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Speaker 1: I'd like us to quickly explore deep into space. Can

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Speaker 1: gravity slingshots help us win that race?

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Speaker 2: If ancient humans killed off the giant kangaroo, why didn't

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Speaker 2: we kill off the African elephant too?

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Speaker 1: How much do tiny black holes like to eat? If

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Speaker 1: I adopt one, will it nap at my feet?

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Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's answers.

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Speaker 3: Will make it right.

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Speaker 1: Welcome to Daniel and Kelly's extraordinarily Curious universe.

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Speaker 3: Hello, I'm Kelly Waiter Smith.

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Speaker 2: I study parasites and space, and I am excited to

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Speaker 2: talk about charismatic megafauna today.

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Speaker 1: Hi. I'm Daniel. I'm a particle physicist, and I never

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Speaker 1: wanted a willing mamoth as a pet.

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Speaker 2: Oh you No, I didn't either. I don't think I

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Speaker 2: want anything bigger than the goats that we have right now?

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Speaker 1: What about a goat sized black hole? Or do goats

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Speaker 1: basically operate as black holes because they eat everything?

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Speaker 3: You know?

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Speaker 2: Our goats are surprisingly picky about what they eat, which

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Speaker 2: I'm winding a little frustrated because I was like, Oh,

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Speaker 2: we're gonna get walking garbage disposals, but ours are like no,

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Speaker 2: I don't want that.

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Speaker 3: I don't want that either, So your goats are not

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Speaker 3: the goat.

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Speaker 2: I wouldn't say that. They are definitely the greatest of

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Speaker 2: all time. And one of them is named Greatest of

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Speaker 2: all Time aka Kevin for short. That's the full name

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Speaker 2: that's on its certificate, because we let children name our goats.

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Speaker 2: So one of them is the goat literally literally. But

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Speaker 2: I had a particularly negative experience with wildlife this morning.

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Speaker 2: I just walking up the hill accidentally smacked a wasp

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Speaker 2: of some sort and my thumb is expanding. Oh and

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Speaker 2: we'll see how big it is by the end of

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Speaker 2: the episode. But I wanted to focus on more positive interactions.

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Speaker 2: Since we're gonna be talking like Africa's charismatic wildlife, I

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Speaker 2: wanted to know what is the most like awe inspiring

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Speaker 2: experience you've had with an animal in nature?

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Speaker 3: Because you and Katrina hike, you're like outdoor people.

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Speaker 1: I think one of the most incredible experiences I've had

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Speaker 1: was seeing a mountain lion close up. Who I grew

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Speaker 1: up in the mountains of northern New Mexico, and there

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Speaker 1: were mountain lions because they were mountains, and you know,

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Speaker 1: sometimes you'd get up in the morning and you'd see

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Speaker 1: their pop rinks in the snow. But one time I

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Speaker 1: actually did spot one, and it's incredible how much they

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Speaker 1: are like housecats, you know, in their smoothness and their

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Speaker 1: their feline charisma, but also how terrifyingly huge they are,

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Speaker 1: because I've often wondered, like, what would my housecat do

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Speaker 1: if it weighed a thousand pounds? And now I know

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Speaker 1: the answer is it would eat me.

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Speaker 2: I mean, most of the time, mountain lions don't go

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Speaker 2: after people. I want to clear the mountain lion's name,

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Speaker 2: and if anybody wants to read more about that, they

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Speaker 2: should check out more ark Elbrock's book on mountain lions.

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Speaker 2: But yeah, so that is beautiful. So like, did you

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Speaker 2: see it at a distance where like how far away

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Speaker 2: was it?

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Speaker 1: It was like maybe eighty feet or something. My parents'

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Speaker 1: backyard was right up against National Forest and so there

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Speaker 1: was just like a lot of trees and canyons back there,

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Speaker 1: and I saw one walking through the trees and I

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Speaker 1: saw it and it saw me, and we like shared

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Speaker 1: a little moment, and I was like, I'm on a

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Speaker 1: tiptoe back inside. You can have the whole outdoors.

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Speaker 2: It's all yours now, buddy, and I assumed that he did.

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Speaker 2: It did not approach you or anything like that.

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Speaker 1: No, no, it did not, and I'm very happy that

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Speaker 1: it went on its way. But it reminds me of

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Speaker 1: this incredible story I heard about European lions. You know,

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Speaker 1: the lions used to roam Europe also, but they were

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Speaker 1: killed off many, many years ago. And the story I

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Speaker 1: heard is that for a long time there was a

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Speaker 1: question about European lions. Do they have mains like African

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Speaker 1: lions or not like North American lions. And we answered

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Speaker 1: this question through cave drawings. People found drawings of lions

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Speaker 1: from tens of thousands of years ago from Paleolithic artists,

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Speaker 1: and it's basically like a lab book and they don't

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Speaker 1: have mains, and you can see like hunting pears even

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Speaker 1: And so that's incredible to me that, like humans, tens

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Speaker 1: of thousands of years ago answered our current science question.

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Speaker 2: Okay, so that is amazing, but how does the absence

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Speaker 2: of seeing mains like so, you know, in Africa, when

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Speaker 2: you get groups that are hunting, it's usually groups of

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Speaker 2: females that are hunting. The females do most of the hunting,

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Speaker 2: So how do you know that, you know, the worthless

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Speaker 2: males just were weren't drawn on the insides of the caves.

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Speaker 1: Yeah, great question. I shouldn't have said hunting pair. I

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Speaker 1: think they had some reason to believe this is like

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Speaker 1: a family unit. But it sort of connects us over

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Speaker 1: space and time to you know, early humans who are

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Speaker 1: also awed by the majesty of megafauna.

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Speaker 3: Yes, absolutely, very cool.

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Speaker 2: And when I asked you that question, I assumed you

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Speaker 2: we're going to pick megafauna because almost almost everyone picks,

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Speaker 2: you know, some large mammal, the largest mammal they've ever seen,

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Speaker 2: is usually the answer to that question.

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Speaker 1: Oh, I see, You've asked other people this question, and

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Speaker 1: nobody has said the time I saw a rat in

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Speaker 1: my kitchen.

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Speaker 3: Well, of course not No, no one has said that.

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Speaker 2: But I think my moment was I was in the

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Speaker 2: woods and I was helping a friend with the snake survey,

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Speaker 2: and a bunch of wood frogs had recently like metamorphosed

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Speaker 2: from tadpoles into like adults, but they were are you know,

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Speaker 2: into the landstage.

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Speaker 3: But they were really tiny.

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Speaker 2: And there were literally hundreds of them, and I noticed

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Speaker 2: them because I like moved my foot forward and all

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Speaker 2: of these tiny things hopped out of the way.

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Speaker 1: Oh my god.

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Speaker 2: And I realized, like, oh my gosh, I'm surrounded by

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Speaker 2: like hundreds of little froglets, these little tiny frogs, and

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Speaker 2: I just sat down and like the sun was coming

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Speaker 2: through the trees and just the right way that it

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Speaker 2: kind of had like a magical feeling. And every time

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Speaker 2: I'd sort of move my hand, all of these little

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Speaker 2: froglets would like hop around, and it was just like,

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Speaker 2: I don't know, it was magic. It was like being

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Speaker 2: in some sort of a fairy book or something. And

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Speaker 2: I think for me that was that was my moment.

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Speaker 1: Well, I have a moment I recall from being in

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Speaker 1: your neck of the woods. Oh, it was more of

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Speaker 1: a horror story than a magical moment. Katrina and I

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Speaker 1: were hiking and backpacking, I think it was in the

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Speaker 1: Blue Ridge Mountains, and we set up our camp and

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Speaker 1: we had a nice campfire, and at the end of

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Speaker 1: the evening we were ready to go back to our tent,

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Speaker 1: and it was only then that we noticed that the

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Speaker 1: ground just outside the extent of the fire was covered

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Speaker 1: in daddy long legs. There were like millions and millions

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Speaker 1: of them, and they were crawling all over our tent

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Speaker 1: and everywhere. It was incredible. We were so grateful that

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Speaker 1: we had zipped our tent closed, so we like sprained

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Speaker 1: it back to the tent open it, jumped in closed it,

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Speaker 1: and was just like terrified of the carpet of Daddy

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Speaker 1: long legs that were outside. I was like, wow, Virginia's crazy.

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Speaker 3: But they can't hurt you.

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Speaker 1: They can't hurt you. But I'm still not gonna like

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Speaker 1: lie down and have Daddy long legs crawl all over me.

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Speaker 2: All right, Well I don't I feel like I'm not

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Speaker 2: really feeling.

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Speaker 1: All right, Zach, you are free to release Daddy long

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Speaker 1: legs all over Kelly was she's asleep. Sure, sure, Wow, amazing.

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Speaker 1: You don't have the same reaction to spiders as other

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Speaker 1: people do.

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Speaker 2: Huh, Well, Daddy long legs aren't really spiders.

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Speaker 1: Oh my gosh. Wow, and that scientific knowledge puts you

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Speaker 1: at ease, it does.

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Speaker 2: Let me make sure that's right. Our Daddy long legs spiders.

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Speaker 2: I think there are racknids. Oh maybe they do still

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Speaker 2: count as spiders. Yeah, all right, so sorry, I guess

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Speaker 2: they are still Teddy long legs are still see.

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Speaker 1: I told you they were creepy like that makes a.

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Speaker 2: Difference, all right, So sorry, you were right, daddy, long

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Speaker 2: legs looks like they are spiders. But I do feel

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Speaker 2: like knowledge makes a huge difference. So we've got these

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Speaker 2: they're called rabid wolf spiders, bad name, right, and they're

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Speaker 2: like big and they do look kind of scary. And

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Speaker 2: when I first moved here, I freaked out because my

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Speaker 2: son likes to roll around in the grass and these

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Speaker 2: are like grass spiders that are in the grass, and

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Speaker 2: so he'd roll around in it. I always see like

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Speaker 2: a big spider running away and it really freaked me out.

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Speaker 2: But I read about them, and now I'm not scared

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Speaker 2: of them, like they're they're not gonna go after my son.

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Speaker 3: It's fine.

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Speaker 2: I do feel like knowledge makes a big difference in

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Speaker 2: my fear outside in general.

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Speaker 1: You're totally right, and of course, knowledge is our business.

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Speaker 1: We're here to help everybody understand the universe better and

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Speaker 1: be less afraid of it, or maybe appropriately afraid of it.

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Speaker 1: So let's get into it, because today we're not here

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Speaker 1: just to talk about my experiences with spiders and Kelly's

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Speaker 1: magical moment with the frogs. We're here to talk about

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Speaker 1: your questions about the universe, things you wonder about, places

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Speaker 1: where you wish you had more knowledge. So we regularly

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Speaker 1: ask our listeners to send in their questions, and we'd

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Speaker 1: love to hear from you. Please write to us to

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Speaker 1: questions at Danielankelly dot org. We always write back to everybody,

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Speaker 1: and sometimes we pick questions to answer here on the

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Speaker 1: pod because we think a lot of people might be

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Speaker 1: interested in the answer, or because I think it'd be

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Speaker 1: fun to joke about it with Kelly.

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Speaker 2: Or because when I get the EMO from you, I

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Speaker 2: don't know the answer and I need to stall for

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Speaker 2: Time's you go.

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Speaker 3: That's the other reason.

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Speaker 1: So, speaking of stalling for time, here's our first question,

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Speaker 1: which is about how to quickly explore the outer Solar

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Speaker 1: System using gravity's help.

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Speaker 4: Hi, Daniel and Kelly. I was thinking about how we

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Speaker 4: use gravitational slingshots permissions such as Voyager, Cassini and New

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Speaker 4: Horizons as we venture further into the Solar System. Would

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Speaker 4: we use this method for human credmissions and what forces

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Speaker 4: would the crew feel if they were slingshotted to their destination? Thanks?

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Speaker 1: All right, and that question was from Rob Pixley. Rob,

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Speaker 1: thank you very much for writing in. Kelly, you're an

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Speaker 1: expert on space and exploration. What do you think about this?

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Speaker 2: Well, I believe that gravitational slingshots are when you use

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Speaker 2: massive objects to gain some speed. But I'm going to

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Speaker 2: wait for you to give some more information. But when

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Speaker 2: I read this, it reminded me of Jules Verne's and

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Speaker 2: I can never say his name right.

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Speaker 3: Thank you, because he's French. Okay, all right, that guy,

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Speaker 3: That French guy.

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Speaker 2: He wrote a book From the Earth to the Moon,

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Speaker 2: and it was about a Baltimore gun club who decided

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Speaker 2: they were going to build a giant gun and shoot

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Speaker 2: people to the moon. And it works. But the problem is, actually,

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Speaker 2: if you were to calculate how many gs the crew

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Speaker 2: would have felt, they would have been probably like liquefied

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Speaker 2: in chapter twenty on the Way to the Moon. They

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Speaker 2: wouldn't have made it. So let's hear about gravitational slingshots.

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Speaker 2: Would this kill humans or nothing?

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Speaker 1: Gravitational slingshots are super awesome. They are a way to

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Speaker 1: boost your speed and change your direction without using any fuel.

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Speaker 1: You know, one of the big issues for getting around

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Speaker 1: the Solar System or getting around the universe is that

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Speaker 1: fuel is heavy and if you use fuel to propel yourself.

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Speaker 1: You need fuel to help you push that fuel, and

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Speaker 1: then you need more fuel to help you push that fuel,

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Speaker 1: and pretty soon you have a gas tank the size

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Speaker 1: of Jupiter just to get anywhere. So it's very nice

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Speaker 1: if you can navigate the universe without using fuel, because

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Speaker 1: then you don't have the additional mass and then need

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Speaker 1: to propel that all that stuff. So for decades, NASA

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Speaker 1: and other folks have been using this technique called a

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Speaker 1: gravitational slingshot, which essentially steals a little bit of speed

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Speaker 1: from a planet or a moon. The way it works

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Speaker 1: is you can approach a big planet and it's gravity

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Speaker 1: you will change your direction. So for example, say you're

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Speaker 1: just coasting, you have no rockets on, and you're approaching Jupiter,

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Speaker 1: and you swing around the back of Jupiter and come

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Speaker 1: out the other side. Now you're going in a new direction. Right.

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Speaker 1: That's not something you can otherwise accomplish, usually without burning

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Speaker 1: some fuel, without thrusters, because a change in direction, even

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Speaker 1: if your overall magnitude is the same, is still an acceleration.

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Speaker 1: To change your direction in space, you've got to have

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Speaker 1: some acceleration. Somebody's got to pull on you. So basically

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Speaker 1: you use the gravity of the planet to pull on

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Speaker 1: you and you can even come out the other side,

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Speaker 1: not just with a change in direction, but with a

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Speaker 1: net increase in speed. And that's why it's called a

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Speaker 1: gravitational slingshot.

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Speaker 2: Well, I don't think we've ever used this on a

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Speaker 2: vehicle carrying humans, because the only option would be the

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Speaker 2: trip to the Moon. But have we used this for

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Speaker 2: our rovers or anything or probes.

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Speaker 1: We've used it for lots of probes, absolutely, because a

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Speaker 1: lot of times we don't have the fuel to get

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Speaker 1: them all the way out to the outer Solar System,

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Speaker 1: and we want to keep them light and it saves fuel.

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Speaker 1: And then also you get to add like another planet

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Speaker 1: on your trip. You're like, hey, I want to go

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Speaker 1: to Saturn, but I'd like to swing by Mars on

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Speaker 1: the way, Or I'd like to go to Neptune. Can

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Speaker 1: we stop by Jupiter? And then you also get to

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Speaker 1: take pictures of Jupiter because you know, none of these

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Speaker 1: things are so well explored that like one more trip

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Speaker 1: is boring, you know. Yeah, so that's like a bonus

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Speaker 1: for these things. And I think the physics of it

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Speaker 1: is really fascinating because it's a little bit counterintuitive, like

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Speaker 1: it feels like free energy, Like where is this speed

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Speaker 1: coming from? And the answer to that question is that

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Speaker 1: you're really taking that speed from the planet. Like if

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Speaker 1: you swing by Jupiter, it changes your direction, it accelerates you,

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Speaker 1: and it effectively slows down. It slows down in its

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Speaker 1: orbit around the Sun. So, for example, if you take

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Speaker 1: a normal space probe and you swing it around Jupiter

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Speaker 1: and it gets sped up in the process, Jupiter slows down,

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Speaker 1: but just by a tiny little bit because the mass

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Speaker 1: of Jupiter is so huge compared to the mass of

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Speaker 1: the probe that it loses I did this calculation one

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Speaker 1: times ten to the negative twenty five kilometers per second

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Speaker 1: of its flow, so basically negligible. However, if you scale

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Speaker 1: this up and you did like, you know, ten to

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Speaker 1: the twenty five space probes, because you want to explore

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Speaker 1: the whole galaxy, you might start having an impact on Jupiter.

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Speaker 1: But basically, think about Jupiter as a huge battery of

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Speaker 1: momentum and you're tapping into that a little bit and

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Speaker 1: adding it to your space probes.

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Speaker 2: So if an aggressive alien civilization wanted to screw up

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Speaker 2: our solar system, could they just send probes by Jupiter

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Speaker 2: enough times to get it to sort of move around

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Speaker 2: and rek havoc on the rest of Us.

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Speaker 1: I guess they could. But you know, if they were

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Speaker 1: capable of doing that, they should just like nudge an

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Speaker 1: asteroid towards Earth. I mean, I'm not giving advice to

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Speaker 1: malevolent aliens. Okay, sounds like I am, so you please

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Speaker 1: if you are malevolent aliens, don't do this, or anybody

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Speaker 1: shouldn't do this. But yeah, the most dangerous thing you

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Speaker 1: could do in the Solar system is nudge a comet,

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Speaker 1: for example, because comments by the time they get to

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Speaker 1: the inner Solar System are going really really fast because

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Speaker 1: they fall from so far away, and they're really are

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Speaker 1: to see in advance because their periods are so long.

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Speaker 1: So yeah, nudging a comet would be the most dangerous thing.

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Speaker 1: I guess the most subtle thing would be tweaking Jupiter.

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Speaker 1: That would be a cool basis for a science fiction novel.

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Speaker 1: Get on it, Daniel, And for those of you who

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Speaker 1: still trying to like Grock, how this works? You know?

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Speaker 1: Another analogy is like think about a moving train and

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Speaker 1: you have a tennis ball. If you throw your tennis

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Speaker 1: ball against the front of the train. Then the train's

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Speaker 1: velocity gets added to the tennis ball's velocity when it

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Speaker 1: bounces off, right, So now it comes back, it's going

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Speaker 1: not just the same velocity as it was when it

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Speaker 1: hit the train. Like if you bounce the tennis ball

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Speaker 1: against a wall, it comes back with the same speed.

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Speaker 1: If you bounce a tennis ball against a train rushing

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Speaker 1: at you, it comes back much much faster. It slows

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Speaker 1: down the train a tiny little bit, nobody's ever going

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Speaker 1: to notice, but it speeds up the tennis ball. And

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Speaker 1: so it's this huge mass ratio that makes this possible.

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Speaker 2: All right, So how fast does this speed up happen?

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Speaker 2: And is it going to be fast enough that you're

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Speaker 2: going to liquefy the humans inside?

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Speaker 1: Right? So two really interesting questions, and that's really what

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Speaker 1: Rob was asking about. So number one, this isn't a

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Speaker 1: great idea for human missions, but not because of the

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Speaker 1: g forces, but because usually it involves going pretty far

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Speaker 1: out of your way. Like you're sending a probe to Pluto.

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Speaker 1: You know it's going to take forever to get there.

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Speaker 1: If you can make it lighter by stopping by Saturn

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Speaker 1: on the way, you don't really care if it's going

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Speaker 1: to slow you down by five years, because it can

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Speaker 1: slow you down by five years, so it's a more

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Speaker 1: economical way to get this speed, But often it requires

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Speaker 1: going really far out of your way, and if you're

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Speaker 1: doing space missions, the goal is to get there fast,

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Speaker 1: to spend less time in space, less time exposed to

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Speaker 1: low gravity, less time exposed to radiation, all this kind

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Speaker 1: of stuff. Now, sometimes it can work if the Solar

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Speaker 1: system is just right. You know, if you want to

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Speaker 1: get to Saturn and Jupiter happens to be in just

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Speaker 1: the right place, then maybe a flyby of Jupiter can

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Speaker 1: help you get to Saturn faster. But usually you just

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Speaker 1: want to go directly there, and so you want chemical

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Speaker 1: rockets or ion thrusters or fusion power or something. So

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Speaker 1: this is good for long missions where you don't really

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Speaker 1: care how long it takes, which is not what we're

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Speaker 1: going for here.

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Speaker 2: Okay, so it would take longer, but I mean, if

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Speaker 2: you're doing like a generation ship on an interstellar journey,

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Speaker 2: you know you're not gonna be alive when you get

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Speaker 2: to the final destination anyway, so why not add an

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Speaker 2: extra five years to your trip to speed it up

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Speaker 2: For the next few generations. So let's assume we decide

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Speaker 2: we're going to do this anyway, or are you going

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Speaker 2: to get killed by the speed.

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Speaker 1: Well, before we answer that, there's another wrinkle, which is

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Speaker 1: you're right if you're like aiming for Alpha Centauri and

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Speaker 1: you want to be redirected and you don't want to

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Speaker 1: spend all that fuel. This is not a terrible idea,

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Speaker 1: but it's going to be more effective the closer you

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Speaker 1: get to the planet, right, because then the more powerful

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Speaker 1: the gravity. However, the closer you get to Jupiter, the

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Speaker 1: more you have to word about the radiation of Jupiter, right,

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Speaker 1: So there's really a trade off there. But here's the

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Speaker 1: thing about the G forces. There aren't any You don't

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Speaker 1: feel any of these G forces. That's right, because gravity

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Speaker 1: is not a force. You feel g forces when you're

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Speaker 1: being accelerated. So for example, if you're on a roller

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Speaker 1: coaster and you reach the bottom of the roller coaster

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Speaker 1: and you start going up, you feel those G forces.

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Speaker 1: Or if you're in a car and you're turning really fast,

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Speaker 1: you feel those G forces. Or if you're in a

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Speaker 1: rocket and somebody burns the rocket really fast to get

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Speaker 1: you going off the planet, you feel those G forces.

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Speaker 1: When you are falling just under gravity, you feel no

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Speaker 1: G forces. So for example, you jump out of an airplane,

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Speaker 1: you don't feel any G forces. Right, you're in freefall.

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Speaker 1: You only feel G forces when there's acceleration, and you

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Speaker 1: only feel acceleration when you're fighting gravity. If you just

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Speaker 1: chill with gravity, man, and go with the flow of

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Speaker 1: the universe, you feel no G forces.

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Speaker 2: Okay, well, so what if what if you're on this

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Speaker 2: interstellar ship. You want to get the Jupiter speed up,

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Speaker 2: and the folks who major interstellarship planned ahead for the

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Speaker 2: problem that low gravity is bad for human bodies. And

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Speaker 2: now you are spinning, so you have artificial gravity in

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Speaker 2: your habitat to help with things like reproduction. Now where

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Speaker 2: you feel on the G forces with the artificial gravity.

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Speaker 1: You feel the artificial gravity absolutely, because that's not gravity, right,

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Speaker 1: that's the force from the structure of the ship holding

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Speaker 1: itself together. The same with like on the surface of

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Speaker 1: the Earth, you feel what we call gravity, but it's

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Speaker 1: really the Earth pushing you up against the natural inclination.

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Speaker 1: You have to fall towards the center of the curvature.

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Speaker 1: So yes, you feel the G forces from the spinning

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Speaker 1: that's real because it's not gravity. But falling into Jupiter's

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Speaker 1: gravitational field doesn't change that at all.

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Speaker 5: Yeah.

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Speaker 2: Okay, so sorry, So I knew that you would feel

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Speaker 2: the artificial gravity, But what I meant is when you're

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Speaker 2: feeling artificial gravity and then you accelerate, Yeah, do you

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Speaker 2: feel that acceleration more strongly when you're under artificial gravity

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Speaker 2: relative to No?

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Speaker 3: Okay, no, no, you're doing cool.

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Speaker 1: Yeah, so that's sort of awesome because you know, you

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Speaker 1: don't feel gravity at all, even though it's having an

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Speaker 1: impact on you, even though you are accelerating, you're changing

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Speaker 1: your vector from the point of view of somebody distant. Right.

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Speaker 1: This is the thing about gr is that it's very confusing.

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Speaker 1: It depends on who who watching from your point of view,

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Speaker 1: you never feel acceleration due to gravity. Somebody else looking

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Speaker 1: from far away, who doesn't see the curvature. They're like, well,

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Speaker 1: according to my coordinates, your velocity is changing and therefore

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Speaker 1: you're having acceleration. And that's cool. Gr Lets everybody have

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Speaker 1: their own calculation. But what do you feel is what's important. Right,

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Speaker 1: You're not going to be torn apart, your stomach's not

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Speaker 1: going to be shredded. Your organs are not going to

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Speaker 1: be squished. Feel free to dive closed to Jupiter in

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Speaker 1: your arcship on your way to Alpha Centauri. You have

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Speaker 1: to worry about the radiation, but you don't have to

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Speaker 1: worry about the g forces.

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Speaker 2: And because I have a pod in physics, I know

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Speaker 2: that GR stands for general relativity.

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Speaker 1: Yes, absolutely, joh relativity one of the most fascinating, beautiful

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Speaker 1: and I think widely misunderstood theories, mostly because of that

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Speaker 1: dang rubber sheet bowling ball analogy out there which confuses everybody.

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Speaker 2: Yeah, but we're here to clear up misconceptions, all right,

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Speaker 2: So let's find out if Rob wants to use a

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Speaker 2: gravitational slingshot for his journey to interest that I've decided

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Speaker 2: he's going on.

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Speaker 4: Hi, Daniel and Kelly, your explanations normally make sense, but

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Speaker 4: offered a great way to look at the scenario from

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Speaker 4: multiple interesting, different perspectives. Thanks again.

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Speaker 1: Okay, we're back and we're answering questions from listeners today.

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Speaker 1: And the next question is about major animals.

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Speaker 2: Major animals, Well, I've never heard them referred to as

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Speaker 2: major before majorly awesome, So I have never been to Spain,

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Speaker 2: how would you pronounce this name, Daniel?

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Speaker 3: Do you know Adamar?

436
00:20:50,600 --> 00:20:52,280
Speaker 1: I've never heard this name before, but it looks to

437
00:20:52,320 --> 00:20:53,080
Speaker 1: me like Adamar.

438
00:20:53,200 --> 00:20:56,760
Speaker 2: Yeah, all right, anyway, fantastic name, and so adam ar

439
00:20:56,840 --> 00:20:57,359
Speaker 2: from Spain.

440
00:20:57,760 --> 00:20:58,800
Speaker 3: Let's hear your question.

441
00:20:59,080 --> 00:21:01,320
Speaker 6: Hello, Danny and Kelly. My name is Adema and I'm

442
00:21:01,320 --> 00:21:04,679
Speaker 6: asking this question from Spain. I recently learned that elephant

443
00:21:04,720 --> 00:21:08,000
Speaker 6: seemed to identify different human languages and react differently depending

444
00:21:08,040 --> 00:21:10,080
Speaker 6: on what they hear, thus being able to know if

445
00:21:10,119 --> 00:21:12,240
Speaker 6: a group of humans poses a threat to them based

446
00:21:12,280 --> 00:21:15,720
Speaker 6: on a language they speak Differently, Rainos seem to adopt

447
00:21:15,720 --> 00:21:19,639
Speaker 6: a more increasive behavior whenever the spots kincas. Some suggesting

448
00:21:19,680 --> 00:21:22,239
Speaker 6: that this could be a consequence of biological adaptation as

449
00:21:22,240 --> 00:21:24,680
Speaker 6: they evolve in contact with humans for many, many times,

450
00:21:24,800 --> 00:21:27,399
Speaker 6: in fact, since the beginning of the Haminites. What is

451
00:21:27,480 --> 00:21:29,520
Speaker 6: most intriguing is that this could be the reason why

452
00:21:29,520 --> 00:21:32,520
Speaker 6: great animals don't exist in any continent other than Africa.

453
00:21:32,680 --> 00:21:35,199
Speaker 6: As our arrival, there was much mosch suven and they

454
00:21:35,240 --> 00:21:37,320
Speaker 6: didn't have time to bolf an adapt to us before

455
00:21:37,320 --> 00:21:40,280
Speaker 6: we hunted them down to extinction. May Kelly give us

456
00:21:40,280 --> 00:21:43,119
Speaker 6: a dieper insight in this matter? Thank you for having me,

457
00:21:43,160 --> 00:21:45,960
Speaker 6: and congratulations for providing us with such an awesome podcast.

458
00:21:46,280 --> 00:21:49,000
Speaker 2: All right, So my opinion on the matter is pretty

459
00:21:49,080 --> 00:21:52,560
Speaker 2: much that Adamar was right right on the money. So

460
00:21:52,600 --> 00:21:55,159
Speaker 2: we're just going to go ahead and talk about the

461
00:21:55,200 --> 00:21:58,320
Speaker 2: science here because it's a really fascinating story and Adamore

462
00:21:58,359 --> 00:22:00,560
Speaker 2: seems to have a good handle on it. But I'm

463
00:22:00,560 --> 00:22:02,280
Speaker 2: just gonna go ahead and reiterate how cool all this

464
00:22:02,280 --> 00:22:02,720
Speaker 2: stuff is.

465
00:22:02,920 --> 00:22:05,520
Speaker 1: Yeah, Kelly, tell us the history. How much more awesome

466
00:22:05,640 --> 00:22:08,160
Speaker 1: was the Earth ten or fifty thousand years ago.

467
00:22:08,359 --> 00:22:09,560
Speaker 3: Before humans came along?

468
00:22:09,600 --> 00:22:13,200
Speaker 2: All right, So there were a lot more large mammals

469
00:22:13,200 --> 00:22:15,640
Speaker 2: on the planet, and by large we mean greater than

470
00:22:15,640 --> 00:22:16,840
Speaker 2: forty four kilograms.

471
00:22:17,080 --> 00:22:20,440
Speaker 1: Why forty four not forty five, not forty Who decided?

472
00:22:20,520 --> 00:22:23,200
Speaker 1: Was there some meeting the forty four kilogram threshold?

473
00:22:23,440 --> 00:22:26,080
Speaker 2: I don't know who decided on the forty four kilogram threshold.

474
00:22:26,119 --> 00:22:28,800
Speaker 2: No doubt it was arbitrary. No, somebody must have looked

475
00:22:28,800 --> 00:22:30,919
Speaker 2: at an animal and been like, you're too small.

476
00:22:32,960 --> 00:22:35,520
Speaker 3: How much do you weigh? You are now our threshold?

477
00:22:36,200 --> 00:22:39,120
Speaker 1: Oh, I didn't hurt that poor animal's feelings.

478
00:22:39,200 --> 00:22:39,680
Speaker 3: Well, we'll get it.

479
00:22:39,920 --> 00:22:41,960
Speaker 2: I mean, the good news if you're below the threshold.

480
00:22:41,960 --> 00:22:44,480
Speaker 2: It sounds like you were maybe less susceptible to extinction

481
00:22:45,000 --> 00:22:47,080
Speaker 2: caused by humans, So maybe you'd be happy if you

482
00:22:47,080 --> 00:22:48,680
Speaker 2: were under this arbitrary threshold.

483
00:22:48,800 --> 00:22:51,440
Speaker 1: So tell us about these megafauna that used to roam

484
00:22:51,520 --> 00:22:51,960
Speaker 1: the earth.

485
00:22:52,200 --> 00:22:55,520
Speaker 2: Okay, So this large megafauna includes things like you mentioned

486
00:22:55,600 --> 00:22:58,720
Speaker 2: at the beginning of the show, like lions that used

487
00:22:58,720 --> 00:23:02,280
Speaker 2: to be found much farther north. There were also giant

488
00:23:02,359 --> 00:23:06,119
Speaker 2: ground sloths. There were kangaroos that were much larger, and

489
00:23:06,160 --> 00:23:08,959
Speaker 2: there were mammoths. There were just lots of much larger

490
00:23:09,040 --> 00:23:13,400
Speaker 2: mammals that were roaming the earth. And somewhere between ten

491
00:23:13,440 --> 00:23:16,320
Speaker 2: to fifty thousand years ago, about two hundred of these

492
00:23:16,400 --> 00:23:18,919
Speaker 2: large mammal species went extinct.

493
00:23:19,160 --> 00:23:19,640
Speaker 1: Wow.

494
00:23:19,760 --> 00:23:23,840
Speaker 2: And this is called the quarternary megafauna extinction QM.

495
00:23:24,280 --> 00:23:26,960
Speaker 1: And is there a bigger trend here that like animals

496
00:23:26,960 --> 00:23:29,800
Speaker 1: get bigger and bigger, because like dinosaurs got really huge

497
00:23:30,240 --> 00:23:31,960
Speaker 1: and then you know, the biggest ones died out, and

498
00:23:31,960 --> 00:23:34,639
Speaker 1: then mammals come along and then they eventually got big.

499
00:23:35,040 --> 00:23:37,800
Speaker 1: Is this some sort of evolutionary trend that like, eventually

500
00:23:37,800 --> 00:23:40,400
Speaker 1: somebody finds the niche of like being too big to eat?

501
00:23:40,600 --> 00:23:42,800
Speaker 2: I mean, I'm sure a lot of things go into

502
00:23:43,359 --> 00:23:47,000
Speaker 2: optimal size for animals. Being big does make you too

503
00:23:47,080 --> 00:23:48,760
Speaker 2: big to eat, but you know, like so t rex

504
00:23:48,840 --> 00:23:52,239
Speaker 2: was a big predator, and you know, blue whales are

505
00:23:52,240 --> 00:23:54,800
Speaker 2: also big predators, but they're going after kraill, So it's

506
00:23:54,840 --> 00:23:56,359
Speaker 2: not they don't have to be big so that they

507
00:23:56,359 --> 00:23:59,359
Speaker 2: can be vicious and take downloaded animals. They're eating teeny

508
00:23:59,359 --> 00:24:02,720
Speaker 2: tiny little creatures called kraill, little crustaceans in the ocean,

509
00:24:03,440 --> 00:24:04,840
Speaker 2: and so, yeah, I'm sure a lot of things go

510
00:24:04,960 --> 00:24:07,600
Speaker 2: into being big, but it is a niche that sometimes

511
00:24:07,640 --> 00:24:11,000
Speaker 2: makes sense to fill. Yeah, about ten to fifty thousand

512
00:24:11,040 --> 00:24:13,240
Speaker 2: years ago, we lost a bunch of these species. And

513
00:24:13,440 --> 00:24:18,720
Speaker 2: the question is why, and you know, probably because it's biology,

514
00:24:18,840 --> 00:24:19,919
Speaker 2: the answer is it depends.

515
00:24:19,960 --> 00:24:21,359
Speaker 3: There's probably a lot of different factors.

516
00:24:21,400 --> 00:24:23,000
Speaker 2: It could have been that climate was changing at the

517
00:24:23,040 --> 00:24:25,840
Speaker 2: time as well, but there's pretty good evidence to suggest

518
00:24:25,880 --> 00:24:28,679
Speaker 2: that one of the major causes of this decline in

519
00:24:28,760 --> 00:24:31,760
Speaker 2: large mammals was the fact that humans were starting to

520
00:24:31,840 --> 00:24:32,760
Speaker 2: move into.

521
00:24:32,520 --> 00:24:36,680
Speaker 3: New areas, so lunch basically lunch. Yes, that's right.

522
00:24:36,840 --> 00:24:41,600
Speaker 2: So, for example, about fourteen of the sixteen large mammal

523
00:24:41,640 --> 00:24:46,160
Speaker 2: species that were present in Australia went extinct between about

524
00:24:46,200 --> 00:24:49,439
Speaker 2: thirty and fifty thousand years ago, and humans showed up

525
00:24:49,480 --> 00:24:52,840
Speaker 2: about forty to sixty thousand years ago, So the numbers

526
00:24:52,840 --> 00:24:55,760
Speaker 2: don't match up exactly, but some evidence that humans show

527
00:24:55,840 --> 00:25:00,359
Speaker 2: up and those species go extinct. In North America, humans

528
00:25:00,440 --> 00:25:04,800
Speaker 2: arrived around like twelve to twenty thousand years ago, and

529
00:25:05,080 --> 00:25:08,159
Speaker 2: eighty three percent of the large mammals in North America,

530
00:25:08,240 --> 00:25:10,960
Speaker 2: which was thirty four out of forty seven species, went

531
00:25:11,040 --> 00:25:14,280
Speaker 2: extinct somewhere between eleven to fifteen thousand years ago. So

532
00:25:14,359 --> 00:25:17,800
Speaker 2: we show up, eighty three percent of the large mammals disappear.

533
00:25:17,960 --> 00:25:20,240
Speaker 1: And I guess it's easy to draw the doged line

534
00:25:20,280 --> 00:25:22,600
Speaker 1: to say, like, well, humans probably killed them, or humans

535
00:25:22,600 --> 00:25:24,879
Speaker 1: maybe ate them or whatever. But it could also be

536
00:25:24,920 --> 00:25:28,359
Speaker 1: more complex, right, Humans arriving could change the ecosystem, and

537
00:25:28,440 --> 00:25:31,639
Speaker 1: these megafauna could be sensitive to like the web underneath

538
00:25:31,640 --> 00:25:33,880
Speaker 1: them that are changing. Maybe humans are eating something else

539
00:25:33,880 --> 00:25:36,720
Speaker 1: the megafauna were eating or something. It could just be

540
00:25:36,760 --> 00:25:38,040
Speaker 1: more complicated.

541
00:25:37,560 --> 00:25:40,399
Speaker 2: Right absolutely, Or maybe we brought some disease that jumped

542
00:25:40,440 --> 00:25:43,360
Speaker 2: from us to them, or we brought some other domesticated

543
00:25:43,400 --> 00:25:46,000
Speaker 2: animals along that killed them in some way, so yeah,

544
00:25:46,000 --> 00:25:48,399
Speaker 2: there's a lot of complicated It's not just necessarily that

545
00:25:48,480 --> 00:25:52,200
Speaker 2: we like ran after them with spears and we ate them, but.

546
00:25:52,160 --> 00:25:53,199
Speaker 1: We probably did a little of that too.

547
00:25:53,440 --> 00:25:54,520
Speaker 3: Yeah, no, I'm not sure.

548
00:25:54,520 --> 00:25:58,240
Speaker 2: There's some fossil evidence that we did some of that too. Yeah,

549
00:25:58,280 --> 00:26:01,480
Speaker 2: we needed to eat. But anyway, there is this correlational

550
00:26:01,520 --> 00:26:04,560
Speaker 2: evidence that when humans show up on a new continent

551
00:26:05,040 --> 00:26:08,600
Speaker 2: not that long after, a large percent of their large

552
00:26:08,600 --> 00:26:09,680
Speaker 2: mammals go extinct.

553
00:26:09,800 --> 00:26:11,959
Speaker 1: And I guess another thing we should consider is there

554
00:26:11,960 --> 00:26:15,359
Speaker 1: could be like confounding factors also, like something which caused

555
00:26:15,400 --> 00:26:18,080
Speaker 1: humans to move there and could also cause the extinction,

556
00:26:18,520 --> 00:26:21,360
Speaker 1: but which wouldn't put the blame on humanity really at all.

557
00:26:21,560 --> 00:26:22,160
Speaker 3: Yeah, that's right.

558
00:26:22,200 --> 00:26:25,240
Speaker 2: So if there were, for example, large climactic changes that

559
00:26:25,359 --> 00:26:28,000
Speaker 2: made some areas bad for humans, and they were migrating

560
00:26:28,320 --> 00:26:30,840
Speaker 2: in search of new food sources or something, right, it

561
00:26:30,880 --> 00:26:32,640
Speaker 2: could be that humans came at the same time as

562
00:26:32,640 --> 00:26:35,240
Speaker 2: the climate change. There have been people who have looked

563
00:26:35,240 --> 00:26:38,160
Speaker 2: into this, and I think that they conclude that humans

564
00:26:38,160 --> 00:26:40,680
Speaker 2: still probably played a role even after you control for

565
00:26:40,760 --> 00:26:42,960
Speaker 2: some other stuff that we know was happening at that time,

566
00:26:43,280 --> 00:26:46,760
Speaker 2: but it probably wasn't just humans, but it looks like mammals.

567
00:26:46,840 --> 00:26:47,600
Speaker 3: Large mammals in.

568
00:26:47,560 --> 00:26:51,359
Speaker 2: Particular were susceptible to death around this time, not just

569
00:26:51,400 --> 00:26:53,280
Speaker 2: because we were hunting them or whatever it was about

570
00:26:53,359 --> 00:26:55,879
Speaker 2: humans that caused them to die, but in particular, large

571
00:26:55,880 --> 00:26:59,199
Speaker 2: mammals tend to have They live a long time, but

572
00:26:59,480 --> 00:27:02,000
Speaker 2: it takes a long time for them to start making babies,

573
00:27:02,119 --> 00:27:04,359
Speaker 2: and when they do make babies, they don't make a

574
00:27:04,400 --> 00:27:06,960
Speaker 2: lot of them. You may remember our conversation about k

575
00:27:07,119 --> 00:27:10,840
Speaker 2: selected species that we had with Katie Golden. So large

576
00:27:10,840 --> 00:27:13,159
Speaker 2: mammals tend to not have a lot of babies to

577
00:27:13,320 --> 00:27:15,440
Speaker 2: begin with, so it's a little bit easier to kill

578
00:27:15,480 --> 00:27:18,000
Speaker 2: them off because they can't sort of bounce back as quickly.

579
00:27:18,119 --> 00:27:21,399
Speaker 1: Fascinating, and so the question really is like, why didn't

580
00:27:21,440 --> 00:27:23,800
Speaker 1: the same thing happen in Africa. It seems like Africa

581
00:27:23,880 --> 00:27:27,880
Speaker 1: has more megafauna than the other continents. Why is that?

582
00:27:28,200 --> 00:27:29,440
Speaker 3: Yeah, that is a great question.

583
00:27:29,520 --> 00:27:32,520
Speaker 2: So during the same period, only ten of the forty

584
00:27:32,560 --> 00:27:35,760
Speaker 2: eight large mammal species in Africa went extinct, and in

585
00:27:35,800 --> 00:27:38,560
Speaker 2: Eurasia they lost nine of twenty six species, so that's

586
00:27:38,560 --> 00:27:42,880
Speaker 2: a much lower percent. The current hypothesis is that humans

587
00:27:42,960 --> 00:27:44,440
Speaker 2: evolved in these areas.

588
00:27:44,760 --> 00:27:46,600
Speaker 3: So as our species.

589
00:27:46,200 --> 00:27:48,720
Speaker 2: Was picking up the skills for hunting and stuff like that,

590
00:27:49,240 --> 00:27:52,040
Speaker 2: we were evolving alongside of these species. So as we

591
00:27:52,080 --> 00:27:54,960
Speaker 2: got better, we didn't get like great at this overnight,

592
00:27:54,960 --> 00:27:57,560
Speaker 2: but as we got better, selection was sort of favoring

593
00:27:57,600 --> 00:28:02,560
Speaker 2: traits in, for example, elephants, to help them stay essentially

594
00:28:02,560 --> 00:28:05,520
Speaker 2: stay away from humans and keep themselves alive in the

595
00:28:05,520 --> 00:28:08,399
Speaker 2: face of this sort of growing super predator which we

596
00:28:08,400 --> 00:28:10,840
Speaker 2: would end up becoming. And so the idea here is

597
00:28:10,840 --> 00:28:15,040
Speaker 2: that Africa and Eurasia, those animals evolved with us, and

598
00:28:15,119 --> 00:28:17,359
Speaker 2: so they were just better able to escape us. But

599
00:28:17,400 --> 00:28:19,879
Speaker 2: then when we went to somewhere new like Australia and

600
00:28:19,880 --> 00:28:23,600
Speaker 2: North America, and these animals had never seen anything like us,

601
00:28:24,560 --> 00:28:26,360
Speaker 2: all of a sudden we show up with our spears

602
00:28:26,400 --> 00:28:30,080
Speaker 2: and they are just no match for the super predators

603
00:28:30,080 --> 00:28:31,440
Speaker 2: who just landed on their continent.

604
00:28:31,640 --> 00:28:35,240
Speaker 1: Wow. Fascinating. So it's actually good luck to evolve together

605
00:28:35,280 --> 00:28:37,280
Speaker 1: with humans, right, rather than just have them show up

606
00:28:37,280 --> 00:28:37,920
Speaker 1: at your doorstep.

607
00:28:38,200 --> 00:28:40,880
Speaker 2: You want humans to be bugging you for thousands of years,

608
00:28:40,960 --> 00:28:44,000
Speaker 2: not just showing up unannounced. When we show up unannounced,

609
00:28:44,040 --> 00:28:46,040
Speaker 2: we are particularly problematic guests.

610
00:28:46,160 --> 00:28:48,560
Speaker 1: And what about this other idea that Adam r raises

611
00:28:48,760 --> 00:28:53,000
Speaker 1: about how elephants can like understand human language and guess

612
00:28:53,040 --> 00:28:54,920
Speaker 1: our intentions. Is there anything to that.

613
00:28:55,000 --> 00:28:57,160
Speaker 2: I don't think Adam Or in particular was trying to

614
00:28:57,200 --> 00:29:01,440
Speaker 2: say that elephants can understand language. They sent a paper

615
00:29:01,480 --> 00:29:05,320
Speaker 2: from twenty fourteen by macomb at All in proceedings of

616
00:29:05,400 --> 00:29:08,520
Speaker 2: the National Academy of Sciences, and essentially what they did

617
00:29:08,560 --> 00:29:11,280
Speaker 2: here was they tried to figure out if elephants, just

618
00:29:11,360 --> 00:29:14,440
Speaker 2: from hearing an audio clip would respond in a way

619
00:29:14,440 --> 00:29:16,680
Speaker 2: that suggested that they knew that different kinds of people

620
00:29:16,720 --> 00:29:19,280
Speaker 2: differed in the risk that they posed to the elephants.

621
00:29:19,440 --> 00:29:19,880
Speaker 1: Wow.

622
00:29:20,040 --> 00:29:20,240
Speaker 3: Yeah.

623
00:29:20,280 --> 00:29:25,000
Speaker 2: For example, the Massi people are pastoralists, so their grazing

624
00:29:25,160 --> 00:29:28,960
Speaker 2: land and water holes are often areas that are also

625
00:29:29,040 --> 00:29:32,320
Speaker 2: used by elephants and are used by the livestock that

626
00:29:32,360 --> 00:29:35,560
Speaker 2: the Massi are sort of walking around the area, and

627
00:29:35,600 --> 00:29:38,360
Speaker 2: so they often come in conflict and sometimes the elephants

628
00:29:38,400 --> 00:29:42,120
Speaker 2: will kill Massi and the Massai need to essentially defend themselves.

629
00:29:42,800 --> 00:29:45,920
Speaker 2: On the other hand, the Kamba people are more agricultural

630
00:29:46,040 --> 00:29:48,600
Speaker 2: and they rarely have run ins with elephants, and when

631
00:29:48,640 --> 00:29:51,080
Speaker 2: they do have run ins, it's usually like a male

632
00:29:51,160 --> 00:29:54,880
Speaker 2: elephant who has sort of invaded their field, and so

633
00:29:55,080 --> 00:29:58,280
Speaker 2: the Kamba people are often leaving alone females and the

634
00:29:58,320 --> 00:30:03,040
Speaker 2: groups of females with their babies. And additionally, human females,

635
00:30:03,160 --> 00:30:07,120
Speaker 2: whether the Massi or Kamba, are unlikely to kill elephants,

636
00:30:07,160 --> 00:30:09,840
Speaker 2: and young boys are also unlikely to kill elephants. The

637
00:30:09,840 --> 00:30:12,680
Speaker 2: people who are most likely to kill elephants are adult men.

638
00:30:13,280 --> 00:30:16,640
Speaker 2: So they did this playback experiment where they had everybody

639
00:30:16,720 --> 00:30:19,840
Speaker 2: read the same sentence, and the sentence was look over there,

640
00:30:20,000 --> 00:30:22,600
Speaker 2: a group of elephants is coming, and they said it

641
00:30:22,680 --> 00:30:25,000
Speaker 2: in their own language, and then they look to see

642
00:30:25,040 --> 00:30:28,600
Speaker 2: what the elephants did. And when you played a Massi

643
00:30:28,680 --> 00:30:32,680
Speaker 2: man saying that sentence, the elephants would bunch together in

644
00:30:32,720 --> 00:30:35,400
Speaker 2: a defensive like huddle, and they would respond in a

645
00:30:35,400 --> 00:30:39,160
Speaker 2: way that suggested that they were experiencing fear because a

646
00:30:39,200 --> 00:30:40,120
Speaker 2: predator was around.

647
00:30:40,280 --> 00:30:40,680
Speaker 1: Wow.

648
00:30:40,920 --> 00:30:42,480
Speaker 2: Yeah, and they did less of that when they heard

649
00:30:42,480 --> 00:30:45,000
Speaker 2: the Kamba people. And remember, these are people that often

650
00:30:45,120 --> 00:30:47,200
Speaker 2: don't end up in positions where they need to defend

651
00:30:47,240 --> 00:30:51,680
Speaker 2: themselves in their livelihoods against elephants. The elephants also responded

652
00:30:51,680 --> 00:30:54,160
Speaker 2: more strongly to the sound of men than women, and

653
00:30:54,200 --> 00:30:57,480
Speaker 2: more strongly to the sound of men massi relative to

654
00:30:57,640 --> 00:31:00,640
Speaker 2: boy massi. So the elephants, you seem to have a

655
00:31:00,640 --> 00:31:03,200
Speaker 2: pretty good sense that, like, humans are risky, but some

656
00:31:03,320 --> 00:31:06,040
Speaker 2: kinds of humans are more risky than others, and so

657
00:31:06,080 --> 00:31:08,640
Speaker 2: they seem to have this like nuanced ability to tell

658
00:31:08,760 --> 00:31:10,360
Speaker 2: human risk and respond accordingly.

659
00:31:10,560 --> 00:31:12,600
Speaker 1: I told you the elephants are listening. They got those

660
00:31:12,600 --> 00:31:15,160
Speaker 1: big ears, and they can tell when you're talking about them.

661
00:31:15,480 --> 00:31:18,800
Speaker 2: That's right, that's right, and they never forget and so

662
00:31:18,800 --> 00:31:21,320
Speaker 2: so you got to be extra careful. But it's worth

663
00:31:21,360 --> 00:31:25,040
Speaker 2: noting that many animals respond to humans as though we

664
00:31:25,080 --> 00:31:28,400
Speaker 2: are risky. And that's even in North America. In Europe,

665
00:31:28,440 --> 00:31:31,880
Speaker 2: they've done playback experiments with badgers that freak out if

666
00:31:31,920 --> 00:31:35,040
Speaker 2: you play sounds at water holes. In Africa, just about

667
00:31:35,080 --> 00:31:38,080
Speaker 2: every species that hears the sound of a human, they'll

668
00:31:38,120 --> 00:31:40,120
Speaker 2: respond more strongly to the sound of a human than

669
00:31:40,120 --> 00:31:41,480
Speaker 2: the sound of a lion.

670
00:31:41,680 --> 00:31:41,880
Speaker 1: Wow.

671
00:31:42,000 --> 00:31:44,400
Speaker 2: So in general, just about any continent you go to,

672
00:31:44,760 --> 00:31:48,280
Speaker 2: the animals know humans often mean trouble. We should we

673
00:31:48,320 --> 00:31:51,800
Speaker 2: should leave town or get defensive. We're going to cause

674
00:31:51,840 --> 00:31:54,160
Speaker 2: some trouble. So this is sort of an unrelated topic

675
00:31:54,640 --> 00:31:57,760
Speaker 2: than the extinction of animals. This is more like what

676
00:31:57,840 --> 00:32:00,720
Speaker 2: are animals doing in this day and age to respond

677
00:32:00,720 --> 00:32:02,800
Speaker 2: to humans? And maybe elephants were doing this back in

678
00:32:02,840 --> 00:32:04,840
Speaker 2: the past and that's what saved them from getting killed

679
00:32:04,840 --> 00:32:07,560
Speaker 2: by us. They just kind of gave us space. But

680
00:32:07,680 --> 00:32:11,640
Speaker 2: in general, humans can be devastating to wildlife.

681
00:32:12,480 --> 00:32:15,120
Speaker 1: Well, let's say some nice things about humans to balance

682
00:32:15,120 --> 00:32:17,240
Speaker 1: it out. You know, I think it's incredible that we

683
00:32:17,280 --> 00:32:20,560
Speaker 1: can unravel these stories. Recently, Hazel made this comment. She

684
00:32:20,640 --> 00:32:23,360
Speaker 1: was like, all sciences basically stuff happened and we figured

685
00:32:23,360 --> 00:32:25,840
Speaker 1: out why. And I was like, you know, that's a

686
00:32:25,880 --> 00:32:29,320
Speaker 1: pretty good point, Hazel. And it touches on this incredible

687
00:32:29,360 --> 00:32:31,360
Speaker 1: thing that we do in science, which is like gather

688
00:32:31,520 --> 00:32:35,560
Speaker 1: these clues that are just like randomly accidentally left imprinted

689
00:32:35,680 --> 00:32:38,200
Speaker 1: on the world to figure out what happened, right, to

690
00:32:38,280 --> 00:32:41,720
Speaker 1: unravel this incredible story you're telling over tens of thousands

691
00:32:41,720 --> 00:32:44,480
Speaker 1: of years about these huge animals that no longer exist

692
00:32:44,600 --> 00:32:48,280
Speaker 1: and why and a complicated interplay between species. It's incredible

693
00:32:48,320 --> 00:32:50,240
Speaker 1: to me that we can unravel these stories, that we

694
00:32:50,320 --> 00:32:53,560
Speaker 1: can pull them out, sometimes literally out of the ground,

695
00:32:54,040 --> 00:32:56,320
Speaker 1: to learn the deep history of our universe.

696
00:32:56,480 --> 00:32:59,640
Speaker 2: Yeah, and you are always a more optimistic and uplifting

697
00:32:59,680 --> 00:33:00,640
Speaker 2: person than I am.

698
00:33:00,800 --> 00:33:02,880
Speaker 3: And so that that's beautiful.

699
00:33:02,440 --> 00:33:05,480
Speaker 2: And I'll attempt to follow in your footsteps by noting

700
00:33:05,880 --> 00:33:08,959
Speaker 2: that by understanding the damage we've done in the past,

701
00:33:09,360 --> 00:33:12,400
Speaker 2: you know, we can try to ameliorate the damage that

702
00:33:12,440 --> 00:33:14,560
Speaker 2: we might be doing now or the damage we might

703
00:33:14,640 --> 00:33:16,560
Speaker 2: be doing in the future. And so, you know, the

704
00:33:16,600 --> 00:33:20,560
Speaker 2: conservation movement has grown in you know, the last couple decades,

705
00:33:20,560 --> 00:33:23,280
Speaker 2: and we're getting better at caring about this stuff and

706
00:33:23,360 --> 00:33:26,560
Speaker 2: trying to at least slow the decline of some of

707
00:33:26,560 --> 00:33:29,520
Speaker 2: these species and in other cases turn around the decline

708
00:33:29,520 --> 00:33:32,760
Speaker 2: of species. So you know, if we can recognize our

709
00:33:32,800 --> 00:33:35,160
Speaker 2: past mistakes, we can hopefully use that information to do

710
00:33:35,240 --> 00:33:36,080
Speaker 2: better in the future.

711
00:33:36,520 --> 00:33:39,520
Speaker 1: Well, can I say something controversial? Do you think that

712
00:33:39,600 --> 00:33:43,680
Speaker 1: an individual species on its own has like inherent value?

713
00:33:43,760 --> 00:33:46,760
Speaker 1: Like should we be conserving every species or should we

714
00:33:46,760 --> 00:33:49,960
Speaker 1: take a bigger, broader view and say, Look, diversity is

715
00:33:50,000 --> 00:33:52,960
Speaker 1: important and that means that new species should be evolving

716
00:33:53,000 --> 00:33:55,720
Speaker 1: and sometimes species disappear, it's just part of the process.

717
00:33:56,240 --> 00:33:58,720
Speaker 1: Should we be trying to hold onto every individual species

718
00:33:58,800 --> 00:34:01,560
Speaker 1: or should we be maintaining diversity sort of in a

719
00:34:01,640 --> 00:34:02,280
Speaker 1: larger sense?

720
00:34:03,000 --> 00:34:06,880
Speaker 3: Wow, all right, So that question deserves like a whole episode.

721
00:34:06,880 --> 00:34:11,000
Speaker 2: But the short answer is, so there's a background extinction rate,

722
00:34:11,120 --> 00:34:16,000
Speaker 2: So you shouldn't necessarily lose sleep if a species goes extinct,

723
00:34:16,120 --> 00:34:17,839
Speaker 2: because that was going to happen whether humans were here

724
00:34:17,920 --> 00:34:20,720
Speaker 2: or not. But I believe the extinction rate is something

725
00:34:20,840 --> 00:34:24,200
Speaker 2: like it's at least ten times higher than we would

726
00:34:24,239 --> 00:34:26,839
Speaker 2: expect it to be based on background levels, So we

727
00:34:26,880 --> 00:34:31,160
Speaker 2: are really speeding things up for any particular species. I mean,

728
00:34:31,200 --> 00:34:34,480
Speaker 2: there are some species that play less important roles in ecosystems,

729
00:34:34,560 --> 00:34:36,960
Speaker 2: losing them would have less of an impact, but that's

730
00:34:37,000 --> 00:34:41,120
Speaker 2: still like a unique product of millions of years of

731
00:34:41,160 --> 00:34:45,280
Speaker 2: evolution that is beautiful and well adapted to its environment

732
00:34:45,320 --> 00:34:48,680
Speaker 2: and is being wiped out, you know, because of us,

733
00:34:48,840 --> 00:34:51,960
Speaker 2: And that to me does feel catastrophic and really sad.

734
00:34:52,200 --> 00:34:53,799
Speaker 2: And you know, I feel like you have to be

735
00:34:53,840 --> 00:34:57,040
Speaker 2: able to accept nuance in these conversations and weigh pros

736
00:34:57,080 --> 00:34:59,160
Speaker 2: and cons and stuff like that, but you know, I

737
00:34:59,440 --> 00:35:02,200
Speaker 2: do feel like time we lose a species, it is sad,

738
00:35:02,280 --> 00:35:04,120
Speaker 2: even if it's just a beetle that was present in

739
00:35:04,160 --> 00:35:05,160
Speaker 2: only one place.

740
00:35:05,000 --> 00:35:08,440
Speaker 1: Or something, well, it is an incredible output of evolution,

741
00:35:08,600 --> 00:35:13,160
Speaker 1: you know, it's like effectively billions of years of biological computation,

742
00:35:13,920 --> 00:35:16,680
Speaker 1: you know, to design this creator that can do something

743
00:35:16,760 --> 00:35:20,480
Speaker 1: amazing or has incredible chemicals in it. Anyway, stay tuned,

744
00:35:20,520 --> 00:35:23,520
Speaker 1: everybody for the upcoming episode where Daniel argues that extinction

745
00:35:23,680 --> 00:35:25,759
Speaker 1: is good. Actually, what.

746
00:35:27,320 --> 00:35:31,080
Speaker 2: Like all the extinction or just like I mean, this

747
00:35:31,160 --> 00:35:35,320
Speaker 2: might be the last episode of Extraordinary Universe.

748
00:35:36,840 --> 00:35:39,160
Speaker 1: All right, well we'll dig into that for another episode.

749
00:35:39,200 --> 00:35:42,240
Speaker 1: In the meantime, let's hear from Adamar about whether Kelly

750
00:35:42,320 --> 00:35:43,400
Speaker 1: answered their question.

751
00:35:43,800 --> 00:35:46,719
Speaker 6: Hello, young guys, and thank you for your response. It

752
00:35:46,800 --> 00:35:50,480
Speaker 6: makes me glad to think that possibly we're not the

753
00:35:50,600 --> 00:35:55,040
Speaker 6: only reason that those animals one extinct, And Kelly's context

754
00:35:55,160 --> 00:35:57,960
Speaker 6: really makes me think in a why that spectrum, like,

755
00:35:58,200 --> 00:36:01,640
Speaker 6: for example, what if it was the disease, what if

756
00:36:01,680 --> 00:36:05,000
Speaker 6: it was a glaciation the same we were running away from,

757
00:36:05,440 --> 00:36:09,400
Speaker 6: or maybe it wasn't other super predator anyway, who knows?

758
00:36:09,760 --> 00:36:32,080
Speaker 6: Thank you and keep up the Wool's work. All right.

759
00:36:32,160 --> 00:36:34,880
Speaker 2: I'm still trying to decide if I can forgive Daniel

760
00:36:34,920 --> 00:36:38,520
Speaker 2: for hinting that extinction caused by humans isn't always bad.

761
00:36:38,920 --> 00:36:41,160
Speaker 2: But you know what, I'm going to distract myself with

762
00:36:41,239 --> 00:36:43,280
Speaker 2: this insightful question from a listener.

763
00:36:43,440 --> 00:36:46,040
Speaker 5: Hey, Daniel and Kelly, really enjoying the podcast. Thank you.

764
00:36:46,280 --> 00:36:48,600
Speaker 5: I have a question for you, and it's about black holes.

765
00:36:48,640 --> 00:36:52,120
Speaker 5: Of course, black holes are usually described as unslakable consumers

766
00:36:52,120 --> 00:36:53,920
Speaker 5: of all matter and energy, but I know in some

767
00:36:54,000 --> 00:36:56,400
Speaker 5: cases the rate of consumption is limited by the energy

768
00:36:56,440 --> 00:36:59,960
Speaker 5: pressure of that consumption process, pushing back on the gravitation

769
00:37:00,200 --> 00:37:03,000
Speaker 5: pull and starving it of additional fuel. I would love

770
00:37:03,040 --> 00:37:04,880
Speaker 5: to hear more about what this might be like on

771
00:37:04,880 --> 00:37:07,800
Speaker 5: a more human scale, with a tiny primordial black hole

772
00:37:08,040 --> 00:37:10,680
Speaker 5: around the Earth generate a tiny accretion disc of matter

773
00:37:10,719 --> 00:37:13,280
Speaker 5: spinning around a light speed, generating the same kind of pressure,

774
00:37:13,320 --> 00:37:15,800
Speaker 5: and shooting out X ray lasers from the top and bottom.

775
00:37:16,160 --> 00:37:18,400
Speaker 5: How big or small would a black hole be to

776
00:37:18,440 --> 00:37:20,560
Speaker 5: have these sorts of effects. When we think of a

777
00:37:20,560 --> 00:37:23,359
Speaker 5: black hole interactive with normal human scale matter, what would

778
00:37:23,360 --> 00:37:25,400
Speaker 5: that look like? How long could the Earth survive with

779
00:37:25,400 --> 00:37:27,919
Speaker 5: a little black hole orbiting around inside of it? Really

780
00:37:27,920 --> 00:37:29,680
Speaker 5: looking forward to hearing more about this. Thank you.

781
00:37:30,120 --> 00:37:32,279
Speaker 1: Thank you David very much for that question. And I

782
00:37:32,320 --> 00:37:33,880
Speaker 1: hope that our answer is not going to help you

783
00:37:34,160 --> 00:37:37,120
Speaker 1: build a miniature black hole to embed into the Earth.

784
00:37:37,440 --> 00:37:39,320
Speaker 1: So We're just going to take it on good faith

785
00:37:39,360 --> 00:37:40,840
Speaker 1: and answer your question anyway.

786
00:37:41,440 --> 00:37:43,520
Speaker 3: That also sounds like a good topic for a sci

787
00:37:43,520 --> 00:37:44,120
Speaker 3: fi novel.

788
00:37:44,719 --> 00:37:46,840
Speaker 1: Let's talk about black holes and start with the basics,

789
00:37:46,880 --> 00:37:49,880
Speaker 1: because David's question involves a lot of sort of sophisticated

790
00:37:49,960 --> 00:37:54,360
Speaker 1: black hole science. Remember, black holes are regions of space

791
00:37:54,440 --> 00:37:57,200
Speaker 1: time where there's so much mass that there's so much

792
00:37:57,239 --> 00:38:01,200
Speaker 1: curvature that anything that falls beyond the event and eventually

793
00:38:01,239 --> 00:38:04,560
Speaker 1: reaches the center it can never escape. And something I

794
00:38:04,560 --> 00:38:06,640
Speaker 1: think a lot of people don't understand about black holes

795
00:38:06,680 --> 00:38:09,320
Speaker 1: is that the event horizon is not a physical surface.

796
00:38:09,760 --> 00:38:12,880
Speaker 1: It's just a designation. We make a dotted line, we draw,

797
00:38:13,400 --> 00:38:15,840
Speaker 1: and actually you never know where the event horizon is

798
00:38:15,880 --> 00:38:19,400
Speaker 1: at any moment. You can only tell in the infinite future. Essentially,

799
00:38:19,600 --> 00:38:22,160
Speaker 1: think about going to the infinite future and then asking

800
00:38:22,200 --> 00:38:26,000
Speaker 1: the question, in what regions of space did particles never escape?

801
00:38:26,200 --> 00:38:28,880
Speaker 1: Will now draw that to be the event horizon, and

802
00:38:28,960 --> 00:38:31,239
Speaker 1: so you can't ever really actually know. You can use

803
00:38:31,320 --> 00:38:34,120
Speaker 1: gr to predict at any moment, but the event horizon

804
00:38:34,200 --> 00:38:37,280
Speaker 1: is just like a categorization. We say, beyond this point,

805
00:38:37,560 --> 00:38:40,680
Speaker 1: nothing has escaped or can escape, and outside that point,

806
00:38:40,760 --> 00:38:44,200
Speaker 1: things can escape. But this is just gravity, right. Black

807
00:38:44,200 --> 00:38:47,480
Speaker 1: holes don't like suck with infinite power or anything. If

808
00:38:47,480 --> 00:38:49,400
Speaker 1: you replace the Sun with the black hole of the

809
00:38:49,440 --> 00:38:51,680
Speaker 1: same mass, we would feel it's gravity and the Earth

810
00:38:51,680 --> 00:38:54,160
Speaker 1: would continue to orbit. So it really is just a

811
00:38:54,200 --> 00:38:55,400
Speaker 1: gravitational object.

812
00:38:55,680 --> 00:38:57,960
Speaker 2: Okay, So at black hole the same size as our

813
00:38:58,040 --> 00:39:01,880
Speaker 2: Sun wouldn't pull on us anymore than our Sun because

814
00:39:01,880 --> 00:39:03,120
Speaker 2: they're similarly dense.

815
00:39:03,480 --> 00:39:05,160
Speaker 1: If it has the same mass and it's at the

816
00:39:05,160 --> 00:39:06,960
Speaker 1: same distance, it would have the same gravity.

817
00:39:06,960 --> 00:39:07,920
Speaker 3: Okay, yeah, right, I'm with you.

818
00:39:08,000 --> 00:39:10,200
Speaker 1: It wouldn't be as bright, and the Earth would be chilly,

819
00:39:10,520 --> 00:39:13,680
Speaker 1: and it would be bad, but not gravitationally, all right.

820
00:39:13,560 --> 00:39:14,520
Speaker 3: I don't want that to happen.

821
00:39:15,880 --> 00:39:18,799
Speaker 2: Does the event horizon always stay at the exact same

822
00:39:18,840 --> 00:39:21,800
Speaker 2: spot or does it shift over time if the black

823
00:39:21,800 --> 00:39:25,280
Speaker 2: hole like absorbs big things that make it bigger.

824
00:39:25,440 --> 00:39:28,279
Speaker 1: Absolutely, the event horizon depends on the mass of the

825
00:39:28,320 --> 00:39:31,440
Speaker 1: black hole and not just on the stuff inside the

826
00:39:31,480 --> 00:39:33,600
Speaker 1: event horizon. Right. This is why you shouldn't think about

827
00:39:33,600 --> 00:39:36,880
Speaker 1: the event horizon as some physical barrier. As you approach

828
00:39:36,880 --> 00:39:40,520
Speaker 1: a black hole, your gravitational energy contributes to the mass

829
00:39:40,560 --> 00:39:43,480
Speaker 1: of the black hole, So the black hole's vent horizon

830
00:39:43,520 --> 00:39:46,359
Speaker 1: actually grows out to meet you as you fall into

831
00:39:46,400 --> 00:39:48,840
Speaker 1: the black hole. So you approach the event horizon, the

832
00:39:48,880 --> 00:39:53,640
Speaker 1: event horizon approaches you. It's like a little gravitational hug. Oh.

833
00:39:53,880 --> 00:39:54,040
Speaker 6: Yeah.

834
00:39:54,080 --> 00:39:55,640
Speaker 2: We talked about what would happen if Zach was in

835
00:39:55,719 --> 00:39:57,719
Speaker 2: a black hole and if we threw him sandwiches, would

836
00:39:57,719 --> 00:39:58,360
Speaker 2: they ever get to it?

837
00:39:58,480 --> 00:40:00,919
Speaker 1: Exactly? And the reason you need to understand that black

838
00:40:00,920 --> 00:40:03,080
Speaker 1: holes are not infinitely powerful is to think about the

839
00:40:03,120 --> 00:40:06,320
Speaker 1: stuff that's orbiting them, because that's what David's question was about.

840
00:40:06,320 --> 00:40:09,040
Speaker 1: This accretion disc. When you think about the images of

841
00:40:09,080 --> 00:40:11,279
Speaker 1: black holes out there in space, they look like a

842
00:40:11,320 --> 00:40:14,719
Speaker 1: glowing donut with a black core, or you know the

843
00:40:14,840 --> 00:40:19,480
Speaker 1: visualization in Interstellar or whatever. They have these luminous discs

844
00:40:19,520 --> 00:40:21,680
Speaker 1: around them. What is that and why aren't they getting

845
00:40:21,719 --> 00:40:24,359
Speaker 1: sucked in? Well, they're not getting sucked into the black

846
00:40:24,400 --> 00:40:26,040
Speaker 1: hole for the same reason the Earth is not getting

847
00:40:26,080 --> 00:40:28,720
Speaker 1: sucked into the Sun. Right, there's a lot of gravity

848
00:40:28,719 --> 00:40:31,359
Speaker 1: from the Sun. Why aren't we just getting sucked into

849
00:40:31,360 --> 00:40:33,520
Speaker 1: the Sun? And the answer is we have velocity. There

850
00:40:33,560 --> 00:40:36,319
Speaker 1: are stable orbits around the Sun, and the same way

851
00:40:36,320 --> 00:40:38,439
Speaker 1: there are stable orbits around a black hole. Because it's

852
00:40:38,480 --> 00:40:42,160
Speaker 1: just a gravitational object. So if you approach a black hole,

853
00:40:42,239 --> 00:40:44,560
Speaker 1: as long as you were outside the event horizon, you

854
00:40:44,600 --> 00:40:48,120
Speaker 1: could orbit around it forever without falling in if you

855
00:40:48,160 --> 00:40:51,239
Speaker 1: were stable and crucially nothing bumped into you to knock

856
00:40:51,280 --> 00:40:52,080
Speaker 1: you out of your orbit.

857
00:40:52,239 --> 00:40:54,000
Speaker 3: That doesn't sound fun, I'll pass.

858
00:40:54,960 --> 00:40:57,080
Speaker 1: And that's the same story for the Earth right now.

859
00:40:57,200 --> 00:40:59,360
Speaker 1: The accretion disc is very different because it's not just

860
00:40:59,440 --> 00:41:01,880
Speaker 1: like one chunk of matter here when chunk of matter there,

861
00:41:02,080 --> 00:41:04,759
Speaker 1: it's just like a huge hot disk of gas and

862
00:41:04,880 --> 00:41:07,640
Speaker 1: dust that has a lot of internal friction. That's why

863
00:41:07,719 --> 00:41:10,560
Speaker 1: it's glowing. The tidal forces from the black hole are

864
00:41:10,560 --> 00:41:13,280
Speaker 1: massaging it and heating it up, and it's rubbing against

865
00:41:13,320 --> 00:41:16,239
Speaker 1: itself and so it's very hot and it's glowing. So

866
00:41:16,280 --> 00:41:18,920
Speaker 1: that's why we can see these black holes. These telescope

867
00:41:18,920 --> 00:41:22,000
Speaker 1: pictures of black holes. Really they're pictures of the hot

868
00:41:22,040 --> 00:41:25,279
Speaker 1: accretion disc around the black hole. So the accretion disc

869
00:41:25,320 --> 00:41:27,839
Speaker 1: is stuff that's orbiting the black hole, hasn't fallen in yet,

870
00:41:27,960 --> 00:41:32,240
Speaker 1: is going too fast, probably will fall in eventually because

871
00:41:32,280 --> 00:41:34,120
Speaker 1: there's a lot of friction there. So you can't just

872
00:41:34,160 --> 00:41:36,160
Speaker 1: like have a stable orbit. But it's sort of like

873
00:41:36,280 --> 00:41:38,520
Speaker 1: on deck to go in the black hole, but not

874
00:41:38,640 --> 00:41:39,280
Speaker 1: there yet.

875
00:41:39,440 --> 00:41:41,520
Speaker 2: And what is that made out of? Is that just

876
00:41:41,560 --> 00:41:45,120
Speaker 2: like the basic dust and junk that you find in space, it's.

877
00:41:44,960 --> 00:41:47,040
Speaker 1: Made out of whatever you've been feeding your black hole.

878
00:41:47,080 --> 00:41:50,640
Speaker 1: But yeah, the universe is mostly hydrogen, so it's always

879
00:41:50,640 --> 00:41:53,279
Speaker 1: a safe bet to say it's mostly hydrogen because that's

880
00:41:53,280 --> 00:41:55,920
Speaker 1: what the universe is. And so yeah, there's gas and

881
00:41:55,960 --> 00:41:59,480
Speaker 1: this dust and whatever, but mostly it's hydrogen there. And

882
00:41:59,600 --> 00:42:02,279
Speaker 1: here's the black hole starts to work against itself because

883
00:42:02,280 --> 00:42:05,239
Speaker 1: the accretion disc is so hot that it glows, right,

884
00:42:05,280 --> 00:42:07,480
Speaker 1: that's where we can see these things. So it emits

885
00:42:07,600 --> 00:42:11,440
Speaker 1: radiation pressure, so it pushes stuff away. Right. We talked

886
00:42:11,440 --> 00:42:13,800
Speaker 1: in a recent episode about how stars are a balance

887
00:42:13,800 --> 00:42:17,120
Speaker 1: between gravity and radiation pressure. The fusion at their hot

888
00:42:17,160 --> 00:42:20,000
Speaker 1: core is producing a lot of energy and that pushes

889
00:42:20,080 --> 00:42:22,399
Speaker 1: out on the star, and if the star is too big,

890
00:42:22,440 --> 00:42:24,480
Speaker 1: it can actually blow the star apart. That's why you

891
00:42:24,480 --> 00:42:27,360
Speaker 1: have like a maximum size of stars. Well, a similar

892
00:42:27,400 --> 00:42:30,359
Speaker 1: thing is happening here. The heat from the accretion disk

893
00:42:30,480 --> 00:42:34,360
Speaker 1: creates radiation which pushes other stuff away. So the hotter

894
00:42:34,440 --> 00:42:36,440
Speaker 1: the black hole, the bigger the black hole, the bigger

895
00:42:36,440 --> 00:42:40,680
Speaker 1: the accretion disk the more it slows down its ability

896
00:42:40,719 --> 00:42:45,160
Speaker 1: to eat stuff. So black holes cannot grow infinitely quickly.

897
00:42:45,400 --> 00:42:47,759
Speaker 1: There's no theoretical upper limit to the size of a

898
00:42:47,800 --> 00:42:51,560
Speaker 1: black hole, but because of this process, this radiation pressure,

899
00:42:51,680 --> 00:42:54,480
Speaker 1: there is an upper limit to how rapidly they can grow.

900
00:42:54,719 --> 00:42:56,640
Speaker 1: You put a black hole in a blob of stuff,

901
00:42:56,800 --> 00:43:00,840
Speaker 1: it can't just like slurp everything out really quickly because

902
00:43:00,880 --> 00:43:02,560
Speaker 1: it's going to get hot and glow and push its

903
00:43:02,560 --> 00:43:03,920
Speaker 1: own food away from itself.

904
00:43:04,160 --> 00:43:07,440
Speaker 3: So what determines the size of the accretion disc.

905
00:43:07,760 --> 00:43:09,560
Speaker 1: It's just how much stuff was there around it. Like

906
00:43:09,600 --> 00:43:11,239
Speaker 1: if you put a black hole in deep space and

907
00:43:11,320 --> 00:43:13,600
Speaker 1: nothing is there, it have no accretion disc. It would

908
00:43:13,640 --> 00:43:15,640
Speaker 1: just be black. We could not see it except for

909
00:43:15,680 --> 00:43:18,239
Speaker 1: its gravitational effects. You drop in the middle of a

910
00:43:18,239 --> 00:43:20,400
Speaker 1: really big blob of stuff, it's going to get a

911
00:43:20,400 --> 00:43:23,640
Speaker 1: big accretion disc. So it just depends on what's around it.

912
00:43:24,320 --> 00:43:27,040
Speaker 1: And this is a really interesting puzzle in physics right

913
00:43:27,080 --> 00:43:30,400
Speaker 1: now because this limit on how quickly black holes can

914
00:43:30,440 --> 00:43:33,320
Speaker 1: grow is one of the reasons why we don't understand

915
00:43:33,440 --> 00:43:36,880
Speaker 1: super massive black holes. We see super massive black holes

916
00:43:36,920 --> 00:43:39,320
Speaker 1: in the early history of the universe, like a billion

917
00:43:39,440 --> 00:43:42,760
Speaker 1: years after the Big bang already we have black holes

918
00:43:42,760 --> 00:43:44,879
Speaker 1: with like billions of times the mass of the Sun.

919
00:43:45,440 --> 00:43:48,040
Speaker 1: But if you do the calculations the limit on the

920
00:43:48,080 --> 00:43:50,640
Speaker 1: speed of which black holes can grow, tell you that's impossible.

921
00:43:50,840 --> 00:43:52,960
Speaker 1: So how did they get so big? That's the big

922
00:43:53,040 --> 00:43:56,120
Speaker 1: question of super massive black holes, although we have some

923
00:43:56,400 --> 00:43:59,600
Speaker 1: interesting hints that like, if the accretion disc is asymmetric,

924
00:43:59,680 --> 00:44:03,080
Speaker 1: then can have what they call super Eddington accretion rates.

925
00:44:03,640 --> 00:44:07,240
Speaker 1: It's fascinating. But David's question is about tiny black holes,

926
00:44:07,239 --> 00:44:10,520
Speaker 1: and he's asking, can they also have accretion discs?

927
00:44:10,840 --> 00:44:13,320
Speaker 2: And you told me that it doesn't matter how big

928
00:44:13,360 --> 00:44:16,200
Speaker 2: a black hole is. What matters is the stuff that started.

929
00:44:16,239 --> 00:44:19,080
Speaker 2: So could a tiny black hole have a huge accretion disk?

930
00:44:20,440 --> 00:44:23,160
Speaker 1: So a tiny black hole can have accretion disc And

931
00:44:23,200 --> 00:44:25,560
Speaker 1: this Eddington limit of the rate of which black holes

932
00:44:25,600 --> 00:44:29,320
Speaker 1: can grow scales with mass, so the limit is smaller

933
00:44:29,360 --> 00:44:32,680
Speaker 1: with smaller mass. So there's like less radiation pressure from

934
00:44:32,719 --> 00:44:35,719
Speaker 1: a smaller mass black hole because it can't heat up

935
00:44:35,719 --> 00:44:38,520
Speaker 1: its accretion discs as much. But at a very small

936
00:44:38,520 --> 00:44:42,560
Speaker 1: black hole, something else happens. Right, black holes don't just

937
00:44:42,640 --> 00:44:45,719
Speaker 1: glow because of their accretion disc They are themselves not

938
00:44:46,080 --> 00:44:49,759
Speaker 1: totally black. We think they glow themselves with a little

939
00:44:49,800 --> 00:44:53,400
Speaker 1: bit of Hawking radiation. This is this bizarre radiation that

940
00:44:53,440 --> 00:44:56,080
Speaker 1: happens because you have an event horizon in quantum fields

941
00:44:56,480 --> 00:44:58,960
Speaker 1: and there's this hand wavy story out there about particles

942
00:44:58,960 --> 00:45:01,959
Speaker 1: and antiparticles or one falls into the event horizon. That's

943
00:45:02,040 --> 00:45:04,680
Speaker 1: just cartoons. It's not really the physics of what's happening.

944
00:45:05,080 --> 00:45:07,600
Speaker 1: But we do think that Hawking radiation might be real.

945
00:45:07,880 --> 00:45:10,680
Speaker 1: And the crucial thing about it is that it's bigger

946
00:45:10,719 --> 00:45:14,600
Speaker 1: for smaller black holes. Really big black holes almost no

947
00:45:14,680 --> 00:45:19,560
Speaker 1: Hawking radiation. Smaller black holes dramatic Hawking radiation. So the

948
00:45:19,600 --> 00:45:22,760
Speaker 1: smaller the black hole gets, the bigger the Hawking radiation.

949
00:45:22,920 --> 00:45:25,520
Speaker 1: So this is actually going to be more radiation pressure

950
00:45:25,880 --> 00:45:28,359
Speaker 1: than the accretion disc. For a small enough black hole,

951
00:45:28,680 --> 00:45:32,279
Speaker 1: the Hawking radiation will be brighter than the glow from

952
00:45:32,320 --> 00:45:33,160
Speaker 1: the accretion disk.

953
00:45:33,480 --> 00:45:35,440
Speaker 3: Okay, so I'm picturing it now.

954
00:45:35,440 --> 00:45:37,880
Speaker 2: There's a black hole in the middle, there's an accretion

955
00:45:38,000 --> 00:45:41,880
Speaker 2: disc around it, and then Hawking radiation extends even beyond that,

956
00:45:42,440 --> 00:45:44,600
Speaker 2: and if you were looking, could do We have a

957
00:45:44,680 --> 00:45:47,840
Speaker 2: kind of telescope that could distinguish those three objects.

958
00:45:48,160 --> 00:45:50,880
Speaker 1: We have a telescope that can see black holes, and

959
00:45:50,960 --> 00:45:53,360
Speaker 1: we've only been able to see super massive black holes

960
00:45:53,920 --> 00:45:57,640
Speaker 1: and so those have essentially no Hawking radiation or unmeasurable amounts,

961
00:45:57,640 --> 00:46:00,319
Speaker 1: so we've never seen Hawking radiation. But if you had

962
00:46:00,360 --> 00:46:02,759
Speaker 1: a small enough black hole and it was nearby, it

963
00:46:02,800 --> 00:46:05,839
Speaker 1: would be very bright in Hawking radiation. So it did

964
00:46:05,840 --> 00:46:07,920
Speaker 1: the calculation and if you had a black hole with

965
00:46:08,000 --> 00:46:11,200
Speaker 1: like forty billion kilograms, which is about the mass of

966
00:46:11,200 --> 00:46:13,799
Speaker 1: the Hoover Dam, then the glow from the accretion disc

967
00:46:13,840 --> 00:46:16,680
Speaker 1: would be about as bright as the glow from Hawking radiation,

968
00:46:17,200 --> 00:46:20,000
Speaker 1: so like pretty bright. But this is tiny, you know,

969
00:46:20,040 --> 00:46:22,239
Speaker 1: this is like a tiny fraction of the mass of

970
00:46:22,239 --> 00:46:24,720
Speaker 1: the Earth. Even so this is really a very small

971
00:46:24,760 --> 00:46:27,600
Speaker 1: black hole. Like the gravity from the Hoover Dam is

972
00:46:27,680 --> 00:46:30,200
Speaker 1: not very powerful. Remember we had that episode about like

973
00:46:30,239 --> 00:46:33,560
Speaker 1: measuring gravity and like the Scottish guys climbing around that mountain,

974
00:46:33,920 --> 00:46:35,960
Speaker 1: that was a much bigger effect because that's a much

975
00:46:35,960 --> 00:46:38,600
Speaker 1: bigger mountain and still very hard to measure. Gravity is

976
00:46:38,600 --> 00:46:40,920
Speaker 1: super weak, So a black hole with the mass of

977
00:46:40,960 --> 00:46:43,759
Speaker 1: the Hoover Dam would not be very powerful, but it

978
00:46:43,800 --> 00:46:47,280
Speaker 1: would be as bright as it's accretion disk. So yes, David,

979
00:46:47,400 --> 00:46:51,080
Speaker 1: small black holes can have accretion disk. It depends on

980
00:46:51,120 --> 00:46:53,120
Speaker 1: what they've been eating. So if you have a tiny

981
00:46:53,120 --> 00:46:55,440
Speaker 1: black hole out in the middle of nowhere, no accretion disk.

982
00:46:55,719 --> 00:46:57,560
Speaker 1: You take a tiny black hole and you PLoP it

983
00:46:57,600 --> 00:47:00,680
Speaker 1: in a huge bed of plasma and hygigen and whatever.

984
00:47:01,000 --> 00:47:02,719
Speaker 1: It will get in accretion disk as well, but it

985
00:47:02,719 --> 00:47:05,200
Speaker 1: will also glow with its own hawking radiation.

986
00:47:05,440 --> 00:47:05,760
Speaker 3: Wow.

987
00:47:05,880 --> 00:47:07,600
Speaker 2: Okay, So then let's get to the last part of

988
00:47:07,680 --> 00:47:10,680
Speaker 2: David's question. If that if you put that black hole

989
00:47:10,719 --> 00:47:14,040
Speaker 2: in the center of the Earth, how long could Earth survive?

990
00:47:14,680 --> 00:47:17,200
Speaker 1: Yeah, this is a fascinating question as well, and I

991
00:47:17,239 --> 00:47:20,239
Speaker 1: thought it was a little unrealistic because we can't make

992
00:47:20,440 --> 00:47:23,359
Speaker 1: a black hole the size of the Hoover Dam. We

993
00:47:23,360 --> 00:47:25,279
Speaker 1: were unlikely to see one. So I thought, well, let's

994
00:47:25,320 --> 00:47:27,440
Speaker 1: take it another step. Let's say we did make a

995
00:47:27,440 --> 00:47:30,640
Speaker 1: black hole. Because, for example, at the Large Hadron Collider,

996
00:47:30,680 --> 00:47:32,799
Speaker 1: we're trying to make black holes all the time. We

997
00:47:32,840 --> 00:47:36,360
Speaker 1: smash protons together. Yeah, we smash protons together in the

998
00:47:36,440 --> 00:47:40,239
Speaker 1: hopes that occasionally they will create a tiny miniature black hole.

999
00:47:40,280 --> 00:47:43,480
Speaker 1: And remember, smaller black holes radiate faster than bigger black holes.

1000
00:47:43,800 --> 00:47:45,960
Speaker 1: So we make a black hole to the large hadron collider.

1001
00:47:46,000 --> 00:47:48,320
Speaker 1: It's going to have like ten to the minus twenty

1002
00:47:48,440 --> 00:47:53,360
Speaker 1: four kilograms of mass. It'll almost instantly radiate itself away, hope.

1003
00:47:53,400 --> 00:47:55,480
Speaker 1: But it would be awesome because then we'd learn something

1004
00:47:55,520 --> 00:47:58,680
Speaker 1: about quantum gravity. It would be incredible. But if you

1005
00:47:58,719 --> 00:48:01,319
Speaker 1: did take one of these things and somehow was able

1006
00:48:01,360 --> 00:48:04,600
Speaker 1: to feed it before it radiated away, and you put

1007
00:48:04,600 --> 00:48:06,160
Speaker 1: it in the center of the Earth, and then you

1008
00:48:06,200 --> 00:48:08,040
Speaker 1: do a calculation of like how long would it take

1009
00:48:08,080 --> 00:48:10,719
Speaker 1: to slurp up everything and consume the entire Earth? That

1010
00:48:10,719 --> 00:48:13,359
Speaker 1: would take about ten thousand years, all right, So.

1011
00:48:13,320 --> 00:48:16,440
Speaker 2: I wouldn't be around anymore. So fine, that's.

1012
00:48:16,360 --> 00:48:18,080
Speaker 1: Right, that's all right, And you would have time to

1013
00:48:18,160 --> 00:48:21,080
Speaker 1: jump on that arcship to Alpha Centauri, and we'd even

1014
00:48:21,120 --> 00:48:23,080
Speaker 1: have time to design and build it, you know, because

1015
00:48:23,120 --> 00:48:25,279
Speaker 1: ten thousand years is a good amount of time, even

1016
00:48:25,320 --> 00:48:26,400
Speaker 1: for space projects.

1017
00:48:26,480 --> 00:48:29,239
Speaker 2: But this ecologist feels like you probably shouldn't do anything

1018
00:48:29,280 --> 00:48:30,920
Speaker 2: to destroy the Earth because there are a lot of

1019
00:48:30,920 --> 00:48:34,680
Speaker 2: species that would get left behind, and every species is important.

1020
00:48:34,760 --> 00:48:37,320
Speaker 3: Dan, Well, extinction's not okay.

1021
00:48:40,000 --> 00:48:42,000
Speaker 1: Do you want to extinctify the mosquitos? How about that

1022
00:48:42,080 --> 00:48:44,560
Speaker 1: wasp that bits you earlier? How's that thumb doing?

1023
00:48:44,600 --> 00:48:47,520
Speaker 2: By the way, it's about thirty percent bigger than the

1024
00:48:47,560 --> 00:48:50,120
Speaker 2: other thumb right now. But I still think that the

1025
00:48:50,239 --> 00:48:54,200
Speaker 2: wasps they are important pollinators in some cases they control

1026
00:48:54,880 --> 00:48:58,400
Speaker 2: like other insect populations, I think it deserves to stay.

1027
00:48:58,760 --> 00:49:01,680
Speaker 2: I might get rid of mosquito. See I'm glad we

1028
00:49:01,719 --> 00:49:04,680
Speaker 2: got rid of small pox there. I accept that there's

1029
00:49:04,719 --> 00:49:08,080
Speaker 2: some nuance, but I'm your answer didn't sound like it

1030
00:49:08,080 --> 00:49:09,520
Speaker 2: was gonna be very nuanced, Daniel.

1031
00:49:10,440 --> 00:49:13,840
Speaker 1: I was just trying to be controversial success. Thank you

1032
00:49:13,960 --> 00:49:16,640
Speaker 1: David for that question. Let us know if we answered it,

1033
00:49:16,680 --> 00:49:18,760
Speaker 1: and follow up questions are always welcome.

1034
00:49:19,120 --> 00:49:21,840
Speaker 7: Hi, Daniel and Kelly, thank you so much for that answer.

1035
00:49:22,040 --> 00:49:24,520
Speaker 7: You did indeed answer the question and my only follow up.

1036
00:49:25,040 --> 00:49:27,040
Speaker 7: If I were to waive my magic wond and create

1037
00:49:27,080 --> 00:49:29,719
Speaker 7: a Hoover Dam sized black hole and situated somewhere that

1038
00:49:29,719 --> 00:49:32,040
Speaker 7: I could watch it feed from ten or twenty meters away,

1039
00:49:32,360 --> 00:49:34,640
Speaker 7: would I be able to enjoy the spectacle for the

1040
00:49:34,760 --> 00:49:37,400
Speaker 7: three or four hundred microseconds it would take for the

1041
00:49:37,440 --> 00:49:40,600
Speaker 7: stream of gamma rays and exotic particles to shred my spacesuit,

1042
00:49:41,040 --> 00:49:43,120
Speaker 7: or would be a teency little firefly I could enjoy

1043
00:49:43,200 --> 00:49:46,040
Speaker 7: until my oxygen ran out. Either way, I promise not

1044
00:49:46,120 --> 00:49:49,480
Speaker 7: to destroy the Earth anytime soon. Thanks again, Thanks.

1045
00:49:49,239 --> 00:49:51,320
Speaker 1: Everyone out there for joining us on this episode. We

1046
00:49:51,480 --> 00:49:54,040
Speaker 1: love hearing from you. Please send us your questions and

1047
00:49:54,160 --> 00:49:57,200
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1048
00:49:57,640 --> 00:50:00,560
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1049
00:50:00,520 --> 00:50:01,600
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1050
00:50:08,400 --> 00:50:11,960
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1051
00:50:12,160 --> 00:50:13,680
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00:50:16,920 --> 00:50:19,560
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1057
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00:50:29,920 --> 00:50:33,120
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1060
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1062
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1063
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