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Speaker 1: Yeah, or hey, I've heard that you are a fan

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Speaker 1: of campfires. Yeah, you know, I'm always up for some more. Well,

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Speaker 1: do you worry about, like far future generations of humanity

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Speaker 1: space settlers living under domes or folks living on colony

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Speaker 1: ships getting to have that same experience? Yeah, it doesn't

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Speaker 1: sound like a good idea to start a campfire on

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Speaker 1: a spaceship. So how are they going to capture that

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Speaker 1: essential human experience or is it going to be lost

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Speaker 1: forever in the endless depths of time. I'm sure they

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Speaker 1: can have a VR campfires. Maybe only a VR extends

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Speaker 1: to having smells. They might in the future. You know,

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Speaker 1: you plug something into your brain and it gives you

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Speaker 1: the experience of being in front of a campfire smelling fumes.

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Speaker 1: Or you can just fly too close to the sun. Yeah,

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Speaker 1: the sun is sort of like a campfire, right, it's burning,

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Speaker 1: and you can toast marshmallows with it if you get

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Speaker 1: close enough. That's the way of the future, plasma toasted

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Speaker 1: marshmallows s'mores. Yeah, and you can do your star gazing

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Speaker 1: right there, looking at the flames, seeing stars up clothes. Yeah,

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Speaker 1: just don't get too close or we'll have Plasma Toasted

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Speaker 1: podcast listeners. Hi am or Hey, I'm a cartoonist and

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Speaker 1: the co author of Frequently Asked Questions about the Universe. Hi.

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Speaker 1: I'm Daniel. I'm a particle physicist and a professor at

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Speaker 1: u C Irvine, and I've just realized that neither of

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Speaker 1: us on this podcast speak English as their first language.

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Speaker 1: And you can probably tell. I'm sure on every episode

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Speaker 1: we speak science instead. That's right. Science was our first language.

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Speaker 1: I mean we were writing papers, I'm sure, out of

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Speaker 1: our cribs, right. Yeah. My first words were F equals M,

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Speaker 1: a question mark. My fair words were P value of

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Speaker 1: oh five nature paper, those words. But anyways, welcome to

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Speaker 1: our podcast, Daniel and Jorge Explain the Universe, a production

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Speaker 1: of our Heart Radio in which we try to translate

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Speaker 1: the incredible mysteries of the cosmos into your native language.

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Speaker 1: We think it might just be possible to decode the

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Speaker 1: incredible froth and quantum insanity of our universe into a

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Speaker 1: language that humans can understand, and we can build some

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Speaker 1: sort of mental model in our heads that describes the incredible,

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Speaker 1: vastness and mysteries of the universe that we can pour

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Speaker 1: all of the incredible knowledge and ignorance of humanity into

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Speaker 1: your brain through your ears. That's right. I think of

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Speaker 1: this podcast as the dual lingo of physics and science,

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Speaker 1: translating all those amazing discoveries and things we've learned about

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Speaker 1: the universe into you know, bad jokes and short sound bites.

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Speaker 1: Are we going to start a signing homework? I think

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Speaker 1: duo lingo has homework? Oh? Does it? I think the

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Speaker 1: whole point is that it doesn't have homework. Oh, I

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Speaker 1: thought that exercises people are like doing their dual lingo

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Speaker 1: challenges and stuff. Oh yeah, it has like challenges and rewards,

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Speaker 1: but I'm not sure that's homework. Should we give people

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Speaker 1: rewards for listening to the podcast? Yes, we should definitely

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Speaker 1: give people rewards. We'll mail them bananas, We'll mail them

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Speaker 1: son toasted marshmallows. But that is interesting that neither of

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Speaker 1: our first languages were English, and look at us today

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Speaker 1: we have a podcast. I mean, how many people get

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Speaker 1: to have a podcast these days? Nobody? That's right, That's right.

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Speaker 1: We are super duper rare in the universe. But it

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Speaker 1: is amazing how you can learn different languages as a kid,

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Speaker 1: and even if English isn't your first language. If you

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Speaker 1: learn it when you're young enough, you can become totally

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Speaker 1: fluent in it. Yeah, and that's because you were born

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Speaker 1: in Israel, right, and so you spoke Heybrew that was

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Speaker 1: your first language. Yeah. I was born in Israel and

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Speaker 1: Spokekeybrew is my first language. And I didn't really start

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Speaker 1: speaking English till we moved to the US and it

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Speaker 1: turned out you needed to use English to communicate, and

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Speaker 1: that's when I started to pick it up around age five.

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Speaker 1: And it's interesting to me to think about like how

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Speaker 1: people think what language is are intuitive to them, because

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Speaker 1: we also think about physics sort of the same way.

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Speaker 1: There's certain ideas and physics that are intuitive to you

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Speaker 1: because you learned them as a young kid, temperature, velocity,

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Speaker 1: this kind of stuff. And then as we grow up

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Speaker 1: it's harder and harder to learn crazy new concepts and

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Speaker 1: to really feel fluent in them. You always feel like

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Speaker 1: in some sense you're translating. Yeah, I guess things like

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Speaker 1: quantum physics and the multiverse, those are all very sort

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Speaker 1: of alien to our intuition because you know, as as

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Speaker 1: when you're kids, you're used to like bouncing a ball

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Speaker 1: and holding a ball and those things aren't quite true

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Speaker 1: down to some molecular level. And it's fascinating the look

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Speaker 1: at the history of physics because when these ideas first

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Speaker 1: came out, the old guard were very against them. It's

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Speaker 1: very difficult for the gray haired physicists to accept some

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Speaker 1: of these ideas. Even folks like Einstein were resistant to

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Speaker 1: some of the crazier concepts. But now it's the kind

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Speaker 1: of thing that we teach in college, and they're even

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Speaker 1: books like, you know, quantum Physics for babies. So I

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Speaker 1: feel like one way that we make progress is by

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Speaker 1: introducing these crazy ideas younger and younger so that physicists

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Speaker 1: confluent in them, and then it can become like virtuosos

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Speaker 1: in these ideas rather than always feeling like they're working

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Speaker 1: in some translated alien language of the universe. Interesting. So

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Speaker 1: I guess if you're pregnant and you're carrying a baby,

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Speaker 1: you should maybe play our podcast to your baby the womb,

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Speaker 1: just to get am used to these ideas, right, So

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Speaker 1: it's kind of shock to them later on when they're

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Speaker 1: that are on about it in grad school exactly get

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Speaker 1: them hooked early. I think there's some ethical questions, hey

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Speaker 1: about pushing our podcast on kids, you know, getting them

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Speaker 1: addicted when they're young. I'm not sure how I feel

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Speaker 1: about that. Yeah, I think there might be some government

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Speaker 1: regulations about children's content, but maybe not fetus is content.

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Speaker 1: You know, maybe that's different way to find the loophole there.

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Speaker 1: But yeah, I do think it's good to teach children

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Speaker 1: to think about the questions of the universe in a

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Speaker 1: different way. But I think fundamentally we're always going to

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Speaker 1: struggle to really understand the nature of the universe in

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Speaker 1: a way that's intuitive to us because it is just weird,

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Speaker 1: and we don't have the immediate experience of some of that,

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Speaker 1: like quantum weirdness, for example, or relativistic weirdness, unless we

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Speaker 1: are living among Bose Einstein condensates and in the vicinity

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Speaker 1: of a black hole. We may never find that stuff intuitive. Well,

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Speaker 1: I guess it's kind of hard, because you know, you

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Speaker 1: need sort of Newtonian, regular old school physics intuition to

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Speaker 1: just like get around the world right and play baseball

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Speaker 1: and play basketball with your friends, and that's sort of

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Speaker 1: how the immediate world around his works. But if you

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Speaker 1: train a kid to be a quantum physicist from the beginning,

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Speaker 1: would they be really sort of like awkward or how

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Speaker 1: to touch with the world around them. You know, are

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Speaker 1: you setting this kid up for being very unpopular? Well,

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Speaker 1: I can't speak to the social aspects of it, but

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Speaker 1: it is an interesting question. If somebody had intuition for relativity,

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Speaker 1: could they still operate in everyday in life. The amazing

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Speaker 1: thing about relativity, though, is that it does reproduce our

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Speaker 1: intuition in our scenarios, right, Like, yes, you can use

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Speaker 1: Newtonian physics to describe motion and gravity, but if you

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Speaker 1: use relativity you get the same answers. It's just a

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Speaker 1: lot more complicated and some Newtony physics is like a

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Speaker 1: lot faster. So like somebody will like correctly predict where

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Speaker 1: the baseball is going to go, but it's gonna be

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Speaker 1: like three hours ago, you know, Like, Okay, I can

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Speaker 1: tell you exactly where that curveball went three hours ago,

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Speaker 1: but I missed the pitch. Yeah, I just don't put

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Speaker 1: that kid in the right field or left field, or

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Speaker 1: center field or any part of the field exactly, Like

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Speaker 1: still doing the calculations. Hold on, I'll get back to you.

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Speaker 1: Games over like two hours ago. Dude, physic that that

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Speaker 1: kid that quantum kid. It sounds like a fun, interesting

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Speaker 1: plot for a novel maybe or a movie. Like you know,

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Speaker 1: you train a whole generation of children to be quantum

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Speaker 1: thinkers because of some special science project or something where

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Speaker 1: we're sending people to the quantum world. Yeah, maybe, and

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Speaker 1: then they can be in like two emotional states at once.

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Speaker 1: I hate this movie and I love this movie at

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Speaker 1: the same time. I laughed, I cried. Wait, maybe that's

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Speaker 1: what movie criticism is. It's all quantum mechanical. Yeah, there

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Speaker 1: you go. People will love it and hate it. And

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Speaker 1: this is just about Jorge coming up with plots for novels.

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Speaker 1: This is about asking questions about the nature of reality

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Speaker 1: and trying to understand it. Are trying to apply our

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Speaker 1: intuition are limited toolbox of ways to think about the universe,

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Speaker 1: to probe deep dark questions about the nature of space

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Speaker 1: and time. Yeah, because there are still big questions that

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Speaker 1: are unanswered out there in the universe and huge pockets

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Speaker 1: of the unknown that we have yet to figure out

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Speaker 1: how it works. And sometimes we like to think about

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Speaker 1: what it might be like to touch those things. I

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Speaker 1: don't know about you, but I've looked at the sun

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Speaker 1: and I've wondered, like, how close could you get to

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Speaker 1: the sun? How hot is it really? You know, if

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Speaker 1: I put my finger on it, just for like a

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Speaker 1: micro second, when I get burned. Maybe I'm the only

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Speaker 1: one who's everyone. Yeah, I think walking around wanting to

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Speaker 1: touch everything is what gets in trouble as a kid.

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Speaker 1: It maybe also turns you into a scientist. You're like,

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Speaker 1: I wonder what happens when I press this button? Sounds

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Speaker 1: like a very dark take a way to get rid

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Speaker 1: of a lot of future scientists. That's right. Those of

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Speaker 1: us who survive learned a valuable lesson about what not

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Speaker 1: to touch. But it is interesting that there are pockets

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Speaker 1: of the unknown out there in the universe and that

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Speaker 1: we may want to touch them just to see what

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Speaker 1: they're like. And there is probably not a bigger hole

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Speaker 1: in our knowledge of the universe as big as black holes.

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Speaker 1: That's right. The deepest, darkest mystery of the universe is

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Speaker 1: what's inside a black hole? What's really going on over there?

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Speaker 1: And so of course the physicist in me wants to

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Speaker 1: reach out and touch one. Yeah, And so there are

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Speaker 1: many questions we can ask about black holes, but today

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Speaker 1: we're going to focus on one. I guess that it

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Speaker 1: is all about the black holes appearance, right in some sense,

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Speaker 1: I guess you could say it's appearance. I guess I

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Speaker 1: would say more like it's physical description. It's more to

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Speaker 1: me about black hole temperature than about black holes ability

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Speaker 1: to find meats for example. So today on the podcast,

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Speaker 1: we'll be tackling the question are black holes hot or not?

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Speaker 1: Isn't that a subjective judgment there, Daniel, like our and

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Speaker 1: are you thinking about attracted the black holes? Isn't everybody

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Speaker 1: attracted to black holes? Black holes are very attractive, even

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Speaker 1: to other black holes. Yeah. You know they say opposites attract,

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Speaker 1: but not in physics, right, In physics, massive attract. But

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Speaker 1: if it's something that doesn't have an opposite anyways, I

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Speaker 1: like big masses, and I cannot lie that might be

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Speaker 1: taking asn't to a hole we don't want to go into.

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Speaker 1: But it is an interesting question to think about whether

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Speaker 1: black holes are hot or not. And I'm guessing you

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Speaker 1: mean temperature, not like hotness, that's right. Yeah, I make

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Speaker 1: no evaluation of whether black holes are attractive or not,

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Speaker 1: but I am interested in the question of whether or

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Speaker 1: not black holes are hot or black holes are cold.

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Speaker 1: It's really fascinating because black holes certainly do contain a

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Speaker 1: lot of energy. Yeah, yeah, they have a lot of energy,

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Speaker 1: for sure, but I feel like it's energy that's like

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Speaker 1: trapped somewhere that you can access, so therefore it should

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Speaker 1: feel really cold. You know. That's good intuition. Sometimes, though,

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Speaker 1: our intuition for these things breaks down. Like it's true

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Speaker 1: that the Sun looks hot, and it is hot, but

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Speaker 1: there's other stuff out there in space, like the interstellar medium,

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Speaker 1: which can be like millions of degrees kelvin, but if

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Speaker 1: I dropped you inside of it, you would freeze to death.

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Speaker 1: So sometimes these things can be a little bit counterintuitive. Interesting.

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Speaker 1: So something can be hot but also cold at the

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Speaker 1: same time. Is that like quantum temperature. In the case

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Speaker 1: of the interstellar medium, it's because it's very dilute, so

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Speaker 1: the individual particles are moving at very very high speed.

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Speaker 1: So technically it's hot, but there's not a lot of it,

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Speaker 1: so it wouldn't be enough to keep you warm. You

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Speaker 1: would freeze to death even as you're being smashed into

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Speaker 1: by these high speed particles. I see. So you're saying,

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Speaker 1: like a black hole could be hot and actually hot

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Speaker 1: or hot and actually cold or something in between. Yeah,

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Speaker 1: it's very weird. Think about what happens when you shoot

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Speaker 1: a laser beam at a black hole? In theory it grows,

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Speaker 1: does it also get hotter? Is it possible to shoot

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Speaker 1: a laser beam at something and cool it down? Or

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Speaker 1: what if you throw out like a campfire into black hole?

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Speaker 1: Does the temperature go up or down? A lazy team

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Speaker 1: is basically just like a high tech physics version of

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Speaker 1: a campfire. Yeah. Or what if you throw Brad Pitt

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Speaker 1: into a black hole? He's pretty hot? I don't know.

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Speaker 1: Is he still hot though? Like as time goes onto

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Speaker 1: is he getting hotter or colder? What do you think? Um?

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Speaker 1: Definitely some of those movies started to stay pretty hot

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Speaker 1: into their old age, for sure. Helen Mirren, you know

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Speaker 1: you could throw her into a black hole. I'm sure

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Speaker 1: we'll get hotter. Helen Mirren is so hot she breaks

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Speaker 1: the laws of physics ceriently, Let's not throw her into

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Speaker 1: a black hole, please, But this is an interesting question

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Speaker 1: our black holes or not? And what would happen if

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Speaker 1: you touch him? Would your hand get burned or would

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Speaker 1: it freeze or get sucked in? I guess would it

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Speaker 1: file restraining order against you. So, as usually, we were

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Speaker 1: wondering how many people out there had thought about this

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Speaker 1: question and whether they think black holes will burn you

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Speaker 1: or freeze you. So thank you very much to all

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Speaker 1: those who participate in answering these random questions. If you'd

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Speaker 1: like to hear your voice speculating business, leave for the podcast.

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Speaker 1: Please don't be shy, it's a lot of fun. Right

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Speaker 1: to us. Two questions at Daniel and Jorge dot com.

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Speaker 1: So think about it for a second. Would use why

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Speaker 1: right or left on a picture of a black hole?

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Speaker 1: There's some people had to say. I guess that would

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Speaker 1: depend on how how you're defining temperature. So temperature generally

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Speaker 1: is defined as the amount of movement of a particular

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Speaker 1: set of matter. So maybe the spinning of a black

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Speaker 1: hole would mean that it has lots of energy, which

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Speaker 1: would mean that it might be hot, And then if

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Speaker 1: the black hole wasn't, spinning might be called I guess

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Speaker 1: if they were hot, they would be giving out lots

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Speaker 1: of high energy radiation, and I guess that would make

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Speaker 1: them easier to spot. I know that they give away

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Speaker 1: hawking radiation, but that seems to me to be low

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Speaker 1: energy and low density radiations. So my guests would be

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Speaker 1: black holes are cold, as the name subjects suggests. So

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Speaker 1: there's a lot of matter, it gets compressed down into

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Speaker 1: a black hole and it gets all smashed at one point.

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Speaker 1: The other thing that's kind of like that's like a star, right,

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Speaker 1: that's really hot because there's all this like energy, and

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Speaker 1: maybe if it's like hot as an temperature, which is

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Speaker 1: kind of standard for energy, we're talking about a lot

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Speaker 1: of matter in a small part, I'm going to call

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Speaker 1: that hot. And this sounds very hot to me. I

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Speaker 1: would say black holes have to be cold because when

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Speaker 1: they stuck in the start of the star is obviously

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Speaker 1: circulated around the black hole until they disappear into it.

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Speaker 1: You can kind of see their light on the horizon.

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Speaker 1: And I feel like if they're hot, then the star

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Speaker 1: would have to then get hotter as it approached it,

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Speaker 1: and I feel like that would then cause more of

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Speaker 1: a supernova or just some kind of explosion happening to

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Speaker 1: the star as it entered the black hole. Definitely, inside

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Speaker 1: a black hole, like the object itself, the pressure death,

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Speaker 1: it has be had that energy that it's right there,

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Speaker 1: but like outside, when you go close by by the

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Speaker 1: black hole, a black hole that doesn't interact with anything.

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Speaker 1: And what I want to say is like, no start

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Speaker 1: close to it to feed on that start nothing, no

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Speaker 1: object close to the black hole to interact with it

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Speaker 1: to make it bigger. So in this case, if the

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Speaker 1: black hole doesn't let the light go out, probably doesn't

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Speaker 1: let the heat go out either. So if you're right there,

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Speaker 1: close to it, you wouldn't be had but inside right

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Speaker 1: there when the pressure is might be hard there. I

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Speaker 1: believe black holes must be really hot because the eating

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Speaker 1: energy in form of cooking nation, so they must be

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Speaker 1: really hot, at least on the surface. That's what I think.

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Speaker 1: My intuitions is called old, So I'm going to go

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Speaker 1: up with hot. All right. A lot of pretty um

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Speaker 1: hot takes on this question. I think my favorite one

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Speaker 1: is my intuitions has cold, So I'm going to guess hot.

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Speaker 1: That person has learned some lessons about how the universe works.

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Speaker 1: Right there. Yeah, a person must have been listening to

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Speaker 1: a podcast in the womb. Is every physics question really

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Speaker 1: a trick question? Is that what they've learned? Yeah? I

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Speaker 1: feel like the universe is a true question. Why it's

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Speaker 1: not really a universe? Is actually just a simulation. That's

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Speaker 1: the trick. Yeah, it's something else right that that seems

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Speaker 1: to be the lesson everything you thought. It is not

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Speaker 1: really the way it is, even your thoughts. Maybe there

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Speaker 1: is no truth, man, Maybe there is the truth. But

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Speaker 1: I think there are a lot of really interesting ideas here.

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Speaker 1: There's ideas about how we can think about black holes

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Speaker 1: because they radiate energy, and also thinking about how black

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Speaker 1: holes absorb energy so they should be hot, or the

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Speaker 1: high pressure inside a black hole that might make it hot.

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Speaker 1: It's a lot of really good ideas. Yeah, And I

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Speaker 1: guess it's all sort of depends on what you mean

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Speaker 1: by hotness, right, Like is it related to something like

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Speaker 1: pressure or how much energy it admits or what happens

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Speaker 1: if you touch it? Right? Sort of maybe depends on

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Speaker 1: what you mean by the question and what it means

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Speaker 1: to be hot. Yeah, And as we learn, the whole

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Speaker 1: concept of temperature is a bit of a slippery topic. Yeah,

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Speaker 1: also whether or not you slip on it. Also. Well,

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Speaker 1: let's start at the beginning, and let's recap for listeners, Daniel,

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Speaker 1: what is the black hole? Like, how do physicists think

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Speaker 1: about what a black hole is? So we have several

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Speaker 1: pictures of what a black hole might be. But the

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Speaker 1: truth is that we're fundamentally not really sure what a

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Speaker 1: black hole is, and that's why this question is really interesting.

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Speaker 1: A black hole temperature really goes to the heart of

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Speaker 1: what we do and do not know about black holes.

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Speaker 1: So we have a couple of ideas about black holes.

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Speaker 1: One is what we call a classical picture of a

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Speaker 1: black hole, which means that it comes from general relativity.

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Speaker 1: If you just follow Einstein's rules about how mass bend

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Speaker 1: space time, and space time tells mass how to move,

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Speaker 1: then you end up in this really puzzling, amazing, sort

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Speaker 1: of weird prediction, which is that gravity has this strange

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Speaker 1: runaway effect. Right, mass pulls on mass, which means it's

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Speaker 1: more massive, and then it has more gravity, which means

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Speaker 1: it pulls harder on other masses, which means it has

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Speaker 1: more gravity, and that just keeps going, and eventually you

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Speaker 1: get this weird thing, a singularity, where space has curved

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Speaker 1: so much that you have created an event horizon in

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Speaker 1: a region past which if something gets too close, it

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Speaker 1: can never leave. No information can leak outside this event horizon.

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Speaker 1: That's sort of the classical view of what a black

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Speaker 1: hole is. A singularity a point of infinite density surrounded

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Speaker 1: by a threshold called the event horizon, like a marker.

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Speaker 1: If you go past it, you can never escape, will

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Speaker 1: be trapped forever. Your future is that singularity. Yeah, I

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Speaker 1: like classic black holes, feel like the classics are always

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Speaker 1: the best. But I think what you mean is like

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Speaker 1: a classic black hole was basically physicists thinking about like

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Speaker 1: what happens at the extreme levels, Like what if I

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Speaker 1: take a whole bunch of mass and I cram it

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Speaker 1: into the smallest possible space, or even like a tiny thought,

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Speaker 1: like what happens if a thought has almost infinite mass? Right,

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Speaker 1: Because gravity is very strange compared to the other forces,

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Speaker 1: as you are alluding to earlier. There's no negative gravity,

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Speaker 1: there's no repulsive gravity. I mean, there's dark energy and

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Speaker 1: is the cosmological constant due to potential energy and fields perhaps,

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Speaker 1: But when you're talking about just masses and objects, you

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Speaker 1: only have attraction, and so there's no balance. Right, just

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Speaker 1: keeps going, and so you have enough mass somewhere, then

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Speaker 1: it's just going to keep getting denser and denser and

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Speaker 1: stronger and stronger until eventually you get infinity. Right, this

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Speaker 1: thing diverges that actually goes to infinite density if you

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Speaker 1: give it enough time, right, Because I think one of

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Speaker 1: the things about gravity is that it gets stronger the

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Speaker 1: closer you get to it. Right, Like the formula for

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Speaker 1: it has the distance to it in the denominator in

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Speaker 1: the bottom, So like if you can cram a lot

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Speaker 1: of mass in a small amount of space, then you

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Speaker 1: can get really close to it, which means that your

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Speaker 1: denominator kind of goes to zero, which means that your

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Speaker 1: force sort of like goes almost to infinity. Yeah, and

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Speaker 1: so gravity, left to its own devices, will always generate

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Speaker 1: black holes. The reason that you're not a black hole,

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Speaker 1: and I'm not a black hole, and the Earth isn't

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Speaker 1: the black hole is that there are other forces out

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Speaker 1: there that can oppose gravity, right. The electromagnetic force and

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Speaker 1: the strong force give us structures that balance out gravity,

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Speaker 1: at least for a time. And then eventually if those

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Speaker 1: things fail, then you know, you collapse into a black hole.

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Speaker 1: But that's the prediction of classical general relativity. This incredibly

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Speaker 1: strange phenomena of an infinitely dense point. You said the

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Speaker 1: word sort of inevitably, and I wonder if that's how

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Speaker 1: you think about it, Like Is it inevitable that a

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Speaker 1: bunch of mass, if you leave it out in space,

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Speaker 1: will become a black hole if you have enough of it,

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Speaker 1: like things will sort of crunch down down to an

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Speaker 1: infinite point. Or is it possible even in the classical sense,

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Speaker 1: that things won't crunch down forever, like the Earth is

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Speaker 1: not crunching down to a black hole? Right? Cool question.

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Speaker 1: If there was only gravity, then it would be inevitable.

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Speaker 1: If you have a bunch of particles floating in space

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Speaker 1: and the only force in the universe is gravity, then

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Speaker 1: it will suck them together into a black hole. The

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Speaker 1: only thing that could resist that if there are no

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Speaker 1: other forces is angularm entem. You can imagine like some

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Speaker 1: blob of stuff coalescing sort of like the Earth and

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Speaker 1: then orbiting a central black hole, but not falling in. Right,

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Speaker 1: So you might imagine maybe that's stable. Maybe a blob

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Speaker 1: of stuff orbiting a black hole could avoid it forever.

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Speaker 1: But you know, even if you're orbiting, even in classical

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Speaker 1: general relativity, you are radiating gravitational waves, so you're losing energy,

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Speaker 1: so eventually you will spiral into the black hole. So

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Speaker 1: in the universe with only gravity, then eventually, yes, black

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Speaker 1: holes are totally inevitable. But as you say, the Earth

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Speaker 1: is not a black hole and probably will not become

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Speaker 1: a black hole because the other forces are stronger than

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Speaker 1: gravity and can oppose it for a while. All right,

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Speaker 1: So that's the sort of classical view of a black hole. Um.

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Speaker 1: But then what's the other view the new black holes?

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Speaker 1: The other view is that we don't know what a

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Speaker 1: black hole is, but it can't be that, you know.

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Speaker 1: It's basically it says, this can't be right. Oh my gosh,

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Speaker 1: it's ridiculous. Infinities are not predictions of physical theories. They

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Speaker 1: are failures of physical theories. It says something is wrong

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Speaker 1: here and it's got to be replaced by some other idea,

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Speaker 1: some quantum version of general relativity. We call that quantum gravity.

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Speaker 1: We don't have that theory, but we can criticize the

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Speaker 1: current theory general relativity for not being consistent with quantum

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Speaker 1: mechanical ideas. And that's because the idea of a singularity.

429
00:22:18,160 --> 00:22:20,440
Speaker 1: You can't have that in quantum mechanics. Well, in general,

430
00:22:20,520 --> 00:22:22,639
Speaker 1: we don't think you can have singularities or infinities in

431
00:22:22,680 --> 00:22:25,439
Speaker 1: physics at all. Like whenever you get infinity is a

432
00:22:25,440 --> 00:22:28,360
Speaker 1: prediction of a physical theory, it's usually a failure. I mean,

433
00:22:28,359 --> 00:22:30,639
Speaker 1: look back the history. For example, the whole discovery of

434
00:22:30,680 --> 00:22:33,840
Speaker 1: quantum mechanics was trying to unravel the source of the

435
00:22:33,920 --> 00:22:38,160
Speaker 1: ultra violet catastrophe. This prediction from classical physics that objects,

436
00:22:38,200 --> 00:22:41,359
Speaker 1: as they got hotter would radiate infinite temperatures. Like it

437
00:22:41,440 --> 00:22:43,679
Speaker 1: was nonsense, right, It was a signed to us that

438
00:22:43,680 --> 00:22:47,119
Speaker 1: there was something wrong, something missing in our calculations that

439
00:22:47,200 --> 00:22:50,600
Speaker 1: gave this crazy prediction. And so anytime you get an infinity,

440
00:22:50,720 --> 00:22:53,240
Speaker 1: it's a sign that probably you're doing something wrong. Like

441
00:22:53,320 --> 00:22:56,840
Speaker 1: we don't see infinities anywhere in the universe. Maybe the

442
00:22:56,920 --> 00:23:00,560
Speaker 1: universe itself is infinite, but we never measure or observe

443
00:23:00,680 --> 00:23:03,919
Speaker 1: infinity directly. It seems like a mathematical failure rather than

444
00:23:03,920 --> 00:23:06,879
Speaker 1: a physical prediction. But more than that, a singularity is

445
00:23:06,880 --> 00:23:09,280
Speaker 1: a really strange thing in the universe. Right. We talked

446
00:23:09,280 --> 00:23:12,280
Speaker 1: about singularities on the podcast several times. But in some sense,

447
00:23:12,520 --> 00:23:15,200
Speaker 1: they're like a path that ends, you know. Quantum mechanics

448
00:23:15,240 --> 00:23:17,439
Speaker 1: says that time goes from the infinite past to the

449
00:23:17,440 --> 00:23:20,760
Speaker 1: infinite future, and you could predict what happens to an object,

450
00:23:21,280 --> 00:23:24,200
Speaker 1: you know, it's deterministic in the sense of like evolving

451
00:23:24,240 --> 00:23:26,800
Speaker 1: its wave function. But a singularity is where like a

452
00:23:26,880 --> 00:23:30,240
Speaker 1: point ends, something falls into the singularity and you can

453
00:23:30,280 --> 00:23:33,000
Speaker 1: no longer predict what's going to happen predictability of physics,

454
00:23:33,000 --> 00:23:35,120
Speaker 1: which is like the foundation of physics. What we try

455
00:23:35,160 --> 00:23:38,480
Speaker 1: to do is predict the future given the present. That

456
00:23:38,600 --> 00:23:42,200
Speaker 1: fails at a singularity, you can't predict what happens after.

457
00:23:42,240 --> 00:23:45,480
Speaker 1: A singularity is like paths out. You know, everything that

458
00:23:45,520 --> 00:23:48,440
Speaker 1: falls in, no matter how it started, has the same fate.

459
00:23:48,480 --> 00:23:51,000
Speaker 1: It's just like is there in the singularity? And so

460
00:23:51,040 --> 00:23:55,040
Speaker 1: that's inconsistent with like quantum information theory and basically everything

461
00:23:55,080 --> 00:23:57,119
Speaker 1: we know about how physics works. It just seems like

462
00:23:57,119 --> 00:23:59,440
Speaker 1: a breakdown more than a prediction. I guess that's why

463
00:23:59,480 --> 00:24:03,720
Speaker 1: they call it a a singularity. It's singular. It's sense

464
00:24:03,800 --> 00:24:06,280
Speaker 1: the coolness. All right, Well, I ask some questions about that,

465
00:24:06,320 --> 00:24:08,600
Speaker 1: and so let's get into more of this idea of

466
00:24:08,640 --> 00:24:11,240
Speaker 1: a quantum black hole, and then let's get to the

467
00:24:11,320 --> 00:24:14,440
Speaker 1: question whether it's hot or not. But first let's take

468
00:24:14,480 --> 00:24:29,080
Speaker 1: a quick break. All right, we are talking about black

469
00:24:29,119 --> 00:24:32,000
Speaker 1: holes and whether or not they are hot or not.

470
00:24:32,400 --> 00:24:34,080
Speaker 1: I guess whether or not you would go on a

471
00:24:34,160 --> 00:24:37,000
Speaker 1: date with a black hole because you're definitely attracted to

472
00:24:37,000 --> 00:24:38,960
Speaker 1: a black hole. Yeah, On the other hand, I also

473
00:24:39,000 --> 00:24:41,399
Speaker 1: think black holes are pretty cool, so I'm not sure

474
00:24:41,440 --> 00:24:44,280
Speaker 1: how to feel about that. Oh boy, now we're mixing

475
00:24:44,320 --> 00:24:47,679
Speaker 1: all kinds of metaphors here. So you're saying there's a

476
00:24:47,720 --> 00:24:50,879
Speaker 1: classical view of black holes means that there's sort of

477
00:24:50,920 --> 00:24:54,159
Speaker 1: a singularity in space because it's sort of the natural

478
00:24:54,200 --> 00:24:56,479
Speaker 1: extension of what happens if you just have gravity in

479
00:24:56,520 --> 00:24:58,920
Speaker 1: the universe. But then there's a quantum mechanical view which

480
00:24:58,920 --> 00:25:02,480
Speaker 1: says that's a singular it's not possible in a quantum world.

481
00:25:02,800 --> 00:25:04,439
Speaker 1: But I guess my question is does it have to

482
00:25:04,480 --> 00:25:07,080
Speaker 1: be possible, Like, isn't the point of a singularity that

483
00:25:07,119 --> 00:25:10,600
Speaker 1: you never actually get there? That's interesting. I mean, we

484
00:25:10,680 --> 00:25:13,520
Speaker 1: are interested in what's going on in the universe, even

485
00:25:13,560 --> 00:25:16,600
Speaker 1: if we can't observe it directly, right, So we definitely

486
00:25:16,640 --> 00:25:21,040
Speaker 1: want like a physical model for what's happening microscopically inside

487
00:25:21,080 --> 00:25:23,879
Speaker 1: a black hole, because that allow us to understand, you know,

488
00:25:23,920 --> 00:25:26,879
Speaker 1: the nature of space and time. It might be that

489
00:25:26,920 --> 00:25:29,399
Speaker 1: we can ever see inside them, and so that you

490
00:25:29,400 --> 00:25:31,760
Speaker 1: know the observe ability is a question. It's sort of

491
00:25:31,800 --> 00:25:34,400
Speaker 1: like thinking about the multiverse. It's useful to think about

492
00:25:34,400 --> 00:25:37,359
Speaker 1: the multiverse, even if you might never observe or go

493
00:25:37,520 --> 00:25:40,040
Speaker 1: to the multiverse. It's still a question we wanted to

494
00:25:40,080 --> 00:25:42,639
Speaker 1: answer to. Right, Well, you say that a singularity is

495
00:25:42,680 --> 00:25:46,600
Speaker 1: inconsistent with quantum mechanics, maybe gives the sense of why

496
00:25:46,680 --> 00:25:49,400
Speaker 1: that is, Like, you know, maybe the singularity is not consistent,

497
00:25:49,440 --> 00:25:52,959
Speaker 1: but maybe getting we're approaching the singularity is consistent all

498
00:25:53,000 --> 00:25:55,080
Speaker 1: the way to infinity. Some of the problems with quantum

499
00:25:55,080 --> 00:25:56,920
Speaker 1: mechanics and black holes we laid out a minute ago,

500
00:25:56,920 --> 00:25:58,680
Speaker 1: but there are other ones. As you say, you know,

501
00:25:58,760 --> 00:26:01,400
Speaker 1: quantum mechanics says that things can be localized in momentum

502
00:26:01,560 --> 00:26:05,640
Speaker 1: and in location perfectly well, right, But a singularity violates that.

503
00:26:05,800 --> 00:26:09,760
Speaker 1: It's an infinitely well localized point in space. And so

504
00:26:09,920 --> 00:26:13,480
Speaker 1: quantum mechanics says, if particles are in an infinitely well

505
00:26:13,520 --> 00:26:17,320
Speaker 1: localized point, they should have an infinite uncertainty in their energy,

506
00:26:17,720 --> 00:26:21,040
Speaker 1: which would mean some of them would have basically infinite energy, right,

507
00:26:21,080 --> 00:26:23,679
Speaker 1: And so it's sort of like physically impossible. There's a

508
00:26:23,680 --> 00:26:28,080
Speaker 1: minimum quantum fuzz to the universe, which has singularity violates,

509
00:26:28,200 --> 00:26:30,280
Speaker 1: and so we just don't think it's possible. That doesn't

510
00:26:30,320 --> 00:26:32,359
Speaker 1: mean that black holes aren't real, right, It might mean

511
00:26:32,400 --> 00:26:34,600
Speaker 1: that black holes are there, but that at their heart

512
00:26:34,840 --> 00:26:38,560
Speaker 1: there isn't a singularity. There's some like weird quantum fuzz happening,

513
00:26:38,600 --> 00:26:40,199
Speaker 1: and you might not be able to tell the difference

514
00:26:40,200 --> 00:26:42,119
Speaker 1: from the outside because from the outside it's all just

515
00:26:42,320 --> 00:26:44,920
Speaker 1: strong gravity. But you know, we want to know what's

516
00:26:44,960 --> 00:26:47,479
Speaker 1: going on inside that black hole, and it does have

517
00:26:47,560 --> 00:26:50,800
Speaker 1: consequences for whether the black hole is hot or not.

518
00:26:51,000 --> 00:26:52,840
Speaker 1: You're saying, like a black hole is still a whole.

519
00:26:52,920 --> 00:26:55,040
Speaker 1: It's still it could still look like a hole to us,

520
00:26:55,119 --> 00:26:57,239
Speaker 1: but at the very center of the black hole, like

521
00:26:57,320 --> 00:26:59,560
Speaker 1: what's going on at the very very center it doesn't

522
00:26:59,640 --> 00:27:02,080
Speaker 1: actually get to a singularity? Or is it kind of

523
00:27:02,080 --> 00:27:04,720
Speaker 1: fuzzy down there? And I guess, just to be contrarian,

524
00:27:04,840 --> 00:27:07,560
Speaker 1: could it be both? Like could there be a singularity?

525
00:27:07,600 --> 00:27:09,879
Speaker 1: And as you get closer to the singularity, you know,

526
00:27:10,000 --> 00:27:13,280
Speaker 1: spaces crunched down so much that you're you're still fuzzy

527
00:27:13,359 --> 00:27:15,280
Speaker 1: but also kind of a singularity, do you know what

528
00:27:15,280 --> 00:27:17,240
Speaker 1: I mean? No, but I like to hear more about

529
00:27:17,280 --> 00:27:19,959
Speaker 1: that idea. How can you be a singularity and fuzzy. Well,

530
00:27:20,000 --> 00:27:22,800
Speaker 1: gravity bend space right in some ways that you're sort

531
00:27:22,800 --> 00:27:25,080
Speaker 1: of compressing space and in the middle of a black hole.

532
00:27:25,680 --> 00:27:28,240
Speaker 1: So as you're a protesting cularity, maybe you're still fuzzy

533
00:27:28,400 --> 00:27:31,280
Speaker 1: in a quantum sense, but spaces crunched down so much

534
00:27:31,320 --> 00:27:34,000
Speaker 1: that you're kind of fuzzy in a very small space.

535
00:27:34,119 --> 00:27:36,320
Speaker 1: That's basically a singularity. I see. I mean it could

536
00:27:36,400 --> 00:27:39,440
Speaker 1: be something you could never approach, or something that sort

537
00:27:39,440 --> 00:27:42,760
Speaker 1: of remains at a certain observable size no matter how

538
00:27:42,760 --> 00:27:45,720
Speaker 1: close you get to it, without actually being a point. Uh.

539
00:27:45,760 --> 00:27:48,760
Speaker 1: And that's true, that's interesting and maybe a possibility for

540
00:27:48,880 --> 00:27:51,199
Speaker 1: quantum mechanical description, but I don't think that would qualify

541
00:27:51,280 --> 00:27:54,760
Speaker 1: as a singularity. It's definitely not what general relativity predicts,

542
00:27:54,800 --> 00:27:56,679
Speaker 1: for example, And you might think, well, why do we

543
00:27:56,720 --> 00:27:59,640
Speaker 1: care what general relativity predicts? And we care because general

544
00:27:59,640 --> 00:28:03,119
Speaker 1: relative he seems to be accurate about everything else in

545
00:28:03,160 --> 00:28:06,080
Speaker 1: our universe. You know, the way that space expands, the

546
00:28:06,119 --> 00:28:09,359
Speaker 1: way the space ripples, the way that objects move through

547
00:28:09,440 --> 00:28:12,400
Speaker 1: space and time, very very precisely. It seems to get

548
00:28:12,480 --> 00:28:16,080
Speaker 1: everything else exactly right, and the math of it is beautiful.

549
00:28:16,160 --> 00:28:18,640
Speaker 1: It's gorgeous. I mean, theoretical physicist who learned it, They

550
00:28:18,680 --> 00:28:21,000
Speaker 1: like fall in love with the equations, and so it

551
00:28:21,040 --> 00:28:24,520
Speaker 1: seems to like speak to something deeply true about the universe.

552
00:28:24,560 --> 00:28:27,000
Speaker 1: So to discover that it's not that there's something that

553
00:28:27,040 --> 00:28:30,240
Speaker 1: it fails to describe is an opportunity to learn something

554
00:28:30,320 --> 00:28:33,840
Speaker 1: really fundamental about the nature of space. Yeah, I guess

555
00:28:33,880 --> 00:28:36,080
Speaker 1: kind of. It's kind of like Newtonian physics. We thought

556
00:28:36,240 --> 00:28:38,920
Speaker 1: was great because it predicted the like the paths of

557
00:28:38,960 --> 00:28:41,920
Speaker 1: the planets and the orbits and whether or not you

558
00:28:41,920 --> 00:28:44,080
Speaker 1: can catch a baseball, but it sort of breaks down

559
00:28:44,080 --> 00:28:46,320
Speaker 1: to a different scales kind of, right, you're saying that

560
00:28:46,440 --> 00:28:48,720
Speaker 1: relativity also sort of works for everything else that we

561
00:28:48,760 --> 00:28:50,560
Speaker 1: see around us, but when you get down to the

562
00:28:50,640 --> 00:28:55,680
Speaker 1: smallest levels, it doesn't have quite a solution that works exactly.

563
00:28:55,720 --> 00:28:57,920
Speaker 1: And we would like to know what the fundamental nature

564
00:28:58,040 --> 00:29:01,040
Speaker 1: of space is. You know, at the smallest level, is

565
00:29:01,080 --> 00:29:04,800
Speaker 1: gravity actually a quantum force mediated by gravitons or is

566
00:29:04,800 --> 00:29:08,400
Speaker 1: space itself quantized? Did this little foam It's more than

567
00:29:08,600 --> 00:29:11,400
Speaker 1: just an academic question of what's that the invisible heart

568
00:29:11,440 --> 00:29:13,680
Speaker 1: of a black hole. Understanding the nature of space and

569
00:29:13,680 --> 00:29:15,880
Speaker 1: time might give us great power over it, you know,

570
00:29:15,960 --> 00:29:20,080
Speaker 1: let us develop warp drives and wormholes and explore the universe,

571
00:29:20,480 --> 00:29:23,080
Speaker 1: and so definitely a question worth asking. Yeah, well, okay,

572
00:29:23,160 --> 00:29:25,320
Speaker 1: let's get back to our main question of this episode,

573
00:29:25,320 --> 00:29:28,480
Speaker 1: which is whether black holes are hot or not? And

574
00:29:28,760 --> 00:29:31,200
Speaker 1: I guess we mean in the sense of temperature. Do

575
00:29:31,320 --> 00:29:33,440
Speaker 1: black holes have a high temperature or do they have

576
00:29:33,480 --> 00:29:36,120
Speaker 1: a very low temperature? And so let's start maybe by

577
00:29:36,240 --> 00:29:39,360
Speaker 1: talking about what temperature means in this context. Yeah, the

578
00:29:39,400 --> 00:29:42,080
Speaker 1: temperature is really slippery and tricky. Sometimes when we talk

579
00:29:42,120 --> 00:29:45,760
Speaker 1: about temperature, we mean like how much energy is in

580
00:29:45,800 --> 00:29:48,560
Speaker 1: the particles inside something. So you have a banana in

581
00:29:48,600 --> 00:29:50,640
Speaker 1: front of you, you can ask is this banana hot

582
00:29:50,800 --> 00:29:53,640
Speaker 1: or not? What you really mean is how much internal

583
00:29:53,720 --> 00:29:56,400
Speaker 1: energy is there? Are the particles inside the banana wiggling

584
00:29:56,440 --> 00:29:59,880
Speaker 1: a lot? Are they frozen in place not wiggling a lot?

585
00:30:00,200 --> 00:30:02,719
Speaker 1: And you can actually do cool calculations to connect like

586
00:30:02,920 --> 00:30:06,000
Speaker 1: how much those guys are wiggling to the apparent temperature

587
00:30:06,040 --> 00:30:08,120
Speaker 1: that you would experience if you like touch the banana.

588
00:30:08,280 --> 00:30:10,600
Speaker 1: That's so if your intuitive sense of temperature, and the

589
00:30:10,640 --> 00:30:13,480
Speaker 1: way you measure temperature usually is by like sticking a

590
00:30:13,520 --> 00:30:17,440
Speaker 1: thermometer in something, and the energy transfers from the banana

591
00:30:17,480 --> 00:30:20,000
Speaker 1: to the thermometer and you read it out on the thermometer.

592
00:30:20,160 --> 00:30:22,680
Speaker 1: That's your intuitive sense of temperature. But that doesn't really

593
00:30:22,680 --> 00:30:25,160
Speaker 1: work with something that you can't touch. So if you

594
00:30:25,160 --> 00:30:27,280
Speaker 1: want to measure the temperature of something you can't touch,

595
00:30:27,320 --> 00:30:29,040
Speaker 1: there are other ways to do it, Like we can

596
00:30:29,080 --> 00:30:31,840
Speaker 1: measure the temperature of the Sun, even though no human

597
00:30:31,920 --> 00:30:34,520
Speaker 1: object has ever touched the Sun and then come back

598
00:30:34,520 --> 00:30:38,240
Speaker 1: out again, right, or like even now they have contact

599
00:30:38,240 --> 00:30:40,400
Speaker 1: list thermometers, right, the kind of is just kind of

600
00:30:40,440 --> 00:30:42,680
Speaker 1: like cover over your forehead and it somehow measures the

601
00:30:42,760 --> 00:30:45,600
Speaker 1: temperature without touching it exactly. So the way they do

602
00:30:45,640 --> 00:30:49,080
Speaker 1: that is by measuring the radiation that you generate, not

603
00:30:49,200 --> 00:30:52,080
Speaker 1: like you know, you're shooting off alpha particles and creating

604
00:30:52,160 --> 00:30:55,360
Speaker 1: hulks everywhere you go or spider Man, but you generate

605
00:30:55,640 --> 00:30:59,400
Speaker 1: energy like you radiate photons everywhere you go, because everything

606
00:30:59,400 --> 00:31:02,959
Speaker 1: in the universe that has a temperature does radiate energy,

607
00:31:03,080 --> 00:31:06,400
Speaker 1: Like the Sun radiates energy in the visible spectrum because

608
00:31:06,440 --> 00:31:09,040
Speaker 1: it's pretty hot, and the Earth radiates energy in a

609
00:31:09,240 --> 00:31:12,840
Speaker 1: much much longer wavelength because it's much colder than the Sun.

610
00:31:12,880 --> 00:31:15,320
Speaker 1: But it still does, and you generate energy at a

611
00:31:15,400 --> 00:31:17,400
Speaker 1: higher wavelength than the Earth does, which is why if

612
00:31:17,400 --> 00:31:20,000
Speaker 1: you put on like infrared goggles, you can see if

613
00:31:20,000 --> 00:31:22,720
Speaker 1: there's somebody hanging out in your backyard at night, because

614
00:31:22,760 --> 00:31:25,240
Speaker 1: they're generating a different kind of light, a light that's

615
00:31:25,240 --> 00:31:27,800
Speaker 1: invisible to your eyes but can be picked up by

616
00:31:27,840 --> 00:31:31,880
Speaker 1: infrared goggles, and that's it's a pretty cool burger or trespasser.

617
00:31:32,200 --> 00:31:34,160
Speaker 1: You can't see them. But I guess maybe the basic

618
00:31:34,280 --> 00:31:36,920
Speaker 1: question is why why does that happen? Like why do

619
00:31:37,080 --> 00:31:41,320
Speaker 1: hot things amid infrared light? Yet has to do with

620
00:31:41,480 --> 00:31:44,920
Speaker 1: energy just liking to get spread out, you know, a microscopically,

621
00:31:44,920 --> 00:31:47,240
Speaker 1: imagine like a blob of stuff, and that blaba stuff

622
00:31:47,240 --> 00:31:51,080
Speaker 1: isn't inactive, right, it's constantly radiating stuff and reabsorbing it.

623
00:31:51,320 --> 00:31:54,480
Speaker 1: So electrons within your banana are shooting off photons and

624
00:31:54,480 --> 00:31:57,520
Speaker 1: then other atoms are reabsorbing that. But near the edges

625
00:31:57,640 --> 00:32:00,200
Speaker 1: that doesn't always get reabsorbed. Some of it just shoots out.

626
00:32:00,280 --> 00:32:02,520
Speaker 1: So that energy is just like getting spread out through

627
00:32:02,560 --> 00:32:06,040
Speaker 1: the universe, partially by radiating stuff. And what's really interesting

628
00:32:06,080 --> 00:32:09,640
Speaker 1: is that the spectrum you emit is controlled by your temperature,

629
00:32:10,040 --> 00:32:11,920
Speaker 1: so if you have a really high temperature, you tend

630
00:32:11,960 --> 00:32:15,560
Speaker 1: to emit at shorter wavelengths. At higher frequencies, you have

631
00:32:15,600 --> 00:32:18,680
Speaker 1: a really low temperature, you tend to emit lower frequencies

632
00:32:18,760 --> 00:32:21,920
Speaker 1: or longer wavelengths. There's, for example, really really hot gas

633
00:32:21,960 --> 00:32:24,320
Speaker 1: emits in the X ray or the ultra violet, and

634
00:32:24,400 --> 00:32:28,240
Speaker 1: really really cold objects like asteroids floating in space emit

635
00:32:28,280 --> 00:32:30,720
Speaker 1: in the infrared. Right. Yeah, because we've talked about in

636
00:32:30,720 --> 00:32:34,160
Speaker 1: this podcast about how temperature is related to the kinetic

637
00:32:34,400 --> 00:32:37,000
Speaker 1: energy or like how fast the particles or something are

638
00:32:37,120 --> 00:32:39,880
Speaker 1: moving within you know, the volume that you're measuring the

639
00:32:39,920 --> 00:32:42,240
Speaker 1: temperature of. But then I guess that question is how

640
00:32:42,240 --> 00:32:44,840
Speaker 1: does that relate to the wavelength of light that's emitted? Like,

641
00:32:44,880 --> 00:32:46,600
Speaker 1: first of all, why does they emit light at all?

642
00:32:46,800 --> 00:32:48,640
Speaker 1: And the second why do they emit light at a

643
00:32:48,680 --> 00:32:51,480
Speaker 1: higher frequency. So we've been talking about them emitting light,

644
00:32:51,640 --> 00:32:53,959
Speaker 1: and by not we just mean photons. Right, Remember that

645
00:32:54,000 --> 00:32:56,840
Speaker 1: by light we don't always mean things that you can see.

646
00:32:57,360 --> 00:32:59,800
Speaker 1: So we're talking about something emitting light, you shouldn't expect

647
00:32:59,800 --> 00:33:01,800
Speaker 1: it to be glowing in a way that your eyeballs

648
00:33:01,840 --> 00:33:03,440
Speaker 1: could pick it up. You sit in a dark room

649
00:33:03,440 --> 00:33:05,200
Speaker 1: with a banana and stare at it. You're still not

650
00:33:05,240 --> 00:33:08,720
Speaker 1: going to see that banana glow because while these are

651
00:33:08,840 --> 00:33:11,760
Speaker 1: photons and they are hitting your eyeballs, your eyeballs can't

652
00:33:11,800 --> 00:33:14,760
Speaker 1: see them. So it's emitting light because it's made out

653
00:33:14,800 --> 00:33:18,000
Speaker 1: of charged particles, you know, electrons and atoms, and when

654
00:33:18,000 --> 00:33:21,480
Speaker 1: those things move and accelerate, they always emit light, you know.

655
00:33:21,480 --> 00:33:23,760
Speaker 1: That's what electrons do. From an electron to accelerate, for

656
00:33:24,000 --> 00:33:26,920
Speaker 1: like change direction, for it to slow down or speed up,

657
00:33:26,960 --> 00:33:29,440
Speaker 1: it has to admit a photon because that's the only

658
00:33:29,480 --> 00:33:31,440
Speaker 1: process that allows it to do it right. It needs

659
00:33:31,480 --> 00:33:33,760
Speaker 1: to like push off of something. The same way, if

660
00:33:33,800 --> 00:33:35,640
Speaker 1: you're in a rocket ship and you want to accelerate,

661
00:33:35,680 --> 00:33:38,040
Speaker 1: you've got to throw something out the back, right, you

662
00:33:38,120 --> 00:33:41,480
Speaker 1: need some mass, some rocket fuel, or some propellant to

663
00:33:41,480 --> 00:33:44,120
Speaker 1: toss out the back. That's the only thing electron can

664
00:33:44,160 --> 00:33:47,760
Speaker 1: do to change its direction, to accelerate or to decelerate

665
00:33:48,120 --> 00:33:50,720
Speaker 1: is to emit a photon. So because the banana is

666
00:33:50,720 --> 00:33:53,280
Speaker 1: made out of charged particles, it tends to emit photons.

667
00:33:53,480 --> 00:33:55,880
Speaker 1: It also emits other stuff, you know, emits neutrinos and

668
00:33:55,920 --> 00:33:58,239
Speaker 1: emits other kinds of radiation from the other kinds of

669
00:33:58,240 --> 00:34:01,440
Speaker 1: forces that it interacts with. But that's why it emits light,

670
00:34:01,640 --> 00:34:04,240
Speaker 1: and that's why emits photons, because it's made of charged particles.

671
00:34:04,360 --> 00:34:08,000
Speaker 1: And why does it emit different frequencies based on its temperature. Well,

672
00:34:08,080 --> 00:34:12,080
Speaker 1: you know, higher energy stuff emits higher frequency photons. You

673
00:34:12,160 --> 00:34:14,920
Speaker 1: have like electrons whizzing around your atom with more energy,

674
00:34:15,000 --> 00:34:17,640
Speaker 1: they have more energy, They will jump down more energy

675
00:34:17,719 --> 00:34:20,920
Speaker 1: levels and they will admit higher energy photons, which have

676
00:34:21,040 --> 00:34:23,840
Speaker 1: higher frequencies and shorter wavelengths. So it's just sort of

677
00:34:23,840 --> 00:34:27,920
Speaker 1: like more energy available because everything moving around has more energy.

678
00:34:28,080 --> 00:34:30,839
Speaker 1: You get on average higher energy photons, not purely. It's

679
00:34:30,840 --> 00:34:33,200
Speaker 1: not like a spectral line, right, There's like a distribution,

680
00:34:33,600 --> 00:34:35,440
Speaker 1: so you get some of the high frequencies some of

681
00:34:35,440 --> 00:34:38,680
Speaker 1: the low frequencies. But the shape shifts as you get

682
00:34:38,680 --> 00:34:41,640
Speaker 1: to higher temperatures. The peak moves and the most likely

683
00:34:41,719 --> 00:34:45,400
Speaker 1: frequency gets higher and higher as the temperature gets higher

684
00:34:45,400 --> 00:34:48,959
Speaker 1: and higher. Interesting, it's almost like you have a bunch

685
00:34:49,040 --> 00:34:51,399
Speaker 1: of atoms and they have some charge to them, and

686
00:34:51,560 --> 00:34:53,840
Speaker 1: it had they have electrons and protons and set them

687
00:34:53,840 --> 00:34:57,040
Speaker 1: and they're all sort of trapped together by the electromagnetic

688
00:34:57,080 --> 00:34:59,520
Speaker 1: forces that are holding them together. Kind of right, or

689
00:34:59,600 --> 00:35:01,919
Speaker 1: something to bumping to each other. And you're saying every time,

690
00:35:02,200 --> 00:35:05,759
Speaker 1: you know, Adam gets pulled into the banana, or a

691
00:35:05,800 --> 00:35:09,480
Speaker 1: gas particle bumps into another gas particle. You know, stuff

692
00:35:09,520 --> 00:35:13,200
Speaker 1: happens in the electromagnetic force, and so that causes photons

693
00:35:13,239 --> 00:35:16,120
Speaker 1: to shoot off. Yeah, exactly. Every time two electrons talk

694
00:35:16,160 --> 00:35:18,200
Speaker 1: to each other, that's a photon. So if you have

695
00:35:18,239 --> 00:35:20,840
Speaker 1: a blob of charge stuff, there's photons everywhere. It's just

696
00:35:20,920 --> 00:35:24,560
Speaker 1: like a huge mass of photons and particles constantly interacting

697
00:35:24,600 --> 00:35:26,200
Speaker 1: with each other, and some of that just bleeds out

698
00:35:26,200 --> 00:35:28,279
Speaker 1: the signs. It's like if you're in an apartment next

699
00:35:28,280 --> 00:35:30,920
Speaker 1: to a party, right and everybody shouting at each other,

700
00:35:30,960 --> 00:35:34,000
Speaker 1: then you're gonna be hearing some of those conversations, right right. Yeah,

701
00:35:34,080 --> 00:35:36,080
Speaker 1: unless you're in the party, then then it's a good time.

702
00:35:37,640 --> 00:35:39,360
Speaker 1: And as they drink more and more, they tend to

703
00:35:39,360 --> 00:35:41,800
Speaker 1: get higher and higher energy, right, and then this analogy

704
00:35:41,840 --> 00:35:45,239
Speaker 1: breaks down, Yeah, physics, as the parties put the main point.

705
00:35:45,920 --> 00:35:47,399
Speaker 1: So in terms of black holes, I think what you're

706
00:35:47,400 --> 00:35:51,840
Speaker 1: saying is that temperature is normally defined as like the

707
00:35:51,880 --> 00:35:54,760
Speaker 1: kinetic energy or how fast the particles of something are moving.

708
00:35:54,760 --> 00:35:57,000
Speaker 1: But it's sort of related to different things in different

709
00:35:57,040 --> 00:35:59,000
Speaker 1: ways that we measured, Like we can measure it by

710
00:35:59,120 --> 00:36:01,640
Speaker 1: touching in and some of kinetic energy moves to you.

711
00:36:01,800 --> 00:36:03,480
Speaker 1: Or you can measure the light that comes from it

712
00:36:03,640 --> 00:36:06,439
Speaker 1: because of this radiation, so that also sort of tells

713
00:36:06,480 --> 00:36:08,200
Speaker 1: you the temperature. And so it kind of sort of

714
00:36:08,239 --> 00:36:11,000
Speaker 1: depends on what do you mean by temperature of a

715
00:36:11,040 --> 00:36:13,440
Speaker 1: black hole? Do you mean like the energy it radiates,

716
00:36:13,520 --> 00:36:15,359
Speaker 1: or do you mean like what would actually happen if

717
00:36:15,400 --> 00:36:17,600
Speaker 1: you touch it? Yeah, Well, the fascinating question about black

718
00:36:17,640 --> 00:36:20,160
Speaker 1: holes is that we don't know what's going on inside

719
00:36:20,200 --> 00:36:24,960
Speaker 1: the microscopically, but we can ask questions about their radiation.

720
00:36:25,320 --> 00:36:27,799
Speaker 1: Do they give off any radiation? And if we use

721
00:36:27,920 --> 00:36:30,359
Speaker 1: radiation as a way to measure temperature, then we can

722
00:36:30,360 --> 00:36:33,000
Speaker 1: talk about the temperature something without having any idea about

723
00:36:33,040 --> 00:36:35,960
Speaker 1: what's going on inside it microscopically, like we can measure

724
00:36:35,960 --> 00:36:38,680
Speaker 1: the temperature of the sun without knowing like how do

725
00:36:38,760 --> 00:36:41,719
Speaker 1: those plasma tubes work inside the sun? What is going

726
00:36:41,760 --> 00:36:43,720
Speaker 1: on at the heart of it. We can still measure

727
00:36:43,840 --> 00:36:46,560
Speaker 1: its temperature the same way they measure your temperature on

728
00:36:46,600 --> 00:36:49,239
Speaker 1: your forehead without touching you, without knowing, like you know,

729
00:36:49,239 --> 00:36:52,200
Speaker 1: are you sick or not, what's going on inside your brain?

730
00:36:52,320 --> 00:36:53,920
Speaker 1: They don't know any of that, but they can still

731
00:36:54,000 --> 00:36:56,960
Speaker 1: measure your temperature. So it's a bit of an extrapolation

732
00:36:57,320 --> 00:36:59,360
Speaker 1: to say we don't know what's going on inside something,

733
00:36:59,480 --> 00:37:02,600
Speaker 1: we measure radiation and then we talk about what temperature

734
00:37:02,680 --> 00:37:04,480
Speaker 1: it has, right. I think what you mean is like

735
00:37:04,520 --> 00:37:07,160
Speaker 1: if you take a step back from the black hole

736
00:37:07,640 --> 00:37:09,440
Speaker 1: and you know, not worry about what's going on at

737
00:37:09,480 --> 00:37:12,399
Speaker 1: the very center, you know, how hot does it look

738
00:37:12,400 --> 00:37:15,080
Speaker 1: from afar? Yeah, we use this concept of temperature a

739
00:37:15,080 --> 00:37:18,000
Speaker 1: lot in physics in a way that might be confusing otherwise.

740
00:37:18,040 --> 00:37:20,680
Speaker 1: Like we talked about the temperature of the cosmic microwave

741
00:37:20,719 --> 00:37:23,680
Speaker 1: background radiation. We say that's two point seven three kelvin.

742
00:37:23,760 --> 00:37:26,120
Speaker 1: What does that mean? Doesn't really have a temperature. What

743
00:37:26,160 --> 00:37:29,400
Speaker 1: it means is that the cosmic microwave background radiation is

744
00:37:29,520 --> 00:37:32,200
Speaker 1: radiation at a wavelength that would be emitted by an

745
00:37:32,239 --> 00:37:35,400
Speaker 1: object at two point seven three kelvin. That's the black

746
00:37:35,440 --> 00:37:38,560
Speaker 1: body radiation for an object at that temperature would be

747
00:37:38,560 --> 00:37:41,040
Speaker 1: the frequency of the CMB. In the same way, we

748
00:37:41,080 --> 00:37:43,719
Speaker 1: can look for radiation coming off of black holes and

749
00:37:43,840 --> 00:37:47,120
Speaker 1: use that to measure its temperature and then trying to

750
00:37:47,160 --> 00:37:51,040
Speaker 1: deduce what might be going on inside of it from that. Well,

751
00:37:51,080 --> 00:37:52,839
Speaker 1: I guess it's kind of weird because you know, I

752
00:37:52,840 --> 00:37:55,279
Speaker 1: imagine that a black hole has particles inside of it

753
00:37:55,400 --> 00:37:57,879
Speaker 1: moving and a certain speed, and it does have sort

754
00:37:57,880 --> 00:38:00,520
Speaker 1: of like a kinetic internal kinetic energy. But you're saying, like,

755
00:38:00,640 --> 00:38:02,400
Speaker 1: let's not even worry about that because we don't really

756
00:38:02,440 --> 00:38:05,880
Speaker 1: know what happens beyond like the black hole's event horizon.

757
00:38:05,960 --> 00:38:07,960
Speaker 1: So let's just take a step back and see how

758
00:38:07,960 --> 00:38:10,359
Speaker 1: hot it looks. Yeah, well, let's start there because that's

759
00:38:10,360 --> 00:38:12,759
Speaker 1: something we can do from the outside, and then let's

760
00:38:12,760 --> 00:38:16,399
Speaker 1: turn that around and try to understand based on its

761
00:38:16,440 --> 00:38:19,520
Speaker 1: temperature what might be going on inside. So let's use

762
00:38:19,600 --> 00:38:22,400
Speaker 1: that as a probe, right, because temperature is like a message.

763
00:38:22,400 --> 00:38:25,960
Speaker 1: It tells us something that's going on inside from afar,

764
00:38:26,120 --> 00:38:28,520
Speaker 1: So without touching something, you can get a little bit

765
00:38:28,520 --> 00:38:30,839
Speaker 1: of information about what might be going on inside. And

766
00:38:30,840 --> 00:38:32,440
Speaker 1: in the end, that's the goal, is to try to

767
00:38:32,520 --> 00:38:35,200
Speaker 1: understand what's going on inside the black hole. Right. But

768
00:38:35,239 --> 00:38:37,920
Speaker 1: I guess it's messed up because you know, the definition

769
00:38:37,920 --> 00:38:40,040
Speaker 1: of a black hole is that nothing can escape of it,

770
00:38:40,160 --> 00:38:42,080
Speaker 1: not even light. What does it mean to measure the

771
00:38:42,160 --> 00:38:44,560
Speaker 1: light coming off of a black hole? If light cannot

772
00:38:44,680 --> 00:38:47,640
Speaker 1: escape a black hole. Yeah, that's true. Nothing can escape

773
00:38:47,680 --> 00:38:50,680
Speaker 1: the event horizon, nothing from inside can ever come out.

774
00:38:50,840 --> 00:38:52,759
Speaker 1: But that doesn't mean that black holes don't radiate. But

775
00:38:52,800 --> 00:38:56,160
Speaker 1: there's a difference in how you describe the radiation from

776
00:38:56,160 --> 00:39:00,839
Speaker 1: black holes. In classical gr like Einstein's pure singularity black

777
00:39:00,880 --> 00:39:04,319
Speaker 1: holes and more moderate attempts like Hawking's view of what

778
00:39:04,360 --> 00:39:06,280
Speaker 1: a black hole is do they give us very different

779
00:39:06,280 --> 00:39:09,920
Speaker 1: senses for what might be going on inside the black hole. Interesting?

780
00:39:09,960 --> 00:39:13,400
Speaker 1: All right, Well, let's get into whether Einstein and Stephen

781
00:39:13,440 --> 00:39:16,480
Speaker 1: Hawking are also hot or not and whether or not

782
00:39:16,520 --> 00:39:19,160
Speaker 1: they're right about the temperature of black holes. Will dive

783
00:39:19,200 --> 00:39:21,319
Speaker 1: into that and what it all means, but first let's

784
00:39:21,360 --> 00:39:36,279
Speaker 1: take another quick break. All right, we're talking about whether

785
00:39:36,320 --> 00:39:39,520
Speaker 1: black holes are hot or not. And it's kind of

786
00:39:39,560 --> 00:39:41,560
Speaker 1: weird to think of black holes as hot because they

787
00:39:41,600 --> 00:39:44,880
Speaker 1: are hols, Like, how can a hole be hot? And

788
00:39:44,920 --> 00:39:47,239
Speaker 1: I was saying earlier, Daniel, how it's weird to think

789
00:39:47,280 --> 00:39:50,640
Speaker 1: of the heat radiated like the light hit radiated by

790
00:39:50,680 --> 00:39:53,920
Speaker 1: a hot black hole because black holes are are black,

791
00:39:54,080 --> 00:39:57,520
Speaker 1: they're by definition things that don't radiate light or trap light.

792
00:39:57,640 --> 00:40:00,920
Speaker 1: How can something be both radiating heat and also trapping

793
00:40:01,120 --> 00:40:03,960
Speaker 1: heat forever? Well, you know, Einstein would agree with you.

794
00:40:04,320 --> 00:40:09,160
Speaker 1: Einstein's general relativity says that black holes are perfect absorbers.

795
00:40:09,360 --> 00:40:12,839
Speaker 1: They do not radiate any light. Anything that hits them

796
00:40:12,880 --> 00:40:16,279
Speaker 1: falls in, and they radiate nothing. And so from the

797
00:40:16,320 --> 00:40:20,880
Speaker 1: general relativistic point of view, black holes are at absolute zero.

798
00:40:20,960 --> 00:40:24,440
Speaker 1: They have zero temperature. What is the expected radiation from

799
00:40:24,440 --> 00:40:27,600
Speaker 1: an object that absolute zero? It's nothing. And so if

800
00:40:27,640 --> 00:40:31,920
Speaker 1: black holes radiate nothing, then therefore they must have zero temperature.

801
00:40:32,320 --> 00:40:35,359
Speaker 1: That's the g R version. The classical view of a

802
00:40:35,360 --> 00:40:39,200
Speaker 1: black hole. All you can know is it's mass, its charge,

803
00:40:39,280 --> 00:40:41,840
Speaker 1: and it's spin, not its temperature, because that would be

804
00:40:41,920 --> 00:40:44,960
Speaker 1: like information about what's going on inside the black hole. So,

805
00:40:45,000 --> 00:40:49,160
Speaker 1: according to Einstein, black holes are cold. They're like infinitely

806
00:40:49,160 --> 00:40:51,799
Speaker 1: cold or perfectly cold. That's right. According to Einstein, you

807
00:40:51,840 --> 00:40:54,279
Speaker 1: can shoot a laser beam at a black hole and

808
00:40:54,360 --> 00:40:56,680
Speaker 1: never heat it up. It will just keep eating that

809
00:40:56,800 --> 00:40:59,560
Speaker 1: laser but never get hotter. All right, well then, but

810
00:40:59,680 --> 00:41:04,120
Speaker 1: what does Stephen Hawkinson? So Stephen Hawking says, actually, if

811
00:41:04,200 --> 00:41:07,520
Speaker 1: we live in a quantum mechanical universe, then that cannot

812
00:41:07,560 --> 00:41:11,320
Speaker 1: be true. So Hawking did his famous calculation where he thought,

813
00:41:11,440 --> 00:41:14,200
Speaker 1: let's think about a black hole, and now, instead of

814
00:41:14,200 --> 00:41:16,479
Speaker 1: thinking about what's going on inside the black hole, because

815
00:41:16,480 --> 00:41:18,920
Speaker 1: we can't and we have no idea how quantum gravity works,

816
00:41:19,040 --> 00:41:20,719
Speaker 1: let's just try to put the black hole in a

817
00:41:20,800 --> 00:41:24,160
Speaker 1: quantum universe and say, how do you do quantum mechanics

818
00:41:24,280 --> 00:41:26,440
Speaker 1: when you have an event horizon if there's something there

819
00:41:26,480 --> 00:41:29,040
Speaker 1: which eats all the information. And so he did a

820
00:41:29,040 --> 00:41:31,960
Speaker 1: bunch of fancy calculations and quantum field theory and he

821
00:41:32,080 --> 00:41:34,239
Speaker 1: discovered that the only way this works, the only way

822
00:41:34,280 --> 00:41:36,880
Speaker 1: you could have like a boundary condition like a black hole,

823
00:41:37,200 --> 00:41:40,000
Speaker 1: is if you have radiation coming out of the black hole.

824
00:41:40,560 --> 00:41:43,680
Speaker 1: So he found like solutions to the quantum field theory

825
00:41:43,840 --> 00:41:47,080
Speaker 1: that require outgoing waves from the black hole. And that's

826
00:41:47,080 --> 00:41:49,520
Speaker 1: really interesting. That says that, like, if you have black

827
00:41:49,560 --> 00:41:52,719
Speaker 1: holes and the universe is quantum mechanical, then they must

828
00:41:52,760 --> 00:41:55,600
Speaker 1: be emitting something. And he went a step further, he said, well,

829
00:41:55,640 --> 00:41:57,719
Speaker 1: you know, how does this radiation work, what does it

830
00:41:57,760 --> 00:41:59,759
Speaker 1: look like? And what he discovered, and this is sort

831
00:41:59,760 --> 00:42:03,360
Speaker 1: of the fascinating moment, is that the radiation spectrum that

832
00:42:03,440 --> 00:42:06,360
Speaker 1: you expect from the vicinity of a black hole follows

833
00:42:06,400 --> 00:42:09,560
Speaker 1: exactly the spectrum you get from black bodies. Black bodies,

834
00:42:09,600 --> 00:42:12,560
Speaker 1: like we talked about earlier, don't just emit at one number, right,

835
00:42:12,600 --> 00:42:14,920
Speaker 1: It's not like the sun emits at only one frequency.

836
00:42:15,200 --> 00:42:17,640
Speaker 1: There's this shape to their spectrum. What he discovered is

837
00:42:17,680 --> 00:42:20,560
Speaker 1: that this radiation that he was predicting black holes emit

838
00:42:20,920 --> 00:42:23,600
Speaker 1: also has a shape, and that shape matches exactly the

839
00:42:23,640 --> 00:42:27,160
Speaker 1: shape you expect from black bodies at a certain temperature,

840
00:42:27,440 --> 00:42:31,160
Speaker 1: at a non zero temperature. So he concluded there must

841
00:42:31,200 --> 00:42:34,440
Speaker 1: be some radiation from black holes, and black holes must

842
00:42:34,520 --> 00:42:37,640
Speaker 1: have a non zero temperature. Well, I feel like maybe

843
00:42:37,640 --> 00:42:39,840
Speaker 1: that's not quite what he said, right, Like he's I

844
00:42:39,840 --> 00:42:43,839
Speaker 1: think what you're saying that he's saying is that, um,

845
00:42:43,960 --> 00:42:47,359
Speaker 1: black holes kind of have to leak stuff out, like

846
00:42:47,400 --> 00:42:50,319
Speaker 1: they can't trap stuff in. Thereforever stuff leaks out. And

847
00:42:50,360 --> 00:42:52,719
Speaker 1: the stuff that the energy that leaks out sort of

848
00:42:52,840 --> 00:42:55,680
Speaker 1: looks like something that would have a temperature, But that

849
00:42:55,719 --> 00:42:58,799
Speaker 1: doesn't necessarily mean it's the temperature of the black hole. Right,

850
00:42:58,920 --> 00:43:01,200
Speaker 1: You're exactly right. And in the paper he even said,

851
00:43:01,239 --> 00:43:04,560
Speaker 1: like be careful about interpreting this literally as a temperature.

852
00:43:04,560 --> 00:43:07,560
Speaker 1: It's more like an effective temperature. It's an attempt to

853
00:43:07,600 --> 00:43:10,479
Speaker 1: describe what might be going on inside the black hole.

854
00:43:10,560 --> 00:43:13,160
Speaker 1: But we don't know microscopically, we have no idea, you know,

855
00:43:13,280 --> 00:43:16,120
Speaker 1: is everything inside the black hole totally frozen? Is this

856
00:43:16,200 --> 00:43:20,520
Speaker 1: like quantum space wiggling? We don't understand what's generating this radiation.

857
00:43:20,640 --> 00:43:22,759
Speaker 1: But it's a way to describe the black hole sort

858
00:43:22,760 --> 00:43:26,080
Speaker 1: of thermodynamically and statistical point of view, right, And so

859
00:43:26,480 --> 00:43:28,880
Speaker 1: he says, you're right, it seems to like it should

860
00:43:28,880 --> 00:43:31,600
Speaker 1: generate a spectrum as if it had a temperature. What

861
00:43:31,719 --> 00:43:34,960
Speaker 1: that temperature means in terms of like the microscopic wiggles inside.

862
00:43:35,040 --> 00:43:38,359
Speaker 1: Hawking didn't say, couldn't say, and we still don't know,

863
00:43:38,520 --> 00:43:40,080
Speaker 1: but I guess can you step us through a little

864
00:43:40,120 --> 00:43:42,240
Speaker 1: bit of how he did it or how he reached

865
00:43:42,239 --> 00:43:44,279
Speaker 1: this conclusion, Like what does it mean that you can't

866
00:43:44,280 --> 00:43:46,440
Speaker 1: have a perfect hole in the universe? Like why does

867
00:43:46,440 --> 00:43:49,440
Speaker 1: it have to leak because of quantum mechanics or what? Yeah,

868
00:43:49,440 --> 00:43:51,920
Speaker 1: because of quantum mechanics. And so you take a black

869
00:43:51,920 --> 00:43:54,240
Speaker 1: hole and you put it in the universe. The universe

870
00:43:54,239 --> 00:43:57,720
Speaker 1: also has fields, and you know, fields for fermions fields

871
00:43:57,719 --> 00:44:00,720
Speaker 1: for bosons, you know, the electromagnetic field, the tron field,

872
00:44:00,760 --> 00:44:02,719
Speaker 1: and now you want to quantize those fields. Is what

873
00:44:02,760 --> 00:44:05,080
Speaker 1: we do in quantum mechanics to get to quantum field theory.

874
00:44:05,120 --> 00:44:07,400
Speaker 1: We say the universe is filled with space, and the

875
00:44:07,440 --> 00:44:10,200
Speaker 1: space has fields in it, and those fields are quantized.

876
00:44:10,440 --> 00:44:13,680
Speaker 1: They can only have certain solutions, right, not any arbitrary

877
00:44:13,719 --> 00:44:17,360
Speaker 1: continuous set of solutions, but only specific solutions like a ladder,

878
00:44:17,640 --> 00:44:20,400
Speaker 1: just like electrons whizzing around an atom have a ladder

879
00:44:20,440 --> 00:44:22,520
Speaker 1: of solutions. And so the thing that he ran up

880
00:44:22,520 --> 00:44:24,560
Speaker 1: against is that you add a black hole to that.

881
00:44:24,560 --> 00:44:27,880
Speaker 1: That changes how you can quantize these fields or for

882
00:44:27,960 --> 00:44:31,640
Speaker 1: that quantization to work. The various consistency conditions on this

883
00:44:31,719 --> 00:44:35,000
Speaker 1: quantization you need, like unitarity, so you're not predicting things

884
00:44:35,080 --> 00:44:37,480
Speaker 1: would have probability more than one and things that not

885
00:44:37,560 --> 00:44:42,719
Speaker 1: contradict themselves. Various internal consistency conditions on the quantization of

886
00:44:42,760 --> 00:44:46,239
Speaker 1: the fields in the presence of a black hole requires

887
00:44:46,360 --> 00:44:49,440
Speaker 1: this radiation to exist, right. I wonder if what it

888
00:44:49,480 --> 00:44:52,480
Speaker 1: means is that you know, he's saying that like you

889
00:44:52,520 --> 00:44:56,279
Speaker 1: can have a perfect event horizon, like you can't have

890
00:44:56,360 --> 00:45:01,400
Speaker 1: like this perfect perfectly smooth boundary where if you cross one,

891
00:45:01,920 --> 00:45:04,560
Speaker 1: you know, tiny little bit, you're in the black hole,

892
00:45:04,600 --> 00:45:06,239
Speaker 1: and where you step out a little bit, you're out

893
00:45:06,280 --> 00:45:08,439
Speaker 1: of the black hole. Maybe what he's saying is that,

894
00:45:08,560 --> 00:45:10,120
Speaker 1: you know, we live in a quantum universe. You can

895
00:45:10,239 --> 00:45:13,600
Speaker 1: have that kind of like stark boundary or certainty, and

896
00:45:13,680 --> 00:45:16,560
Speaker 1: so as a result, you can have a fuzzy event

897
00:45:16,560 --> 00:45:19,440
Speaker 1: horizon and which will tend to leak. I think that's

898
00:45:19,480 --> 00:45:21,600
Speaker 1: one way to interpret it, but I think it's dangerous

899
00:45:21,640 --> 00:45:25,080
Speaker 1: to try to come up with a microscopic interpretation. I mean,

900
00:45:25,120 --> 00:45:27,240
Speaker 1: I love that your brain immediately goes to, like, what's

901
00:45:27,239 --> 00:45:29,520
Speaker 1: happening right there at the edge, What does that really

902
00:45:29,520 --> 00:45:32,240
Speaker 1: mean for an individual particle? The truth is to understand

903
00:45:32,280 --> 00:45:34,480
Speaker 1: that we need a theory of quantum gravity. We have

904
00:45:34,520 --> 00:45:38,200
Speaker 1: to understand how gravity affects quantum particles, and we just

905
00:45:38,239 --> 00:45:40,719
Speaker 1: don't you know, quantum particles can do these weird things

906
00:45:40,719 --> 00:45:43,000
Speaker 1: like have a probability be in two different places at

907
00:45:43,000 --> 00:45:45,719
Speaker 1: the same time. How does gravity affect that does a

908
00:45:45,800 --> 00:45:49,440
Speaker 1: tug halfway on both of the places where the particle

909
00:45:49,680 --> 00:45:52,759
Speaker 1: is Like, we just don't understand the microscopic picture of

910
00:45:52,840 --> 00:45:55,600
Speaker 1: quantum mechanics and gravity at all, So we can't really

911
00:45:55,640 --> 00:45:58,279
Speaker 1: tell a story about what happens right at the edge

912
00:45:58,600 --> 00:46:01,040
Speaker 1: of the event horizon for quanty of objects, but we

913
00:46:01,080 --> 00:46:03,680
Speaker 1: can tell a story about the temperature of these black

914
00:46:03,719 --> 00:46:06,320
Speaker 1: holes sort of in this indirect way. Well, I guess

915
00:46:06,320 --> 00:46:08,719
Speaker 1: I feel like you're saying there are two answers. One

916
00:46:08,760 --> 00:46:12,080
Speaker 1: is any saying from afar a black hole will seem

917
00:46:12,120 --> 00:46:14,520
Speaker 1: like it has zero temperature, and from a far Stephen

918
00:46:14,520 --> 00:46:16,839
Speaker 1: Hawkins says, the black hole should have a little bit

919
00:46:16,880 --> 00:46:20,160
Speaker 1: of a temperature and almost like it was kind of hot.

920
00:46:20,200 --> 00:46:22,720
Speaker 1: But neither of those really tell you what the real

921
00:46:22,719 --> 00:46:25,279
Speaker 1: temperature is inside of the black hole. Right, Like, I'm

922
00:46:25,280 --> 00:46:27,920
Speaker 1: thinking of the black hole as this like perfect cooler

923
00:46:28,040 --> 00:46:31,040
Speaker 1: that doesn't let any heat out, And say, if you

924
00:46:31,080 --> 00:46:34,440
Speaker 1: stick of, you know something hot or something cold inside

925
00:46:34,440 --> 00:46:36,759
Speaker 1: of the cooler, Like it has a temperature inside of there,

926
00:46:36,960 --> 00:46:39,520
Speaker 1: but from the outside it's gonna look totally different. Right

927
00:46:39,560 --> 00:46:42,280
Speaker 1: from the outside of perfect cooler will seems super cold,

928
00:46:42,520 --> 00:46:45,120
Speaker 1: or if you're Stephen Hawkins, the cooler will leak out

929
00:46:45,200 --> 00:46:46,879
Speaker 1: or look a little bit warm, But that doesn't tell

930
00:46:46,920 --> 00:46:48,520
Speaker 1: you like how hot or cold it is on the

931
00:46:48,520 --> 00:46:51,719
Speaker 1: inside of the cooler. No you're totally right. Neither of

932
00:46:51,719 --> 00:46:55,080
Speaker 1: these tell us what's going on inside and the program.

933
00:46:55,120 --> 00:46:57,080
Speaker 1: The way to make progress is to try to build

934
00:46:57,120 --> 00:46:59,680
Speaker 1: up from the ground up a theory of quantum gravity

935
00:47:00,160 --> 00:47:02,880
Speaker 1: that would describe the kind of radiation we would see

936
00:47:03,040 --> 00:47:05,759
Speaker 1: from afar, and so people are working on that. They're

937
00:47:05,760 --> 00:47:08,160
Speaker 1: trying to do that, you know, the loop quantum gravity

938
00:47:08,200 --> 00:47:10,640
Speaker 1: folks are trying to do that. They're trying to describe

939
00:47:10,800 --> 00:47:14,160
Speaker 1: this radiation is like the shaking of the vibrations of

940
00:47:14,160 --> 00:47:16,759
Speaker 1: the quanta of space, you know, this film. In the

941
00:47:16,760 --> 00:47:19,840
Speaker 1: other direction, people in string theory are trying to describe

942
00:47:19,880 --> 00:47:21,640
Speaker 1: what's going on at the heart of the black hole

943
00:47:21,640 --> 00:47:24,400
Speaker 1: in terms of like vibrating strings, and they've actually had

944
00:47:24,400 --> 00:47:28,120
Speaker 1: a lot of success. These supersymmetric black holes have been

945
00:47:28,120 --> 00:47:32,240
Speaker 1: able to predict very well this expected distribution of radiation

946
00:47:32,360 --> 00:47:33,880
Speaker 1: from a black hole. It's like one of the biggest

947
00:47:33,920 --> 00:47:37,279
Speaker 1: successes of string theory as a theory for quantum gravity. So,

948
00:47:37,320 --> 00:47:39,360
Speaker 1: you know, if we can make careful measurements of the

949
00:47:39,400 --> 00:47:41,520
Speaker 1: black hole from the outside and then come from the

950
00:47:41,520 --> 00:47:44,440
Speaker 1: other direction and try to predict those measurements, we might

951
00:47:44,480 --> 00:47:46,680
Speaker 1: be able to get some inside as to what's going

952
00:47:46,760 --> 00:47:50,160
Speaker 1: on inside, right, because it is that we've talked about before.

953
00:47:50,160 --> 00:47:52,719
Speaker 1: It is possible to go into a black hole, right, Like,

954
00:47:52,719 --> 00:47:55,080
Speaker 1: for certain black holes, you can go past the event

955
00:47:55,120 --> 00:47:58,000
Speaker 1: horizon without getting shredded to bits, and so it is

956
00:47:58,000 --> 00:48:00,360
Speaker 1: sort of possible to go into a black hole and

957
00:48:00,400 --> 00:48:02,839
Speaker 1: measure the temperature inside of a black hole. I mean,

958
00:48:02,840 --> 00:48:05,440
Speaker 1: you wouldn't be able to tell anybody on the outside,

959
00:48:05,520 --> 00:48:08,080
Speaker 1: but it is technically to like no possible to know

960
00:48:08,239 --> 00:48:11,280
Speaker 1: that the temperature of a black hole inside of one. Right, Yeah,

961
00:48:11,320 --> 00:48:13,960
Speaker 1: that's true. You can fall inside a black hole, and

962
00:48:14,040 --> 00:48:16,680
Speaker 1: for large enough black holes you can survive the title

963
00:48:16,760 --> 00:48:20,440
Speaker 1: forces just past the event horizon. Eventually you will get shredded,

964
00:48:20,480 --> 00:48:22,680
Speaker 1: but yeah, you can fall past the event horizon and

965
00:48:22,719 --> 00:48:25,919
Speaker 1: do experiments. You know, if it's a classical black hole

966
00:48:26,000 --> 00:48:27,680
Speaker 1: and you're not really going to learn anything until you

967
00:48:27,719 --> 00:48:30,719
Speaker 1: get to the singularity. Anyway, if it's a quantum black hole,

968
00:48:30,800 --> 00:48:32,560
Speaker 1: then they might still be in the extended region, and

969
00:48:32,640 --> 00:48:35,200
Speaker 1: so you could do some experiments there, you like, not

970
00:48:35,280 --> 00:48:37,239
Speaker 1: quite at the core of the black hole, but like

971
00:48:37,280 --> 00:48:42,719
Speaker 1: in the rind of the black hole, the crust, the

972
00:48:42,760 --> 00:48:44,520
Speaker 1: cross there you go the crust. But I think the

973
00:48:44,600 --> 00:48:48,080
Speaker 1: calculations are also super fascinating because the numbers themselves are

974
00:48:48,160 --> 00:48:50,920
Speaker 1: really weird. If you ask, all, right, what is the

975
00:48:50,960 --> 00:48:53,600
Speaker 1: temperature of a black hole that has the mass of

976
00:48:53,680 --> 00:48:56,680
Speaker 1: the sun, for example, you know, Einstein says, oh, it's zero,

977
00:48:57,080 --> 00:49:00,239
Speaker 1: Hawking says, no, it's not zero, but it's point zero

978
00:49:00,280 --> 00:49:04,120
Speaker 1: zero zero zero zero zero zero six kelvin. So like,

979
00:49:04,280 --> 00:49:06,800
Speaker 1: black holes are not zero, but they're definitely not hot.

980
00:49:07,280 --> 00:49:10,640
Speaker 1: It's still a pretty cold object, you mean, from afar,

981
00:49:10,920 --> 00:49:13,680
Speaker 1: like outside of the cooler. For outside of the cooler,

982
00:49:14,080 --> 00:49:16,479
Speaker 1: the coolers are pretty cool. Yeah, we're always talking about

983
00:49:16,480 --> 00:49:18,759
Speaker 1: from afar because we don't know what's going on inside this.

984
00:49:18,840 --> 00:49:21,240
Speaker 1: So these black hole temperature is always what you measure

985
00:49:21,280 --> 00:49:24,320
Speaker 1: from the radiation that might be coming off the black holes,

986
00:49:24,640 --> 00:49:27,000
Speaker 1: the leaking, you mean, the leaking. The thing that's really

987
00:49:27,000 --> 00:49:30,720
Speaker 1: weird is that this temperature is inversely proportional to mass.

988
00:49:30,800 --> 00:49:33,600
Speaker 1: We've talked about this before that larger black holes radiate

989
00:49:33,760 --> 00:49:37,160
Speaker 1: less and smaller black holes radiate more, which means smaller

990
00:49:37,200 --> 00:49:40,840
Speaker 1: black holes are warmer. So as black holes get larger,

991
00:49:40,960 --> 00:49:43,600
Speaker 1: they get colder. Einstein says, you shoot a laser beam

992
00:49:43,600 --> 00:49:46,280
Speaker 1: at a black hole, it just stays at zero. Kelvin

993
00:49:46,440 --> 00:49:48,560
Speaker 1: Hawking says, you shoot a laser beam at a black hole,

994
00:49:48,640 --> 00:49:51,719
Speaker 1: it gets colder, whereas if I shoot a laser of you,

995
00:49:51,840 --> 00:49:55,440
Speaker 1: you would get hotter and and more annoyed kind of, yeah,

996
00:49:55,440 --> 00:50:00,560
Speaker 1: I would get louder. Yeah, Oh that's interesting. So it's

997
00:50:00,600 --> 00:50:03,080
Speaker 1: almost like you're putting more energy into the black hole,

998
00:50:03,239 --> 00:50:06,799
Speaker 1: but from the outside it's looked looking like it's losing energy. Yeah,

999
00:50:06,880 --> 00:50:09,080
Speaker 1: it looks like it's getting colder and colder, which is

1000
00:50:09,120 --> 00:50:11,400
Speaker 1: hard to understand, but think about like what might be

1001
00:50:11,440 --> 00:50:13,920
Speaker 1: going on inside the black hole. It's gravity is getting

1002
00:50:13,920 --> 00:50:17,640
Speaker 1: stronger and stronger, and so time is slowing down inside

1003
00:50:17,680 --> 00:50:20,600
Speaker 1: the black hole, and so things are moving more slowly,

1004
00:50:20,680 --> 00:50:24,400
Speaker 1: which you can kind of understand is maybe having lower temperature. Right, So,

1005
00:50:24,400 --> 00:50:26,200
Speaker 1: again we don't know anything about what's going on inside

1006
00:50:26,200 --> 00:50:28,440
Speaker 1: a black hole, but trying to put together like a

1007
00:50:28,520 --> 00:50:31,880
Speaker 1: rough intuition for how black holes could be getting colder

1008
00:50:32,000 --> 00:50:35,240
Speaker 1: as they get larger. Time dilation kind of helps that picture.

1009
00:50:35,440 --> 00:50:37,480
Speaker 1: Oh I see, or could it be that you know,

1010
00:50:37,560 --> 00:50:40,280
Speaker 1: as you add more mass or energy to the black hole,

1011
00:50:40,800 --> 00:50:43,880
Speaker 1: like that gets stronger, so it pull stuff in more

1012
00:50:44,120 --> 00:50:46,920
Speaker 1: and so there's less leakage and so it looks colder,

1013
00:50:47,080 --> 00:50:48,360
Speaker 1: you know what I mean, Like, the more mass the

1014
00:50:48,400 --> 00:50:51,320
Speaker 1: black hole has, the better the coda that is keeping

1015
00:50:51,360 --> 00:50:54,080
Speaker 1: it hidden from us, And so maybe it just looks

1016
00:50:54,120 --> 00:50:56,640
Speaker 1: colder to us. Yeah, in which case, maybe black holes

1017
00:50:56,960 --> 00:50:59,920
Speaker 1: don't follow these laws of black body radiation that every

1018
00:51:00,000 --> 00:51:02,600
Speaker 1: anything else in the universe does, right, because they have

1019
00:51:02,719 --> 00:51:06,120
Speaker 1: this event horizon. Black body radiation can describe everything in

1020
00:51:06,120 --> 00:51:09,399
Speaker 1: the universe that has charged particles. So, for example, dark

1021
00:51:09,440 --> 00:51:12,239
Speaker 1: matter also doesn't follow that rule because dark matter doesn't

1022
00:51:12,280 --> 00:51:15,440
Speaker 1: have electric charge and so it doesn't radiate photons based

1023
00:51:15,440 --> 00:51:17,799
Speaker 1: on its temperature. Maybe the event horizon of a black

1024
00:51:17,800 --> 00:51:20,439
Speaker 1: hole also prevents this kind of radiation, and so maybe

1025
00:51:20,440 --> 00:51:23,200
Speaker 1: there's a mismatch them between the temperature we observe from

1026
00:51:23,200 --> 00:51:26,319
Speaker 1: AFAR and the actual temperature inside a black hole. In

1027
00:51:26,320 --> 00:51:29,960
Speaker 1: a more intuitive sense, I called the cooler theory. It's

1028
00:51:29,960 --> 00:51:33,840
Speaker 1: definitely cooler than any theory I've heard before. Yeah, should

1029
00:51:33,840 --> 00:51:36,359
Speaker 1: we come up with a great acronym for it, better

1030
00:51:36,400 --> 00:51:40,400
Speaker 1: than the j CT or haze cooler theory? There you go. Well,

1031
00:51:40,440 --> 00:51:42,520
Speaker 1: I feel like what you're saying is that to answer

1032
00:51:42,560 --> 00:51:44,759
Speaker 1: the question whether a black hole is hot or not,

1033
00:51:44,960 --> 00:51:47,560
Speaker 1: the the answer is, um, we don't know, you know,

1034
00:51:47,600 --> 00:51:50,480
Speaker 1: it's sort of like asking is that dress blue with

1035
00:51:50,560 --> 00:51:53,040
Speaker 1: black stripes or what with gold stars? It's like it

1036
00:51:53,080 --> 00:51:55,239
Speaker 1: depends on who you ask. Yeah, because we don't know

1037
00:51:55,280 --> 00:51:58,439
Speaker 1: what's going on inside a black hole microscopically, We don't

1038
00:51:58,480 --> 00:52:01,800
Speaker 1: know what it's true temperature. We have this weird clue

1039
00:52:01,840 --> 00:52:04,719
Speaker 1: that black holes do radiat a little bit, and that

1040
00:52:04,760 --> 00:52:07,960
Speaker 1: tells us something about what might be happening inside of them,

1041
00:52:08,000 --> 00:52:09,640
Speaker 1: but we don't know if it really is a clue

1042
00:52:09,640 --> 00:52:12,040
Speaker 1: about the microscopic nature of the black hole. Were just

1043
00:52:12,080 --> 00:52:14,759
Speaker 1: the black holes leak in a weird different way than

1044
00:52:14,800 --> 00:52:18,440
Speaker 1: anything else, right, Because even this leakage theory, this hawkings

1045
00:52:18,560 --> 00:52:21,240
Speaker 1: radiation is still theoretical, Like, we haven't seen that hawking

1046
00:52:21,360 --> 00:52:24,080
Speaker 1: radiation in actual life. That's right, We have never ever

1047
00:52:24,120 --> 00:52:27,560
Speaker 1: seen any hawking radiation from anything. We've looked for black

1048
00:52:27,600 --> 00:52:31,000
Speaker 1: holes evaporating rapidly and giving bright flashes at the end

1049
00:52:31,040 --> 00:52:33,399
Speaker 1: of their life, but we've never seen If we could

1050
00:52:33,440 --> 00:52:35,480
Speaker 1: create black holes of a large hadron collider and then

1051
00:52:35,520 --> 00:52:38,040
Speaker 1: we could see them evaporate on short time skills, that

1052
00:52:38,040 --> 00:52:41,000
Speaker 1: would be exciting, but nobody has ever seen hawking radiation,

1053
00:52:41,080 --> 00:52:43,040
Speaker 1: So it's a black hole hot or not. I feel

1054
00:52:43,080 --> 00:52:45,480
Speaker 1: like you can't really swipe right or left here, you

1055
00:52:45,560 --> 00:52:47,360
Speaker 1: have to just close the app. I don't know, what

1056
00:52:47,640 --> 00:52:49,400
Speaker 1: do you? What do you do? I think black holes

1057
00:52:49,400 --> 00:52:52,880
Speaker 1: are either zero or very very very very very cold.

1058
00:52:53,000 --> 00:52:56,000
Speaker 1: There's no chance they're actually hot. I see you're saying,

1059
00:52:56,160 --> 00:52:59,320
Speaker 1: doesn't matter they're hot or not. They're they're pretty cool. Yeah, exactly,

1060
00:53:00,400 --> 00:53:04,520
Speaker 1: they're still pretty cute. You would still date them, is

1061
00:53:04,719 --> 00:53:07,880
Speaker 1: I think what's is what you're saying. I definitely want

1062
00:53:07,920 --> 00:53:11,879
Speaker 1: to hang out with black holes, yes, forever. Alright, Well,

1063
00:53:11,880 --> 00:53:14,400
Speaker 1: it's an interesting question to tackle, and I think it

1064
00:53:14,400 --> 00:53:16,680
Speaker 1: tells you a lot about what we still don't know

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Speaker 1: about the universe. You know, there are still places that

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Speaker 1: we know exists and our out when we have pictures

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Speaker 1: of but where our theories about the universe breakdown and

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Speaker 1: we need to come up with new theories that maybe

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Speaker 1: people out there are working on or that will work on.

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Speaker 1: In our efforts to understand the universe are usually through

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Speaker 1: the lens of concepts that we understand motion and temperature,

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Speaker 1: and sometimes those very concepts breakdown in the weird contexts

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Speaker 1: that are our universe. Alright, Well, we hope you enjoyed that.

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Speaker 1: Thanks for joining us, see you next time. Thanks for listening,

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Speaker 1: and remember that Daniel and Jorge explained. The Universe is

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Speaker 1: a production of I heart Radio from More podcast from

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Speaker 1: my heart Radio, visit the i heart Radio app, Apple Podcasts,

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Speaker 1: or wherever you listen to your favorite shows. H