Listener Questions #18

Daniel and Kelly answer questions about gravtational slingshots, megafauna and microscopic black holes!

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Episode Transcript

Speaker 1 (00:07):
I'd like us to quickly explore deep into space. Can
gravity slingshots help us win that race?

Speaker 2 (00:13):
If ancient humans killed off the giant kangaroo, why didn't
we kill off the African elephant too?

Speaker 1 (00:20):
How much do tiny black holes like to eat? If
I adopt one, will it nap at my feet?

Speaker 2 (00:25):
Whatever questions keep you up at night, Daniel and Kelly's answers.

Speaker 3 (00:29):
Will make it right.

Speaker 1 (00:30):
Welcome to Daniel and Kelly's extraordinarily Curious universe.

Speaker 3 (00:47):
Hello, I'm Kelly Waiter Smith.

Speaker 2 (00:48):
I study parasites and space, and I am excited to
talk about charismatic megafauna today.

Speaker 1 (00:56):
Hi. I'm Daniel. I'm a particle physicist, and I never
wanted a willing mamoth as a pet.

Speaker 2 (01:01):
Oh you No, I didn't either. I don't think I
want anything bigger than the goats that we have right now?

Speaker 1 (01:06):
What about a goat sized black hole? Or do goats
basically operate as black holes because they eat everything?

Speaker 3 (01:12):
You know?

Speaker 2 (01:12):
Our goats are surprisingly picky about what they eat, which
I'm winding a little frustrated because I was like, Oh,
we're gonna get walking garbage disposals, but ours are like no,
I don't want that.

Speaker 3 (01:22):
I don't want that either, So your goats are not
the goat.

Speaker 2 (01:25):
I wouldn't say that. They are definitely the greatest of
all time. And one of them is named Greatest of
all Time aka Kevin for short. That's the full name
that's on its certificate, because we let children name our goats.
So one of them is the goat literally literally. But
I had a particularly negative experience with wildlife this morning.

(01:47):
I just walking up the hill accidentally smacked a wasp
of some sort and my thumb is expanding. Oh and
we'll see how big it is by the end of
the episode. But I wanted to focus on more positive interactions.
Since we're gonna be talking like Africa's charismatic wildlife, I
wanted to know what is the most like awe inspiring
experience you've had with an animal in nature?

Speaker 3 (02:09):
Because you and Katrina hike, you're like outdoor people.

Speaker 1 (02:11):
I think one of the most incredible experiences I've had
was seeing a mountain lion close up. Who I grew
up in the mountains of northern New Mexico, and there
were mountain lions because they were mountains, and you know,
sometimes you'd get up in the morning and you'd see
their pop rinks in the snow. But one time I
actually did spot one, and it's incredible how much they

(02:31):
are like housecats, you know, in their smoothness and their
their feline charisma, but also how terrifyingly huge they are,
because I've often wondered, like, what would my housecat do
if it weighed a thousand pounds? And now I know
the answer is it would eat me.

Speaker 2 (02:50):
I mean, most of the time, mountain lions don't go
after people. I want to clear the mountain lion's name,
and if anybody wants to read more about that, they
should check out more ark Elbrock's book on mountain lions.
But yeah, so that is beautiful. So like, did you
see it at a distance where like how far away
was it?

Speaker 1 (03:08):
It was like maybe eighty feet or something. My parents'
backyard was right up against National Forest and so there
was just like a lot of trees and canyons back there,
and I saw one walking through the trees and I
saw it and it saw me, and we like shared
a little moment, and I was like, I'm on a
tiptoe back inside. You can have the whole outdoors.

Speaker 2 (03:27):
It's all yours now, buddy, and I assumed that he did.
It did not approach you or anything like that.

Speaker 1 (03:32):
No, no, it did not, and I'm very happy that
it went on its way. But it reminds me of
this incredible story I heard about European lions. You know,
the lions used to roam Europe also, but they were
killed off many, many years ago. And the story I
heard is that for a long time there was a
question about European lions. Do they have mains like African
lions or not like North American lions. And we answered

(03:55):
this question through cave drawings. People found drawings of lions
from tens of thousands of years ago from Paleolithic artists,
and it's basically like a lab book and they don't
have mains, and you can see like hunting pears even
And so that's incredible to me that, like humans, tens
of thousands of years ago answered our current science question.

Speaker 2 (04:15):
Okay, so that is amazing, but how does the absence
of seeing mains like so, you know, in Africa, when
you get groups that are hunting, it's usually groups of
females that are hunting. The females do most of the hunting,
So how do you know that, you know, the worthless
males just were weren't drawn on the insides of the caves.

Speaker 1 (04:33):
Yeah, great question. I shouldn't have said hunting pair. I
think they had some reason to believe this is like
a family unit. But it sort of connects us over
space and time to you know, early humans who are
also awed by the majesty of megafauna.

Speaker 3 (04:45):
Yes, absolutely, very cool.

Speaker 2 (04:47):
And when I asked you that question, I assumed you
we're going to pick megafauna because almost almost everyone picks,
you know, some large mammal, the largest mammal they've ever seen,
is usually the answer to that question.

Speaker 1 (04:59):
Oh, I see, You've asked other people this question, and
nobody has said the time I saw a rat in
my kitchen.

Speaker 3 (05:04):
Well, of course not No, no one has said that.

Speaker 2 (05:06):
But I think my moment was I was in the
woods and I was helping a friend with the snake survey,
and a bunch of wood frogs had recently like metamorphosed
from tadpoles into like adults, but they were are you know,
into the landstage.

Speaker 3 (05:20):
But they were really tiny.

Speaker 2 (05:22):
And there were literally hundreds of them, and I noticed
them because I like moved my foot forward and all
of these tiny things hopped out of the way.

Speaker 1 (05:29):
Oh my god.

Speaker 2 (05:30):
And I realized, like, oh my gosh, I'm surrounded by
like hundreds of little froglets, these little tiny frogs, and
I just sat down and like the sun was coming
through the trees and just the right way that it
kind of had like a magical feeling. And every time
I'd sort of move my hand, all of these little
froglets would like hop around, and it was just like,
I don't know, it was magic. It was like being
in some sort of a fairy book or something. And

(05:52):
I think for me that was that was my moment.

Speaker 1 (05:55):
Well, I have a moment I recall from being in
your neck of the woods. Oh, it was more of
a horror story than a magical moment. Katrina and I
were hiking and backpacking, I think it was in the
Blue Ridge Mountains, and we set up our camp and
we had a nice campfire, and at the end of
the evening we were ready to go back to our tent,
and it was only then that we noticed that the
ground just outside the extent of the fire was covered

(06:17):
in daddy long legs. There were like millions and millions
of them, and they were crawling all over our tent
and everywhere. It was incredible. We were so grateful that
we had zipped our tent closed, so we like sprained
it back to the tent open it, jumped in closed it,
and was just like terrified of the carpet of Daddy
long legs that were outside. I was like, wow, Virginia's crazy.

Speaker 3 (06:38):
But they can't hurt you.

Speaker 1 (06:41):
They can't hurt you. But I'm still not gonna like
lie down and have Daddy long legs crawl all over me.

Speaker 2 (06:46):
All right, Well I don't I feel like I'm not
really feeling.

Speaker 1 (06:52):
All right, Zach, you are free to release Daddy long
legs all over Kelly was she's asleep. Sure, sure, Wow, amazing.
You don't have the same reaction to spiders as other
people do.

Speaker 2 (07:04):
Huh, Well, Daddy long legs aren't really spiders.

Speaker 1 (07:07):
Oh my gosh. Wow, and that scientific knowledge puts you
at ease, it does.

Speaker 2 (07:12):
Let me make sure that's right. Our Daddy long legs spiders.
I think there are racknids. Oh maybe they do still
count as spiders. Yeah, all right, so sorry, I guess
they are still Teddy long legs are still see.

Speaker 1 (07:24):
I told you they were creepy like that makes a.

Speaker 2 (07:26):
Difference, all right, So sorry, you were right, daddy, long
legs looks like they are spiders. But I do feel
like knowledge makes a huge difference. So we've got these
they're called rabid wolf spiders, bad name, right, and they're
like big and they do look kind of scary. And
when I first moved here, I freaked out because my
son likes to roll around in the grass and these

(07:46):
are like grass spiders that are in the grass, and
so he'd roll around in it. I always see like
a big spider running away and it really freaked me out.
But I read about them, and now I'm not scared
of them, like they're they're not gonna go after my son.

Speaker 3 (07:58):
It's fine.

Speaker 2 (07:59):
I do feel like knowledge makes a big difference in
my fear outside in general.

Speaker 1 (08:04):
You're totally right, and of course, knowledge is our business.
We're here to help everybody understand the universe better and
be less afraid of it, or maybe appropriately afraid of it.
So let's get into it, because today we're not here
just to talk about my experiences with spiders and Kelly's
magical moment with the frogs. We're here to talk about
your questions about the universe, things you wonder about, places
where you wish you had more knowledge. So we regularly

(08:27):
ask our listeners to send in their questions, and we'd
love to hear from you. Please write to us to
questions at Danielankelly dot org. We always write back to everybody,
and sometimes we pick questions to answer here on the
pod because we think a lot of people might be
interested in the answer, or because I think it'd be
fun to joke about it with Kelly.

Speaker 2 (08:45):
Or because when I get the EMO from you, I
don't know the answer and I need to stall for
Time's you go.

Speaker 3 (08:52):
That's the other reason.

Speaker 1 (08:54):
So, speaking of stalling for time, here's our first question,
which is about how to quickly explore the outer Solar
System using gravity's help.

Speaker 4 (09:04):
Hi, Daniel and Kelly. I was thinking about how we
use gravitational slingshots permissions such as Voyager, Cassini and New
Horizons as we venture further into the Solar System. Would
we use this method for human credmissions and what forces
would the crew feel if they were slingshotted to their destination? Thanks?

Speaker 1 (09:20):
All right, and that question was from Rob Pixley. Rob,
thank you very much for writing in. Kelly, you're an
expert on space and exploration. What do you think about this?

Speaker 2 (09:29):
Well, I believe that gravitational slingshots are when you use
massive objects to gain some speed. But I'm going to
wait for you to give some more information. But when
I read this, it reminded me of Jules Verne's and
I can never say his name right.

Speaker 3 (09:44):
Thank you, because he's French. Okay, all right, that guy,
That French guy.

Speaker 2 (09:47):
He wrote a book From the Earth to the Moon,
and it was about a Baltimore gun club who decided
they were going to build a giant gun and shoot
people to the moon. And it works. But the problem is, actually,
if you were to calculate how many gs the crew
would have felt, they would have been probably like liquefied
in chapter twenty on the Way to the Moon. They

(10:08):
wouldn't have made it. So let's hear about gravitational slingshots.
Would this kill humans or nothing?

Speaker 1 (10:14):
Gravitational slingshots are super awesome. They are a way to
boost your speed and change your direction without using any fuel.
You know, one of the big issues for getting around
the Solar System or getting around the universe is that
fuel is heavy and if you use fuel to propel yourself.
You need fuel to help you push that fuel, and
then you need more fuel to help you push that fuel,

(10:34):
and pretty soon you have a gas tank the size
of Jupiter just to get anywhere. So it's very nice
if you can navigate the universe without using fuel, because
then you don't have the additional mass and then need
to propel that all that stuff. So for decades, NASA
and other folks have been using this technique called a
gravitational slingshot, which essentially steals a little bit of speed
from a planet or a moon. The way it works

(10:56):
is you can approach a big planet and it's gravity
you will change your direction. So for example, say you're
just coasting, you have no rockets on, and you're approaching Jupiter,
and you swing around the back of Jupiter and come
out the other side. Now you're going in a new direction. Right.
That's not something you can otherwise accomplish, usually without burning
some fuel, without thrusters, because a change in direction, even

(11:18):
if your overall magnitude is the same, is still an acceleration.
To change your direction in space, you've got to have
some acceleration. Somebody's got to pull on you. So basically
you use the gravity of the planet to pull on
you and you can even come out the other side,
not just with a change in direction, but with a
net increase in speed. And that's why it's called a
gravitational slingshot.

Speaker 2 (11:38):
Well, I don't think we've ever used this on a
vehicle carrying humans, because the only option would be the
trip to the Moon. But have we used this for
our rovers or anything or probes.

Speaker 1 (11:49):
We've used it for lots of probes, absolutely, because a
lot of times we don't have the fuel to get
them all the way out to the outer Solar System,
and we want to keep them light and it saves fuel.
And then also you get to add like another planet
on your trip. You're like, hey, I want to go
to Saturn, but I'd like to swing by Mars on
the way, Or I'd like to go to Neptune. Can
we stop by Jupiter? And then you also get to

(12:09):
take pictures of Jupiter because you know, none of these
things are so well explored that like one more trip
is boring, you know. Yeah, so that's like a bonus
for these things. And I think the physics of it
is really fascinating because it's a little bit counterintuitive, like
it feels like free energy, Like where is this speed
coming from? And the answer to that question is that
you're really taking that speed from the planet. Like if

(12:30):
you swing by Jupiter, it changes your direction, it accelerates you,
and it effectively slows down. It slows down in its
orbit around the Sun. So, for example, if you take
a normal space probe and you swing it around Jupiter
and it gets sped up in the process, Jupiter slows down,
but just by a tiny little bit because the mass
of Jupiter is so huge compared to the mass of

(12:52):
the probe that it loses I did this calculation one
times ten to the negative twenty five kilometers per second
of its flow, so basically negligible. However, if you scale
this up and you did like, you know, ten to
the twenty five space probes, because you want to explore
the whole galaxy, you might start having an impact on Jupiter.
But basically, think about Jupiter as a huge battery of

(13:15):
momentum and you're tapping into that a little bit and
adding it to your space probes.

Speaker 2 (13:20):
So if an aggressive alien civilization wanted to screw up
our solar system, could they just send probes by Jupiter
enough times to get it to sort of move around
and rek havoc on the rest of Us.

Speaker 1 (13:32):
I guess they could. But you know, if they were
capable of doing that, they should just like nudge an
asteroid towards Earth. I mean, I'm not giving advice to
malevolent aliens. Okay, sounds like I am, so you please
if you are malevolent aliens, don't do this, or anybody
shouldn't do this. But yeah, the most dangerous thing you
could do in the Solar system is nudge a comet,

(13:52):
for example, because comments by the time they get to
the inner Solar System are going really really fast because
they fall from so far away, and they're really are
to see in advance because their periods are so long.
So yeah, nudging a comet would be the most dangerous thing.
I guess the most subtle thing would be tweaking Jupiter.
That would be a cool basis for a science fiction novel.
Get on it, Daniel, And for those of you who
still trying to like Grock, how this works? You know?

(14:15):
Another analogy is like think about a moving train and
you have a tennis ball. If you throw your tennis
ball against the front of the train. Then the train's
velocity gets added to the tennis ball's velocity when it
bounces off, right, So now it comes back, it's going
not just the same velocity as it was when it
hit the train. Like if you bounce the tennis ball
against a wall, it comes back with the same speed.

(14:36):
If you bounce a tennis ball against a train rushing
at you, it comes back much much faster. It slows
down the train a tiny little bit, nobody's ever going
to notice, but it speeds up the tennis ball. And
so it's this huge mass ratio that makes this possible.

Speaker 2 (14:49):
All right, So how fast does this speed up happen?
And is it going to be fast enough that you're
going to liquefy the humans inside?

Speaker 1 (14:56):
Right? So two really interesting questions, and that's really what
Rob was asking about. So number one, this isn't a
great idea for human missions, but not because of the
g forces, but because usually it involves going pretty far
out of your way. Like you're sending a probe to Pluto.
You know it's going to take forever to get there.
If you can make it lighter by stopping by Saturn
on the way, you don't really care if it's going

(15:17):
to slow you down by five years, because it can
slow you down by five years, so it's a more
economical way to get this speed, But often it requires
going really far out of your way, and if you're
doing space missions, the goal is to get there fast,
to spend less time in space, less time exposed to
low gravity, less time exposed to radiation, all this kind
of stuff. Now, sometimes it can work if the Solar

(15:38):
system is just right. You know, if you want to
get to Saturn and Jupiter happens to be in just
the right place, then maybe a flyby of Jupiter can
help you get to Saturn faster. But usually you just
want to go directly there, and so you want chemical
rockets or ion thrusters or fusion power or something. So
this is good for long missions where you don't really

(15:59):
care how long it takes, which is not what we're
going for here.

Speaker 2 (16:03):
Okay, so it would take longer, but I mean, if
you're doing like a generation ship on an interstellar journey,
you know you're not gonna be alive when you get
to the final destination anyway, so why not add an
extra five years to your trip to speed it up
For the next few generations. So let's assume we decide
we're going to do this anyway, or are you going
to get killed by the speed.

Speaker 1 (16:24):
Well, before we answer that, there's another wrinkle, which is
you're right if you're like aiming for Alpha Centauri and
you want to be redirected and you don't want to
spend all that fuel. This is not a terrible idea,
but it's going to be more effective the closer you
get to the planet, right, because then the more powerful
the gravity. However, the closer you get to Jupiter, the
more you have to word about the radiation of Jupiter, right,
So there's really a trade off there. But here's the

(16:46):
thing about the G forces. There aren't any You don't
feel any of these G forces. That's right, because gravity
is not a force. You feel g forces when you're
being accelerated. So for example, if you're on a roller
coaster and you reach the bottom of the roller coaster
and you start going up, you feel those G forces.
Or if you're in a car and you're turning really fast,

(17:07):
you feel those G forces. Or if you're in a
rocket and somebody burns the rocket really fast to get
you going off the planet, you feel those G forces.
When you are falling just under gravity, you feel no
G forces. So for example, you jump out of an airplane,
you don't feel any G forces. Right, you're in freefall.
You only feel G forces when there's acceleration, and you

(17:29):
only feel acceleration when you're fighting gravity. If you just
chill with gravity, man, and go with the flow of
the universe, you feel no G forces.

Speaker 2 (17:39):
Okay, well, so what if what if you're on this
interstellar ship. You want to get the Jupiter speed up,
and the folks who major interstellarship planned ahead for the
problem that low gravity is bad for human bodies. And
now you are spinning, so you have artificial gravity in
your habitat to help with things like reproduction. Now where
you feel on the G forces with the artificial gravity.

Speaker 1 (18:02):
You feel the artificial gravity absolutely, because that's not gravity, right,
that's the force from the structure of the ship holding
itself together. The same with like on the surface of
the Earth, you feel what we call gravity, but it's
really the Earth pushing you up against the natural inclination.
You have to fall towards the center of the curvature.
So yes, you feel the G forces from the spinning

(18:23):
that's real because it's not gravity. But falling into Jupiter's
gravitational field doesn't change that at all.

Speaker 5 (18:30):
Yeah.

Speaker 2 (18:30):
Okay, so sorry, So I knew that you would feel
the artificial gravity, But what I meant is when you're
feeling artificial gravity and then you accelerate, Yeah, do you
feel that acceleration more strongly when you're under artificial gravity
relative to No?

Speaker 3 (18:42):
Okay, no, no, you're doing cool.

Speaker 1 (18:44):
Yeah, so that's sort of awesome because you know, you
don't feel gravity at all, even though it's having an
impact on you, even though you are accelerating, you're changing
your vector from the point of view of somebody distant. Right.
This is the thing about gr is that it's very confusing.
It depends on who who watching from your point of view,
you never feel acceleration due to gravity. Somebody else looking

(19:05):
from far away, who doesn't see the curvature. They're like, well,
according to my coordinates, your velocity is changing and therefore
you're having acceleration. And that's cool. Gr Lets everybody have
their own calculation. But what do you feel is what's important. Right,
You're not going to be torn apart, your stomach's not
going to be shredded. Your organs are not going to
be squished. Feel free to dive closed to Jupiter in

(19:25):
your arcship on your way to Alpha Centauri. You have
to worry about the radiation, but you don't have to
worry about the g forces.

Speaker 2 (19:32):
And because I have a pod in physics, I know
that GR stands for general relativity.

Speaker 1 (19:37):
Yes, absolutely, joh relativity one of the most fascinating, beautiful
and I think widely misunderstood theories, mostly because of that
dang rubber sheet bowling ball analogy out there which confuses everybody.

Speaker 2 (19:50):
Yeah, but we're here to clear up misconceptions, all right,
So let's find out if Rob wants to use a
gravitational slingshot for his journey to interest that I've decided
he's going on.

Speaker 4 (20:03):
Hi, Daniel and Kelly, your explanations normally make sense, but
offered a great way to look at the scenario from
multiple interesting, different perspectives. Thanks again.

Speaker 1 (20:31):
Okay, we're back and we're answering questions from listeners today.
And the next question is about major animals.

Speaker 2 (20:38):
Major animals, Well, I've never heard them referred to as
major before majorly awesome, So I have never been to Spain,
how would you pronounce this name, Daniel?

Speaker 3 (20:49):
Do you know Adamar?

Speaker 1 (20:50):
I've never heard this name before, but it looks to
me like Adamar.

Speaker 2 (20:53):
Yeah, all right, anyway, fantastic name, and so adam ar
from Spain.

Speaker 3 (20:57):
Let's hear your question.

Speaker 6 (20:59):
Hello, Danny and Kelly. My name is Adema and I'm
asking this question from Spain. I recently learned that elephant
seemed to identify different human languages and react differently depending
on what they hear, thus being able to know if
a group of humans poses a threat to them based
on a language they speak Differently, Rainos seem to adopt
a more increasive behavior whenever the spots kincas. Some suggesting

(21:19):
that this could be a consequence of biological adaptation as
they evolve in contact with humans for many, many times,
in fact, since the beginning of the Haminites. What is
most intriguing is that this could be the reason why
great animals don't exist in any continent other than Africa.
As our arrival, there was much mosch suven and they
didn't have time to bolf an adapt to us before
we hunted them down to extinction. May Kelly give us

(21:40):
a dieper insight in this matter? Thank you for having me,
and congratulations for providing us with such an awesome podcast.

Speaker 2 (21:46):
All right, So my opinion on the matter is pretty
much that Adamar was right right on the money. So
we're just going to go ahead and talk about the
science here because it's a really fascinating story and Adamore
seems to have a good handle on it. But I'm
just gonna go ahead and reiterate how cool all this
stuff is.

Speaker 1 (22:02):
Yeah, Kelly, tell us the history. How much more awesome
was the Earth ten or fifty thousand years ago.

Speaker 3 (22:08):
Before humans came along?

Speaker 2 (22:09):
All right, So there were a lot more large mammals
on the planet, and by large we mean greater than
forty four kilograms.

Speaker 1 (22:17):
Why forty four not forty five, not forty Who decided?
Was there some meeting the forty four kilogram threshold?

Speaker 2 (22:23):
I don't know who decided on the forty four kilogram threshold.
No doubt it was arbitrary. No, somebody must have looked
at an animal and been like, you're too small.

Speaker 3 (22:32):
How much do you weigh? You are now our threshold?

Speaker 1 (22:36):
Oh, I didn't hurt that poor animal's feelings.

Speaker 3 (22:39):
Well, we'll get it.

Speaker 2 (22:39):
I mean, the good news if you're below the threshold.
It sounds like you were maybe less susceptible to extinction
caused by humans, So maybe you'd be happy if you
were under this arbitrary threshold.

Speaker 1 (22:48):
So tell us about these megafauna that used to roam
the earth.

Speaker 2 (22:52):
Okay, So this large megafauna includes things like you mentioned
at the beginning of the show, like lions that used
to be found much farther north. There were also giant
ground sloths. There were kangaroos that were much larger, and
there were mammoths. There were just lots of much larger
mammals that were roaming the earth. And somewhere between ten

(23:13):
to fifty thousand years ago, about two hundred of these
large mammal species went extinct.

Speaker 1 (23:19):
Wow.

Speaker 2 (23:19):
And this is called the quarternary megafauna extinction QM.

Speaker 1 (23:24):
And is there a bigger trend here that like animals
get bigger and bigger, because like dinosaurs got really huge
and then you know, the biggest ones died out, and
then mammals come along and then they eventually got big.
Is this some sort of evolutionary trend that like, eventually
somebody finds the niche of like being too big to eat?

Speaker 2 (23:40):
I mean, I'm sure a lot of things go into
optimal size for animals. Being big does make you too
big to eat, but you know, like so t rex
was a big predator, and you know, blue whales are
also big predators, but they're going after kraill, So it's
not they don't have to be big so that they
can be vicious and take downloaded animals. They're eating teeny
tiny little creatures called kraill, little crustaceans in the ocean,

(24:03):
and so, yeah, I'm sure a lot of things go
into being big, but it is a niche that sometimes
makes sense to fill. Yeah, about ten to fifty thousand
years ago, we lost a bunch of these species. And
the question is why, and you know, probably because it's biology,
the answer is it depends.

Speaker 3 (24:19):
There's probably a lot of different factors.

Speaker 2 (24:21):
It could have been that climate was changing at the
time as well, but there's pretty good evidence to suggest
that one of the major causes of this decline in
large mammals was the fact that humans were starting to
move into.

Speaker 3 (24:32):
New areas, so lunch basically lunch. Yes, that's right.

Speaker 2 (24:36):
So, for example, about fourteen of the sixteen large mammal
species that were present in Australia went extinct between about
thirty and fifty thousand years ago, and humans showed up
about forty to sixty thousand years ago, So the numbers
don't match up exactly, but some evidence that humans show
up and those species go extinct. In North America, humans

(25:00):
arrived around like twelve to twenty thousand years ago, and
eighty three percent of the large mammals in North America,
which was thirty four out of forty seven species, went
extinct somewhere between eleven to fifteen thousand years ago. So
we show up, eighty three percent of the large mammals disappear.

Speaker 1 (25:17):
And I guess it's easy to draw the doged line
to say, like, well, humans probably killed them, or humans
maybe ate them or whatever. But it could also be
more complex, right, Humans arriving could change the ecosystem, and
these megafauna could be sensitive to like the web underneath
them that are changing. Maybe humans are eating something else
the megafauna were eating or something. It could just be
more complicated.

Speaker 2 (25:37):
Right absolutely, Or maybe we brought some disease that jumped
from us to them, or we brought some other domesticated
animals along that killed them in some way, so yeah,
there's a lot of complicated It's not just necessarily that
we like ran after them with spears and we ate them, but.

Speaker 1 (25:52):
We probably did a little of that too.

Speaker 3 (25:53):
Yeah, no, I'm not sure.

Speaker 2 (25:54):
There's some fossil evidence that we did some of that too. Yeah,
we needed to eat. But anyway, there is this correlational
evidence that when humans show up on a new continent
not that long after, a large percent of their large
mammals go extinct.

Speaker 1 (26:09):
And I guess another thing we should consider is there
could be like confounding factors also, like something which caused
humans to move there and could also cause the extinction,
but which wouldn't put the blame on humanity really at all.

Speaker 3 (26:21):
Yeah, that's right.

Speaker 2 (26:22):
So if there were, for example, large climactic changes that
made some areas bad for humans, and they were migrating
in search of new food sources or something, right, it
could be that humans came at the same time as
the climate change. There have been people who have looked
into this, and I think that they conclude that humans
still probably played a role even after you control for
some other stuff that we know was happening at that time,

(26:43):
but it probably wasn't just humans, but it looks like mammals.

Speaker 3 (26:46):
Large mammals in.

Speaker 2 (26:47):
Particular were susceptible to death around this time, not just
because we were hunting them or whatever it was about
humans that caused them to die, but in particular, large
mammals tend to have They live a long time, but
it takes a long time for them to start making babies,
and when they do make babies, they don't make a
lot of them. You may remember our conversation about k
selected species that we had with Katie Golden. So large

(27:10):
mammals tend to not have a lot of babies to
begin with, so it's a little bit easier to kill
them off because they can't sort of bounce back as quickly.

Speaker 1 (27:18):
Fascinating, and so the question really is like, why didn't
the same thing happen in Africa. It seems like Africa
has more megafauna than the other continents. Why is that?

Speaker 3 (27:28):
Yeah, that is a great question.

Speaker 2 (27:29):
So during the same period, only ten of the forty
eight large mammal species in Africa went extinct, and in
Eurasia they lost nine of twenty six species, so that's
a much lower percent. The current hypothesis is that humans
evolved in these areas.

Speaker 3 (27:44):
So as our species.

Speaker 2 (27:46):
Was picking up the skills for hunting and stuff like that,
we were evolving alongside of these species. So as we
got better, we didn't get like great at this overnight,
but as we got better, selection was sort of favoring
traits in, for example, elephants, to help them stay essentially
stay away from humans and keep themselves alive in the
face of this sort of growing super predator which we

(28:08):
would end up becoming. And so the idea here is
that Africa and Eurasia, those animals evolved with us, and
so they were just better able to escape us. But
then when we went to somewhere new like Australia and
North America, and these animals had never seen anything like us,
all of a sudden we show up with our spears
and they are just no match for the super predators

(28:30):
who just landed on their continent.

Speaker 1 (28:31):
Wow. Fascinating. So it's actually good luck to evolve together
with humans, right, rather than just have them show up
at your doorstep.

Speaker 2 (28:38):
You want humans to be bugging you for thousands of years,
not just showing up unannounced. When we show up unannounced,
we are particularly problematic guests.

Speaker 1 (28:46):
And what about this other idea that Adam r raises
about how elephants can like understand human language and guess
our intentions. Is there anything to that.

Speaker 2 (28:55):
I don't think Adam Or in particular was trying to
say that elephants can understand language. They sent a paper
from twenty fourteen by macomb at All in proceedings of
the National Academy of Sciences, and essentially what they did
here was they tried to figure out if elephants, just
from hearing an audio clip would respond in a way
that suggested that they knew that different kinds of people

(29:16):
differed in the risk that they posed to the elephants.

Speaker 1 (29:19):
Wow.

Speaker 3 (29:20):
Yeah.

Speaker 2 (29:20):
For example, the Massi people are pastoralists, so their grazing
land and water holes are often areas that are also
used by elephants and are used by the livestock that
the Massi are sort of walking around the area, and
so they often come in conflict and sometimes the elephants
will kill Massi and the Massai need to essentially defend themselves.

(29:42):
On the other hand, the Kamba people are more agricultural
and they rarely have run ins with elephants, and when
they do have run ins, it's usually like a male
elephant who has sort of invaded their field, and so
the Kamba people are often leaving alone females and the
groups of females with their babies. And additionally, human females,

(30:03):
whether the Massi or Kamba, are unlikely to kill elephants,
and young boys are also unlikely to kill elephants. The
people who are most likely to kill elephants are adult men.
So they did this playback experiment where they had everybody
read the same sentence, and the sentence was look over there,
a group of elephants is coming, and they said it
in their own language, and then they look to see

(30:25):
what the elephants did. And when you played a Massi
man saying that sentence, the elephants would bunch together in
a defensive like huddle, and they would respond in a
way that suggested that they were experiencing fear because a
predator was around.

Speaker 1 (30:40):
Wow.

Speaker 2 (30:40):
Yeah, and they did less of that when they heard
the Kamba people. And remember, these are people that often
don't end up in positions where they need to defend
themselves in their livelihoods against elephants. The elephants also responded
more strongly to the sound of men than women, and
more strongly to the sound of men massi relative to
boy massi. So the elephants, you seem to have a
pretty good sense that, like, humans are risky, but some

(31:03):
kinds of humans are more risky than others, and so
they seem to have this like nuanced ability to tell
human risk and respond accordingly.

Speaker 1 (31:10):
I told you the elephants are listening. They got those
big ears, and they can tell when you're talking about them.

Speaker 2 (31:15):
That's right, that's right, and they never forget and so
so you got to be extra careful. But it's worth
noting that many animals respond to humans as though we
are risky. And that's even in North America. In Europe,
they've done playback experiments with badgers that freak out if
you play sounds at water holes. In Africa, just about
every species that hears the sound of a human, they'll

(31:38):
respond more strongly to the sound of a human than
the sound of a lion.

Speaker 1 (31:41):
Wow.

Speaker 2 (31:42):
So in general, just about any continent you go to,
the animals know humans often mean trouble. We should we
should leave town or get defensive. We're going to cause
some trouble. So this is sort of an unrelated topic
than the extinction of animals. This is more like what
are animals doing in this day and age to respond
to humans? And maybe elephants were doing this back in

(32:02):
the past and that's what saved them from getting killed
by us. They just kind of gave us space. But
in general, humans can be devastating to wildlife.

Speaker 1 (32:12):
Well, let's say some nice things about humans to balance
it out. You know, I think it's incredible that we
can unravel these stories. Recently, Hazel made this comment. She
was like, all sciences basically stuff happened and we figured
out why. And I was like, you know, that's a
pretty good point, Hazel. And it touches on this incredible
thing that we do in science, which is like gather
these clues that are just like randomly accidentally left imprinted

(32:35):
on the world to figure out what happened, right, to
unravel this incredible story you're telling over tens of thousands
of years about these huge animals that no longer exist
and why and a complicated interplay between species. It's incredible
to me that we can unravel these stories, that we
can pull them out, sometimes literally out of the ground,
to learn the deep history of our universe.

Speaker 2 (32:56):
Yeah, and you are always a more optimistic and uplifting
person than I am.

Speaker 3 (33:00):
And so that that's beautiful.

Speaker 2 (33:02):
And I'll attempt to follow in your footsteps by noting
that by understanding the damage we've done in the past,
you know, we can try to ameliorate the damage that
we might be doing now or the damage we might
be doing in the future. And so, you know, the
conservation movement has grown in you know, the last couple decades,
and we're getting better at caring about this stuff and

(33:23):
trying to at least slow the decline of some of
these species and in other cases turn around the decline
of species. So you know, if we can recognize our
past mistakes, we can hopefully use that information to do
better in the future.

Speaker 1 (33:36):
Well, can I say something controversial? Do you think that
an individual species on its own has like inherent value?
Like should we be conserving every species or should we
take a bigger, broader view and say, Look, diversity is
important and that means that new species should be evolving
and sometimes species disappear, it's just part of the process.
Should we be trying to hold onto every individual species

(33:58):
or should we be maintaining diversity sort of in a
larger sense?

Speaker 3 (34:03):
Wow, all right, So that question deserves like a whole episode.

Speaker 2 (34:06):
But the short answer is, so there's a background extinction rate,
So you shouldn't necessarily lose sleep if a species goes extinct,
because that was going to happen whether humans were here
or not. But I believe the extinction rate is something
like it's at least ten times higher than we would
expect it to be based on background levels, So we
are really speeding things up for any particular species. I mean,

(34:31):
there are some species that play less important roles in ecosystems,
losing them would have less of an impact, but that's
still like a unique product of millions of years of
evolution that is beautiful and well adapted to its environment
and is being wiped out, you know, because of us,
And that to me does feel catastrophic and really sad.

(34:52):
And you know, I feel like you have to be
able to accept nuance in these conversations and weigh pros
and cons and stuff like that, but you know, I
do feel like time we lose a species, it is sad,
even if it's just a beetle that was present in
only one place.

Speaker 1 (35:05):
Or something, well, it is an incredible output of evolution,
you know, it's like effectively billions of years of biological computation,
you know, to design this creator that can do something
amazing or has incredible chemicals in it. Anyway, stay tuned,
everybody for the upcoming episode where Daniel argues that extinction
is good. Actually, what.

Speaker 2 (35:27):
Like all the extinction or just like I mean, this
might be the last episode of Extraordinary Universe.

Speaker 1 (35:36):
All right, well we'll dig into that for another episode.
In the meantime, let's hear from Adamar about whether Kelly
answered their question.

Speaker 6 (35:43):
Hello, young guys, and thank you for your response. It
makes me glad to think that possibly we're not the
only reason that those animals one extinct, And Kelly's context
really makes me think in a why that spectrum, like,
for example, what if it was the disease, what if
it was a glaciation the same we were running away from,

(36:05):
or maybe it wasn't other super predator anyway, who knows?
Thank you and keep up the Wool's work. All right.

Speaker 2 (36:32):
I'm still trying to decide if I can forgive Daniel
for hinting that extinction caused by humans isn't always bad.
But you know what, I'm going to distract myself with
this insightful question from a listener.

Speaker 5 (36:43):
Hey, Daniel and Kelly, really enjoying the podcast. Thank you.
I have a question for you, and it's about black holes.
Of course, black holes are usually described as unslakable consumers
of all matter and energy, but I know in some
cases the rate of consumption is limited by the energy
pressure of that consumption process, pushing back on the gravitation
pull and starving it of additional fuel. I would love
to hear more about what this might be like on

(37:04):
a more human scale, with a tiny primordial black hole
around the Earth generate a tiny accretion disc of matter
spinning around a light speed, generating the same kind of pressure,
and shooting out X ray lasers from the top and bottom.
How big or small would a black hole be to
have these sorts of effects. When we think of a
black hole interactive with normal human scale matter, what would
that look like? How long could the Earth survive with

(37:25):
a little black hole orbiting around inside of it? Really
looking forward to hearing more about this. Thank you.

Speaker 1 (37:30):
Thank you David very much for that question. And I
hope that our answer is not going to help you
build a miniature black hole to embed into the Earth.
So We're just going to take it on good faith
and answer your question anyway.

Speaker 3 (37:41):
That also sounds like a good topic for a sci
fi novel.

Speaker 1 (37:44):
Let's talk about black holes and start with the basics,
because David's question involves a lot of sort of sophisticated
black hole science. Remember, black holes are regions of space
time where there's so much mass that there's so much
curvature that anything that falls beyond the event and eventually
reaches the center it can never escape. And something I
think a lot of people don't understand about black holes

(38:06):
is that the event horizon is not a physical surface.
It's just a designation. We make a dotted line, we draw,
and actually you never know where the event horizon is
at any moment. You can only tell in the infinite future. Essentially,
think about going to the infinite future and then asking
the question, in what regions of space did particles never escape?
Will now draw that to be the event horizon, and

(38:28):
so you can't ever really actually know. You can use
gr to predict at any moment, but the event horizon
is just like a categorization. We say, beyond this point,
nothing has escaped or can escape, and outside that point,
things can escape. But this is just gravity, right. Black
holes don't like suck with infinite power or anything. If
you replace the Sun with the black hole of the

(38:49):
same mass, we would feel it's gravity and the Earth
would continue to orbit. So it really is just a
gravitational object.

Speaker 2 (38:55):
Okay, So at black hole the same size as our
Sun wouldn't pull on us anymore than our Sun because
they're similarly dense.

Speaker 1 (39:03):
If it has the same mass and it's at the
same distance, it would have the same gravity.

Speaker 3 (39:06):
Okay, yeah, right, I'm with you.

Speaker 1 (39:08):
It wouldn't be as bright, and the Earth would be chilly,
and it would be bad, but not gravitationally, all right.

Speaker 3 (39:13):
I don't want that to happen.

Speaker 2 (39:15):
Does the event horizon always stay at the exact same
spot or does it shift over time if the black
hole like absorbs big things that make it bigger.

Speaker 1 (39:25):
Absolutely, the event horizon depends on the mass of the
black hole and not just on the stuff inside the
event horizon. Right. This is why you shouldn't think about
the event horizon as some physical barrier. As you approach
a black hole, your gravitational energy contributes to the mass
of the black hole, So the black hole's vent horizon
actually grows out to meet you as you fall into

(39:46):
the black hole. So you approach the event horizon, the
event horizon approaches you. It's like a little gravitational hug. Oh.

Speaker 6 (39:53):
Yeah.

Speaker 2 (39:54):
We talked about what would happen if Zach was in
a black hole and if we threw him sandwiches, would
they ever get to it?

Speaker 1 (39:58):
Exactly? And the reason you need to understand that black
holes are not infinitely powerful is to think about the
stuff that's orbiting them, because that's what David's question was about.
This accretion disc. When you think about the images of
black holes out there in space, they look like a
glowing donut with a black core, or you know the
visualization in Interstellar or whatever. They have these luminous discs

(40:19):
around them. What is that and why aren't they getting
sucked in? Well, they're not getting sucked into the black
hole for the same reason the Earth is not getting
sucked into the Sun. Right, there's a lot of gravity
from the Sun. Why aren't we just getting sucked into
the Sun? And the answer is we have velocity. There
are stable orbits around the Sun, and the same way
there are stable orbits around a black hole. Because it's
just a gravitational object. So if you approach a black hole,

(40:42):
as long as you were outside the event horizon, you
could orbit around it forever without falling in if you
were stable and crucially nothing bumped into you to knock
you out of your orbit.

Speaker 3 (40:52):
That doesn't sound fun, I'll pass.

Speaker 1 (40:54):
And that's the same story for the Earth right now.
The accretion disc is very different because it's not just
like one chunk of matter here when chunk of matter there,
it's just like a huge hot disk of gas and
dust that has a lot of internal friction. That's why
it's glowing. The tidal forces from the black hole are
massaging it and heating it up, and it's rubbing against
itself and so it's very hot and it's glowing. So

(41:16):
that's why we can see these black holes. These telescope
pictures of black holes. Really they're pictures of the hot
accretion disc around the black hole. So the accretion disc
is stuff that's orbiting the black hole, hasn't fallen in yet,
is going too fast, probably will fall in eventually because
there's a lot of friction there. So you can't just
like have a stable orbit. But it's sort of like
on deck to go in the black hole, but not

(41:38):
there yet.

Speaker 2 (41:39):
And what is that made out of? Is that just
like the basic dust and junk that you find in space, it's.

Speaker 1 (41:44):
Made out of whatever you've been feeding your black hole.
But yeah, the universe is mostly hydrogen, so it's always
a safe bet to say it's mostly hydrogen because that's
what the universe is. And so yeah, there's gas and
this dust and whatever, but mostly it's hydrogen there. And
here's the black hole starts to work against itself because
the accretion disc is so hot that it glows, right,

(42:05):
that's where we can see these things. So it emits
radiation pressure, so it pushes stuff away. Right. We talked
in a recent episode about how stars are a balance
between gravity and radiation pressure. The fusion at their hot
core is producing a lot of energy and that pushes
out on the star, and if the star is too big,
it can actually blow the star apart. That's why you
have like a maximum size of stars. Well, a similar

(42:27):
thing is happening here. The heat from the accretion disk
creates radiation which pushes other stuff away. So the hotter
the black hole, the bigger the black hole, the bigger
the accretion disk the more it slows down its ability
to eat stuff. So black holes cannot grow infinitely quickly.
There's no theoretical upper limit to the size of a

(42:47):
black hole, but because of this process, this radiation pressure,
there is an upper limit to how rapidly they can grow.
You put a black hole in a blob of stuff,
it can't just like slurp everything out really quickly because
it's going to get hot and glow and push its
own food away from itself.

Speaker 3 (43:04):
So what determines the size of the accretion disc.

Speaker 1 (43:07):
It's just how much stuff was there around it. Like
if you put a black hole in deep space and
nothing is there, it have no accretion disc. It would
just be black. We could not see it except for
its gravitational effects. You drop in the middle of a
really big blob of stuff, it's going to get a
big accretion disc. So it just depends on what's around it.
And this is a really interesting puzzle in physics right
now because this limit on how quickly black holes can

(43:30):
grow is one of the reasons why we don't understand
super massive black holes. We see super massive black holes
in the early history of the universe, like a billion
years after the Big bang already we have black holes
with like billions of times the mass of the Sun.
But if you do the calculations the limit on the
speed of which black holes can grow, tell you that's impossible.

(43:50):
So how did they get so big? That's the big
question of super massive black holes, although we have some
interesting hints that like, if the accretion disc is asymmetric,
then can have what they call super Eddington accretion rates.
It's fascinating. But David's question is about tiny black holes,
and he's asking, can they also have accretion discs?

Speaker 2 (44:10):
And you told me that it doesn't matter how big
a black hole is. What matters is the stuff that started.
So could a tiny black hole have a huge accretion disk?

Speaker 1 (44:20):
So a tiny black hole can have accretion disc And
this Eddington limit of the rate of which black holes
can grow scales with mass, so the limit is smaller
with smaller mass. So there's like less radiation pressure from
a smaller mass black hole because it can't heat up
its accretion discs as much. But at a very small
black hole, something else happens. Right, black holes don't just

(44:42):
glow because of their accretion disc They are themselves not
totally black. We think they glow themselves with a little
bit of Hawking radiation. This is this bizarre radiation that
happens because you have an event horizon in quantum fields
and there's this hand wavy story out there about particles
and antiparticles or one falls into the event horizon. That's
just cartoons. It's not really the physics of what's happening.

(45:05):
But we do think that Hawking radiation might be real.
And the crucial thing about it is that it's bigger
for smaller black holes. Really big black holes almost no
Hawking radiation. Smaller black holes dramatic Hawking radiation. So the
smaller the black hole gets, the bigger the Hawking radiation.
So this is actually going to be more radiation pressure

(45:25):
than the accretion disc. For a small enough black hole,
the Hawking radiation will be brighter than the glow from
the accretion disk.

Speaker 3 (45:33):
Okay, so I'm picturing it now.

Speaker 2 (45:35):
There's a black hole in the middle, there's an accretion
disc around it, and then Hawking radiation extends even beyond that,
and if you were looking, could do We have a
kind of telescope that could distinguish those three objects.

Speaker 1 (45:48):
We have a telescope that can see black holes, and
we've only been able to see super massive black holes
and so those have essentially no Hawking radiation or unmeasurable amounts,
so we've never seen Hawking radiation. But if you had
a small enough black hole and it was nearby, it
would be very bright in Hawking radiation. So it did
the calculation and if you had a black hole with
like forty billion kilograms, which is about the mass of

(46:11):
the Hoover Dam, then the glow from the accretion disc
would be about as bright as the glow from Hawking radiation,
so like pretty bright. But this is tiny, you know,
this is like a tiny fraction of the mass of
the Earth. Even so this is really a very small
black hole. Like the gravity from the Hoover Dam is
not very powerful. Remember we had that episode about like
measuring gravity and like the Scottish guys climbing around that mountain,

(46:33):
that was a much bigger effect because that's a much
bigger mountain and still very hard to measure. Gravity is
super weak, So a black hole with the mass of
the Hoover Dam would not be very powerful, but it
would be as bright as it's accretion disk. So yes, David,
small black holes can have accretion disk. It depends on
what they've been eating. So if you have a tiny
black hole out in the middle of nowhere, no accretion disk.

(46:55):
You take a tiny black hole and you PLoP it
in a huge bed of plasma and hygigen and whatever.
It will get in accretion disk as well, but it
will also glow with its own hawking radiation.

Speaker 3 (47:05):
Wow.

Speaker 2 (47:05):
Okay, So then let's get to the last part of
David's question. If that if you put that black hole
in the center of the Earth, how long could Earth survive?

Speaker 1 (47:14):
Yeah, this is a fascinating question as well, and I
thought it was a little unrealistic because we can't make
a black hole the size of the Hoover Dam. We
were unlikely to see one. So I thought, well, let's
take it another step. Let's say we did make a
black hole. Because, for example, at the Large Hadron Collider,
we're trying to make black holes all the time. We
smash protons together. Yeah, we smash protons together in the

(47:36):
hopes that occasionally they will create a tiny miniature black hole.
And remember, smaller black holes radiate faster than bigger black holes.
So we make a black hole to the large hadron collider.
It's going to have like ten to the minus twenty
four kilograms of mass. It'll almost instantly radiate itself away, hope.
But it would be awesome because then we'd learn something
about quantum gravity. It would be incredible. But if you

(47:58):
did take one of these things and somehow was able
to feed it before it radiated away, and you put
it in the center of the Earth, and then you
do a calculation of like how long would it take
to slurp up everything and consume the entire Earth? That
would take about ten thousand years, all right, So.

Speaker 2 (48:13):
I wouldn't be around anymore. So fine, that's.

Speaker 1 (48:16):
Right, that's all right, And you would have time to
jump on that arcship to Alpha Centauri, and we'd even
have time to design and build it, you know, because
ten thousand years is a good amount of time, even
for space projects.

Speaker 2 (48:26):
But this ecologist feels like you probably shouldn't do anything
to destroy the Earth because there are a lot of
species that would get left behind, and every species is important.

Speaker 3 (48:34):
Dan, Well, extinction's not okay.

Speaker 1 (48:40):
Do you want to extinctify the mosquitos? How about that
wasp that bits you earlier? How's that thumb doing?

Speaker 2 (48:44):
By the way, it's about thirty percent bigger than the
other thumb right now. But I still think that the
wasps they are important pollinators in some cases they control
like other insect populations, I think it deserves to stay.
I might get rid of mosquito. See I'm glad we
got rid of small pox there. I accept that there's

(49:04):
some nuance, but I'm your answer didn't sound like it
was gonna be very nuanced, Daniel.

Speaker 1 (49:10):
I was just trying to be controversial success. Thank you
David for that question. Let us know if we answered it,
and follow up questions are always welcome.

Speaker 7 (49:19):
Hi, Daniel and Kelly, thank you so much for that answer.
You did indeed answer the question and my only follow up.
If I were to waive my magic wond and create
a Hoover Dam sized black hole and situated somewhere that
I could watch it feed from ten or twenty meters away,
would I be able to enjoy the spectacle for the
three or four hundred microseconds it would take for the
stream of gamma rays and exotic particles to shred my spacesuit,

(49:41):
or would be a teency little firefly I could enjoy
until my oxygen ran out. Either way, I promise not
to destroy the Earth anytime soon. Thanks again, Thanks.

Speaker 1 (49:49):
Everyone out there for joining us on this episode. We
love hearing from you. Please send us your questions and
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