Speaker 1: I'd like us to quickly explore deep into space. Can
Speaker 1: gravity slingshots help us win that race?
Speaker 2: If ancient humans killed off the giant kangaroo, why didn't
Speaker 2: we kill off the African elephant too?
Speaker 1: How much do tiny black holes like to eat? If
Speaker 1: I adopt one, will it nap at my feet?
Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's answers.
Speaker 3: Will make it right.
Speaker 1: Welcome to Daniel and Kelly's extraordinarily Curious universe.
Speaker 3: Hello, I'm Kelly Waiter Smith.
Speaker 2: I study parasites and space, and I am excited to
Speaker 2: talk about charismatic megafauna today.
Speaker 1: Hi. I'm Daniel. I'm a particle physicist, and I never
Speaker 1: wanted a willing mamoth as a pet.
Speaker 2: Oh you No, I didn't either. I don't think I
Speaker 2: want anything bigger than the goats that we have right now?
Speaker 1: What about a goat sized black hole? Or do goats
Speaker 1: basically operate as black holes because they eat everything?
Speaker 3: You know?
Speaker 2: Our goats are surprisingly picky about what they eat, which
Speaker 2: I'm winding a little frustrated because I was like, Oh,
Speaker 2: we're gonna get walking garbage disposals, but ours are like no,
Speaker 2: I don't want that.
Speaker 3: I don't want that either, So your goats are not
Speaker 3: the goat.
Speaker 2: I wouldn't say that. They are definitely the greatest of
Speaker 2: all time. And one of them is named Greatest of
Speaker 2: all Time aka Kevin for short. That's the full name
Speaker 2: that's on its certificate, because we let children name our goats.
Speaker 2: So one of them is the goat literally literally. But
Speaker 2: I had a particularly negative experience with wildlife this morning.
Speaker 2: I just walking up the hill accidentally smacked a wasp
Speaker 2: of some sort and my thumb is expanding. Oh and
Speaker 2: we'll see how big it is by the end of
Speaker 2: the episode. But I wanted to focus on more positive interactions.
Speaker 2: Since we're gonna be talking like Africa's charismatic wildlife, I
Speaker 2: wanted to know what is the most like awe inspiring
Speaker 2: experience you've had with an animal in nature?
Speaker 3: Because you and Katrina hike, you're like outdoor people.
Speaker 1: I think one of the most incredible experiences I've had
Speaker 1: was seeing a mountain lion close up. Who I grew
Speaker 1: up in the mountains of northern New Mexico, and there
Speaker 1: were mountain lions because they were mountains, and you know,
Speaker 1: sometimes you'd get up in the morning and you'd see
Speaker 1: their pop rinks in the snow. But one time I
Speaker 1: actually did spot one, and it's incredible how much they
Speaker 1: are like housecats, you know, in their smoothness and their
Speaker 1: their feline charisma, but also how terrifyingly huge they are,
Speaker 1: because I've often wondered, like, what would my housecat do
Speaker 1: if it weighed a thousand pounds? And now I know
Speaker 1: the answer is it would eat me.
Speaker 2: I mean, most of the time, mountain lions don't go
Speaker 2: after people. I want to clear the mountain lion's name,
Speaker 2: and if anybody wants to read more about that, they
Speaker 2: should check out more ark Elbrock's book on mountain lions.
Speaker 2: But yeah, so that is beautiful. So like, did you
Speaker 2: see it at a distance where like how far away
Speaker 2: was it?
Speaker 1: It was like maybe eighty feet or something. My parents'
Speaker 1: backyard was right up against National Forest and so there
Speaker 1: was just like a lot of trees and canyons back there,
Speaker 1: and I saw one walking through the trees and I
Speaker 1: saw it and it saw me, and we like shared
Speaker 1: a little moment, and I was like, I'm on a
Speaker 1: tiptoe back inside. You can have the whole outdoors.
Speaker 2: It's all yours now, buddy, and I assumed that he did.
Speaker 2: It did not approach you or anything like that.
Speaker 1: No, no, it did not, and I'm very happy that
Speaker 1: it went on its way. But it reminds me of
Speaker 1: this incredible story I heard about European lions. You know,
Speaker 1: the lions used to roam Europe also, but they were
Speaker 1: killed off many, many years ago. And the story I
Speaker 1: heard is that for a long time there was a
Speaker 1: question about European lions. Do they have mains like African
Speaker 1: lions or not like North American lions. And we answered
Speaker 1: this question through cave drawings. People found drawings of lions
Speaker 1: from tens of thousands of years ago from Paleolithic artists,
Speaker 1: and it's basically like a lab book and they don't
Speaker 1: have mains, and you can see like hunting pears even
Speaker 1: And so that's incredible to me that, like humans, tens
Speaker 1: of thousands of years ago answered our current science question.
Speaker 2: Okay, so that is amazing, but how does the absence
Speaker 2: of seeing mains like so, you know, in Africa, when
Speaker 2: you get groups that are hunting, it's usually groups of
Speaker 2: females that are hunting. The females do most of the hunting,
Speaker 2: So how do you know that, you know, the worthless
Speaker 2: males just were weren't drawn on the insides of the caves.
Speaker 1: Yeah, great question. I shouldn't have said hunting pair. I
Speaker 1: think they had some reason to believe this is like
Speaker 1: a family unit. But it sort of connects us over
Speaker 1: space and time to you know, early humans who are
Speaker 1: also awed by the majesty of megafauna.
Speaker 3: Yes, absolutely, very cool.
Speaker 2: And when I asked you that question, I assumed you
Speaker 2: we're going to pick megafauna because almost almost everyone picks,
Speaker 2: you know, some large mammal, the largest mammal they've ever seen,
Speaker 2: is usually the answer to that question.
Speaker 1: Oh, I see, You've asked other people this question, and
Speaker 1: nobody has said the time I saw a rat in
Speaker 1: my kitchen.
Speaker 3: Well, of course not No, no one has said that.
Speaker 2: But I think my moment was I was in the
Speaker 2: woods and I was helping a friend with the snake survey,
Speaker 2: and a bunch of wood frogs had recently like metamorphosed
Speaker 2: from tadpoles into like adults, but they were are you know,
Speaker 2: into the landstage.
Speaker 3: But they were really tiny.
Speaker 2: And there were literally hundreds of them, and I noticed
Speaker 2: them because I like moved my foot forward and all
Speaker 2: of these tiny things hopped out of the way.
Speaker 1: Oh my god.
Speaker 2: And I realized, like, oh my gosh, I'm surrounded by
Speaker 2: like hundreds of little froglets, these little tiny frogs, and
Speaker 2: I just sat down and like the sun was coming
Speaker 2: through the trees and just the right way that it
Speaker 2: kind of had like a magical feeling. And every time
Speaker 2: I'd sort of move my hand, all of these little
Speaker 2: froglets would like hop around, and it was just like,
Speaker 2: I don't know, it was magic. It was like being
Speaker 2: in some sort of a fairy book or something. And
Speaker 2: I think for me that was that was my moment.
Speaker 1: Well, I have a moment I recall from being in
Speaker 1: your neck of the woods. Oh, it was more of
Speaker 1: a horror story than a magical moment. Katrina and I
Speaker 1: were hiking and backpacking, I think it was in the
Speaker 1: Blue Ridge Mountains, and we set up our camp and
Speaker 1: we had a nice campfire, and at the end of
Speaker 1: the evening we were ready to go back to our tent,
Speaker 1: and it was only then that we noticed that the
Speaker 1: ground just outside the extent of the fire was covered
Speaker 1: in daddy long legs. There were like millions and millions
Speaker 1: of them, and they were crawling all over our tent
Speaker 1: and everywhere. It was incredible. We were so grateful that
Speaker 1: we had zipped our tent closed, so we like sprained
Speaker 1: it back to the tent open it, jumped in closed it,
Speaker 1: and was just like terrified of the carpet of Daddy
Speaker 1: long legs that were outside. I was like, wow, Virginia's crazy.
Speaker 3: But they can't hurt you.
Speaker 1: They can't hurt you. But I'm still not gonna like
Speaker 1: lie down and have Daddy long legs crawl all over me.
Speaker 2: All right, Well I don't I feel like I'm not
Speaker 2: really feeling.
Speaker 1: All right, Zach, you are free to release Daddy long
Speaker 1: legs all over Kelly was she's asleep. Sure, sure, Wow, amazing.
Speaker 1: You don't have the same reaction to spiders as other
Speaker 1: people do.
Speaker 2: Huh, Well, Daddy long legs aren't really spiders.
Speaker 1: Oh my gosh. Wow, and that scientific knowledge puts you
Speaker 1: at ease, it does.
Speaker 2: Let me make sure that's right. Our Daddy long legs spiders.
Speaker 2: I think there are racknids. Oh maybe they do still
Speaker 2: count as spiders. Yeah, all right, so sorry, I guess
Speaker 2: they are still Teddy long legs are still see.
Speaker 1: I told you they were creepy like that makes a.
Speaker 2: Difference, all right, So sorry, you were right, daddy, long
Speaker 2: legs looks like they are spiders. But I do feel
Speaker 2: like knowledge makes a huge difference. So we've got these
Speaker 2: they're called rabid wolf spiders, bad name, right, and they're
Speaker 2: like big and they do look kind of scary. And
Speaker 2: when I first moved here, I freaked out because my
Speaker 2: son likes to roll around in the grass and these
Speaker 2: are like grass spiders that are in the grass, and
Speaker 2: so he'd roll around in it. I always see like
Speaker 2: a big spider running away and it really freaked me out.
Speaker 2: But I read about them, and now I'm not scared
Speaker 2: of them, like they're they're not gonna go after my son.
Speaker 3: It's fine.
Speaker 2: I do feel like knowledge makes a big difference in
Speaker 2: my fear outside in general.
Speaker 1: You're totally right, and of course, knowledge is our business.
Speaker 1: We're here to help everybody understand the universe better and
Speaker 1: be less afraid of it, or maybe appropriately afraid of it.
Speaker 1: So let's get into it, because today we're not here
Speaker 1: just to talk about my experiences with spiders and Kelly's
Speaker 1: magical moment with the frogs. We're here to talk about
Speaker 1: your questions about the universe, things you wonder about, places
Speaker 1: where you wish you had more knowledge. So we regularly
Speaker 1: ask our listeners to send in their questions, and we'd
Speaker 1: love to hear from you. Please write to us to
Speaker 1: questions at Danielankelly dot org. We always write back to everybody,
Speaker 1: and sometimes we pick questions to answer here on the
Speaker 1: pod because we think a lot of people might be
Speaker 1: interested in the answer, or because I think it'd be
Speaker 1: fun to joke about it with Kelly.
Speaker 2: Or because when I get the EMO from you, I
Speaker 2: don't know the answer and I need to stall for
Speaker 2: Time's you go.
Speaker 3: That's the other reason.
Speaker 1: So, speaking of stalling for time, here's our first question,
Speaker 1: which is about how to quickly explore the outer Solar
Speaker 1: System using gravity's help.
Speaker 4: Hi, Daniel and Kelly. I was thinking about how we
Speaker 4: use gravitational slingshots permissions such as Voyager, Cassini and New
Speaker 4: Horizons as we venture further into the Solar System. Would
Speaker 4: we use this method for human credmissions and what forces
Speaker 4: would the crew feel if they were slingshotted to their destination? Thanks?
Speaker 1: All right, and that question was from Rob Pixley. Rob,
Speaker 1: thank you very much for writing in. Kelly, you're an
Speaker 1: expert on space and exploration. What do you think about this?
Speaker 2: Well, I believe that gravitational slingshots are when you use
Speaker 2: massive objects to gain some speed. But I'm going to
Speaker 2: wait for you to give some more information. But when
Speaker 2: I read this, it reminded me of Jules Verne's and
Speaker 2: I can never say his name right.
Speaker 3: Thank you, because he's French. Okay, all right, that guy,
Speaker 3: That French guy.
Speaker 2: He wrote a book From the Earth to the Moon,
Speaker 2: and it was about a Baltimore gun club who decided
Speaker 2: they were going to build a giant gun and shoot
Speaker 2: people to the moon. And it works. But the problem is, actually,
Speaker 2: if you were to calculate how many gs the crew
Speaker 2: would have felt, they would have been probably like liquefied
Speaker 2: in chapter twenty on the Way to the Moon. They
Speaker 2: wouldn't have made it. So let's hear about gravitational slingshots.
Speaker 2: Would this kill humans or nothing?
Speaker 1: Gravitational slingshots are super awesome. They are a way to
Speaker 1: boost your speed and change your direction without using any fuel.
Speaker 1: You know, one of the big issues for getting around
Speaker 1: the Solar System or getting around the universe is that
Speaker 1: fuel is heavy and if you use fuel to propel yourself.
Speaker 1: You need fuel to help you push that fuel, and
Speaker 1: then you need more fuel to help you push that fuel,
Speaker 1: and pretty soon you have a gas tank the size
Speaker 1: of Jupiter just to get anywhere. So it's very nice
Speaker 1: if you can navigate the universe without using fuel, because
Speaker 1: then you don't have the additional mass and then need
Speaker 1: to propel that all that stuff. So for decades, NASA
Speaker 1: and other folks have been using this technique called a
Speaker 1: gravitational slingshot, which essentially steals a little bit of speed
Speaker 1: from a planet or a moon. The way it works
Speaker 1: is you can approach a big planet and it's gravity
Speaker 1: you will change your direction. So for example, say you're
Speaker 1: just coasting, you have no rockets on, and you're approaching Jupiter,
Speaker 1: and you swing around the back of Jupiter and come
Speaker 1: out the other side. Now you're going in a new direction. Right.
Speaker 1: That's not something you can otherwise accomplish, usually without burning
Speaker 1: some fuel, without thrusters, because a change in direction, even
Speaker 1: if your overall magnitude is the same, is still an acceleration.
Speaker 1: To change your direction in space, you've got to have
Speaker 1: some acceleration. Somebody's got to pull on you. So basically
Speaker 1: you use the gravity of the planet to pull on
Speaker 1: you and you can even come out the other side,
Speaker 1: not just with a change in direction, but with a
Speaker 1: net increase in speed. And that's why it's called a
Speaker 1: gravitational slingshot.
Speaker 2: Well, I don't think we've ever used this on a
Speaker 2: vehicle carrying humans, because the only option would be the
Speaker 2: trip to the Moon. But have we used this for
Speaker 2: our rovers or anything or probes.
Speaker 1: We've used it for lots of probes, absolutely, because a
Speaker 1: lot of times we don't have the fuel to get
Speaker 1: them all the way out to the outer Solar System,
Speaker 1: and we want to keep them light and it saves fuel.
Speaker 1: And then also you get to add like another planet
Speaker 1: on your trip. You're like, hey, I want to go
Speaker 1: to Saturn, but I'd like to swing by Mars on
Speaker 1: the way, Or I'd like to go to Neptune. Can
Speaker 1: we stop by Jupiter? And then you also get to
Speaker 1: take pictures of Jupiter because you know, none of these
Speaker 1: things are so well explored that like one more trip
Speaker 1: is boring, you know. Yeah, so that's like a bonus
Speaker 1: for these things. And I think the physics of it
Speaker 1: is really fascinating because it's a little bit counterintuitive, like
Speaker 1: it feels like free energy, Like where is this speed
Speaker 1: coming from? And the answer to that question is that
Speaker 1: you're really taking that speed from the planet. Like if
Speaker 1: you swing by Jupiter, it changes your direction, it accelerates you,
Speaker 1: and it effectively slows down. It slows down in its
Speaker 1: orbit around the Sun. So, for example, if you take
Speaker 1: a normal space probe and you swing it around Jupiter
Speaker 1: and it gets sped up in the process, Jupiter slows down,
Speaker 1: but just by a tiny little bit because the mass
Speaker 1: of Jupiter is so huge compared to the mass of
Speaker 1: the probe that it loses I did this calculation one
Speaker 1: times ten to the negative twenty five kilometers per second
Speaker 1: of its flow, so basically negligible. However, if you scale
Speaker 1: this up and you did like, you know, ten to
Speaker 1: the twenty five space probes, because you want to explore
Speaker 1: the whole galaxy, you might start having an impact on Jupiter.
Speaker 1: But basically, think about Jupiter as a huge battery of
Speaker 1: momentum and you're tapping into that a little bit and
Speaker 1: adding it to your space probes.
Speaker 2: So if an aggressive alien civilization wanted to screw up
Speaker 2: our solar system, could they just send probes by Jupiter
Speaker 2: enough times to get it to sort of move around
Speaker 2: and rek havoc on the rest of Us.
Speaker 1: I guess they could. But you know, if they were
Speaker 1: capable of doing that, they should just like nudge an
Speaker 1: asteroid towards Earth. I mean, I'm not giving advice to
Speaker 1: malevolent aliens. Okay, sounds like I am, so you please
Speaker 1: if you are malevolent aliens, don't do this, or anybody
Speaker 1: shouldn't do this. But yeah, the most dangerous thing you
Speaker 1: could do in the Solar system is nudge a comet,
Speaker 1: for example, because comments by the time they get to
Speaker 1: the inner Solar System are going really really fast because
Speaker 1: they fall from so far away, and they're really are
Speaker 1: to see in advance because their periods are so long.
Speaker 1: So yeah, nudging a comet would be the most dangerous thing.
Speaker 1: I guess the most subtle thing would be tweaking Jupiter.
Speaker 1: That would be a cool basis for a science fiction novel.
Speaker 1: Get on it, Daniel, And for those of you who
Speaker 1: still trying to like Grock, how this works? You know?
Speaker 1: Another analogy is like think about a moving train and
Speaker 1: you have a tennis ball. If you throw your tennis
Speaker 1: ball against the front of the train. Then the train's
Speaker 1: velocity gets added to the tennis ball's velocity when it
Speaker 1: bounces off, right, So now it comes back, it's going
Speaker 1: not just the same velocity as it was when it
Speaker 1: hit the train. Like if you bounce the tennis ball
Speaker 1: against a wall, it comes back with the same speed.
Speaker 1: If you bounce a tennis ball against a train rushing
Speaker 1: at you, it comes back much much faster. It slows
Speaker 1: down the train a tiny little bit, nobody's ever going
Speaker 1: to notice, but it speeds up the tennis ball. And
Speaker 1: so it's this huge mass ratio that makes this possible.
Speaker 2: All right, So how fast does this speed up happen?
Speaker 2: And is it going to be fast enough that you're
Speaker 2: going to liquefy the humans inside?
Speaker 1: Right? So two really interesting questions, and that's really what
Speaker 1: Rob was asking about. So number one, this isn't a
Speaker 1: great idea for human missions, but not because of the
Speaker 1: g forces, but because usually it involves going pretty far
Speaker 1: out of your way. Like you're sending a probe to Pluto.
Speaker 1: You know it's going to take forever to get there.
Speaker 1: If you can make it lighter by stopping by Saturn
Speaker 1: on the way, you don't really care if it's going
Speaker 1: to slow you down by five years, because it can
Speaker 1: slow you down by five years, so it's a more
Speaker 1: economical way to get this speed, But often it requires
Speaker 1: going really far out of your way, and if you're
Speaker 1: doing space missions, the goal is to get there fast,
Speaker 1: to spend less time in space, less time exposed to
Speaker 1: low gravity, less time exposed to radiation, all this kind
Speaker 1: of stuff. Now, sometimes it can work if the Solar
Speaker 1: system is just right. You know, if you want to
Speaker 1: get to Saturn and Jupiter happens to be in just
Speaker 1: the right place, then maybe a flyby of Jupiter can
Speaker 1: help you get to Saturn faster. But usually you just
Speaker 1: want to go directly there, and so you want chemical
Speaker 1: rockets or ion thrusters or fusion power or something. So
Speaker 1: this is good for long missions where you don't really
Speaker 1: care how long it takes, which is not what we're
Speaker 1: going for here.
Speaker 2: Okay, so it would take longer, but I mean, if
Speaker 2: you're doing like a generation ship on an interstellar journey,
Speaker 2: you know you're not gonna be alive when you get
Speaker 2: to the final destination anyway, so why not add an
Speaker 2: extra five years to your trip to speed it up
Speaker 2: For the next few generations. So let's assume we decide
Speaker 2: we're going to do this anyway, or are you going
Speaker 2: to get killed by the speed.
Speaker 1: Well, before we answer that, there's another wrinkle, which is
Speaker 1: you're right if you're like aiming for Alpha Centauri and
Speaker 1: you want to be redirected and you don't want to
Speaker 1: spend all that fuel. This is not a terrible idea,
Speaker 1: but it's going to be more effective the closer you
Speaker 1: get to the planet, right, because then the more powerful
Speaker 1: the gravity. However, the closer you get to Jupiter, the
Speaker 1: more you have to word about the radiation of Jupiter, right,
Speaker 1: So there's really a trade off there. But here's the
Speaker 1: thing about the G forces. There aren't any You don't
Speaker 1: feel any of these G forces. That's right, because gravity
Speaker 1: is not a force. You feel g forces when you're
Speaker 1: being accelerated. So for example, if you're on a roller
Speaker 1: coaster and you reach the bottom of the roller coaster
Speaker 1: and you start going up, you feel those G forces.
Speaker 1: Or if you're in a car and you're turning really fast,
Speaker 1: you feel those G forces. Or if you're in a
Speaker 1: rocket and somebody burns the rocket really fast to get
Speaker 1: you going off the planet, you feel those G forces.
Speaker 1: When you are falling just under gravity, you feel no
Speaker 1: G forces. So for example, you jump out of an airplane,
Speaker 1: you don't feel any G forces. Right, you're in freefall.
Speaker 1: You only feel G forces when there's acceleration, and you
Speaker 1: only feel acceleration when you're fighting gravity. If you just
Speaker 1: chill with gravity, man, and go with the flow of
Speaker 1: the universe, you feel no G forces.
Speaker 2: Okay, well, so what if what if you're on this
Speaker 2: interstellar ship. You want to get the Jupiter speed up,
Speaker 2: and the folks who major interstellarship planned ahead for the
Speaker 2: problem that low gravity is bad for human bodies. And
Speaker 2: now you are spinning, so you have artificial gravity in
Speaker 2: your habitat to help with things like reproduction. Now where
Speaker 2: you feel on the G forces with the artificial gravity.
Speaker 1: You feel the artificial gravity absolutely, because that's not gravity, right,
Speaker 1: that's the force from the structure of the ship holding
Speaker 1: itself together. The same with like on the surface of
Speaker 1: the Earth, you feel what we call gravity, but it's
Speaker 1: really the Earth pushing you up against the natural inclination.
Speaker 1: You have to fall towards the center of the curvature.
Speaker 1: So yes, you feel the G forces from the spinning
Speaker 1: that's real because it's not gravity. But falling into Jupiter's
Speaker 1: gravitational field doesn't change that at all.
Speaker 5: Yeah.
Speaker 2: Okay, so sorry, So I knew that you would feel
Speaker 2: the artificial gravity, But what I meant is when you're
Speaker 2: feeling artificial gravity and then you accelerate, Yeah, do you
Speaker 2: feel that acceleration more strongly when you're under artificial gravity
Speaker 2: relative to No?
Speaker 3: Okay, no, no, you're doing cool.
Speaker 1: Yeah, so that's sort of awesome because you know, you
Speaker 1: don't feel gravity at all, even though it's having an
Speaker 1: impact on you, even though you are accelerating, you're changing
Speaker 1: your vector from the point of view of somebody distant. Right.
Speaker 1: This is the thing about gr is that it's very confusing.
Speaker 1: It depends on who who watching from your point of view,
Speaker 1: you never feel acceleration due to gravity. Somebody else looking
Speaker 1: from far away, who doesn't see the curvature. They're like, well,
Speaker 1: according to my coordinates, your velocity is changing and therefore
Speaker 1: you're having acceleration. And that's cool. Gr Lets everybody have
Speaker 1: their own calculation. But what do you feel is what's important. Right,
Speaker 1: You're not going to be torn apart, your stomach's not
Speaker 1: going to be shredded. Your organs are not going to
Speaker 1: be squished. Feel free to dive closed to Jupiter in
Speaker 1: your arcship on your way to Alpha Centauri. You have
Speaker 1: to worry about the radiation, but you don't have to
Speaker 1: worry about the g forces.
Speaker 2: And because I have a pod in physics, I know
Speaker 2: that GR stands for general relativity.
Speaker 1: Yes, absolutely, joh relativity one of the most fascinating, beautiful
Speaker 1: and I think widely misunderstood theories, mostly because of that
Speaker 1: dang rubber sheet bowling ball analogy out there which confuses everybody.
Speaker 2: Yeah, but we're here to clear up misconceptions, all right,
Speaker 2: So let's find out if Rob wants to use a
Speaker 2: gravitational slingshot for his journey to interest that I've decided
Speaker 2: he's going on.
Speaker 4: Hi, Daniel and Kelly, your explanations normally make sense, but
Speaker 4: offered a great way to look at the scenario from
Speaker 4: multiple interesting, different perspectives. Thanks again.
Speaker 1: Okay, we're back and we're answering questions from listeners today.
Speaker 1: And the next question is about major animals.
Speaker 2: Major animals, Well, I've never heard them referred to as
Speaker 2: major before majorly awesome, So I have never been to Spain,
Speaker 2: how would you pronounce this name, Daniel?
Speaker 3: Do you know Adamar?
Speaker 1: I've never heard this name before, but it looks to
Speaker 1: me like Adamar.
Speaker 2: Yeah, all right, anyway, fantastic name, and so adam ar
Speaker 2: from Spain.
Speaker 3: Let's hear your question.
Speaker 6: Hello, Danny and Kelly. My name is Adema and I'm
Speaker 6: asking this question from Spain. I recently learned that elephant
Speaker 6: seemed to identify different human languages and react differently depending
Speaker 6: on what they hear, thus being able to know if
Speaker 6: a group of humans poses a threat to them based
Speaker 6: on a language they speak Differently, Rainos seem to adopt
Speaker 6: a more increasive behavior whenever the spots kincas. Some suggesting
Speaker 6: that this could be a consequence of biological adaptation as
Speaker 6: they evolve in contact with humans for many, many times,
Speaker 6: in fact, since the beginning of the Haminites. What is
Speaker 6: most intriguing is that this could be the reason why
Speaker 6: great animals don't exist in any continent other than Africa.
Speaker 6: As our arrival, there was much mosch suven and they
Speaker 6: didn't have time to bolf an adapt to us before
Speaker 6: we hunted them down to extinction. May Kelly give us
Speaker 6: a dieper insight in this matter? Thank you for having me,
Speaker 6: and congratulations for providing us with such an awesome podcast.
Speaker 2: All right, So my opinion on the matter is pretty
Speaker 2: much that Adamar was right right on the money. So
Speaker 2: we're just going to go ahead and talk about the
Speaker 2: science here because it's a really fascinating story and Adamore
Speaker 2: seems to have a good handle on it. But I'm
Speaker 2: just gonna go ahead and reiterate how cool all this
Speaker 2: stuff is.
Speaker 1: Yeah, Kelly, tell us the history. How much more awesome
Speaker 1: was the Earth ten or fifty thousand years ago.
Speaker 3: Before humans came along?
Speaker 2: All right, So there were a lot more large mammals
Speaker 2: on the planet, and by large we mean greater than
Speaker 2: forty four kilograms.
Speaker 1: Why forty four not forty five, not forty Who decided?
Speaker 1: Was there some meeting the forty four kilogram threshold?
Speaker 2: I don't know who decided on the forty four kilogram threshold.
Speaker 2: No doubt it was arbitrary. No, somebody must have looked
Speaker 2: at an animal and been like, you're too small.
Speaker 3: How much do you weigh? You are now our threshold?
Speaker 1: Oh, I didn't hurt that poor animal's feelings.
Speaker 3: Well, we'll get it.
Speaker 2: I mean, the good news if you're below the threshold.
Speaker 2: It sounds like you were maybe less susceptible to extinction
Speaker 2: caused by humans, So maybe you'd be happy if you
Speaker 2: were under this arbitrary threshold.
Speaker 1: So tell us about these megafauna that used to roam
Speaker 1: the earth.
Speaker 2: Okay, So this large megafauna includes things like you mentioned
Speaker 2: at the beginning of the show, like lions that used
Speaker 2: to be found much farther north. There were also giant
Speaker 2: ground sloths. There were kangaroos that were much larger, and
Speaker 2: there were mammoths. There were just lots of much larger
Speaker 2: mammals that were roaming the earth. And somewhere between ten
Speaker 2: to fifty thousand years ago, about two hundred of these
Speaker 2: large mammal species went extinct.
Speaker 1: Wow.
Speaker 2: And this is called the quarternary megafauna extinction QM.
Speaker 1: And is there a bigger trend here that like animals
Speaker 1: get bigger and bigger, because like dinosaurs got really huge
Speaker 1: and then you know, the biggest ones died out, and
Speaker 1: then mammals come along and then they eventually got big.
Speaker 1: Is this some sort of evolutionary trend that like, eventually
Speaker 1: somebody finds the niche of like being too big to eat?
Speaker 2: I mean, I'm sure a lot of things go into
Speaker 2: optimal size for animals. Being big does make you too
Speaker 2: big to eat, but you know, like so t rex
Speaker 2: was a big predator, and you know, blue whales are
Speaker 2: also big predators, but they're going after kraill, So it's
Speaker 2: not they don't have to be big so that they
Speaker 2: can be vicious and take downloaded animals. They're eating teeny
Speaker 2: tiny little creatures called kraill, little crustaceans in the ocean,
Speaker 2: and so, yeah, I'm sure a lot of things go
Speaker 2: into being big, but it is a niche that sometimes
Speaker 2: makes sense to fill. Yeah, about ten to fifty thousand
Speaker 2: years ago, we lost a bunch of these species. And
Speaker 2: the question is why, and you know, probably because it's biology,
Speaker 2: the answer is it depends.
Speaker 3: There's probably a lot of different factors.
Speaker 2: It could have been that climate was changing at the
Speaker 2: time as well, but there's pretty good evidence to suggest
Speaker 2: that one of the major causes of this decline in
Speaker 2: large mammals was the fact that humans were starting to
Speaker 2: move into.
Speaker 3: New areas, so lunch basically lunch. Yes, that's right.
Speaker 2: So, for example, about fourteen of the sixteen large mammal
Speaker 2: species that were present in Australia went extinct between about
Speaker 2: thirty and fifty thousand years ago, and humans showed up
Speaker 2: about forty to sixty thousand years ago, So the numbers
Speaker 2: don't match up exactly, but some evidence that humans show
Speaker 2: up and those species go extinct. In North America, humans
Speaker 2: arrived around like twelve to twenty thousand years ago, and
Speaker 2: eighty three percent of the large mammals in North America,
Speaker 2: which was thirty four out of forty seven species, went
Speaker 2: extinct somewhere between eleven to fifteen thousand years ago. So
Speaker 2: we show up, eighty three percent of the large mammals disappear.
Speaker 1: And I guess it's easy to draw the doged line
Speaker 1: to say, like, well, humans probably killed them, or humans
Speaker 1: maybe ate them or whatever. But it could also be
Speaker 1: more complex, right, Humans arriving could change the ecosystem, and
Speaker 1: these megafauna could be sensitive to like the web underneath
Speaker 1: them that are changing. Maybe humans are eating something else
Speaker 1: the megafauna were eating or something. It could just be
Speaker 1: more complicated.
Speaker 2: Right absolutely, Or maybe we brought some disease that jumped
Speaker 2: from us to them, or we brought some other domesticated
Speaker 2: animals along that killed them in some way, so yeah,
Speaker 2: there's a lot of complicated It's not just necessarily that
Speaker 2: we like ran after them with spears and we ate them, but.
Speaker 1: We probably did a little of that too.
Speaker 3: Yeah, no, I'm not sure.
Speaker 2: There's some fossil evidence that we did some of that too. Yeah,
Speaker 2: we needed to eat. But anyway, there is this correlational
Speaker 2: evidence that when humans show up on a new continent
Speaker 2: not that long after, a large percent of their large
Speaker 2: mammals go extinct.
Speaker 1: And I guess another thing we should consider is there
Speaker 1: could be like confounding factors also, like something which caused
Speaker 1: humans to move there and could also cause the extinction,
Speaker 1: but which wouldn't put the blame on humanity really at all.
Speaker 3: Yeah, that's right.
Speaker 2: So if there were, for example, large climactic changes that
Speaker 2: made some areas bad for humans, and they were migrating
Speaker 2: in search of new food sources or something, right, it
Speaker 2: could be that humans came at the same time as
Speaker 2: the climate change. There have been people who have looked
Speaker 2: into this, and I think that they conclude that humans
Speaker 2: still probably played a role even after you control for
Speaker 2: some other stuff that we know was happening at that time,
Speaker 2: but it probably wasn't just humans, but it looks like mammals.
Speaker 3: Large mammals in.
Speaker 2: Particular were susceptible to death around this time, not just
Speaker 2: because we were hunting them or whatever it was about
Speaker 2: humans that caused them to die, but in particular, large
Speaker 2: mammals tend to have They live a long time, but
Speaker 2: it takes a long time for them to start making babies,
Speaker 2: and when they do make babies, they don't make a
Speaker 2: lot of them. You may remember our conversation about k
Speaker 2: selected species that we had with Katie Golden. So large
Speaker 2: mammals tend to not have a lot of babies to
Speaker 2: begin with, so it's a little bit easier to kill
Speaker 2: them off because they can't sort of bounce back as quickly.
Speaker 1: Fascinating, and so the question really is like, why didn't
Speaker 1: the same thing happen in Africa. It seems like Africa
Speaker 1: has more megafauna than the other continents. Why is that?
Speaker 3: Yeah, that is a great question.
Speaker 2: So during the same period, only ten of the forty
Speaker 2: eight large mammal species in Africa went extinct, and in
Speaker 2: Eurasia they lost nine of twenty six species, so that's
Speaker 2: a much lower percent. The current hypothesis is that humans
Speaker 2: evolved in these areas.
Speaker 3: So as our species.
Speaker 2: Was picking up the skills for hunting and stuff like that,
Speaker 2: we were evolving alongside of these species. So as we
Speaker 2: got better, we didn't get like great at this overnight,
Speaker 2: but as we got better, selection was sort of favoring
Speaker 2: traits in, for example, elephants, to help them stay essentially
Speaker 2: stay away from humans and keep themselves alive in the
Speaker 2: face of this sort of growing super predator which we
Speaker 2: would end up becoming. And so the idea here is
Speaker 2: that Africa and Eurasia, those animals evolved with us, and
Speaker 2: so they were just better able to escape us. But
Speaker 2: then when we went to somewhere new like Australia and
Speaker 2: North America, and these animals had never seen anything like us,
Speaker 2: all of a sudden we show up with our spears
Speaker 2: and they are just no match for the super predators
Speaker 2: who just landed on their continent.
Speaker 1: Wow. Fascinating. So it's actually good luck to evolve together
Speaker 1: with humans, right, rather than just have them show up
Speaker 1: at your doorstep.
Speaker 2: You want humans to be bugging you for thousands of years,
Speaker 2: not just showing up unannounced. When we show up unannounced,
Speaker 2: we are particularly problematic guests.
Speaker 1: And what about this other idea that Adam r raises
Speaker 1: about how elephants can like understand human language and guess
Speaker 1: our intentions. Is there anything to that.
Speaker 2: I don't think Adam Or in particular was trying to
Speaker 2: say that elephants can understand language. They sent a paper
Speaker 2: from twenty fourteen by macomb at All in proceedings of
Speaker 2: the National Academy of Sciences, and essentially what they did
Speaker 2: here was they tried to figure out if elephants, just
Speaker 2: from hearing an audio clip would respond in a way
Speaker 2: that suggested that they knew that different kinds of people
Speaker 2: differed in the risk that they posed to the elephants.
Speaker 1: Wow.
Speaker 3: Yeah.
Speaker 2: For example, the Massi people are pastoralists, so their grazing
Speaker 2: land and water holes are often areas that are also
Speaker 2: used by elephants and are used by the livestock that
Speaker 2: the Massi are sort of walking around the area, and
Speaker 2: so they often come in conflict and sometimes the elephants
Speaker 2: will kill Massi and the Massai need to essentially defend themselves.
Speaker 2: On the other hand, the Kamba people are more agricultural
Speaker 2: and they rarely have run ins with elephants, and when
Speaker 2: they do have run ins, it's usually like a male
Speaker 2: elephant who has sort of invaded their field, and so
Speaker 2: the Kamba people are often leaving alone females and the
Speaker 2: groups of females with their babies. And additionally, human females,
Speaker 2: whether the Massi or Kamba, are unlikely to kill elephants,
Speaker 2: and young boys are also unlikely to kill elephants. The
Speaker 2: people who are most likely to kill elephants are adult men.
Speaker 2: So they did this playback experiment where they had everybody
Speaker 2: read the same sentence, and the sentence was look over there,
Speaker 2: a group of elephants is coming, and they said it
Speaker 2: in their own language, and then they look to see
Speaker 2: what the elephants did. And when you played a Massi
Speaker 2: man saying that sentence, the elephants would bunch together in
Speaker 2: a defensive like huddle, and they would respond in a
Speaker 2: way that suggested that they were experiencing fear because a
Speaker 2: predator was around.
Speaker 1: Wow.
Speaker 2: Yeah, and they did less of that when they heard
Speaker 2: the Kamba people. And remember, these are people that often
Speaker 2: don't end up in positions where they need to defend
Speaker 2: themselves in their livelihoods against elephants. The elephants also responded
Speaker 2: more strongly to the sound of men than women, and
Speaker 2: more strongly to the sound of men massi relative to
Speaker 2: boy massi. So the elephants, you seem to have a
Speaker 2: pretty good sense that, like, humans are risky, but some
Speaker 2: kinds of humans are more risky than others, and so
Speaker 2: they seem to have this like nuanced ability to tell
Speaker 2: human risk and respond accordingly.
Speaker 1: I told you the elephants are listening. They got those
Speaker 1: big ears, and they can tell when you're talking about them.
Speaker 2: That's right, that's right, and they never forget and so
Speaker 2: so you got to be extra careful. But it's worth
Speaker 2: noting that many animals respond to humans as though we
Speaker 2: are risky. And that's even in North America. In Europe,
Speaker 2: they've done playback experiments with badgers that freak out if
Speaker 2: you play sounds at water holes. In Africa, just about
Speaker 2: every species that hears the sound of a human, they'll
Speaker 2: respond more strongly to the sound of a human than
Speaker 2: the sound of a lion.
Speaker 1: Wow.
Speaker 2: So in general, just about any continent you go to,
Speaker 2: the animals know humans often mean trouble. We should we
Speaker 2: should leave town or get defensive. We're going to cause
Speaker 2: some trouble. So this is sort of an unrelated topic
Speaker 2: than the extinction of animals. This is more like what
Speaker 2: are animals doing in this day and age to respond
Speaker 2: to humans? And maybe elephants were doing this back in
Speaker 2: the past and that's what saved them from getting killed
Speaker 2: by us. They just kind of gave us space. But
Speaker 2: in general, humans can be devastating to wildlife.
Speaker 1: Well, let's say some nice things about humans to balance
Speaker 1: it out. You know, I think it's incredible that we
Speaker 1: can unravel these stories. Recently, Hazel made this comment. She
Speaker 1: was like, all sciences basically stuff happened and we figured
Speaker 1: out why. And I was like, you know, that's a
Speaker 1: pretty good point, Hazel. And it touches on this incredible
Speaker 1: thing that we do in science, which is like gather
Speaker 1: these clues that are just like randomly accidentally left imprinted
Speaker 1: on the world to figure out what happened, right, to
Speaker 1: unravel this incredible story you're telling over tens of thousands
Speaker 1: of years about these huge animals that no longer exist
Speaker 1: and why and a complicated interplay between species. It's incredible
Speaker 1: to me that we can unravel these stories, that we
Speaker 1: can pull them out, sometimes literally out of the ground,
Speaker 1: to learn the deep history of our universe.
Speaker 2: Yeah, and you are always a more optimistic and uplifting
Speaker 2: person than I am.
Speaker 3: And so that that's beautiful.
Speaker 2: And I'll attempt to follow in your footsteps by noting
Speaker 2: that by understanding the damage we've done in the past,
Speaker 2: you know, we can try to ameliorate the damage that
Speaker 2: we might be doing now or the damage we might
Speaker 2: be doing in the future. And so, you know, the
Speaker 2: conservation movement has grown in you know, the last couple decades,
Speaker 2: and we're getting better at caring about this stuff and
Speaker 2: trying to at least slow the decline of some of
Speaker 2: these species and in other cases turn around the decline
Speaker 2: of species. So you know, if we can recognize our
Speaker 2: past mistakes, we can hopefully use that information to do
Speaker 2: better in the future.
Speaker 1: Well, can I say something controversial? Do you think that
Speaker 1: an individual species on its own has like inherent value?
Speaker 1: Like should we be conserving every species or should we
Speaker 1: take a bigger, broader view and say, Look, diversity is
Speaker 1: important and that means that new species should be evolving
Speaker 1: and sometimes species disappear, it's just part of the process.
Speaker 1: Should we be trying to hold onto every individual species
Speaker 1: or should we be maintaining diversity sort of in a
Speaker 1: larger sense?
Speaker 3: Wow, all right, So that question deserves like a whole episode.
Speaker 2: But the short answer is, so there's a background extinction rate,
Speaker 2: So you shouldn't necessarily lose sleep if a species goes extinct,
Speaker 2: because that was going to happen whether humans were here
Speaker 2: or not. But I believe the extinction rate is something
Speaker 2: like it's at least ten times higher than we would
Speaker 2: expect it to be based on background levels, So we
Speaker 2: are really speeding things up for any particular species. I mean,
Speaker 2: there are some species that play less important roles in ecosystems,
Speaker 2: losing them would have less of an impact, but that's
Speaker 2: still like a unique product of millions of years of
Speaker 2: evolution that is beautiful and well adapted to its environment
Speaker 2: and is being wiped out, you know, because of us,
Speaker 2: And that to me does feel catastrophic and really sad.
Speaker 2: And you know, I feel like you have to be
Speaker 2: able to accept nuance in these conversations and weigh pros
Speaker 2: and cons and stuff like that, but you know, I
Speaker 2: do feel like time we lose a species, it is sad,
Speaker 2: even if it's just a beetle that was present in
Speaker 2: only one place.
Speaker 1: Or something, well, it is an incredible output of evolution,
Speaker 1: you know, it's like effectively billions of years of biological computation,
Speaker 1: you know, to design this creator that can do something
Speaker 1: amazing or has incredible chemicals in it. Anyway, stay tuned,
Speaker 1: everybody for the upcoming episode where Daniel argues that extinction
Speaker 1: is good. Actually, what.
Speaker 2: Like all the extinction or just like I mean, this
Speaker 2: might be the last episode of Extraordinary Universe.
Speaker 1: All right, well we'll dig into that for another episode.
Speaker 1: In the meantime, let's hear from Adamar about whether Kelly
Speaker 1: answered their question.
Speaker 6: Hello, young guys, and thank you for your response. It
Speaker 6: makes me glad to think that possibly we're not the
Speaker 6: only reason that those animals one extinct, And Kelly's context
Speaker 6: really makes me think in a why that spectrum, like,
Speaker 6: for example, what if it was the disease, what if
Speaker 6: it was a glaciation the same we were running away from,
Speaker 6: or maybe it wasn't other super predator anyway, who knows?
Speaker 6: Thank you and keep up the Wool's work. All right.
Speaker 2: I'm still trying to decide if I can forgive Daniel
Speaker 2: for hinting that extinction caused by humans isn't always bad.
Speaker 2: But you know what, I'm going to distract myself with
Speaker 2: this insightful question from a listener.
Speaker 5: Hey, Daniel and Kelly, really enjoying the podcast. Thank you.
Speaker 5: I have a question for you, and it's about black holes.
Speaker 5: Of course, black holes are usually described as unslakable consumers
Speaker 5: of all matter and energy, but I know in some
Speaker 5: cases the rate of consumption is limited by the energy
Speaker 5: pressure of that consumption process, pushing back on the gravitation
Speaker 5: pull and starving it of additional fuel. I would love
Speaker 5: to hear more about what this might be like on
Speaker 5: a more human scale, with a tiny primordial black hole
Speaker 5: around the Earth generate a tiny accretion disc of matter
Speaker 5: spinning around a light speed, generating the same kind of pressure,
Speaker 5: and shooting out X ray lasers from the top and bottom.
Speaker 5: How big or small would a black hole be to
Speaker 5: have these sorts of effects. When we think of a
Speaker 5: black hole interactive with normal human scale matter, what would
Speaker 5: that look like? How long could the Earth survive with
Speaker 5: a little black hole orbiting around inside of it? Really
Speaker 5: looking forward to hearing more about this. Thank you.
Speaker 1: Thank you David very much for that question. And I
Speaker 1: hope that our answer is not going to help you
Speaker 1: build a miniature black hole to embed into the Earth.
Speaker 1: So We're just going to take it on good faith
Speaker 1: and answer your question anyway.
Speaker 3: That also sounds like a good topic for a sci
Speaker 3: fi novel.
Speaker 1: Let's talk about black holes and start with the basics,
Speaker 1: because David's question involves a lot of sort of sophisticated
Speaker 1: black hole science. Remember, black holes are regions of space
Speaker 1: time where there's so much mass that there's so much
Speaker 1: curvature that anything that falls beyond the event and eventually
Speaker 1: reaches the center it can never escape. And something I
Speaker 1: think a lot of people don't understand about black holes
Speaker 1: is that the event horizon is not a physical surface.
Speaker 1: It's just a designation. We make a dotted line, we draw,
Speaker 1: and actually you never know where the event horizon is
Speaker 1: at any moment. You can only tell in the infinite future. Essentially,
Speaker 1: think about going to the infinite future and then asking
Speaker 1: the question, in what regions of space did particles never escape?
Speaker 1: Will now draw that to be the event horizon, and
Speaker 1: so you can't ever really actually know. You can use
Speaker 1: gr to predict at any moment, but the event horizon
Speaker 1: is just like a categorization. We say, beyond this point,
Speaker 1: nothing has escaped or can escape, and outside that point,
Speaker 1: things can escape. But this is just gravity, right. Black
Speaker 1: holes don't like suck with infinite power or anything. If
Speaker 1: you replace the Sun with the black hole of the
Speaker 1: same mass, we would feel it's gravity and the Earth
Speaker 1: would continue to orbit. So it really is just a
Speaker 1: gravitational object.
Speaker 2: Okay, So at black hole the same size as our
Speaker 2: Sun wouldn't pull on us anymore than our Sun because
Speaker 2: they're similarly dense.
Speaker 1: If it has the same mass and it's at the
Speaker 1: same distance, it would have the same gravity.
Speaker 3: Okay, yeah, right, I'm with you.
Speaker 1: It wouldn't be as bright, and the Earth would be chilly,
Speaker 1: and it would be bad, but not gravitationally, all right.
Speaker 3: I don't want that to happen.
Speaker 2: Does the event horizon always stay at the exact same
Speaker 2: spot or does it shift over time if the black
Speaker 2: hole like absorbs big things that make it bigger.
Speaker 1: Absolutely, the event horizon depends on the mass of the
Speaker 1: black hole and not just on the stuff inside the
Speaker 1: event horizon. Right. This is why you shouldn't think about
Speaker 1: the event horizon as some physical barrier. As you approach
Speaker 1: a black hole, your gravitational energy contributes to the mass
Speaker 1: of the black hole, So the black hole's vent horizon
Speaker 1: actually grows out to meet you as you fall into
Speaker 1: the black hole. So you approach the event horizon, the
Speaker 1: event horizon approaches you. It's like a little gravitational hug. Oh.
Speaker 6: Yeah.
Speaker 2: We talked about what would happen if Zach was in
Speaker 2: a black hole and if we threw him sandwiches, would
Speaker 2: they ever get to it?
Speaker 1: Exactly? And the reason you need to understand that black
Speaker 1: holes are not infinitely powerful is to think about the
Speaker 1: stuff that's orbiting them, because that's what David's question was about.
Speaker 1: This accretion disc. When you think about the images of
Speaker 1: black holes out there in space, they look like a
Speaker 1: glowing donut with a black core, or you know the
Speaker 1: visualization in Interstellar or whatever. They have these luminous discs
Speaker 1: around them. What is that and why aren't they getting
Speaker 1: sucked in? Well, they're not getting sucked into the black
Speaker 1: hole for the same reason the Earth is not getting
Speaker 1: sucked into the Sun. Right, there's a lot of gravity
Speaker 1: from the Sun. Why aren't we just getting sucked into
Speaker 1: the Sun? And the answer is we have velocity. There
Speaker 1: are stable orbits around the Sun, and the same way
Speaker 1: there are stable orbits around a black hole. Because it's
Speaker 1: just a gravitational object. So if you approach a black hole,
Speaker 1: as long as you were outside the event horizon, you
Speaker 1: could orbit around it forever without falling in if you
Speaker 1: were stable and crucially nothing bumped into you to knock
Speaker 1: you out of your orbit.
Speaker 3: That doesn't sound fun, I'll pass.
Speaker 1: And that's the same story for the Earth right now.
Speaker 1: The accretion disc is very different because it's not just
Speaker 1: like one chunk of matter here when chunk of matter there,
Speaker 1: it's just like a huge hot disk of gas and
Speaker 1: dust that has a lot of internal friction. That's why
Speaker 1: it's glowing. The tidal forces from the black hole are
Speaker 1: massaging it and heating it up, and it's rubbing against
Speaker 1: itself and so it's very hot and it's glowing. So
Speaker 1: that's why we can see these black holes. These telescope
Speaker 1: pictures of black holes. Really they're pictures of the hot
Speaker 1: accretion disc around the black hole. So the accretion disc
Speaker 1: is stuff that's orbiting the black hole, hasn't fallen in yet,
Speaker 1: is going too fast, probably will fall in eventually because
Speaker 1: there's a lot of friction there. So you can't just
Speaker 1: like have a stable orbit. But it's sort of like
Speaker 1: on deck to go in the black hole, but not
Speaker 1: there yet.
Speaker 2: And what is that made out of? Is that just
Speaker 2: like the basic dust and junk that you find in space, it's.
Speaker 1: Made out of whatever you've been feeding your black hole.
Speaker 1: But yeah, the universe is mostly hydrogen, so it's always
Speaker 1: a safe bet to say it's mostly hydrogen because that's
Speaker 1: what the universe is. And so yeah, there's gas and
Speaker 1: this dust and whatever, but mostly it's hydrogen there. And
Speaker 1: here's the black hole starts to work against itself because
Speaker 1: the accretion disc is so hot that it glows, right,
Speaker 1: that's where we can see these things. So it emits
Speaker 1: radiation pressure, so it pushes stuff away. Right. We talked
Speaker 1: in a recent episode about how stars are a balance
Speaker 1: between gravity and radiation pressure. The fusion at their hot
Speaker 1: core is producing a lot of energy and that pushes
Speaker 1: out on the star, and if the star is too big,
Speaker 1: it can actually blow the star apart. That's why you
Speaker 1: have like a maximum size of stars. Well, a similar
Speaker 1: thing is happening here. The heat from the accretion disk
Speaker 1: creates radiation which pushes other stuff away. So the hotter
Speaker 1: the black hole, the bigger the black hole, the bigger
Speaker 1: the accretion disk the more it slows down its ability
Speaker 1: to eat stuff. So black holes cannot grow infinitely quickly.
Speaker 1: There's no theoretical upper limit to the size of a
Speaker 1: black hole, but because of this process, this radiation pressure,
Speaker 1: there is an upper limit to how rapidly they can grow.
Speaker 1: You put a black hole in a blob of stuff,
Speaker 1: it can't just like slurp everything out really quickly because
Speaker 1: it's going to get hot and glow and push its
Speaker 1: own food away from itself.
Speaker 3: So what determines the size of the accretion disc.
Speaker 1: It's just how much stuff was there around it. Like
Speaker 1: if you put a black hole in deep space and
Speaker 1: nothing is there, it have no accretion disc. It would
Speaker 1: just be black. We could not see it except for
Speaker 1: its gravitational effects. You drop in the middle of a
Speaker 1: really big blob of stuff, it's going to get a
Speaker 1: big accretion disc. So it just depends on what's around it.
Speaker 1: And this is a really interesting puzzle in physics right
Speaker 1: now because this limit on how quickly black holes can
Speaker 1: grow is one of the reasons why we don't understand
Speaker 1: super massive black holes. We see super massive black holes
Speaker 1: in the early history of the universe, like a billion
Speaker 1: years after the Big bang already we have black holes
Speaker 1: with like billions of times the mass of the Sun.
Speaker 1: But if you do the calculations the limit on the
Speaker 1: speed of which black holes can grow, tell you that's impossible.
Speaker 1: So how did they get so big? That's the big
Speaker 1: question of super massive black holes, although we have some
Speaker 1: interesting hints that like, if the accretion disc is asymmetric,
Speaker 1: then can have what they call super Eddington accretion rates.
Speaker 1: It's fascinating. But David's question is about tiny black holes,
Speaker 1: and he's asking, can they also have accretion discs?
Speaker 2: And you told me that it doesn't matter how big
Speaker 2: a black hole is. What matters is the stuff that started.
Speaker 2: So could a tiny black hole have a huge accretion disk?
Speaker 1: So a tiny black hole can have accretion disc And
Speaker 1: this Eddington limit of the rate of which black holes
Speaker 1: can grow scales with mass, so the limit is smaller
Speaker 1: with smaller mass. So there's like less radiation pressure from
Speaker 1: a smaller mass black hole because it can't heat up
Speaker 1: its accretion discs as much. But at a very small
Speaker 1: black hole, something else happens. Right, black holes don't just
Speaker 1: glow because of their accretion disc They are themselves not
Speaker 1: totally black. We think they glow themselves with a little
Speaker 1: bit of Hawking radiation. This is this bizarre radiation that
Speaker 1: happens because you have an event horizon in quantum fields
Speaker 1: and there's this hand wavy story out there about particles
Speaker 1: and antiparticles or one falls into the event horizon. That's
Speaker 1: just cartoons. It's not really the physics of what's happening.
Speaker 1: But we do think that Hawking radiation might be real.
Speaker 1: And the crucial thing about it is that it's bigger
Speaker 1: for smaller black holes. Really big black holes almost no
Speaker 1: Hawking radiation. Smaller black holes dramatic Hawking radiation. So the
Speaker 1: smaller the black hole gets, the bigger the Hawking radiation.
Speaker 1: So this is actually going to be more radiation pressure
Speaker 1: than the accretion disc. For a small enough black hole,
Speaker 1: the Hawking radiation will be brighter than the glow from
Speaker 1: the accretion disk.
Speaker 3: Okay, so I'm picturing it now.
Speaker 2: There's a black hole in the middle, there's an accretion
Speaker 2: disc around it, and then Hawking radiation extends even beyond that,
Speaker 2: and if you were looking, could do We have a
Speaker 2: kind of telescope that could distinguish those three objects.
Speaker 1: We have a telescope that can see black holes, and
Speaker 1: we've only been able to see super massive black holes
Speaker 1: and so those have essentially no Hawking radiation or unmeasurable amounts,
Speaker 1: so we've never seen Hawking radiation. But if you had
Speaker 1: a small enough black hole and it was nearby, it
Speaker 1: would be very bright in Hawking radiation. So it did
Speaker 1: the calculation and if you had a black hole with
Speaker 1: like forty billion kilograms, which is about the mass of
Speaker 1: the Hoover Dam, then the glow from the accretion disc
Speaker 1: would be about as bright as the glow from Hawking radiation,
Speaker 1: so like pretty bright. But this is tiny, you know,
Speaker 1: this is like a tiny fraction of the mass of
Speaker 1: the Earth. Even so this is really a very small
Speaker 1: black hole. Like the gravity from the Hoover Dam is
Speaker 1: not very powerful. Remember we had that episode about like
Speaker 1: measuring gravity and like the Scottish guys climbing around that mountain,
Speaker 1: that was a much bigger effect because that's a much
Speaker 1: bigger mountain and still very hard to measure. Gravity is
Speaker 1: super weak, So a black hole with the mass of
Speaker 1: the Hoover Dam would not be very powerful, but it
Speaker 1: would be as bright as it's accretion disk. So yes, David,
Speaker 1: small black holes can have accretion disk. It depends on
Speaker 1: what they've been eating. So if you have a tiny
Speaker 1: black hole out in the middle of nowhere, no accretion disk.
Speaker 1: You take a tiny black hole and you PLoP it
Speaker 1: in a huge bed of plasma and hygigen and whatever.
Speaker 1: It will get in accretion disk as well, but it
Speaker 1: will also glow with its own hawking radiation.
Speaker 3: Wow.
Speaker 2: Okay, So then let's get to the last part of
Speaker 2: David's question. If that if you put that black hole
Speaker 2: in the center of the Earth, how long could Earth survive?
Speaker 1: Yeah, this is a fascinating question as well, and I
Speaker 1: thought it was a little unrealistic because we can't make
Speaker 1: a black hole the size of the Hoover Dam. We
Speaker 1: were unlikely to see one. So I thought, well, let's
Speaker 1: take it another step. Let's say we did make a
Speaker 1: black hole. Because, for example, at the Large Hadron Collider,
Speaker 1: we're trying to make black holes all the time. We
Speaker 1: smash protons together. Yeah, we smash protons together in the
Speaker 1: hopes that occasionally they will create a tiny miniature black hole.
Speaker 1: And remember, smaller black holes radiate faster than bigger black holes.
Speaker 1: So we make a black hole to the large hadron collider.
Speaker 1: It's going to have like ten to the minus twenty
Speaker 1: four kilograms of mass. It'll almost instantly radiate itself away, hope.
Speaker 1: But it would be awesome because then we'd learn something
Speaker 1: about quantum gravity. It would be incredible. But if you
Speaker 1: did take one of these things and somehow was able
Speaker 1: to feed it before it radiated away, and you put
Speaker 1: it in the center of the Earth, and then you
Speaker 1: do a calculation of like how long would it take
Speaker 1: to slurp up everything and consume the entire Earth? That
Speaker 1: would take about ten thousand years, all right, So.
Speaker 2: I wouldn't be around anymore. So fine, that's.
Speaker 1: Right, that's all right, And you would have time to
Speaker 1: jump on that arcship to Alpha Centauri, and we'd even
Speaker 1: have time to design and build it, you know, because
Speaker 1: ten thousand years is a good amount of time, even
Speaker 1: for space projects.
Speaker 2: But this ecologist feels like you probably shouldn't do anything
Speaker 2: to destroy the Earth because there are a lot of
Speaker 2: species that would get left behind, and every species is important.
Speaker 3: Dan, Well, extinction's not okay.
Speaker 1: Do you want to extinctify the mosquitos? How about that
Speaker 1: wasp that bits you earlier? How's that thumb doing?
Speaker 2: By the way, it's about thirty percent bigger than the
Speaker 2: other thumb right now. But I still think that the
Speaker 2: wasps they are important pollinators in some cases they control
Speaker 2: like other insect populations, I think it deserves to stay.
Speaker 2: I might get rid of mosquito. See I'm glad we
Speaker 2: got rid of small pox there. I accept that there's
Speaker 2: some nuance, but I'm your answer didn't sound like it
Speaker 2: was gonna be very nuanced, Daniel.
Speaker 1: I was just trying to be controversial success. Thank you
Speaker 1: David for that question. Let us know if we answered it,
Speaker 1: and follow up questions are always welcome.
Speaker 7: Hi, Daniel and Kelly, thank you so much for that answer.
Speaker 7: You did indeed answer the question and my only follow up.
Speaker 7: If I were to waive my magic wond and create
Speaker 7: a Hoover Dam sized black hole and situated somewhere that
Speaker 7: I could watch it feed from ten or twenty meters away,
Speaker 7: would I be able to enjoy the spectacle for the
Speaker 7: three or four hundred microseconds it would take for the
Speaker 7: stream of gamma rays and exotic particles to shred my spacesuit,
Speaker 7: or would be a teency little firefly I could enjoy
Speaker 7: until my oxygen ran out. Either way, I promise not
Speaker 7: to destroy the Earth anytime soon. Thanks again, Thanks.
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