Latest / Daniel and Kelly’s Extraordinary Universe / Black Hole Questions!

Transcript

Black Hole Questions! · Daniel and Kelly’s Extraordinary Universe

0:01
Speaker 1: Hey, it' Jorhan Daniel here, and we want to tell
0:03
Speaker 1: you about our new book. It's called Frequently Asked Questions
0:06
Speaker 1: about the Universe because you have questions about the universe,
0:09
Speaker 1: and so we decided to write a book all about them.
0:12
Speaker 1: We talk about your questions, we give some answers, we
0:14
Speaker 1: make a bunch of silly jokes as usual, and we
0:17
Speaker 1: tackle all kinds of questions, including what happens if I
0:20
Speaker 1: fall into a black hole? Or is there another version
0:22
Speaker 1: of you out there that's right? Like usual, we tackle
0:25
Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.
0:29
Speaker 1: If you want to support the podcast, please get the
0:31
Speaker 1: book and get a copy not just for yourself, but
0:34
Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,
0:39
Speaker 1: and for the aliens. So get your copy of Frequently
0:42
Speaker 1: Asked Questions about the Universe is available for pre order now,
0:46
Speaker 1: coming out November two. You can find more details at
0:49
Speaker 1: the book's website, Universe f a Q dot com. Thanks
0:53
Speaker 1: for your support, and if you have a hamster that
0:55
Speaker 1: can read, please let us know. We'd love to have
0:57
Speaker 1: them on the podcast. Hey, Jorge, why do you think
1:10
Speaker 1: we get so many questions about black holes. Well, you know,
1:14
Speaker 1: it's the mystery. You know, they're so inscrutable. They're like
1:18
Speaker 1: the reclusive celebrities of the universe exactly right, Like the
1:21
Speaker 1: more they avoid the paparazzi, the more people want to
1:24
Speaker 1: know about them. That could be true, but I was
1:26
Speaker 1: actually wondering if it might be the exact opposite. What
1:30
Speaker 1: do you mean, Well, what if black holes are like
1:32
Speaker 1: the car crash of the universe. They're like a cosmic
1:34
Speaker 1: disaster that you can't drive by without slowing down to
1:37
Speaker 1: check it out. Saying physicists are just rubber neckers, cosmic
1:41
Speaker 1: rubber neckers. That sounds kind of dangerous, like you might
1:43
Speaker 1: cause another accident by not watching where you were driving
1:46
Speaker 1: your spaceship. Exactly. That's the gravitational runaway effects of the
1:50
Speaker 1: black holes. Slow down to check it out, get sucked in,
1:52
Speaker 1: make a bigger black hole. That's how I feel about
1:54
Speaker 1: driving in Los Angeles. It's like an infinite black hole
1:57
Speaker 1: that you will never escape. I am Jorge made cartoonists
2:15
Speaker 1: and the creator of PhD comics. Hi, I'm Daniel. I'm
2:18
Speaker 1: a particle physicist and a professor at U C. Irvine,
2:21
Speaker 1: but I almost never go up to Los Angeles. Really
2:24
Speaker 1: do you avoid it like a black hole. If it
2:28
Speaker 1: was a black hole, it would suck me in. So yeah,
2:30
Speaker 1: I'm trying to stay in orbit around Los Angeles instead
2:33
Speaker 1: of falling into the singularity, yes, where time slows down
2:36
Speaker 1: through plastic surgery apparently. But yeah, I mean you're kind
2:39
Speaker 1: of famous now, Daniel. You don't get calls from Hollywood
2:42
Speaker 1: these days. I screened my calls, so if they're calling,
2:45
Speaker 1: I'm just not picking them up. You look for the
2:46
Speaker 1: aira code. If it's your local air code, it's ma'am.
2:49
Speaker 1: If it's three one oh, then it's someone from Hollywood,
2:51
Speaker 1: like Jorge, so you just hang up. Also, you know,
2:54
Speaker 1: there's famous and then there's Los Angeles famous. You can
2:56
Speaker 1: be like super famous in Orange County and be nobody
2:59
Speaker 1: in Los Angeles. But anyways, welcome to our podcast, Daniel
3:02
Speaker 1: and Jorge Explain the Universe, a production of I Heart Radio,
3:05
Speaker 1: in which we ask all the biggest and famous and
3:08
Speaker 1: most time dilated questions of the universe. We ask all
3:12
Speaker 1: of them about where it came from, where it's going,
3:14
Speaker 1: what it's made out of, and how it all works.
3:16
Speaker 1: We dive deep into the questions about black holes and
3:19
Speaker 1: neutron stars and galaxies and tiny particles and quaisars and
3:23
Speaker 1: everything in between, because we think it's possible to download
3:26
Speaker 1: all of that into your amazing brain and hold for
3:29
Speaker 1: a moment an understanding of the entire universe. Yeah, because
3:33
Speaker 1: it is a pretty famous universe. Everyone seems to know
3:36
Speaker 1: about it. Everyone's fan. I would hope, you know, it's
3:39
Speaker 1: everywhere he got. He can't get away from this universe,
3:42
Speaker 1: and it's pretty fascinating, even it's black sheep. You know,
3:45
Speaker 1: everyone wants to know about the black Sheep of the celebrities. Yes,
3:48
Speaker 1: have you been checking out the universe's reviews on yelp? Yes,
3:51
Speaker 1: I think it. It has about infinite stars and also
3:54
Speaker 1: infinite thumbs, but you know it's about fifty up and them.
3:57
Speaker 1: That's right, And you know nobody has any other are alternatives.
4:00
Speaker 1: It's not like people like, hey, I was in this
4:02
Speaker 1: other universe the other day and they have better chips.
4:05
Speaker 1: So you know, this is basically all we got learned
4:07
Speaker 1: to love at people. Maybe you just need to get
4:09
Speaker 1: out more than you You might find other universes if
4:11
Speaker 1: you just, you know, get out of your Orange County
4:13
Speaker 1: Bubble l A does seem like another universe sometimes, not
4:17
Speaker 1: just because it's weird, but because it takes forever to
4:19
Speaker 1: get there. Definitely an alternate reality for sure. But anyways, Yeah,
4:24
Speaker 1: people are curious not just about the universe but about
4:27
Speaker 1: the things in it, especially things that are extra mysterious,
4:30
Speaker 1: and those are the things that drive physics. We look
4:33
Speaker 1: around in the universe and we say, do we understand
4:35
Speaker 1: how this works? Does that bit over there makes sense?
4:38
Speaker 1: And if it doesn't, then we focus our brains on
4:40
Speaker 1: and try to understand how could that possibly work? How
4:42
Speaker 1: could that make sense? How could that be consistent with
4:45
Speaker 1: what we know about the nature of space and time
4:48
Speaker 1: and energy, And so the weirdest things are also the
4:51
Speaker 1: best opportunities to learn something about the universe. Yeah, because
4:55
Speaker 1: when you look around, I guess it's all pretty bright
4:56
Speaker 1: and beautiful and majestic and cosmic, but everyone's in a
5:00
Speaker 1: When you look at into the universe, there is a
5:02
Speaker 1: basically a big hole, like a big hole in our
5:04
Speaker 1: knowledge and also literally figuratively and in all the ways
5:08
Speaker 1: there there are actual holes in the universe. There are
5:11
Speaker 1: holes in the universe, and you know, to answer the
5:13
Speaker 1: question to our intro. I think one reason that they're
5:15
Speaker 1: fascinating is because they are so different from what we experience.
5:19
Speaker 1: You know, it's not just like, hey, there's a banana
5:22
Speaker 1: out there in space, like we know bananas, We bananas,
5:24
Speaker 1: were familiar with bananas. You know, it's something out there
5:27
Speaker 1: in space which is so different from our everyday experience,
5:30
Speaker 1: so bizarre that we just sort of like want to
5:33
Speaker 1: see it. Yeah, and so to be on the podcast,
5:35
Speaker 1: we'll be tackling unanswered questions about black holes. Now, Daniel,
5:45
Speaker 1: I assume it's not just bananas out there. We don't know,
5:49
Speaker 1: you know, maybe bananas are the fundamental element of the
5:52
Speaker 1: universe and it is just all bananas all the way down.
5:55
Speaker 1: That's a viable theory. It sounds like a slippery slope there.
6:00
Speaker 1: We just gotta peel back the layers of reality until
6:03
Speaker 1: we reveal the banana inside. But yeah, black holes. A
6:07
Speaker 1: lot of people have questions about black holes, and you're
6:10
Speaker 1: asking me earlier why they're so mysterious. Like everyone, you
6:13
Speaker 1: get a lot of questions about black holes, right, Yeah,
6:15
Speaker 1: I say like a third of all the questions we
6:17
Speaker 1: get are about black holes. What happens if you fall
6:19
Speaker 1: in them, What would they look like if you did this?
6:21
Speaker 1: What would happen if you shoot two black holes at
6:23
Speaker 1: each other? All sorts of questions people love to think
6:25
Speaker 1: about black holes. Interesting a third of the questions. That's amazing.
6:30
Speaker 1: It's like, it's some black hole in your It does
6:33
Speaker 1: make my inbox pretty dense. But I love it. I
6:36
Speaker 1: love thinking about black holes just as much as our
6:38
Speaker 1: listeners do for the same reasons, you know. And the
6:41
Speaker 1: cool thing about black holes is that we all understand
6:44
Speaker 1: them about as well, you know. I love that we
6:46
Speaker 1: can bring our listeners to the very forefront of knowledge,
6:48
Speaker 1: because in the case of black holes, it's not that
6:50
Speaker 1: far away. You know. We just don't understand very much
6:54
Speaker 1: about these weird, mysterious objects. I think that's why they're
6:57
Speaker 1: so fascinating to physicists, because they represent such a great
7:00
Speaker 1: opportunity to learn something new and shocking about the universe. Yeah,
7:04
Speaker 1: so today we're answering questions that we've gotten about black
7:07
Speaker 1: holes from listener. It's just like you, and we've got
7:10
Speaker 1: three pretty interesting questions, one of them about the mass
7:13
Speaker 1: of a black hole, about mini black holes, and also
7:17
Speaker 1: about whether or not black holes can explain dark matter.
7:21
Speaker 1: So let's jump into our first question right away here,
7:23
Speaker 1: and it comes from Levi from the Ukraine. I didn't
7:27
Speaker 1: know m Levi are Ukraine, and I had two questions
7:31
Speaker 1: about my favorite topic, which is black holes. First, how
7:36
Speaker 1: is the mass of a black hole calculated? And second?
7:41
Speaker 1: Is there anybody to know when an event horizon of
7:44
Speaker 1: a black hole begins? If I were to say, take
7:46
Speaker 1: a rocket ship to the black hole and this sene
7:48
Speaker 1: our galaxy, is there any way that I could know
7:51
Speaker 1: when I need to turn that thing around before I
7:53
Speaker 1: become spaghetti? Thank you? M M. Interesting question? Now? Was
7:58
Speaker 1: he allowed two questions? I feel like he's not good
8:00
Speaker 1: extra question in his question imploded into a black hole
8:03
Speaker 1: because of its density, he had it multiplied. It seems
8:07
Speaker 1: so you just can't stop asking questions. Once you start
8:09
Speaker 1: thinking about black holes, the questions just proliferate. What do
8:12
Speaker 1: you think it's captured the imagination of not just our listeners,
8:15
Speaker 1: but it seems like everyone out there has questions about
8:18
Speaker 1: black holes. I think it's just the opportunity to see
8:21
Speaker 1: something hidden, to learn something new. You know. The thing
8:23
Speaker 1: that captivates me about the black hole is knowing that
8:26
Speaker 1: one of the greatest mysteries in modern physics. How to
8:30
Speaker 1: reconcile crazy intense gravity and quantum little particles, how to
8:35
Speaker 1: bring those together into one idea is out there, and
8:37
Speaker 1: it's hidden inside a black hole. So if we could
8:40
Speaker 1: only peek inside, we could learn the very nature of
8:43
Speaker 1: space and time. There's so much we could know by
8:46
Speaker 1: the universe if only we could see inside a black hole.
8:49
Speaker 1: And yet he's hidden from us. So it's sort of
8:51
Speaker 1: like somebody saying, I have the secrets you want, and
8:54
Speaker 1: they're written on this envelope and I'm gonna burn it.
8:56
Speaker 1: I'm gonna throw in the fire instead of opening it
8:58
Speaker 1: to you. That would kill you. Oh man, if you's
9:01
Speaker 1: so frustrating to know the answers are out there and
9:03
Speaker 1: not be able to get them, that's very frustrating. These
9:06
Speaker 1: there a big red button into that envelope. That would
9:08
Speaker 1: drive doubly crazy. But all right, let's jump into Levi's
9:11
Speaker 1: questions here. The first one is how do you calculate
9:13
Speaker 1: the mass of a black hole? Now I'm guessing down
9:17
Speaker 1: or there are not gigantic scales we can use to
9:20
Speaker 1: measure the mass of a black hole, A sort of
9:23
Speaker 1: if we can Yeah, scales work by using gravity. Right,
9:27
Speaker 1: If you put something on a scale, you're measuring its weight,
9:30
Speaker 1: and its weight is the force of gravity on it,
9:32
Speaker 1: which is determined by its mass. And so to measure
9:35
Speaker 1: the mass of something you can use the strength of
9:37
Speaker 1: the gravitational pull on it, which depends on the object's mass.
9:41
Speaker 1: Now out there in space, You're right, there's not some
9:43
Speaker 1: like massive scale we can put it on. But we
9:46
Speaker 1: can see how the black hole tugs on things around
9:49
Speaker 1: it which are visible, and that's one way we can
9:52
Speaker 1: measure its mass, and so you can see the effects
9:54
Speaker 1: of its mass on the things around it. I guess
9:56
Speaker 1: kind of like our son, right, Like if our son
9:59
Speaker 1: with a different and mass, like if it was bigger
10:01
Speaker 1: or smaller than our orbit around it would be different. Right,
10:05
Speaker 1: Like you could tell what the mass of the Sun
10:07
Speaker 1: is maybe from our orbit. Yeah, if you measure just
10:10
Speaker 1: the velocity and location of the Earth as it moved
10:12
Speaker 1: around the Sun, you can deduce exactly the mass of
10:15
Speaker 1: the Sun because you can tell what gravitational force is
10:18
Speaker 1: necessary to move the Earth in that path, and that
10:21
Speaker 1: would tell you how much mass you need to provide
10:23
Speaker 1: that gravitational force. So, yeah, the Earth is like a
10:26
Speaker 1: little scale that's measuring the Sun all the time. But
10:29
Speaker 1: what do you need to know the mass of the
10:30
Speaker 1: Earth too, pretty accurately? Yes, absolutely, you need to know
10:33
Speaker 1: the mass of the Earth. And don't say you just
10:35
Speaker 1: use the sun, because then now we're in a circular argument. No,
10:39
Speaker 1: you need to use the mass of the Earth. Absolutely.
10:41
Speaker 1: The mass of the Earth you can get using like
10:43
Speaker 1: your knowledge of what it's made out of and it's volume.
10:46
Speaker 1: So if you know the radius of the Earth, like
10:48
Speaker 1: its size, and your understanding roughly what it's made out of,
10:50
Speaker 1: then you can tell its mass, or you can bootstrap.
10:53
Speaker 1: You can say, well, I'm gonna look at the moon
10:55
Speaker 1: and see how the moon moves around the Earth, and
10:57
Speaker 1: that's going to tell me the mass of the Earth
10:58
Speaker 1: if again you know the mass to the moon. Yeah,
11:02
Speaker 1: and so on and so on. I guess at some point,
11:04
Speaker 1: maybe the question is at some point when do you
11:06
Speaker 1: have to guess? Right, because something you have to guess
11:09
Speaker 1: what the moon is made out of, or even the
11:11
Speaker 1: Earth you cannot have to guess. I mean, we have
11:13
Speaker 1: some measurements, but we ultimately you're sort of guessing what's
11:17
Speaker 1: inside the Earth. Yeah, in the end, you do need
11:19
Speaker 1: to know the mass of one of the objects to
11:20
Speaker 1: measure the mass the other. But there's also some constraints.
11:23
Speaker 1: They're like, what you really need to know is the
11:25
Speaker 1: product of the two masses, right, mass one times mass too.
11:29
Speaker 1: So if you make enough measurements of pairs of objects
11:32
Speaker 1: and you can narrow that down, you get like enough
11:34
Speaker 1: systems of equations that you can constrain it. But yeah,
11:37
Speaker 1: you also do need to say something about what they
11:39
Speaker 1: are made out of to get some information about how
11:41
Speaker 1: much mass one of them has. You can also measure
11:43
Speaker 1: the mass of the Earth by flipping that around and saying, here,
11:46
Speaker 1: I have an object whose mass I know, and that
11:48
Speaker 1: can measure the gravitational effect on it, and from that
11:51
Speaker 1: I can measure the mass of the Earth. To build
11:53
Speaker 1: like a calibration object, like a test object, like a
11:55
Speaker 1: one kilogram pound of platinum or something. Yeah, you can
11:59
Speaker 1: see how much it pulls on like a known weight,
12:02
Speaker 1: and then that's how you would estimate the mass of
12:04
Speaker 1: the Earth. And that's just sort of definition. All you say, like,
12:06
Speaker 1: this is the definition of a kilogram this object, and
12:09
Speaker 1: from that you can measure essentially the ratio of its
12:12
Speaker 1: mass to the mass of the Earth. You can say
12:14
Speaker 1: how massive is the Earth in terms of this object
12:17
Speaker 1: I'm defining to be one kilogram, and then you can
12:19
Speaker 1: bootstrap your way up to the Sun and basically everything
12:22
Speaker 1: else in the universe. Right, you can strap your boot.
12:24
Speaker 1: You can boot your strap. But what about for like
12:27
Speaker 1: a black hole? I mean, they're so far away, we've
12:30
Speaker 1: barely seen one directly. You know, we can see the
12:33
Speaker 1: things flying around it, But how do we know what
12:35
Speaker 1: those things are? I mean, they're just like bright little pinpoints, right, yes,
12:38
Speaker 1: So one way we can see the black holes exist
12:41
Speaker 1: is by seeing their gravitational effect on stuff nearby. Because
12:44
Speaker 1: black holes, of course are black, they don't admit any
12:47
Speaker 1: radiation directly, or if they're emitting hawking radiation, then we
12:50
Speaker 1: can't see it. It's too faint. So you're right, we
12:52
Speaker 1: need to know the mass of the objects nearby. And so,
12:55
Speaker 1: for example, the black hole the center of our galaxy
12:58
Speaker 1: has some stars whizzing very close by to it, and
13:01
Speaker 1: we can measure the mass of those stars by looking
13:04
Speaker 1: at the light they emit, because we have a pretty
13:06
Speaker 1: good model for how the brightness of a star is
13:09
Speaker 1: related to its mass. So we did a whole episode
13:11
Speaker 1: on how you measure the mass of stars. And that's
13:14
Speaker 1: not perfect, it's not exact, but it's pretty good, right,
13:17
Speaker 1: it's based on like models and some observations, and so
13:20
Speaker 1: just from the light that you get from those stars
13:22
Speaker 1: around the black hole, you can say, well, that's a
13:24
Speaker 1: a stage so and so star weighs about they usually
13:27
Speaker 1: wait about this much and so there, and it's curving
13:30
Speaker 1: around the black hole this much. So therefore that black
13:33
Speaker 1: holes probably there's many kilograms exactly. And those models are
13:37
Speaker 1: pretty good, and we validate them using binary star systems
13:40
Speaker 1: where we can see two stars, we can measure their brightness,
13:42
Speaker 1: and we can see how they move around each other,
13:44
Speaker 1: and so we can really validate those models pretty well.
13:47
Speaker 1: I mean, there are uncertainties, but we can trust those
13:49
Speaker 1: because remember there are a lot of binary star systems
13:51
Speaker 1: out there in the universe, many more than you might expect.
13:54
Speaker 1: So that lets us measure the mass of the stars
13:55
Speaker 1: and from that deduced the mass of the black hole.
13:58
Speaker 1: Because remember, black holes don't emit any information from their
14:01
Speaker 1: inside except for the total mass of the black hole,
14:05
Speaker 1: which can be deduced by its gravitational effect. That's the
14:08
Speaker 1: only information that comes out other than the black holes
14:11
Speaker 1: spin and charge. And also do you have to account
14:13
Speaker 1: for like the camera adding ten pounds, like does the
14:16
Speaker 1: telescope at you know, ten million kims? No, the black
14:19
Speaker 1: holes agent is very particular by the cameras. We used
14:22
Speaker 1: to take their pictures nicely. These is doubles. When it's
14:25
Speaker 1: taking the naked pictures. I said, take a profile above
14:27
Speaker 1: the accretion disk. That's when it looks good, all right.
14:29
Speaker 1: And there's also sort of a different way to measure
14:31
Speaker 1: the mass of a black hole, which is by looking
14:33
Speaker 1: at its size. Like if we ever do get better
14:36
Speaker 1: pictures of a black hole, you might be able to
14:38
Speaker 1: tell how heavy it is by just seeing its size, right,
14:41
Speaker 1: Because the size of the event horizon depends on the
14:44
Speaker 1: mass of the black hole. Yeah, they're very closely connected.
14:46
Speaker 1: As the black hole eats more and gets more mass
14:49
Speaker 1: than it is gaining in size, the size the event
14:51
Speaker 1: horizon is growing, and so if you could measure the
14:55
Speaker 1: event horizon, then you could deduce its mass. Measuring the
14:58
Speaker 1: event horizon is tricky though, because you need to see
15:00
Speaker 1: photons like whizzing around it. So you need a direct
15:03
Speaker 1: picture and we've done that for one, maybe two black
15:06
Speaker 1: holes now. But it's much harder, obviously, And so that
15:08
Speaker 1: brings us to the second question leave I had, which
15:11
Speaker 1: is like, if I'm trying to check out a black hole, like,
15:13
Speaker 1: could I tell where the actual event horizon is? Like,
15:17
Speaker 1: at what point do you want to make sure you
15:19
Speaker 1: turn around before you get sucked in forever? Well, I
15:22
Speaker 1: would say turn around now, do not take that trip
15:24
Speaker 1: to the black hole. It's not a good idea. Don't
15:28
Speaker 1: even buy the ticket sets when you should turn around. Right,
15:30
Speaker 1: So it is a good idea to think about where
15:33
Speaker 1: a black hole begins, where it's event horizon is, so
15:36
Speaker 1: that if you are a billionaire scientist, entrepreneur and you
15:40
Speaker 1: do take that trip to the center of the Milky
15:42
Speaker 1: Way to study the black hole, you know when to
15:44
Speaker 1: turn around. And one thing you could do, if you
15:47
Speaker 1: know the mass of the black hole is, you could
15:49
Speaker 1: just calculate it. You could say, well, I know how
15:51
Speaker 1: massive it is, so I know the point of no return.
15:54
Speaker 1: I can calculate the event horizon. So, yeah, there's a
15:57
Speaker 1: point at a distance from the center of the black
15:59
Speaker 1: hole at which now even light can escape, right. I
16:01
Speaker 1: think maybe that's what LEVI is asking, Like, what's the
16:03
Speaker 1: point where not even light can escape. That's the event horizon,
16:07
Speaker 1: and from a distance you can sort of see it, right, Like,
16:09
Speaker 1: it's sort of where when you look at a black hole,
16:12
Speaker 1: and we've looked at one, it looks like a big
16:15
Speaker 1: black circle, and so that's generally where the event horizon is,
16:18
Speaker 1: although it's not exact right. That's right, the black circle
16:21
Speaker 1: you see when you look at a black hole is
16:23
Speaker 1: actually bigger than the event horizon because you can't see
16:26
Speaker 1: photons that like fly just above the event horizon from
16:30
Speaker 1: behind the black hole. Those we get curved and fall
16:33
Speaker 1: into the black hole. So there's the event horizon itself,
16:36
Speaker 1: and then there's like a shadow that the black hole
16:38
Speaker 1: makes that's even larger than the event horizon. You can
16:41
Speaker 1: get closer than the shadow, you see it looks bigger
16:43
Speaker 1: than it actually is. And as you get closer and
16:46
Speaker 1: closer to the black hole, that shadow grows and it
16:49
Speaker 1: grows to take over more and more of your view.
16:52
Speaker 1: So if you're very close to the black hole, for example,
16:54
Speaker 1: then it might appear to take up like half of
16:56
Speaker 1: your entire view. Right. That's kind of the tricky thing
17:00
Speaker 1: about black holes is that there's so much distortion around
17:02
Speaker 1: them that you know, from afar, they look like a
17:05
Speaker 1: nice clean circle, But as you get closer, everything gets
17:08
Speaker 1: distorted and kind of blown out of proportion, and so
17:11
Speaker 1: it's gonna be really hard to tell when you've reached
17:14
Speaker 1: the actual event horizon, right, because, like you're saying, the
17:17
Speaker 1: black hole is gonna start taking a bit more and
17:19
Speaker 1: more of your field of view, and you're gonna be
17:21
Speaker 1: like in my inn or am I out? I don't know,
17:23
Speaker 1: yeah exactly, And so this is very dangerous not to
17:25
Speaker 1: be recommended or endorsed. But as you get closer and
17:28
Speaker 1: closer to the black hole, the image of it grows
17:31
Speaker 1: larger and larger, and as you say, what you're seeing
17:33
Speaker 1: is not anymore a good representation of what's actually there.
17:37
Speaker 1: Like when you look around yourself in your room, the
17:39
Speaker 1: stuff you see is the stuff that's there, because the
17:41
Speaker 1: light is moving in a straight line from whatever it
17:44
Speaker 1: is to your eyes, and so you can look around
17:46
Speaker 1: and say, oh, that's over there and this is over here.
17:48
Speaker 1: But if there are like lenses around you that bend
17:50
Speaker 1: the light, then you get distorted images. Imagine you're in
17:53
Speaker 1: a fun house mirror. What you see is not what's
17:55
Speaker 1: actually there, and that's what's happening with the black hole.
17:58
Speaker 1: Light is no longer following straight lines, so what you
18:00
Speaker 1: see is a distortion. And it's really interesting. As you
18:03
Speaker 1: get closer and closer to the black hole than the
18:05
Speaker 1: shadow of the black hole, this big black image of
18:08
Speaker 1: the event horizon gets larger and larger eventually becomes more
18:12
Speaker 1: than just half of your view. It like takes up
18:15
Speaker 1: most of your view, and the rest of the universe
18:17
Speaker 1: is squeezed down into a smaller and smaller circle. And
18:20
Speaker 1: you can get a clue about when you're back to
18:22
Speaker 1: cross the event horizon, because when you cross the event horizon,
18:25
Speaker 1: that circle that there's the rest of the universe is
18:28
Speaker 1: now shrinking down to a tiny little dot. And once
18:31
Speaker 1: you fall inside the event horizon, then the rest of
18:33
Speaker 1: the universe is now exactly one tiny little point where
18:36
Speaker 1: light from the universe can still reach you. Yeah, it's
18:39
Speaker 1: a pretty trippy experience and pretty extreme and and actually,
18:42
Speaker 1: if you want to know more about this, it's conveniently
18:45
Speaker 1: a question we answer in our new book. Right Daniel
18:47
Speaker 1: frequently ask questions about the universe. That's right, This is
18:50
Speaker 1: a frequently asked question. What would it be like to
18:53
Speaker 1: fall into a black hole, and the book is a
18:55
Speaker 1: lot of fun. It's out on November two one. You
18:59
Speaker 1: can check it out at you reverse f a q
19:01
Speaker 1: dot com. It's filled with answers and a bunch of
19:03
Speaker 1: really awesome cartoons at or he drew. They give you
19:06
Speaker 1: a sense for what it would look like to fall
19:08
Speaker 1: into a black hole. Yeah, order a copy for yourself,
19:10
Speaker 1: for your nieces and nephews, uncles and best friends. But
19:14
Speaker 1: we do sort of go into a lot of details
19:16
Speaker 1: because there are a lot of details about going into
19:18
Speaker 1: the black hole, and I'm not sure we can cover
19:20
Speaker 1: all of them. So please check out the book if
19:22
Speaker 1: you are actually that curious, because there are a lot
19:24
Speaker 1: of complications, like not only does the black hole take
19:27
Speaker 1: up your whole field of view, but also like it's
19:29
Speaker 1: possible for you to get inside a black hole without
19:32
Speaker 1: getting stretched into spaghetti. It sort of all depends on
19:36
Speaker 1: these details about the mass of the black hole, right,
19:39
Speaker 1: And that's right. So if you're interested that, dig into
19:41
Speaker 1: that copy of that book and let us know if
19:43
Speaker 1: you have any follow up questions. All right, So, the
19:46
Speaker 1: basic answers for Levi is you can calculate the mess
19:49
Speaker 1: with a black hole by how the things around it
19:51
Speaker 1: are moving. And also when you need to turn around
19:53
Speaker 1: when you visit a black hole, before you visit a
19:56
Speaker 1: black hole, when you need to turn around right exactly
19:59
Speaker 1: before you start arching Airbnb for black hole opportunities. Yeah,
20:03
Speaker 1: don't believe those pictures. They distort the space inside of
20:07
Speaker 1: the airbnbs. All right, let's get into our two other
20:11
Speaker 1: listener questions about black holes. One of them is about
20:13
Speaker 1: mini black holes and the other one is about dark matter.
20:17
Speaker 1: But first, let's take a quick break. All right, we're
20:32
Speaker 1: answering questions about black holes from listeners, and you get
20:37
Speaker 1: a lot of questions about black holes. I do. I
20:39
Speaker 1: have a lot of questions for about black holes. I
20:41
Speaker 1: read a lot about black holes, and we get lots
20:43
Speaker 1: of questions from the listeners about black holes because everybody
20:47
Speaker 1: wants to know what's going on. I see, And what
20:49
Speaker 1: proportion of the questions you get do you actually know
20:51
Speaker 1: the answer? We'll have a wonderful backup, which is if
20:53
Speaker 1: I don't know the answer, I just send them a
20:55
Speaker 1: link to our book we have no idea and say
20:58
Speaker 1: that's the answer. Go buy a copy of the book.
21:01
Speaker 1: Oh boy, you're plugging away today. I'm plugging away. But
21:04
Speaker 1: also I think people like to hear that the question
21:07
Speaker 1: they've asked is not one that has an answer. Of
21:09
Speaker 1: course people would like to know the answer, but it's
21:11
Speaker 1: also satisfying to feel like, Oh, I'm at the forefront
21:14
Speaker 1: of human knowledge. I have questions, just like Kip Thorne
21:18
Speaker 1: has questions, or just like very Barish has questions. These
21:20
Speaker 1: Nobel Prize winners who also don't understand what's going on
21:24
Speaker 1: inside a black hole. Welcome to the club, the curious
21:26
Speaker 1: about black holes club. All right, so our second question
21:30
Speaker 1: is from Tim and he has a question about mini
21:32
Speaker 1: black holes. Hello, Daniel, Joaii, and Katie. I've got to
21:36
Speaker 1: question about many black holes. If you were to have
21:39
Speaker 1: some super large head dron collider and create miniature black
21:43
Speaker 1: holes that immediately disappear with Hawking radiation, how would you
21:47
Speaker 1: detect that Hawking radiation? And what would you learn since
21:51
Speaker 1: all the information other than the mass of the black
21:55
Speaker 1: hole is essentially destroyed? Curious about the answer? Shoots? Alright,
22:01
Speaker 1: awesome question here. There's a lot in this question. There's
22:04
Speaker 1: the idea of MENI black holes, there's the idea of
22:07
Speaker 1: Hawking radiation. And he asked about quantum information. I know
22:11
Speaker 1: so many good questions and so many fun opportunities to
22:15
Speaker 1: learn about black holes by creating them a particle colliders.
22:18
Speaker 1: All right, so let's dig into it, Daniel, What is
22:20
Speaker 1: a medi black hole? I guess it's just a small
22:22
Speaker 1: black hole. Are there's possible? How do you make them? Yeah?
22:24
Speaker 1: Black holes can come in almost any size. There is
22:27
Speaker 1: an absolute minimum size to a black hole, but it's
22:30
Speaker 1: pretty small. You can make a black hole that's the
22:32
Speaker 1: size of the galaxy. You can make a black hole
22:35
Speaker 1: that's like, you know, the size of a particle. Almost
22:37
Speaker 1: The crucial thing is not the mass, it's the density.
22:41
Speaker 1: If you compact enough stuff into a small enough space,
22:44
Speaker 1: then you can create a black hole. Is this combination
22:47
Speaker 1: of mass and radius. You know, for example, if you
22:49
Speaker 1: took the Earth, you could compact it into a peanut
22:52
Speaker 1: and that would be a black hole. So the mass
22:54
Speaker 1: of the Earth is enough to make a black hole,
22:56
Speaker 1: is just not dense enough. And so you can make
22:58
Speaker 1: many black holes by poor enough energy or enough mass
23:01
Speaker 1: into a small enough space. And that's what you do
23:04
Speaker 1: at the large Hadron collider. Right, you think you're making
23:07
Speaker 1: mini black holes, or you know you're making mini black holes.
23:09
Speaker 1: We hope we're making many black holes. We haven't yet
23:12
Speaker 1: seen any. But that is exactly what we do at
23:14
Speaker 1: the Hadron Collider and it Aeron Collider, is that we
23:17
Speaker 1: pour a lot of energy into a very small space
23:20
Speaker 1: and we let the universe decide what comes out. We
23:22
Speaker 1: take advantage of the quantum mechanical nature, the probabilistic nature
23:26
Speaker 1: of the rules of physics that say, if you have
23:28
Speaker 1: a little ball of energy there, it can basically turn
23:31
Speaker 1: into anything. It might turn into some new particle you
23:33
Speaker 1: haven't seen before, it might turn into a black hole, right,
23:36
Speaker 1: And so you sometimes you get enough energy pack into
23:39
Speaker 1: such a small space that you make a mini tiny
23:41
Speaker 1: black hole about the size of like a particle. And
23:44
Speaker 1: so those are actually black holes, just like the ones
23:47
Speaker 1: at the center of the galaxies. They're just really really small,
23:50
Speaker 1: and something special happens to them, right. They don't last
23:52
Speaker 1: very long, that's right. And so to be clear, we
23:54
Speaker 1: have not to our knowledge made any of these black holes.
23:57
Speaker 1: We have not seen any. It's hypothetical to fear radical
24:00
Speaker 1: idea that perhaps it's possible to make these black holes
24:04
Speaker 1: by colliding particles together. And so we are looking for them,
24:06
Speaker 1: and the thing you have to understand about many black
24:08
Speaker 1: holes is that they don't last very long. Like big
24:11
Speaker 1: black holes can last for billions of years as they
24:13
Speaker 1: keep eating stuff. But all black holes emit radiation. They
24:16
Speaker 1: don't actually keep all of their information is inside. They
24:20
Speaker 1: leak a little bit of mass all the time. It's
24:22
Speaker 1: called hawking radiation. And this happens faster if you're a
24:26
Speaker 1: small black hole. So a big black hole hardly emits
24:29
Speaker 1: any hawking radiation. It can last for a long time.
24:32
Speaker 1: A little black hole will very rapidly evaporate by giving
24:35
Speaker 1: away all of its mass in terms of hawking radiation.
24:38
Speaker 1: So the smaller the black hole is, the quicker it disappears,
24:41
Speaker 1: which is actually good because you want your black holes
24:43
Speaker 1: to evaporate rather than growing and gobbling up the earth.
24:46
Speaker 1: All right, So then the tiny black holes evaporate quickly.
24:49
Speaker 1: And the question I guess is can you detect that
24:51
Speaker 1: hawking radiation? And what would you learn from it? Yes,
24:54
Speaker 1: So these black holes, if you made them, they would
24:56
Speaker 1: basically explode almost instantaneously. The kind we're talking about making
25:00
Speaker 1: it the large Hadron collider would last like ten to
25:02
Speaker 1: the minus twenty seven seconds, and they would just admit
25:05
Speaker 1: a bunch of hawking radiation. But what is that hawking radiation?
25:08
Speaker 1: And how would you see it? The cool thing about
25:10
Speaker 1: black holes is that they couple gravitationally, right, They're connected
25:13
Speaker 1: to everything that has mass. They don't care about things
25:16
Speaker 1: electric charge or strong charge or weak charge, so there's
25:19
Speaker 1: sort of democratic. They turn into like all kinds of
25:21
Speaker 1: particles with basically equal probability, And so that means that
25:25
Speaker 1: what you would see is just a huge spray of
25:27
Speaker 1: a bunch of different particles, like a huge explosion at
25:30
Speaker 1: the center of your detector, with a lot more energy
25:33
Speaker 1: than you would typically seem I see, but you're eagually
25:36
Speaker 1: like to see like an electron or a proton or
25:39
Speaker 1: men kind of right. I mean, depending on how much
25:42
Speaker 1: energy they have, they might be more probable, but there's
25:45
Speaker 1: no constraint about what particular particles you'll see, that's what
25:48
Speaker 1: you're saying. Yeah, And because the particles that feel the
25:50
Speaker 1: strong force, like quarks and gluons, have so many more varieties,
25:54
Speaker 1: because for example, for the upcork, there's the red upcork,
25:58
Speaker 1: the green upcork, and the blue upcork, where the electron
26:01
Speaker 1: doesn't feel that, and so it only has one version.
26:03
Speaker 1: That means there are more versions of quirks and gluons,
26:06
Speaker 1: So you're more likely going to get quarks and gluons
26:08
Speaker 1: than electrons and muans, just because there are more of those,
26:12
Speaker 1: and black holes are democratic, So most likely what you're
26:15
Speaker 1: gonna see is a big spray of quarks and gluons
26:17
Speaker 1: that fly out, and quirks and gluons. We don't see
26:20
Speaker 1: those directly because quirks and gluons can't be by themselves,
26:23
Speaker 1: so instead each one turns into its own stream of particles.
26:26
Speaker 1: So what does a black hole look like? In our
26:28
Speaker 1: detector at CERN It looks like seven or ten streams
26:32
Speaker 1: of particles all coming out of the center of the collision. Well,
26:34
Speaker 1: I think the question that Tim had was like, could
26:37
Speaker 1: you learn or would you learn anything from that stream
26:39
Speaker 1: of particles? And it sort of seems like you wouldn't
26:42
Speaker 1: write because it just be a random spray of particles, right, Yeah,
26:45
Speaker 1: And this is a subtle point here, because you can't
26:48
Speaker 1: look at an individual collision that has like ten of
26:50
Speaker 1: these sprays of particles and say that's a smoking gun
26:52
Speaker 1: signature of a black hole, because there are other ways
26:55
Speaker 1: for that to happen. Sometimes two protons collide and you
26:57
Speaker 1: do get ten quarks flying out, which makes ten of
27:00
Speaker 1: these streams of particles. So that does happen. So we
27:02
Speaker 1: can't specifically say this was a black hole, that was
27:05
Speaker 1: a black hole. All we can do is say, look,
27:07
Speaker 1: we see more of these collisions that lead to ten
27:09
Speaker 1: or twelve sprays of particles than we expected from non
27:13
Speaker 1: black hole sources. So we can like statistically say we
27:16
Speaker 1: think we're making black holes because we see more of
27:19
Speaker 1: these weird kind of events than we can explain otherwise.
27:22
Speaker 1: And this weird kind of event is just what we
27:24
Speaker 1: expected to see from black holes. So we can't definitively
27:27
Speaker 1: say a black hole is created on Tuesday at four pm,
27:30
Speaker 1: but we can't say over the last year, we think
27:32
Speaker 1: we made ten of them. Well, I see, you can't
27:34
Speaker 1: study like a particular mini black hole. You can study
27:37
Speaker 1: kind of like a statistically what's going on in your collider.
27:40
Speaker 1: But I think Tim was sort of making the connection
27:42
Speaker 1: to this idea that we've talked about before, which is
27:45
Speaker 1: an inside of a black hole, quantum information is destroyed.
27:49
Speaker 1: So does that mean that when a mini black hole evaporates,
27:53
Speaker 1: there's no information in the Hawking radiation. Yeah, this is
27:56
Speaker 1: not something that we understand because we think that quantum
27:58
Speaker 1: information can't be stroids, and so we wonder if somehow
28:02
Speaker 1: that hockey information does have encoded in it the quantum
28:05
Speaker 1: information that went into the black hole. And we had
28:08
Speaker 1: recently a fun podcast episode where we talked about people
28:10
Speaker 1: who recently made a breakthrough about how this might work
28:13
Speaker 1: as super fascinating, but it's not something we understand very well.
28:16
Speaker 1: But the information is being destroyed in a black hole
28:18
Speaker 1: is just about the particles that went into it, which
28:20
Speaker 1: is like the two protons you smashed together. So you
28:23
Speaker 1: don't really care that much about that quantum information. It's
28:26
Speaker 1: not like useful or interesting. But if you do make
28:28
Speaker 1: black holes, you can learn something much more interesting about
28:31
Speaker 1: the universe. You can gain like contextual information because you
28:34
Speaker 1: can learn something about quantum gravity. If we make black
28:37
Speaker 1: holes with a large Hadron collider, it means that gravity
28:40
Speaker 1: is much stronger at very short distances than it is
28:43
Speaker 1: at long distances. Something weird and different is going on
28:47
Speaker 1: when two particles get really close together, their gravity gets different,
28:50
Speaker 1: and that's a clue about maybe the whole nature of space,
28:53
Speaker 1: about how many dimensions there are two space itself. Well,
28:57
Speaker 1: what do you mean, Like you would shoot things together,
28:59
Speaker 1: create many black goals, and then you would see how
29:03
Speaker 1: it interacts with the things around it. Like, can you
29:05
Speaker 1: actually get a sense of, you know, what happens as
29:08
Speaker 1: you get that close to mini black holes or is
29:10
Speaker 1: it maybe hidden in the fact that you do or
29:12
Speaker 1: do not get mini black holes. Yeah, it's the fact
29:14
Speaker 1: that you make black holes, and also their typical energy
29:17
Speaker 1: tells you something about how they are made. You can't
29:20
Speaker 1: study an individual black hole or like put things near
29:23
Speaker 1: it or anything like that. But one thing we are
29:25
Speaker 1: really curious about is why gravity seems to be so weak.
29:28
Speaker 1: You know, gravity is so much weaker than all of
29:30
Speaker 1: the other forces. Like we say, often you can defeat
29:33
Speaker 1: the entire gravity the Earth by using a simple kitchen
29:36
Speaker 1: magnet to pull on a screw, for example. So why
29:38
Speaker 1: is gravity so weak? It's not something we understand. One
29:42
Speaker 1: possible explanation is that maybe gravity is so weak because
29:45
Speaker 1: it's leaking out. It's like getting diluted. Because there are
29:49
Speaker 1: other ways that you can move through space other than
29:52
Speaker 1: the three were familiar with. So these are called extra dimensions,
29:55
Speaker 1: Like maybe space doesn't have just three dimensions, maybe it
29:59
Speaker 1: has eleven or twenty six, but only gravity can feel those,
30:04
Speaker 1: and so when you're far away from something, you're not
30:06
Speaker 1: really feeling it's true gravity because most of it's leaked
30:09
Speaker 1: out into these other dimensions. But these other dimensions might
30:11
Speaker 1: be really really small and compact, so if you get
30:14
Speaker 1: really close to something, you might feel it's like true
30:17
Speaker 1: strength of its gravity. So the idea is if you
30:19
Speaker 1: smash two protons together and you bring them really close
30:22
Speaker 1: together with enough energy, then they might feel that strong
30:25
Speaker 1: gravity enough to make a black hole. So the fact
30:27
Speaker 1: that you made the black hole would tap you off
30:30
Speaker 1: that gravity is getting strong at short distances and maybe
30:33
Speaker 1: reveal something about the existence of those other dimensions of
30:36
Speaker 1: space and time. So you're saying that if you do
30:38
Speaker 1: make black holes at the large Harding glider, then maybe
30:41
Speaker 1: that points to the existence of extra dimensions. Yes, exactly,
30:45
Speaker 1: so we can't learn that much from one black hole,
30:47
Speaker 1: but if we can prove that we have been making them,
30:50
Speaker 1: then that suggests that there must be extra dimensions space
30:52
Speaker 1: and time, and the pattern in which they appear, like
30:55
Speaker 1: the energy that they come with and how often we
30:58
Speaker 1: make them, can give us a clue to like how
31:00
Speaker 1: many dimensions are there and what radius do they have,
31:04
Speaker 1: because these aren't dimensions like the ones we're familiar with,
31:06
Speaker 1: like x, y, and z that we move around in.
31:08
Speaker 1: These are like a little looped dimensions. They're like moving
31:11
Speaker 1: a little circle, or they are only like a centimeter wide.
31:14
Speaker 1: They're really weird and strange dimensions. But lots of theories
31:17
Speaker 1: of physics actually insist on having more dimensions, like string theory. Yeah,
31:21
Speaker 1: and conveniently that's another topic we cover in our book.
31:24
Speaker 1: But it sort of sounds like the answer for tim
31:26
Speaker 1: here is that we haven't detected any mini black holes
31:29
Speaker 1: in you're in the colliders, but if you if you
31:32
Speaker 1: do create them, hey, you would see this big shower
31:35
Speaker 1: of sort of random particles, maybe mostly quirks, and be
31:39
Speaker 1: would point to the existence of extra dimensions. That's right,
31:42
Speaker 1: that's one explanation. There are other theories that also predict
31:45
Speaker 1: the creation of black holes, and so if we did
31:48
Speaker 1: see them, the theories would go crazy coming up with
31:50
Speaker 1: new ideas to explain our data. It would be very
31:53
Speaker 1: very exciting. And for those of you nervous about the
31:55
Speaker 1: safety aspect of this, don't worry. We've done all the
31:57
Speaker 1: calculations and we're confident we can't make black hole is
32:00
Speaker 1: big enough to eat. That's good to know, always reassuring
32:05
Speaker 1: that you've done the calculations and that you never make mistakes. Right,
32:08
Speaker 1: that's right. We've never ever made a mistake that destroyed
32:10
Speaker 1: the Earth. Right, that's a pretty good track record. Yeah, yeah,
32:13
Speaker 1: so far zero for zero. All right, well, let's get
32:16
Speaker 1: into our last question about black holes from a listener,
32:19
Speaker 1: and this one has to do with dark matter. But
32:22
Speaker 1: first let's take another quick break. All right, we're answering
32:37
Speaker 1: questions from listeners about black holes because they're so cool
32:40
Speaker 1: and mysterious and dark. And our last question comes from Jue,
32:44
Speaker 1: who has a question about whether black holes can explain
32:48
Speaker 1: a little bit of missing mass. If there's missing gravity
32:51
Speaker 1: in the galaxy, why can't we attribute it too the
32:55
Speaker 1: black hole in the center of it since we don't
32:57
Speaker 1: know it's mass. M interesting question, and first of all,
33:00
Speaker 1: we're missing mass, like did we misplace some mass in
33:03
Speaker 1: the galaxy? Oops? I thought you were going to bring
33:06
Speaker 1: it home? Where is it that the galaxy going a
33:08
Speaker 1: quick diet or something? In a go keto? You look
33:11
Speaker 1: in great these days, milky Way. Maybe it's like only
33:13
Speaker 1: two percent milky way or like low fat milky way
33:16
Speaker 1: skin milky way. All right, so there is some missing
33:20
Speaker 1: mass in the galaxy, right, I know this one. It's like,
33:22
Speaker 1: if you measure how the stars in the galaxy are
33:24
Speaker 1: spinning around, they are spinning around faster than they would
33:29
Speaker 1: be if there was only stars and planets in the galaxy. Right,
33:32
Speaker 1: there's something else missing from the mass of how we
33:36
Speaker 1: see the galaxy spinning exactly, just like we were talking about.
33:39
Speaker 1: You can deduce the mass that the Sun has to
33:42
Speaker 1: be to explain the Earth's motion. You can do the
33:44
Speaker 1: same thing with the whole galaxy. Measure the motion of
33:47
Speaker 1: the stars and from that deduce the mass of all
33:50
Speaker 1: the stuff that has to be pulling on those stars
33:52
Speaker 1: to keep them moving in a circle. It's exactly the
33:55
Speaker 1: same strategy, right, And this is kind of how people
33:58
Speaker 1: first started thinking about dark matter, which is that they
34:01
Speaker 1: saw that the galaxies were spinning faster than they would
34:04
Speaker 1: be if if the stars were to stay in the galaxy,
34:08
Speaker 1: and so they hypothesized like, hey, maybe there's some invisible mass.
34:12
Speaker 1: We'll call it dark matter, and that's what's keeping all
34:14
Speaker 1: the stars in the galaxy I usually think about it
34:16
Speaker 1: the other direction. They measure the velocity of the stars,
34:19
Speaker 1: and then they asked, how much gravity do you need
34:21
Speaker 1: to explain that motion to keep the stars from flying up?
34:24
Speaker 1: And then they couldn't find that much mass. They looked
34:26
Speaker 1: at all the stars and all the dust and all
34:29
Speaker 1: the things they could see, and it just didn't add up.
34:31
Speaker 1: It wasn't even close. So that was a big puzzle
34:34
Speaker 1: for decades, right, And so the idea of a lot
34:39
Speaker 1: of invisible mass out there in the universe is kind
34:42
Speaker 1: of crazy. So a lot of people are like, are
34:43
Speaker 1: you sure that sounds crazy? How do you know that
34:46
Speaker 1: maybe the black hole at the center of the galaxy
34:49
Speaker 1: isn't just heavier than you think it is. Maybe that
34:51
Speaker 1: would explain why the stars are not flying off into space. Yeah,
34:54
Speaker 1: it's a great question because it points to like our uncertainty,
34:57
Speaker 1: like how do you know how massive those stars are?
35:00
Speaker 1: And how do you know the other things in the galaxy?
35:01
Speaker 1: How well do you know their mass? And so it's
35:03
Speaker 1: just like pointing at you know, other places we could
35:06
Speaker 1: be making mistakes, which is a great scientific exercise, like
35:09
Speaker 1: to go back and think, maybe we just missestimated the
35:11
Speaker 1: number of stars, or maybe we missestimated their mass, or
35:14
Speaker 1: maybe it's all hiding at the center of the galaxy
35:17
Speaker 1: inside that black hole. Yeah, so the question is like,
35:19
Speaker 1: could a bigger black hole at the center of the
35:22
Speaker 1: galaxy explain how all the stars are moving around the
35:26
Speaker 1: galaxy or does it have to be something like dark matter.
35:28
Speaker 1: So there's sort of three answers, two knows, and then
35:31
Speaker 1: maybe yes. So the first know is that we actually
35:35
Speaker 1: kind of do know the mass of the black hole
35:37
Speaker 1: at the center of the galaxy. It's not just some
35:39
Speaker 1: huge cosmic noob that we can turn up and down
35:42
Speaker 1: and say nobody knows, So we can just set it
35:44
Speaker 1: to anything. As we talked about just a few minutes ago.
35:47
Speaker 1: We can measure the mass of black holes by looking
35:49
Speaker 1: at the movement of stars near it. And the one
35:52
Speaker 1: near the center of our Milky Way is actually super
35:54
Speaker 1: awesome because there's a star that gets really really close
35:58
Speaker 1: to it. It whizz is right by, It ends up
35:59
Speaker 1: going super fast and allows us to make a pretty
36:02
Speaker 1: precise measurement of the mass of the black hole at
36:04
Speaker 1: the center of the Milky Way. I see, so there
36:07
Speaker 1: isn't like a mysterious black hole at the center of
36:09
Speaker 1: the galaxy. There's one that we can measure. Yeah, we've
36:12
Speaker 1: measured its mass pretty well, and there's a bunch of
36:14
Speaker 1: stars moving around it. And this is this really awesome
36:17
Speaker 1: video you should watch. It took like decades to make
36:20
Speaker 1: of them observing the black hole and seeing the motion
36:23
Speaker 1: of the stars around it, and you can watch it
36:25
Speaker 1: in time lapse. You know, it took them twenty years,
36:26
Speaker 1: but you can watch the whole thing in twenty seconds,
36:28
Speaker 1: and you can see these stars moving around some obvious,
36:32
Speaker 1: invisible object, like they're bending their path around what seems
36:35
Speaker 1: to be nothing and therefore must be something. Right, And
36:38
Speaker 1: it's pretty massive, I imagine, right, it's a pretty massive
36:41
Speaker 1: black hole at the center of our galaxy. Yeah, it's
36:43
Speaker 1: pretty heavy. It has four point one million times the
36:47
Speaker 1: mass of our star, so it's pretty hefty. And I
36:50
Speaker 1: just want to make a plug for U. C. L
36:52
Speaker 1: a that won the Nobel Prize for these observations very recently.
36:56
Speaker 1: So go check out that video. It's pretty cool, but
36:58
Speaker 1: it's a pretty massive black hole hole, but it can't
37:01
Speaker 1: explain all of the dark matter. Number one, because we
37:04
Speaker 1: know it's mass, but number two also, it's in the
37:06
Speaker 1: wrong place to explain the dark matter, right, Like, even
37:10
Speaker 1: if we didn't know the mass of the black hole
37:12
Speaker 1: at the center of the galaxy, Like, even if we
37:14
Speaker 1: were wrong, one giant mass at the center of the
37:17
Speaker 1: galaxy wouldn't explain how the all the stars are moving.
37:19
Speaker 1: That's exactly right, because even if you increase the mass
37:22
Speaker 1: of the black hole to account for all the missing stuff,
37:26
Speaker 1: it wouldn't give you stars moving the way our stars
37:29
Speaker 1: are moving. And that's because we can look at the
37:30
Speaker 1: velocity of stars very close to the center of the
37:33
Speaker 1: galaxy and the velocity stars further away from the center
37:36
Speaker 1: of the galaxy. So what we need is dark matter
37:38
Speaker 1: to explain all of those different velocities stars closer to
37:41
Speaker 1: the center and stars further from the center, and every
37:44
Speaker 1: star it's motion tells you about how much mass is
37:47
Speaker 1: sort of in a sphere that's closer to the center
37:49
Speaker 1: of the galaxy. Event it like, stars are not affected
37:52
Speaker 1: by stuff that's further away from them, only by stuff
37:55
Speaker 1: that's closer to them. So as you look at stars
37:57
Speaker 1: as a function of their distance, you know is that
38:00
Speaker 1: you need a distribution of mass that's sort of spread
38:02
Speaker 1: out to the galaxy. If you only put a huge
38:05
Speaker 1: blob of mass at the very center. It would make
38:07
Speaker 1: the stars near the core of the galaxy move way
38:10
Speaker 1: too fast, for example, right, right, because that's kind of
38:13
Speaker 1: an interesting property of mass. It's like, you know, if
38:16
Speaker 1: you're really far away from it, you might as well
38:18
Speaker 1: treat it as a like a thought. But if you're
38:21
Speaker 1: really close to it, then it does matter whether or
38:23
Speaker 1: not it's like diffused in the little tiny ball in
38:26
Speaker 1: the middle or in a giant cloud that actually there
38:28
Speaker 1: is actually sort of engulfs you. Right, Yeah, if you're
38:31
Speaker 1: inside of it, then you're only sensitive to the parts
38:34
Speaker 1: of it that are closer to the center. Just like
38:36
Speaker 1: if you drill the whole inside the Earth and jumped inside,
38:40
Speaker 1: the force of gravity on you would decrease as you
38:43
Speaker 1: are closer and closer because a lot of the stuff
38:44
Speaker 1: would now be outside of your shell. You could ignore it,
38:48
Speaker 1: and when you get to the very center, there would
38:49
Speaker 1: be no force of gravity, so you can no longer
38:52
Speaker 1: treat and the Earth is like just a point particle.
38:54
Speaker 1: Was the mass of the Earth, and so it's the
38:55
Speaker 1: same thing with the galaxy. In order to explain the
38:58
Speaker 1: velocity of stars, we have to distribute be the mass
39:00
Speaker 1: in just the right way to make these stars go
39:03
Speaker 1: fast and these starts to go a little slower. So
39:05
Speaker 1: the cool thing about this velocity measurement is that we're
39:07
Speaker 1: not only sensitive to the overall amount of missing mass,
39:10
Speaker 1: but also how it's distributed through the galaxy. Right. I
39:14
Speaker 1: like that analogy about the Earth because like, if you
39:17
Speaker 1: fall to the center of the Earth, and you're at
39:19
Speaker 1: the center of the Earth, basically the Earth is all
39:21
Speaker 1: around you and it's pulling you in every direction, so
39:23
Speaker 1: you're basically weightless right in the middle of the Earth. Yeah,
39:26
Speaker 1: there's no force of gravity at the center of the Earth. Yeah,
39:28
Speaker 1: And so the same would be with a galaxy. Like
39:31
Speaker 1: if you're at the center of the galaxy and you
39:34
Speaker 1: would feel the dark matter pulling all around you, so
39:36
Speaker 1: you wouldn't feel this mass, but if you were out
39:39
Speaker 1: in the edge of the galaxy, you would feel the
39:42
Speaker 1: mass of the dark matter like it was a point
39:45
Speaker 1: in the middle. Yeah, exactly. So imagine now a star
39:48
Speaker 1: that's very close to the center of the galaxy. If
39:50
Speaker 1: you took all the dark matter and you put it
39:52
Speaker 1: inside the black hole, that would mean that that star
39:54
Speaker 1: is feeling all of that gravity, would be moving really
39:57
Speaker 1: really fast. If instead you took that dark matter, you
40:00
Speaker 1: spread it out through the galaxy, then most of it
40:02
Speaker 1: wouldn't affect that star near the core, because, as you say,
40:05
Speaker 1: it would all be balanced out, it will all be
40:06
Speaker 1: on the outside of it. It would be null. And
40:09
Speaker 1: so you can tell how it's distributed by looking at
40:12
Speaker 1: the velocity stars that are close to the center and
40:14
Speaker 1: then a little further away. In a little further away,
40:16
Speaker 1: a distributed mass of dark matter makes a very different
40:18
Speaker 1: prediction than dark matter concentrated all at the core of
40:21
Speaker 1: the galaxy. All right, So then that's the answer of
40:24
Speaker 1: the answer is that a black hole cannot explain the
40:27
Speaker 1: missing mass in the galaxies and the trajectory of stars.
40:30
Speaker 1: You kind of need something large and diffused like how
40:34
Speaker 1: we think dark matter is. But there's also a possible
40:37
Speaker 1: yes maybe to his answer, which is that we don't
40:40
Speaker 1: think that all of the dark matter is in the
40:43
Speaker 1: black hole the center of our galaxy. But remember that
40:45
Speaker 1: we don't know what dark matter is, and there's a
40:48
Speaker 1: possibility that dark matter, though it's spread out through the galaxy,
40:51
Speaker 1: might be a bunch of smaller black holes, right like
40:54
Speaker 1: primordial black holes. Right, Yes, black holes made in the
40:58
Speaker 1: very first few moments before there was and stuff and
41:00
Speaker 1: matter in the universe. They could still be around and
41:03
Speaker 1: they could account for the dark matter. It's one of
41:06
Speaker 1: the theories that are out there. It's maybe not the
41:08
Speaker 1: most common or highly voted theory of dark matter, but
41:11
Speaker 1: it's still possible. It's still plausible, and we haven't figured
41:14
Speaker 1: out what dark matter is, so it could just be
41:16
Speaker 1: a bunch of black holes spread out through the galaxy. Wow,
41:19
Speaker 1: that sounds a little horrifying to know then, Like if
41:21
Speaker 1: you were flying through space, it's like riddled with minds
41:24
Speaker 1: kind of right. You might be flying through space and
41:26
Speaker 1: there's a hole. You've flying through a cloud of little
41:29
Speaker 1: tiny black holes. That wouldn't be good for your spaceship, right,
41:32
Speaker 1: that would not be good for your spaceship. But you know,
41:33
Speaker 1: it's eaten zero earths so far, so it must be
41:37
Speaker 1: pretty safe so far. Zero. No, We've been flying through
41:41
Speaker 1: the galaxy for billions of years, right, and we have
41:44
Speaker 1: not yet run into a black hole. On the other hand,
41:47
Speaker 1: we don't know if there are other planets out there
41:49
Speaker 1: that have fallen into primordial black holes, because they've they
41:51
Speaker 1: had we wouldn't see them, so it's not really a
41:53
Speaker 1: great argument. All right. Well, then the answer is that
41:56
Speaker 1: a black hole at the center of the galaxy wouldn't
41:58
Speaker 1: explain dark matter. But maybe dark matter is explained by little,
42:02
Speaker 1: tiny black holes everywhere. But it's great thinking one to
42:05
Speaker 1: try to come up with some other explanation for dark
42:08
Speaker 1: matter in terms of like the things we do know
42:10
Speaker 1: and our uncertainties about them. It's a great way to
42:13
Speaker 1: exercise your brain and do physics and think about different hypotheses.
42:17
Speaker 1: So great idea. Cool. So those are three awesome questions
42:20
Speaker 1: about black holes than you do think. We've on our
42:23
Speaker 1: job here to fill the black hole of questions about
42:26
Speaker 1: black holes a little bit. Yeah. The problem is that
42:28
Speaker 1: the black hole questions just grow the more you feed them.
42:31
Speaker 1: The bigger gets, the stronger it's pulled, the more we
42:33
Speaker 1: want to know. It's just kind of like science that way.
42:36
Speaker 1: The more we ask questions and get answers, the more
42:38
Speaker 1: questions we have. Yeah, and hopefully we won't get stuck
42:41
Speaker 1: in them forever. At some point we'll get out of
42:43
Speaker 1: them or maybe Inside the black Hole is a really
42:45
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42:48
Speaker 1: a cozy reading nook to enjoy it in Yeah, who
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42:54
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43:02
Speaker 1: f a q dot com. You might find a black hole,
43:04
Speaker 1: or you might find a lot of interesting knowledge that's
43:07
Speaker 1: right and funny cartoon, and so go check it out,
43:09
Speaker 1: Go be a scientist. Those of you who write in
43:11
Speaker 1: asking how can we support the podcast, this is how
43:14
Speaker 1: you can support the podcast. Please go out there and
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43:19
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43:22
Speaker 1: And more importantly, it's also those of you wondering, like
43:24
Speaker 1: how can I tell my friends or my cousin or
43:27
Speaker 1: my uncle or my mom, Like how cool all of
43:30
Speaker 1: this stuff is this book? I think it's a great
43:32
Speaker 1: way into these topics. You think it's going to convert
43:34
Speaker 1: the physics skeptics out there are an all physicists skeptics.
43:37
Speaker 1: I thought that was your thing, like that was your identifier. Yeah,
43:41
Speaker 1: but some people are skeptics about physicists, skeptic about skepticism,
43:45
Speaker 1: meta skeptics. All right, well, please go check it out
43:48
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43:51
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43:53
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43:56
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44:00
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44:02
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