Latest / Daniel and Kelly’s Extraordinary Universe / Listener Questions 60,491: Mini solar systems, greek physics and black holes!

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Listener Questions 60,491: Mini solar systems, greek physics and black holes! · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, So we're answering more listener questions today.
• 0:11
  Speaker 2: Oh, yes, we are.
• 0:13
  Speaker 1: What number is it today?
• 0:14
  Speaker 2: You know, I sort of gave up on giving them
• 0:16
  Speaker 2: numbers in order why. I figured, you know, we just
• 0:19
  Speaker 2: go on vibes rather than being limited by the traditional
• 0:22
  Speaker 2: numbering system.
• 0:24
  Speaker 1: So we're just doing random numbers now? Or are their
• 0:27
  Speaker 1: secret codes embedded in the numbers.
• 0:29
  Speaker 2: I'm not just going to give that answer away right now.
• 0:33
  Speaker 1: I see. So you were just picking numbers out of the.
• 0:35
  Speaker 2: Air, just the same way we answer questions, picking answers
• 0:38
  Speaker 2: out of the air, and sometimes it aligns with reality.
• 0:42
  Speaker 1: You're just a physicist of typing on a typewriter, one
• 0:46
  Speaker 1: of many, and then statistically, eventually one of you will
• 0:52
  Speaker 1: type out the answers to the universe. Maybe you'll be
• 0:54
  Speaker 1: the number of this episode. Hi am Joege, a cartoonist
• 1:12
  Speaker 1: and the author of Oliver's Great Big Universe.
• 1:15
  Speaker 2: Hi. I'm Daniel. I'm a particle physicist, professor at UC Irvine,
• 1:19
  Speaker 2: and I hope to one day type in the true
• 1:22
  Speaker 2: explanation for the universe.
• 1:24
  Speaker 1: Like you come up with it yourself or are you're
• 1:25
  Speaker 1: just taking notes?
• 1:28
  Speaker 2: Well, you know, Mozart said he was basically taking dictation
• 1:31
  Speaker 2: from God. So maybe I can just be a vessel
• 1:34
  Speaker 2: for the truth.
• 1:36
  Speaker 1: I say, you're born again? Is that what's going on?
• 1:41
  Speaker 2: If I could one day be the Mozart of physics,
• 1:43
  Speaker 2: I feel like that would be pretty good.
• 1:45
  Speaker 1: Maybe they'll call Mozart the White Sun of music.
• 1:52
  Speaker 2: Oh man, that's so ridiculous. I can't laugh about it.
• 1:57
  Speaker 1: I just blew your mind. But you got a dream big.
• 1:59
  Speaker 2: That's like at my university, Rice, they got tired of
• 2:02
  Speaker 2: people calling them the Harvard of the South, so they
• 2:05
  Speaker 2: printed up a bunch of shirts saying Harvard is the
• 2:07
  Speaker 2: Rice of the.
• 2:08
  Speaker 1: North aspirational t shirts.
• 2:13
  Speaker 2: Yeah. Yeah, it's a clever joke, but not really, folks.
• 2:16
  Speaker 1: So if you're the most sort of physics, would that
• 2:17
  Speaker 1: make me the Soliary of physics? Or am I the
• 2:21
  Speaker 1: Mozart of podcast hosting?
• 2:25
  Speaker 2: No, man, you're the Beethoven of cartooning.
• 2:28
  Speaker 1: There you go.
• 2:30
  Speaker 2: I think maybe we should get Bach to physics though, hmm.
• 2:34
  Speaker 1: Or maybe there's a bag of basket weaving already. But anyways,
• 2:39
  Speaker 1: welcome to our podcast, Daniel and Jorge Explain the Universe,
• 2:41
  Speaker 1: a production of iHeartRadio.
• 2:43
  Speaker 2: In which we do our best to compose a symphony
• 2:46
  Speaker 2: of understanding to bring into harmony your brain with the universe.
• 2:51
  Speaker 2: We think that everything that's out there is somehow following
• 2:54
  Speaker 2: physical laws, laws that are rational, that are mathematical. That
• 2:58
  Speaker 2: makes sense to our tiny little human brains. Our goal
• 3:02
  Speaker 2: is to bring you up to speed with a current
• 3:03
  Speaker 2: effort to write down the opera of the universe and
• 3:07
  Speaker 2: perform it for you.
• 3:08
  Speaker 1: That's right. We try to belt out the melody of
• 3:11
  Speaker 1: the loss of physics and also singing the praises of
• 3:14
  Speaker 1: the amazing scientists that are out there trying to discover
• 3:17
  Speaker 1: what is the song of the universe and in what
• 3:20
  Speaker 1: key is it in?
• 3:22
  Speaker 2: Do you think when we have the final melodic understanding
• 3:26
  Speaker 2: of the universe we'll find it beautiful and harmonious? What
• 3:30
  Speaker 2: if it's like Philip Glass, just like a bunch of
• 3:31
  Speaker 2: random notes.
• 3:32
  Speaker 1: You mean, like, are we gonna like the music of
• 3:34
  Speaker 1: the universe? Yeah? Or is it not going to be
• 3:37
  Speaker 1: of our taste?
• 3:38
  Speaker 2: Yeah? Exactly. For the same reason, I wonder why we
• 3:40
  Speaker 2: often find the earth beautiful in random landscapes. We're like,
• 3:44
  Speaker 2: oh wow, look how pretty? Why do we find it pretty?
• 3:47
  Speaker 2: Does that mean we're likely to find the explanations for
• 3:49
  Speaker 2: the universe also to be pretty or beautiful or just
• 3:52
  Speaker 2: sort of subjectively appealing.
• 3:54
  Speaker 1: M you mean to give us thumbs down? If you
• 3:56
  Speaker 1: didn't like it, you're like, oh, that's the universe. Swipe left,
• 4:00
  Speaker 1: no thanks.
• 4:01
  Speaker 3: Yeah.
• 4:01
  Speaker 2: I wonder if there are aliens out there that have
• 4:03
  Speaker 2: evolved on their planet and they're like, man, this place
• 4:05
  Speaker 2: is kind of a dump, and they would also think
• 4:07
  Speaker 2: the universe is just kind of blah, whereas it's sort
• 4:11
  Speaker 2: of human to find our surroundings beautiful, or maybe it's not.
• 4:14
  Speaker 2: Maybe that's universal.
• 4:15
  Speaker 1: Who knows, Well, don't I say that beauty and our
• 4:18
  Speaker 1: appreciation of what we find beautiful is maybe genetic, Like
• 4:21
  Speaker 1: we've evolved to like certain colors and certain landscapes just
• 4:25
  Speaker 1: because maybe it helps us survive. Maybe only the physicists
• 4:30
  Speaker 1: who find the universe beautiful are the ones who are
• 4:32
  Speaker 1: going to survive.
• 4:35
  Speaker 2: How does it help us survive to like trees and
• 4:38
  Speaker 2: hills and waterfalls and that kind of stuff?
• 4:41
  Speaker 1: Well, all of those things are signs of life, right,
• 4:44
  Speaker 1: Like it's helpful to like water and green, right, So.
• 4:49
  Speaker 2: What does it say about me that I like desert scenes?
• 4:51
  Speaker 1: It means maybe you were born in Israel.
• 4:57
  Speaker 2: Or have very dry tastes.
• 4:58
  Speaker 1: All of your ancestors they didn't like deserts. Probably, uh,
• 5:01
  Speaker 1: they didn't quite make it me.
• 5:03
  Speaker 2: Yeah, but none of my ancestors were born in the desert,
• 5:06
  Speaker 2: so that doesn't really work anyway. It's not a time
• 5:09
  Speaker 2: to dig into Daniel's evolutionary history.
• 5:11
  Speaker 1: Yeah, the whites and line is not our topic here today.
• 5:14
  Speaker 1: Our topic here today is questions. Questions that scientists ask
• 5:18
  Speaker 1: about the universe, that they ask about how things work,
• 5:21
  Speaker 1: and that trickle down to what everyday people are asking
• 5:24
  Speaker 1: about their everyday lives.
• 5:25
  Speaker 2: That's right. We are all curious about the music of
• 5:28
  Speaker 2: the universe. Is it possible to make sense of it?
• 5:30
  Speaker 2: Can we boil down everything that's out there into ideas
• 5:33
  Speaker 2: that fit into our heads? And we encourage you to
• 5:37
  Speaker 2: also ask questions about the nature of the universe. And
• 5:40
  Speaker 2: we want to hear your questions. We want to hear
• 5:43
  Speaker 2: from you when things don't make sense, when you need
• 5:45
  Speaker 2: a little bit of help sticking ideas together and explaining
• 5:49
  Speaker 2: everything that you see out there in the universe.
• 5:51
  Speaker 1: That's right. Sometimes people send us questions and sometimes we
• 5:54
  Speaker 1: answer them here on the podcast, and so to the
• 5:57
  Speaker 1: on the program, we'll be tackling listener questions. Now, Daniel,
• 6:06
  Speaker 1: you gave this one an odd number. What was the number?
• 6:08
  Speaker 2: You gave it six hundred and seventy two, four hundred
• 6:12
  Speaker 2: and ninety one.
• 6:13
  Speaker 1: And that number was that random? Or is this your
• 6:16
  Speaker 1: go to random number?
• 6:18
  Speaker 2: That's not my go to random number. Last time you
• 6:20
  Speaker 2: were making fun of me for keeping track of these
• 6:22
  Speaker 2: episodes since they'd gotten to such a large number. So
• 6:25
  Speaker 2: I decided, let's just go with vibes. And I felt like,
• 6:28
  Speaker 2: what number does this episode want to be? And that's
• 6:32
  Speaker 2: the number I typed out.
• 6:33
  Speaker 1: Interesting, so this episode talked to you even though we
• 6:36
  Speaker 1: haven't recorded it yet.
• 6:38
  Speaker 2: That's right, We had met yet recorded. But of course
• 6:40
  Speaker 2: I thought about it in advance, and I thought, what
• 6:42
  Speaker 2: number does this map to? If I had to pick
• 6:44
  Speaker 2: a number for this episode, what would it be? And
• 6:47
  Speaker 2: that's what came out. I see.
• 6:48
  Speaker 1: So it basically it means nothing.
• 6:52
  Speaker 2: It's a one dimensional representation of the high dimensional complexity
• 6:56
  Speaker 2: of the ideas in this episode.
• 6:58
  Speaker 1: So yeah, nothing, that's right, because we have no big
• 7:02
  Speaker 1: ideas here on the program, only tiny ideas.
• 7:05
  Speaker 2: Our big idea is to stimulate crazy questions and ideas
• 7:08
  Speaker 2: in your mind out there. So thanks very much to
• 7:11
  Speaker 2: everybody who sends in your questions. Still be shy, write
• 7:14
  Speaker 2: to us two questions at danieland Jorge dot com. We
• 7:17
  Speaker 2: will answer everybody's questions and we might even pick yours
• 7:20
  Speaker 2: to talk about here on the podcast.
• 7:22
  Speaker 1: Yeah, like we're doing here today. And so today we
• 7:24
  Speaker 1: have three great questions from listeners. We have a question
• 7:27
  Speaker 1: about micro's solar systems, but whether the universe really is
• 7:32
  Speaker 1: all Greek to physicists, and also a question about whether
• 7:36
  Speaker 1: a black hole could destroy our planet, so to cheerful.
• 7:40
  Speaker 2: Topics cosmic importance, I.
• 7:44
  Speaker 1: Am getting six hundred seventy two four one hundred and
• 7:47
  Speaker 1: ninety one vive here.
• 7:48
  Speaker 2: Yeah, right, just feeling it, aren't you? You're feeling it?
• 7:51
  Speaker 1: No, I was being totally totally fake there. So let's
• 7:57
  Speaker 1: jump into our first question, and it comes from Tim.
• 8:00
  Speaker 3: Hey, Daniel, curious if there is such a thing as
• 8:04
  Speaker 3: a small solar system out there somewhere, maybe a place
• 8:08
  Speaker 3: where the planets are the size of marbles or something.
• 8:13
  Speaker 3: I don't think so. I would imagine for this to happen,
• 8:16
  Speaker 3: the star would have to form, which would require a
• 8:19
  Speaker 3: lot of material. But I was just wondering if physics
• 8:22
  Speaker 3: supported us.
• 8:23
  Speaker 2: Thanks all right.
• 8:25
  Speaker 1: I think it's kind of ironic that Tim is asking
• 8:27
  Speaker 1: about tiny solar systems. You know, tiny Tim.
• 8:33
  Speaker 2: Maybe tiny Tim is an ironic nickname, and Tim is
• 8:36
  Speaker 2: like a very large dude.
• 8:38
  Speaker 1: A huge dude like you to John from Robin Hood.
• 8:43
  Speaker 2: Exactly. But I love that Tim's question is about scales
• 8:47
  Speaker 2: because I often wonder about that in the universe, like
• 8:51
  Speaker 2: why do things form in the universe at certain sizes
• 8:53
  Speaker 2: and not other sizes? What does that reveal about the
• 8:56
  Speaker 2: fundamental workings of the universe. Can you have solar systems
• 9:00
  Speaker 2: that are super duper tiny and super duper huge, or
• 9:03
  Speaker 2: is there a reason why galaxies tend to be a
• 9:05
  Speaker 2: certain size and stars tend to be a certain size
• 9:07
  Speaker 2: and planets a certain size? What does that teach us
• 9:10
  Speaker 2: about the fundamental rules of the universe and how they
• 9:12
  Speaker 2: come into balance.
• 9:14
  Speaker 1: Yeah, pretty interesting question about scales out there. And I
• 9:17
  Speaker 1: think we've tackled like the what's the largest planet? But
• 9:20
  Speaker 1: this question is interesting because it talks about, you know,
• 9:23
  Speaker 1: what is the smallest solar system you could have?
• 9:25
  Speaker 2: Yeah, And there's a couple of different angles here, like
• 9:27
  Speaker 2: can you have a miniature sun, What is the smallest
• 9:30
  Speaker 2: possible star you could form? And also how small can
• 9:34
  Speaker 2: you make a planet? So I think both of these
• 9:36
  Speaker 2: are really interesting questions.
• 9:38
  Speaker 1: Yeah, pretty cool, So maybe let's tackle them one at
• 9:40
  Speaker 1: a time. I mean, to a solar system, you need
• 9:42
  Speaker 1: a soul as a sun. So what's the smallest sun
• 9:46
  Speaker 1: that you could make or have?
• 9:48
  Speaker 2: So if you want your solar system to have a
• 9:50
  Speaker 2: sun in the middle of it, and by sun you
• 9:52
  Speaker 2: mean something that's giving off energy, that's fusing, that's creating
• 9:56
  Speaker 2: light and heavier elements at its core, then there is
• 9:59
  Speaker 2: a minimum size there because you need enough stuff for
• 10:03
  Speaker 2: gravity to have enough power to compress the core of
• 10:06
  Speaker 2: this object to be high pressure and high temperature and
• 10:09
  Speaker 2: for fusion to start. There's a reason, for example, why
• 10:12
  Speaker 2: the Sun is glowing and Jupiter is not. Even though
• 10:15
  Speaker 2: Jupiter is an enormous ball of hydrogen and other stuff
• 10:20
  Speaker 2: which could fuse, there isn't enough gravity in Jupiter to
• 10:23
  Speaker 2: kick star fusion at its core. There's not enough pressure
• 10:26
  Speaker 2: in temperature to get that going. So there is a
• 10:29
  Speaker 2: threshold there. There is a minimum size you can have
• 10:32
  Speaker 2: for a star to begin fusion to begin.
• 10:36
  Speaker 1: But could there be one that has already started, or
• 10:39
  Speaker 1: what if you kickstart one, would it just blow everything away?
• 10:42
  Speaker 2: Yeah, that's a cool question. Essentially, you're asking could you
• 10:45
  Speaker 2: ignite a star by injecting fusion into it and then
• 10:49
  Speaker 2: let it go the way you can? For example, have
• 10:51
  Speaker 2: a piece of wood sitting in front of you. It's
• 10:52
  Speaker 2: not burning, but if you heat it up, then it
• 10:55
  Speaker 2: will actually ignite and the rest of the fuel will burn.
• 10:58
  Speaker 2: That I don't think will happen with fusion, because fusion
• 11:01
  Speaker 2: needs a certain temperature and a certain pressure in order
• 11:04
  Speaker 2: to be sustained, Like, it'll just fizzle out if you
• 11:06
  Speaker 2: don't maintain those conditions.
• 11:08
  Speaker 1: You need a certain amount of density too, right.
• 11:10
  Speaker 2: Yeah, yeah, because fusion is hard to accomplish. You know,
• 11:13
  Speaker 2: protons don't like to stick together with other protons. They're
• 11:16
  Speaker 2: both positively charged. They push against each other pretty hard,
• 11:20
  Speaker 2: and so you got to really squeeze them together. You
• 11:22
  Speaker 2: got to make sure it's enough density that have nowhere
• 11:25
  Speaker 2: else to go in order for some fusion to happen.
• 11:27
  Speaker 2: And even if you do that, mostly the protons are
• 11:30
  Speaker 2: not fusing. That's why stars can burn for so long,
• 11:33
  Speaker 2: because there's comparatively little fusion happening. Most of the protons
• 11:37
  Speaker 2: in the center of the Sun are not fusing with
• 11:39
  Speaker 2: other protons. It's a tiny fraction where that's actually accomplished.
• 11:43
  Speaker 2: And that only happens when you have an object like
• 11:46
  Speaker 2: eighty times the mass of Jupiter. So you take Jupiter
• 11:50
  Speaker 2: and you add like seventy nine more jupiters, then you'd
• 11:53
  Speaker 2: have enough mass to create the conditions at the core
• 11:56
  Speaker 2: to make a star.
• 11:57
  Speaker 1: Like it will start burning on its own, for sure,
• 12:00
  Speaker 1: or do you still need something to kind of trigger it.
• 12:03
  Speaker 2: It'll start burning on its own. And that's how all
• 12:05
  Speaker 2: stars have started. You know, enough mass has coalesced together
• 12:08
  Speaker 2: to create the conditions, and then fusion is inevitable because
• 12:11
  Speaker 2: there's enough protons banging against other protons and they fuse
• 12:16
  Speaker 2: and they create energy and that sustains itself.
• 12:19
  Speaker 1: Don't you need sometimes like a supernova to go off
• 12:22
  Speaker 1: somewhere for you to start burning a star.
• 12:25
  Speaker 2: You don't need a supernova for the star to start burning.
• 12:28
  Speaker 2: You do need something to trigger the gravitation or runaway
• 12:31
  Speaker 2: effect to form the star. Like you might have a
• 12:34
  Speaker 2: huge cloud of gas and dust, you know, just like
• 12:36
  Speaker 2: a big molecular cloud. What makes it actually collapse into
• 12:40
  Speaker 2: a star is a little bit of a question. You
• 12:42
  Speaker 2: might just have like a seed of a slightly heavier
• 12:44
  Speaker 2: element from something else, or you could have a shockwave
• 12:47
  Speaker 2: from a supernova that just like triggers the collapse. That
• 12:50
  Speaker 2: collapse still takes millions and millions of years. And then
• 12:53
  Speaker 2: once the star forms, fusion starts at the core.
• 12:58
  Speaker 1: Could a supernova trigger a tiny star to start burning
• 13:01
  Speaker 1: or not? Or as you said, it just wouldn't sustain itself.
• 13:04
  Speaker 2: Yeah, it just wouldn't sustain itself because it's not hot
• 13:06
  Speaker 2: enough and there's not enough pressure. So even if you
• 13:09
  Speaker 2: like created your own fusion at the heart of a star,
• 13:12
  Speaker 2: that heat would then just dissipate and wouldn't ignite more fusion.
• 13:16
  Speaker 2: You need that temperature and that pressure, like we do
• 13:18
  Speaker 2: that here on Earth and magnetize fusion and we can
• 13:21
  Speaker 2: get a few fusion reactions to go. But unless you
• 13:23
  Speaker 2: have enough temperature and pressure and density, it doesn't ignice
• 13:27
  Speaker 2: so that it's self sustaining.
• 13:29
  Speaker 1: So then what's the smallest star we could get or
• 13:32
  Speaker 1: have in nature?
• 13:33
  Speaker 2: So in order to have our kind of fusion, like
• 13:35
  Speaker 2: the kind of fusion in our star, you need eighty
• 13:37
  Speaker 2: times the mass of.
• 13:38
  Speaker 1: Jupiter eighty times the mass. But then how big would
• 13:41
  Speaker 1: that sun be? It wouldn't be eighty times bigger than
• 13:43
  Speaker 1: Jupiter necessarily, it might be more compact.
• 13:46
  Speaker 2: Oh that's right, it wouldn't be eighty times the volume
• 13:48
  Speaker 2: of Jupiter because it'd be much more dense. But we
• 13:50
  Speaker 2: have lots of small stars in the galaxy. Of fact,
• 13:53
  Speaker 2: our star is quite heavy and quite big compared to
• 13:56
  Speaker 2: the average star, which is a red dwarf. So red
• 13:58
  Speaker 2: dwarfs go down to like ten percent of the mass
• 14:01
  Speaker 2: of the Sun.
• 14:01
  Speaker 1: I'm asking, like, how big is it? Is it bigger
• 14:03
  Speaker 1: than Jupiter? Is it smaller than Jupiter? What's the diameter
• 14:06
  Speaker 1: of this smallest sun?
• 14:09
  Speaker 2: So these things are not actually much bigger than Jupiter
• 14:12
  Speaker 2: because as you add more mass to them, they just
• 14:14
  Speaker 2: get denser and denser, in the same way that like
• 14:17
  Speaker 2: a rocky planet can't get much bigger than Earth. It
• 14:20
  Speaker 2: just gets denser and denser. There are stars out there
• 14:23
  Speaker 2: whose radius is not much bigger than Jupiter, but they
• 14:27
  Speaker 2: are burning. There are red dwarfs, and they have fusion
• 14:29
  Speaker 2: at their core, so they wouldn't be much larger than Jupiter.
• 14:32
  Speaker 2: They're just a lot more massive.
• 14:33
  Speaker 1: Interesting, so the lower limit for the size of a
• 14:36
  Speaker 1: star is about the size of Jupiter.
• 14:38
  Speaker 2: Then yeah, order magnitude Jupiter. So you couldn't have a
• 14:41
  Speaker 2: solar system the size of marbles, but you could have
• 14:44
  Speaker 2: a Jupiter sized star at the heart of a solar system.
• 14:49
  Speaker 1: But then what is a brown dwarf.
• 14:50
  Speaker 2: Yeah, so if you require the kind of fusion that
• 14:52
  Speaker 2: happens at the heart of our star, like true fusion,
• 14:56
  Speaker 2: then you need that much mass. But it is possible
• 14:58
  Speaker 2: to have a different kind into fusion happening at the
• 15:01
  Speaker 2: heart of a star, called deuterium fusion, and this happens
• 15:04
  Speaker 2: sometimes in objects we call brown dwarfs, which are just
• 15:08
  Speaker 2: like big jupiters. You have like ten times the mass
• 15:10
  Speaker 2: of Jupiter, then you can get this other kind of
• 15:13
  Speaker 2: nuclear fusion going where deuterium and protons combined to make
• 15:17
  Speaker 2: helium three and it releases a little bit of heat,
• 15:20
  Speaker 2: but it's not as hot and not as productive as
• 15:22
  Speaker 2: the kind of fusion that happens at the heart of
• 15:24
  Speaker 2: our star. So brown dwarfs are called brown because they
• 15:27
  Speaker 2: don't like glow. They don't give off photons the same
• 15:29
  Speaker 2: way that red dwarfs, and like yellow stars like our sun, dom.
• 15:34
  Speaker 1: So they're more like simmering, but they're still burning inside.
• 15:37
  Speaker 1: So what do they look like from the outside of
• 15:39
  Speaker 1: your standing next to one, like a glowy Jupiter or what.
• 15:42
  Speaker 2: There's a whole range of course of brown dwarfs from
• 15:45
  Speaker 2: low temperature to higher temperatures. Some of them do glow.
• 15:48
  Speaker 2: They don't glow as bright as the Sun, but they
• 15:50
  Speaker 2: do glow brighter than Jupiter of course, And of course
• 15:52
  Speaker 2: Jupiter gives off a lot of radiation on its own,
• 15:55
  Speaker 2: but not like a brown dwarf. So yeah, it'd be
• 15:57
  Speaker 2: sort of like intermediate between Jupiter and an actual sun.
• 16:01
  Speaker 1: And how big would those be?
• 16:02
  Speaker 2: Those are again not much bigger than Jupiter, right, because
• 16:05
  Speaker 2: as you keep adding masks, it doesn't get larger, it
• 16:08
  Speaker 2: just gets denser.
• 16:09
  Speaker 1: But it would maybe only be like ten times more
• 16:12
  Speaker 1: massive than Jupiter, in which case, like a solar system
• 16:15
  Speaker 1: with a star like that would maybe look a lot
• 16:17
  Speaker 1: like Jupiter with its moods.
• 16:18
  Speaker 2: Yeah, exactly, something like that. So definitely not marble sized,
• 16:22
  Speaker 2: but smaller than our solar system for sure.
• 16:25
  Speaker 1: And would that sun give enough light to maybe sustain
• 16:29
  Speaker 1: life or I guess it depends on what kind of life.
• 16:32
  Speaker 2: There's a lot of debate about whether you can have
• 16:35
  Speaker 2: life around a brown dwarf, whether there is a sort
• 16:38
  Speaker 2: of a habitable zone around there. I don't think we
• 16:40
  Speaker 2: know enough about brown dwarfs to say for sure.
• 16:42
  Speaker 1: M I guess it maybe depends on the size of
• 16:46
  Speaker 1: the planet, which is sort of Tim's other part of
• 16:48
  Speaker 1: the question, which is maybe what's the smallest planet you
• 16:52
  Speaker 1: could have.
• 16:53
  Speaker 2: Yeah, this is a really interesting question, and it sort
• 16:55
  Speaker 2: of comes down to the nature of like how you
• 16:57
  Speaker 2: define a planet and also like how things get right
• 17:00
  Speaker 2: because there's a lot of stuff out there in the
• 17:02
  Speaker 2: Solar System. You know, there's rocks like the Earth, but
• 17:05
  Speaker 2: there's also tiny little rocks just floating out there all
• 17:08
  Speaker 2: the way down from asteroids to meteoroids to just like
• 17:11
  Speaker 2: grains of dust, And you might ask, like, could you
• 17:14
  Speaker 2: consider all those things planets. Well, we have requirements for
• 17:18
  Speaker 2: what a planet is. Planets have to orbit the Sun,
• 17:21
  Speaker 2: not some other object, which is like why the Moon
• 17:24
  Speaker 2: is not a planet. They also have to have enough
• 17:27
  Speaker 2: gravity to make themselves round, like if you're long in
• 17:31
  Speaker 2: cigar shaped, you're not a planet. This is a way
• 17:34
  Speaker 2: to avoid calling every tiny piece of dust that's orbiting
• 17:37
  Speaker 2: the Solar system of planet. And then the last requirement
• 17:41
  Speaker 2: is that has to clear its neighborhood, has to be
• 17:43
  Speaker 2: like the dominant gravitational thing in its neighborhood. And so
• 17:47
  Speaker 2: that sort of sets an effective minimum size for a planet.
• 17:51
  Speaker 1: What would be that size? How many kilometers?
• 17:53
  Speaker 2: Yeah, it's interesting. It depends a little bit on what
• 17:55
  Speaker 2: it's made out of. Like, first of all, like why
• 17:58
  Speaker 2: does gravity make things round? Well, gravity makes things round
• 18:01
  Speaker 2: because it likes to pull stuff down. You know, imagine
• 18:04
  Speaker 2: a spherical planet, then you put a very tall mountain
• 18:06
  Speaker 2: on it. Eventually gravity is going to pull that mountain down,
• 18:09
  Speaker 2: especially if there's weathering effects on the planet that shake
• 18:12
  Speaker 2: things or tectonics, et cetera.
• 18:14
  Speaker 1: And by down you mean like the center of whatever
• 18:17
  Speaker 1: it is.
• 18:17
  Speaker 2: Right mm hmmm yeah, And so sphere is like the
• 18:20
  Speaker 2: gravitationally most stable object. If something is a perfect sphere,
• 18:23
  Speaker 2: there's nowhere for anything to fall further down. So gravity
• 18:27
  Speaker 2: likes to make things round, but it can't always do that, right,
• 18:30
  Speaker 2: Like you take a pencil, a pencil has its own gravity,
• 18:32
  Speaker 2: but not enough for gravity to make it into like
• 18:34
  Speaker 2: a round ball. Right, So the amount of stuff you
• 18:37
  Speaker 2: need in order to become round also depends a little
• 18:39
  Speaker 2: bit on your mass. So as things get bigger, they
• 18:43
  Speaker 2: have more gravity, and then gravity can overcome the internal
• 18:46
  Speaker 2: strength of an object and make it round. And so
• 18:50
  Speaker 2: there's this size called like the potato radius, around which
• 18:54
  Speaker 2: gravity starts to round things out.
• 18:57
  Speaker 1: I feel though that maybe that's a like a very
• 18:59
  Speaker 1: human set a definition of a planet, Like we just
• 19:03
  Speaker 1: want our planets to be round. But I wonder if
• 19:05
  Speaker 1: there could be, you know, some body out there is
• 19:07
  Speaker 1: some oddly shaped asteroid or giant rock that maybe has
• 19:12
  Speaker 1: evolved life, and then those aliens would call their little
• 19:15
  Speaker 1: rock a planet, right, or at least they would call
• 19:17
  Speaker 1: it home.
• 19:18
  Speaker 2: For sure. Our definition of planet is human centric. We
• 19:21
  Speaker 2: made this thing up, and you're right weak interested in
• 19:23
  Speaker 2: planets because that's the first thing we noticed. We live
• 19:26
  Speaker 2: on one. To us, it's the most important part of
• 19:28
  Speaker 2: the Solar System. In reality, the Solar System is failed
• 19:31
  Speaker 2: the huge, beautiful spectrum of different shaped objects. And this
• 19:35
  Speaker 2: is just like people drawing dotted lines around certain kinds
• 19:38
  Speaker 2: of them and then trying to defend those dotted lines
• 19:40
  Speaker 2: even though they're ridiculous and arbitrary. Yeah, you could probably
• 19:43
  Speaker 2: have life form on not around objects and then those
• 19:46
  Speaker 2: aliens might think that our distinction is arbitrary. But you know,
• 19:51
  Speaker 2: Tim is a human. He's asking questions from a human perspective.
• 19:55
  Speaker 1: Is he?
• 19:55
  Speaker 2: Now, I'm not veteretan.
• 19:58
  Speaker 1: I mean, if I'm so tiny, then maybe he's.
• 20:02
  Speaker 2: But the minimum size to make something round if you're
• 20:06
  Speaker 2: like made of ice or water is like four hundred kilometers.
• 20:10
  Speaker 2: That's when things tend to form like potato shapes. If
• 20:13
  Speaker 2: you're made of rock, it's about twice that big, and
• 20:16
  Speaker 2: so you need like eight hundred kilometer wide. Stuff tend
• 20:19
  Speaker 2: to be pretty round. So that's like the minimum size
• 20:21
  Speaker 2: for an object for gravity to make it roundish ooh.
• 20:26
  Speaker 1: Well, I feel like maybe also are your definition of
• 20:29
  Speaker 1: a sun is also the human centric because that's what
• 20:32
  Speaker 1: happens in our sun is the regular kind of fusion.
• 20:35
  Speaker 1: But aren't some stars out there at that astronomers call stars,
• 20:39
  Speaker 1: aren't they just like really hot rocks.
• 20:41
  Speaker 2: Well, there are objects out there called white dwarfs, which
• 20:44
  Speaker 2: are the remnants of stars. They're not burning anymore, there's
• 20:48
  Speaker 2: no fusion happening at their core. They're leftover bits of
• 20:52
  Speaker 2: stars that have ended their life. And those are called
• 20:55
  Speaker 2: like white dwarfs.
• 20:56
  Speaker 1: And you can see them in the night sky sometimes, right.
• 20:58
  Speaker 2: I don't know that you can see them with the
• 21:00
  Speaker 2: naked eye. We have detected a few of them, but
• 21:03
  Speaker 2: they're pretty hard because they don't glow the same way
• 21:04
  Speaker 2: that other stars do.
• 21:06
  Speaker 1: But you still call them stars though, right, because they're
• 21:08
  Speaker 1: emitting a lot of radiation.
• 21:10
  Speaker 2: They do emit a lot of radiation. I don't know
• 21:12
  Speaker 2: if astronomers would call them stars or stellar remnants, but yeah,
• 21:17
  Speaker 2: they're definitely related to stars.
• 21:19
  Speaker 1: Because I wonder if you can just have maybe like
• 21:21
  Speaker 1: a super duper hot marvel out there in space, and
• 21:25
  Speaker 1: then have really really tiny marbles orbiting around that hot marble,
• 21:28
  Speaker 1: and then maybe you can call that a solar system,
• 21:31
  Speaker 1: and maybe things have evolved in those teeny tiny marble
• 21:34
  Speaker 1: planets and they're living in their little marble existence, marveling
• 21:39
  Speaker 1: at how small they are.
• 21:42
  Speaker 2: Yeah, that's certainly possible. You could take a scoop of
• 21:45
  Speaker 2: neutron star material, right, that'd be a hot blob of stuff,
• 21:49
  Speaker 2: and you could put a few rocks in orbit around it,
• 21:53
  Speaker 2: and you could call that a solar system.
• 21:54
  Speaker 1: Sure, right, and then the thing in the middle of
• 21:56
  Speaker 1: the hot stuff in the middle would be admitting light and
• 21:58
  Speaker 1: that might sustain life in those little tiny rocks or
• 22:01
  Speaker 1: being around it.
• 22:02
  Speaker 2: Yeah. Absolutely. I don't know how long that would last
• 22:05
  Speaker 2: because you don't have that much stuff, and so it's
• 22:06
  Speaker 2: going to radiate its heat out pretty fast. I don't
• 22:09
  Speaker 2: know if there's really time for life to evolve under
• 22:11
  Speaker 2: those circumstances. But you know, if you're setting up a
• 22:14
  Speaker 2: little vivarium in space, you could put some microbes on
• 22:18
  Speaker 2: there and then you could say, hey, look, I have
• 22:19
  Speaker 2: a solar system with life on it.
• 22:20
  Speaker 1: Yeah. Yeah, it'd be like instead of sea monkeys, the space.
• 22:24
  Speaker 2: Monkeys exactly, space monkeys.
• 22:27
  Speaker 1: Well, it sounds like the answer for tim is that
• 22:29
  Speaker 1: you could have a teeny tiny marble sized solar system.
• 22:32
  Speaker 1: Like that's technically possible if you make it, but maybe
• 22:35
  Speaker 1: naturally occurring. It'd be kind of uh hard to find
• 22:39
  Speaker 1: something like that.
• 22:40
  Speaker 2: Yeah. The universe has certain scales because of the forces
• 22:44
  Speaker 2: of gravity and the strength of other materials. Gives us
• 22:48
  Speaker 2: a minimum size for stars and a minimum size for planets.
• 22:52
  Speaker 2: I think that's really interesting and it really does reveal
• 22:54
  Speaker 2: something about the balance of the various forces in our universe.
• 22:58
  Speaker 1: Yeah, because in the end, everything is limited by physics, right,
• 23:03
  Speaker 1: not our imagination.
• 23:04
  Speaker 2: I'm certainly limited by physics.
• 23:05
  Speaker 1: Yeah, all right, well, thanks Tim for that question. Let's
• 23:08
  Speaker 1: get to our next question, and this one is about
• 23:11
  Speaker 1: the Greeks and what they knew about the universe, So
• 23:15
  Speaker 1: we'll dig into that, but first let's take a quick break.
• 23:31
  Speaker 3: Right.
• 23:31
  Speaker 1: We're answering listener questions here today, and our next question
• 23:33
  Speaker 1: comes from Michael.
• 23:36
  Speaker 4: I thought about an off hand comment you made many
• 23:38
  Speaker 4: episodes ago about things we still don't understand that the
• 23:41
  Speaker 4: ancient Greeks didn't understand. So my question tonight is what
• 23:45
  Speaker 4: are the three most opique things we still don't have
• 23:47
  Speaker 4: a good answer for since the Greeks, and what is
• 23:50
  Speaker 4: our best understanding of them now? And what was the
• 23:53
  Speaker 4: most common ancient understanding of them?
• 23:56
  Speaker 2: All?
• 23:56
  Speaker 1: Right, awesome question from Michael. He's basically asking what is
• 24:01
  Speaker 1: still all Greek to us?
• 24:05
  Speaker 2: Yeah, apparently I made some comment about how there are
• 24:08
  Speaker 2: still questions we haven't answered that the Greek's puzzled about,
• 24:12
  Speaker 2: which is super awesome because it just means that some
• 24:14
  Speaker 2: of these questions are timeless. It also excites me to
• 24:17
  Speaker 2: imagine that one day we might know the answers that
• 24:20
  Speaker 2: in the future. Physicists and philosophers could look back at
• 24:23
  Speaker 2: Us and lump Us in with like Aristotle as the clueless,
• 24:27
  Speaker 2: pre knowledge kind of human before we really understood how
• 24:32
  Speaker 2: things were.
• 24:33
  Speaker 1: I see. Well, in that case, would being called the
• 24:35
  Speaker 1: Aristotle of the twenty first century be a good thing
• 24:38
  Speaker 1: or a bad thing?
• 24:39
  Speaker 2: Oh?
• 24:39
  Speaker 3: Yeah?
• 24:39
  Speaker 2: Being the Aristotle of anything would be awesome? Well that
• 24:42
  Speaker 2: is super smart? Yeah, yeah, yeah, I wouldn't mind being
• 24:45
  Speaker 2: the Aristotle of baking. I could be the Aristotle of naps.
• 24:49
  Speaker 2: That sounds wonderful.
• 24:51
  Speaker 1: You do it in a toga anyways? Right, all right, Well,
• 24:56
  Speaker 1: I guess Michael's question is kind of a little bit straightforward.
• 24:59
  Speaker 1: He saying, what did we not know back then when
• 25:02
  Speaker 1: the Greeks were hanging on and thinking about the universe
• 25:04
  Speaker 1: that we still don't know today?
• 25:06
  Speaker 2: Yeah, great question, Michael on The answer is pretty basic stuff,
• 25:10
  Speaker 2: you know, questions that like your kids might ask you. So,
• 25:14
  Speaker 2: question number one is like, how did the universe come
• 25:17
  Speaker 2: to be? Did it come to be?
• 25:19
  Speaker 3: Right?
• 25:19
  Speaker 2: Really? What is the age of the universe? What is
• 25:22
  Speaker 2: its origin? This is not something we know the answer to,
• 25:25
  Speaker 2: and definitely something the Greeks didn't understand.
• 25:29
  Speaker 1: Is there a record of the Greeks asking this question
• 25:32
  Speaker 1: or wondering about it.
• 25:33
  Speaker 2: Oh, absolutely, and a lot of Greek mythology tries to
• 25:37
  Speaker 2: explain how they thought the universe came to be. But
• 25:41
  Speaker 2: their answers were not at all scientific, you know, as
• 25:44
  Speaker 2: much as the Greeks made progress in trying to understand
• 25:46
  Speaker 2: the nature of the universe around them, the answers to
• 25:49
  Speaker 2: the question of the origin of the universe really read
• 25:52
  Speaker 2: like pure mythology. You know, they talk about gods that
• 25:55
  Speaker 2: created the air, a god named Chaos, and then another
• 26:00
  Speaker 2: that created the earth, and you know, created Mount Olympus,
• 26:04
  Speaker 2: and then battles between these gods that formed the earth
• 26:07
  Speaker 2: that they know about, and then came forth darkness, and
• 26:10
  Speaker 2: then came forth the night. The whole thing just reads
• 26:13
  Speaker 2: like pure mythology.
• 26:16
  Speaker 1: But I guess that's mythology and religion in Greek times.
• 26:19
  Speaker 1: But I wonder if everyone back then believe these things,
• 26:24
  Speaker 1: or did, maybe like Aristotle, think have other questions or
• 26:27
  Speaker 1: maybe other theories about the beginning of the universe.
• 26:30
  Speaker 2: It's certainly not possible to know for sure what all
• 26:33
  Speaker 2: the Greeks thought about these things, because remember, we have
• 26:35
  Speaker 2: a tiny fragment of all the Greek writing the Greeks
• 26:39
  Speaker 2: were very prolific, thought about lots of things, wrote about
• 26:42
  Speaker 2: a lot of things. And when we talk about our
• 26:44
  Speaker 2: knowledge of the Greeks, we talk about what has survived,
• 26:47
  Speaker 2: and that's really a tiny fraction of everything that was written.
• 26:50
  Speaker 2: And in many cases we have only like references to
• 26:53
  Speaker 2: discussions about other topics that Aristotle mentioned. I'm sure that
• 26:57
  Speaker 2: there are people thinking about the origin of the universe
• 27:00
  Speaker 2: in Greek times that we have not captured. And actually
• 27:03
  Speaker 2: we live right now at a very exciting moment because
• 27:05
  Speaker 2: we're using new technology to read ancient scroll that have
• 27:09
  Speaker 2: never been read before, ones that were burned in fire
• 27:12
  Speaker 2: and in volcanic destructions, where we have like the Charred Scroll,
• 27:16
  Speaker 2: but we never have read it before because if you
• 27:18
  Speaker 2: try to open it up, it just falls apart. And
• 27:20
  Speaker 2: now to have new scanning technology that can read the
• 27:23
  Speaker 2: scrolls without unrolling them, and so for the first time
• 27:26
  Speaker 2: we're discovering huge numbers of new Greek writings, which is
• 27:30
  Speaker 2: going to change completely our understanding of what the Greeks thought.
• 27:33
  Speaker 2: But that said, even Aristotle and these other guys, they're
• 27:37
  Speaker 2: basically philosophers, and at the time these were the cutting
• 27:40
  Speaker 2: edge ideas for how the universe came to be?
• 27:42
  Speaker 1: Right, right, Well, I wonder if he had asked Aristotle
• 27:45
  Speaker 1: so he thought the universe began? What do you think
• 27:47
  Speaker 1: he would say? Would he say zeus or would he
• 27:50
  Speaker 1: say beats me?
• 27:51
  Speaker 2: I suspect the Aristotle would say that he didn't know.
• 27:54
  Speaker 2: I mean, Aristotle and the Greeks had trouble even conceiving
• 27:58
  Speaker 2: of the cosmos. Like this question, we're asking, where did
• 28:01
  Speaker 2: the universe come from? They didn't even really understand the
• 28:04
  Speaker 2: universe the same way that we do. They mostly thought
• 28:07
  Speaker 2: about the Earth and the Solar System and a few stars.
• 28:10
  Speaker 2: They had no concept for even like how big the
• 28:13
  Speaker 2: universe was, which we'll talk about in a minute. So
• 28:16
  Speaker 2: it's sort of like asking him a question. It wouldn't
• 28:18
  Speaker 2: even understand the question.
• 28:20
  Speaker 1: Right because they just didn't know as much as we
• 28:22
  Speaker 1: do now.
• 28:23
  Speaker 2: Yeah, exactly, And yet even today we still don't have
• 28:26
  Speaker 2: an answer to this question. We have a few ideas
• 28:29
  Speaker 2: for where the universe came from. We know at least
• 28:31
  Speaker 2: how old it is, like we can date the evolution
• 28:34
  Speaker 2: of the universe back almost fourteen billion years. That's often
• 28:38
  Speaker 2: quoted as the age of the universe, but we really
• 28:41
  Speaker 2: don't know what came before that. We don't know if
• 28:43
  Speaker 2: there was a singularity and the universe was burst somehow
• 28:47
  Speaker 2: just before that, as general relativity says, or if there
• 28:49
  Speaker 2: was some other weird state that predated that early hot
• 28:53
  Speaker 2: moment that we can describe, and the universe was like
• 28:56
  Speaker 2: infinitely old before that in just some other form that's
• 28:59
  Speaker 2: now beyond our understanding and capacity to describe. So we
• 29:04
  Speaker 2: still don't have any idea really how the universe came
• 29:07
  Speaker 2: to be, how long it's been around. We do have
• 29:10
  Speaker 2: some concept for at least how old it must be,
• 29:13
  Speaker 2: so that's something. But we're still struggling to answer this
• 29:16
  Speaker 2: very basic question that the Greeks wondered about.
• 29:19
  Speaker 1: Wait, wait, are you saying that maybe the Greeks could
• 29:22
  Speaker 1: still be right? He said that maybe it's all chaos
• 29:25
  Speaker 1: before the big bank like make them correct.
• 29:29
  Speaker 2: I mean, in principle, it could all just be some
• 29:31
  Speaker 2: simulation run by external superintelligent beings and you could call
• 29:36
  Speaker 2: those the Greek gods. So yeah, I guess in that sense,
• 29:38
  Speaker 2: the Greeks could still be right.
• 29:40
  Speaker 1: All right, Well, what's another question that we know that
• 29:42
  Speaker 1: they were asking that we're still asking today.
• 29:44
  Speaker 2: Another question is how much of the universe is there? Right?
• 29:48
  Speaker 2: How big is the universe? And it's really fun to
• 29:51
  Speaker 2: dig into like what the Greeks thought about the universe,
• 29:54
  Speaker 2: because the Greeks were really careful and trying to understand
• 29:58
  Speaker 2: the nature of the Solar System, the Earth, and the
• 30:00
  Speaker 2: planets in the sun. They're very geometrical, very mathematical about
• 30:04
  Speaker 2: what they saw happening in the night sky. But then
• 30:07
  Speaker 2: it's very difficult for them to think much beyond that,
• 30:10
  Speaker 2: for them to cast their minds and understand how big
• 30:13
  Speaker 2: the universe really was.
• 30:15
  Speaker 1: Right, Well, back then, did they believe that the Earth
• 30:18
  Speaker 1: was the center of the universe and that the Sun
• 30:19
  Speaker 1: went around the Earth?
• 30:21
  Speaker 2: Yeah? Absolutely, they thought the Earth was the center of
• 30:23
  Speaker 2: the Solar system and everything went around the Earth. And
• 30:27
  Speaker 2: the reason they thought this is not because they were stupid,
• 30:30
  Speaker 2: it's actually because they had a misunderstanding of how big
• 30:33
  Speaker 2: the universe was. Like they considered the idea that maybe
• 30:38
  Speaker 2: the Earth and all the other planets went around the Sun. Absolutely,
• 30:41
  Speaker 2: and they're thinking was, well, if that's true, then we
• 30:44
  Speaker 2: should see the stars move in the sky. And they
• 30:47
  Speaker 2: were right, because as the Earth moves around the Sun,
• 30:49
  Speaker 2: we do see the stars wiggle in the sky. It's
• 30:52
  Speaker 2: called the parallax effect, like we have a different perspective
• 30:55
  Speaker 2: on the stars from one side of the Sun and
• 30:57
  Speaker 2: the other. They looked up at the stars and they
• 30:59
  Speaker 2: didn't see any whigs because they didn't yet have the
• 31:01
  Speaker 2: capacity to see the tiny wiggles of the star. The
• 31:04
  Speaker 2: parallax effect was too small for humans to detect until
• 31:07
  Speaker 2: like the eighteenth century. So they concluded from that the
• 31:10
  Speaker 2: Earth was not moving around the Sun.
• 31:12
  Speaker 1: Whoa, they actually had like data to back this up.
• 31:15
  Speaker 2: Yeah, exactly. Their mistake was they thought the stars were
• 31:19
  Speaker 2: super duper close and so the parallax should be pretty obvious. Actually,
• 31:23
  Speaker 2: the stars are much much further away than they could
• 31:25
  Speaker 2: even conceive of, and so while the parallax effect is there,
• 31:29
  Speaker 2: the stars are wiggling in the sky, they just couldn't
• 31:32
  Speaker 2: see it. So their mistake in thinking that the stars
• 31:35
  Speaker 2: were much closer than they were is actually what led
• 31:38
  Speaker 2: them to misunderstand the structure of our solar system. But
• 31:41
  Speaker 2: it was very logical and very reasonable.
• 31:43
  Speaker 1: Like just one tiny assumption, right, Like one assumption in
• 31:46
  Speaker 1: their thinking and can really throw you off.
• 31:49
  Speaker 2: Mm hm. And yet they also knew that the Earth
• 31:52
  Speaker 2: was tiny. We have evidence in their writing, like Marcus
• 31:55
  Speaker 2: Aurelius said that, quote, the whole Earth is a point
• 31:58
  Speaker 2: in space, and Aristotle described the Earth as quote no
• 32:01
  Speaker 2: great size relative to the cosmos. So they knew that
• 32:05
  Speaker 2: the Earth was a tiny dot in space. They just
• 32:08
  Speaker 2: couldn't even conceive of how big that space actually was.
• 32:13
  Speaker 1: They knew it was a dot, but actually it's like
• 32:16
  Speaker 1: a super duper tiny micro.
• 32:17
  Speaker 2: Dot exactly, It's like a dot of a dot. And
• 32:21
  Speaker 2: today we know that the universe is much vaster than
• 32:24
  Speaker 2: they could conceive of, at least ninety two billion light
• 32:27
  Speaker 2: years across, And yet we don't know if that entire
• 32:30
  Speaker 2: observable universe is just a dot in some much vaster universe,
• 32:34
  Speaker 2: potentially even infinite. So we basically have no clue as
• 32:38
  Speaker 2: to the absolute answer to this question of how big
• 32:41
  Speaker 2: is the universe?
• 32:42
  Speaker 1: No, I see so like proportionally like, if the size
• 32:46
  Speaker 1: of the possible universe is from zero to infinity, we're
• 32:49
  Speaker 1: still pretty clueless because infinity is infinity. So we have
• 32:54
  Speaker 1: no idea. Right it could be that we have as
• 32:57
  Speaker 1: much of an idea plus or minus a few percent
• 33:00
  Speaker 1: the Greeks.
• 33:01
  Speaker 2: Well, you know, in the same whether we've made progress
• 33:03
  Speaker 2: and understanding the age of the universe. We know at
• 33:05
  Speaker 2: least how old it is, and we know at least
• 33:08
  Speaker 2: how big the universe is, So we've made some measurable progress.
• 33:11
  Speaker 2: But you're right, that could be a zero percent fraction
• 33:13
  Speaker 2: of the actual size of the universe.
• 33:15
  Speaker 1: All right, great question for Michael. It sounds like we
• 33:18
  Speaker 1: still have a lot that we haven't figured out since
• 33:21
  Speaker 1: the Greeks.
• 33:22
  Speaker 2: Yeah, if we had Aristotle over for dinner, we could
• 33:24
  Speaker 2: teach him a bunch of stuff, But I think in
• 33:26
  Speaker 2: the end he would still be unsatisfied because his fundamental
• 33:30
  Speaker 2: questions have not yet been answered.
• 33:32
  Speaker 1: Well, I feel like he would just spend the whole
• 33:34
  Speaker 1: night playing with your iPhone. He'd be like, what is
• 33:36
  Speaker 1: this magic?
• 33:37
  Speaker 2: I what now? He'd probably fall for our phishing scheme
• 33:40
  Speaker 2: immediately and send all of our money to Nigeria or something.
• 33:43
  Speaker 1: He'd be watching YouTube all night. Probably.
• 33:46
  Speaker 2: It makes me wonder if I had dinner with physicists
• 33:49
  Speaker 2: from one thousand or two thousand years in the future,
• 33:51
  Speaker 2: would they have answers to these questions? Would they have
• 33:54
  Speaker 2: made measurable progress but still have no real fundamental answers.
• 33:59
  Speaker 2: That's exhilarating, but also potentially frustrating.
• 34:01
  Speaker 1: Nice, and that's why you want to freeze yourself, right,
• 34:04
  Speaker 1: Oh yeah, absolutely, let's do it just for that dinner
• 34:06
  Speaker 1: date in the future, multiple dinner date. Do you have
• 34:08
  Speaker 1: the book it now, I'm gonna leave it. I'm gonna
• 34:13
  Speaker 1: have dinner with your great great great great great great
• 34:15
  Speaker 1: great great grandkids. It's on the calendar. Yeah, don't forget.
• 34:19
  Speaker 1: I sent them a calendar invite. Absolutely, don't forget. To
• 34:22
  Speaker 1: defrost me. Please.
• 34:24
  Speaker 2: My daughter sends me calendar invites for like ten years
• 34:26
  Speaker 2: in the future or thirty years in the future.
• 34:29
  Speaker 1: Oh yeah, for like asking you for money.
• 34:32
  Speaker 2: Yeah, like buy Hazel a car.
• 34:34
  Speaker 1: Say hey, Dad, buy me a car in.
• 34:35
  Speaker 2: Five years, Yeah, exactly.
• 34:39
  Speaker 1: All right, well, thank you, Michael. Now let's get to
• 34:41
  Speaker 1: our last question, which is about whether a tiny black
• 34:45
  Speaker 1: hole could still destroy the Earth. And so let's get
• 34:48
  Speaker 1: it to that question. But first let's take another quick break.
• 35:04
  Speaker 3: Right.
• 35:04
  Speaker 1: We're answering listener questions here to the and our last
• 35:06
  Speaker 1: question is about the destruction of our planet by a
• 35:11
  Speaker 1: small black hole. The question that comes from Scott. My
• 35:14
  Speaker 1: name is Scott and from medical like Washington, and my
• 35:17
  Speaker 1: question is if a black hole were to suddenly pop
• 35:20
  Speaker 1: into existence about the size of a.
• 35:22
  Speaker 2: Pea in the middle of the Earth.
• 35:25
  Speaker 1: Would it eat the planet? And if so, about how
• 35:27
  Speaker 1: long would it take? Thank you all right? Another tiny question,
• 35:31
  Speaker 1: I feel like.
• 35:33
  Speaker 2: A cosmic question about tiny things.
• 35:35
  Speaker 1: And big destruction. Here is Scott's question is that if
• 35:40
  Speaker 1: you suddenly made a pie sized black hole appear in
• 35:44
  Speaker 1: the middle of the planet, would it eat up the
• 35:47
  Speaker 1: planet and swallow us all into this black hole? Or
• 35:50
  Speaker 1: would we survive?
• 35:51
  Speaker 2: Yeah? Great question?
• 35:53
  Speaker 1: And how long would we be alive if it ends
• 35:56
  Speaker 1: up killing us?
• 35:57
  Speaker 2: How much time do you have to pack and board
• 35:59
  Speaker 2: a ship off the planet? Right?
• 36:01
  Speaker 1: How long can you taken that before waking up to
• 36:04
  Speaker 1: meet your doom in your toga? Well, Daniel, what's he
• 36:09
  Speaker 1: asked for this question? What are some of the basics
• 36:12
  Speaker 1: of black holes? We need to know?
• 36:14
  Speaker 2: So remember that black holes are like a deformation in
• 36:17
  Speaker 2: space and time. They are a place where there's so
• 36:20
  Speaker 2: much energy concentrated in a tiny little spot that space
• 36:23
  Speaker 2: has curved so much that you formed an event horizon,
• 36:27
  Speaker 2: which means nothing can ever escape. An important thing to
• 36:30
  Speaker 2: understand is black holes can basically eat anything. You throw
• 36:33
  Speaker 2: anything into a black hole, it just adds to its energy.
• 36:37
  Speaker 2: You drop into shark, it gets more massive and it
• 36:40
  Speaker 2: gets bigger, right exactly, There's a close relationship between the
• 36:43
  Speaker 2: mass of the black hole and its radius, and so
• 36:46
  Speaker 2: as you add stuff to the black hole, it tends
• 36:48
  Speaker 2: to grow. The only exception to this is if you
• 36:50
  Speaker 2: had a black hole isolated in space, it would emit
• 36:54
  Speaker 2: hawking radiation and gradually disappear. So if you don't feed
• 36:58
  Speaker 2: a black hole, it will eventually fade out of existence.
• 37:02
  Speaker 2: But any black hole that's near stuff, it's going to
• 37:04
  Speaker 2: grab that stuff, pull it in and grow. There's no
• 37:07
  Speaker 2: way for the Earth to hang out with like a
• 37:08
  Speaker 2: black hole inside of it without that black hole eventually
• 37:11
  Speaker 2: eating the planet. So Scott's question number one is like,
• 37:14
  Speaker 2: is it going to eat the planet? And the answer
• 37:16
  Speaker 2: is yes. So do you have a black hole the
• 37:18
  Speaker 2: heart of the planet. That black hole already has a
• 37:21
  Speaker 2: lot of gravity. He's talking about a black hole the
• 37:23
  Speaker 2: size of a pea. Well, a black hole the size
• 37:26
  Speaker 2: of pea doesn't sound very large, like a pea doesn't
• 37:28
  Speaker 2: have much gravity, but to make a black hole of
• 37:31
  Speaker 2: that size would require about as much mass as the Earth.
• 37:35
  Speaker 2: So now you're talking about about as much mass of
• 37:37
  Speaker 2: the Earth concentrated down to a pee that's gonna have
• 37:40
  Speaker 2: a very strong gravitational effect. Put it anywhere inside the Earth,
• 37:44
  Speaker 2: it's going to pull that part of the Earth apart.
• 37:46
  Speaker 2: It's going to feed itself on the Earth, and then
• 37:48
  Speaker 2: it's going to grow and get more gravity, and you
• 37:50
  Speaker 2: have a very rapid runaway effect there where everything eventually
• 37:53
  Speaker 2: falls into this new black hole.
• 37:56
  Speaker 1: Right, because I guess if you PLoP it in the
• 37:58
  Speaker 1: middle of the Earth, it has material to eat right away, right, Like,
• 38:02
  Speaker 1: what would happen if you PLoP a p sized black
• 38:04
  Speaker 1: hole in the middle space with nothing around it? Would
• 38:06
  Speaker 1: it just evaporate or would it stick around for a
• 38:09
  Speaker 1: long time?
• 38:09
  Speaker 2: Yeah? Absolutely, If you don't feed a black hole, it
• 38:11
  Speaker 2: will evaporate. How long it takes to evaporate depends on
• 38:14
  Speaker 2: its size, because the Hawking radiation depends on the temperature,
• 38:17
  Speaker 2: and the temperature is connected to the size. And actually
• 38:20
  Speaker 2: bigger black holes are colder, tend to radiate more slowly,
• 38:24
  Speaker 2: So the smaller the black hole, the more the radiation.
• 38:27
  Speaker 2: So really big black holes very gently radiate and shrinks
• 38:31
  Speaker 2: very slowly. As they get smaller and smaller, they radiate faster.
• 38:34
  Speaker 2: And faster till eventually they disappear in quite a bright
• 38:38
  Speaker 2: flash of light, which would make evaporating black holes from
• 38:40
  Speaker 2: hawking radiation something we might be able to see out
• 38:43
  Speaker 2: in the night sky. We've never actually seen one before,
• 38:46
  Speaker 2: but people are looking for it. But yeah, you put
• 38:49
  Speaker 2: it in the center of the Earth, it's going to
• 38:50
  Speaker 2: gobble it.
• 38:50
  Speaker 1: Up, right, It's going to start eating the Earth, and
• 38:52
  Speaker 1: then it's going to grow. But then I wonder if
• 38:55
  Speaker 1: it would eat all of the Earth, Like I wonder
• 38:57
  Speaker 1: if at some point we'll eat the inside of the Earth,
• 39:00
  Speaker 1: but maybe it'll leave a space between it and the
• 39:03
  Speaker 1: outer shell of the Earth.
• 39:05
  Speaker 2: Yeah, it actually gets a little bit complicated. What we
• 39:07
  Speaker 2: often do in physics is just start with like the
• 39:09
  Speaker 2: simplest scenario. Imagine all the mass of the Earth is
• 39:12
  Speaker 2: just like a bunch of balls on the surface of
• 39:14
  Speaker 2: the Earth and they all fall into the black hole.
• 39:17
  Speaker 2: And you can ask, like how long does it take
• 39:19
  Speaker 2: all of that mass to fall into the black hole?
• 39:22
  Speaker 2: And so that would take about ten ish minutes for
• 39:25
  Speaker 2: all the mass of the Earth to fall into this
• 39:27
  Speaker 2: central black hole. That's like the fastest it could possibly happen,
• 39:31
  Speaker 2: you know, like around ten minutes before everything actually reaches
• 39:35
  Speaker 2: the black.
• 39:35
  Speaker 1: Hole, Like if it just goes straight in.
• 39:37
  Speaker 2: Yeah, if it just goes straight in, And that's the
• 39:39
  Speaker 2: most efficient, the fastest way.
• 39:41
  Speaker 1: And then you made this calculation, how just by like
• 39:43
  Speaker 1: measuring how long a ball on the surface of Earth
• 39:46
  Speaker 1: would take to fall into the center of a black
• 39:48
  Speaker 1: hole in the middle of Earth.
• 39:49
  Speaker 2: Yeah, essentially simple gravity for a simple object, not interacting
• 39:53
  Speaker 2: with anything else, And that's the fastest possible thing. Nothing
• 39:56
  Speaker 2: is interfering with these objects. But that ignores a lot
• 39:59
  Speaker 2: of it important physics, like the Earth is spinning, and
• 40:02
  Speaker 2: what would happen if the black hole actually did start
• 40:05
  Speaker 2: to eat the center of the Earth is black holes
• 40:07
  Speaker 2: have tremendous tidal forces, and those tidal forces would heat
• 40:11
  Speaker 2: up the stuff near the black hole. Like surrounding every
• 40:14
  Speaker 2: black hole we actually see out there in the universe
• 40:16
  Speaker 2: is an accretion disk of stuff that's swirling around it
• 40:20
  Speaker 2: and hasn't yet fallen in. So this new black hole
• 40:22
  Speaker 2: in the center of the Earth would compress and heat
• 40:25
  Speaker 2: up the stuff around the Earth, and it would create
• 40:27
  Speaker 2: a lot of radiation which would push stuff out away
• 40:30
  Speaker 2: from the black hole. So what we see in reality
• 40:33
  Speaker 2: out there in the universe is that there's a maximum
• 40:35
  Speaker 2: rate at which black holes can grow because they have
• 40:38
  Speaker 2: very strong gravity to pull stuff in, but they also
• 40:40
  Speaker 2: tend to create accretion disks, which create radiation to push
• 40:43
  Speaker 2: stuff away. So black holes cannot form super duper quickly
• 40:47
  Speaker 2: because of this effect.
• 40:49
  Speaker 1: Because if things bolt into quickly, then they tend to
• 40:51
  Speaker 1: explode as they go in, which would push the stuff
• 40:54
  Speaker 1: that's in line to fall in away exactly.
• 40:56
  Speaker 2: And stuff is also rotating right, so it doesn't fall
• 40:59
  Speaker 2: in immediately. It tends to swirl around the black hole
• 41:03
  Speaker 2: before it falls in. It gets heated up, and it
• 41:05
  Speaker 2: radiates and it pushes out on other stuff. And so
• 41:08
  Speaker 2: while the minimum time for this to happen is like
• 41:10
  Speaker 2: ten ish minutes, in reality it would probably take much
• 41:13
  Speaker 2: much longer because it would form an accretion disk, and
• 41:16
  Speaker 2: it would take a long time for that accretion disc
• 41:18
  Speaker 2: to all fall into the black hole. Eventually, it still would, but.
• 41:22
  Speaker 1: It would take much much longer, Like how much, Because
• 41:25
  Speaker 1: I think that's the question.
• 41:26
  Speaker 2: Yeah, I don't have a solid answer for that, because
• 41:27
  Speaker 2: that requires calculations that are very complicated and require like
• 41:32
  Speaker 2: really intense gravity and multibody simulations. I'd estimate thousands of
• 41:37
  Speaker 2: years or maybe even millions of years before the last
• 41:40
  Speaker 2: bits of the Earth actually do fall into this new
• 41:42
  Speaker 2: black hole, but the Earth would very rapidly be uninhabitable.
• 41:47
  Speaker 2: Like this is answering the question of when the last
• 41:50
  Speaker 2: tiny bit of earth dust falls into the black hole.
• 41:53
  Speaker 2: That might take thousands or millions of years, but still
• 41:55
  Speaker 2: you would not want to be on the surface of
• 41:58
  Speaker 2: the Earth for more than a few minutes after that
• 42:00
  Speaker 2: black hole is created, because it's going to get very
• 42:02
  Speaker 2: unpleasant very quickly.
• 42:04
  Speaker 1: Like it's going to basically break up the Earth right
• 42:06
  Speaker 1: shatter it. Yeah, exactly, they can collapse under its own
• 42:09
  Speaker 1: sort of weight.
• 42:10
  Speaker 3: Hm.
• 42:11
  Speaker 2: Ten minutes is the fastest possible time for the Earth
• 42:13
  Speaker 2: to disappear, which tells you that the timescale for effects
• 42:17
  Speaker 2: to appear on the surface of the Earth is minutes.
• 42:20
  Speaker 2: So the Earth is going to get pulled apart and
• 42:22
  Speaker 2: distorted and all sorts of craziness. That's going to happen
• 42:24
  Speaker 2: within minutes, even if the complete hoovering up all the
• 42:28
  Speaker 2: last bit of the Earth might take much longer because
• 42:30
  Speaker 2: of the feedback effect from black hole radiation.
• 42:35
  Speaker 1: So all benus you want to get on.
• 42:38
  Speaker 2: That spaceship asap. That's the answer.
• 42:41
  Speaker 1: Isn't there some science fiction story where they some aliens
• 42:44
  Speaker 1: have created a planet with a black hole in the middle,
• 42:46
  Speaker 1: like that's powering it or something.
• 42:48
  Speaker 2: I haven't read a book like that. In principle, it's
• 42:50
  Speaker 2: possible to have a stable structure around a black hole,
• 42:54
  Speaker 2: like if it's strong enough and far enough away and
• 42:57
  Speaker 2: thin enough to avoid tidal forces, then yeah, you could
• 43:00
  Speaker 2: build a big spherical structure kind of like a disin
• 43:04
  Speaker 2: sphere around a black.
• 43:05
  Speaker 1: Hole and a giant shell, right.
• 43:08
  Speaker 2: Yeah, like a giant shell. And if you pour stuff
• 43:10
  Speaker 2: into the black hole, you could use the hawking radiation
• 43:13
  Speaker 2: from the black hole as an energy source. We even
• 43:16
  Speaker 2: talked about using black holes to power a space ship,
• 43:19
  Speaker 2: have a whole episode about that. So, yeah, all these
• 43:21
  Speaker 2: things are potentially possible, but it depends a lot of
• 43:24
  Speaker 2: the details, and you don't build that kind of thing
• 43:26
  Speaker 2: by just plopping a black hole at the center of
• 43:28
  Speaker 2: an existing planet.
• 43:30
  Speaker 1: And it's also unstables that I remember about it, but
• 43:34
  Speaker 1: I guess maybe then. An extension of Scott's question is
• 43:38
  Speaker 1: what's the smallest black hole we could survive? Or is
• 43:41
  Speaker 1: it that any size black hole there is plopped in
• 43:44
  Speaker 1: the middle of the Earth would eventually swallow us up.
• 43:47
  Speaker 2: Yeah, any size black hole that's plopped in the center
• 43:50
  Speaker 2: of the Earth gets bigger, and so there is no
• 43:52
  Speaker 2: minimum size we could survive because every black hole just
• 43:55
  Speaker 2: grows to be a larger black hole.
• 43:57
  Speaker 1: But don't you talk about in the Large Hadron Collider
• 44:00
  Speaker 1: make black holes or you might be making black holes,
• 44:02
  Speaker 1: but they disappear very quickly.
• 44:04
  Speaker 2: Yeah, if you made a super tiny microscopic black hole
• 44:07
  Speaker 2: in a vacuum, like we might do with the Large
• 44:09
  Speaker 2: Hadron Collider, then it could evaporate too quickly to absorb
• 44:12
  Speaker 2: any other material. If you put it in the center
• 44:15
  Speaker 2: of the Earth, then you have no chance. Even a
• 44:17
  Speaker 2: microscopic black hole will eventually get bigger. But if you
• 44:20
  Speaker 2: make a microscopic black hole and a vacuum, it'll evaporate
• 44:23
  Speaker 2: before it's dangerous.
• 44:24
  Speaker 1: Unless you created knocks on the wall of the Large
• 44:27
  Speaker 1: pattern Collider, would that be bad news?
• 44:30
  Speaker 2: Black hole we make at the LHC will actually have
• 44:32
  Speaker 2: a lot of velocity, so it's not just going to
• 44:34
  Speaker 2: stay there inside the LEDC and actually fly off and
• 44:38
  Speaker 2: just go through the Earth or into outer space before
• 44:40
  Speaker 2: it has a chance to eat anything. They've done all
• 44:42
  Speaker 2: these calculations, and they're pretty convinced that it's not dangerous.
• 44:46
  Speaker 2: So you know, I mean, fundamentally, we do not understand
• 44:53
  Speaker 2: microscopic black holes because it requires a theory of quantum
• 44:57
  Speaker 2: gravity to predict what would happen. Because now you're talking
• 44:59
  Speaker 2: about gravity of quantum objects, which are uncertain, and so
• 45:03
  Speaker 2: it's not something we really know how to calculate. And
• 45:06
  Speaker 2: all the calculations done for like black holes with a
• 45:08
  Speaker 2: large Hadron collider, they use a semi classical approximation of
• 45:12
  Speaker 2: quantum gravity in which nobody really believes.
• 45:14
  Speaker 1: Anyway, you're not really making me feel more comfortable.
• 45:17
  Speaker 2: Here, Daniel. I wasn't the goal.
• 45:19
  Speaker 1: Your assurance is only getting worse.
• 45:22
  Speaker 2: I'm telling you we don't really understand super microscopic black
• 45:25
  Speaker 2: holes anyway.
• 45:26
  Speaker 1: I see, And so therefore we should believe you when
• 45:28
  Speaker 1: you say not to worry about it.
• 45:30
  Speaker 2: I didn't say not to worry about it. I said
• 45:31
  Speaker 2: they've done the calculations, and they tell us not to
• 45:33
  Speaker 2: worry about it.
• 45:34
  Speaker 1: Uh huh. And now you're telling us.
• 45:37
  Speaker 2: I'm saying I'm not worried about it. Oh well, in
• 45:41
  Speaker 2: that case, but remember you can always check the website.
• 45:45
  Speaker 2: Has the large Hadron collider destroyed the world yet? Dot
• 45:48
  Speaker 2: com which we always keep up to date.
• 45:50
  Speaker 1: Right, right, although there would be a delay technically right,
• 45:53
  Speaker 1: so it could be wrong for about five minutes.
• 46:00
  Speaker 2: I don't know about five minutes. I think you'd be
• 46:01
  Speaker 2: updated faster than that.
• 46:03
  Speaker 1: I hear a lot of nervous laughter here, Daniel.
• 46:05
  Speaker 2: If you're destroyed by a black hole and you have
• 46:06
  Speaker 2: complains about that website, feel free to email me.
• 46:09
  Speaker 1: Yeah, well you get it in time, though.
• 46:13
  Speaker 2: I've promised to answer all emails, and so I'm going
• 46:15
  Speaker 2: to do my best.
• 46:16
  Speaker 1: Yeah, yeah, you might have to break that promise. All right. Well,
• 46:19
  Speaker 1: I think that's the answer for sCOD, which is yes,
• 46:22
  Speaker 1: if you put a pea sized black hole, which would
• 46:24
  Speaker 1: be the equivalent of a black hole with the mass
• 46:27
  Speaker 1: of the Earth in the middle of the Earth, next
• 46:30
  Speaker 1: to all of the material inside the Earth, then yeah,
• 46:33
  Speaker 1: it would quickly grow and swallow us all up, or
• 46:36
  Speaker 1: at least destroy the Earth and then eventually swallow our
• 46:40
  Speaker 1: remnants up.
• 46:41
  Speaker 2: Don't do it, Scott, bad idea.
• 46:43
  Speaker 1: Don't do it, Scott, don't do it, Daniel.
• 46:47
  Speaker 2: We're not creating pea sized black holes.
• 46:49
  Speaker 1: Man, oh right, although you said any size is dangerous,
• 46:57
  Speaker 1: so you're not helping me sleep, not my job, all right. Well,
• 47:04
  Speaker 1: thanks to everyone who sent in their questions. We always
• 47:08
  Speaker 1: appreciate it.
• 47:08
  Speaker 2: And thanks everybody who's curious about the universe and shares
• 47:12
  Speaker 2: sarah curiosity with us. This whole podcast project is just
• 47:15
  Speaker 2: us marinating in the joy of your curiosity. Thanks very
• 47:18
  Speaker 2: much everybody.
• 47:20
  Speaker 1: You hope you enjoyed that. Thanks for joining us. See
• 47:23
  Speaker 1: you next time.
• 47:28
  Speaker 2: For more science and curiosity, come find us on social
• 47:31
  Speaker 2: media where we answer questions and post videos. We're on Twitter, Discord, Instant,
• 47:36
  Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel
• 47:39
  Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
• 47:43
  Speaker 2: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
• 47:48
  Speaker 2: or wherever you listen to your favorite shows.