaker 2>on where the electron is. Electron is a little quantum

0:21:01.520 --> 0:21:04.359
<v Speaker 2>particle with quantum effects. Then maybe it has like a

0:21:04.400 --> 0:21:06.760
<v Speaker 2>fifty percent chance to be at this altitude and fifty

0:21:06.720 --> 0:21:09.160
<v Speaker 2>percent chance to be at that altitude, in which case

0:21:09.200 --> 0:21:12.600
<v Speaker 2>it would feel different amounts of gravity. And so how

0:21:12.640 --> 0:21:15.159
<v Speaker 2>do you calculate the gravity on a quantum particle, We

0:21:15.200 --> 0:21:18.320
<v Speaker 2>don't know. The theory of quantum gravity would tell us

0:21:18.359 --> 0:21:21.159
<v Speaker 2>how to do that, but general relativity doesn't tell us

0:21:21.200 --> 0:21:23.640
<v Speaker 2>how to do that. General relativity requires that you know

0:21:23.840 --> 0:21:28.800
<v Speaker 2>where the electron is, and so it ignores its quantum nature.

0:21:29.160 --> 0:21:31.160
<v Speaker 2>So if the quantum nature of the electron is important,

0:21:31.160 --> 0:21:34.000
<v Speaker 2>it's doing quantumy stuff, then we don't know how to

0:21:34.040 --> 0:21:35.760
<v Speaker 2>calculate the force of gravity.

0:21:35.800 --> 0:21:36.000
<v Speaker 3>On it.

0:21:36.040 --> 0:21:39.399
<v Speaker 2>But also we can't measure the force of gravity on

0:21:39.440 --> 0:21:42.119
<v Speaker 2>a tiny little object because the force is so small

0:21:42.160 --> 0:21:43.639
<v Speaker 2>because its mass is so small.

0:21:44.600 --> 0:21:48.040
<v Speaker 1>Sounds like a great situation and maybe one that we

0:21:48.119 --> 0:21:50.160
<v Speaker 1>need a little bit more time on. So let's dig

0:21:50.160 --> 0:21:54.040
<v Speaker 1>into that scenario and dig into well, how exactly these

0:21:54.080 --> 0:21:56.720
<v Speaker 1>two theories don't match up, and then we'll get into

0:21:56.880 --> 0:21:58.800
<v Speaker 1>a little bit of the math that makes it so

0:21:58.880 --> 0:22:00.879
<v Speaker 1>hard to integrate the tube. So let's do that. But

0:22:00.920 --> 0:22:16.080
<v Speaker 1>first let's take a quick break. All right, we're talking

0:22:16.119 --> 0:22:20.800
<v Speaker 1>about why quantum gravity theory that unites quantum mechanics and

0:22:20.960 --> 0:22:24.400
<v Speaker 1>general relativity it's so hard to come up with and

0:22:24.440 --> 0:22:28.320
<v Speaker 1>to make these two theories play well together. And so Daniel,

0:22:28.320 --> 0:22:31.159
<v Speaker 1>we're talking about a scenario in which I have an

0:22:31.200 --> 0:22:34.600
<v Speaker 1>electron in near Earth orbit. It's out there in space

0:22:34.800 --> 0:22:37.520
<v Speaker 1>above the atmosphere, and I'm trying to figure out what's

0:22:37.520 --> 0:22:39.439
<v Speaker 1>going to happen to this electron. Is it going to

0:22:39.440 --> 0:22:42.000
<v Speaker 1>fall to Earth? What path is it going to take

0:22:42.080 --> 0:22:44.960
<v Speaker 1>as it falls to Earth? And you're saying that it's

0:22:45.000 --> 0:22:48.120
<v Speaker 1>hard to theoretically predict what's going to happen, right, because

0:22:48.160 --> 0:22:50.760
<v Speaker 1>it's definitely going to fall if I put an electron

0:22:50.800 --> 0:22:54.320
<v Speaker 1>on your Earth, right, like it's going to do something,

0:22:54.560 --> 0:22:56.399
<v Speaker 1>but we don't really have a good theory to predict

0:22:56.440 --> 0:22:57.080
<v Speaker 1>what it's going to do.

0:22:57.160 --> 0:22:59.280
<v Speaker 2>Is that what you're saying, we can't be very very

0:22:59.280 --> 0:23:02.640
<v Speaker 2>precise about its predictions. We can be approximate. Like, there's

0:23:02.640 --> 0:23:04.959
<v Speaker 2>two approaches you can take. You can say, I'm going

0:23:05.000 --> 0:23:06.879
<v Speaker 2>to ignore the quantum mechanical part of it. I'm just

0:23:06.920 --> 0:23:09.440
<v Speaker 2>going to treat the electron like it's a tiny little

0:23:09.520 --> 0:23:12.320
<v Speaker 2>rock or a tiny little ball. I'm going to calculate

0:23:12.320 --> 0:23:15.000
<v Speaker 2>its gravity and I think about how it's basically in

0:23:15.200 --> 0:23:17.600
<v Speaker 2>orbit around the Earth. And you can do that and

0:23:17.640 --> 0:23:20.640
<v Speaker 2>you get very good predictions, and you can calculate how

0:23:20.640 --> 0:23:22.920
<v Speaker 2>things boil off the top of the atmosphere or they

0:23:22.960 --> 0:23:25.800
<v Speaker 2>fall to Earth, or whether they're in stable orbits or not.

0:23:25.880 --> 0:23:29.200
<v Speaker 2>So basically, ignore the quantum nature of the electron, treat

0:23:29.200 --> 0:23:32.479
<v Speaker 2>it like a tiny classical object and do gravity on it.

0:23:32.720 --> 0:23:33.520
<v Speaker 2>That's one approach.

0:23:33.640 --> 0:23:36.440
<v Speaker 1>But then you're saying it's hard to know how much

0:23:36.440 --> 0:23:40.159
<v Speaker 1>gravity is applied to the electron because of quantum mechanics,

0:23:40.320 --> 0:23:42.800
<v Speaker 1>or is it hard? Can you just say, like the

0:23:42.960 --> 0:23:45.640
<v Speaker 1>electron has this much mass and it's a little tiny rock,

0:23:45.680 --> 0:23:48.000
<v Speaker 1>and so that's how much gravity's going to feel or

0:23:48.119 --> 0:23:49.560
<v Speaker 1>is that at some level wrong?

0:23:49.800 --> 0:23:52.399
<v Speaker 2>Well, that's at some level wrong because you're ignoring the

0:23:52.480 --> 0:23:54.480
<v Speaker 2>quantum nature of the electron. You're treating it like a

0:23:54.520 --> 0:23:56.239
<v Speaker 2>tiny rock, and it's not a tiny rock.

0:23:56.359 --> 0:23:57.919
<v Speaker 1>Yeah, but I guess. I mean, like, if you do

0:23:58.000 --> 0:24:01.000
<v Speaker 1>treat it like a rock, do you get something wildly

0:24:01.080 --> 0:24:03.560
<v Speaker 1>off or do you get something that seems to be

0:24:03.600 --> 0:24:04.440
<v Speaker 1>pretty exact?

0:24:04.720 --> 0:24:06.840
<v Speaker 2>You get something that works pretty well. As long as

0:24:06.840 --> 0:24:09.440
<v Speaker 2>it doesn't have any interactions. As long as that electron

0:24:09.520 --> 0:24:12.639
<v Speaker 2>is not interacting with any other particles, it's mostly just

0:24:12.680 --> 0:24:15.720
<v Speaker 2>ignoring them, then yeah, you get something that's correct.

0:24:15.520 --> 0:24:17.320
<v Speaker 1>Like it's going to follow the same path as a

0:24:17.320 --> 0:24:17.879
<v Speaker 1>little rock.

0:24:18.240 --> 0:24:20.520
<v Speaker 2>Yes, as long as it's not interacting. But if it's

0:24:20.560 --> 0:24:22.879
<v Speaker 2>in a soup of other electrons and charged particles and

0:24:22.920 --> 0:24:26.320
<v Speaker 2>it's interacting with those, then boom, it's quantum nature becomes

0:24:26.400 --> 0:24:31.720
<v Speaker 2>important and those quantum effects dwarf gravity. They completely take over.

0:24:32.320 --> 0:24:34.840
<v Speaker 2>So you can either ignore the quantum effects and just

0:24:34.880 --> 0:24:37.480
<v Speaker 2>do the gravity, or you can ignore the gravity and

0:24:37.680 --> 0:24:41.040
<v Speaker 2>just do the quantum effects. For an electron, only one

0:24:41.080 --> 0:24:43.920
<v Speaker 2>of those is relevant at a time, and that's why

0:24:43.960 --> 0:24:46.679
<v Speaker 2>you don't need quantum gravity to think about electrons. You

0:24:46.680 --> 0:24:50.440
<v Speaker 2>can do either quantum mechanics or gravity. They're never both

0:24:50.560 --> 0:24:51.800
<v Speaker 2>relevant at the same time.

0:24:52.160 --> 0:24:54.359
<v Speaker 1>But I guess to an approximation. So then when do

0:24:54.400 --> 0:24:56.240
<v Speaker 1>you get into trouble? Like when is it a problem

0:24:56.240 --> 0:24:58.760
<v Speaker 1>that these two are not unified? But what's the scenario?

0:24:58.880 --> 0:25:02.000
<v Speaker 1>Like it's in gravitaational orbit around the Earth, the electron

0:25:02.200 --> 0:25:04.600
<v Speaker 1>is and it's sort of a little bit interacting with

0:25:04.640 --> 0:25:06.879
<v Speaker 1>another electron. Then it's like we don't know what to do.

0:25:07.119 --> 0:25:09.639
<v Speaker 2>As long as it has a quantum interaction, that's just

0:25:09.680 --> 0:25:12.720
<v Speaker 2>going to dominate because the quantum forces are so much

0:25:12.760 --> 0:25:16.000
<v Speaker 2>more powerful than gravity. You know, they're like ten to

0:25:16.040 --> 0:25:18.600
<v Speaker 2>the thirty times as powerful as gravity.

0:25:18.920 --> 0:25:21.440
<v Speaker 1>But like what if it's like ten to thirty one

0:25:21.560 --> 0:25:24.720
<v Speaker 1>times further away, wouldn't it be at the same level

0:25:24.720 --> 0:25:25.280
<v Speaker 1>of gravity.

0:25:25.440 --> 0:25:28.640
<v Speaker 2>I mean gravity falls with distance just like quantum forces do. Right,

0:25:28.840 --> 0:25:31.080
<v Speaker 2>So it's not a matter of distance, it's a matter

0:25:31.119 --> 0:25:34.040
<v Speaker 2>of the mass to charge ratio. Like if you have

0:25:34.080 --> 0:25:38.080
<v Speaker 2>two electrons, they feel a very strong electromagnetic repulsion because

0:25:38.080 --> 0:25:41.320
<v Speaker 2>of their charge. They don't feel a very strong gravitational

0:25:41.359 --> 0:25:44.840
<v Speaker 2>attraction because of their mass. The electromagnetic force there is

0:25:44.880 --> 0:25:47.360
<v Speaker 2>always more powerful at any distance.

0:25:47.520 --> 0:25:49.760
<v Speaker 1>I thought maybe the scenario you're trying to paint was like,

0:25:49.760 --> 0:25:52.320
<v Speaker 1>I have an electron out there in space, and it's

0:25:52.320 --> 0:25:55.680
<v Speaker 1>been attracted by gravity to the giant Earth, but maybe

0:25:55.680 --> 0:25:59.040
<v Speaker 1>it's also sort of being repelled by another electron that's nearby,

0:25:59.480 --> 0:26:01.040
<v Speaker 1>and so then we don't know what's going to happen.

0:26:01.320 --> 0:26:03.600
<v Speaker 2>You have a scenario we have a single electron orbiting

0:26:03.640 --> 0:26:06.760
<v Speaker 2>the Earth, and then some very distant electron is very

0:26:06.760 --> 0:26:09.679
<v Speaker 2>gently pushing on it with the same power as the

0:26:09.800 --> 0:26:11.120
<v Speaker 2>gravity of the entire Earth.

0:26:11.400 --> 0:26:14.000
<v Speaker 1>Yes, Is that like the scenario that you run into

0:26:14.000 --> 0:26:15.919
<v Speaker 1>problems or can you still handle it?

0:26:16.400 --> 0:26:19.600
<v Speaker 2>No, that's a cool idea. That's a scenario where gravity

0:26:19.760 --> 0:26:22.439
<v Speaker 2>and quantum forces are at the same level, and so

0:26:22.600 --> 0:26:24.880
<v Speaker 2>you can't ignore one of them. You have to take

0:26:24.920 --> 0:26:27.119
<v Speaker 2>both into account, and we don't know how to do

0:26:27.160 --> 0:26:30.120
<v Speaker 2>that prediction. That kind of experiment is also pretty hard

0:26:30.160 --> 0:26:33.880
<v Speaker 2>to realize because you need an isolated electron affected by

0:26:34.000 --> 0:26:37.760
<v Speaker 2>only one other electron that's super far away, So it's

0:26:37.800 --> 0:26:40.320
<v Speaker 2>not like practically something we could set up. Otherwise that

0:26:40.320 --> 0:26:42.200
<v Speaker 2>would be really awesome. It would tell us something about

0:26:42.280 --> 0:26:43.080
<v Speaker 2>quantum gravity.

0:26:43.160 --> 0:26:45.960
<v Speaker 1>Yeah, yeah, But that's a physical problem about a physics problem,

0:26:46.080 --> 0:26:49.000
<v Speaker 1>so you know, are couch surfing and Dana Jones doesn't care.

0:26:49.080 --> 0:26:50.960
<v Speaker 2>The other way to tackle this is to say, well,

0:26:50.960 --> 0:26:53.640
<v Speaker 2>what if you have a really really massive quantum particle

0:26:53.880 --> 0:26:57.080
<v Speaker 2>particle that is feeling quantum forces but actually has enough

0:26:57.119 --> 0:27:00.440
<v Speaker 2>mass that it's gravity can't be ignored, and that's when

0:27:00.440 --> 0:27:01.000
<v Speaker 2>you end up at.

0:27:00.920 --> 0:27:03.800
<v Speaker 1>A black hole? All right? So can you be more

0:27:03.800 --> 0:27:06.640
<v Speaker 1>specific about what the problem is, like we don't know

0:27:06.680 --> 0:27:09.200
<v Speaker 1>how to tell what the particle is going to do next,

0:27:09.480 --> 0:27:11.439
<v Speaker 1>or we can't predict how it's going to interact. Can

0:27:11.480 --> 0:27:14.520
<v Speaker 1>you describing words what the problem is at the indecentnarios?

0:27:14.680 --> 0:27:17.240
<v Speaker 2>The problem is that our two theories, general relativity and

0:27:17.320 --> 0:27:20.520
<v Speaker 2>quantum mechanics make different predictions about what's going to happen.

0:27:21.200 --> 0:27:23.080
<v Speaker 1>What do you mean, like one theory says that the

0:27:23.119 --> 0:27:24.960
<v Speaker 1>electron is going to turn right and the other theory

0:27:24.960 --> 0:27:26.320
<v Speaker 1>says the electric is going to turn left.

0:27:26.640 --> 0:27:29.240
<v Speaker 2>Yeah. For example, general relativity is a classical theory, and

0:27:29.280 --> 0:27:32.680
<v Speaker 2>so it assumes electrons have a very definitive location at

0:27:32.680 --> 0:27:35.560
<v Speaker 2>every point in time, whereas quantum mechanics says no, this

0:27:35.640 --> 0:27:38.760
<v Speaker 2>is probabilistic, and you can get things like interference. General

0:27:38.800 --> 0:27:41.320
<v Speaker 2>relativity says, I'm ignoring all that interference stuff, and it's

0:27:41.359 --> 0:27:44.040
<v Speaker 2>going to make a prediction based on treating the electron

0:27:44.160 --> 0:27:46.880
<v Speaker 2>like it's a little rock flying through space. So they're

0:27:46.880 --> 0:27:48.880
<v Speaker 2>going to come up with very different predictions for what's

0:27:48.880 --> 0:27:51.840
<v Speaker 2>going to happen. General relativity doesn't allowed for like entanglement

0:27:51.920 --> 0:27:55.320
<v Speaker 2>or any of the other important quantum effects that totally

0:27:55.359 --> 0:27:57.080
<v Speaker 2>control what happens to an electron.

0:27:57.280 --> 0:28:00.639
<v Speaker 1>I see, because quantum mechanics also might change which direction

0:28:00.760 --> 0:28:01.560
<v Speaker 1>the electron goes.

0:28:01.600 --> 0:28:06.040
<v Speaker 2>Absolutely, yeah, Electromagnetism is a quantum effect, right, Those forces,

0:28:06.080 --> 0:28:08.760
<v Speaker 2>all the forces in the universe that cause acceleration, the

0:28:08.760 --> 0:28:12.600
<v Speaker 2>weak force, electromagnetism, the strong force, These are all quantum effects.

0:28:12.600 --> 0:28:16.399
<v Speaker 2>They all operate on the probabilistic wave functions that control

0:28:16.480 --> 0:28:20.440
<v Speaker 2>these particles. General relativity ignores those. So you ask quantum

0:28:20.480 --> 0:28:23.360
<v Speaker 2>mechanics and gr what's going to happen to this electron.

0:28:23.640 --> 0:28:25.439
<v Speaker 2>They disagree about what's going to happen.

0:28:25.960 --> 0:28:27.639
<v Speaker 1>Well, maybe this is the point where we have to

0:28:27.680 --> 0:28:30.280
<v Speaker 1>get more into the math, because you know, as a

0:28:30.320 --> 0:28:32.240
<v Speaker 1>lad person, I might just say, like, can you just

0:28:32.240 --> 0:28:35.320
<v Speaker 1>add these two things, like why can't just have a

0:28:35.400 --> 0:28:39.720
<v Speaker 1>particle that gravity pulls on its average position, and so

0:28:39.840 --> 0:28:43.120
<v Speaker 1>the average position curves according to gravity, but then where

0:28:43.280 --> 0:28:46.000
<v Speaker 1>it is exactly might be fuzzy due to quantum mechanics.

0:28:46.080 --> 0:28:47.840
<v Speaker 2>Yes, so what you're trying to do right now is

0:28:47.880 --> 0:28:49.920
<v Speaker 2>come up with the theory of quantum gravity. You're trying

0:28:49.920 --> 0:28:51.880
<v Speaker 2>to say, can I get all the good bits of

0:28:51.920 --> 0:28:54.760
<v Speaker 2>general relativity and all the good bits of quantum mechanics

0:28:54.760 --> 0:28:57.360
<v Speaker 2>and smooth them together to make a theory of quantum

0:28:57.360 --> 0:29:00.560
<v Speaker 2>gravity that makes one prediction? Right? And that's the topic

0:29:00.560 --> 0:29:03.480
<v Speaker 2>of the episode. Why is that so hard? And people

0:29:03.520 --> 0:29:05.520
<v Speaker 2>have been working on it for one hundred years. It

0:29:05.640 --> 0:29:08.080
<v Speaker 2>sounds straightforward, but there's a bunch of reasons why it's

0:29:08.120 --> 0:29:10.720
<v Speaker 2>actually quite tricky. One of them is the problem you

0:29:10.800 --> 0:29:13.520
<v Speaker 2>just mentioned, which is this question of like space and

0:29:13.600 --> 0:29:18.280
<v Speaker 2>time and probability. You know, quantum particles don't have definitive locations,

0:29:18.760 --> 0:29:22.960
<v Speaker 2>and general relativity doesn't allow for probabilities in space time.

0:29:23.400 --> 0:29:25.640
<v Speaker 2>What you just described is like, well, what if the

0:29:25.680 --> 0:29:28.560
<v Speaker 2>electron is allowed to have a probability being here or there?

0:29:28.640 --> 0:29:31.240
<v Speaker 2>And so we just say, like space has a probability

0:29:31.240 --> 0:29:35.120
<v Speaker 2>of being curved here and a probability of being curved there. Right,

0:29:35.480 --> 0:29:39.120
<v Speaker 2>that's like a pretty deep change to how general relativity works,

0:29:39.360 --> 0:29:42.200
<v Speaker 2>and the mathematics of it breaks down, Like general relativity

0:29:42.200 --> 0:29:44.480
<v Speaker 2>doesn't allow for those probabilities?

0:29:45.040 --> 0:29:47.280
<v Speaker 1>What do you mean, like doesn't allow it? Like you

0:29:47.320 --> 0:29:49.680
<v Speaker 1>just don't know how to write it down, or like

0:29:50.000 --> 0:29:53.120
<v Speaker 1>you get nonsensical answers, or it's like trying to fit

0:29:53.160 --> 0:29:55.120
<v Speaker 1>a square peg in a round hole. You know, am

0:29:55.120 --> 0:29:57.800
<v Speaker 1>I trying to use fractions to you know, compute things

0:29:57.800 --> 0:29:59.600
<v Speaker 1>to certain decimal point or something.

0:30:00.080 --> 0:30:02.520
<v Speaker 2>Yeah, the mathematics of general relativity is hard.

0:30:02.560 --> 0:30:02.720
<v Speaker 1>You know.

0:30:02.760 --> 0:30:06.400
<v Speaker 2>It took Einstein like ten years to figure out how

0:30:06.400 --> 0:30:08.920
<v Speaker 2>to wrangle these equations to make any sense of them.

0:30:09.280 --> 0:30:11.840
<v Speaker 2>He had this idea that maybe space was curved and

0:30:11.880 --> 0:30:14.520
<v Speaker 2>that was explaining what gravity really was. But to make

0:30:14.520 --> 0:30:17.280
<v Speaker 2>the math work to even Einstein in a decade, and

0:30:17.320 --> 0:30:19.080
<v Speaker 2>it takes a lot of people a lot of time

0:30:19.120 --> 0:30:21.480
<v Speaker 2>to understand and to wrestle with the equations, which turn

0:30:21.560 --> 0:30:24.360
<v Speaker 2>out to be really really complicated. It's not like one

0:30:24.360 --> 0:30:27.520
<v Speaker 2>equation for a general relativity that says more mass means

0:30:27.560 --> 0:30:31.800
<v Speaker 2>more curvature. It's a matrix of equations. There's like sixteen

0:30:31.880 --> 0:30:35.440
<v Speaker 2>coupled equations which are really hairy, and if you add

0:30:35.440 --> 0:30:38.240
<v Speaker 2>to those the probability that space is may be curved

0:30:38.240 --> 0:30:42.160
<v Speaker 2>here and maybe curved there, it increases the complexity exponentially,

0:30:42.400 --> 0:30:44.960
<v Speaker 2>and it makes those equations impossible to even write down.

0:30:44.960 --> 0:30:47.680
<v Speaker 2>We don't know how to write down equations that both

0:30:47.760 --> 0:30:52.000
<v Speaker 2>describe space as a curvature of this differential geometric manifold

0:30:52.400 --> 0:30:55.360
<v Speaker 2>and allow for probabilities, like we just don't have the

0:30:55.360 --> 0:30:57.760
<v Speaker 2>tools for it. It might be that somebody out there

0:30:57.800 --> 0:31:02.360
<v Speaker 2>is developing some cool theory probabilistic manifolds that later will

0:31:02.400 --> 0:31:04.520
<v Speaker 2>be able to slip in to build the theory of

0:31:04.560 --> 0:31:07.360
<v Speaker 2>quantum gravity. But it's like we need a power tool

0:31:07.400 --> 0:31:08.800
<v Speaker 2>and all we have is a handsaw.

0:31:08.920 --> 0:31:10.360
<v Speaker 1>Yeah, Like you say, like if we just don't have

0:31:10.440 --> 0:31:13.640
<v Speaker 1>the right tools that will both fit a square peg

0:31:13.680 --> 0:31:14.600
<v Speaker 1>and a round hole.

0:31:14.440 --> 0:31:15.960
<v Speaker 2>And we don't know if we're missing the right tool,

0:31:16.000 --> 0:31:18.480
<v Speaker 2>Maybe that's just the wrong direction, right. It could be

0:31:18.560 --> 0:31:20.720
<v Speaker 2>that that's not the right way to try to build

0:31:20.720 --> 0:31:23.520
<v Speaker 2>the theory of quantum gravity. But a lot of times

0:31:23.560 --> 0:31:26.560
<v Speaker 2>it is the case that progress in mathematics is limiting

0:31:26.600 --> 0:31:29.760
<v Speaker 2>progress in physics. Einstein was only able to build general

0:31:29.800 --> 0:31:33.440
<v Speaker 2>relativity because the theories of differential geometry had been developed

0:31:33.480 --> 0:31:37.000
<v Speaker 2>like ten fifteen years earlier by mathematicians who didn't care

0:31:37.040 --> 0:31:39.800
<v Speaker 2>at all about gravity or physics. They just thought it

0:31:39.840 --> 0:31:42.760
<v Speaker 2>was cool to think about like wiggly shapes in their mind,

0:31:43.000 --> 0:31:44.840
<v Speaker 2>and so this kind of stuff happens all the time.

0:31:45.640 --> 0:31:48.080
<v Speaker 1>I see you're saying it's all the mathematicians fault, like

0:31:48.120 --> 0:31:49.640
<v Speaker 1>they're holding you back. Man.

0:31:49.840 --> 0:31:52.360
<v Speaker 2>Math is the language of physics, and in the end,

0:31:52.480 --> 0:31:55.719
<v Speaker 2>it's mathematical problems that are preventing us from building theories

0:31:55.720 --> 0:31:59.320
<v Speaker 2>of quantum gravity. And what you described is basically trying

0:31:59.360 --> 0:32:02.480
<v Speaker 2>to make space quantum mechanical. You can also go the

0:32:02.560 --> 0:32:04.200
<v Speaker 2>other direction, and you can say, well, what if we

0:32:04.320 --> 0:32:07.640
<v Speaker 2>try to make gravity itself quantum mechanical. What if we

0:32:07.680 --> 0:32:10.640
<v Speaker 2>try to describe the theory of gravity as a quantum

0:32:10.720 --> 0:32:14.720
<v Speaker 2>force instead of this whole crazy curvature of space and time,

0:32:15.040 --> 0:32:17.239
<v Speaker 2>And then you run into a completely different kind of

0:32:17.240 --> 0:32:18.800
<v Speaker 2>mathematical mm I see.

0:32:18.920 --> 0:32:21.320
<v Speaker 1>I think what you're saying is like each of these

0:32:21.320 --> 0:32:23.560
<v Speaker 1>two theories work, but only if they ignore each other.

0:32:23.720 --> 0:32:27.200
<v Speaker 1>Like quantum mechanics assumes that space doesn't bend and there

0:32:27.240 --> 0:32:30.600
<v Speaker 1>is no gravity. Basically gravity doesn't exist. To quantum mechanics,

0:32:31.040 --> 0:32:34.760
<v Speaker 1>and general relativity assumes that things are not fuzzy at

0:32:34.800 --> 0:32:37.880
<v Speaker 1>any level exactly, which works for a lot of situations,

0:32:37.880 --> 0:32:40.959
<v Speaker 1>but in some situations you have to take them into

0:32:41.000 --> 0:32:42.440
<v Speaker 1>account both at the same time.

0:32:42.360 --> 0:32:45.360
<v Speaker 2>Exactly, and it's amazing that both of them work. They

0:32:45.400 --> 0:32:47.840
<v Speaker 2>tell very different stories about what's really happening in the universe,

0:32:48.320 --> 0:32:50.960
<v Speaker 2>and in almost every scenario you can ignore one.

0:32:51.320 --> 0:32:51.600
<v Speaker 1>Right.

0:32:52.280 --> 0:32:54.120
<v Speaker 2>It's like you have two friends that are like different

0:32:54.200 --> 0:32:56.120
<v Speaker 2>kinds of movies or something, and most of the time

0:32:56.160 --> 0:32:57.960
<v Speaker 2>you can just ignore one friend and listen to the

0:32:58.000 --> 0:33:01.640
<v Speaker 2>other friend. But sometimes they have opinions about the same

0:33:01.720 --> 0:33:03.200
<v Speaker 2>kind of movie, and you're like, well, is this movie

0:33:03.200 --> 0:33:04.840
<v Speaker 2>good or bad? I don't know who to listen to.

0:33:05.480 --> 0:33:08.600
<v Speaker 2>And for general relativity and quantum mechanics, currently they only

0:33:08.640 --> 0:33:13.000
<v Speaker 2>overlap in places we cannot see inside black holes, so

0:33:13.040 --> 0:33:15.920
<v Speaker 2>we don't know who's fundamentally right, or if either of

0:33:15.960 --> 0:33:16.520
<v Speaker 2>them are right.

0:33:17.360 --> 0:33:19.520
<v Speaker 1>I see. It's like having a friend who only watches

0:33:19.520 --> 0:33:22.640
<v Speaker 1>sci fi movies and then having another friend who only

0:33:22.680 --> 0:33:25.840
<v Speaker 1>watches romantic comedies. And usually you can have perfectly good

0:33:25.880 --> 0:33:29.280
<v Speaker 1>conversations with either of them. But let's say science fiction

0:33:29.400 --> 0:33:32.000
<v Speaker 1>wrap the comedy comes out. Now there's true.

0:33:31.760 --> 0:33:34.040
<v Speaker 2>Exactly exactly right. Now you can't hang out with your

0:33:34.040 --> 0:33:35.760
<v Speaker 2>friends anymore, right, boom the universe.

0:33:36.640 --> 0:33:40.720
<v Speaker 1>You gotta stop watching movies. You can stage your couch

0:33:40.760 --> 0:33:45.040
<v Speaker 1>and just do physics and math all day. Has this

0:33:45.120 --> 0:33:46.200
<v Speaker 1>already happened to you, Ben?

0:33:47.400 --> 0:33:50.560
<v Speaker 2>I think Passengers was not a sci fi romantic comedy.

0:33:50.680 --> 0:33:53.719
<v Speaker 1>Oh there you go, And that was very controversial.

0:33:53.320 --> 0:33:54.000
<v Speaker 2>Man, exactly.

0:33:54.240 --> 0:33:58.640
<v Speaker 1>Nobody likes that we don't have the math tools or

0:33:58.680 --> 0:34:01.719
<v Speaker 1>framework or theories that let us tackle these two things

0:34:01.760 --> 0:34:03.240
<v Speaker 1>at the same time. What are some other ways that

0:34:03.240 --> 0:34:05.240
<v Speaker 1>make it hard to unify these two things?

0:34:05.400 --> 0:34:07.720
<v Speaker 2>So a really popular approach is to trying to make

0:34:07.720 --> 0:34:11.319
<v Speaker 2>a theory of quantum gravity that has a graviton. Say,

0:34:11.440 --> 0:34:14.120
<v Speaker 2>you know, Einstein, that was cute. We like your idea

0:34:14.120 --> 0:34:16.520
<v Speaker 2>of Kurt space time. It's pretty, but maybe it's just

0:34:16.520 --> 0:34:19.200
<v Speaker 2>fundamentally the wrong direction. Maybe if you zoom in, what

0:34:19.239 --> 0:34:21.640
<v Speaker 2>really is happening is that gravity is a force and

0:34:21.680 --> 0:34:26.040
<v Speaker 2>it's exchanging gravitons, and I mean, then we can describe

0:34:26.080 --> 0:34:28.520
<v Speaker 2>the whole theory of gravity back sort of as like

0:34:28.560 --> 0:34:32.120
<v Speaker 2>a quantized version of Newton's theory. And people have tried

0:34:32.160 --> 0:34:33.960
<v Speaker 2>to do this because that'd be pretty right if we

0:34:33.960 --> 0:34:36.160
<v Speaker 2>could just like add gravity to the standard model and

0:34:36.200 --> 0:34:39.840
<v Speaker 2>have another particle and ignore this whole curvature business. That

0:34:39.880 --> 0:34:40.560
<v Speaker 2>would be cool.

0:34:40.719 --> 0:34:42.319
<v Speaker 1>So that would be going back to the idea that

0:34:42.320 --> 0:34:45.080
<v Speaker 1>gravity is a force, not a bending of space and

0:34:45.120 --> 0:34:45.960
<v Speaker 1>time exactly.

0:34:46.120 --> 0:34:49.040
<v Speaker 2>So to tell philosophically a very different story from what

0:34:49.120 --> 0:34:52.040
<v Speaker 2>Einstein is telling us about how the universe works, they

0:34:52.040 --> 0:34:54.600
<v Speaker 2>would say there is no curvature. There are these tiny,

0:34:54.600 --> 0:34:57.879
<v Speaker 2>little invisible gravitons being passed back and forth. The same

0:34:57.920 --> 0:35:00.920
<v Speaker 2>way that like electromagnetism you think about in terms of

0:35:01.120 --> 0:35:04.200
<v Speaker 2>electric fields that are sort of like virtual photons being

0:35:04.239 --> 0:35:07.040
<v Speaker 2>passed back and forth, you can think of gravity in

0:35:07.160 --> 0:35:10.520
<v Speaker 2>terms of gravitons being passed back and forth. So that's

0:35:10.560 --> 0:35:13.680
<v Speaker 2>one direction. The problem is nobody can make that math

0:35:13.800 --> 0:35:16.600
<v Speaker 2>work either. When you do the calculations there and you

0:35:16.640 --> 0:35:19.000
<v Speaker 2>ask like, well, what happens if you try to collide

0:35:19.000 --> 0:35:22.560
<v Speaker 2>two black holes together, or even two protons together, you

0:35:22.600 --> 0:35:26.000
<v Speaker 2>get nonsense answers. You get answers like, well, the probability

0:35:26.000 --> 0:35:28.480
<v Speaker 2>of this happening is one hundred and fifty percent, and

0:35:28.520 --> 0:35:31.319
<v Speaker 2>the probability of that happening is one thousand percent, Just

0:35:31.320 --> 0:35:34.000
<v Speaker 2>like numbers that do not make sense you can't have

0:35:34.080 --> 0:35:38.640
<v Speaker 2>probabilities greater than one. But that's what these calculations spit out.

0:35:38.880 --> 0:35:40.759
<v Speaker 1>Like if you assume a gravitin exists, then you get

0:35:40.800 --> 0:35:45.600
<v Speaker 1>these weird answers, but more fundamentally, like you're ignoring general relativity, right,

0:35:45.680 --> 0:35:48.800
<v Speaker 1>You're ignoring things that a lot of experiments have verified

0:35:48.840 --> 0:35:51.279
<v Speaker 1>that Eisin was right, and so you're sort of not

0:35:51.360 --> 0:35:52.920
<v Speaker 1>really solving the problem, right, are you.

0:35:53.120 --> 0:35:54.720
<v Speaker 2>Well, you'd have to think about it as an upgrade

0:35:54.760 --> 0:35:57.560
<v Speaker 2>to general relativity. You'd have to reproduce all the predictions

0:35:57.560 --> 0:36:00.320
<v Speaker 2>of general relativity. So you need to develop a theory

0:36:00.360 --> 0:36:03.800
<v Speaker 2>of gravitons, which when you zoom out, looks a lot

0:36:03.840 --> 0:36:06.640
<v Speaker 2>like general relativity, and that people actually can do. There

0:36:06.680 --> 0:36:10.759
<v Speaker 2>are theories of quantum gravity that involve graviton exchange that

0:36:10.800 --> 0:36:13.279
<v Speaker 2>when you zoom out, look a lot like general relativity.

0:36:13.480 --> 0:36:15.399
<v Speaker 1>So space time is not being bent.

0:36:15.560 --> 0:36:17.560
<v Speaker 2>Yeah, they tell a different story, but they make the

0:36:17.560 --> 0:36:21.040
<v Speaker 2>same predictions about like the motions of objects.

0:36:20.880 --> 0:36:25.000
<v Speaker 1>Including things like gravitational ways and frame dragging and all that, all.

0:36:24.880 --> 0:36:27.000
<v Speaker 2>That kind of stuff. The problem is what happens at

0:36:27.000 --> 0:36:28.640
<v Speaker 2>the small scale when you try to think about like

0:36:29.000 --> 0:36:32.080
<v Speaker 2>when two particles scatter against each other, or when two

0:36:32.120 --> 0:36:35.560
<v Speaker 2>black holes are being eaten, then this theory breaks down.

0:36:35.760 --> 0:36:37.799
<v Speaker 1>But generativity still works for those.

0:36:37.920 --> 0:36:40.520
<v Speaker 2>General relativity still works for those. But we think it's wrong, right.

0:36:40.560 --> 0:36:43.440
<v Speaker 2>General relativity, we think is giving the wrong answer for

0:36:43.480 --> 0:36:46.080
<v Speaker 2>what happens when two protons collide or what's at the

0:36:46.080 --> 0:36:48.600
<v Speaker 2>heart of a black hole, because it's ignoring the quantum

0:36:48.600 --> 0:36:51.520
<v Speaker 2>mechanical effects. You try to build a theory of quantum

0:36:51.560 --> 0:36:55.080
<v Speaker 2>gravity that has gravitons and explains all of general relativity

0:36:55.400 --> 0:36:59.239
<v Speaker 2>and gives you a gravitational quantum mechanical prediction for what

0:36:59.280 --> 0:37:02.440
<v Speaker 2>happens when two particles collider, two black holes collide, Then

0:37:02.440 --> 0:37:04.319
<v Speaker 2>you get all sorts of nonsense. You get all sorts

0:37:04.320 --> 0:37:06.840
<v Speaker 2>of infinities that we don't know how to wrangle.

0:37:07.120 --> 0:37:10.279
<v Speaker 1>M I see, So graviton not a great ivid you

0:37:10.360 --> 0:37:11.719
<v Speaker 1>or one that hasn't worked so far?

0:37:12.160 --> 0:37:15.880
<v Speaker 2>Yeah, exactly. There are also sort of fundamental problems we

0:37:16.000 --> 0:37:18.640
<v Speaker 2>just don't know how to solve for quantum gravity, like

0:37:19.120 --> 0:37:22.560
<v Speaker 2>deep inconsistencies between the picture of the universe we get

0:37:22.560 --> 0:37:25.040
<v Speaker 2>from general relativity and the picture of the universe we

0:37:25.080 --> 0:37:28.160
<v Speaker 2>get from quantum mechanics about how physics should work. That

0:37:28.239 --> 0:37:30.120
<v Speaker 2>we just don't know how to reconcile. Well, what do

0:37:30.200 --> 0:37:32.360
<v Speaker 2>you mean, Like what like a deep principle in physics

0:37:32.480 --> 0:37:35.600
<v Speaker 2>is this idea of locality that things should be near

0:37:35.640 --> 0:37:38.560
<v Speaker 2>each other to affect each other, that you shouldn't have

0:37:38.680 --> 0:37:41.560
<v Speaker 2>like an electron over here affecting something really really far

0:37:41.600 --> 0:37:45.960
<v Speaker 2>away in the universe, especially in quantum mechanics, and in

0:37:46.040 --> 0:37:49.520
<v Speaker 2>quantum mechanics, we have this deep connection between the distances

0:37:49.560 --> 0:37:53.040
<v Speaker 2>between things and their energies. Like the reason that we

0:37:53.160 --> 0:37:56.080
<v Speaker 2>use the Large Hadron Collider to study really really really

0:37:56.120 --> 0:37:59.880
<v Speaker 2>tiny things is you need really high energy to study

0:38:00.080 --> 0:38:03.480
<v Speaker 2>really small distance scales. Like things that have a lot

0:38:03.520 --> 0:38:06.160
<v Speaker 2>of energy interact with each other very very.

0:38:06.000 --> 0:38:10.239
<v Speaker 1>Closely, because if things have low energy, then they don't

0:38:10.239 --> 0:38:11.600
<v Speaker 1>interact with the things around them.

0:38:11.880 --> 0:38:13.880
<v Speaker 2>If things have low energy, then they can interact with

0:38:13.920 --> 0:38:16.719
<v Speaker 2>stuff that's further away. Another way to think about it

0:38:16.760 --> 0:38:19.480
<v Speaker 2>is in terms of the wavelength of stuff. You know

0:38:19.560 --> 0:38:22.319
<v Speaker 2>that you need like really high energy photons to see

0:38:22.360 --> 0:38:25.480
<v Speaker 2>really really small stuff. With lower energy photons they have

0:38:25.480 --> 0:38:29.680
<v Speaker 2>a longer wavelength you can't like resolve small details. That's why,

0:38:29.719 --> 0:38:32.360
<v Speaker 2>for example, when you want pictures of really really tiny stuff,

0:38:32.680 --> 0:38:36.160
<v Speaker 2>you use high frequency photons you go beyond that to

0:38:36.239 --> 0:38:39.600
<v Speaker 2>use like electrons to take pictures of atoms, for example.

0:38:39.920 --> 0:38:41.560
<v Speaker 2>So you want to see the universe on a really

0:38:41.600 --> 0:38:44.000
<v Speaker 2>small scale, you need to use really high.

0:38:43.840 --> 0:38:47.280
<v Speaker 1>Energy probes, maybe to say high frequency instead of high energy.

0:38:47.440 --> 0:38:51.000
<v Speaker 2>Yeah, energy and frequency very closely connected. In quantum mechanics,

0:38:51.040 --> 0:38:54.640
<v Speaker 2>you need very high frequency stuff to see really short distances.

0:38:55.040 --> 0:38:55.760
<v Speaker 1>Okay, okay.

0:38:55.920 --> 0:38:59.239
<v Speaker 2>In general relativity they have the opposite relationship. As you

0:38:59.320 --> 0:39:03.800
<v Speaker 2>add energy to something in general relativity, then its influence

0:39:03.920 --> 0:39:08.279
<v Speaker 2>grows to longer distances. So quantum mechanics, higher energy means

0:39:08.320 --> 0:39:13.000
<v Speaker 2>shorter distances. In general relativity, higher energy means larger distances.

0:39:13.520 --> 0:39:16.360
<v Speaker 2>Like think about what happens to a black hole's radius.

0:39:16.640 --> 0:39:19.120
<v Speaker 2>As you add energy to a black hole, black hole

0:39:19.160 --> 0:39:22.840
<v Speaker 2>gets bigger, you add more energy, black hole keeps getting bigger.

0:39:23.160 --> 0:39:26.400
<v Speaker 2>The short styled radius, the distance from the singularity to

0:39:26.440 --> 0:39:29.080
<v Speaker 2>the event horizon, just keeps growing as the black hole

0:39:29.120 --> 0:39:32.400
<v Speaker 2>gets more massive. So, somehow general relativity doesn't have the

0:39:32.400 --> 0:39:37.240
<v Speaker 2>same relationship between energy and frequency and the distances involved.

0:39:37.280 --> 0:39:41.399
<v Speaker 2>They have like this deeply opposite relationship. This might sound

0:39:41.440 --> 0:39:45.040
<v Speaker 2>like sort of weirdly philosophically handwavy to you, but it

0:39:45.120 --> 0:39:46.120
<v Speaker 2>sort of tells.

0:39:45.840 --> 0:39:48.840
<v Speaker 1>You about it not at all. I don't know what

0:39:48.920 --> 0:39:49.200
<v Speaker 1>you mean.

0:39:50.320 --> 0:39:52.440
<v Speaker 2>But the reason it's important is that it tells us

0:39:52.440 --> 0:39:54.759
<v Speaker 2>that these two theories have like a fundamentally different sort

0:39:54.800 --> 0:39:58.040
<v Speaker 2>of philosophical foundation. Like one of them is very very local,

0:39:58.120 --> 0:40:00.759
<v Speaker 2>the other one is very non local. So when we

0:40:00.800 --> 0:40:03.280
<v Speaker 2>go to make a theory of quantum gravity, we're like, hmm,

0:40:03.280 --> 0:40:05.520
<v Speaker 2>these two things are kind of like very different. How

0:40:05.560 --> 0:40:07.600
<v Speaker 2>do we bring them together? It's like, how do you

0:40:07.640 --> 0:40:10.600
<v Speaker 2>get your science fiction fan friend and your rom com

0:40:10.719 --> 0:40:13.440
<v Speaker 2>fan friend together into a single movie If they have

0:40:13.640 --> 0:40:17.000
<v Speaker 2>just like really opposing needs for pacing and jokes and

0:40:17.040 --> 0:40:20.960
<v Speaker 2>whatever in the movie, it might be fundamentally impossible. If

0:40:20.960 --> 0:40:23.239
<v Speaker 2>these two things are so deeply in conflict.

0:40:23.480 --> 0:40:25.640
<v Speaker 1>It sounds like you're just kind of maybe saying the

0:40:25.640 --> 0:40:28.480
<v Speaker 1>same thing we talked about before, which is like, you know,

0:40:28.560 --> 0:40:31.879
<v Speaker 1>quantum gravity is good for things that are small, and

0:40:32.040 --> 0:40:34.480
<v Speaker 1>general relativity is good for things that are really big,

0:40:35.000 --> 0:40:37.880
<v Speaker 1>but there is a certain overlap between them, and that's

0:40:37.920 --> 0:40:38.880
<v Speaker 1>where you get into trouble.

0:40:39.040 --> 0:40:41.759
<v Speaker 2>Yeah, exactly, But I think there's one more layer there, Like,

0:40:41.840 --> 0:40:44.879
<v Speaker 2>imagine you have a singularity, so at the tiny little

0:40:44.920 --> 0:40:48.279
<v Speaker 2>spot with a huge amount of mass. Right, so it's

0:40:48.360 --> 0:40:51.880
<v Speaker 2>quantum mechanically important but also has a huge amount of mass.

0:40:52.160 --> 0:40:55.760
<v Speaker 2>General relativity says it affects things really really far away

0:40:55.840 --> 0:40:58.799
<v Speaker 2>because it creates a black hole. Who's event horizon can

0:40:58.920 --> 0:41:02.000
<v Speaker 2>be really really far away. Quantum mechanics says, no, it

0:41:02.000 --> 0:41:04.640
<v Speaker 2>can only interact with stuff really really nearby, because that's

0:41:04.719 --> 0:41:06.279
<v Speaker 2>really really tiny frequency.

0:41:06.560 --> 0:41:08.840
<v Speaker 1>Well, I would say that it can only interact quantum

0:41:08.840 --> 0:41:11.480
<v Speaker 1>mechanically with things that are close by, but then it

0:41:11.520 --> 0:41:14.680
<v Speaker 1>can interact through gravity or generativity for things that are

0:41:14.719 --> 0:41:17.360
<v Speaker 1>far away, like way back to the same spot.

0:41:19.160 --> 0:41:21.480
<v Speaker 2>Yeah, exactly, we're back to the same spot that if

0:41:21.480 --> 0:41:23.880
<v Speaker 2>you have quantum gravity, then you don't know can it

0:41:23.920 --> 0:41:27.280
<v Speaker 2>only interact nearby in its vicinity or can it interact

0:41:27.280 --> 0:41:31.000
<v Speaker 2>far away as well? Gravity says far away, Quantum mechanics

0:41:31.000 --> 0:41:33.920
<v Speaker 2>says nearby. We don't know what quantum gravity says. It

0:41:33.960 --> 0:41:36.480
<v Speaker 2>seems like maybe impossible to come up with a theory

0:41:36.480 --> 0:41:37.840
<v Speaker 2>that satisfies both m.

0:41:38.440 --> 0:41:40.120
<v Speaker 1>Just like it's impossible to come up with a good

0:41:40.239 --> 0:41:42.600
<v Speaker 1>sci fi rom com.

0:41:42.719 --> 0:41:45.200
<v Speaker 2>Exactly, they're fundamentally opposed.

0:41:45.320 --> 0:41:47.879
<v Speaker 1>All right, Well, let's dig into some of the other

0:41:47.920 --> 0:41:52.080
<v Speaker 1>ways that make it hard to unify generalativity and quantum mechanics.

0:41:52.120 --> 0:42:06.719
<v Speaker 1>But first, let's take another quick break. All right, we're

0:42:06.719 --> 0:42:11.279
<v Speaker 1>talking about quantum gravity. Can we unite quantum mechanics and

0:42:11.920 --> 0:42:15.240
<v Speaker 1>general relativity which has gravity in it? So far, Daniel,

0:42:15.239 --> 0:42:16.440
<v Speaker 1>you're saying it's really hard.

0:42:16.560 --> 0:42:19.480
<v Speaker 2>It's really hard. Some of the smartest people in the

0:42:19.600 --> 0:42:22.680
<v Speaker 2>universe have tried for decades and failed.

0:42:22.520 --> 0:42:25.120
<v Speaker 1>In the universe. That's a big claim.

0:42:25.440 --> 0:42:27.920
<v Speaker 2>Well, the smartest people in the universe, it could be

0:42:28.000 --> 0:42:30.839
<v Speaker 2>aliens out there much smarter than us. I don't know.

0:42:30.880 --> 0:42:32.920
<v Speaker 2>Are they people though? Are aliens people?

0:42:33.280 --> 0:42:35.840
<v Speaker 1>Well, you're assuming that the smartest people on Earth have

0:42:35.960 --> 0:42:36.800
<v Speaker 1>become physicists.

0:42:36.840 --> 0:42:39.439
<v Speaker 2>Oh that's a good point. Yeah, I know that people

0:42:39.480 --> 0:42:41.760
<v Speaker 2>out there who are like hedge fund bros.

0:42:41.800 --> 0:42:45.480
<v Speaker 1>Yeah, or cartoonist maybe you know. I'm just saying you're

0:42:45.480 --> 0:42:46.920
<v Speaker 1>sort of making a general assumption.

0:42:46.960 --> 0:42:49.359
<v Speaker 2>Here are you saying you're not a physicist? I think

0:42:49.680 --> 0:42:52.120
<v Speaker 2>years in basically you're a physicist by now.

0:42:52.320 --> 0:42:55.960
<v Speaker 1>Oh, if that's true, then I have a diploma for

0:42:56.000 --> 0:42:57.560
<v Speaker 1>you to sign. Yeah.

0:42:57.600 --> 0:43:00.000
<v Speaker 2>I think we gave you that podcast diploma physics.

0:43:00.200 --> 0:43:02.880
<v Speaker 1>Right, I'm so waiting for that in the mail. It

0:43:02.960 --> 0:43:04.959
<v Speaker 1>must have gotten lost. I guess you sent it, right.

0:43:05.840 --> 0:43:07.400
<v Speaker 2>But we sent it. Yeah, you should definitely get a

0:43:07.400 --> 0:43:09.480
<v Speaker 2>physical copy. You do like a discount at dollar.

0:43:09.520 --> 0:43:13.520
<v Speaker 1>Stories like this is an imaginary diploma again for an

0:43:13.600 --> 0:43:18.720
<v Speaker 1>imaginary field of study. All right, So it's hard to

0:43:18.760 --> 0:43:22.080
<v Speaker 1>combine these two big theories. We talked about how the

0:43:22.120 --> 0:43:24.799
<v Speaker 1>math makes it really difficult. The philosophy of them make

0:43:24.880 --> 0:43:26.719
<v Speaker 1>it really difficult. What are some other ways that make

0:43:26.760 --> 0:43:27.080
<v Speaker 1>it hard?

0:43:27.160 --> 0:43:29.800
<v Speaker 2>People argue about the fundamental story of space and time

0:43:30.360 --> 0:43:33.360
<v Speaker 2>that quantum gravity will have to tell us, because quantum

0:43:33.400 --> 0:43:37.280
<v Speaker 2>mechanics and general relativity really do tell very very different stories.

0:43:37.320 --> 0:43:39.799
<v Speaker 2>Here in quantum mechanics, we have kind of like a

0:43:39.840 --> 0:43:43.520
<v Speaker 2>Newtonian view of space and time. We say space and time,

0:43:43.640 --> 0:43:47.480
<v Speaker 2>they're backdrops, they're absolute, they're fixed, and we put quantum

0:43:47.520 --> 0:43:50.120
<v Speaker 2>fields on top of that space and time. We assume

0:43:50.440 --> 0:43:53.640
<v Speaker 2>that space and time already exists somehow, and we say

0:43:53.680 --> 0:43:56.360
<v Speaker 2>that this quantum fields in that space and time, and

0:43:56.400 --> 0:43:58.920
<v Speaker 2>those fields operate and they're part of space. But we

0:43:58.920 --> 0:44:02.120
<v Speaker 2>don't ask about where space comes from or what it is.

0:44:02.160 --> 0:44:04.880
<v Speaker 2>That's kind of stuff. It's like a fixed background, we

0:44:04.960 --> 0:44:09.320
<v Speaker 2>call it. But in general relativity, space time is dynamical.

0:44:09.360 --> 0:44:11.719
<v Speaker 2>It's not like fixed can bend and twist, and it

0:44:11.719 --> 0:44:15.799
<v Speaker 2>doesn't like exist inside some other kind of space. We

0:44:15.880 --> 0:44:19.280
<v Speaker 2>have this way to like calculate the relative distance between points,

0:44:19.719 --> 0:44:23.399
<v Speaker 2>but space itself is not like some new field that's

0:44:23.440 --> 0:44:26.759
<v Speaker 2>sitting inside some sort of meta space or superspace or

0:44:26.800 --> 0:44:30.480
<v Speaker 2>subspace or some other kind of space. It tells us

0:44:30.520 --> 0:44:34.320
<v Speaker 2>that there is no fixed background. So people describe general

0:44:34.320 --> 0:44:38.840
<v Speaker 2>relativity as background independent, like the universe. Space itself is

0:44:38.880 --> 0:44:43.160
<v Speaker 2>not sitting inside some sort of deeper box, and which

0:44:43.200 --> 0:44:44.799
<v Speaker 2>is kind of weird because it makes you feel a

0:44:44.800 --> 0:44:47.680
<v Speaker 2>little like unmoored from the foundations of reality.

0:44:48.600 --> 0:44:52.320
<v Speaker 1>But I guess maybe couldn't you just have quantum mechanics

0:44:52.360 --> 0:44:55.560
<v Speaker 1>sit on top of a bendy stretch hey space time,

0:44:56.360 --> 0:44:58.879
<v Speaker 1>you know, sort of like you know, the planet Earth

0:44:58.920 --> 0:45:01.480
<v Speaker 1>of the Sun or moving through space time and they're

0:45:01.480 --> 0:45:05.000
<v Speaker 1>getting they're flowing through the curvature and all the bending.

0:45:05.480 --> 0:45:08.920
<v Speaker 1>Couldn't you have quantum fields also kind of right on

0:45:09.000 --> 0:45:11.279
<v Speaker 1>top of the curves of space time. Mm hmm.

0:45:11.480 --> 0:45:14.719
<v Speaker 2>And I love how you just like casually suggesting these solutions,

0:45:15.040 --> 0:45:17.400
<v Speaker 2>which are like the whole areas of research.

0:45:18.080 --> 0:45:22.600
<v Speaker 1>Working for twenty years, Daniel, come on, I mean I

0:45:22.680 --> 0:45:24.880
<v Speaker 1>just spent five to twenty minutes talking about this, and

0:45:24.920 --> 0:45:26.720
<v Speaker 1>I already know how to come up with the answer.

0:45:27.480 --> 0:45:30.279
<v Speaker 2>You're basically a business so long. No, I don't mean

0:45:30.320 --> 0:45:32.000
<v Speaker 2>to make it at all. I mean that these are

0:45:32.120 --> 0:45:34.640
<v Speaker 2>actually really clever ways forward, and these are exactly the

0:45:34.640 --> 0:45:37.520
<v Speaker 2>things that people are working on at the cutting edge.

0:45:37.600 --> 0:45:40.840
<v Speaker 2>It turns out to be complicated. You can do quantum

0:45:40.840 --> 0:45:44.279
<v Speaker 2>mechanics on curved space, you can put these fields on

0:45:44.480 --> 0:45:48.200
<v Speaker 2>curved space time, and mostly it works as long as

0:45:48.239 --> 0:45:51.440
<v Speaker 2>the curvature is small, So like if they're a little

0:45:51.440 --> 0:45:54.080
<v Speaker 2>bit curved, things are fine. As soon as the curvature

0:45:54.120 --> 0:45:56.960
<v Speaker 2>becomes large, you get back to all those crazy infinities

0:45:56.960 --> 0:45:59.920
<v Speaker 2>that we can't wrangle in all sorts of nonsense predictions.

0:46:00.280 --> 0:46:03.840
<v Speaker 2>So the quantum mechanical theory breaks down if the curvature

0:46:03.920 --> 0:46:06.120
<v Speaker 2>is really really high. So we just don't know how

0:46:06.160 --> 0:46:07.759
<v Speaker 2>to do those kinds of calculations.

0:46:08.040 --> 0:46:08.200
<v Speaker 3>Mm.

0:46:09.640 --> 0:46:12.719
<v Speaker 1>And that includes time, right because like in general relativity,

0:46:13.160 --> 0:46:15.880
<v Speaker 1>time can slow down and time can speed up. And

0:46:15.920 --> 0:46:17.120
<v Speaker 1>so you're saying you don't know how to do that

0:46:17.160 --> 0:46:18.640
<v Speaker 1>in quantum mechanics.

0:46:18.280 --> 0:46:20.680
<v Speaker 2>Exactly, we don't know how to do that in quantum mechanics. Again,

0:46:20.760 --> 0:46:23.400
<v Speaker 2>when the curvature is high, for what they call weak

0:46:23.520 --> 0:46:26.880
<v Speaker 2>field gravity, where it's like a very small effect gravity,

0:46:27.120 --> 0:46:29.920
<v Speaker 2>then we can do those calculations and even feel the

0:46:29.920 --> 0:46:33.360
<v Speaker 2>influence of gravity, not just negligible gravity, just weak gravity.

0:46:33.600 --> 0:46:36.000
<v Speaker 2>But when gravity gets strong, which is what it does

0:46:36.120 --> 0:46:38.600
<v Speaker 2>near a black hole, where we think these two things

0:46:38.640 --> 0:46:41.480
<v Speaker 2>are both important, we don't know how to do those calculations.

0:46:41.560 --> 0:46:45.040
<v Speaker 2>That's when quantum mechanics on curve space breaks down because

0:46:45.040 --> 0:46:47.600
<v Speaker 2>of all these infinities we can't grapple with all.

0:46:47.680 --> 0:46:51.360
<v Speaker 1>Right, Well, as we mentioned, we're not quite experts in

0:46:51.440 --> 0:46:54.400
<v Speaker 1>this topic, but we don't Maybe we will talk to

0:46:54.480 --> 0:46:56.440
<v Speaker 1>one of the smartest people in the universe who is

0:46:56.800 --> 0:46:58.640
<v Speaker 1>tackling this problem directly.

0:46:59.040 --> 0:47:02.600
<v Speaker 2>That's right down to Nathan, whose father is a listener

0:47:02.600 --> 0:47:05.400
<v Speaker 2>of the podcast and listen to the podcast mostly so

0:47:05.440 --> 0:47:08.440
<v Speaker 2>you can have a hope of understanding his son's research.

0:47:08.880 --> 0:47:11.960
<v Speaker 2>Nathan is a physics brad student at Arizona State University,

0:47:12.280 --> 0:47:15.960
<v Speaker 2>a well known department with experts in cosmology and theories

0:47:16.000 --> 0:47:18.760
<v Speaker 2>of quantum gravity, and he was kind enough to spend

0:47:18.760 --> 0:47:21.680
<v Speaker 2>five minutes talking to me about his research and so.

0:47:21.640 --> 0:47:25.719
<v Speaker 1>Here at Daniel's interview with Nathan Berwick, Quantum Gravity researcher.

0:47:26.440 --> 0:47:30.000
<v Speaker 2>So then it's my pleasure to welcome Nathan to the podcast. Nathan,

0:47:30.160 --> 0:47:33.040
<v Speaker 2>please introduce yourself and tell the listeners who you are.

0:47:33.800 --> 0:47:39.000
<v Speaker 3>Yes, I'm Nathan Berwick. I'm currently a first year PhD

0:47:39.080 --> 0:47:46.080
<v Speaker 3>student at Arizona State University studying physics and cosmology and

0:47:46.239 --> 0:47:51.160
<v Speaker 3>hoping to continue doing so and move into ideally stuff

0:47:51.200 --> 0:47:52.680
<v Speaker 3>along the lines of quantum gravity.

0:47:52.800 --> 0:47:55.960
<v Speaker 2>Awesome. Well, we often talk on the podcast about how

0:47:56.080 --> 0:47:58.919
<v Speaker 2>science is just a bunch of people following their curiosity

0:47:59.040 --> 0:48:02.080
<v Speaker 2>and pushing forward the forefront of knowledge. So tell us

0:48:02.120 --> 0:48:05.480
<v Speaker 2>what is it about physics and gr that drew you in,

0:48:05.560 --> 0:48:08.080
<v Speaker 2>that made you decide you want to spend your life

0:48:08.200 --> 0:48:09.240
<v Speaker 2>on this question.

0:48:10.040 --> 0:48:13.480
<v Speaker 3>That's a really good question. So I think part of

0:48:13.520 --> 0:48:15.359
<v Speaker 3>it is just I always kind of grew up as

0:48:15.440 --> 0:48:18.919
<v Speaker 3>a curious kid, and you know, when I was younger,

0:48:18.960 --> 0:48:21.080
<v Speaker 3>I always knew I wanted to be like a scientist

0:48:21.239 --> 0:48:26.000
<v Speaker 3>in air quotes. But eventually I sort of narrowed in

0:48:26.040 --> 0:48:29.840
<v Speaker 3>on physics, and I think as soon as I learned

0:48:29.840 --> 0:48:32.680
<v Speaker 3>about like the most basic concepts in general relativity, sort

0:48:32.680 --> 0:48:35.759
<v Speaker 3>of the idea that space time is one great big

0:48:35.760 --> 0:48:38.520
<v Speaker 3>thing and gravity is just the curvature of that it

0:48:38.600 --> 0:48:42.600
<v Speaker 3>was just immediately alluring, especially when you start to consider

0:48:43.560 --> 0:48:47.120
<v Speaker 3>how gravity is, like are most interacted with force at

0:48:47.200 --> 0:48:50.120
<v Speaker 3>least sort of perceptually. You know, we talk about it

0:48:50.160 --> 0:48:53.600
<v Speaker 3>a lot. You don't really talk about how electromagnet doesn't

0:48:53.640 --> 0:48:56.080
<v Speaker 3>really plays a role in your life very often. But

0:48:56.440 --> 0:49:01.359
<v Speaker 3>it's also very poorly understood in general, and there's still

0:49:01.400 --> 0:49:04.200
<v Speaker 3>like a lot of really big open questions to be

0:49:04.280 --> 0:49:07.320
<v Speaker 3>answered for general relativity. And I think that sort of

0:49:07.400 --> 0:49:11.759
<v Speaker 3>openness is very much an invitation to explore, which I

0:49:11.800 --> 0:49:12.200
<v Speaker 3>really like.

0:49:12.360 --> 0:49:14.000
<v Speaker 2>So you're not going to give your dad any credit

0:49:14.040 --> 0:49:15.920
<v Speaker 2>for encouraging you to study physics.

0:49:17.280 --> 0:49:19.040
<v Speaker 5>I think, I think I definitely should.

0:49:20.200 --> 0:49:24.080
<v Speaker 3>Yeah, No, he definitely like fostered my curiosity in physics

0:49:24.120 --> 0:49:26.600
<v Speaker 3>growing up. Both my parents did, but my dad was

0:49:26.640 --> 0:49:30.080
<v Speaker 3>always fascinated in physics, and so from just like really

0:49:30.120 --> 0:49:33.680
<v Speaker 3>small things, you know, we'd always find questions on the internet,

0:49:33.719 --> 0:49:35.319
<v Speaker 3>you know, whether it be a bad string theory, which

0:49:35.360 --> 0:49:37.800
<v Speaker 3>is always like a very big, you know, media topic

0:49:37.840 --> 0:49:40.200
<v Speaker 3>and whatnot. But he definitely played a very big role

0:49:40.600 --> 0:49:41.920
<v Speaker 3>in me wanting to do physics.

0:49:42.680 --> 0:49:45.239
<v Speaker 2>So a lot of people say that general relativity, once

0:49:45.280 --> 0:49:48.799
<v Speaker 2>you fully understand it, is deep and beautiful. Do you

0:49:48.840 --> 0:49:51.120
<v Speaker 2>have that kind of esthetic reaction to it?

0:49:51.600 --> 0:49:53.239
<v Speaker 3>Yeah, I think a lot of the beauty of it

0:49:53.280 --> 0:49:57.719
<v Speaker 3>comes from the idea alone that it's all just curvat true,

0:49:58.560 --> 0:50:01.960
<v Speaker 3>that gravity is in essence just curvature of this big

0:50:02.480 --> 0:50:05.080
<v Speaker 3>manifold which you may or may not well, which you

0:50:05.080 --> 0:50:08.439
<v Speaker 3>can't really visualize. But that, for me is the part

0:50:08.440 --> 0:50:13.279
<v Speaker 3>of the esthetic that general relativity has is just like

0:50:13.320 --> 0:50:15.520
<v Speaker 3>a breakdown into a more fundamental concept.

0:50:15.800 --> 0:50:19.279
<v Speaker 2>So if gr is so gorgeous and it works so well,

0:50:19.360 --> 0:50:22.640
<v Speaker 2>all these experiments confirming Einstein all the time, how can

0:50:22.640 --> 0:50:25.000
<v Speaker 2>it be wrong? I mean, is it wrong in the

0:50:25.040 --> 0:50:28.000
<v Speaker 2>way that like Newton's gravity is wrong where it was

0:50:28.040 --> 0:50:31.120
<v Speaker 2>telling fundamentally the wrong story about what was happening but

0:50:31.160 --> 0:50:33.759
<v Speaker 2>we didn't really notice until we dug into the details.

0:50:34.400 --> 0:50:37.439
<v Speaker 2>Or is it mostly telling the right story just needs

0:50:37.480 --> 0:50:40.160
<v Speaker 2>some like corrections and band aids here and there.

0:50:40.440 --> 0:50:40.720
<v Speaker 5>Yeah.

0:50:40.760 --> 0:50:43.360
<v Speaker 3>So that's a really good question, and I think it

0:50:43.360 --> 0:50:46.600
<v Speaker 3>really depends on how much of the last one hundred

0:50:46.680 --> 0:50:50.759
<v Speaker 3>years you're willing to disregard, and you know that that

0:50:50.880 --> 0:50:54.480
<v Speaker 3>has certain consequences but also benefits. But I think the

0:50:54.520 --> 0:51:00.520
<v Speaker 3>most generally accepted perspective right now is that it needs

0:50:59.800 --> 0:51:05.960
<v Speaker 3>because general relativity, as this idea of gravity being caused

0:51:05.960 --> 0:51:10.440
<v Speaker 3>by space time curvature, is so so rigorously tested at

0:51:10.480 --> 0:51:13.480
<v Speaker 3>the moment, you know, we keep trying to knock Einstein

0:51:13.560 --> 0:51:17.160
<v Speaker 3>down and find errors in his theory somewhere, but every

0:51:17.239 --> 0:51:22.080
<v Speaker 3>single time like he just was right. And so that's

0:51:22.080 --> 0:51:25.600
<v Speaker 3>a difficult thing to try and find errors in. But

0:51:25.640 --> 0:51:30.920
<v Speaker 3>there's obviously still big questions. So quantum gravity is probably

0:51:30.920 --> 0:51:36.279
<v Speaker 3>the largest area of questions regarding general relativity, and a

0:51:36.280 --> 0:51:39.160
<v Speaker 3>lot of that has to do with just quantum mechanics

0:51:39.160 --> 0:51:41.879
<v Speaker 3>not playing nicely when you try and think about how

0:51:41.920 --> 0:51:44.600
<v Speaker 3>gravitational fields work with it. General relativity doesn't have any

0:51:44.640 --> 0:51:49.560
<v Speaker 3>fundamental understanding of what probability distribution looks like. There's no

0:51:49.719 --> 0:51:54.200
<v Speaker 3>like wave function understanding when you start getting into the

0:51:54.320 --> 0:51:56.279
<v Speaker 3>smaller regimes for general relativity.

0:51:56.760 --> 0:51:59.320
<v Speaker 2>So that's a really big topic, like general relativity and

0:51:59.360 --> 0:52:02.279
<v Speaker 2>quantm mechanics. What are you actually researching right now? Like

0:52:02.320 --> 0:52:04.720
<v Speaker 2>what are you working on today today?

0:52:04.960 --> 0:52:09.680
<v Speaker 3>So throughout the last semester, I've been working on what

0:52:09.719 --> 0:52:13.600
<v Speaker 3>are called scalar tensor theories, which I actually think you

0:52:13.640 --> 0:52:16.759
<v Speaker 3>guys did an episode fairly recently on no hair theorems.

0:52:16.800 --> 0:52:20.680
<v Speaker 3>For black holes, and that's very much what I'm working

0:52:20.680 --> 0:52:24.719
<v Speaker 3>on at the moment, just showing that there's no sort

0:52:24.760 --> 0:52:28.920
<v Speaker 3>of scalar hairs for certain types of theories.

0:52:29.200 --> 0:52:32.760
<v Speaker 2>Cool. So then I'm gonna ask you to speculate unscientifically.

0:52:33.320 --> 0:52:36.200
<v Speaker 2>What do you think is inside a black hole?

0:52:37.719 --> 0:52:38.640
<v Speaker 5>Oh? Boy?

0:52:38.800 --> 0:52:41.400
<v Speaker 3>What do I think is inside a black hole? Speculative

0:52:41.400 --> 0:52:43.520
<v Speaker 3>answer is, well, if it's a big black hole, there's

0:52:43.520 --> 0:52:46.440
<v Speaker 3>probably stuff sort of floating around in there being eaten up.

0:52:46.520 --> 0:52:51.160
<v Speaker 3>But I like to think that there's this sort of

0:52:51.200 --> 0:52:56.560
<v Speaker 3>taboo in physics of natural infinities. They aren't there're usually

0:52:56.560 --> 0:53:00.160
<v Speaker 3>when there's an infinity, it's something horribly horribly wrong. And

0:53:00.200 --> 0:53:02.520
<v Speaker 3>that was sort of the big hub up when they

0:53:02.560 --> 0:53:04.560
<v Speaker 3>figured out that black holes could be a thing that

0:53:04.640 --> 0:53:08.200
<v Speaker 3>actually existed, was that it just felt wrong that there

0:53:08.200 --> 0:53:12.200
<v Speaker 3>could be such a dense object that's just so infinitely packed.

0:53:12.719 --> 0:53:15.000
<v Speaker 3>I like to think that it is just, you know,

0:53:15.120 --> 0:53:20.200
<v Speaker 3>a perfectly oh infinite density singularity, just because I think

0:53:20.840 --> 0:53:24.279
<v Speaker 3>it'd be very wild and wacky and cool to have

0:53:24.320 --> 0:53:30.279
<v Speaker 3>this very strange yet natural like divergence or infinity just

0:53:30.400 --> 0:53:31.640
<v Speaker 3>existing in the universe.

0:53:32.000 --> 0:53:34.640
<v Speaker 2>Do you think the singularity inside a black hole is

0:53:34.719 --> 0:53:38.000
<v Speaker 2>as dense as boba, you know, these chewy blobs of

0:53:38.040 --> 0:53:41.759
<v Speaker 2>death that people inexplicably like shooting up their straws as

0:53:41.760 --> 0:53:44.799
<v Speaker 2>they enjoy and otherwise relaxing beverage. I happen to know

0:53:44.960 --> 0:53:46.560
<v Speaker 2>your father agrees with me on this.

0:53:49.480 --> 0:53:51.680
<v Speaker 5>He sent me a clip of this just the other day.

0:53:54.960 --> 0:53:57.319
<v Speaker 3>I certainly hope that boba is it not at all

0:53:57.480 --> 0:54:01.759
<v Speaker 3>comparable to singularities. But I suppose you never know what

0:54:01.960 --> 0:54:05.200
<v Speaker 3>that would be, the hell that my dad would die on.

0:54:05.280 --> 0:54:08.080
<v Speaker 2>I think, well, I think maybe your dad should open

0:54:08.160 --> 0:54:11.320
<v Speaker 2>up a black hole boba shop that sells black hole boba,

0:54:11.600 --> 0:54:16.479
<v Speaker 2>super dense, super dense little chunks of destruction. All right, Nathan,

0:54:16.520 --> 0:54:18.719
<v Speaker 2>thanks very much for taking some time to talk to

0:54:18.800 --> 0:54:21.400
<v Speaker 2>us about your work on the forefront of understanding of

0:54:21.400 --> 0:54:24.080
<v Speaker 2>general relativity, and good luck figuring it all out.

0:54:24.640 --> 0:54:26.279
<v Speaker 5>Thank you very much. Thank you for having me.

0:54:27.560 --> 0:54:32.680
<v Speaker 1>All right, interesting chat there, pretty controversial about both boba

0:54:32.719 --> 0:54:33.480
<v Speaker 1>and black holes.

0:54:34.280 --> 0:54:36.760
<v Speaker 2>You know, this is the cutting edge of food science

0:54:36.880 --> 0:54:38.640
<v Speaker 2>and quantum gravity.

0:54:38.520 --> 0:54:44.719
<v Speaker 1>That's right, and sugary drinks, yes, But it's interesting that

0:54:45.360 --> 0:54:48.200
<v Speaker 1>he seems to follow pretty strongly on the general latuty side.

0:54:48.200 --> 0:54:50.439
<v Speaker 1>He thinks inside of black holes are singularities.

0:54:50.560 --> 0:54:53.800
<v Speaker 2>Yeah, I've seen this in a lot of quantum gravity theorists,

0:54:53.840 --> 0:54:57.839
<v Speaker 2>that they are intoxicated by the beauty of general relativity.

0:54:58.239 --> 0:55:01.000
<v Speaker 2>It's sort of hard to overstate the this has on people.

0:55:01.040 --> 0:55:04.239
<v Speaker 2>When they are able to import Einstein's equations into their

0:55:04.280 --> 0:55:06.920
<v Speaker 2>mind and they can see the universe in terms of

0:55:06.960 --> 0:55:10.240
<v Speaker 2>this differential manifold, they feel like the scales have fallen

0:55:10.280 --> 0:55:12.120
<v Speaker 2>from their eyes and they're seeing the universe the way

0:55:12.120 --> 0:55:14.560
<v Speaker 2>it really is, and it has to be true. So

0:55:14.640 --> 0:55:17.520
<v Speaker 2>they want to preserve this vision of the universe as

0:55:17.520 --> 0:55:21.480
<v Speaker 2>having curved space time. It's not exactly religious, but it's

0:55:21.480 --> 0:55:23.239
<v Speaker 2>almost like a spiritual experience.

0:55:23.480 --> 0:55:26.440
<v Speaker 1>Oh my goodness. This is coming from, of course, a

0:55:26.520 --> 0:55:30.560
<v Speaker 1>quantum mechanics particle researcher. Right, you're trying to say that

0:55:30.760 --> 0:55:34.000
<v Speaker 1>the other side are a bunch of religious zillids because

0:55:34.040 --> 0:55:35.480
<v Speaker 1>your side is obviously right.

0:55:35.560 --> 0:55:38.120
<v Speaker 2>I mean, they like boba, so so you can't trust

0:55:38.120 --> 0:55:38.759
<v Speaker 2>them at all.

0:55:40.440 --> 0:55:42.919
<v Speaker 1>Well, boba are like particles, so I would have thought

0:55:42.960 --> 0:55:44.840
<v Speaker 1>they're fuzzy particles, so I would have value you be

0:55:44.920 --> 0:55:45.440
<v Speaker 1>a big fan.

0:55:45.600 --> 0:55:47.920
<v Speaker 2>No, they're macroscopic, man, They're dominated by gravity.

0:55:48.080 --> 0:55:52.480
<v Speaker 1>Mm. Well, I wonder if maybe there is a singularity,

0:55:52.520 --> 0:55:55.400
<v Speaker 1>you know, and maybe it's also fuzzy at the center

0:55:55.440 --> 0:55:57.680
<v Speaker 1>of it. It's just that maybe in a singularity, space

0:55:57.880 --> 0:56:02.040
<v Speaker 1>is so compressed or so squish together, that maybe the

0:56:02.360 --> 0:56:04.279
<v Speaker 1>quantum certainties also get squished down.

0:56:04.520 --> 0:56:06.600
<v Speaker 2>Maybe we're gonna solve quantum gravity right here on this

0:56:06.640 --> 0:56:07.680
<v Speaker 2>podcast today.

0:56:08.000 --> 0:56:11.440
<v Speaker 1>Yeah, yeah, let's do it. Why wait one hundred years,

0:56:11.520 --> 0:56:14.040
<v Speaker 1>let's come up with that romantic comedy sci fi movie

0:56:14.160 --> 0:56:14.520
<v Speaker 1>right now?

0:56:14.600 --> 0:56:17.759
<v Speaker 2>Why is quantum gravity so hard? Because nobody asked a cartoonist.

0:56:18.280 --> 0:56:23.239
<v Speaker 2>There you go, boom, question answered, boom.

0:56:23.320 --> 0:56:28.719
<v Speaker 1>Done. Let's go tackle something harder, like cancer or democracy.

0:56:31.120 --> 0:56:34.560
<v Speaker 1>All right, Well, you're on one side, people like Nathan

0:56:34.600 --> 0:56:36.680
<v Speaker 1>are on the other side. Sounds like we still have

0:56:36.719 --> 0:56:37.319
<v Speaker 1>a long way to go.

0:56:37.480 --> 0:56:38.960
<v Speaker 2>We do have a long way to go, and there

0:56:38.960 --> 0:56:43.440
<v Speaker 2>are deep philosophical and mathematical hurdles to overcome. We want

0:56:43.560 --> 0:56:45.440
<v Speaker 2>to have a single theory of the universe, one that

0:56:45.560 --> 0:56:48.440
<v Speaker 2>gives us a complete picture of what's really happening the

0:56:48.480 --> 0:56:51.920
<v Speaker 2>source code for the universe. But so far none of

0:56:51.960 --> 0:56:54.000
<v Speaker 2>our attempts actually compute.

0:56:53.640 --> 0:56:56.400
<v Speaker 1>And so it's an active area of research, maybe waiting

0:56:56.440 --> 0:56:59.960
<v Speaker 1>for the next person to tackle this and possibly solve it,

0:57:00.480 --> 0:57:03.240
<v Speaker 1>and that could be you out there asking these questions,

0:57:03.320 --> 0:57:06.840
<v Speaker 1>listening to this podcast, wondering how the universe works.

0:57:06.960 --> 0:57:10.400
<v Speaker 2>I hope that future genius doesn't suffer an unfortunate boba accident,

0:57:10.760 --> 0:57:14.040
<v Speaker 2>choking to death before they can share their insights with humanity.

0:57:14.160 --> 0:57:18.080
<v Speaker 1>Oh my gosh, it's a little bit dark there, a

0:57:18.120 --> 0:57:20.720
<v Speaker 1>little bit dark. I think you need a pretty large

0:57:20.720 --> 0:57:22.280
<v Speaker 1>bubba ball. There's choking.

0:57:22.360 --> 0:57:24.920
<v Speaker 2>Then it's boba relativity.

0:57:25.120 --> 0:57:27.960
<v Speaker 1>That's right, the answer, the choking hazard of a boba

0:57:28.480 --> 0:57:32.000
<v Speaker 1>is really all right. Well, stay tuned. You hope you

0:57:32.080 --> 0:57:35.320
<v Speaker 1>enjoyed that. Thanks for joining us, See you next night.

0:57:39.320 --> 0:57:42.200
<v Speaker 2>For more science and curiosity, come find us on social

0:57:42.240 --> 0:57:47.200
<v Speaker 2>media where we answer questions and post videos. We're on Twitter, Discord, Instant,

0:57:47.240 --> 0:57:50.960
<v Speaker 2>and now TikTok. Thanks for listening, and remember that Daniel

0:57:51.000 --> 0:57:54.440
<v Speaker 2>and Jorge Explain the Universe is a production of iHeart Radio.

0:57:54.720 --> 0:57:58.600
<v Speaker 2>For more podcasts from iHeart Radio, visit the iHeartRadio app,

0:57:58.880 --> 0:58:02.320
<v Speaker 2>Apple Podcasts, or wherever you listen to your favorite shows.