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Is the length of a day changing? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: Hey, Daniel, do your days feel longer or shorter as
• 0:10
  Speaker 1: you get older?
• 0:11
  Speaker 2: Are you saying I'm old?
• 0:13
  Speaker 1: Okay, No, I'm saying you're older, which is an objective
• 0:17
  Speaker 1: fact about the universe and time.
• 0:20
  Speaker 2: Well, you know, as I get older, I'm sleeping less
• 0:23
  Speaker 2: and that definitely makes my days feel longer because I'm
• 0:26
  Speaker 2: awake for more hours.
• 0:28
  Speaker 1: Even are you counting naps, Katie?
• 0:31
  Speaker 2: Don't tell everyone that I nap in my office during
• 0:33
  Speaker 2: the workday, even while being paid as a university professor.
• 0:37
  Speaker 1: That's a humble brag if I've ever heard one. And also,
• 0:40
  Speaker 1: you just told everyone.
• 0:41
  Speaker 2: Now, Oh, I think I'm getting too old for this
• 0:44
  Speaker 2: whole thing. Hi. I'm Daniel. I'm a particle physicist and
• 1:02
  Speaker 2: a professor at UC Irvine, and I get paid whether
• 1:05
  Speaker 2: I nap or not.
• 1:06
  Speaker 1: I am Katie. I am a professional nap or I
• 1:11
  Speaker 1: am so good at naps you wouldn't even believe it.
• 1:13
  Speaker 1: I also run a podcast called Creature Feature. I am
• 1:17
  Speaker 1: a biology educator.
• 1:18
  Speaker 2: Hmmm, And if you ever had an episode about naps
• 1:22
  Speaker 2: in the animal world, I actually have.
• 1:24
  Speaker 1: Like there's a lot of animals that do sleep in
• 1:27
  Speaker 1: weird ways, like little like micro naps that birds do
• 1:31
  Speaker 1: where they do like little tiny, itty bitty naps throughout
• 1:34
  Speaker 1: the day in order to stay alert, or like weird
• 1:38
  Speaker 1: giraffe sleeping schedules, where it's like they sleep in these
• 1:42
  Speaker 1: weird chunks and wake up throughout the night but sleep
• 1:45
  Speaker 1: like a lot. It's very interesting the idea of this,
• 1:48
  Speaker 1: like you know, sleep during the night, bewake during the day,
• 1:51
  Speaker 1: and sleep in a solid chunk is very much just
• 1:53
  Speaker 1: like a human quirk, right, A lot of animals sleep differently.
• 1:57
  Speaker 2: Well, I wonder about that with my dog. I never
• 1:59
  Speaker 2: find him sleeping in the same place in the morning
• 2:02
  Speaker 2: as he went to sleep in the evening, and I wonder, like,
• 2:04
  Speaker 2: does he have a night sleep? Is he just like
• 2:06
  Speaker 2: napping a bunch, because he also like sleeps most of
• 2:09
  Speaker 2: the day. So what is my dog doing in the middle.
• 2:12
  Speaker 1: Of the night, king he's online on dog Internet.
• 2:18
  Speaker 2: No, I mean recording his own podcast, wondering what I'm
• 2:20
  Speaker 2: doing rough stuff.
• 2:23
  Speaker 1: Yeah, there is an idea that human beings are not
• 2:28
  Speaker 1: necessarily meant to just sleep throughout the night, that when
• 2:32
  Speaker 1: we had natural light and slept sort of just in
• 2:37
  Speaker 1: piles of humans inside of caves or something that we
• 2:39
  Speaker 1: would wake up in intervals during the night, because we
• 2:43
  Speaker 1: have a sleep cycle right where we enter deep sleep
• 2:46
  Speaker 1: and then come out of it and then re enter
• 2:47
  Speaker 1: deep sleep. So the idea is that it might actually
• 2:50
  Speaker 1: be natural for us to wake up a few times
• 2:52
  Speaker 1: throughout the night and then fall back asleep, but that
• 2:55
  Speaker 1: we're sort of forced into a more rigid schedule with
• 2:58
  Speaker 1: our sleep and not now during the day and things
• 3:01
  Speaker 1: like that.
• 3:02
  Speaker 2: Well, what is natural about being a human is wondering
• 3:05
  Speaker 2: about how the universe works, and so welcome to the
• 3:07
  Speaker 2: podcast Daniel and Jorge Explain the Universe, a production of
• 3:11
  Speaker 2: iHeartRadio in which we try to do just that, dig
• 3:15
  Speaker 2: into the fundamental mechanisms of the universe, the tiniest particles,
• 3:19
  Speaker 2: the largest planets, the strangest black holes, and the weirdest
• 3:23
  Speaker 2: twists in the nature of the universe and space and time.
• 3:27
  Speaker 2: We want to understand how everything works, from the tiniest
• 3:30
  Speaker 2: little bits to the beautiful emergent phenomena that guide and
• 3:33
  Speaker 2: shape our daily lives, including the patterns of day and
• 3:37
  Speaker 2: night that control how tired, how sleepy we feel, and
• 3:40
  Speaker 2: how long we are awake. Katie, how long do you
• 3:43
  Speaker 2: sleep every night?
• 3:44
  Speaker 1: I know a lot of people can function with little sleep.
• 3:46
  Speaker 1: I need a lot of sleep to be coherent, so
• 3:50
  Speaker 1: I sleep maybe eight hours every night, and then unless
• 3:55
  Speaker 1: I have enough coffee, I will want like an hour
• 3:59
  Speaker 1: nap during the day. So that's nine hours of sleep
• 4:02
  Speaker 1: every day, or eight hours plus coffee.
• 4:06
  Speaker 2: I'm so glad to hear you're such a robust sleeper.
• 4:09
  Speaker 2: But sleeping is very important to our sense of well
• 4:12
  Speaker 2: being and to our ability to function and to understand
• 4:15
  Speaker 2: the universe. And our sleep patterns, of course, come from
• 4:18
  Speaker 2: the basic structure and dynamics of the solar system, the
• 4:22
  Speaker 2: Earth moving around the Sun, the way it spins. All
• 4:25
  Speaker 2: of this. Shapes are seasons, shapes are daily cycles. It's
• 4:28
  Speaker 2: really physics that sets the context for our entire lives.
• 4:32
  Speaker 1: It really is amazing how the day night cycle has
• 4:36
  Speaker 1: shaped the behavior of every living animal that has any
• 4:40
  Speaker 1: kind of photo receptor on its body. Like there's this
• 4:44
  Speaker 1: mass migration of plankton every day every night where like
• 4:49
  Speaker 1: during the night, all these little tiny, itty bitty microscopic
• 4:53
  Speaker 1: organisms come up from the depths of the ocean to
• 4:55
  Speaker 1: the surface because they are trying to evade per dation
• 5:00
  Speaker 1: during the daylight. So this day night cycle controls like
• 5:03
  Speaker 1: the largest mass migration that happens every day. And then
• 5:08
  Speaker 1: you know, of course it affects humans, but every animal's
• 5:11
  Speaker 1: behavior is impacted by this day night cycle and by
• 5:16
  Speaker 1: how many hours the sun is out, how many hours
• 5:20
  Speaker 1: the moon is out, and then the in between, like
• 5:22
  Speaker 1: animals that are crepuscular are there during dawn and dusk.
• 5:26
  Speaker 1: So it is really like all the behaviors of animals
• 5:29
  Speaker 1: to be so different if the Earth just was like
• 5:34
  Speaker 1: a little further from the Sun or a little closer,
• 5:36
  Speaker 1: a little smaller. You know, of course there would be
• 5:39
  Speaker 1: other factors that would change if we were closer to
• 5:41
  Speaker 1: the Sun or further from the Sun.
• 5:43
  Speaker 2: And at the root of it is physics, right, Physics
• 5:46
  Speaker 2: determines how fast the Earth spins and how long it
• 5:49
  Speaker 2: takes to go around the Sun. And as I'm always
• 5:51
  Speaker 2: saying that when we dig into the details of how
• 5:54
  Speaker 2: the universe works, what we're really learning about is the
• 5:56
  Speaker 2: context of our lives. We learn about where we are
• 6:00
  Speaker 2: the universe in time and in space, why we are here,
• 6:03
  Speaker 2: how it is that we ended up here, and how
• 6:06
  Speaker 2: long we should expect to be here, and for these
• 6:08
  Speaker 2: circumstances that we find so fundamental. So essential to our
• 6:11
  Speaker 2: lives how long we can rely on them to continue?
• 6:15
  Speaker 1: Are you telling me that night could just go away?
• 6:18
  Speaker 1: Because I would be so sad? I really, I really
• 6:21
  Speaker 1: like my sleep.
• 6:22
  Speaker 2: Well, a basic part of our experience here on Earth
• 6:25
  Speaker 2: is the night in days cycle. And it seems like
• 6:28
  Speaker 2: something fundamental, something that comes from the very spin of
• 6:31
  Speaker 2: the earth, something that probably has been unchanging for thousands
• 6:34
  Speaker 2: or millions or maybe even billions of years. But today
• 6:37
  Speaker 2: in the podcast, we're going to dig into exactly that question.
• 6:42
  Speaker 2: So on today's episode we'll be asking the question, is
• 6:49
  Speaker 2: the length of a day changing?
• 6:53
  Speaker 1: Does this mean we could all live longer? Because if
• 6:56
  Speaker 1: a day is longer, then you know we live longer, right,
• 7:01
  Speaker 1: That's how it works.
• 7:03
  Speaker 2: Well, if it day is longer, you might live fewer days, right,
• 7:06
  Speaker 2: even though which day is longer? If you want to
• 7:09
  Speaker 2: live more days, you need shorter days, right, right? Living
• 7:13
  Speaker 2: any longer just changing the units.
• 7:17
  Speaker 1: But if you change the units psychologically, does that make
• 7:20
  Speaker 1: a difference. I know, we got to get into what
• 7:23
  Speaker 1: people think about this topic. But there is this really
• 7:26
  Speaker 1: interesting phenomenon where people have studied what it's like to
• 7:29
  Speaker 1: be in a cave for a long period of time
• 7:32
  Speaker 1: because you do not have any input in terms of
• 7:35
  Speaker 1: what time of day it is, so you don't get
• 7:38
  Speaker 1: any kind of sunlight, you don't get any moonlight, and
• 7:41
  Speaker 1: most importantly, you get no change and you get no
• 7:44
  Speaker 1: change in temperature. It's just total stasis and people completely
• 7:49
  Speaker 1: lose track of time. They have no idea how long
• 7:51
  Speaker 1: they've been in there. Like there is a guy who
• 7:53
  Speaker 1: I think massively underestimated how much time he had been
• 7:57
  Speaker 1: in that cave.
• 7:57
  Speaker 2: There's that French guy. He went into a cave for
• 8:00
  Speaker 2: a few months and had no information about how time
• 8:03
  Speaker 2: was passing. And when he came out and asked him
• 8:05
  Speaker 2: how many days have passed, and he was a month
• 8:07
  Speaker 2: off after just three months.
• 8:09
  Speaker 1: Yeah, yeah, I think he had like underestimated it by
• 8:12
  Speaker 1: a month thout the time and there was shorter so
• 8:15
  Speaker 1: I guess. Yeah, but our perception of the sun cycle
• 8:19
  Speaker 1: may actually change how much we perceive sort of time,
• 8:24
  Speaker 1: So you know, that's very interesting. But yeah, I don't know.
• 8:27
  Speaker 1: I'm really curious to find out about this because that's
• 8:30
  Speaker 1: so interesting. I don't know if a day is changing,
• 8:32
  Speaker 1: what do people think?
• 8:34
  Speaker 2: Well, in some sense, units are irrelevant, right, you live
• 8:37
  Speaker 2: the same amount of time, and no matter whether days
• 8:39
  Speaker 2: are longer or shorter. But you're right, it does psychologically
• 8:42
  Speaker 2: make a difference. I mean, you run faster in centimeters
• 8:46
  Speaker 2: per second than you do in meters per second. It's
• 8:48
  Speaker 2: the same speed.
• 8:49
  Speaker 1: The instant way to gain more fitness, to be more fit,
• 8:53
  Speaker 1: just change your units.
• 8:54
  Speaker 2: My family is a tradition that when we go on
• 8:56
  Speaker 2: vacation within the United States, we pretend we're in a
• 8:59
  Speaker 2: foreign country where the exchange rate is different, so everything
• 9:01
  Speaker 2: seems cheaper because it makes us relax smaller on vacation, like, oh,
• 9:06
  Speaker 2: you know it cost ten dollars, that's only five dollars
• 9:08
  Speaker 2: in vacation dollars.
• 9:10
  Speaker 1: Hey, yeah, so yeah, it's I have food money, which
• 9:14
  Speaker 1: is not real money. Like I'm buying food. I need
• 9:17
  Speaker 1: this for my body. It's not real money. It's food money.
• 9:20
  Speaker 2: So sometimes these definitions do change the way we experience
• 9:24
  Speaker 2: these things. But on today's episode, we're interested in a
• 9:26
  Speaker 2: deeper question, which is about the rotation of the earth
• 9:29
  Speaker 2: itself and whether that is changing. So I was curious
• 9:32
  Speaker 2: about whether people out there had thoughts on this question.
• 9:35
  Speaker 2: So I went out there to ask our group of
• 9:37
  Speaker 2: volunteers if they thought the length of a day was changing.
• 9:42
  Speaker 2: Before you hear these answers, think about it for a
• 9:44
  Speaker 2: second yourself. What do you think about the possibility that
• 9:46
  Speaker 2: the Earth's rotation could be changing with time. Here's what
• 9:51
  Speaker 2: our volunteer had to say.
• 9:53
  Speaker 3: As far as I know, the speed of the rotation
• 9:56
  Speaker 3: of the Earth is going down, so the days are
• 10:01
  Speaker 3: getting longer and longer, but very very slowly.
• 10:05
  Speaker 2: Unfortunately, this time we only have one volunteer response, so
• 10:08
  Speaker 2: you're hearing one single solitary voice.
• 10:11
  Speaker 1: Guys, you got to get in here and you got
• 10:13
  Speaker 1: to start making puns, because that's you'll know. Daniel will
• 10:17
  Speaker 1: definitely read your answer. If you throw a pun in there,
• 10:22
  Speaker 1: or an honest engagement with the question at hand, that
• 10:26
  Speaker 1: might also be good.
• 10:27
  Speaker 2: If you'd like to join this group for future episodes,
• 10:29
  Speaker 2: please don't be shying right to me two questions at
• 10:32
  Speaker 2: Daniel Atjorhan dot com. You might be the single solitary
• 10:35
  Speaker 2: voice on a future episode, and if.
• 10:37
  Speaker 1: You are, you win a prize, and that prize is
• 10:40
  Speaker 1: a little thumbs up. Can you hear it? I'm giving
• 10:42
  Speaker 1: it right now? Yeah. Yeah, So I guess like I
• 10:47
  Speaker 1: understand that if I roll a ball right, it'll stop
• 10:52
  Speaker 1: rolling right, it will lose momentum. Uh. The Earth is
• 10:56
  Speaker 1: more or less a huge ball. The way I understand
• 10:59
  Speaker 1: it is the reason we keep moving around and rotating
• 11:03
  Speaker 1: is because of things like the sun. Like we are
• 11:07
  Speaker 1: orbiting the sun, and so that doesn't seem like that
• 11:11
  Speaker 1: should change unless the Sun changes, and then our other rotation,
• 11:15
  Speaker 1: rotating around our axis, I thought had something to do
• 11:19
  Speaker 1: with both the Sun and maybe like our molten core.
• 11:24
  Speaker 1: I gotta admit to you I have not thought too
• 11:27
  Speaker 1: much about it for a while.
• 11:29
  Speaker 2: Well, the first step is to figure out what exactly
• 11:32
  Speaker 2: is it we're talking about, because it turns out that
• 11:35
  Speaker 2: the definition of a day itself is a little bit
• 11:38
  Speaker 2: slippery and involves a lot of the things that you mentioned.
• 11:41
  Speaker 2: The most boring definition of a day is just like
• 11:44
  Speaker 2: a certain number of seconds. The definition of a second,
• 11:47
  Speaker 2: of course, just comes from how long it takes a
• 11:50
  Speaker 2: caesium atom to do like nine trillion oscillations. So that's
• 11:54
  Speaker 2: defined in terms of some like physical standard. And then
• 11:58
  Speaker 2: one definition of a day is just eighty six thousand,
• 12:01
  Speaker 2: four hundred seconds, just thirty six hundred seconds per hour
• 12:04
  Speaker 2: times twenty four hours, and that gives you a definition
• 12:08
  Speaker 2: of a day, but that's just like a fixed number
• 12:10
  Speaker 2: of seconds. It has no relationship to like how fast
• 12:12
  Speaker 2: the Earth is actually spinning. It's just like historically this
• 12:16
  Speaker 2: is roughly what a day was like.
• 12:18
  Speaker 1: They should have named that show twenty four eighty six thousand,
• 12:22
  Speaker 1: four hundred, because that's a bigger number and therefore cooler.
• 12:25
  Speaker 1: You can have more opportunities to build tensions.
• 12:30
  Speaker 2: Astronomically speaking, we might think of a day as what
• 12:34
  Speaker 2: astronomers call a solar day, which is the time between
• 12:38
  Speaker 2: high noons, Like when the Sun is exactly above you
• 12:41
  Speaker 2: in the sky. How many seconds between that and the
• 12:43
  Speaker 2: next time it happens. And that makes a lot of sense,
• 12:47
  Speaker 2: and it sort of aligns with what we imagine to
• 12:49
  Speaker 2: be a day. But there's a subtle wrinkle there, which
• 12:52
  Speaker 2: is that in the time it takes for the Earth
• 12:55
  Speaker 2: to spin, we're also moving around the Sun. So one
• 13:00
  Speaker 2: solar day is actually slightly more than one full rotation.
• 13:04
  Speaker 2: If you imagine, like the direction you're facing on the
• 13:07
  Speaker 2: first noon, then when the Earth has gone around the Sun,
• 13:10
  Speaker 2: you're now not facing the same direction on the next noon.
• 13:13
  Speaker 2: Because the Earth rotates in the same direction it moves.
• 13:17
  Speaker 2: You have to point at a slightly different angle, so
• 13:20
  Speaker 2: it's slightly more than one actual rotation of the Earth
• 13:22
  Speaker 2: is a solar day.
• 13:24
  Speaker 1: I'm having flashbacks to geometry class when we learned like
• 13:27
  Speaker 1: arcs and stuff, and it's like, oh, when will I
• 13:30
  Speaker 1: need to know this? When will this come in handy?
• 13:33
  Speaker 2: So the most precise definition of a day comes from
• 13:36
  Speaker 2: a stellar day, which is relative to like the fixed stars,
• 13:40
  Speaker 2: which they also move, of course, but they move on
• 13:42
  Speaker 2: a much longer timescale, so we can imagine that they're fixed.
• 13:45
  Speaker 2: So the stellar day is like how long it takes
• 13:48
  Speaker 2: the Earth's surface to rotate one time. It's not relative
• 13:52
  Speaker 2: to the motion of the Earth around the Sun. It's
• 13:54
  Speaker 2: more independent in that sense. Or from the surface of
• 13:57
  Speaker 2: the Earth, you can say how long it takes for
• 13:59
  Speaker 2: a star to return to the same position in the sky.
• 14:02
  Speaker 2: That's a stellar day.
• 14:03
  Speaker 1: Okay, that seems like it would be the most consistent. Also,
• 14:06
  Speaker 1: it just sounds really cheerful, like have a stellar days.
• 14:11
  Speaker 2: It does. And you pointed out something else earlier, which
• 14:14
  Speaker 2: is like, all this depends on the motion of stuff
• 14:17
  Speaker 2: through space and specifically the Earth's spin. Right, the Earth
• 14:21
  Speaker 2: is spinning as it goes around the Sun, and A
• 14:23
  Speaker 2: basic fact we learn in physics is conservation of Angland momentum.
• 14:28
  Speaker 2: In our universe, momentum is conserved, which means if you
• 14:30
  Speaker 2: have a certain amount of momentum and you do a
• 14:32
  Speaker 2: bunch of stuff, things bounce into each other or off
• 14:35
  Speaker 2: walls or whatever, and you add up the momentum before
• 14:37
  Speaker 2: and after, it has to be the same. That comes
• 14:40
  Speaker 2: from a deep symmetry in the universe. Space translation that
• 14:43
  Speaker 2: it doesn't matter where in the universe you do an
• 14:45
  Speaker 2: experiment or where your solar system is, laws of physics
• 14:48
  Speaker 2: should be the same. We also conserve Angler momentum, which
• 14:52
  Speaker 2: is related to how fast things rotate and how their
• 14:55
  Speaker 2: mass is distributed. And Angler momentum conservation also comes from
• 14:59
  Speaker 2: a deep symmetry the universe. In this case, it's the
• 15:01
  Speaker 2: rotational invariance. The fact that there's no preferred direction in
• 15:05
  Speaker 2: the universe is why we have angular momentum conservation. We
• 15:09
  Speaker 2: have a whole bunch of episodes about Nuther's theorem and
• 15:11
  Speaker 2: the connection between symmetries and conservation laws, but in this case,
• 15:15
  Speaker 2: it suggests to us that like, hey, the Earth is
• 15:18
  Speaker 2: out there in space not really interacting with much, shouldn't
• 15:21
  Speaker 2: it spin be constant if there's conservation of angular momentum.
• 15:25
  Speaker 1: I'm assuming that it is actually interacting with stuff though.
• 15:29
  Speaker 2: Yeah, so that simple model would suggest the Earth is
• 15:31
  Speaker 2: spinning and it doesn't interact with other stuff, and so
• 15:33
  Speaker 2: its spin should be the same. You set something spinning
• 15:36
  Speaker 2: in space, you come back a billion years later, it
• 15:38
  Speaker 2: should still be spinning. But there's two important caveats. One
• 15:42
  Speaker 2: is the one you mentioned. The Earth actually does interact
• 15:45
  Speaker 2: with other stuff. There's not just the Earth and the Sun.
• 15:48
  Speaker 2: There's Jupiter, there's the moon. All these other little tugs
• 15:51
  Speaker 2: can change the rotation of the Earth. We only have
• 15:55
  Speaker 2: conservation of angular momentum within a closed system. If you
• 15:59
  Speaker 2: have a force on them objects, or technically to have
• 16:01
  Speaker 2: a torque on an object from something else, then you
• 16:03
  Speaker 2: can change its spin. So, for example, you set something
• 16:07
  Speaker 2: spinning out in space, it will spin forever, but then
• 16:09
  Speaker 2: if you put your finger on it, you can slow
• 16:11
  Speaker 2: it down. That anglementum is overall conserved. It gets transferred
• 16:15
  Speaker 2: to you or to whoever's doing the tug in. But
• 16:18
  Speaker 2: in this case there are things tugging and tweaking the Earth.
• 16:21
  Speaker 1: It's like when you roll a ball, it slows down
• 16:23
  Speaker 1: not because that is, you know, the natural order of
• 16:26
  Speaker 1: things to slow down, but it is being slowed down
• 16:29
  Speaker 1: by like the ground and the air, and.
• 16:33
  Speaker 2: In this case it's mostly the moon. And we'll dig into.
• 16:36
  Speaker 1: Ooh, the moon. I knew it was the moon's fault.
• 16:40
  Speaker 2: And the second reason why the simple model of the
• 16:43
  Speaker 2: Earth spinning the same way in space forever doesn't work
• 16:47
  Speaker 2: is that the Earth is not a simple ball. The
• 16:49
  Speaker 2: Earth has layers. There's the atmosphere, there's the surface, there's
• 16:52
  Speaker 2: the inner layers, there's the ocean. There's all sorts of
• 16:55
  Speaker 2: stuff going on. We're actually interested in what affects the
• 16:59
  Speaker 2: length of a day. Is only the motion of the surface, right,
• 17:02
  Speaker 2: So the Earth is made of these different shells that
• 17:05
  Speaker 2: can spin at different speeds, and only one of them
• 17:08
  Speaker 2: determines the length of a day. And so those things
• 17:11
  Speaker 2: interact and there's coupling between them that can affect how
• 17:14
  Speaker 2: quickly the surface spins, which affects the length of a day.
• 17:17
  Speaker 1: Okay, so we may be getting slowed down by our
• 17:22
  Speaker 1: own layers here on Earth, or also the moon, which
• 17:25
  Speaker 1: begs the question do we need to get rid of
• 17:28
  Speaker 1: the moon. Yeah, let's take a break. I'm gonna just
• 17:33
  Speaker 1: pull out this corkboard I have about Katie's big plan
• 17:37
  Speaker 1: to destroy the Moon, which is very normal, and then
• 17:41
  Speaker 1: we will return and I'm sure I will have convinced
• 17:44
  Speaker 1: Daniel of my plan. So we're back. You know, let's
• 18:02
  Speaker 1: just put a pin in that destroy the Moon plan,
• 18:05
  Speaker 1: and let's talk more about what exactly are the factors
• 18:09
  Speaker 1: impacting the Earth's movements and what could be getting in
• 18:13
  Speaker 1: our way of having a normal stellar day.
• 18:17
  Speaker 2: I'm not going to let you do that, Katie. I'm
• 18:19
  Speaker 2: not going to let you just like try to normalize
• 18:20
  Speaker 2: this concept of destroying the Moon and moving on and
• 18:24
  Speaker 2: pretending it's just like part of the discourse. A totally
• 18:26
  Speaker 2: reasonable question. Can I ask, No, why didn't realize you
• 18:31
  Speaker 2: were an anti moonight?
• 18:32
  Speaker 1: I'm just asking questions, Daniel. I'm not I'm a moon centrist.
• 18:38
  Speaker 2: Like questions like should we lock Katie up and torture
• 18:41
  Speaker 2: her dog? I mean, some questions happen the obvious answer
• 18:45
  Speaker 2: of no.
• 18:46
  Speaker 1: Well, the pro moon crowd sugar is violent, is all
• 18:49
  Speaker 1: I'm going to say.
• 18:52
  Speaker 2: You know, we answered a question from a listener about
• 18:54
  Speaker 2: destroying the moon, and our answer was a definitive, Please
• 18:57
  Speaker 2: don't do that anybody, and it applies also to who
• 19:00
  Speaker 2: guest hosts, okay.
• 19:02
  Speaker 1: Because of the backwash, probably right, yeah, right now. I
• 19:06
  Speaker 1: like the moon. I like it. It's like a big
• 19:08
  Speaker 1: glowing cracker, and I like that about it. That's a
• 19:12
  Speaker 1: more right. And the Moon's not destroyed and the chunks
• 19:18
  Speaker 1: don't hit your eye, that's a more look, I mean.
• 19:22
  Speaker 2: You make it an Italian joke, all right. But the
• 19:24
  Speaker 2: Moon does play a big role in the rotation speed
• 19:27
  Speaker 2: of the Earth. Because the Earth is not just a
• 19:30
  Speaker 2: ball floating in space spinning on its own. We're in
• 19:33
  Speaker 2: a relationship with another big ball out there in space,
• 19:36
  Speaker 2: and the Moon is not that small a ball. It
• 19:39
  Speaker 2: has a lot of gravitational impact on the Earth.
• 19:42
  Speaker 1: It's like how you know if you have a kid,
• 19:44
  Speaker 1: just because they're small doesn't mean they're not gonna affect
• 19:47
  Speaker 1: your day.
• 19:50
  Speaker 2: In this case, the moon has a pretty strong gravitational
• 19:53
  Speaker 2: effect on the Earth, but not in the way you
• 19:56
  Speaker 2: might be thinking. We're all familiar with the tidal forces.
• 19:59
  Speaker 2: How the moon pulls on some of the ocean bodies
• 20:02
  Speaker 2: and makes water deeper and shallower in some respects. That's
• 20:05
  Speaker 2: because of tidal forces. The moon pulls on the Earth
• 20:08
  Speaker 2: with its gravity, and some parts of the Earth are
• 20:11
  Speaker 2: closer to the Moon than other parts, which means they
• 20:13
  Speaker 2: get stronger gravity from the Moon.
• 20:15
  Speaker 1: Yeah, tides go in, tides go out. You can explain that.
• 20:19
  Speaker 2: You can't explain that absolutely. That's not a mystery of science.
• 20:24
  Speaker 2: In particular, that tends to pull the Earth and its
• 20:27
  Speaker 2: oceans into more of a football shape because it's pulling
• 20:30
  Speaker 2: harder on the closer bits and more gently on the
• 20:32
  Speaker 2: further bits. So we're all familiar with the ocean tides,
• 20:35
  Speaker 2: but there are also land tides. The Moon is doing
• 20:39
  Speaker 2: the same thing to the Earth as it's doing to
• 20:41
  Speaker 2: its oceans. It's doing the same thing to the crust,
• 20:43
  Speaker 2: to the mantle, to the actual body of the Earth
• 20:46
  Speaker 2: as happens to the ocean. So we have a whole
• 20:49
  Speaker 2: episode about land tides. They're not as dramatic as ocean
• 20:53
  Speaker 2: tides because the Earth itself is not as flexible as
• 20:56
  Speaker 2: the oceans are squishable and sloshable. That's a technical turn.
• 21:00
  Speaker 1: They have washability, but they are there.
• 21:04
  Speaker 2: As the Moon goes around the Earth, it changes the
• 21:07
  Speaker 2: shape of the Earth. It's making the Earth more of
• 21:10
  Speaker 2: a football, and that football is pointing towards the Moon.
• 21:14
  Speaker 1: So is that like it is actually like moving things,
• 21:17
  Speaker 1: like slightly moving tectonic plates or something, or is it
• 21:21
  Speaker 1: more that it is just the entire crust is sort
• 21:24
  Speaker 1: of warping.
• 21:26
  Speaker 2: Yeah, the entire crust is sort of warping. But the
• 21:29
  Speaker 2: crust is also resisting that. Right. If the Earth was
• 21:31
  Speaker 2: made of diamond, than the Moon would have a much
• 21:34
  Speaker 2: smaller impact. So the impact of the Moon on the
• 21:37
  Speaker 2: Earth's shape depends on the structure of the Earth and
• 21:40
  Speaker 2: this tension in there, and there's friction in there because
• 21:44
  Speaker 2: what essentially is happening is that it's squeezing the Earth.
• 21:47
  Speaker 2: This is one way that you can keep an object
• 21:50
  Speaker 2: hot just through tidal forces. Some of the moons surrounding Jupiter,
• 21:53
  Speaker 2: for example, have such strong tidal forces that they're kept
• 21:57
  Speaker 2: hot like they have lava on the inside because the
• 22:00
  Speaker 2: internal friction generated by Jupiter like effectively massaging its moons.
• 22:05
  Speaker 2: In this case, the Moon is massaging the Earth and
• 22:08
  Speaker 2: in doing so is transferring heat to the Earth, and
• 22:11
  Speaker 2: so the rotational system is losing that energy. So what's
• 22:15
  Speaker 2: happening is the Moon's rotation around the Earth is becoming slower,
• 22:19
  Speaker 2: and the Earth and the Moon's rotations are also slowing down.
• 22:23
  Speaker 1: So the heat that is generated by the Earth sort
• 22:26
  Speaker 1: of going a little football shaped. That slows down the
• 22:31
  Speaker 1: rotation of the Earth and the Moon.
• 22:35
  Speaker 2: Yeah, it slows down the rotation of both of them
• 22:37
  Speaker 2: around their axis, and of the Moon around the Earth,
• 22:40
  Speaker 2: and it makes the Moon drift further away because it's
• 22:43
  Speaker 2: going more slowly. So the Moon very gradually is getting
• 22:46
  Speaker 2: further away because there's less energy in that rotation as
• 22:49
  Speaker 2: that energy is getting transferred into the Earth and the Moon.
• 22:52
  Speaker 1: The heat energy comes from somewhere, and it is coming
• 22:55
  Speaker 1: from what would have been the rotational energy.
• 22:58
  Speaker 2: And this is how tidal locking happens. In many scenarios
• 23:01
  Speaker 2: of two bodies will be tidally locked, so they're always
• 23:05
  Speaker 2: facing each other with the same side. The Moon is
• 23:07
  Speaker 2: already tidly locked to the Earth, and given enough time,
• 23:11
  Speaker 2: the Moon will slow down the rotation of the Earth. Eventually,
• 23:15
  Speaker 2: the rotation of the Earth will take twenty eight of
• 23:17
  Speaker 2: our current days, So the Moon is having a pretty
• 23:20
  Speaker 2: strong effect on the rotation of the Earth.
• 23:23
  Speaker 1: I hate that. I don't like that at all, Daniel,
• 23:26
  Speaker 1: because I don't want to wait a whole month to
• 23:29
  Speaker 1: go to bedtime, because I love bedtime and I love sleeping.
• 23:33
  Speaker 1: I also don't want to wait twenty eight days to
• 23:35
  Speaker 1: wake up in the morning because I'm gonna, really, I'm
• 23:38
  Speaker 1: gonna be so angry and so like, don't even you
• 23:43
  Speaker 1: dare speak to me until I've had that monthly coffee.
• 23:46
  Speaker 2: I know. Wouldn't it be weird if a year was
• 23:48
  Speaker 2: like twelve days long? That'd be really strange. Yeah, it'd
• 23:51
  Speaker 2: be like your birthday every couple of weeks.
• 23:54
  Speaker 1: I feel like we would have to undergo some kind
• 23:56
  Speaker 1: of radical evolution. I mean, everything would at the point,
• 24:00
  Speaker 1: how long is that going to take, Daniel, because I
• 24:03
  Speaker 1: need a plan.
• 24:04
  Speaker 2: It's a pretty slow process. Actually, every century it affects
• 24:08
  Speaker 2: the rotation of the Earth by two point three milliseconds.
• 24:12
  Speaker 2: So this is a pretty small effect, although over you know,
• 24:16
  Speaker 2: cosmological time scales, it's dramatic. Just after the Moon was
• 24:20
  Speaker 2: formed and a huge collision of some proto planet with
• 24:23
  Speaker 2: the pre Earth, we think that the rate that the
• 24:26
  Speaker 2: Earth was spinning was about six hours for one rotation,
• 24:29
  Speaker 2: so day was just six hours long, and now it's
• 24:31
  Speaker 2: around twenty four hours long, and eventually it'll be twenty
• 24:34
  Speaker 2: eight days long. All that is getting slowed down gradually
• 24:38
  Speaker 2: by the Moon.
• 24:39
  Speaker 1: Do you think there will still be life on the
• 24:41
  Speaker 1: planet at that point or are we going to be
• 24:44
  Speaker 1: undergoing some problems that would make it difficult for life
• 24:48
  Speaker 1: to survive that situation.
• 24:50
  Speaker 2: This is deep in the future, and so between now
• 24:53
  Speaker 2: and then we could get hit by comets. The Sun
• 24:56
  Speaker 2: will expand and it will get brighter. So a lot
• 24:58
  Speaker 2: of things are going to change. Any difficulty to extrapolate
• 25:01
  Speaker 2: that far in the future. I mean, if we even
• 25:03
  Speaker 2: survive the next ten years without blowing ourselves to smithereens right,
• 25:07
  Speaker 2: But this is definitely one effect.
• 25:09
  Speaker 1: So you're an optimist, is what you're saying. You're an optimist.
• 25:13
  Speaker 2: I'm saying we don't know, We can't know, and I
• 25:16
  Speaker 2: think sometimes not knowing is better than knowing. Yeah, I
• 25:19
  Speaker 2: don't know. That makes me an optimist or a pessimist.
• 25:24
  Speaker 1: Okay, So the Moon is interfering with our spin here.
• 25:27
  Speaker 1: It's a harshing our mellow or maybe enhancing our mellow.
• 25:32
  Speaker 1: I don't know. I'm pro moon. Don't worry about that.
• 25:35
  Speaker 1: But is there anything else that is going on that
• 25:39
  Speaker 1: is affecting our jam around the Sun?
• 25:42
  Speaker 2: So many other things are going on, and some of
• 25:45
  Speaker 2: them are fighting back against the powers of the Moon. So,
• 25:48
  Speaker 2: for example, our oceans and climate change and the glaciers,
• 25:52
  Speaker 2: all of these things are working in the other direction
• 25:55
  Speaker 2: to actually speed up the rotation of the Earth.
• 25:58
  Speaker 1: Whoa, So so there are anti moon forces on Earth? Yes,
• 26:03
  Speaker 1: all right, So I get why the oceans are anti
• 26:07
  Speaker 1: moon because the Moon's always messing with them. But all right,
• 26:10
  Speaker 1: so we've got glaciers that are melting. How does that
• 26:15
  Speaker 1: increase our spin?
• 26:16
  Speaker 2: So even though angular momentum has to be conserved, that
• 26:19
  Speaker 2: doesn't mean necessarily that the spin velocity of the surface
• 26:22
  Speaker 2: has to be conserved. In the same way that if
• 26:24
  Speaker 2: you're a figure skeater and you have a fixed angular momentum,
• 26:27
  Speaker 2: you can pull your arms into be going faster. What
• 26:30
  Speaker 2: you've done is you've changed where your mass is distributed.
• 26:33
  Speaker 2: And since angular momentum depends not just on your spin velocity,
• 26:37
  Speaker 2: but on how that mass is distributed from the spin axis. Like,
• 26:40
  Speaker 2: the more mass you have far away from a spin axis,
• 26:43
  Speaker 2: the more angular momentum you have. So if you bring
• 26:45
  Speaker 2: that mass in closer to the axis, you have to
• 26:48
  Speaker 2: be spinning faster to have the same angular momentum. And
• 26:51
  Speaker 2: so if you can somehow make the Earth more compact,
• 26:54
  Speaker 2: then you can make it spin faster. One way to
• 26:56
  Speaker 2: do that is to bring massive stuff that's high up
• 26:59
  Speaker 2: i e. Frozen water in glaciers down lower. And so
• 27:03
  Speaker 2: for example, if you take all of the glaciers on
• 27:06
  Speaker 2: Earth and all the snow and you melt it and
• 27:09
  Speaker 2: you bring it down so closer to the rotation axis
• 27:11
  Speaker 2: of the Earth, then that has the effect of speeding
• 27:15
  Speaker 2: up the Earth's rotation.
• 27:17
  Speaker 1: I see. So you're more evenly distributing that mass because
• 27:20
  Speaker 1: like the ocean levels rise, but these very high peaks
• 27:24
  Speaker 1: in terms of glaciers lower down. So like now that
• 27:28
  Speaker 1: mouse is more evenly distributed, you know, which is bad
• 27:33
  Speaker 1: for us, but good if you want to spin really fast.
• 27:36
  Speaker 2: Yeah, exactly. Like if you wanted to slow down the
• 27:39
  Speaker 2: spin of the Earth, you could build really really tall
• 27:41
  Speaker 2: towers and lift a bunch of really big glaciers up
• 27:45
  Speaker 2: to the tops of them. That would slow down the
• 27:47
  Speaker 2: spin of the Earth. The melting of the glaciers is
• 27:49
  Speaker 2: basically the opposite. Says, oh, we already have a bunch
• 27:52
  Speaker 2: of these glaciers kind of elevated at the tops of mountains,
• 27:55
  Speaker 2: and so let's bring them down as low as we can,
• 27:59
  Speaker 2: and that will speed up the spin of the pair.
• 28:01
  Speaker 1: I see you've been peeking at my plans for Katie's
• 28:03
  Speaker 1: sky a glue.
• 28:06
  Speaker 2: There's another effect there, which is the weight of the
• 28:08
  Speaker 2: glaciers also changes a little bit the shape of the
• 28:11
  Speaker 2: Earth because there's so much ice in the polar regions.
• 28:14
  Speaker 2: What happens if that all melts is you get this
• 28:16
  Speaker 2: redistribution of ice and you get this post glacial rebound
• 28:20
  Speaker 2: where you no longer have this dramatic weight pushing down
• 28:23
  Speaker 2: the ground in the polar regions, and so that comes
• 28:26
  Speaker 2: back out a little bit. But because it's close to
• 28:28
  Speaker 2: the axis, it doesn't affect the spin of the Earth,
• 28:31
  Speaker 2: and so overall the effect is to bring more stuff
• 28:34
  Speaker 2: closer to the spin axis.
• 28:36
  Speaker 1: Okay, so by losing the weight of the poles, would
• 28:40
  Speaker 1: that make it go slower faster?
• 28:42
  Speaker 2: That makes it go faster, Yeah, because you have more
• 28:45
  Speaker 2: weight now closer to the poles. This effect is not
• 28:48
  Speaker 2: as big as the effect of the moon. It's like
• 28:51
  Speaker 2: negative point six milliseconds per century, where it's remember the
• 28:55
  Speaker 2: moon was plus two point three milliseconds per century. So
• 28:59
  Speaker 2: over all the long term effect is like one point
• 29:02
  Speaker 2: seven milliseconds per century gets added to our day. So
• 29:06
  Speaker 2: the moon really is dominating. The effect of the glaciers
• 29:09
  Speaker 2: is like a quarter of the effect of the moon.
• 29:11
  Speaker 1: Right, And we should not melt all the glaciers. I
• 29:14
  Speaker 1: think it is important to state the penguins need them,
• 29:18
  Speaker 1: polar bears need them. This is yes, no, no, Let's
• 29:24
  Speaker 1: keep the moon where it is. Let's keep the glaciers
• 29:25
  Speaker 1: where they is. If we can, like, don't do this.
• 29:29
  Speaker 1: But if you do do this, and you melt all
• 29:31
  Speaker 1: the glaciers and now you have this like evenly distributed water,
• 29:34
  Speaker 1: it doesn't seem like it'd be just as simple as like, well,
• 29:37
  Speaker 1: now the Earth's sort of more compact. It's not just
• 29:40
  Speaker 1: like pulling your arms in, right if you're an ice skater,
• 29:43
  Speaker 1: because it is, water has its own properties.
• 29:45
  Speaker 2: Yes, there's a big water cycle on the Earth, and
• 29:47
  Speaker 2: the water interacts heavily with the atmosphere, and so the
• 29:51
  Speaker 2: moon and the melting of the glaciers and climate change
• 29:54
  Speaker 2: sort of dominate the longer term effects, like over centuries. Definitely,
• 29:58
  Speaker 2: the length of a day is increasing, but there are
• 30:00
  Speaker 2: also much shorter term effects where the Earth is speeding
• 30:02
  Speaker 2: up and slowing down due to changes in the atmosphere.
• 30:06
  Speaker 2: Think what the Earth is a bunch of shells. You
• 30:08
  Speaker 2: have like the inner core, you have the surface, you
• 30:10
  Speaker 2: have the atmosphere. If you need to conserve angular momentum,
• 30:14
  Speaker 2: you could speed up one of them and slow down
• 30:16
  Speaker 2: another one, right the same way that like an astronaut
• 30:19
  Speaker 2: in space can change how they're spinning by moving their
• 30:22
  Speaker 2: arms around, So some parts of them can be spinning faster,
• 30:25
  Speaker 2: some parts of them can be spinning slower. And the
• 30:28
  Speaker 2: atmosphere doesn't have to spin at the same rate as
• 30:31
  Speaker 2: the earth.
• 30:32
  Speaker 1: Right, So that's kind of like how like gyroscopes work. Right,
• 30:36
  Speaker 1: you have like different layers and then different spinning, and
• 30:39
  Speaker 1: then you get pork and then I don't remember the rest.
• 30:43
  Speaker 2: Ah, that's exactly right, And this is a big source
• 30:46
  Speaker 2: of like weather on Earth and wind. Right. Wind is
• 30:49
  Speaker 2: basically when the atmosphere and the surface are not spinning
• 30:52
  Speaker 2: at the same speed, and so you feel it.
• 30:54
  Speaker 1: Right like when you're watching clouds move up ahead, it
• 30:57
  Speaker 1: does feel like there is a you know, a layer
• 31:00
  Speaker 1: moving above us mm hmm.
• 31:03
  Speaker 2: And a lot of this is due to the clouds
• 31:05
  Speaker 2: and the water cycle like, think about what happens when
• 31:08
  Speaker 2: water is moving through its natural progression of evaporation and precipitation.
• 31:13
  Speaker 2: When water evaporates, it's going up, right, and so when
• 31:17
  Speaker 2: it goes up, it can't be rotating at the same
• 31:20
  Speaker 2: speed to conserve angular momentum. It needs to be going slower, right.
• 31:24
  Speaker 2: Or think about it another way. If everything was rotating together,
• 31:28
  Speaker 2: then things at higher altitudes are actually moving faster because
• 31:31
  Speaker 2: they have a longer path, sort of like runners on
• 31:34
  Speaker 2: the outside laps of a race have to be moving
• 31:36
  Speaker 2: faster to keep up.
• 31:38
  Speaker 1: So as water is evaporating, is that because the water
• 31:41
  Speaker 1: starts out slower and it's like merging into the high
• 31:45
  Speaker 1: speed lane, but at a slower speed than the water
• 31:48
  Speaker 1: in the atmosphere? Is that's slowing down the atmosphere exactly.
• 31:52
  Speaker 2: And so as water rises, it falls behind because it's
• 31:55
  Speaker 2: not moving as fast, right, So it's effectively slowing down
• 32:00
  Speaker 2: the atmosphere. And this is why we get hurricanes.
• 32:03
  Speaker 1: Oh wow, okay, I mean I was going to say,
• 32:06
  Speaker 1: this is just how like traffic works, right, Nobody knows
• 32:09
  Speaker 1: how to zipper. Apparently water also doesn't know how to zipper,
• 32:12
  Speaker 1: and it slows down all the traffic, But how does
• 32:15
  Speaker 1: that cause hurricanes?
• 32:16
  Speaker 2: So as water is rising, the direction in which it
• 32:19
  Speaker 2: falls behind depends on the direction of the Earth's spin
• 32:23
  Speaker 2: and also the latitude the distance from the equator. Stuff
• 32:27
  Speaker 2: at the equator is traveling the fastest, and stuff of
• 32:29
  Speaker 2: the poles is not moving around the Earth at all,
• 32:32
  Speaker 2: just spins in place. So as water rises, some parts
• 32:35
  Speaker 2: fall behind more than others because they're traveling at different speeds.
• 32:39
  Speaker 2: This is basically how the Corioles effect works, and that's why,
• 32:42
  Speaker 2: for example, you get hurricanes going in one direction in
• 32:45
  Speaker 2: the northern hemisphere and the other direction on the southern hemistere.
• 32:49
  Speaker 2: We have a whole episode about tropical storms and hurricanes
• 32:52
  Speaker 2: and even space hurricanes that relates to this.
• 32:55
  Speaker 1: But toilets do flush in the same direction no.
• 32:58
  Speaker 2: Matter where you are, Yes, they do. I mean, listeners,
• 33:00
  Speaker 2: you tell me I've never been to the Sun's hemisphere.
• 33:04
  Speaker 2: But the idea is that essentially you have transfer of
• 33:07
  Speaker 2: velocity and angle momentum between these two layers, and so
• 33:10
  Speaker 2: you can make the atmosphere move slower by loading it
• 33:14
  Speaker 2: up with water, where you can make it move faster
• 33:16
  Speaker 2: by dumping water. And if the atmosphere is moving faster
• 33:20
  Speaker 2: or slower. The surface also moves faster or slower, because again,
• 33:23
  Speaker 2: angular momentum is roughly conserved, and so by speeding up
• 33:27
  Speaker 2: one layer, you can slow down another layer. And we
• 33:30
  Speaker 2: all know, of course how they can transfer angular momentum
• 33:32
  Speaker 2: between each other. That's basically a wind. Right when wind
• 33:35
  Speaker 2: is blowing across the surface of the Earth, it can
• 33:38
  Speaker 2: actually speed up the earth, or if the Earth is
• 33:41
  Speaker 2: moving faster, it's leaving the atmosphere behind that also creates wind.
• 33:45
  Speaker 2: So our experience of wind and storms, this is like
• 33:48
  Speaker 2: the surface and the atmosphere exchanging angular momentum.
• 33:52
  Speaker 1: I guess I never thought of the weather as exchanging
• 33:56
  Speaker 1: angular momentum. So next time I'm out, I'm gonna be like, wow,
• 33:59
  Speaker 1: look at this exchange of angular momentum today. Lovely, isn't it.
• 34:03
  Speaker 2: Yeah, Well, this is really what dominates the change in
• 34:06
  Speaker 2: the length of a day on the day to day
• 34:09
  Speaker 2: or month to month cycle. Like we talked about it
• 34:11
  Speaker 2: more detail in a little bit, But the length of
• 34:13
  Speaker 2: the day changes by quite a bit through the year
• 34:15
  Speaker 2: and over the years, and these short term effects really
• 34:17
  Speaker 2: are dominated by what's going on in the atmosphere. So
• 34:21
  Speaker 2: the weather changes the length of a day. Isn't that
• 34:24
  Speaker 2: kind of crazy?
• 34:25
  Speaker 1: That is crazy. I've always suspected it though, because sometimes
• 34:28
  Speaker 1: when the weather's really bad, the day just goes on
• 34:31
  Speaker 1: and on and on. I'm sure that's what you mean. Well,
• 34:34
  Speaker 1: let's take a quick break and when we get back,
• 34:37
  Speaker 1: we're going to talk about more ways that the Earth's
• 34:40
  Speaker 1: own issues is messing with It's been all right. So
• 34:56
  Speaker 1: the Earth is a complicated sphere. Not not exactly a sphere,
• 35:01
  Speaker 1: you know, more of an what is it, It's more
• 35:03
  Speaker 1: of an oblong right, a.
• 35:05
  Speaker 2: Little bit of a squashed basketball.
• 35:06
  Speaker 1: Actually, oh, there we go. That's what it was said
• 35:09
  Speaker 1: right by the first astronauts, is like, look at that
• 35:11
  Speaker 1: squash basketball, the little blue squashed basketball. So we've talked
• 35:16
  Speaker 1: about the effect that the moon has. We've talked about
• 35:18
  Speaker 1: the melting of the glaciers, and also the atmosphere and weather.
• 35:23
  Speaker 2: M hmmm.
• 35:24
  Speaker 1: Are there other factors internal to Earth that effects spin?
• 35:28
  Speaker 2: Yeah, we talked about what's out beyond the Earth. We
• 35:31
  Speaker 2: talked about what's above the surface, but what's going on
• 35:33
  Speaker 2: below the surface also has a big impact on how
• 35:36
  Speaker 2: fast the surface is spinning. The basic idea there is
• 35:39
  Speaker 2: the same that if the core spins at different speeds,
• 35:43
  Speaker 2: then the surface will spin at different speeds. Like if
• 35:46
  Speaker 2: something happened to speed up the core, then the surface
• 35:49
  Speaker 2: would slow down, or if the core went slower, the
• 35:52
  Speaker 2: surface would go faster, for the same gyroscopic reasons, right
• 35:56
  Speaker 2: conservation of angular momentum. And we have a big, big,
• 36:00
  Speaker 2: heavy core at the center of the Earth that spins
• 36:03
  Speaker 2: in weird ways, and how it spins and how that
• 36:06
  Speaker 2: spin changes definitely affects the length of the day.
• 36:09
  Speaker 1: When I visualize the Earth's core, I do see a
• 36:14
  Speaker 1: lava lamp, And I know that's probably not exactly accurate,
• 36:18
  Speaker 1: but that's how I imagine it, Like a bunch of hot,
• 36:21
  Speaker 1: gloopy substances kind of wiggling around each other inside there.
• 36:26
  Speaker 2: Yeah, that's not a bad mental model of.
• 36:31
  Speaker 1: I knew I could learn something from my bad taste
• 36:33
  Speaker 1: and home to core.
• 36:35
  Speaker 2: We have a few layers inside the Earth, but the
• 36:37
  Speaker 2: core is a big blob of iron and nickel. It's
• 36:41
  Speaker 2: about the size of Pluto. And because it's a massive
• 36:44
  Speaker 2: small changes in its spin will affect the spin of
• 36:47
  Speaker 2: the rest of the planet. And you might wonder, like, well,
• 36:50
  Speaker 2: how do we even know what's inside the planet and
• 36:52
  Speaker 2: how fast it's spinning. Well, nobody's been able to drill
• 36:56
  Speaker 2: down there and see it directly because.
• 36:58
  Speaker 1: Willis didnt hang on.
• 37:01
  Speaker 2: We can kind of ultrasound the earth, right, How does
• 37:04
  Speaker 2: an ultrasound work? How do you see a baby in
• 37:07
  Speaker 2: a pregnant woman's belly without opening her up? Of course,
• 37:10
  Speaker 2: as you send little sound waves down in there, ultrasound
• 37:13
  Speaker 2: emids high frequency sound waves higher than you can hear
• 37:17
  Speaker 2: infrasound would be very low frequency ultrasound amidst those sound waves.
• 37:21
  Speaker 2: And then based on how those soundwaves move to the
• 37:23
  Speaker 2: body and reflect and bounce back and interfere, we get
• 37:27
  Speaker 2: a picture of what's going on, sort of like knocking
• 37:30
  Speaker 2: on a wall to see whether it's tallow or not.
• 37:32
  Speaker 2: And as you move around you get different sounds. You
• 37:35
  Speaker 2: can sort of like make a mental image for what's
• 37:37
  Speaker 2: going on out there based on those sounds. And we
• 37:41
  Speaker 2: can do the same thing with the Earth.
• 37:43
  Speaker 1: So we take the Earth to the universe's largest obgy
• 37:47
  Speaker 1: in do an ultrasound on it. What are we seeing
• 37:51
  Speaker 1: in there?
• 37:51
  Speaker 2: So imagine we have like an earthquake, which is a
• 37:53
  Speaker 2: big sonic event. It creates pressure waves inside the Earth.
• 37:58
  Speaker 2: Those waves propagate through the earth. Earth. It is basically
• 38:00
  Speaker 2: like a fluid. Those pressure waves pass through the same way,
• 38:04
  Speaker 2: like if you slap the surface of the water, you're
• 38:06
  Speaker 2: gonna get waves moving through the water. So you have
• 38:09
  Speaker 2: a big earthquake and you get waves moving through the Earth.
• 38:12
  Speaker 2: Now if they meet a layer where like the density
• 38:14
  Speaker 2: of the earth is changing a lot, then those waves
• 38:17
  Speaker 2: are going to reflect and refract the same way like
• 38:20
  Speaker 2: light moving through glass or light moving through water will
• 38:23
  Speaker 2: change direction and some of it will bounce back. Density
• 38:26
  Speaker 2: waves moving through the earth will do the same thing.
• 38:29
  Speaker 2: So that's how we know that there are different layers
• 38:32
  Speaker 2: inside the Earth because we see these reflections. Earthquakes send
• 38:36
  Speaker 2: these waves down and we see how they bounce back
• 38:39
  Speaker 2: and bounce all around. We actually have to build complicated
• 38:42
  Speaker 2: models for how we expect these things to bounce around
• 38:45
  Speaker 2: and then compare them to the measurements we make around
• 38:48
  Speaker 2: the globe with seismometers of how things are wiggling. So yeah,
• 38:52
  Speaker 2: it's basically like a big obgy in for the.
• 38:54
  Speaker 1: Earth, right, So earthquakes is the obgy in for Earth,
• 39:00
  Speaker 1: got it? And then we measure those and then we
• 39:03
  Speaker 1: can figure out what is that feedback the pattern of
• 39:06
  Speaker 1: sort of interference and what that is saying about what's
• 39:09
  Speaker 1: going on. How do we know what it is made
• 39:13
  Speaker 1: out of? Right? Like, do we just expect different sort
• 39:16
  Speaker 1: of feedback patterns from different substances or are we getting
• 39:22
  Speaker 1: direct samples of the stuff that isn't the guy center
• 39:26
  Speaker 1: of the earth.
• 39:28
  Speaker 2: We're effectively measuring the density because the density controls the
• 39:32
  Speaker 2: speed of sound. As things are denser, sound travels more
• 39:35
  Speaker 2: quickly through them. That's why sound moves more rapidly through
• 39:38
  Speaker 2: water or steel than it does through the air. Because
• 39:41
  Speaker 2: sound are pressure waves, and if those atoms are more
• 39:44
  Speaker 2: tightly packed, then they have stronger bonds between them. Then
• 39:47
  Speaker 2: rippling one is going to ripple the other one more
• 39:50
  Speaker 2: quickly than if they're like farther apart or more loosely bound.
• 39:54
  Speaker 2: So the speed at which sound travels indicates the density
• 39:58
  Speaker 2: of the material. So by seeing how long it takes
• 40:01
  Speaker 2: those waves to propagate through the earth and when they return,
• 40:04
  Speaker 2: we can get an idea for the density of each
• 40:07
  Speaker 2: of the layers. And not just the density, we can
• 40:10
  Speaker 2: also measure the speed of their rotation because how fast
• 40:14
  Speaker 2: that inner layer is moving changes what the wave looks like.
• 40:17
  Speaker 2: When it bounces back. We all know about the Doppler
• 40:20
  Speaker 2: effect that, like a police siren going by you will
• 40:23
  Speaker 2: sound different as it's approaching you and as it's Yeah, exactly,
• 40:29
  Speaker 2: the same thing is true for waves that bounce off
• 40:32
  Speaker 2: of an object. If you use the radar to measure
• 40:35
  Speaker 2: that police cars velocity as it was going by, the
• 40:38
  Speaker 2: waves that come back to you tell you something about
• 40:41
  Speaker 2: the velocity of the police car. And in the same way,
• 40:44
  Speaker 2: waves that bounce off inner layers of the earth tell
• 40:47
  Speaker 2: us about the velocity of those layers. So we can
• 40:50
  Speaker 2: use these waves not just to image the earth and
• 40:52
  Speaker 2: tell where stuff is, but also how fast it's going,
• 40:56
  Speaker 2: though that takes more precise and crisper measurements.
• 41:00
  Speaker 1: I mean, it seems kind of hard to do that though,
• 41:02
  Speaker 1: For we always have to wait for an earthquake to happen,
• 41:06
  Speaker 1: and we can't really predict where the earthquake is going
• 41:09
  Speaker 1: to be. How do we do that?
• 41:11
  Speaker 2: So the best way to do that actually is to
• 41:13
  Speaker 2: create our own sonic waves rather than just wait for earthquakes.
• 41:17
  Speaker 1: And hey, big hammer, then big hammer.
• 41:20
  Speaker 2: Basically big physics hammer. Because there was a period after
• 41:24
  Speaker 2: the development of nuclear weapons and before we stopped testing
• 41:27
  Speaker 2: them that we did tests underground. So first we had
• 41:30
  Speaker 2: nuclear weapons and we tested them above ground, which was
• 41:33
  Speaker 2: exceptionally stupid because of the atmospheric radiation. Then we realized
• 41:37
  Speaker 2: that's not such a good idea, so then we started
• 41:39
  Speaker 2: testing them underground.
• 41:41
  Speaker 1: My dad some.
• 41:43
  Speaker 2: Of these test sites. You would explode a nuclear bomb
• 41:46
  Speaker 2: underground and then you would measure the impact and that
• 41:49
  Speaker 2: would create huge sonic oscillations in the crust of the
• 41:51
  Speaker 2: earth and very crisp, very clean because it was high intensity,
• 41:56
  Speaker 2: and also very brief, so it wrung the earth like
• 41:59
  Speaker 2: a perfect.
• 42:00
  Speaker 1: Whoa, Okay, so I've got it. Like several questions. One
• 42:04
  Speaker 1: is when you explode a nuke underground, where does all
• 42:09
  Speaker 1: that radiation go? Does it just sort of sink into
• 42:11
  Speaker 1: the earth somewhere, So that's question number one.
• 42:15
  Speaker 2: It's absorbed by the material immediately surrounding the explosion, so
• 42:18
  Speaker 2: it doesn't sink. It just gets deposited in the surrounding
• 42:22
  Speaker 2: dirt and rock.
• 42:23
  Speaker 1: So are there like pockets of radiation in these areas
• 42:26
  Speaker 1: where we tested these nukes, Yes, there are, gross it's
• 42:31
  Speaker 1: like a zip on the earth. Question number two is
• 42:35
  Speaker 1: how big I've seen a basement that doesn't seem big
• 42:38
  Speaker 1: enough to do a nuke inside of. So, like, how
• 42:41
  Speaker 1: big were these areas where they tested.
• 42:43
  Speaker 2: These Yeah, well the holes themselves are not that large
• 42:46
  Speaker 2: because you want them surrounded by the rock.
• 42:48
  Speaker 1: Yeah, okay, so then you put it down into the
• 42:52
  Speaker 1: hole and then it explodes into the rock, leaving what
• 42:57
  Speaker 1: kind of like how big is that exploded?
• 43:00
  Speaker 2: These nuclear explosions have significant impact on the rock for
• 43:04
  Speaker 2: you know, meters and meters and tens of meters, and
• 43:07
  Speaker 2: then you surrounded by various sensors so you can measure
• 43:09
  Speaker 2: the energy and the length of the shockwave and all
• 43:12
  Speaker 2: sorts of stuff. And not only do you create sensors
• 43:15
  Speaker 2: for your own explosions, because of the Cold War, the
• 43:18
  Speaker 2: US government invested deeply in seismic sensors so we could
• 43:23
  Speaker 2: study the Soviet explosions because we wanted to see when
• 43:26
  Speaker 2: they were testing nuclear weapons. And if you tapped one underground,
• 43:29
  Speaker 2: everybody across the Earth can figure it out. So it
• 43:32
  Speaker 2: was sort of like a golden age for seismology because
• 43:35
  Speaker 2: not only were there these crisp events that created these
• 43:38
  Speaker 2: ripples around the Earth, but also the US government invested
• 43:42
  Speaker 2: in the best possible set of seismographs, so we could
• 43:45
  Speaker 2: get data about Soviet tests. So there's this window of
• 43:49
  Speaker 2: like fifteen years in the end of the last century
• 43:52
  Speaker 2: when there's this excellent seismographic data about what's going on
• 43:56
  Speaker 2: inside the earth.
• 43:58
  Speaker 1: We were staring down nuclear annihilation, but at least we
• 44:02
  Speaker 1: got some good data from it.
• 44:04
  Speaker 2: You know, there's so many times when important science is
• 44:07
  Speaker 2: writing on the back of like either whimsical consumer electronics
• 44:12
  Speaker 2: where people spending like billions of dollars on their gadgets,
• 44:16
  Speaker 2: or the military industrial complex where you know, they spend
• 44:19
  Speaker 2: billions of dollars on satellites or something else, and we
• 44:22
  Speaker 2: can gather science data from it. And because science funding
• 44:25
  Speaker 2: is a tiny fraction of consumer spending or military spending,
• 44:28
  Speaker 2: we always got to take advantage of that whenever we can. Yeah,
• 44:32
  Speaker 2: and so there were some folks who pretty recently dug
• 44:34
  Speaker 2: up these old tapes and this is like science heroism
• 44:38
  Speaker 2: because they had to find these data and pull them
• 44:40
  Speaker 2: off of magnetic tapes, and remember how it was stored,
• 44:43
  Speaker 2: and sometimes you have to like bake these tapes to
• 44:46
  Speaker 2: the magnetic particles adhere better to the actual tape.
• 44:49
  Speaker 1: What you bacon, Oh, you know, tapes on nuclear explosions
• 44:53
  Speaker 1: done in the sixties and seventies.
• 44:55
  Speaker 2: And so pretty recently they found this data, they pulled
• 44:58
  Speaker 2: it off, they analyzed it, and they discovered something fascinating
• 45:01
  Speaker 2: about the core of the Earth. We always expected that
• 45:04
  Speaker 2: the core is rotating slightly faster than the surface of
• 45:07
  Speaker 2: the Earth, but what they found is that it was
• 45:09
  Speaker 2: much more variable than they expected. There's sometimes when the
• 45:12
  Speaker 2: core is rotating faster, and sometimes when the core is
• 45:15
  Speaker 2: rotating slower than the surface of the Earth. The surface
• 45:18
  Speaker 2: like catches up to it and passes it, and then
• 45:20
  Speaker 2: the core rotates faster.
• 45:22
  Speaker 1: Do you think that this is random or do you
• 45:24
  Speaker 1: think there's some kind of cyclical nature to the core.
• 45:27
  Speaker 2: What they discovered is that the oscillates in like six
• 45:30
  Speaker 2: year periods, where like one is going faster and the
• 45:32
  Speaker 2: other is going faster. And this is not something we
• 45:35
  Speaker 2: understand very well. You know, the inner parts of the
• 45:38
  Speaker 2: Earth are sort of a mystery, and you know, the
• 45:40
  Speaker 2: flow of energy there and the convection cells as things
• 45:43
  Speaker 2: are moving up and bubbling and frothing inside the earth
• 45:46
  Speaker 2: are something we're still trying to understand. So this is
• 45:48
  Speaker 2: a really interesting and fascinating clue for geologists. For those
• 45:52
  Speaker 2: people who saw news coverage about it, it was a little
• 45:54
  Speaker 2: bit misleading. It suggested that the Earth's core is changing direction,
• 45:58
  Speaker 2: that it's like rotating one way and then stops and
• 46:01
  Speaker 2: rotates the other way. That's not exactly what's happening. What's
• 46:04
  Speaker 2: happening is that's going faster than the surface and then
• 46:06
  Speaker 2: sometimes slower than the surface. So it's changing direction relative
• 46:10
  Speaker 2: to the surface, but not like relative to the Sun
• 46:13
  Speaker 2: or something like that. It's not like it's actually changing direction.
• 46:17
  Speaker 2: That would be much more dramatic and more awesome, but
• 46:19
  Speaker 2: that's not the scenario. But what it does mean is
• 46:22
  Speaker 2: that it's affecting the length of the day because it
• 46:24
  Speaker 2: affects how quickly the surface is rotating.
• 46:26
  Speaker 1: Okay, so this is a call out, so I'll keep
• 46:28
  Speaker 1: it anonymous. But I did have a strange science teacher
• 46:33
  Speaker 1: in elementary school who told us that the Earth's core
• 46:37
  Speaker 1: would change directions sometime in our lifetimes and that the
• 46:42
  Speaker 1: poles would switch and we would all get deadly skin cancer.
• 46:48
  Speaker 1: Is that true?
• 46:50
  Speaker 2: The Earth's core is not going to change direction except
• 46:52
  Speaker 2: for relative to the surface of the Earth. So in
• 46:56
  Speaker 2: that sense, yes, the magnetic north and south pole is
• 46:59
  Speaker 2: something of a fun miss and it does flip every
• 47:01
  Speaker 2: once in a while, but these flips tend to be
• 47:03
  Speaker 2: like tens of thousands of years, so probably not within
• 47:06
  Speaker 2: our lifetime. Although it's a little bit chaotic. It's much
• 47:09
  Speaker 2: more chaotic than the flip in the sun, which is
• 47:12
  Speaker 2: very regular, but again not something that we understand.
• 47:16
  Speaker 1: Okay, well, you know who you are, science teacher that
• 47:19
  Speaker 1: I had, You're wrong.
• 47:23
  Speaker 2: We're all just learning about the nature of the labors, right,
• 47:25
  Speaker 2: everybody's just updating their information.
• 47:28
  Speaker 1: That's a much kinder way to put it all. Right,
• 47:31
  Speaker 1: So we are having this oscillation of the Earth's core.
• 47:35
  Speaker 1: It is sometimes slower and sometimes faster than how the
• 47:38
  Speaker 1: crust is moving, and so that is having an impact
• 47:41
  Speaker 1: on the spin of the Earth.
• 47:43
  Speaker 2: Yeah, and so there are these long term effects, right.
• 47:45
  Speaker 2: The moon is the most dominant long term effect that's
• 47:48
  Speaker 2: slowing down the rotation of the Earth and making days longer.
• 47:53
  Speaker 2: The melting of glaciers is the most important effect long
• 47:57
  Speaker 2: term that's speeding up the rotation of the Earth, though
• 48:00
  Speaker 2: it's not as dramatic as the effect of the moon.
• 48:03
  Speaker 2: On shorter timescales, we have like the rotation of the core,
• 48:07
  Speaker 2: which affects things on a few year timescales, like six
• 48:10
  Speaker 2: year cycles. Then there's the atmosphere that changes things on
• 48:13
  Speaker 2: a much shorter timescale, and so for example, there's like
• 48:17
  Speaker 2: an annual period of the length of the day changing
• 48:20
  Speaker 2: of like a third of a millisecond per day, maximizing
• 48:24
  Speaker 2: like in February, and then again like in May. And
• 48:28
  Speaker 2: so there's these funny wiggles in the length of a day.
• 48:30
  Speaker 2: If you look at the data, it goes up and
• 48:32
  Speaker 2: down through the years on these longer cycles, and then
• 48:35
  Speaker 2: there's these really fast variations throughout the year. So like
• 48:38
  Speaker 2: even during a year, not every day is the same length.
• 48:43
  Speaker 2: In fact, recently we had a day June twenty ninth,
• 48:45
  Speaker 2: my mom's birthday, I think got a coincidence two thousand
• 48:49
  Speaker 2: and two, which was the shortest day ever on record.
• 48:52
  Speaker 1: Oh my gosh, that is so unfair to your mom.
• 48:55
  Speaker 1: That's so unfair.
• 48:57
  Speaker 2: Her birthday was like a millisecond and a half more
• 49:00
  Speaker 2: than twenty four hours.
• 49:01
  Speaker 1: She was taking injustice. Injustice, Just make it up to
• 49:06
  Speaker 1: her for next birthday, give her like one point six
• 49:11
  Speaker 1: extra milliseconds of birthday time.
• 49:15
  Speaker 2: And so overall, the length of a day is not
• 49:17
  Speaker 2: changing on timescales, so we can really measure, as much
• 49:20
  Speaker 2: as we joke about it, a mill a second and
• 49:22
  Speaker 2: a half of your birthday is not something you're going
• 49:24
  Speaker 2: to notice is at length of an eye, but it
• 49:27
  Speaker 2: is something that's changing. You know. These things that we
• 49:30
  Speaker 2: think are constant, like the moon and the sun and
• 49:33
  Speaker 2: the rotation of the Earth, these things are functions of time.
• 49:37
  Speaker 2: They are descriptions of where we are in the moment,
• 49:40
  Speaker 2: and on much longer cosmological time scales, these things are
• 49:44
  Speaker 2: changing dramatically. The rotation of the Earth was a sixth
• 49:47
  Speaker 2: hour day and it's on its way to becoming a
• 49:49
  Speaker 2: twenty eight day long day, and so here we are
• 49:53
  Speaker 2: sort of in the middle of that vast cosmic journey.
• 49:55
  Speaker 2: At one particular moment, we think it's the moment that
• 49:59
  Speaker 2: defines what it's like to be on Earth, but it's
• 50:01
  Speaker 2: not really. It's just one slice of an incredibly deep history.
• 50:05
  Speaker 1: So if I sleep for like ten hours, right, I
• 50:10
  Speaker 1: could say, hey, I'm not oversleeping, I'm just planning for
• 50:14
  Speaker 1: the future.
• 50:16
  Speaker 2: You're just incredibly far sighted, that's right.
• 50:19
  Speaker 1: This is actually not laziness. This is I'm trying to
• 50:23
  Speaker 1: evolve for our eventual lengthened day night cycles.
• 50:28
  Speaker 2: Well, to me, it's fascinating that if these things change,
• 50:31
  Speaker 2: but change very slowly, life on Earth has a chance
• 50:34
  Speaker 2: to adapt. Right, It's curious to me, like, what will
• 50:37
  Speaker 2: life be like on Earth when the day night cycle
• 50:40
  Speaker 2: is twenty eight of our current days, or even a
• 50:43
  Speaker 2: week of our current days. I feel like everything on
• 50:46
  Speaker 2: Earth must be different. I mean, the weather patterns are
• 50:48
  Speaker 2: going to be very different. The entire experience of life
• 50:51
  Speaker 2: on Earth and what it takes to survive will be
• 50:54
  Speaker 2: vastly different.
• 50:55
  Speaker 1: It is so hard to imagine because it really that
• 50:57
  Speaker 1: day night cycle does determine the behavior of every creature
• 51:02
  Speaker 1: on Earth and how massively you would have to adapt
• 51:07
  Speaker 1: and change to you know, you may have just entire
• 51:11
  Speaker 1: you know, nocturnal species, and you'd have to also adapt
• 51:14
  Speaker 1: to the how cold it would get. Right, if you
• 51:16
  Speaker 1: have one side of the planet that's not facing the sun,
• 51:19
  Speaker 1: it's going to be a lot colder than the other side,
• 51:22
  Speaker 1: and the other side it's gonna be a lot hotter.
• 51:24
  Speaker 1: It is unfathomable the amount of change if there is
• 51:27
  Speaker 1: still life on Earth, Like what the adaptations would have
• 51:29
  Speaker 1: to be in that situation.
• 51:32
  Speaker 2: And what would our podcast releasing schedule be in that
• 51:35
  Speaker 2: kind of scenario? Are we releasing more often less often?
• 51:38
  Speaker 2: I'm losing track?
• 51:39
  Speaker 1: Yeah, it'll have to be based on the commute, the
• 51:42
  Speaker 1: once a month commute.
• 51:45
  Speaker 2: All right, Well, thanks Katie for joining us and spinning
• 51:47
  Speaker 2: your mind around this topic, and thanks everybody for joining
• 51:51
  Speaker 2: us on this trip around the surface of the Earth
• 51:53
  Speaker 2: and understanding the fundamentals of its rotation.
• 51:57
  Speaker 1: Yeah, I have a stellar day everyone.
• 52:00
  Speaker 2: A little bit shorter than your solar day. All right everyone,
• 52:04
  Speaker 2: Thanks again. Tune in next time for more science and curiosity.
• 52:12
  Speaker 2: Come find us on social media, where we answer questions
• 52:15
  Speaker 2: and post videos. We're on Twitter, Discorg, Instant and now TikTok.
• 52:20
  Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain
• 52:23
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 52:27
  Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 52:31
  Speaker 2: you listen to your favorite shows.