Speaker 1: Hey, Katie, have you ever been to Las Vegas? I
Speaker 1: have once, and so what did you think about America's
Speaker 1: favorite adult playground?
Speaker 2: Well, I can't really tell you.
Speaker 1: Is that because it was so much fun you remember nothing?
Speaker 2: I mean, it is a bit of an information black hole.
Speaker 1: You mean, like you don't want to talk about it.
Speaker 1: Like what happens in Vegas stays in Vegas.
Speaker 2: It is a singular experience for sure.
Speaker 1: All right, we'll leave that past. The Katie event arrived.
Speaker 2: Like they're just handing out margarite?
Speaker 3: Is there? What am I supposed to say?
Speaker 4: Hi?
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
Speaker 1: UC Irvine, and I have definitely been to Vegas.
Speaker 2: I am Katie Golden, I am made out of particles.
Speaker 2: I host a podcast about animals, and I mostly liked
Speaker 2: the food from Las Vegas, not so much the casinos.
Speaker 1: I recently went to Vegas with my thirteen year old daughter,
Speaker 1: which was quite an experience to see it through her eyes.
Speaker 1: Definitely a place to go at least once.
Speaker 2: It is a fascinating city. I regret that I have
Speaker 2: not been there since they have put the giant orban.
Speaker 1: Yeah, the orb is cool. There's definitely a lot of
Speaker 1: stuff you can do even if you're not eighteen or
Speaker 1: twenty one plus, though some of the stuff she wanted
Speaker 1: to do, like drive tanks through the desert and shoot
Speaker 1: automatic weapons were definitely age restricted.
Speaker 2: Yeah, I have a friend who I think shot guns
Speaker 2: from a helicopter in Vegas. There's a lot of things
Speaker 2: you can do.
Speaker 1: There's all sorts of crazy stuff you can do in Vegas,
Speaker 1: stuff that helps you understand who you are and who
Speaker 1: you aren't. And Welcome to the podcast Daniel and Jorge
Speaker 1: Explain the Universe, in which we try to explain to
Speaker 1: you what the universe is and what the universe isn't.
Speaker 1: We try to pull back the curtain and help you
Speaker 1: understand what's going on out there in the deepest, darkest
Speaker 1: regions of.
Speaker 2: Space, such as Las Vegas.
Speaker 1: There is no Vegas casino yet called the black Hole,
Speaker 1: but I am assuming one it will eventually open up.
Speaker 2: That is a missed opportunity, or like a mini golf
Speaker 2: course called the black.
Speaker 1: Holes that just sucks in all the balls. Well, on
Speaker 1: this podcast, we do try to explain to you black
Speaker 1: holes and also how everything works on the smallest scales
Speaker 1: because we don't just want to describe the universe to you.
Speaker 1: We want to explain it. We want you to get
Speaker 1: an understanding, a microscopic picture of how everything around you
Speaker 1: actually works. We want to dive deep into the very
Speaker 1: nature of reality and come out with a bottom up
Speaker 1: understanding of how the universe actually works. My friend Jorge
Speaker 1: can't be here today, but I'm very glad to be
Speaker 1: joined by one of our regular co hosts. Thanks Katie
Speaker 1: for joining us on this black Hole of an episode.
Speaker 2: I am excited because no matter how many times you
Speaker 2: explain to me what a black hole is, I still
Speaker 2: feel like I cannot wrap my head around it. So surely,
Speaker 2: surely this will be the episode where I understand black holes.
Speaker 1: Well, I would say there's probably nobody out there who
Speaker 1: fully deeply understands black holes, because to fully deeply understand something,
Speaker 1: I think we need a particle level explanation for it.
Speaker 1: You know, we need to be able to moot up
Speaker 1: from the tiniest little bits and say, here's what's really
Speaker 1: happening at the smallest scales when you get sucked into
Speaker 1: a black hole or when photons try to escape. And
Speaker 1: the reason I say that nobody understands them is that
Speaker 1: we do not have a particle level understanding of black
Speaker 1: hole holes. The way, for example, we can understand what
Speaker 1: happens when photons go through glass, They interact with the atoms,
Speaker 1: the electrons and all that stuff in there, and it
Speaker 1: bends their path, and we have some way to tell
Speaker 1: a story microscopically if what's happening to those photons and
Speaker 1: related to what we see actually macroscopically, we can't do
Speaker 1: that for black holes because we don't understand particles and gravity.
Speaker 1: We have no theory of quantum gravity that tells us
Speaker 1: what happens to particles when they feel gravity, and that's
Speaker 1: what black holes are all about. Gravity. So we don't
Speaker 1: have this sort of deep down, microscopic understanding of black holes.
Speaker 1: So probably nobody understands, but that doesn't stop us from
Speaker 1: asking questions and from trying to grapple with what we
Speaker 1: have learned about black holes. Then, on this podcast, we
Speaker 1: encourage everybody to think deeply about the universe and to
Speaker 1: try to fit these ideas into their heads, to ask
Speaker 1: themselves questions to see does this make sense to you?
Speaker 1: Is it possible for you to grapple with what we
Speaker 1: do and do not know about black holes.
Speaker 2: The problem, Daniel is I have a finite number of neurons,
Speaker 2: a finite sort of number of synaptic pathways in my brain,
Speaker 2: and it is very difficult for those little guys to
Speaker 2: understand all we know about black holes and what we
Speaker 2: don't know about black holes. If we were somehow able
Speaker 2: to measure everything about a black hole, do you think
Speaker 2: we could even fully understand it? As humans?
Speaker 1: It's a deep question in philosophy, like are we even
Speaker 1: capable of describing the universe in our minds? Can we
Speaker 1: understand the universe? And not a question I know the
Speaker 1: answer to or I think anybody knows the answer to. Amazingly,
Speaker 1: so far we have been able to do it, to
Speaker 1: write these little mathematical models, tell ourselves these little stories
Speaker 1: in our minds, and use them to explain everything that
Speaker 1: we see and everything we experience, everything our experiments tell us.
Speaker 1: Is it possible for us to understand them? The smartest
Speaker 1: human I don't know. I think there probably is a
Speaker 1: limit to how smart the smartest human is, and so
Speaker 1: it might be that the universe it's just more complex
Speaker 1: than that, and that no human, regardless of how smart
Speaker 1: they are, could ever understand it. But you know, we've
Speaker 1: been making a lot of progress in recent years asking
Speaker 1: and answering questions about the deepest nature of the universe
Speaker 1: and about black holes. So I'm kind of bullish on
Speaker 1: the possibility for some humans someday to understand it. And
Speaker 1: that's not just limited to like the Albert Einsteins of
Speaker 1: the world. I think it's possible for basically everybody out
Speaker 1: there to get some kind of intuitive grasp or how
Speaker 1: black holes work. One thing I love about hearing from
Speaker 1: listeners to the podcast is that it's been teaching them
Speaker 1: to think like a physicist, you know, like, what does
Speaker 1: that mean? To think like a physicist? It means to
Speaker 1: try to understand the world around you, to tell yourself stories,
Speaker 1: to ask yourself questions, to say, do I understand how
Speaker 1: this works? To put these models in your head and
Speaker 1: like turn them around and say, well, if that's true,
Speaker 1: doesn't it mean this or how does this connect with
Speaker 1: this other thing I do understand? And that's especially important
Speaker 1: for weird things like black holes. So we get lots
Speaker 1: of questions from listeners who're doing just that. Wh we're
Speaker 1: trying to think like a physicist about black holes? To
Speaker 1: try to incorporate it into the mathematical stories in their minds.
Speaker 2: This podcast is Daniel's secret weapon of trying to convert
Speaker 2: everyone into physicists. We are onto you, Daniel. You are
Speaker 2: trying to create an army of physicists. There are so
Speaker 2: many questions that I have about black holes. It's hard
Speaker 2: for me to even think about how to phrase my
Speaker 2: confusion about black holes into a question. So just being
Speaker 2: able to ask a distinct, coherent question about black holes,
Speaker 2: I think is impressive.
Speaker 1: I mean, your question about black holes is like black holes,
Speaker 1: what's the deal with that?
Speaker 2: Yeah? My question is like, huh what.
Speaker 1: That's the first step, right, is to be confused, and
Speaker 1: then the second second step is to try to weave
Speaker 1: together a few bits of information and say, like, what
Speaker 1: parts specifically of the story don't make sense to me?
Speaker 1: Which parts do I need to understand better in order
Speaker 1: to have something in my mind that does work where
Speaker 1: the understanding does click. Because what I'd love is for
Speaker 1: people to have that moment where they're like, oh, I
Speaker 1: get it. This connects with that thing, and now it
Speaker 1: kind of makes sense to me, even though it's pretty
Speaker 1: weird and a lot of people out there are trying
Speaker 1: to do that, and many of them have run into
Speaker 1: the same stumbling block. And so today on the podcast,
Speaker 1: I want to answer a very common question that we
Speaker 1: get about black holes. Can gravity escape a black hole?
Speaker 2: I feel like I'm going crossside just trying to think
Speaker 2: about this question.
Speaker 1: I love this question because it reveals that people are
Speaker 1: being physicists. They're thinking about what a black hole is,
Speaker 1: how everything gets sucked into it, how nothing can escape.
Speaker 1: But they're also thinking, hold on a second, we feel
Speaker 1: gravity from a black hole. How's that possible? How can
Speaker 1: the gravity get out of the black hole? And right there,
Speaker 1: that's being a physicist, that's saying I was told this,
Speaker 1: But there's also that how do I make this and
Speaker 1: that work together? How do I put it together in
Speaker 1: my head to tell a story that makes sense.
Speaker 2: So what you're asking us to do is to listen
Speaker 2: to what you're saying and then go hold on, Daniel,
Speaker 2: you just said this. Are you lying to us?
Speaker 1: Everybody's doing their best, nobody's lying to anybody. But in
Speaker 1: the end, learning is a very personal experience, and an
Speaker 1: explanation that makes sense to one person doesn't work for
Speaker 1: somebody else. So that's why in this podcast, we often
Speaker 1: try two or three different analogies or explanations or ways
Speaker 1: to communicate an idea, and that's what you're here for, Katie,
Speaker 1: also to make sure that what I'm saying makes sense
Speaker 1: to you.
Speaker 2: My method of learning is definitely food based metaphors. I'm
Speaker 2: very food motivated.
Speaker 1: Is your appetite something like a black hole?
Speaker 2: It's something like that. Yeah, one could say I'm a
Speaker 2: bit of a black hole, but yeah, I mean, it's
Speaker 2: a very interesting question because it's hard for me to
Speaker 2: think of gravity as like a thing, right, like a
Speaker 2: thing that can escape something. Gravity to me is like, well,
Speaker 2: I don't even know exactly what gravity is. I remember
Speaker 2: from previous podcasts the things that you've taught me about gravity,
Speaker 2: but it is so hard for me to conceptualize gravity
Speaker 2: because it feels like it is like a kind of
Speaker 2: thing woven into like the universe, that is not necessarily like,
Speaker 2: you know, a physical matter thing, but it has everything
Speaker 2: to do with physics. So it's it's a very confusing
Speaker 2: kind of concept. And then you add to that the
Speaker 2: black hole, which itself is quite confusing, and so this
Speaker 2: question feels no pun intended, but very heavy.
Speaker 1: Exactly well, you put your finger on. Really the concepts
Speaker 1: here that are entertangled. You know, what do we know
Speaker 1: about gravity? How is gravitation information communicated? Like? How is
Speaker 1: it that you are feeling gravity from the sun even
Speaker 1: though the Sun is super dup far away and not
Speaker 1: touching you. Does that count as information you're getting from
Speaker 1: the sun? What kind of stuff is captured by a
Speaker 1: black hole? And what isn't captured by a black hole?
Speaker 1: Is that information? How does that all work? You know?
Speaker 1: Do you need to pass little particles back and forth
Speaker 1: in order to feel gravity or what. So. One of
Speaker 1: the reasons I love this question is that it combines
Speaker 1: all of these fun, interesting, fascinating and difficult questions together,
Speaker 1: and going through it I think is really helpful to
Speaker 1: clarify for people what a black hole is and what
Speaker 1: a black hole isn't and how physicists think about it.
Speaker 1: But before we hear about how physicists think about it,
Speaker 1: I wanted to hear what everybody else out there was
Speaker 1: thinking about it. So we have a nice little team
Speaker 1: of volunteers who answer questions for the podcast before we
Speaker 1: dig into them. Helps me understand what people are thinking
Speaker 1: and helps you calibrate your thoughts against the other listeners.
Speaker 1: So thanks very much to everybody who participates. You want
Speaker 1: to jump in for a future episode, we would love, love,
Speaker 1: love to have your voice on the team. Right to me.
Speaker 1: Two questions at Danielandjorge dot com, So think about it
Speaker 1: for a moment before you hear these answers. Do you
Speaker 1: think gravity can escape a black hole? Here's what people
Speaker 1: had to say.
Speaker 5: I feel like, since it kind of depends on the
Speaker 5: mass of an object, it just moves with that object,
Speaker 5: so it would be dependent on the object being able
Speaker 5: to escape the black hole.
Speaker 6: It really matters what we think of as gravity. If
Speaker 6: you think it's gravito gravitons, like with the quantum theories,
Speaker 6: then I guess it escapes. I think, yeah, gravity can
Speaker 6: escape black holes, otherwise I wouldn't be stucking everything in.
Speaker 7: Gravity is a distortion in space time, So I would
Speaker 7: say that gravity itself cannot escape. Actually it's being created
Speaker 7: by the black hole itself. But if we are talking
Speaker 7: about gravitational waves, I believe it can escape a black
Speaker 7: hole if it is outside the event horizon. I even
Speaker 7: think that gravitational waves were discovered by watching collisions of
Speaker 7: black holes and stuff like that. So my guess is yes,
Speaker 7: under the right circumstances, gravitational waves should be able to
Speaker 7: escape a black hole.
Speaker 4: I can't even wrap my head around the question.
Speaker 5: I didn't even know those words could go together.
Speaker 4: I guess it can escape, because isn't that kind of
Speaker 4: what gravitational waves are.
Speaker 2: I love all of the references to gravitational waves because
Speaker 2: we did an episode on that recently.
Speaker 1: We did absolutely an episode on gravitational waves, and that's
Speaker 1: going to turn out to be crucial in understanding what
Speaker 1: is gravitational information and what is not, what is trapped
Speaker 1: within the black hole, and what is not trapped within
Speaker 1: the black hole. Absolutely, so, gravitational waves are a really
Speaker 1: helpful way to think about that.
Speaker 2: I get the root of this question. Is this seeming paradox, right,
Speaker 2: the idea that nothing can escape from a black hole,
Speaker 2: and yet we do know about black holes, We get
Speaker 2: information about black holes, But how can we receive any
Speaker 2: information about a black hole if it is something that
Speaker 2: is all consuming and nothing can escape it?
Speaker 1: Boom Exactly, Adie, you were officially a physicist because you
Speaker 1: are putting together those two ideas that you understand and saying,
Speaker 1: how can these two things be compatible. How can we
Speaker 1: weave them together into a singular understanding of black holes?
Speaker 1: And what it's going to take is a little bit
Speaker 1: of a refinement of the idea of what a black
Speaker 1: hole is and what a black hole isn't to make
Speaker 1: this all work together in your head.
Speaker 2: Well, now that you have proclaimed I am a physicist,
Speaker 2: I am just gonna waltz into like the hard drung
Speaker 2: collider and be like physicists coming through. Let's smash some particles.
Speaker 3: Guys.
Speaker 1: That's right, you have officially a PhD in podcast physics
Speaker 1: from the Daniel and Jorge University.
Speaker 2: Worth its weight in gold. So yes, I would love
Speaker 2: some clarification on what a black hole is. You know,
Speaker 2: I know it's a big, sucky thing. I understand that
Speaker 2: it has something to do with just an incredible density
Speaker 2: of matter, and furthermore that gravity is very much a
Speaker 2: defining characteristic of a black hole.
Speaker 1: Then let's make sure we know what it is we're
Speaker 1: talking about. So a black hole is a region of
Speaker 1: space where the curvature of space is so powerful that
Speaker 1: nothing that's inside that region can escape to outside, and
Speaker 1: that region is defined by this threshold, not really like
Speaker 1: a barrier, not like a physical wall. There's not got
Speaker 1: a dotted line somebody draws in space that says beyond
Speaker 1: this point, if you pass, then you will ever escape.
Speaker 1: You'll be trapped within that region forever.
Speaker 2: Someone's got to put a sign up, a warning, you know, warning,
Speaker 2: do not pass this region. You will be spaghettified into
Speaker 2: a black hole. But I mean, when you say space
Speaker 2: is curved, you know, this is definitely a concept I've
Speaker 2: been introduced to before, but it's still something that I
Speaker 2: struggle to understand because when I think of curvature, right,
Speaker 2: I think of like a physical object that is warped,
Speaker 2: or like say, I think of fabric and I feel like,
Speaker 2: you know, I think of pulling down on the fabric
Speaker 2: and then they're being sort of a curvature and things
Speaker 2: falling into it, and then that's how I think about gravity.
Speaker 2: But I believe that is not really exactly the correct
Speaker 2: understanding of it. Space is not like a piece of
Speaker 2: fabric that you pull on and things fall into that
Speaker 2: sort of like dip. But what exactly does curvature mean
Speaker 2: in terms of space?
Speaker 1: Yeah? Good, It's important to think about in terms of
Speaker 1: curvature because I think a lot of people think about
Speaker 1: black holes in sort of a Newtonian way, where gravity
Speaker 1: is a force and the force of gravity is so
Speaker 1: strong that it's sucking stuff up right, And that cartoon
Speaker 1: model of a black hole breaks down very quickly because
Speaker 1: it can't explain to you, like, well, why does light
Speaker 1: get trapped by a black hole? Why can't a photon
Speaker 1: not leave a black hole? Because the Newtonian picture of gravity,
Speaker 1: gravity is a force between objects with mass, and photons
Speaker 1: have no mass, so they should feel no gravity, and
Speaker 1: so they should be able to escape. In order to
Speaker 1: have an understanding of what black holes are, you really
Speaker 1: have to move your thinking of gravity is from this
Speaker 1: idea of forces between objects with mass to an apparent
Speaker 1: force something that actually results from, as you say, the
Speaker 1: curvature of space itself. So what do we mean by
Speaker 1: the curvature of space itself? Means that space has a
Speaker 1: characteristic to it that's invisible, something you can't see when
Speaker 1: you look at it. You look at some chunk of
Speaker 1: space and you can't tell whether or not it's curved.
Speaker 1: But if you shine a laser beam through it, it
Speaker 1: will either go in a straight line or it will not.
Speaker 1: It will curve, it will bend. This way, or will
Speaker 1: bend that way, because space has this additional, weird property
Speaker 1: that Newton never imagined. And on the smaller scale, what
Speaker 1: it means is that the relative distances between two points
Speaker 1: can get changed. So when we say that like space
Speaker 1: is curved or space is bent, it means that you
Speaker 1: can take two locations in space, you can effectively make
Speaker 1: them closer together, or you can make them further apart.
Speaker 1: And what that does is it changes the path that
Speaker 1: light will take through that space, because light always takes
Speaker 1: the shortest path between two points. Now you're changing what
Speaker 1: the relative distances are between two points, and so you're
Speaker 1: changing the path that light will take. But I think
Speaker 1: the most intuitive way to think about it is that
Speaker 1: like space has this additional bit to it, this characteristic
Speaker 1: so when a photon is passing through it, basically the
Speaker 1: space tells the photon where to go, doesn't just pass
Speaker 1: through blindly.
Speaker 2: It's so interesting because I think the reason it's such
Speaker 2: a difficult concept is that as humans we deal with
Speaker 2: physics all the time, but we can observe Newtonian physics.
Speaker 2: We can observe that type of physics, So it's I
Speaker 2: think easier to think of particles when even like particles
Speaker 2: that you can't observe with the naked eye when they
Speaker 2: are behaving according to forces, because we can on the
Speaker 2: more macro level observe forces. You can see a ball
Speaker 2: knocking into a ball, you can see something fall down
Speaker 2: a hole. But with gravity, even though yes, it's true,
Speaker 2: we can observe gravity. We see it all the time,
Speaker 2: right because you know, you jump up, you fall down.
Speaker 2: It's one of the main problems that we have to
Speaker 2: encounter as a physical being in the world, and yet
Speaker 2: we can't actually see or kind of experience this like
Speaker 2: secret framework behind gravity, which is that what you described,
Speaker 2: like the relative distance between two things like becoming shorter
Speaker 2: and like the actual like you know, space like reality
Speaker 2: sort of warping in a way. It's like so easy
Speaker 2: to fall into that trap of thinking of it in
Speaker 2: terms of the type of physics that we see and
Speaker 2: we observe.
Speaker 1: It's confusing precisely because it's invisible. You can't see this
Speaker 1: curvature of space. You can only see its effect, and
Speaker 1: the effect of the curvature of space looks in almost
Speaker 1: every case as if there was a force there. It
Speaker 1: looks like there is this force we call gravity that's
Speaker 1: pulling on things, when really things are just following the
Speaker 1: curvature of space. The shape of space itself is changing
Speaker 1: the direction in which things move. And if you can't
Speaker 1: see space doing it, it's like a bunch of stage
Speaker 1: hands wearing black nudging stuff. Then you imagine that there's
Speaker 1: a force there. And so that's why we call gravity
Speaker 1: and a parent force. It's not an actual force the
Speaker 1: way like electromagnetism is, or the weak force or the
Speaker 1: strong force. It's just the effect of the invisible curvature
Speaker 1: of space.
Speaker 2: So I hop down from let's say a safe height
Speaker 2: and land on the ground. I am not really getting
Speaker 2: sucked into the ground, because this is an effect of gravity, right,
Speaker 2: The gravity of Earth is affecting me, and so I'm
Speaker 2: not really getting sucked to the ground, but I am
Speaker 2: like sort of just following where space is curving.
Speaker 1: Yeah, that's a great example. Let's walk through it in
Speaker 1: the sort of Newtonian intuitive picture, and then let's move
Speaker 1: over to the Einstein space curvature picture. You'll find that
Speaker 1: it's a very different story about exactly the same thing.
Speaker 1: So in the Newtonian way of thinking, where gravity is
Speaker 1: a force, you are standing on a chair, and you
Speaker 1: imagine that there's a force of gravity pulling you down,
Speaker 1: and there's a force of the chair pulling you up,
Speaker 1: and when you stand on the chair, all forces are balanced,
Speaker 1: so you're not going anywhere. You jump off the chair
Speaker 1: and then you fall down because all you have is
Speaker 1: the force of gravity pulling you down. There's nothing pushing
Speaker 1: you up until you hit the surface of the Earth,
Speaker 1: right in the surace of the Earth, and it's now
Speaker 1: pushing back up on you, and so the forces are
Speaker 1: now balanced and you're not moving anymore. Cool. So that's
Speaker 1: the Newtonian picture. Einstein says, actually that's all wrong, that jerk.
Speaker 1: There is no force of gravity, and that when you're falling,
Speaker 1: when you jump off that chair, what's happening is you're
Speaker 1: following the curvature of the Earth. You're in free fall.
Speaker 1: There is no force on you at all. And in fact,
Speaker 1: if you are carrying a little accelerometer with you, something
Speaker 1: which can measure whether you're accelerating, essentially if there's any
Speaker 1: force on you. Example of an accelerometer is just like
Speaker 1: a ball in a box, Like is the ball pushed
Speaker 1: towards one side or the other? Where Like a bowling
Speaker 1: ball in a truck will tell you whether you're breaking
Speaker 1: or accelerating. If you jump off that chair and you're
Speaker 1: holding an accelerometer, you can do this experiment. You will
Speaker 1: not measure any acceleration. You will not measure anything because
Speaker 1: in that case, you are not accelerating. Einstein says that
Speaker 1: you're actually accelerating when you're standing on the chair. That
Speaker 1: what you're doing there is you're accelerating against the curvature
Speaker 1: of the Earth. And also when you're standing on the earth,
Speaker 1: you're accelerating upwards against your natural path, which would be
Speaker 1: following the curvature of gravity towards the center of the Earth.
Speaker 2: The chair is essentially blocking where you should go naturally
Speaker 2: go by following where space is telling you to go.
Speaker 1: Exactly, if you jump off the chair, you're in free fall.
Speaker 1: You're not accelerating at all. You see people who are
Speaker 1: still on their chairs as accelerating upwards against the natural
Speaker 1: direction gravity wants to take you.
Speaker 2: So, if I'm holding something like a feather, say, and
Speaker 2: I jump off a chair, the feather goes slower than me.
Speaker 2: Is the only reason that happens because of wind resistance.
Speaker 1: Yeah, in that case, it's the air is accelerating the
Speaker 1: feather up. It's preventing the feather from following the curvature
Speaker 1: of space. The air itself is pushing on the feather.
Speaker 2: And that's why an ant can survive really high falls,
Speaker 2: whereas a person could not. Even though the ant seems
Speaker 2: much more structurally delicate than a human because it's so small,
Speaker 2: The air is basically like this huge you know resistance,
Speaker 2: this huge force that is, you know, blocking the ant
Speaker 2: from I guess following the curvature of space.
Speaker 7: Yeah.
Speaker 1: I think there's also something there about the structure of
Speaker 1: ants when they land, but I'm not a biologist.
Speaker 2: They just stick the dismount amazingly. If you zoom in
Speaker 2: on an ant, it does a little summrsalt, lands, and
Speaker 2: then takes a little bow.
Speaker 1: So this picture of gravity is this curvature in space
Speaker 1: rather than a force, gives us a new way to
Speaker 1: think about a black hole. It's not a very dense
Speaker 1: mass that has very strong sucking gravity because of all
Speaker 1: the mass in it. It's a region of space where
Speaker 1: the curvature is such that there is no path outwards,
Speaker 1: where every direction is towards the center of the black hole.
Speaker 1: Anything that's flying along is going to follow the curvature
Speaker 1: of space, including photons. Photons in Einstein's gravity can be
Speaker 1: bent because they follow the curvature of space, not because
Speaker 1: of this Newtonian force between masses. So if Hodan that
Speaker 1: goes past the event horizon is trapped by the structure
Speaker 1: of space itself, because every path forward now takes it
Speaker 1: towards the center of the black hole. And that's where
Speaker 1: this apparent mental paradox comes from that you mentioned earlier.
Speaker 1: If a black hole traps everything, if everything is encapsulated
Speaker 1: inside the black hole because of the structure of space,
Speaker 1: then how is it possible for us to even know
Speaker 1: about it? How's that gravitational information leaving this trash can
Speaker 1: of space time.
Speaker 2: I do want to hear about sort of this idea
Speaker 2: of information not being able to escape a black hole,
Speaker 2: because that just it sounds weird, right to like say
Speaker 2: like information is trapped somewhere, because when we think about information,
Speaker 2: you know, it's like, wait, so I can't use Google
Speaker 2: in a black hole? What does that mean? But maybe
Speaker 2: we should take a quick break before we do that,
Speaker 2: digest the curvature of the space. See, I need food
Speaker 2: metaphors for me to learn and then when we get back,
Speaker 2: I would love to learn more about what it really
Speaker 2: means to say that information cannot escape. All right, So
Speaker 2: I think I'm starting to get a grasp on this
Speaker 2: idea of gravity being sort of a curvature of space,
Speaker 2: not a force. But I do want to hear more
Speaker 2: about what it means when information can't escape a black hole, because, like, again,
Speaker 2: when I think of information, I'm like, well, I'm looking
Speaker 2: on Wikipedia about how ants can stick the dismount. What
Speaker 2: does it mean when information cannot escape a black hole?
Speaker 1: Well, fortunately, if you fall into a black hole, you
Speaker 1: can still access Wikipedia because information can go into Wikipedia.
Speaker 1: You can't request specific page because we can't hear from you,
Speaker 1: but we can send you information. We could just like
Speaker 1: randomly send you Wikipedia pages even after you've.
Speaker 2: Fallen in I would like to get some Netflix and
Speaker 2: stuff if I'm in a black hole, because it seems
Speaker 2: if I'm still alive, it seems really kind of like
Speaker 2: a lot of time I'm going to spend in there.
Speaker 2: I need some entertainment, you know what.
Speaker 1: I think maybe nobody does. What everybody should do is
Speaker 1: prepare their Like, if I fall into a black hole,
Speaker 1: what Netflix shows. Should you beam to me the way
Speaker 1: people like you know, prepare a will other end of
Speaker 1: life information? Like, I'd like to know this about people
Speaker 1: in my life, so I know what to beam to them, right.
Speaker 2: Yeah, exactly, I need to start working on a list.
Speaker 2: But yeah, so information can't escape a black hole? What
Speaker 2: is going on there? And what do we mean by information?
Speaker 1: Really? Yeah? Great? And here's where we need to zoom
Speaker 1: back down again to the particle level when we talk
Speaker 1: about information, Like, imagine that you are inside the black
Speaker 1: hole and you want to request a Wikipedia page about something,
Speaker 1: make a Sioux fla, and you want a recipe or something.
Speaker 1: In order to request that information, you have to send
Speaker 1: something physical outside of the black hole. The way information
Speaker 1: works is that it's transmitted physically. The way you are
Speaker 1: hearing this podcast right now is wiggles in electrons or
Speaker 1: photons being beamed across the Earth. All information is transmitted
Speaker 1: as particles or some kind of a wave. And so
Speaker 1: if particles cannot escape a black hole, then you cannot
Speaker 1: send information outside the black hole because to send that
Speaker 1: information would require sending something physical, a photon, an electron,
Speaker 1: something outside of the black hole. So that's where this
Speaker 1: idea comes from that no information can leave a black
Speaker 1: hole because no thing can leave a black hole, and
Speaker 1: you need things to transmit information. Information in the end
Speaker 1: is physical.
Speaker 2: So I cannot order a pizza from a black hole,
Speaker 2: which seems a little scary.
Speaker 1: So get your pizza order in before you fall into
Speaker 1: the black hole. That's the key. It's just a little
Speaker 1: bit of planning.
Speaker 2: I am writing it in sort of my black hole
Speaker 2: instruction list, that please send pizza into the black hole.
Speaker 2: Should I go in there.
Speaker 1: I think you should ask for spaghetti, actually, because everything
Speaker 1: we send in is getting spaghettified anyway, so you might
Speaker 1: as well start with spaghetti.
Speaker 2: You are what you eat, especially in a black hole,
Speaker 2: if you're eating spaghetti.
Speaker 1: But let's get specific about what we mean by information,
Speaker 1: because this is the crux of the issue. This is
Speaker 1: how we're going to understand later why you can feel
Speaker 1: gravity from outside a black hole, but you can't order
Speaker 1: pizza from within the black hole. And what we mean
Speaker 1: by information is sort of like an update, a change
Speaker 1: of state, so you're communicating something is different, Like if
Speaker 1: Katie and I are across the room from each other,
Speaker 1: she can send me information by like shooting photons at
Speaker 1: me right. For example, if she doesn't shoot any photons
Speaker 1: at me, I can assume like, Okay, Katie's still there.
Speaker 1: I haven't heard from her in a while. But if
Speaker 1: I want any new information from Katie, if you want
Speaker 1: any updates on her situation, she wants to warn me
Speaker 1: about something, or tell me about the pizza she wants,
Speaker 1: or change her list of Netflix shows she wants to watch,
Speaker 1: then she would need to send me some information, some
Speaker 1: electrons or some photons. So information is sort of like
Speaker 1: an update. It's like something new that.
Speaker 2: You're learning, right, So it kind of makes me think
Speaker 2: of like, uh, you know, the basis behind things like computers.
Speaker 2: You have to have little on off things and you know,
Speaker 2: this is a system inside of a computer like a
Speaker 2: zero one an on or and off, and that change
Speaker 2: from off to on is a sort of bit of
Speaker 2: information that can be expanded into of course, the complexity
Speaker 2: of computer. It's the same thing I think with you know,
Speaker 2: in terms of the brain, where you have either a
Speaker 2: synapse has fired or it has not, there's a little
Speaker 2: more complexity because it's it's a large biological process. So
Speaker 2: you have, you know, some states that are somewhat in between,
Speaker 2: you know. But essentially it's like this on off state.
Speaker 2: You need to you be able to clearly have an
Speaker 2: off position and an on position and have that reach
Speaker 2: from one you know, like be able you know, even
Speaker 2: with like say a neuron, you are shooting neurotransmitters from
Speaker 2: one end of a neuron to the other end of
Speaker 2: another neuron. So it's like it's very much like in
Speaker 2: our day to day life we experience this concept of
Speaker 2: information exactly.
Speaker 1: And so you could also think about information from the
Speaker 1: sense of like affecting the future. Information is something that
Speaker 1: somebody in the future can use to make a decision.
Speaker 1: Like if I could tell you what the Powerball winning
Speaker 1: numbers are, you can be a billionaire tomorrow because you
Speaker 1: would know exactly what numbers to put in. So if
Speaker 1: I have information, I can send it to somebody and
Speaker 1: they can use that to make a decision. It can
Speaker 1: like change the future if I am sending them information.
Speaker 1: This is closely connected with another concept we've talked about
Speaker 1: on the podcast a lot, which is this causal link, right,
Speaker 1: like causes and effects how they can be connected. Because
Speaker 1: there's already a limit to how you can affect the
Speaker 1: future in the universe. Like, for example, I can't change
Speaker 1: the future in Andromeda tomorrow. Andromeda is so many light
Speaker 1: years away that any information I send to Andromeda will
Speaker 1: not arrive for millions of years, and so nothing I
Speaker 1: do today can get any information to Andromeda by tomorrow.
Speaker 2: So we cannot get a pizza from or to Andromeda
Speaker 2: anytime soon.
Speaker 1: That's right. We can't even tell Andromeda about what kind
Speaker 1: of pizzas they should order, which in principle could travel
Speaker 1: at the maximum speed of information, which is light speed.
Speaker 1: And so we have this concept we call a light cone,
Speaker 1: which tells you where in the universe your information can reach.
Speaker 1: You can send signals, you can turn on flashing lights,
Speaker 1: but people outside your light cone will not see it,
Speaker 1: and so the light cone expands as time goes on.
Speaker 1: You send a flare. Now that information propagates through the
Speaker 1: universe and eventually will reach the edges of the universe.
Speaker 1: Your light cone is expanding in time from every moment.
Speaker 1: But there is a limitation there, right, There are already
Speaker 1: parts of the universe that your information cannot reach at
Speaker 1: an arbitrary time, So there's a limit to the information.
Speaker 1: You can't send any information to people outside your light cone.
Speaker 2: I don't know if this is a pretty rudimentary question,
Speaker 2: but from Earth, right, we can't see every star in existence,
Speaker 2: can we? Or are we able to see, like get
Speaker 2: light information from every star in existence? From Earth?
Speaker 1: We can't because the universe is not old enough. Right,
Speaker 1: The universe is finite age, So there are some stars
Speaker 1: that are so distant that light from them has not
Speaker 1: had time to arrive here. Plus you've got a factor
Speaker 1: in the expansion or the universe. It gets much more complicated.
Speaker 1: But no, there definitely starts who have sent photons towards
Speaker 1: us but have not yet arrived.
Speaker 2: So it is a matter of timing where because like
Speaker 2: all this stars that we see right now, like that
Speaker 2: information is really old, that light information that we're receiving now,
Speaker 2: that's exactly right.
Speaker 1: Yeah, that information is very old, and it's a matter
Speaker 1: of timing. And if space was simple, space was always flat,
Speaker 1: if there was no curvature, photons always traveled in a
Speaker 1: straight direction and at the speed of light, then the
Speaker 1: only limit to information would be timing. But the curvature
Speaker 1: of space changes things. And in curved space, your light
Speaker 1: cone is not a simple cone. It gets bent, it
Speaker 1: gets distorted. Near a black hole or anywhere where space
Speaker 1: is curved. Your light cone gets twisted because it changes
Speaker 1: where photons go. Right, you send out a flash of light.
Speaker 1: Now they're going in some directions, not in other directions.
Speaker 1: They get twisted, they get bent. Once you pass over
Speaker 1: the event horizon, your light cone is now just pointed
Speaker 1: towards the center of the singularity. Any flare you set off,
Speaker 1: all photons are going to end up going towards the singularity.
Speaker 1: So your light cone is now sort of trapped behind
Speaker 1: this barrier. And that's what we mean when we say
Speaker 1: information cannot escape a black hole. I mean that nobody
Speaker 1: passed that threshold can ever send you a photon that
Speaker 1: arrives to you.
Speaker 2: If a photon approaches a black hole but doesn't pass
Speaker 2: the event horizon, can its light cones still get bent,
Speaker 2: but not fall into the black hole.
Speaker 1: Oh yeah. In fact, there's a region near black holes
Speaker 1: where photons can orbit. They can get trapped and forever
Speaker 1: loop around a black hole, which is pretty cool, or
Speaker 1: they can do other weird things like pass around the
Speaker 1: backside of a black hole and then come back. So
Speaker 1: you can shoot it like a laser beam just above
Speaker 1: a black hole and kind of come around the backside
Speaker 1: and zap you in the eyeball from below the black hole.
Speaker 2: It's like a laser boomerang.
Speaker 1: So the key thing to understand there is that information
Speaker 1: is about changes of state, how things change, getting updates
Speaker 1: about what's going on, decisions that are made, new facts
Speaker 1: that arise. Information is about changes of state.
Speaker 2: So with gravity, Now, I thought that we had talked
Speaker 2: about a previous episode about how with gravity there is
Speaker 2: a phenomenon known as gravitational waves, which would indicate that
Speaker 2: gravity can change. Right, you can have changes in gravity.
Speaker 2: So why would it be considered that gravity is not
Speaker 2: a form of information.
Speaker 1: Yes, great example, So gravitational wave is a great example
Speaker 1: of gravity changing. Right. We talked about gravity in terms
Speaker 1: of the curvature of space. So imagine space has some
Speaker 1: curvature because of the arrangements of masses in it. So
Speaker 1: space has that curvature, and that curvature is just fixed,
Speaker 1: it's constant. Right. Now, take one of those masses, the
Speaker 1: Sun maybe, and wiggle it. You put your finger on it,
Speaker 1: you shake it back and forth. If you wiggle the Sun,
Speaker 1: you're changing where the mass is. You're changing how space
Speaker 1: is bent. So what's happening to there is the curvature
Speaker 1: is changing. You're moving the Sun to the left, and
Speaker 1: you're moving it to the right, and you're moving it
Speaker 1: to the left again, you're moving it to the right,
Speaker 1: and that's information and that information propagates out at the
Speaker 1: speed of light. And so if you're far away from
Speaker 1: the Sun when somebody's wiggling it, you don't feel those
Speaker 1: changes instantly. It takes time for that information to get
Speaker 1: to you. So Katie wiggles the Sun. Eight minutes later,
Speaker 1: I feel the gravity on Earth shaking a little bit.
Speaker 1: It gets stronger, it gets weaker, it gets stronger, it
Speaker 1: gets weaker. That's a gravitational wave. That's information moving through
Speaker 1: the gravitational field. So I think that's sort of a
Speaker 1: long answer to your question, which is can you send
Speaker 1: information through gravity? And the answer is yes, And that's
Speaker 1: what gravitational waves are. There's information sent through the gravitational field.
Speaker 1: The crucial thing is that that's all about a change
Speaker 1: in the gravitational field. There's no information being propagated when
Speaker 1: the sun is static. The field is not changing. There's
Speaker 1: no information there. When you move the sun, when you've
Speaker 1: wiggled it, that's sending information.
Speaker 2: So Earth has gravity, obviously, but when the Earth moves,
Speaker 2: you're getting some change in gravity, and so you're getting
Speaker 2: gravitational waves. And so that change of the Earth moving
Speaker 2: is sending out information in terms of the change in gravity.
Speaker 1: Absolutely, And when the Earth orbits the Sun, because it's
Speaker 1: effectively moving through space and changing the Earth's gravitational field,
Speaker 1: we are generating gravitational waves. Our orbit around the Sun
Speaker 1: generates gravitational waves, and it actually contributes to the decay
Speaker 1: of Earth's orbit because gravitational waves contain energy, so we're
Speaker 1: radiating away some of our energy every time we go
Speaker 1: around the Sun. You just did an episode about this
Speaker 1: about how stable is the Earth's orbit, and it turns
Speaker 1: out that's a very very small effect in terms of
Speaker 1: the stability of the Earth's orbit. But in principle, yes,
Speaker 1: we are generating gravitational waves which contain information, and if
Speaker 1: you had a sensitive enough gravitational wave detector, you could
Speaker 1: pick up those wiggles in space time that are telling
Speaker 1: you about how the Earth is moving.
Speaker 2: So gravity can convey information. It can be considered a
Speaker 2: form of information if it is a change in the gravity.
Speaker 2: So with a black hole, why aren't we seeing a
Speaker 2: chain in gravity, because I would assume if we're not
Speaker 2: getting gravitational information from a black hole, that would mean
Speaker 2: that there is not a change in the gravity of
Speaker 2: a black hole.
Speaker 1: Yes, exactly, and so now I think we have all
Speaker 1: the pieces in place to try to answer this question,
Speaker 1: which is a black hole does of course have gravity,
Speaker 1: and you can feel its gravity from a distance. You
Speaker 1: are a light year from a black hole, you will
Speaker 1: feel its gravity. But what you can't feel are changes
Speaker 1: to its gravity. So if there's something going on inside
Speaker 1: the event horizon, Katie's in there and she's doing a dance,
Speaker 1: or she's rearranging her living room or whatever, you can't
Speaker 1: get that kind of information. If you change the configuration
Speaker 1: of the masses inside the black hole, in principle, that
Speaker 1: generates gravitational waves, but those are trapped within the event horizon.
Speaker 1: So nothing that's happening within the event horizon is generating
Speaker 1: any gravitational information that's escaping. All you're feeling is the
Speaker 1: static field of the black hole, the one that was
Speaker 1: created when it was formed. So you have a black
Speaker 1: hole and it has a static gravitational field. Nothing is
Speaker 1: changing and anything that happens inside the event horizon is
Speaker 1: going to generate gravitational waves, but they don't leave the
Speaker 1: black hole. So you can have gravity outside the black
Speaker 1: hole from its original formation without knowing what's going on
Speaker 1: later inside the event horizon, without getting any information from
Speaker 1: inside the event horizon. The only information you have is
Speaker 1: the existence of the black hole from when it was created,
Speaker 1: which is not information from inside the event horizon. Another
Speaker 1: way to think about it is you create the black hole,
Speaker 1: you're then freezing that gravitational field. Nothing that happens pas
Speaker 1: the event horizon can then change the gravitational field outside
Speaker 1: the black hole. Now, that's all if the black hole
Speaker 1: is not moving and so it has a static, unchanging
Speaker 1: gravitational field. If you wiggle a black hole or if
Speaker 1: black holes merge, that motion creates ripples in the gravitational field,
Speaker 1: just like a d when the Sun or the Earth moves.
Speaker 1: But that's motion of the event horizon. It's not information
Speaker 1: from inside the event horizon about what's going on within it.
Speaker 1: Another way to say it is that from the outside
Speaker 1: you can see if the black hole is wiggling, but
Speaker 1: that's not information from inside the event horizon. You can't
Speaker 1: tell if things inside are wiggling, only if the whole
Speaker 1: thing is moving.
Speaker 2: I mean that's interesting because it's like, I suspect this
Speaker 2: might be the wrong way to conceptualize it, but in
Speaker 2: my head, I'm thinking of sort of a Russian nesting doll,
Speaker 2: where it's like the black hole is the main one,
Speaker 2: the main sort of gravitational field, and inside you could
Speaker 2: have like the little tiny doll dancing around doing stuff,
Speaker 2: but none of that is reaching outside of this nesting
Speaker 2: doll because like the bigger one is essentially this like
Speaker 2: static large gravitational field, and nothing is getting outside of it.
Speaker 1: Yeah, I think that's a great way to think about it.
Speaker 1: Another useful thing to think through is how a black
Speaker 1: hole gets formed, the moment in which a black hole
Speaker 1: is created. I think that can really help people crystallize
Speaker 1: how that information is propagated through the universe and why
Speaker 1: no more information is ever sent out from that object.
Speaker 2: All right, let's take a quick break as I mentally
Speaker 2: prepare my mind to be blown. I'll lay out a tarp,
Speaker 2: and then when we get back, please tell me how
Speaker 2: a black hole is created. All right, So I'm officially
Speaker 2: ready for my brain to explode from the information of
Speaker 2: how a black hole is formed.
Speaker 1: So all you have to do to form a black
Speaker 1: hole is just order enough pizzas. Really, that's all it takes. Okay,
Speaker 1: So we know that there are black holes out there
Speaker 1: in the universe and that they are created, right, they're
Speaker 1: a black holes that have not existed since the beginning
Speaker 1: of the universe. So there has to be some moment
Speaker 1: when there wasn't a black hole and when there is
Speaker 1: a black hole. And I think the thinking through that
Speaker 1: moment really can help people understand what we're talking about
Speaker 1: when we say a black hole, what it means for
Speaker 1: information to be trapped within it. And so there's lots
Speaker 1: of ways that a black hole can be made in
Speaker 1: the universe, But let's try to think about like the
Speaker 1: simplest possible configuration and in general relativity, one very frequently
Speaker 1: used example is like a sphere of rocks. Imagine you
Speaker 1: have like tiny little bits of dust or pebbles, and
Speaker 1: you have a perfectly symmetrical sphere of it. Okay, and
Speaker 1: now gravity is pulling it and so it's collapsing. It's
Speaker 1: going to pull towards itself and get denser and denser
Speaker 1: and denser. Now, how do you make a black hole.
Speaker 1: You make a black hole by having enough stuff in
Speaker 1: a small enough space. It's all about the density of matter.
Speaker 1: You could take the Earth and squeeze it into a
Speaker 1: peanut to get a black hole. You could take the
Speaker 1: Sun and squeeze it into like a three kilometer wide object.
Speaker 1: To get a black hole. You could take a huge
Speaker 1: blob of stuff and squeeze it. The point is to
Speaker 1: get high enough density. So now you have this hollow
Speaker 1: fear of pebbles. Right, everything's like the same distance from
Speaker 1: the center, and it's collapsing slowly. At some point it's
Speaker 1: going to be dense enough to pass this threshold and
Speaker 1: become a black hole. It's going to be a moment
Speaker 1: before it passes that threshold where it's just like a
Speaker 1: sphere of stuff that has gravity, and then a moment
Speaker 1: after passes that threshold, now it's a black hole.
Speaker 2: How does the incredible density cause Essentially, what I'm imagining
Speaker 2: is like pinching the curvature of space such that everything
Speaker 2: is going towards that point, Like, how does density cause
Speaker 2: that to happen?
Speaker 1: We talked about how gravity is actually just the curvature
Speaker 1: of space. We didn't talk about how you make that
Speaker 1: curvature why bits of space are curved here or not
Speaker 1: curved there. So the missing piece is density energy density.
Speaker 1: If you have a chunk of space with a lot
Speaker 1: of energy in it, be it mass or photons or
Speaker 1: any kind of energy, then that space gets curved. So
Speaker 1: the simplest version of general relativity is mass tells space
Speaker 1: how to bend. Space tells mass how to move, and
Speaker 1: so it's that first bit that mass tells space how
Speaker 1: to bend. The more energy density, usually in the form
Speaker 1: of mass, that you pile into a little chunk of space,
Speaker 1: the more curvature you get. When you cross past some threshold,
Speaker 1: then you have so much curvature that nothing can escape anymore.
Speaker 1: So that's the moment you become a black hole. So
Speaker 1: you take this sphere of dust again, it's a hollow sphere.
Speaker 1: It's not filled on the center. If it's really really big,
Speaker 1: then you have a lot of empty space. Also, you're
Speaker 1: including density is very very low, you don't have a
Speaker 1: black hole. As you collapse it, the radius gets smaller
Speaker 1: and smaller. All the bits get closer and closer together.
Speaker 1: Eventually you pass over the short siled radius, the radius
Speaker 1: of an event horizon for that amount of stuff, and
Speaker 1: then you have enough density that there's enough curvature that
Speaker 1: you've got a black hole.
Speaker 2: So mass which we can observe is sort of tied
Speaker 2: to this hidden world of gravity which we cannot see.
Speaker 2: We can feel the effects of, but we cannot see
Speaker 2: the curvature of space. But that curvature of space has
Speaker 2: direct connections to all the mass that we can directly observe.
Speaker 1: Yeah, that's exactly right. And remember that's not just mass.
Speaker 1: Right in Newton's physics, it's just mass, but in Einstein's
Speaker 1: relativity it's energy density. That's why photons and other massless
Speaker 1: things can actually contribute to the curvature of space. You
Speaker 1: can actually just make a black hole by overlapping powerful
Speaker 1: laser beams. Pure photons can make a black hole in theory.
Speaker 2: Okay, how do you know that, Daniel, or are you
Speaker 2: working on that? Are you doing that?
Speaker 1: I can either deny nor confirm those experiments.
Speaker 2: That's incredible that just through light, if you cram enough
Speaker 2: light into a small enough area, not only are you
Speaker 2: going to like blow out your retinas, you're going to
Speaker 2: create a black hole.
Speaker 1: So now let's go back to our collapsing sphere of
Speaker 1: pebbles or dust or rocks or whatever. What happens when
Speaker 1: it creates a black hole? What is changing in space
Speaker 1: the moment before it creates a black hole? What do
Speaker 1: you have? What you have gravity?
Speaker 2: Right?
Speaker 1: If somebody is going to shoot a photon or a
Speaker 1: particle near it, it's going to be bending space and
Speaker 1: it's going to affect the path of that stuff. Right,
Speaker 1: You're going to feel the effective force of gravity from
Speaker 1: this sphere of rocks, right, because it has mass, it's
Speaker 1: curving space. It's giving you that effect. No big deal,
Speaker 1: no surprise there. What happens when it crosses that threshold
Speaker 1: and becomes a black hole? Well, nothing changes from that
Speaker 1: point of view, right, because the mass hasn't changed, the
Speaker 1: overall energy hasn't changed. So if you're in the outside,
Speaker 1: when this sphere becomes a black hole, nothing changes gravitationally,
Speaker 1: the gravitational field is still the same. And that makes sense, right.
Speaker 1: It's not like the gravity disappears when the thing becomes
Speaker 1: a black hole. It changes from a big sphere of
Speaker 1: dust to a black hole. But if it has the
Speaker 1: same mass, it has the same gravity as before it
Speaker 1: became a black hole.
Speaker 2: Okay, so you have this amount of gravity that just
Speaker 2: before sure the black hole is created, and then once
Speaker 2: the black hole happens, that gravity is the same. So
Speaker 2: can you not add any more gravity to a black hole?
Speaker 2: Like you cannot, Like say, you put more stuff into
Speaker 2: a black hole, you put more particles into that black hole,
Speaker 2: you shoot some lasers. There's no more gravity that you
Speaker 2: can add to that.
Speaker 1: That's a great question, actually really illustrates this point very nicely.
Speaker 1: Absolutely you can. Right, if you shoot a laser into
Speaker 1: the black hole, or you throw a more mast in
Speaker 1: the black hole, you are going to increase its gravity,
Speaker 1: and that information will propagate outwards. Right, you add to
Speaker 1: a black hole, you add to its gravity. You can
Speaker 1: feel more gravity now somewhere else. That information will propagate
Speaker 1: outwards as a gravitational waves, a change in the gravitational
Speaker 1: field of the black hole. But that's external, right, that's
Speaker 1: not information coming from within the black hole. That stuff
Speaker 1: you're adding from the outside. If you have just a
Speaker 1: black hole and it's collapsed and you're not changing its
Speaker 1: gravitational field, then what does it mean for information to
Speaker 1: not be able to aesc if you're still feeling its gravity?
Speaker 1: What that means, is that anything that's happening to that
Speaker 1: stuff that fell into the black hole, you can't tell. Basically,
Speaker 1: the gravitation field is just frozen from that stuff. If
Speaker 1: that stuff goes in and does a funny dance or
Speaker 1: becomes a singularity, or becomes a quantum fuzzball, or does whatever,
Speaker 1: you can't ever see. It can't ever tell you anything
Speaker 1: about it. You can't ever learn anything about the configuration
Speaker 1: of the mass within the event horizon. The gravitational field
Speaker 1: of that stuff still exists, but it's now frozen in time.
Speaker 1: You will get no more updates. If you take that
Speaker 1: stuff inside the black hole and wiggle it around, generating
Speaker 1: a bunch of gravitational waves within the event horizon, those
Speaker 1: waves are trapped within the event horizon. Outside you will
Speaker 1: still see the same exact gravitational field. And that's why
Speaker 1: we made the distinction earlier about information being about updates,
Speaker 1: because that gravitational field can be static. There's no information
Speaker 1: escaping from within the black hole. It's just sort of
Speaker 1: like think about the event horizon itself as having that
Speaker 1: gravity or the last information you got about this stuff
Speaker 1: was just before it falls into the black hole. It's
Speaker 1: that gravitational field. You're feeling no updates, no information means
Speaker 1: that gravitational field is effectively frozen.
Speaker 2: So would it be fair to say that we can
Speaker 2: get information from the existence of a black hole, and
Speaker 2: we can get information by shooting information into a black
Speaker 2: hole and then that sort of changing the characteristics of
Speaker 2: the black hole. But we cannot get any information from
Speaker 2: anything that is already inside of the black hole.
Speaker 1: Exactly, because that would require communicating something physically. Right, if
Speaker 1: you wanted to send information from within the black hole,
Speaker 1: you'd need to like take a bowling ball and wiggle it,
Speaker 1: which would generate gravitational waves. But I can't feel that
Speaker 1: from the outside. What I feel is the gravitational field
Speaker 1: of the stuff the moment it became a black hole.
Speaker 1: That's when it got frozen in time. All the gravitational
Speaker 1: waves generated inside of it, an updates to that gravitational
Speaker 1: field are now trapped the same way that like if
Speaker 1: you shoot photons or if you shoot electrons. Right, I remember,
Speaker 1: information is physical. None of that physical information.
Speaker 2: Can leave all right, But now hear me out. If
Speaker 2: you had a really long string and you were sitting
Speaker 2: here on Earth with a dixie cup attached to your end,
Speaker 2: and I'm all the way in a black hole with
Speaker 2: that string and a dixie cup on my end. No,
Speaker 2: I cannot communicate any information to you, even if somehow
Speaker 2: that string was strong enough to survive the black hole.
Speaker 7: Right.
Speaker 1: Well, there, you're creating a new paradox because there is
Speaker 1: no string strong enough to survive the black hole. Right
Speaker 1: Because as you zoom in microscopically to that string, it's
Speaker 1: really just a bunch of particles transmitting information to each
Speaker 1: other using electrons or using photons, and those photons cannot
Speaker 1: escape the black hole. But you know, electrons and photons
Speaker 1: are a great way to think about this information. Also,
Speaker 1: like say you take an electron and you just have
Speaker 1: an electron in space. Electron has an electric field, right,
Speaker 1: a static field all through space. It gets stronger as
Speaker 1: you're closer to it, and weaker as you get further away. Now,
Speaker 1: what happens if you shake that electron. You shake that electron,
Speaker 1: you're changing the electric field. And that change is a photon.
Speaker 1: It's physical information. It's changing the field of the electron
Speaker 1: that is transmitting the information. The static, frozen constant existence
Speaker 1: of the field is not information, which is why stationary
Speaker 1: electrons don't generate photons in the same way that like,
Speaker 1: the existence of the black hole and its gravitational field
Speaker 1: is sort of like old information from before it became
Speaker 1: a black hole when it was created. Any new information
Speaker 1: created within it by moving the stuff inside is not
Speaker 1: going to be transmitted. So information gravitational waves or photons
Speaker 1: really are about changes in the field, not about the
Speaker 1: existence of the field itself.
Speaker 2: So in my string and cup analogy, of course the
Speaker 2: string would not survive. But you know, with a hypothetical string,
Speaker 2: I could be shaken it, I could be talking into
Speaker 2: the Dixie cup. But as soon as that information, you know,
Speaker 2: is basically the part of the hypothetical string outside of
Speaker 2: the event horizon is getting nothing from the string inside.
Speaker 2: From within the event horizon.
Speaker 1: Exactly, your string is going to be dangling towards the
Speaker 1: center of the black hole. All the information you create
Speaker 1: is going to get funneled towards the center of the
Speaker 1: black hole.
Speaker 2: Wow. Well, I'm gonna really emphasize that if I am
Speaker 2: in a black hole. Pepperoni pizza is good. Also, do
Speaker 2: a nice carbonara, just keep them common for eternity. I
Speaker 2: suppose that sounds good.
Speaker 1: It's good to get that information now before you fall
Speaker 1: into the black hole.
Speaker 2: Right could happen any day. We are sponsored by black
Speaker 2: Hole Insurance. Make sure to set up your affares before
Speaker 2: you get sucked into a black hole, or should I say,
Speaker 2: not sucked into a black hole, but follow the curvature
Speaker 2: of space into a black hole.
Speaker 1: So you should think about black holes as barriers to information.
Speaker 1: But I hope this podcast has helped you understand a
Speaker 1: little bit more what that means, what information really is,
Speaker 1: because what's inside a black hole can affect what's outside
Speaker 1: a black hole. The creation of the black hole itself
Speaker 1: affects space time near the black hole. But sort of
Speaker 1: in a simplified way. We can only know a few
Speaker 1: things about the black hole. We can know it's mass,
Speaker 1: we can know it's charge, we can know its spin.
Speaker 1: Anything else that happens within the black hole can't change
Speaker 1: what's happening on the outside. The changes behind the barrier,
Speaker 1: wiggles and rearrangements of the stuff within the black hole
Speaker 1: can't influence things on the outside. So I think the
Speaker 1: crucial concept there is that information really is about changing
Speaker 1: the internal arrangements. That's what you're prevented from knowing not
Speaker 1: the existence of the black hole, but what's going on
Speaker 1: inside of it.
Speaker 2: So I could be inside of the black hole, drunk
Speaker 2: off of Martini's, standing on the black hole jack table
Speaker 2: and screaming out the lyrics to a Katie Perry song,
Speaker 2: and no one would ever know.
Speaker 1: Only people within the black hole and closer to the center.
Speaker 1: But hopefully what happens inside a black hole stays inside
Speaker 1: a black hole.
Speaker 2: Yeah, well that's good information to know, because I know
Speaker 2: now where I'm going to do my next Vegas trip
Speaker 2: and it's not in Vegas.
Speaker 1: All right. Well, I want everybody out there to keep
Speaker 1: thinking like a physicist, trying to bring pieces of understanding
Speaker 1: together and weave them into a deeper, more profound model
Speaker 1: in your head about how the universe works, how these
Speaker 1: things all interact, and when things don't jive together, when
Speaker 1: they don't make sense to you, or when you feel
Speaker 1: like you have hit upon a contradition right to us,
Speaker 1: we will help you figure it out. Questions at Danielanjorge
Speaker 1: dot com. Our goal is to turn everybody into a physicist.
Speaker 2: You and your army of physicists. What are you planning?
Speaker 1: I can neither confirm nor deny our plan. Thanks very
Speaker 1: much Katie for joining me on this path towards the
Speaker 1: center of understanding following the curvature of explanations.
Speaker 2: Thank you for all the information. I'm glad we're not
Speaker 2: broadcasting from a black hole where nobody would.
Speaker 1: Know, and thanks everybody for listening. Tune in next time.
Speaker 4: Hey, this is Joege from the podcast and I'm super
Speaker 4: excited to announce that my new book, Oliver's Great Big Universe,
Speaker 4: is out now. It has humor, cartoons, a fun story,
Speaker 4: and lots of awesome signs, and it's perfect for kids
Speaker 4: that are into science, but also kids who are not
Speaker 4: into science yet. There are chapters about black holes the
Speaker 4: planet's dark energy, but at the heart of it is
Speaker 4: a story about friendship and figuring out your place in
Speaker 4: the world, so please check it out. You can get
Speaker 4: it in stores, online, and at Great Big Universe dot net.
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explain
Speaker 1: the universe is a productive of iHeartRadio. For more podcasts
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