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Are black holes hot or not? · Daniel and Kelly’s Extraordinary Universe

• 0:02
  Speaker 1: Yeah, or hey, I've heard that you are a fan
• 0:11
  Speaker 1: of campfires. Yeah, you know, I'm always up for some more. Well,
• 0:15
  Speaker 1: do you worry about, like far future generations of humanity
• 0:20
  Speaker 1: space settlers living under domes or folks living on colony
• 0:23
  Speaker 1: ships getting to have that same experience? Yeah, it doesn't
• 0:28
  Speaker 1: sound like a good idea to start a campfire on
• 0:30
  Speaker 1: a spaceship. So how are they going to capture that
• 0:32
  Speaker 1: essential human experience or is it going to be lost
• 0:35
  Speaker 1: forever in the endless depths of time. I'm sure they
• 0:39
  Speaker 1: can have a VR campfires. Maybe only a VR extends
• 0:43
  Speaker 1: to having smells. They might in the future. You know,
• 0:46
  Speaker 1: you plug something into your brain and it gives you
• 0:47
  Speaker 1: the experience of being in front of a campfire smelling fumes.
• 0:52
  Speaker 1: Or you can just fly too close to the sun. Yeah,
• 0:54
  Speaker 1: the sun is sort of like a campfire, right, it's burning,
• 0:57
  Speaker 1: and you can toast marshmallows with it if you get
• 0:59
  Speaker 1: close enough. That's the way of the future, plasma toasted
• 1:02
  Speaker 1: marshmallows s'mores. Yeah, and you can do your star gazing
• 1:05
  Speaker 1: right there, looking at the flames, seeing stars up clothes. Yeah,
• 1:09
  Speaker 1: just don't get too close or we'll have Plasma Toasted
• 1:12
  Speaker 1: podcast listeners. Hi am or Hey, I'm a cartoonist and
• 1:29
  Speaker 1: the co author of Frequently Asked Questions about the Universe. Hi.
• 1:33
  Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
• 1:36
  Speaker 1: u C Irvine, and I've just realized that neither of
• 1:40
  Speaker 1: us on this podcast speak English as their first language.
• 1:43
  Speaker 1: And you can probably tell. I'm sure on every episode
• 1:48
  Speaker 1: we speak science instead. That's right. Science was our first language.
• 1:53
  Speaker 1: I mean we were writing papers, I'm sure, out of
• 1:55
  Speaker 1: our cribs, right. Yeah. My first words were F equals M,
• 1:58
  Speaker 1: a question mark. My fair words were P value of
• 2:02
  Speaker 1: oh five nature paper, those words. But anyways, welcome to
• 2:08
  Speaker 1: our podcast, Daniel and Jorge Explain the Universe, a production
• 2:11
  Speaker 1: of our Heart Radio in which we try to translate
• 2:14
  Speaker 1: the incredible mysteries of the cosmos into your native language.
• 2:18
  Speaker 1: We think it might just be possible to decode the
• 2:21
  Speaker 1: incredible froth and quantum insanity of our universe into a
• 2:26
  Speaker 1: language that humans can understand, and we can build some
• 2:29
  Speaker 1: sort of mental model in our heads that describes the incredible,
• 2:33
  Speaker 1: vastness and mysteries of the universe that we can pour
• 2:36
  Speaker 1: all of the incredible knowledge and ignorance of humanity into
• 2:40
  Speaker 1: your brain through your ears. That's right. I think of
• 2:43
  Speaker 1: this podcast as the dual lingo of physics and science,
• 2:46
  Speaker 1: translating all those amazing discoveries and things we've learned about
• 2:50
  Speaker 1: the universe into you know, bad jokes and short sound bites.
• 2:53
  Speaker 1: Are we going to start a signing homework? I think
• 2:55
  Speaker 1: duo lingo has homework? Oh? Does it? I think the
• 2:57
  Speaker 1: whole point is that it doesn't have homework. Oh, I
• 2:59
  Speaker 1: thought that exercises people are like doing their dual lingo
• 3:02
  Speaker 1: challenges and stuff. Oh yeah, it has like challenges and rewards,
• 3:06
  Speaker 1: but I'm not sure that's homework. Should we give people
• 3:09
  Speaker 1: rewards for listening to the podcast? Yes, we should definitely
• 3:12
  Speaker 1: give people rewards. We'll mail them bananas, We'll mail them
• 3:16
  Speaker 1: son toasted marshmallows. But that is interesting that neither of
• 3:19
  Speaker 1: our first languages were English, and look at us today
• 3:22
  Speaker 1: we have a podcast. I mean, how many people get
• 3:24
  Speaker 1: to have a podcast these days? Nobody? That's right, That's right.
• 3:28
  Speaker 1: We are super duper rare in the universe. But it
• 3:32
  Speaker 1: is amazing how you can learn different languages as a kid,
• 3:35
  Speaker 1: and even if English isn't your first language. If you
• 3:37
  Speaker 1: learn it when you're young enough, you can become totally
• 3:40
  Speaker 1: fluent in it. Yeah, and that's because you were born
• 3:42
  Speaker 1: in Israel, right, and so you spoke Heybrew that was
• 3:44
  Speaker 1: your first language. Yeah. I was born in Israel and
• 3:47
  Speaker 1: Spokekeybrew is my first language. And I didn't really start
• 3:49
  Speaker 1: speaking English till we moved to the US and it
• 3:51
  Speaker 1: turned out you needed to use English to communicate, and
• 3:54
  Speaker 1: that's when I started to pick it up around age five.
• 3:56
  Speaker 1: And it's interesting to me to think about like how
• 3:58
  Speaker 1: people think what language is are intuitive to them, because
• 4:01
  Speaker 1: we also think about physics sort of the same way.
• 4:03
  Speaker 1: There's certain ideas and physics that are intuitive to you
• 4:07
  Speaker 1: because you learned them as a young kid, temperature, velocity,
• 4:10
  Speaker 1: this kind of stuff. And then as we grow up
• 4:12
  Speaker 1: it's harder and harder to learn crazy new concepts and
• 4:15
  Speaker 1: to really feel fluent in them. You always feel like
• 4:18
  Speaker 1: in some sense you're translating. Yeah, I guess things like
• 4:21
  Speaker 1: quantum physics and the multiverse, those are all very sort
• 4:24
  Speaker 1: of alien to our intuition because you know, as as
• 4:28
  Speaker 1: when you're kids, you're used to like bouncing a ball
• 4:30
  Speaker 1: and holding a ball and those things aren't quite true
• 4:32
  Speaker 1: down to some molecular level. And it's fascinating the look
• 4:35
  Speaker 1: at the history of physics because when these ideas first
• 4:38
  Speaker 1: came out, the old guard were very against them. It's
• 4:41
  Speaker 1: very difficult for the gray haired physicists to accept some
• 4:44
  Speaker 1: of these ideas. Even folks like Einstein were resistant to
• 4:47
  Speaker 1: some of the crazier concepts. But now it's the kind
• 4:49
  Speaker 1: of thing that we teach in college, and they're even
• 4:51
  Speaker 1: books like, you know, quantum Physics for babies. So I
• 4:53
  Speaker 1: feel like one way that we make progress is by
• 4:56
  Speaker 1: introducing these crazy ideas younger and younger so that physicists
• 5:00
  Speaker 1: confluent in them, and then it can become like virtuosos
• 5:03
  Speaker 1: in these ideas rather than always feeling like they're working
• 5:06
  Speaker 1: in some translated alien language of the universe. Interesting. So
• 5:11
  Speaker 1: I guess if you're pregnant and you're carrying a baby,
• 5:13
  Speaker 1: you should maybe play our podcast to your baby the womb,
• 5:18
  Speaker 1: just to get am used to these ideas, right, So
• 5:20
  Speaker 1: it's kind of shock to them later on when they're
• 5:23
  Speaker 1: that are on about it in grad school exactly get
• 5:26
  Speaker 1: them hooked early. I think there's some ethical questions, hey
• 5:29
  Speaker 1: about pushing our podcast on kids, you know, getting them
• 5:32
  Speaker 1: addicted when they're young. I'm not sure how I feel
• 5:34
  Speaker 1: about that. Yeah, I think there might be some government
• 5:37
  Speaker 1: regulations about children's content, but maybe not fetus is content.
• 5:42
  Speaker 1: You know, maybe that's different way to find the loophole there.
• 5:46
  Speaker 1: But yeah, I do think it's good to teach children
• 5:48
  Speaker 1: to think about the questions of the universe in a
• 5:50
  Speaker 1: different way. But I think fundamentally we're always going to
• 5:54
  Speaker 1: struggle to really understand the nature of the universe in
• 5:56
  Speaker 1: a way that's intuitive to us because it is just weird,
• 6:00
  Speaker 1: and we don't have the immediate experience of some of that,
• 6:02
  Speaker 1: like quantum weirdness, for example, or relativistic weirdness, unless we
• 6:06
  Speaker 1: are living among Bose Einstein condensates and in the vicinity
• 6:09
  Speaker 1: of a black hole. We may never find that stuff intuitive. Well,
• 6:13
  Speaker 1: I guess it's kind of hard, because you know, you
• 6:15
  Speaker 1: need sort of Newtonian, regular old school physics intuition to
• 6:19
  Speaker 1: just like get around the world right and play baseball
• 6:22
  Speaker 1: and play basketball with your friends, and that's sort of
• 6:24
  Speaker 1: how the immediate world around his works. But if you
• 6:27
  Speaker 1: train a kid to be a quantum physicist from the beginning,
• 6:30
  Speaker 1: would they be really sort of like awkward or how
• 6:33
  Speaker 1: to touch with the world around them. You know, are
• 6:35
  Speaker 1: you setting this kid up for being very unpopular? Well,
• 6:39
  Speaker 1: I can't speak to the social aspects of it, but
• 6:41
  Speaker 1: it is an interesting question. If somebody had intuition for relativity,
• 6:45
  Speaker 1: could they still operate in everyday in life. The amazing
• 6:48
  Speaker 1: thing about relativity, though, is that it does reproduce our
• 6:50
  Speaker 1: intuition in our scenarios, right, Like, yes, you can use
• 6:53
  Speaker 1: Newtonian physics to describe motion and gravity, but if you
• 6:57
  Speaker 1: use relativity you get the same answers. It's just a
• 7:00
  Speaker 1: lot more complicated and some Newtony physics is like a
• 7:03
  Speaker 1: lot faster. So like somebody will like correctly predict where
• 7:07
  Speaker 1: the baseball is going to go, but it's gonna be
• 7:09
  Speaker 1: like three hours ago, you know, Like, Okay, I can
• 7:12
  Speaker 1: tell you exactly where that curveball went three hours ago,
• 7:15
  Speaker 1: but I missed the pitch. Yeah, I just don't put
• 7:18
  Speaker 1: that kid in the right field or left field, or
• 7:20
  Speaker 1: center field or any part of the field exactly, Like
• 7:24
  Speaker 1: still doing the calculations. Hold on, I'll get back to you.
• 7:26
  Speaker 1: Games over like two hours ago. Dude, physic that that
• 7:31
  Speaker 1: kid that quantum kid. It sounds like a fun, interesting
• 7:34
  Speaker 1: plot for a novel maybe or a movie. Like you know,
• 7:36
  Speaker 1: you train a whole generation of children to be quantum
• 7:39
  Speaker 1: thinkers because of some special science project or something where
• 7:43
  Speaker 1: we're sending people to the quantum world. Yeah, maybe, and
• 7:45
  Speaker 1: then they can be in like two emotional states at once.
• 7:48
  Speaker 1: I hate this movie and I love this movie at
• 7:50
  Speaker 1: the same time. I laughed, I cried. Wait, maybe that's
• 7:52
  Speaker 1: what movie criticism is. It's all quantum mechanical. Yeah, there
• 7:55
  Speaker 1: you go. People will love it and hate it. And
• 7:59
  Speaker 1: this is just about Jorge coming up with plots for novels.
• 8:02
  Speaker 1: This is about asking questions about the nature of reality
• 8:05
  Speaker 1: and trying to understand it. Are trying to apply our
• 8:07
  Speaker 1: intuition are limited toolbox of ways to think about the universe,
• 8:10
  Speaker 1: to probe deep dark questions about the nature of space
• 8:14
  Speaker 1: and time. Yeah, because there are still big questions that
• 8:17
  Speaker 1: are unanswered out there in the universe and huge pockets
• 8:21
  Speaker 1: of the unknown that we have yet to figure out
• 8:23
  Speaker 1: how it works. And sometimes we like to think about
• 8:26
  Speaker 1: what it might be like to touch those things. I
• 8:29
  Speaker 1: don't know about you, but I've looked at the sun
• 8:30
  Speaker 1: and I've wondered, like, how close could you get to
• 8:33
  Speaker 1: the sun? How hot is it really? You know, if
• 8:35
  Speaker 1: I put my finger on it, just for like a
• 8:37
  Speaker 1: micro second, when I get burned. Maybe I'm the only
• 8:41
  Speaker 1: one who's everyone. Yeah, I think walking around wanting to
• 8:44
  Speaker 1: touch everything is what gets in trouble as a kid.
• 8:48
  Speaker 1: It maybe also turns you into a scientist. You're like,
• 8:50
  Speaker 1: I wonder what happens when I press this button? Sounds
• 8:54
  Speaker 1: like a very dark take a way to get rid
• 8:58
  Speaker 1: of a lot of future scientists. That's right. Those of
• 9:00
  Speaker 1: us who survive learned a valuable lesson about what not
• 9:03
  Speaker 1: to touch. But it is interesting that there are pockets
• 9:05
  Speaker 1: of the unknown out there in the universe and that
• 9:07
  Speaker 1: we may want to touch them just to see what
• 9:08
  Speaker 1: they're like. And there is probably not a bigger hole
• 9:12
  Speaker 1: in our knowledge of the universe as big as black holes.
• 9:16
  Speaker 1: That's right. The deepest, darkest mystery of the universe is
• 9:20
  Speaker 1: what's inside a black hole? What's really going on over there?
• 9:23
  Speaker 1: And so of course the physicist in me wants to
• 9:26
  Speaker 1: reach out and touch one. Yeah, And so there are
• 9:28
  Speaker 1: many questions we can ask about black holes, but today
• 9:31
  Speaker 1: we're going to focus on one. I guess that it
• 9:33
  Speaker 1: is all about the black holes appearance, right in some sense,
• 9:36
  Speaker 1: I guess you could say it's appearance. I guess I
• 9:38
  Speaker 1: would say more like it's physical description. It's more to
• 9:40
  Speaker 1: me about black hole temperature than about black holes ability
• 9:43
  Speaker 1: to find meats for example. So today on the podcast,
• 9:47
  Speaker 1: we'll be tackling the question are black holes hot or not?
• 9:57
  Speaker 1: Isn't that a subjective judgment there, Daniel, like our and
• 10:00
  Speaker 1: are you thinking about attracted the black holes? Isn't everybody
• 10:02
  Speaker 1: attracted to black holes? Black holes are very attractive, even
• 10:05
  Speaker 1: to other black holes. Yeah. You know they say opposites attract,
• 10:08
  Speaker 1: but not in physics, right, In physics, massive attract. But
• 10:14
  Speaker 1: if it's something that doesn't have an opposite anyways, I
• 10:18
  Speaker 1: like big masses, and I cannot lie that might be
• 10:20
  Speaker 1: taking asn't to a hole we don't want to go into.
• 10:24
  Speaker 1: But it is an interesting question to think about whether
• 10:26
  Speaker 1: black holes are hot or not. And I'm guessing you
• 10:28
  Speaker 1: mean temperature, not like hotness, that's right. Yeah, I make
• 10:32
  Speaker 1: no evaluation of whether black holes are attractive or not,
• 10:35
  Speaker 1: but I am interested in the question of whether or
• 10:37
  Speaker 1: not black holes are hot or black holes are cold.
• 10:40
  Speaker 1: It's really fascinating because black holes certainly do contain a
• 10:43
  Speaker 1: lot of energy. Yeah, yeah, they have a lot of energy,
• 10:46
  Speaker 1: for sure, but I feel like it's energy that's like
• 10:48
  Speaker 1: trapped somewhere that you can access, so therefore it should
• 10:52
  Speaker 1: feel really cold. You know. That's good intuition. Sometimes, though,
• 10:55
  Speaker 1: our intuition for these things breaks down. Like it's true
• 10:59
  Speaker 1: that the Sun looks hot, and it is hot, but
• 11:02
  Speaker 1: there's other stuff out there in space, like the interstellar medium,
• 11:06
  Speaker 1: which can be like millions of degrees kelvin, but if
• 11:09
  Speaker 1: I dropped you inside of it, you would freeze to death.
• 11:12
  Speaker 1: So sometimes these things can be a little bit counterintuitive. Interesting.
• 11:16
  Speaker 1: So something can be hot but also cold at the
• 11:19
  Speaker 1: same time. Is that like quantum temperature. In the case
• 11:23
  Speaker 1: of the interstellar medium, it's because it's very dilute, so
• 11:26
  Speaker 1: the individual particles are moving at very very high speed.
• 11:29
  Speaker 1: So technically it's hot, but there's not a lot of it,
• 11:32
  Speaker 1: so it wouldn't be enough to keep you warm. You
• 11:34
  Speaker 1: would freeze to death even as you're being smashed into
• 11:37
  Speaker 1: by these high speed particles. I see. So you're saying,
• 11:40
  Speaker 1: like a black hole could be hot and actually hot
• 11:43
  Speaker 1: or hot and actually cold or something in between. Yeah,
• 11:46
  Speaker 1: it's very weird. Think about what happens when you shoot
• 11:48
  Speaker 1: a laser beam at a black hole? In theory it grows,
• 11:52
  Speaker 1: does it also get hotter? Is it possible to shoot
• 11:55
  Speaker 1: a laser beam at something and cool it down? Or
• 11:58
  Speaker 1: what if you throw out like a campfire into black hole?
• 12:00
  Speaker 1: Does the temperature go up or down? A lazy team
• 12:03
  Speaker 1: is basically just like a high tech physics version of
• 12:05
  Speaker 1: a campfire. Yeah. Or what if you throw Brad Pitt
• 12:09
  Speaker 1: into a black hole? He's pretty hot? I don't know.
• 12:12
  Speaker 1: Is he still hot though? Like as time goes onto
• 12:14
  Speaker 1: is he getting hotter or colder? What do you think? Um?
• 12:20
  Speaker 1: Definitely some of those movies started to stay pretty hot
• 12:22
  Speaker 1: into their old age, for sure. Helen Mirren, you know
• 12:25
  Speaker 1: you could throw her into a black hole. I'm sure
• 12:27
  Speaker 1: we'll get hotter. Helen Mirren is so hot she breaks
• 12:30
  Speaker 1: the laws of physics ceriently, Let's not throw her into
• 12:34
  Speaker 1: a black hole, please, But this is an interesting question
• 12:36
  Speaker 1: our black holes or not? And what would happen if
• 12:38
  Speaker 1: you touch him? Would your hand get burned or would
• 12:40
  Speaker 1: it freeze or get sucked in? I guess would it
• 12:43
  Speaker 1: file restraining order against you. So, as usually, we were
• 12:46
  Speaker 1: wondering how many people out there had thought about this
• 12:48
  Speaker 1: question and whether they think black holes will burn you
• 12:51
  Speaker 1: or freeze you. So thank you very much to all
• 12:53
  Speaker 1: those who participate in answering these random questions. If you'd
• 12:57
  Speaker 1: like to hear your voice speculating business, leave for the podcast.
• 13:01
  Speaker 1: Please don't be shy, it's a lot of fun. Right
• 13:03
  Speaker 1: to us. Two questions at Daniel and Jorge dot com.
• 13:06
  Speaker 1: So think about it for a second. Would use why
• 13:08
  Speaker 1: right or left on a picture of a black hole?
• 13:11
  Speaker 1: There's some people had to say. I guess that would
• 13:14
  Speaker 1: depend on how how you're defining temperature. So temperature generally
• 13:19
  Speaker 1: is defined as the amount of movement of a particular
• 13:26
  Speaker 1: set of matter. So maybe the spinning of a black
• 13:31
  Speaker 1: hole would mean that it has lots of energy, which
• 13:35
  Speaker 1: would mean that it might be hot, And then if
• 13:38
  Speaker 1: the black hole wasn't, spinning might be called I guess
• 13:41
  Speaker 1: if they were hot, they would be giving out lots
• 13:45
  Speaker 1: of high energy radiation, and I guess that would make
• 13:49
  Speaker 1: them easier to spot. I know that they give away
• 13:53
  Speaker 1: hawking radiation, but that seems to me to be low
• 13:58
  Speaker 1: energy and low density radiations. So my guests would be
• 14:02
  Speaker 1: black holes are cold, as the name subjects suggests. So
• 14:08
  Speaker 1: there's a lot of matter, it gets compressed down into
• 14:11
  Speaker 1: a black hole and it gets all smashed at one point.
• 14:14
  Speaker 1: The other thing that's kind of like that's like a star, right,
• 14:16
  Speaker 1: that's really hot because there's all this like energy, and
• 14:19
  Speaker 1: maybe if it's like hot as an temperature, which is
• 14:22
  Speaker 1: kind of standard for energy, we're talking about a lot
• 14:24
  Speaker 1: of matter in a small part, I'm going to call
• 14:26
  Speaker 1: that hot. And this sounds very hot to me. I
• 14:28
  Speaker 1: would say black holes have to be cold because when
• 14:31
  Speaker 1: they stuck in the start of the star is obviously
• 14:33
  Speaker 1: circulated around the black hole until they disappear into it.
• 14:36
  Speaker 1: You can kind of see their light on the horizon.
• 14:38
  Speaker 1: And I feel like if they're hot, then the star
• 14:41
  Speaker 1: would have to then get hotter as it approached it,
• 14:44
  Speaker 1: and I feel like that would then cause more of
• 14:46
  Speaker 1: a supernova or just some kind of explosion happening to
• 14:50
  Speaker 1: the star as it entered the black hole. Definitely, inside
• 14:53
  Speaker 1: a black hole, like the object itself, the pressure death,
• 14:58
  Speaker 1: it has be had that energy that it's right there,
• 15:03
  Speaker 1: but like outside, when you go close by by the
• 15:09
  Speaker 1: black hole, a black hole that doesn't interact with anything.
• 15:13
  Speaker 1: And what I want to say is like, no start
• 15:16
  Speaker 1: close to it to feed on that start nothing, no
• 15:21
  Speaker 1: object close to the black hole to interact with it
• 15:24
  Speaker 1: to make it bigger. So in this case, if the
• 15:28
  Speaker 1: black hole doesn't let the light go out, probably doesn't
• 15:33
  Speaker 1: let the heat go out either. So if you're right there,
• 15:38
  Speaker 1: close to it, you wouldn't be had but inside right
• 15:42
  Speaker 1: there when the pressure is might be hard there. I
• 15:46
  Speaker 1: believe black holes must be really hot because the eating
• 15:51
  Speaker 1: energy in form of cooking nation, so they must be
• 15:55
  Speaker 1: really hot, at least on the surface. That's what I think.
• 15:58
  Speaker 1: My intuitions is called old, So I'm going to go
• 16:02
  Speaker 1: up with hot. All right. A lot of pretty um
• 16:05
  Speaker 1: hot takes on this question. I think my favorite one
• 16:08
  Speaker 1: is my intuitions has cold, So I'm going to guess hot.
• 16:12
  Speaker 1: That person has learned some lessons about how the universe works.
• 16:15
  Speaker 1: Right there. Yeah, a person must have been listening to
• 16:18
  Speaker 1: a podcast in the womb. Is every physics question really
• 16:21
  Speaker 1: a trick question? Is that what they've learned? Yeah? I
• 16:27
  Speaker 1: feel like the universe is a true question. Why it's
• 16:31
  Speaker 1: not really a universe? Is actually just a simulation. That's
• 16:33
  Speaker 1: the trick. Yeah, it's something else right that that seems
• 16:36
  Speaker 1: to be the lesson everything you thought. It is not
• 16:38
  Speaker 1: really the way it is, even your thoughts. Maybe there
• 16:42
  Speaker 1: is no truth, man, Maybe there is the truth. But
• 16:44
  Speaker 1: I think there are a lot of really interesting ideas here.
• 16:46
  Speaker 1: There's ideas about how we can think about black holes
• 16:49
  Speaker 1: because they radiate energy, and also thinking about how black
• 16:52
  Speaker 1: holes absorb energy so they should be hot, or the
• 16:54
  Speaker 1: high pressure inside a black hole that might make it hot.
• 16:58
  Speaker 1: It's a lot of really good ideas. Yeah, And I
• 17:00
  Speaker 1: guess it's all sort of depends on what you mean
• 17:02
  Speaker 1: by hotness, right, Like is it related to something like
• 17:05
  Speaker 1: pressure or how much energy it admits or what happens
• 17:08
  Speaker 1: if you touch it? Right? Sort of maybe depends on
• 17:10
  Speaker 1: what you mean by the question and what it means
• 17:12
  Speaker 1: to be hot. Yeah, And as we learn, the whole
• 17:14
  Speaker 1: concept of temperature is a bit of a slippery topic. Yeah,
• 17:18
  Speaker 1: also whether or not you slip on it. Also. Well,
• 17:20
  Speaker 1: let's start at the beginning, and let's recap for listeners, Daniel,
• 17:23
  Speaker 1: what is the black hole? Like, how do physicists think
• 17:25
  Speaker 1: about what a black hole is? So we have several
• 17:28
  Speaker 1: pictures of what a black hole might be. But the
• 17:30
  Speaker 1: truth is that we're fundamentally not really sure what a
• 17:34
  Speaker 1: black hole is, and that's why this question is really interesting.
• 17:37
  Speaker 1: A black hole temperature really goes to the heart of
• 17:40
  Speaker 1: what we do and do not know about black holes.
• 17:43
  Speaker 1: So we have a couple of ideas about black holes.
• 17:46
  Speaker 1: One is what we call a classical picture of a
• 17:48
  Speaker 1: black hole, which means that it comes from general relativity.
• 17:51
  Speaker 1: If you just follow Einstein's rules about how mass bend
• 17:55
  Speaker 1: space time, and space time tells mass how to move,
• 17:58
  Speaker 1: then you end up in this really puzzling, amazing, sort
• 18:01
  Speaker 1: of weird prediction, which is that gravity has this strange
• 18:04
  Speaker 1: runaway effect. Right, mass pulls on mass, which means it's
• 18:08
  Speaker 1: more massive, and then it has more gravity, which means
• 18:10
  Speaker 1: it pulls harder on other masses, which means it has
• 18:13
  Speaker 1: more gravity, and that just keeps going, and eventually you
• 18:16
  Speaker 1: get this weird thing, a singularity, where space has curved
• 18:20
  Speaker 1: so much that you have created an event horizon in
• 18:22
  Speaker 1: a region past which if something gets too close, it
• 18:26
  Speaker 1: can never leave. No information can leak outside this event horizon.
• 18:30
  Speaker 1: That's sort of the classical view of what a black
• 18:32
  Speaker 1: hole is. A singularity a point of infinite density surrounded
• 18:36
  Speaker 1: by a threshold called the event horizon, like a marker.
• 18:40
  Speaker 1: If you go past it, you can never escape, will
• 18:42
  Speaker 1: be trapped forever. Your future is that singularity. Yeah, I
• 18:45
  Speaker 1: like classic black holes, feel like the classics are always
• 18:48
  Speaker 1: the best. But I think what you mean is like
• 18:49
  Speaker 1: a classic black hole was basically physicists thinking about like
• 18:53
  Speaker 1: what happens at the extreme levels, Like what if I
• 18:55
  Speaker 1: take a whole bunch of mass and I cram it
• 18:58
  Speaker 1: into the smallest possible space, or even like a tiny thought,
• 19:01
  Speaker 1: like what happens if a thought has almost infinite mass? Right,
• 19:06
  Speaker 1: Because gravity is very strange compared to the other forces,
• 19:08
  Speaker 1: as you are alluding to earlier. There's no negative gravity,
• 19:11
  Speaker 1: there's no repulsive gravity. I mean, there's dark energy and
• 19:15
  Speaker 1: is the cosmological constant due to potential energy and fields perhaps,
• 19:19
  Speaker 1: But when you're talking about just masses and objects, you
• 19:21
  Speaker 1: only have attraction, and so there's no balance. Right, just
• 19:24
  Speaker 1: keeps going, and so you have enough mass somewhere, then
• 19:28
  Speaker 1: it's just going to keep getting denser and denser and
• 19:30
  Speaker 1: stronger and stronger until eventually you get infinity. Right, this
• 19:34
  Speaker 1: thing diverges that actually goes to infinite density if you
• 19:37
  Speaker 1: give it enough time, right, Because I think one of
• 19:39
  Speaker 1: the things about gravity is that it gets stronger the
• 19:42
  Speaker 1: closer you get to it. Right, Like the formula for
• 19:45
  Speaker 1: it has the distance to it in the denominator in
• 19:47
  Speaker 1: the bottom, So like if you can cram a lot
• 19:49
  Speaker 1: of mass in a small amount of space, then you
• 19:51
  Speaker 1: can get really close to it, which means that your
• 19:54
  Speaker 1: denominator kind of goes to zero, which means that your
• 19:57
  Speaker 1: force sort of like goes almost to infinity. Yeah, and
• 20:00
  Speaker 1: so gravity, left to its own devices, will always generate
• 20:02
  Speaker 1: black holes. The reason that you're not a black hole,
• 20:05
  Speaker 1: and I'm not a black hole, and the Earth isn't
• 20:06
  Speaker 1: the black hole is that there are other forces out
• 20:09
  Speaker 1: there that can oppose gravity, right. The electromagnetic force and
• 20:12
  Speaker 1: the strong force give us structures that balance out gravity,
• 20:16
  Speaker 1: at least for a time. And then eventually if those
• 20:18
  Speaker 1: things fail, then you know, you collapse into a black hole.
• 20:21
  Speaker 1: But that's the prediction of classical general relativity. This incredibly
• 20:25
  Speaker 1: strange phenomena of an infinitely dense point. You said the
• 20:28
  Speaker 1: word sort of inevitably, and I wonder if that's how
• 20:30
  Speaker 1: you think about it, Like Is it inevitable that a
• 20:32
  Speaker 1: bunch of mass, if you leave it out in space,
• 20:34
  Speaker 1: will become a black hole if you have enough of it,
• 20:36
  Speaker 1: like things will sort of crunch down down to an
• 20:39
  Speaker 1: infinite point. Or is it possible even in the classical sense,
• 20:41
  Speaker 1: that things won't crunch down forever, like the Earth is
• 20:44
  Speaker 1: not crunching down to a black hole? Right? Cool question.
• 20:46
  Speaker 1: If there was only gravity, then it would be inevitable.
• 20:49
  Speaker 1: If you have a bunch of particles floating in space
• 20:51
  Speaker 1: and the only force in the universe is gravity, then
• 20:54
  Speaker 1: it will suck them together into a black hole. The
• 20:56
  Speaker 1: only thing that could resist that if there are no
• 20:58
  Speaker 1: other forces is angularm entem. You can imagine like some
• 21:01
  Speaker 1: blob of stuff coalescing sort of like the Earth and
• 21:04
  Speaker 1: then orbiting a central black hole, but not falling in. Right,
• 21:07
  Speaker 1: So you might imagine maybe that's stable. Maybe a blob
• 21:10
  Speaker 1: of stuff orbiting a black hole could avoid it forever.
• 21:13
  Speaker 1: But you know, even if you're orbiting, even in classical
• 21:15
  Speaker 1: general relativity, you are radiating gravitational waves, so you're losing energy,
• 21:20
  Speaker 1: so eventually you will spiral into the black hole. So
• 21:24
  Speaker 1: in the universe with only gravity, then eventually, yes, black
• 21:27
  Speaker 1: holes are totally inevitable. But as you say, the Earth
• 21:31
  Speaker 1: is not a black hole and probably will not become
• 21:33
  Speaker 1: a black hole because the other forces are stronger than
• 21:35
  Speaker 1: gravity and can oppose it for a while. All right,
• 21:37
  Speaker 1: So that's the sort of classical view of a black hole. Um.
• 21:40
  Speaker 1: But then what's the other view the new black holes?
• 21:43
  Speaker 1: The other view is that we don't know what a
• 21:45
  Speaker 1: black hole is, but it can't be that, you know.
• 21:48
  Speaker 1: It's basically it says, this can't be right. Oh my gosh,
• 21:51
  Speaker 1: it's ridiculous. Infinities are not predictions of physical theories. They
• 21:55
  Speaker 1: are failures of physical theories. It says something is wrong
• 21:59
  Speaker 1: here and it's got to be replaced by some other idea,
• 22:02
  Speaker 1: some quantum version of general relativity. We call that quantum gravity.
• 22:07
  Speaker 1: We don't have that theory, but we can criticize the
• 22:10
  Speaker 1: current theory general relativity for not being consistent with quantum
• 22:14
  Speaker 1: mechanical ideas. And that's because the idea of a singularity.
• 22:18
  Speaker 1: You can't have that in quantum mechanics. Well, in general,
• 22:20
  Speaker 1: we don't think you can have singularities or infinities in
• 22:22
  Speaker 1: physics at all. Like whenever you get infinity is a
• 22:25
  Speaker 1: prediction of a physical theory, it's usually a failure. I mean,
• 22:28
  Speaker 1: look back the history. For example, the whole discovery of
• 22:30
  Speaker 1: quantum mechanics was trying to unravel the source of the
• 22:33
  Speaker 1: ultra violet catastrophe. This prediction from classical physics that objects,
• 22:38
  Speaker 1: as they got hotter would radiate infinite temperatures. Like it
• 22:41
  Speaker 1: was nonsense, right, It was a signed to us that
• 22:43
  Speaker 1: there was something wrong, something missing in our calculations that
• 22:47
  Speaker 1: gave this crazy prediction. And so anytime you get an infinity,
• 22:50
  Speaker 1: it's a sign that probably you're doing something wrong. Like
• 22:53
  Speaker 1: we don't see infinities anywhere in the universe. Maybe the
• 22:56
  Speaker 1: universe itself is infinite, but we never measure or observe
• 23:00
  Speaker 1: infinity directly. It seems like a mathematical failure rather than
• 23:03
  Speaker 1: a physical prediction. But more than that, a singularity is
• 23:06
  Speaker 1: a really strange thing in the universe. Right. We talked
• 23:09
  Speaker 1: about singularities on the podcast several times. But in some sense,
• 23:12
  Speaker 1: they're like a path that ends, you know. Quantum mechanics
• 23:15
  Speaker 1: says that time goes from the infinite past to the
• 23:17
  Speaker 1: infinite future, and you could predict what happens to an object,
• 23:21
  Speaker 1: you know, it's deterministic in the sense of like evolving
• 23:24
  Speaker 1: its wave function. But a singularity is where like a
• 23:26
  Speaker 1: point ends, something falls into the singularity and you can
• 23:30
  Speaker 1: no longer predict what's going to happen predictability of physics,
• 23:33
  Speaker 1: which is like the foundation of physics. What we try
• 23:35
  Speaker 1: to do is predict the future given the present. That
• 23:38
  Speaker 1: fails at a singularity, you can't predict what happens after.
• 23:42
  Speaker 1: A singularity is like paths out. You know, everything that
• 23:45
  Speaker 1: falls in, no matter how it started, has the same fate.
• 23:48
  Speaker 1: It's just like is there in the singularity? And so
• 23:51
  Speaker 1: that's inconsistent with like quantum information theory and basically everything
• 23:55
  Speaker 1: we know about how physics works. It just seems like
• 23:57
  Speaker 1: a breakdown more than a prediction. I guess that's why
• 23:59
  Speaker 1: they call it a a singularity. It's singular. It's sense
• 24:03
  Speaker 1: the coolness. All right, Well, I ask some questions about that,
• 24:06
  Speaker 1: and so let's get into more of this idea of
• 24:08
  Speaker 1: a quantum black hole, and then let's get to the
• 24:11
  Speaker 1: question whether it's hot or not. But first let's take
• 24:14
  Speaker 1: a quick break. All right, we are talking about black
• 24:29
  Speaker 1: holes and whether or not they are hot or not.
• 24:32
  Speaker 1: I guess whether or not you would go on a
• 24:34
  Speaker 1: date with a black hole because you're definitely attracted to
• 24:37
  Speaker 1: a black hole. Yeah, On the other hand, I also
• 24:39
  Speaker 1: think black holes are pretty cool, so I'm not sure
• 24:41
  Speaker 1: how to feel about that. Oh boy, now we're mixing
• 24:44
  Speaker 1: all kinds of metaphors here. So you're saying there's a
• 24:47
  Speaker 1: classical view of black holes means that there's sort of
• 24:50
  Speaker 1: a singularity in space because it's sort of the natural
• 24:54
  Speaker 1: extension of what happens if you just have gravity in
• 24:56
  Speaker 1: the universe. But then there's a quantum mechanical view which
• 24:58
  Speaker 1: says that's a singular it's not possible in a quantum world.
• 25:02
  Speaker 1: But I guess my question is does it have to
• 25:04
  Speaker 1: be possible, Like, isn't the point of a singularity that
• 25:07
  Speaker 1: you never actually get there? That's interesting. I mean, we
• 25:10
  Speaker 1: are interested in what's going on in the universe, even
• 25:13
  Speaker 1: if we can't observe it directly, right, So we definitely
• 25:16
  Speaker 1: want like a physical model for what's happening microscopically inside
• 25:21
  Speaker 1: a black hole, because that allow us to understand, you know,
• 25:23
  Speaker 1: the nature of space and time. It might be that
• 25:26
  Speaker 1: we can ever see inside them, and so that you
• 25:29
  Speaker 1: know the observe ability is a question. It's sort of
• 25:31
  Speaker 1: like thinking about the multiverse. It's useful to think about
• 25:34
  Speaker 1: the multiverse, even if you might never observe or go
• 25:37
  Speaker 1: to the multiverse. It's still a question we wanted to
• 25:40
  Speaker 1: answer to. Right, Well, you say that a singularity is
• 25:42
  Speaker 1: inconsistent with quantum mechanics, maybe gives the sense of why
• 25:46
  Speaker 1: that is, Like, you know, maybe the singularity is not consistent,
• 25:49
  Speaker 1: but maybe getting we're approaching the singularity is consistent all
• 25:53
  Speaker 1: the way to infinity. Some of the problems with quantum
• 25:55
  Speaker 1: mechanics and black holes we laid out a minute ago,
• 25:56
  Speaker 1: but there are other ones. As you say, you know,
• 25:58
  Speaker 1: quantum mechanics says that things can be localized in momentum
• 26:01
  Speaker 1: and in location perfectly well, right, But a singularity violates that.
• 26:05
  Speaker 1: It's an infinitely well localized point in space. And so
• 26:09
  Speaker 1: quantum mechanics says, if particles are in an infinitely well
• 26:13
  Speaker 1: localized point, they should have an infinite uncertainty in their energy,
• 26:17
  Speaker 1: which would mean some of them would have basically infinite energy, right,
• 26:21
  Speaker 1: And so it's sort of like physically impossible. There's a
• 26:23
  Speaker 1: minimum quantum fuzz to the universe, which has singularity violates,
• 26:28
  Speaker 1: and so we just don't think it's possible. That doesn't
• 26:30
  Speaker 1: mean that black holes aren't real, right, It might mean
• 26:32
  Speaker 1: that black holes are there, but that at their heart
• 26:34
  Speaker 1: there isn't a singularity. There's some like weird quantum fuzz happening,
• 26:38
  Speaker 1: and you might not be able to tell the difference
• 26:40
  Speaker 1: from the outside because from the outside it's all just
• 26:42
  Speaker 1: strong gravity. But you know, we want to know what's
• 26:44
  Speaker 1: going on inside that black hole, and it does have
• 26:47
  Speaker 1: consequences for whether the black hole is hot or not.
• 26:51
  Speaker 1: You're saying, like a black hole is still a whole.
• 26:52
  Speaker 1: It's still it could still look like a hole to us,
• 26:55
  Speaker 1: but at the very center of the black hole, like
• 26:57
  Speaker 1: what's going on at the very very center it doesn't
• 26:59
  Speaker 1: actually get to a singularity? Or is it kind of
• 27:02
  Speaker 1: fuzzy down there? And I guess, just to be contrarian,
• 27:04
  Speaker 1: could it be both? Like could there be a singularity?
• 27:07
  Speaker 1: And as you get closer to the singularity, you know,
• 27:10
  Speaker 1: spaces crunched down so much that you're you're still fuzzy
• 27:13
  Speaker 1: but also kind of a singularity, do you know what
• 27:15
  Speaker 1: I mean? No, but I like to hear more about
• 27:17
  Speaker 1: that idea. How can you be a singularity and fuzzy. Well,
• 27:20
  Speaker 1: gravity bend space right in some ways that you're sort
• 27:22
  Speaker 1: of compressing space and in the middle of a black hole.
• 27:25
  Speaker 1: So as you're a protesting cularity, maybe you're still fuzzy
• 27:28
  Speaker 1: in a quantum sense, but spaces crunched down so much
• 27:31
  Speaker 1: that you're kind of fuzzy in a very small space.
• 27:34
  Speaker 1: That's basically a singularity. I see. I mean it could
• 27:36
  Speaker 1: be something you could never approach, or something that sort
• 27:39
  Speaker 1: of remains at a certain observable size no matter how
• 27:42
  Speaker 1: close you get to it, without actually being a point. Uh.
• 27:45
  Speaker 1: And that's true, that's interesting and maybe a possibility for
• 27:48
  Speaker 1: quantum mechanical description, but I don't think that would qualify
• 27:51
  Speaker 1: as a singularity. It's definitely not what general relativity predicts,
• 27:54
  Speaker 1: for example, And you might think, well, why do we
• 27:56
  Speaker 1: care what general relativity predicts? And we care because general
• 27:59
  Speaker 1: relative he seems to be accurate about everything else in
• 28:03
  Speaker 1: our universe. You know, the way that space expands, the
• 28:06
  Speaker 1: way the space ripples, the way that objects move through
• 28:09
  Speaker 1: space and time, very very precisely. It seems to get
• 28:12
  Speaker 1: everything else exactly right, and the math of it is beautiful.
• 28:16
  Speaker 1: It's gorgeous. I mean, theoretical physicist who learned it, They
• 28:18
  Speaker 1: like fall in love with the equations, and so it
• 28:21
  Speaker 1: seems to like speak to something deeply true about the universe.
• 28:24
  Speaker 1: So to discover that it's not that there's something that
• 28:27
  Speaker 1: it fails to describe is an opportunity to learn something
• 28:30
  Speaker 1: really fundamental about the nature of space. Yeah, I guess
• 28:33
  Speaker 1: kind of. It's kind of like Newtonian physics. We thought
• 28:36
  Speaker 1: was great because it predicted the like the paths of
• 28:38
  Speaker 1: the planets and the orbits and whether or not you
• 28:41
  Speaker 1: can catch a baseball, but it sort of breaks down
• 28:44
  Speaker 1: to a different scales kind of, right, you're saying that
• 28:46
  Speaker 1: relativity also sort of works for everything else that we
• 28:48
  Speaker 1: see around us, but when you get down to the
• 28:50
  Speaker 1: smallest levels, it doesn't have quite a solution that works exactly.
• 28:55
  Speaker 1: And we would like to know what the fundamental nature
• 28:58
  Speaker 1: of space is. You know, at the smallest level, is
• 29:01
  Speaker 1: gravity actually a quantum force mediated by gravitons or is
• 29:04
  Speaker 1: space itself quantized? Did this little foam It's more than
• 29:08
  Speaker 1: just an academic question of what's that the invisible heart
• 29:11
  Speaker 1: of a black hole. Understanding the nature of space and
• 29:13
  Speaker 1: time might give us great power over it, you know,
• 29:15
  Speaker 1: let us develop warp drives and wormholes and explore the universe,
• 29:20
  Speaker 1: and so definitely a question worth asking. Yeah, well, okay,
• 29:23
  Speaker 1: let's get back to our main question of this episode,
• 29:25
  Speaker 1: which is whether black holes are hot or not? And
• 29:28
  Speaker 1: I guess we mean in the sense of temperature. Do
• 29:31
  Speaker 1: black holes have a high temperature or do they have
• 29:33
  Speaker 1: a very low temperature? And so let's start maybe by
• 29:36
  Speaker 1: talking about what temperature means in this context. Yeah, the
• 29:39
  Speaker 1: temperature is really slippery and tricky. Sometimes when we talk
• 29:42
  Speaker 1: about temperature, we mean like how much energy is in
• 29:45
  Speaker 1: the particles inside something. So you have a banana in
• 29:48
  Speaker 1: front of you, you can ask is this banana hot
• 29:50
  Speaker 1: or not? What you really mean is how much internal
• 29:53
  Speaker 1: energy is there? Are the particles inside the banana wiggling
• 29:56
  Speaker 1: a lot? Are they frozen in place not wiggling a lot?
• 30:00
  Speaker 1: And you can actually do cool calculations to connect like
• 30:02
  Speaker 1: how much those guys are wiggling to the apparent temperature
• 30:06
  Speaker 1: that you would experience if you like touch the banana.
• 30:08
  Speaker 1: That's so if your intuitive sense of temperature, and the
• 30:10
  Speaker 1: way you measure temperature usually is by like sticking a
• 30:13
  Speaker 1: thermometer in something, and the energy transfers from the banana
• 30:17
  Speaker 1: to the thermometer and you read it out on the thermometer.
• 30:20
  Speaker 1: That's your intuitive sense of temperature. But that doesn't really
• 30:22
  Speaker 1: work with something that you can't touch. So if you
• 30:25
  Speaker 1: want to measure the temperature of something you can't touch,
• 30:27
  Speaker 1: there are other ways to do it, Like we can
• 30:29
  Speaker 1: measure the temperature of the Sun, even though no human
• 30:31
  Speaker 1: object has ever touched the Sun and then come back
• 30:34
  Speaker 1: out again, right, or like even now they have contact
• 30:38
  Speaker 1: list thermometers, right, the kind of is just kind of
• 30:40
  Speaker 1: like cover over your forehead and it somehow measures the
• 30:42
  Speaker 1: temperature without touching it exactly. So the way they do
• 30:45
  Speaker 1: that is by measuring the radiation that you generate, not
• 30:49
  Speaker 1: like you know, you're shooting off alpha particles and creating
• 30:52
  Speaker 1: hulks everywhere you go or spider Man, but you generate
• 30:55
  Speaker 1: energy like you radiate photons everywhere you go, because everything
• 30:59
  Speaker 1: in the universe that has a temperature does radiate energy,
• 31:03
  Speaker 1: Like the Sun radiates energy in the visible spectrum because
• 31:06
  Speaker 1: it's pretty hot, and the Earth radiates energy in a
• 31:09
  Speaker 1: much much longer wavelength because it's much colder than the Sun.
• 31:12
  Speaker 1: But it still does, and you generate energy at a
• 31:15
  Speaker 1: higher wavelength than the Earth does, which is why if
• 31:17
  Speaker 1: you put on like infrared goggles, you can see if
• 31:20
  Speaker 1: there's somebody hanging out in your backyard at night, because
• 31:22
  Speaker 1: they're generating a different kind of light, a light that's
• 31:25
  Speaker 1: invisible to your eyes but can be picked up by
• 31:27
  Speaker 1: infrared goggles, and that's it's a pretty cool burger or trespasser.
• 31:32
  Speaker 1: You can't see them. But I guess maybe the basic
• 31:34
  Speaker 1: question is why why does that happen? Like why do
• 31:37
  Speaker 1: hot things amid infrared light? Yet has to do with
• 31:41
  Speaker 1: energy just liking to get spread out, you know, a microscopically,
• 31:44
  Speaker 1: imagine like a blob of stuff, and that blaba stuff
• 31:47
  Speaker 1: isn't inactive, right, it's constantly radiating stuff and reabsorbing it.
• 31:51
  Speaker 1: So electrons within your banana are shooting off photons and
• 31:54
  Speaker 1: then other atoms are reabsorbing that. But near the edges
• 31:57
  Speaker 1: that doesn't always get reabsorbed. Some of it just shoots out.
• 32:00
  Speaker 1: So that energy is just like getting spread out through
• 32:02
  Speaker 1: the universe, partially by radiating stuff. And what's really interesting
• 32:06
  Speaker 1: is that the spectrum you emit is controlled by your temperature,
• 32:10
  Speaker 1: so if you have a really high temperature, you tend
• 32:11
  Speaker 1: to emit at shorter wavelengths. At higher frequencies, you have
• 32:15
  Speaker 1: a really low temperature, you tend to emit lower frequencies
• 32:18
  Speaker 1: or longer wavelengths. There's, for example, really really hot gas
• 32:21
  Speaker 1: emits in the X ray or the ultra violet, and
• 32:24
  Speaker 1: really really cold objects like asteroids floating in space emit
• 32:28
  Speaker 1: in the infrared. Right. Yeah, because we've talked about in
• 32:30
  Speaker 1: this podcast about how temperature is related to the kinetic
• 32:34
  Speaker 1: energy or like how fast the particles or something are
• 32:37
  Speaker 1: moving within you know, the volume that you're measuring the
• 32:39
  Speaker 1: temperature of. But then I guess that question is how
• 32:42
  Speaker 1: does that relate to the wavelength of light that's emitted? Like,
• 32:44
  Speaker 1: first of all, why does they emit light at all?
• 32:46
  Speaker 1: And the second why do they emit light at a
• 32:48
  Speaker 1: higher frequency. So we've been talking about them emitting light,
• 32:51
  Speaker 1: and by not we just mean photons. Right, Remember that
• 32:54
  Speaker 1: by light we don't always mean things that you can see.
• 32:57
  Speaker 1: So we're talking about something emitting light, you shouldn't expect
• 32:59
  Speaker 1: it to be glowing in a way that your eyeballs
• 33:01
  Speaker 1: could pick it up. You sit in a dark room
• 33:03
  Speaker 1: with a banana and stare at it. You're still not
• 33:05
  Speaker 1: going to see that banana glow because while these are
• 33:08
  Speaker 1: photons and they are hitting your eyeballs, your eyeballs can't
• 33:11
  Speaker 1: see them. So it's emitting light because it's made out
• 33:14
  Speaker 1: of charged particles, you know, electrons and atoms, and when
• 33:18
  Speaker 1: those things move and accelerate, they always emit light, you know.
• 33:21
  Speaker 1: That's what electrons do. From an electron to accelerate, for
• 33:24
  Speaker 1: like change direction, for it to slow down or speed up,
• 33:26
  Speaker 1: it has to admit a photon because that's the only
• 33:29
  Speaker 1: process that allows it to do it right. It needs
• 33:31
  Speaker 1: to like push off of something. The same way, if
• 33:33
  Speaker 1: you're in a rocket ship and you want to accelerate,
• 33:35
  Speaker 1: you've got to throw something out the back, right, you
• 33:38
  Speaker 1: need some mass, some rocket fuel, or some propellant to
• 33:41
  Speaker 1: toss out the back. That's the only thing electron can
• 33:44
  Speaker 1: do to change its direction, to accelerate or to decelerate
• 33:48
  Speaker 1: is to emit a photon. So because the banana is
• 33:50
  Speaker 1: made out of charged particles, it tends to emit photons.
• 33:53
  Speaker 1: It also emits other stuff, you know, emits neutrinos and
• 33:55
  Speaker 1: emits other kinds of radiation from the other kinds of
• 33:58
  Speaker 1: forces that it interacts with. But that's why it emits light,
• 34:01
  Speaker 1: and that's why emits photons, because it's made of charged particles.
• 34:04
  Speaker 1: And why does it emit different frequencies based on its temperature. Well,
• 34:08
  Speaker 1: you know, higher energy stuff emits higher frequency photons. You
• 34:12
  Speaker 1: have like electrons whizzing around your atom with more energy,
• 34:15
  Speaker 1: they have more energy, They will jump down more energy
• 34:17
  Speaker 1: levels and they will admit higher energy photons, which have
• 34:21
  Speaker 1: higher frequencies and shorter wavelengths. So it's just sort of
• 34:23
  Speaker 1: like more energy available because everything moving around has more energy.
• 34:28
  Speaker 1: You get on average higher energy photons, not purely. It's
• 34:30
  Speaker 1: not like a spectral line, right, There's like a distribution,
• 34:33
  Speaker 1: so you get some of the high frequencies some of
• 34:35
  Speaker 1: the low frequencies. But the shape shifts as you get
• 34:38
  Speaker 1: to higher temperatures. The peak moves and the most likely
• 34:41
  Speaker 1: frequency gets higher and higher as the temperature gets higher
• 34:45
  Speaker 1: and higher. Interesting, it's almost like you have a bunch
• 34:49
  Speaker 1: of atoms and they have some charge to them, and
• 34:51
  Speaker 1: it had they have electrons and protons and set them
• 34:53
  Speaker 1: and they're all sort of trapped together by the electromagnetic
• 34:57
  Speaker 1: forces that are holding them together. Kind of right, or
• 34:59
  Speaker 1: something to bumping to each other. And you're saying every time,
• 35:02
  Speaker 1: you know, Adam gets pulled into the banana, or a
• 35:05
  Speaker 1: gas particle bumps into another gas particle. You know, stuff
• 35:09
  Speaker 1: happens in the electromagnetic force, and so that causes photons
• 35:13
  Speaker 1: to shoot off. Yeah, exactly. Every time two electrons talk
• 35:16
  Speaker 1: to each other, that's a photon. So if you have
• 35:18
  Speaker 1: a blob of charge stuff, there's photons everywhere. It's just
• 35:20
  Speaker 1: like a huge mass of photons and particles constantly interacting
• 35:24
  Speaker 1: with each other, and some of that just bleeds out
• 35:26
  Speaker 1: the signs. It's like if you're in an apartment next
• 35:28
  Speaker 1: to a party, right and everybody shouting at each other,
• 35:30
  Speaker 1: then you're gonna be hearing some of those conversations, right right. Yeah,
• 35:34
  Speaker 1: unless you're in the party, then then it's a good time.
• 35:37
  Speaker 1: And as they drink more and more, they tend to
• 35:39
  Speaker 1: get higher and higher energy, right, and then this analogy
• 35:41
  Speaker 1: breaks down, Yeah, physics, as the parties put the main point.
• 35:45
  Speaker 1: So in terms of black holes, I think what you're
• 35:47
  Speaker 1: saying is that temperature is normally defined as like the
• 35:51
  Speaker 1: kinetic energy or how fast the particles of something are moving.
• 35:54
  Speaker 1: But it's sort of related to different things in different
• 35:57
  Speaker 1: ways that we measured, Like we can measure it by
• 35:59
  Speaker 1: touching in and some of kinetic energy moves to you.
• 36:01
  Speaker 1: Or you can measure the light that comes from it
• 36:03
  Speaker 1: because of this radiation, so that also sort of tells
• 36:06
  Speaker 1: you the temperature. And so it kind of sort of
• 36:08
  Speaker 1: depends on what do you mean by temperature of a
• 36:11
  Speaker 1: black hole? Do you mean like the energy it radiates,
• 36:13
  Speaker 1: or do you mean like what would actually happen if
• 36:15
  Speaker 1: you touch it? Yeah, Well, the fascinating question about black
• 36:17
  Speaker 1: holes is that we don't know what's going on inside
• 36:20
  Speaker 1: the microscopically, but we can ask questions about their radiation.
• 36:25
  Speaker 1: Do they give off any radiation? And if we use
• 36:27
  Speaker 1: radiation as a way to measure temperature, then we can
• 36:30
  Speaker 1: talk about the temperature something without having any idea about
• 36:33
  Speaker 1: what's going on inside it microscopically, like we can measure
• 36:35
  Speaker 1: the temperature of the sun without knowing like how do
• 36:38
  Speaker 1: those plasma tubes work inside the sun? What is going
• 36:41
  Speaker 1: on at the heart of it. We can still measure
• 36:43
  Speaker 1: its temperature the same way they measure your temperature on
• 36:46
  Speaker 1: your forehead without touching you, without knowing, like you know,
• 36:49
  Speaker 1: are you sick or not, what's going on inside your brain?
• 36:52
  Speaker 1: They don't know any of that, but they can still
• 36:54
  Speaker 1: measure your temperature. So it's a bit of an extrapolation
• 36:57
  Speaker 1: to say we don't know what's going on inside something,
• 36:59
  Speaker 1: we measure radiation and then we talk about what temperature
• 37:02
  Speaker 1: it has, right. I think what you mean is like
• 37:04
  Speaker 1: if you take a step back from the black hole
• 37:07
  Speaker 1: and you know, not worry about what's going on at
• 37:09
  Speaker 1: the very center, you know, how hot does it look
• 37:12
  Speaker 1: from afar? Yeah, we use this concept of temperature a
• 37:15
  Speaker 1: lot in physics in a way that might be confusing otherwise.
• 37:18
  Speaker 1: Like we talked about the temperature of the cosmic microwave
• 37:20
  Speaker 1: background radiation. We say that's two point seven three kelvin.
• 37:23
  Speaker 1: What does that mean? Doesn't really have a temperature. What
• 37:26
  Speaker 1: it means is that the cosmic microwave background radiation is
• 37:29
  Speaker 1: radiation at a wavelength that would be emitted by an
• 37:32
  Speaker 1: object at two point seven three kelvin. That's the black
• 37:35
  Speaker 1: body radiation for an object at that temperature would be
• 37:38
  Speaker 1: the frequency of the CMB. In the same way, we
• 37:41
  Speaker 1: can look for radiation coming off of black holes and
• 37:43
  Speaker 1: use that to measure its temperature and then trying to
• 37:47
  Speaker 1: deduce what might be going on inside of it from that. Well,
• 37:51
  Speaker 1: I guess it's kind of weird because you know, I
• 37:52
  Speaker 1: imagine that a black hole has particles inside of it
• 37:55
  Speaker 1: moving and a certain speed, and it does have sort
• 37:57
  Speaker 1: of like a kinetic internal kinetic energy. But you're saying, like,
• 38:00
  Speaker 1: let's not even worry about that because we don't really
• 38:02
  Speaker 1: know what happens beyond like the black hole's event horizon.
• 38:05
  Speaker 1: So let's just take a step back and see how
• 38:07
  Speaker 1: hot it looks. Yeah, well, let's start there because that's
• 38:10
  Speaker 1: something we can do from the outside, and then let's
• 38:12
  Speaker 1: turn that around and try to understand based on its
• 38:16
  Speaker 1: temperature what might be going on inside. So let's use
• 38:19
  Speaker 1: that as a probe, right, because temperature is like a message.
• 38:22
  Speaker 1: It tells us something that's going on inside from afar,
• 38:26
  Speaker 1: So without touching something, you can get a little bit
• 38:28
  Speaker 1: of information about what might be going on inside. And
• 38:30
  Speaker 1: in the end, that's the goal, is to try to
• 38:32
  Speaker 1: understand what's going on inside the black hole. Right. But
• 38:35
  Speaker 1: I guess it's messed up because you know, the definition
• 38:37
  Speaker 1: of a black hole is that nothing can escape of it,
• 38:40
  Speaker 1: not even light. What does it mean to measure the
• 38:42
  Speaker 1: light coming off of a black hole? If light cannot
• 38:44
  Speaker 1: escape a black hole. Yeah, that's true. Nothing can escape
• 38:47
  Speaker 1: the event horizon, nothing from inside can ever come out.
• 38:50
  Speaker 1: But that doesn't mean that black holes don't radiate. But
• 38:52
  Speaker 1: there's a difference in how you describe the radiation from
• 38:56
  Speaker 1: black holes. In classical gr like Einstein's pure singularity black
• 39:00
  Speaker 1: holes and more moderate attempts like Hawking's view of what
• 39:04
  Speaker 1: a black hole is do they give us very different
• 39:06
  Speaker 1: senses for what might be going on inside the black hole. Interesting?
• 39:09
  Speaker 1: All right, Well, let's get into whether Einstein and Stephen
• 39:13
  Speaker 1: Hawking are also hot or not and whether or not
• 39:16
  Speaker 1: they're right about the temperature of black holes. Will dive
• 39:19
  Speaker 1: into that and what it all means, but first let's
• 39:21
  Speaker 1: take another quick break. All right, we're talking about whether
• 39:36
  Speaker 1: black holes are hot or not. And it's kind of
• 39:39
  Speaker 1: weird to think of black holes as hot because they
• 39:41
  Speaker 1: are hols, Like, how can a hole be hot? And
• 39:44
  Speaker 1: I was saying earlier, Daniel, how it's weird to think
• 39:47
  Speaker 1: of the heat radiated like the light hit radiated by
• 39:50
  Speaker 1: a hot black hole because black holes are are black,
• 39:54
  Speaker 1: they're by definition things that don't radiate light or trap light.
• 39:57
  Speaker 1: How can something be both radiating heat and also trapping
• 40:01
  Speaker 1: heat forever? Well, you know, Einstein would agree with you.
• 40:04
  Speaker 1: Einstein's general relativity says that black holes are perfect absorbers.
• 40:09
  Speaker 1: They do not radiate any light. Anything that hits them
• 40:12
  Speaker 1: falls in, and they radiate nothing. And so from the
• 40:16
  Speaker 1: general relativistic point of view, black holes are at absolute zero.
• 40:20
  Speaker 1: They have zero temperature. What is the expected radiation from
• 40:24
  Speaker 1: an object that absolute zero? It's nothing. And so if
• 40:27
  Speaker 1: black holes radiate nothing, then therefore they must have zero temperature.
• 40:32
  Speaker 1: That's the g R version. The classical view of a
• 40:35
  Speaker 1: black hole. All you can know is it's mass, its charge,
• 40:39
  Speaker 1: and it's spin, not its temperature, because that would be
• 40:41
  Speaker 1: like information about what's going on inside the black hole. So,
• 40:45
  Speaker 1: according to Einstein, black holes are cold. They're like infinitely
• 40:49
  Speaker 1: cold or perfectly cold. That's right. According to Einstein, you
• 40:51
  Speaker 1: can shoot a laser beam at a black hole and
• 40:54
  Speaker 1: never heat it up. It will just keep eating that
• 40:56
  Speaker 1: laser but never get hotter. All right, well then, but
• 40:59
  Speaker 1: what does Stephen Hawkinson? So Stephen Hawking says, actually, if
• 41:04
  Speaker 1: we live in a quantum mechanical universe, then that cannot
• 41:07
  Speaker 1: be true. So Hawking did his famous calculation where he thought,
• 41:11
  Speaker 1: let's think about a black hole, and now, instead of
• 41:14
  Speaker 1: thinking about what's going on inside the black hole, because
• 41:16
  Speaker 1: we can't and we have no idea how quantum gravity works,
• 41:19
  Speaker 1: let's just try to put the black hole in a
• 41:20
  Speaker 1: quantum universe and say, how do you do quantum mechanics
• 41:24
  Speaker 1: when you have an event horizon if there's something there
• 41:26
  Speaker 1: which eats all the information. And so he did a
• 41:29
  Speaker 1: bunch of fancy calculations and quantum field theory and he
• 41:32
  Speaker 1: discovered that the only way this works, the only way
• 41:34
  Speaker 1: you could have like a boundary condition like a black hole,
• 41:37
  Speaker 1: is if you have radiation coming out of the black hole.
• 41:40
  Speaker 1: So he found like solutions to the quantum field theory
• 41:43
  Speaker 1: that require outgoing waves from the black hole. And that's
• 41:47
  Speaker 1: really interesting. That says that, like, if you have black
• 41:49
  Speaker 1: holes and the universe is quantum mechanical, then they must
• 41:52
  Speaker 1: be emitting something. And he went a step further, he said, well,
• 41:55
  Speaker 1: you know, how does this radiation work, what does it
• 41:57
  Speaker 1: look like? And what he discovered, and this is sort
• 41:59
  Speaker 1: of the fascinating moment, is that the radiation spectrum that
• 42:03
  Speaker 1: you expect from the vicinity of a black hole follows
• 42:06
  Speaker 1: exactly the spectrum you get from black bodies. Black bodies,
• 42:09
  Speaker 1: like we talked about earlier, don't just emit at one number, right,
• 42:12
  Speaker 1: It's not like the sun emits at only one frequency.
• 42:15
  Speaker 1: There's this shape to their spectrum. What he discovered is
• 42:17
  Speaker 1: that this radiation that he was predicting black holes emit
• 42:20
  Speaker 1: also has a shape, and that shape matches exactly the
• 42:23
  Speaker 1: shape you expect from black bodies at a certain temperature,
• 42:27
  Speaker 1: at a non zero temperature. So he concluded there must
• 42:31
  Speaker 1: be some radiation from black holes, and black holes must
• 42:34
  Speaker 1: have a non zero temperature. Well, I feel like maybe
• 42:37
  Speaker 1: that's not quite what he said, right, Like he's I
• 42:39
  Speaker 1: think what you're saying that he's saying is that, um,
• 42:43
  Speaker 1: black holes kind of have to leak stuff out, like
• 42:47
  Speaker 1: they can't trap stuff in. Thereforever stuff leaks out. And
• 42:50
  Speaker 1: the stuff that the energy that leaks out sort of
• 42:52
  Speaker 1: looks like something that would have a temperature, But that
• 42:55
  Speaker 1: doesn't necessarily mean it's the temperature of the black hole. Right,
• 42:58
  Speaker 1: You're exactly right. And in the paper he even said,
• 43:01
  Speaker 1: like be careful about interpreting this literally as a temperature.
• 43:04
  Speaker 1: It's more like an effective temperature. It's an attempt to
• 43:07
  Speaker 1: describe what might be going on inside the black hole.
• 43:10
  Speaker 1: But we don't know microscopically, we have no idea, you know,
• 43:13
  Speaker 1: is everything inside the black hole totally frozen? Is this
• 43:16
  Speaker 1: like quantum space wiggling? We don't understand what's generating this radiation.
• 43:20
  Speaker 1: But it's a way to describe the black hole sort
• 43:22
  Speaker 1: of thermodynamically and statistical point of view, right, And so
• 43:26
  Speaker 1: he says, you're right, it seems to like it should
• 43:28
  Speaker 1: generate a spectrum as if it had a temperature. What
• 43:31
  Speaker 1: that temperature means in terms of like the microscopic wiggles inside.
• 43:35
  Speaker 1: Hawking didn't say, couldn't say, and we still don't know,
• 43:38
  Speaker 1: but I guess can you step us through a little
• 43:40
  Speaker 1: bit of how he did it or how he reached
• 43:42
  Speaker 1: this conclusion, Like what does it mean that you can't
• 43:44
  Speaker 1: have a perfect hole in the universe? Like why does
• 43:46
  Speaker 1: it have to leak because of quantum mechanics or what? Yeah,
• 43:49
  Speaker 1: because of quantum mechanics. And so you take a black
• 43:51
  Speaker 1: hole and you put it in the universe. The universe
• 43:54
  Speaker 1: also has fields, and you know, fields for fermions fields
• 43:57
  Speaker 1: for bosons, you know, the electromagnetic field, the tron field,
• 44:00
  Speaker 1: and now you want to quantize those fields. Is what
• 44:02
  Speaker 1: we do in quantum mechanics to get to quantum field theory.
• 44:05
  Speaker 1: We say the universe is filled with space, and the
• 44:07
  Speaker 1: space has fields in it, and those fields are quantized.
• 44:10
  Speaker 1: They can only have certain solutions, right, not any arbitrary
• 44:13
  Speaker 1: continuous set of solutions, but only specific solutions like a ladder,
• 44:17
  Speaker 1: just like electrons whizzing around an atom have a ladder
• 44:20
  Speaker 1: of solutions. And so the thing that he ran up
• 44:22
  Speaker 1: against is that you add a black hole to that.
• 44:24
  Speaker 1: That changes how you can quantize these fields or for
• 44:27
  Speaker 1: that quantization to work. The various consistency conditions on this
• 44:31
  Speaker 1: quantization you need, like unitarity, so you're not predicting things
• 44:35
  Speaker 1: would have probability more than one and things that not
• 44:37
  Speaker 1: contradict themselves. Various internal consistency conditions on the quantization of
• 44:42
  Speaker 1: the fields in the presence of a black hole requires
• 44:46
  Speaker 1: this radiation to exist, right. I wonder if what it
• 44:49
  Speaker 1: means is that you know, he's saying that like you
• 44:52
  Speaker 1: can have a perfect event horizon, like you can't have
• 44:56
  Speaker 1: like this perfect perfectly smooth boundary where if you cross one,
• 45:01
  Speaker 1: you know, tiny little bit, you're in the black hole,
• 45:04
  Speaker 1: and where you step out a little bit, you're out
• 45:06
  Speaker 1: of the black hole. Maybe what he's saying is that,
• 45:08
  Speaker 1: you know, we live in a quantum universe. You can
• 45:10
  Speaker 1: have that kind of like stark boundary or certainty, and
• 45:13
  Speaker 1: so as a result, you can have a fuzzy event
• 45:16
  Speaker 1: horizon and which will tend to leak. I think that's
• 45:19
  Speaker 1: one way to interpret it, but I think it's dangerous
• 45:21
  Speaker 1: to try to come up with a microscopic interpretation. I mean,
• 45:25
  Speaker 1: I love that your brain immediately goes to, like, what's
• 45:27
  Speaker 1: happening right there at the edge, What does that really
• 45:29
  Speaker 1: mean for an individual particle? The truth is to understand
• 45:32
  Speaker 1: that we need a theory of quantum gravity. We have
• 45:34
  Speaker 1: to understand how gravity affects quantum particles, and we just
• 45:38
  Speaker 1: don't you know, quantum particles can do these weird things
• 45:40
  Speaker 1: like have a probability be in two different places at
• 45:43
  Speaker 1: the same time. How does gravity affect that does a
• 45:45
  Speaker 1: tug halfway on both of the places where the particle
• 45:49
  Speaker 1: is Like, we just don't understand the microscopic picture of
• 45:52
  Speaker 1: quantum mechanics and gravity at all, So we can't really
• 45:55
  Speaker 1: tell a story about what happens right at the edge
• 45:58
  Speaker 1: of the event horizon for quanty of objects, but we
• 46:01
  Speaker 1: can tell a story about the temperature of these black
• 46:03
  Speaker 1: holes sort of in this indirect way. Well, I guess
• 46:06
  Speaker 1: I feel like you're saying there are two answers. One
• 46:08
  Speaker 1: is any saying from afar a black hole will seem
• 46:12
  Speaker 1: like it has zero temperature, and from a far Stephen
• 46:14
  Speaker 1: Hawkins says, the black hole should have a little bit
• 46:16
  Speaker 1: of a temperature and almost like it was kind of hot.
• 46:20
  Speaker 1: But neither of those really tell you what the real
• 46:22
  Speaker 1: temperature is inside of the black hole. Right, Like, I'm
• 46:25
  Speaker 1: thinking of the black hole as this like perfect cooler
• 46:28
  Speaker 1: that doesn't let any heat out, And say, if you
• 46:31
  Speaker 1: stick of, you know something hot or something cold inside
• 46:34
  Speaker 1: of the cooler, Like it has a temperature inside of there,
• 46:36
  Speaker 1: but from the outside it's gonna look totally different. Right
• 46:39
  Speaker 1: from the outside of perfect cooler will seems super cold,
• 46:42
  Speaker 1: or if you're Stephen Hawkins, the cooler will leak out
• 46:45
  Speaker 1: or look a little bit warm, But that doesn't tell
• 46:46
  Speaker 1: you like how hot or cold it is on the
• 46:48
  Speaker 1: inside of the cooler. No you're totally right. Neither of
• 46:51
  Speaker 1: these tell us what's going on inside and the program.
• 46:55
  Speaker 1: The way to make progress is to try to build
• 46:57
  Speaker 1: up from the ground up a theory of quantum gravity
• 47:00
  Speaker 1: that would describe the kind of radiation we would see
• 47:03
  Speaker 1: from afar, and so people are working on that. They're
• 47:05
  Speaker 1: trying to do that, you know, the loop quantum gravity
• 47:08
  Speaker 1: folks are trying to do that. They're trying to describe
• 47:10
  Speaker 1: this radiation is like the shaking of the vibrations of
• 47:14
  Speaker 1: the quanta of space, you know, this film. In the
• 47:16
  Speaker 1: other direction, people in string theory are trying to describe
• 47:19
  Speaker 1: what's going on at the heart of the black hole
• 47:21
  Speaker 1: in terms of like vibrating strings, and they've actually had
• 47:24
  Speaker 1: a lot of success. These supersymmetric black holes have been
• 47:28
  Speaker 1: able to predict very well this expected distribution of radiation
• 47:32
  Speaker 1: from a black hole. It's like one of the biggest
• 47:33
  Speaker 1: successes of string theory as a theory for quantum gravity. So,
• 47:37
  Speaker 1: you know, if we can make careful measurements of the
• 47:39
  Speaker 1: black hole from the outside and then come from the
• 47:41
  Speaker 1: other direction and try to predict those measurements, we might
• 47:44
  Speaker 1: be able to get some inside as to what's going
• 47:46
  Speaker 1: on inside, right, because it is that we've talked about before.
• 47:50
  Speaker 1: It is possible to go into a black hole, right, Like,
• 47:52
  Speaker 1: for certain black holes, you can go past the event
• 47:55
  Speaker 1: horizon without getting shredded to bits, and so it is
• 47:58
  Speaker 1: sort of possible to go into a black hole and
• 48:00
  Speaker 1: measure the temperature inside of a black hole. I mean,
• 48:02
  Speaker 1: you wouldn't be able to tell anybody on the outside,
• 48:05
  Speaker 1: but it is technically to like no possible to know
• 48:08
  Speaker 1: that the temperature of a black hole inside of one. Right, Yeah,
• 48:11
  Speaker 1: that's true. You can fall inside a black hole, and
• 48:14
  Speaker 1: for large enough black holes you can survive the title
• 48:16
  Speaker 1: forces just past the event horizon. Eventually you will get shredded,
• 48:20
  Speaker 1: but yeah, you can fall past the event horizon and
• 48:22
  Speaker 1: do experiments. You know, if it's a classical black hole
• 48:26
  Speaker 1: and you're not really going to learn anything until you
• 48:27
  Speaker 1: get to the singularity. Anyway, if it's a quantum black hole,
• 48:30
  Speaker 1: then they might still be in the extended region, and
• 48:32
  Speaker 1: so you could do some experiments there, you like, not
• 48:35
  Speaker 1: quite at the core of the black hole, but like
• 48:37
  Speaker 1: in the rind of the black hole, the crust, the
• 48:42
  Speaker 1: cross there you go the crust. But I think the
• 48:44
  Speaker 1: calculations are also super fascinating because the numbers themselves are
• 48:48
  Speaker 1: really weird. If you ask, all, right, what is the
• 48:50
  Speaker 1: temperature of a black hole that has the mass of
• 48:53
  Speaker 1: the sun, for example, you know, Einstein says, oh, it's zero,
• 48:57
  Speaker 1: Hawking says, no, it's not zero, but it's point zero
• 49:00
  Speaker 1: zero zero zero zero zero zero six kelvin. So like,
• 49:04
  Speaker 1: black holes are not zero, but they're definitely not hot.
• 49:07
  Speaker 1: It's still a pretty cold object, you mean, from afar,
• 49:10
  Speaker 1: like outside of the cooler. For outside of the cooler,
• 49:14
  Speaker 1: the coolers are pretty cool. Yeah, we're always talking about
• 49:16
  Speaker 1: from afar because we don't know what's going on inside this.
• 49:18
  Speaker 1: So these black hole temperature is always what you measure
• 49:21
  Speaker 1: from the radiation that might be coming off the black holes,
• 49:24
  Speaker 1: the leaking, you mean, the leaking. The thing that's really
• 49:27
  Speaker 1: weird is that this temperature is inversely proportional to mass.
• 49:30
  Speaker 1: We've talked about this before that larger black holes radiate
• 49:33
  Speaker 1: less and smaller black holes radiate more, which means smaller
• 49:37
  Speaker 1: black holes are warmer. So as black holes get larger,
• 49:40
  Speaker 1: they get colder. Einstein says, you shoot a laser beam
• 49:43
  Speaker 1: at a black hole, it just stays at zero. Kelvin
• 49:46
  Speaker 1: Hawking says, you shoot a laser beam at a black hole,
• 49:48
  Speaker 1: it gets colder, whereas if I shoot a laser of you,
• 49:51
  Speaker 1: you would get hotter and and more annoyed kind of, yeah,
• 49:55
  Speaker 1: I would get louder. Yeah, Oh that's interesting. So it's
• 50:00
  Speaker 1: almost like you're putting more energy into the black hole,
• 50:03
  Speaker 1: but from the outside it's looked looking like it's losing energy. Yeah,
• 50:06
  Speaker 1: it looks like it's getting colder and colder, which is
• 50:09
  Speaker 1: hard to understand, but think about like what might be
• 50:11
  Speaker 1: going on inside the black hole. It's gravity is getting
• 50:13
  Speaker 1: stronger and stronger, and so time is slowing down inside
• 50:17
  Speaker 1: the black hole, and so things are moving more slowly,
• 50:20
  Speaker 1: which you can kind of understand is maybe having lower temperature. Right, So,
• 50:24
  Speaker 1: again we don't know anything about what's going on inside
• 50:26
  Speaker 1: a black hole, but trying to put together like a
• 50:28
  Speaker 1: rough intuition for how black holes could be getting colder
• 50:32
  Speaker 1: as they get larger. Time dilation kind of helps that picture.
• 50:35
  Speaker 1: Oh I see, or could it be that you know,
• 50:37
  Speaker 1: as you add more mass or energy to the black hole,
• 50:40
  Speaker 1: like that gets stronger, so it pull stuff in more
• 50:44
  Speaker 1: and so there's less leakage and so it looks colder,
• 50:47
  Speaker 1: you know what I mean, Like, the more mass the
• 50:48
  Speaker 1: black hole has, the better the coda that is keeping
• 50:51
  Speaker 1: it hidden from us, And so maybe it just looks
• 50:54
  Speaker 1: colder to us. Yeah, in which case, maybe black holes
• 50:56
  Speaker 1: don't follow these laws of black body radiation that every
• 51:00
  Speaker 1: anything else in the universe does, right, because they have
• 51:02
  Speaker 1: this event horizon. Black body radiation can describe everything in
• 51:06
  Speaker 1: the universe that has charged particles. So, for example, dark
• 51:09
  Speaker 1: matter also doesn't follow that rule because dark matter doesn't
• 51:12
  Speaker 1: have electric charge and so it doesn't radiate photons based
• 51:15
  Speaker 1: on its temperature. Maybe the event horizon of a black
• 51:17
  Speaker 1: hole also prevents this kind of radiation, and so maybe
• 51:20
  Speaker 1: there's a mismatch them between the temperature we observe from
• 51:23
  Speaker 1: AFAR and the actual temperature inside a black hole. In
• 51:26
  Speaker 1: a more intuitive sense, I called the cooler theory. It's
• 51:29
  Speaker 1: definitely cooler than any theory I've heard before. Yeah, should
• 51:33
  Speaker 1: we come up with a great acronym for it, better
• 51:36
  Speaker 1: than the j CT or haze cooler theory? There you go. Well,
• 51:40
  Speaker 1: I feel like what you're saying is that to answer
• 51:42
  Speaker 1: the question whether a black hole is hot or not,
• 51:44
  Speaker 1: the the answer is, um, we don't know, you know,
• 51:47
  Speaker 1: it's sort of like asking is that dress blue with
• 51:50
  Speaker 1: black stripes or what with gold stars? It's like it
• 51:53
  Speaker 1: depends on who you ask. Yeah, because we don't know
• 51:55
  Speaker 1: what's going on inside a black hole microscopically, We don't
• 51:58
  Speaker 1: know what it's true temperature. We have this weird clue
• 52:01
  Speaker 1: that black holes do radiat a little bit, and that
• 52:04
  Speaker 1: tells us something about what might be happening inside of them,
• 52:08
  Speaker 1: but we don't know if it really is a clue
• 52:09
  Speaker 1: about the microscopic nature of the black hole. Were just
• 52:12
  Speaker 1: the black holes leak in a weird different way than
• 52:14
  Speaker 1: anything else, right, Because even this leakage theory, this hawkings
• 52:18
  Speaker 1: radiation is still theoretical, Like, we haven't seen that hawking
• 52:21
  Speaker 1: radiation in actual life. That's right, We have never ever
• 52:24
  Speaker 1: seen any hawking radiation from anything. We've looked for black
• 52:27
  Speaker 1: holes evaporating rapidly and giving bright flashes at the end
• 52:31
  Speaker 1: of their life, but we've never seen If we could
• 52:33
  Speaker 1: create black holes of a large hadron collider and then
• 52:35
  Speaker 1: we could see them evaporate on short time skills, that
• 52:38
  Speaker 1: would be exciting, but nobody has ever seen hawking radiation,
• 52:41
  Speaker 1: So it's a black hole hot or not. I feel
• 52:43
  Speaker 1: like you can't really swipe right or left here, you
• 52:45
  Speaker 1: have to just close the app. I don't know, what
• 52:47
  Speaker 1: do you? What do you do? I think black holes
• 52:49
  Speaker 1: are either zero or very very very very very cold.
• 52:53
  Speaker 1: There's no chance they're actually hot. I see you're saying,
• 52:56
  Speaker 1: doesn't matter they're hot or not. They're they're pretty cool. Yeah, exactly,
• 53:00
  Speaker 1: they're still pretty cute. You would still date them, is
• 53:04
  Speaker 1: I think what's is what you're saying. I definitely want
• 53:07
  Speaker 1: to hang out with black holes, yes, forever. Alright, Well,
• 53:11
  Speaker 1: it's an interesting question to tackle, and I think it
• 53:14
  Speaker 1: tells you a lot about what we still don't know
• 53:16
  Speaker 1: about the universe. You know, there are still places that
• 53:19
  Speaker 1: we know exists and our out when we have pictures
• 53:21
  Speaker 1: of but where our theories about the universe breakdown and
• 53:24
  Speaker 1: we need to come up with new theories that maybe
• 53:26
  Speaker 1: people out there are working on or that will work on.
• 53:29
  Speaker 1: In our efforts to understand the universe are usually through
• 53:32
  Speaker 1: the lens of concepts that we understand motion and temperature,
• 53:36
  Speaker 1: and sometimes those very concepts breakdown in the weird contexts
• 53:40
  Speaker 1: that are our universe. Alright, Well, we hope you enjoyed that.
• 53:44
  Speaker 1: Thanks for joining us, see you next time. Thanks for listening,
• 53:54
  Speaker 1: and remember that Daniel and Jorge explained. The Universe is
• 53:57
  Speaker 1: a production of I heart Radio from More podcast from
• 54:01
  Speaker 1: my heart Radio, visit the i heart Radio app, Apple Podcasts,
• 54:05
  Speaker 1: or wherever you listen to your favorite shows. H