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

Episode Date: June 25, 2024

Daniel and Katie spin a tale of how the velocity of the Earth's surface is changing under our feet.See omnystudio.com/listener for privacy information.

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which is an objective fact about the universe and time. Well, you know, as I get older, I'm sleeping less, and that definitely makes my days feel longer because I'm awake for more hours. Oh, even are you counting naps? Sh, Katie, don't tell everyone that I nap in my office during the workday, even while being paid as a university professor. That's a humble brag if I've ever heard.

And also you just told everyone that. Oh, I think I'm getting too old for this whole thing. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I get paid whether I nap or not. I am Katie. I am a professional napper. I am so good at naps. You wouldn't even believe it.

I also run a podcast called Creature Feature. I am a biology educator. And have you ever had an episode about naps in the animal world? I actually have. Like there's a lot of animals that do sleep in weird ways. Like little micro-naps that birds do where they do like little tiny, itty-bitty naps throughout the day in order to stay alert. or like weird giraffe sleeping schedules

where it's like they sleep in these weird chunks and wake up throughout the night but sleep like a lot it's very interesting. The idea of this like, you know, sleep during the night, be awake during the day and sleep in a solid chunk is very much just like a human quirk, right? A lot of animals sleep differently. Well, I wonder about that with my dog.

I never find him sleeping in the same place in the morning as he went to sleep in the evening. And I wonder like, does he have a night's sleep? is he just like napping a bunch? Because he also like sleeps most of the day. So what is my dog doing in the middle of the night, Katie? He's online on dog internet. He's recording his own podcast wondering what I'm doing.

Rough stuff. Yeah. There is an idea that human beings are not necessarily meant to just sleep throughout the night. That when we had natural light and slept sort of. sort of just in piles of humans inside of caves or something, that we would wake up in intervals during the night because we have a sleep cycle, right, where we enter deep sleep and then come out of it

and then reenter deep sleep. So the idea is that it might actually be natural for us to wake up a few times throughout the night and then fall back asleep, but that we're sort of forced into a more rigid schedule with our sleep and not napping during the day and things like that. Well, what is natural about being human is wondering about how the universe works and so welcome to the podcast daniel and horay explain the

universe a production of iHeart radio in which we try to do just that dig into the fundamental mechanisms of the universe the tiniest particles the largest planets the strangest black holes and the weirdest twists in the nature of the universe and space and time we want to understand how everything works from the tiny little bits to the beautiful emergent phenomena that guide and shape our daily lives, including the patterns of day and night that control how tired, how sleepy we feel, and how long we are awake. Katie, how long do you sleep every night? I know a lot of people can function with little sleep.

I need a lot of sleep to be coherent. So I sleep maybe eight hours every night. And then unless I have enough coffee, I will want like an hour nap during the day. So that's nine hours of sleep every day or eight hours. plus coffee. I'm so glad to hear you're such a robust sleeper. But sleeping is very important to our sense of well-being and to our ability to function and to understand the universe.

And our sleep patterns, of course, come from the basic structure and dynamics of the solar system, the earth, moving around the sun, the way it spins. All of this shapes our seasons, shapes our daily cycles. It's really physics that sets the context for our entire lives. It really is amazing how the day-night cycle has shaped the behavior of every living animal that has any kind of photoreceptor on its body. Like there's this mass migration of plankton every day, every night, where like during the night all these little tiny, itty-bitty microscopic organisms

come up from the depths of the ocean to the surface because they are trying to evade predation during the daylight. So this day-night cycle controls like the largest mass migration that happens every day. And then, you know, of course it affects humans, but every animal's behavior is impacted by this day-night cycle and by how many hours the sun is out, how many hours the moon is out, and then the in-between, like animals that are crepuscular are there during dawn and dusk. So it is really like all the behaviors of animals to be so,

different if the earth just was like a little further from the sun or a little closer or a little smaller, you know, of course there would be other factors that would change if we were closer to the sun or further from the sun. And at the root of it is physics, right? Physics determines how fast the earth spins and how long it takes to go around the sun. And as I'm always saying, that when we dig into the details of how the universe works, what we're really learning about is the context of our lives. We learn about where we are in the universe, in time and in space, why we are here, how it is that we ended up here, and how long we should expect to be here. And for these circumstances that we find so fundamental, so essential to our lives, how long we can rely on

them to continue. Are you telling me that night could just go away because I would be so sad? I really, I really like my sleep. Well, a basic part of our experience here on Earth is the night and day cycle. And it seems like something fundamental, something that comes from the very spin of the earth, something that probably has been unchanging for thousands or millions or maybe even billions of years. But today on the podcast, we're going to dig into exactly that question. So on today's episode, we'll be asking the question. Is the length of a day changing? Hmm. Does this mean we could all live longer?

Because if a day is longer, then, you know, we live longer, right? That's how it works. Well, if a day is longer, you might live fewer days, right? Even though each day is longer. If you want to live more days, you need shorter days. That's not actually living any longer. You're just changing the units, right? But if you change the units psychologically, does that make a difference?

I know we've got to get into what people think about this topic, but there is this really interesting phenomenon where people have studied what it's like to be in a cave for a long period of time because you do not have any input in terms of what time of day it is. So you don't get any kind of sunlight,

you don't get any moonlight, and most importantly you get no change and you get no change in temperature. It's just total stasis and people completely lose track of time. They have no idea how long they've been in there. Like there was a guy who, I think, massively underestimated how much time he had been in that cave.

There's that French guy. He went into a cave for a few months and had no information about how time was passing. And when he came out, they asked him how many days have passed. And he was a month off after just three months. Yeah. Yeah. I think he had like underestimated it by a month about the time and there was shorter. So I guess, yeah, but our perception of the sun cycle may actually change how much we perceive

sort of time. So, you know, that's very interesting. But yeah, I don't know. I'm really curious to find out about this because that's so interesting. I don't know if a day is changing. What do people think? Well, in some sense, units are irrelevant, right? You live the same amount of time and no matter whether days are longer or shorter. But you're right, it does psychologically make a difference. I mean, you run faster in centimeters per second than you do in meters per second It gets the same speed. The instant way to gain more fitness, to be to be more fit. Just change your units.

My family has a tradition that when we go on vacation within the United States, we pretend we're in a foreign country where the exchange rate is different, so everything seems cheaper because it makes us relax more on vacation. Like, oh, you know, it costs $10. That's only $5 in vacation dollars. Hey, yeah. Yeah. I have food money, which is not real money.

Like, I'm buying food. I need this for my body. It's not real money. It's food money. So sometimes these definitions do change the way we experience these things. But on today's episode, we're interested in a deeper question, which is about the rotation of the earth itself and whether that is changing. So I was curious about whether people out there had thoughts on this question.

So I went out there to ask our group of volunteers if they thought the length of a day was changing. Before you hear these answers, think about it for a second yourself. What do you think about the possibility that the earth's rotation could be changing with time. Here's what our volunteer had to say. As far as I know, the

speed of the rotation of the earth is going down so the days are getting longer and longer, but very, very slowly. Unfortunately, this time we only had one volunteer response. You're hearing one single solitary voice.

Guys, you got to get in here and you got to start making puns because that's, you'll know, Daniel will definitely read your answer if you throw a pun in there. Or an honest engagement with the question at hand. That might also be good. If you'd like to join this group for future episodes, please don't be shy.

Write to me to Questions at Danielandhorpe.com. You might be the single solitary voice on a future episode. And if you are, you win a prize. And that prize is a little thumbs up. Can you hear it? I'm giving it right now. Yeah, yeah. So I guess like I understand that if I roll a ball, right, it'll stop rolling, right?

It will lose momentum. The earth is more or less a huge ball. The way I understand it is the reason we keep moving around and rotating is because of things like the sun. Like we are orbiting the sun. And so that doesn't seem like that should change unless the sun changes. and then our other rotation, rotating around our axis, I thought had something to do with both the sun and maybe like our molten core.

I got to admit to you, I have not thought too much about it for a while. Well, the first step is to figure out, like, what exactly is it we're talking about? Because it turns out that the definition of a day itself is a little bit slippery and involves a lot of the things that you mentioned. The most boring definition of a day is just like a certain number of seconds. The definition of a second, of course, just comes from how long it takes a cesium atom to do like 9 trillion oscillations.

So that's defined in terms of some like physical standard. And then one definition of a day is just 86,400 seconds, just 3,600 seconds per hour times 24 hours. And that gives you a definition of a day. But that's just like a fixed number of seconds. It has no relationship to like how fast the Earth is actually spinning. It's just like historically this is roughly what a day was like. They should have named that show 24, 86,400. Because that's a bigger number and therefore cooler.

You can have more opportunities to build tension. That's right. Astronomically speaking, we might think of a day as what astronomers call a solar day, which is the time between high news. Like when the sun is exactly above you in the sky, how many seconds between that and the next time it happens? And that makes a lot of sense and it sort of aligns with what we imagine to be a day, but there's a subtle wrinkle there, which is that in the time it takes for the earth to spin, or also moving around the sun. And so one solar day is actually slightly more than one full rotation. If you imagine like the direction you're facing on the first noon,

then when the earth has gone around the sun, you're now not facing the same direction on the next noon. Because the earth rotates in the same direction it moves, you have to point at a slightly different angle. So it's slightly more than one actual rotation of the earth is a solar day. I'm having flashbacks to geometry class when we learned like arcs and stuff. And it's like, oh, when will I need to know this? When will this come in handy?

So the most precise definition of a day comes from a stellar day, which is relative to like the fixed stars, which they also move, of course, but they move on a much longer time scale. So we can imagine that they're fixed. So the stellar day is like how long it takes the Earth's surface to rotate one time. It's not relative to the motion of the Earth around the sun. It's more independent in that sense. Or from the surface of the Earth, you can say how long it takes for a star to return to the same position in the sky. That's a stellar day. Okay. That seems like it would be the most consistent. Also, it just sounds really cheerful. Like, have a stellar day. that's right it does and you pointed out something else earlier which is like all this depends on the motion of stuff through space and specifically the earth's spin right the earth is spinning as it goes around the sun and the basic fact we learn in physics is conservation of angular momentum in our universe momentum is conserved which means if you have a certain amount of momentum and you do a bunch of stuff things bounce into each other or off walls or whatever and you add up the momentum before and after it has to be the same And that comes from a deep symmetry in the universe, space translation, that it doesn't matter where in the universe you do an experiment or where your solar system is, the laws of physics should be the same. We also conserve angular momentum, which is related to how fast things rotate and how their mass is distributed. And angular momentum conservation also comes from a deep symmetry of the universe. In this case, it's the rotational invariance. The fact that there's no preferred direction in the universe is why we have angular momentum conservation.

We have a whole bunch of episodes about Nuthers' theorem and the connection between symmetries and conservation laws. But in this case, it suggests to us that, like, hey, the Earth is out there in space, not really interacting with much. Shouldn't its spin be constant if there's conservation of angular momentum? I'm assuming that it is actually interacting with stuff, though. Yeah, so that simple model would suggest the Earth is spinning and it doesn't interact with other stuff, and so it spin should be the same.

You set something spinning in space, you come back a billion years later, you should still be spitting. But there's two important caveats. One is the one you mentioned. The Earth actually does interact with other stuff. There's not just the Earth and the Sun. There's Jupiter. There's the moon. All these other little tugs can change the rotation of the Earth. We only have conservation of angular momentum within a closed system. If you have a force on that object or technically if you have a torque on an object from something else, then you can change its spin. So for example, you set something spinning out in space. It will spin forever. but then if you put your finger on it, you can slow it down.

That angle momentum is overall conserved. It gets transferred to you or to whoever's doing the tugging. But in this case, there are things tugging and tweaking the earth. It's like when you roll a ball, it slows down, not because that is, you know, the natural order of things to slow down, but it is being slowed down by, like, the ground and the air. And in this case, it's mostly the moon, and we'll dig into that. Ooh, the moon. I knew it was the moon's fault.

And the second reason why the simple model of the earth spinning the same way in space forever doesn't work is that the earth is not a simple ball. The earth has layers. There's the atmosphere. There's the surface. There's the inner layers. There's the ocean. There's all sorts of stuff going on.

We're actually interested in what affects the length of a day is only the motion of the surface, right? So the earth is made of these different shells that can spin at different speeds. and only one of them determines the length of a day. And so if those things interact and there's coupling between them, that can affect how quickly the surface spins, which affects the length of a day. Okay. So we may be getting slowed down by our own layers here on Earth

or also the moon, which begs the question, do we need to get rid of the moon? Yeah, let's take a break. I'm going to just pull out this cork board I have about Katie's big plan to destroy the moon, which is very normal. And then we will return, and I'm sure I will have convinced Daniel of my plan.

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Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, sis, what if I could promise you you never had to listen to a condescending finance, bro, tell you how to manage your money again. Welcome to Brown Ambition. This is the hard part when you pay down those credit cards. If you haven't gotten to the bottom of why you were racking up credit or turning to credit cards, you may just recreate the same problem a year from now. When you do feel like you are bleeding from these high interest rates, I would start shopping for a debt consolidation loan, starting with your local credit union, shopping around online,

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I haven't audition in like over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah. We've got some of the biggest actors, musicians, content creators, and culture shifters, sharing their real stories of failure and success. You were destined to be a start. We talk all about what's viral and trending with a little bit of chisement, a lot of laughs,

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and what could be getting in our way of having a normal, stellar day. I'm not going to let you do that, Katie. I'm not going to let you just like try to normalize this concept of destroying the moon. And then moving on and pretending it's just like part of the discourse, a totally reasonable question people can ask. No. Why didn't realize you were an anti-moonite? I'm just asking questions, Daniel.

I'm not, I'm a moon centrist. Like questions like, should we lock Katie up and torture her dog? I mean, some questions have the obvious answer of no. Wow, the pro-moon crowd sure is violent is all I'm going to say. You know, we answered a question from a listener about destroying the moon. And our answer was a definitive, please don't do that, anybody. And that applies also to guest hosts, okay? Because of the backwash, probably, right?

Yeah, right. Now, I like the moon. I like it. It's like a big glowing cracker. And I like that about it. That's a moree, right? And that's a more. All right.

When the moon's not destroyed and the chunks don't hit your eye, that's a more. Look at me, you make it an Italian joke. All right, but the moon does play a big role in the rotation speed of the earth because the earth is not just a ball floating in space spinning on its own. We're in a relationship with another big ball out there in space. And the moon is not that small a ball. It has a lot of gravitational impact on the earth. It's like how, you know, if you have a kid just because they're small,

doesn't mean they're not going to affect your day. In this case, the moon has a pretty strong gravitational effect on the earth, but not in the way you might be thinking. We're all familiar with the tidal forces. Now, the moon pulls on some of the ocean bodies and makes water deeper and shallower in some respects. That's because of tidal forces. The moon pulls on the earth with its gravity, and some parts of the earth are closer to the moon than other parts, which means they get stronger gravity from the moon. Yeah, tides go in, tides go out. You can't explain that.

You can't explain that. Absolutely. That's not a mystery of science. No. In particular, that tends to pull the Earth and its oceans into more of a football shape because it's pulling harder on the closer bits and more gently on the further bits. So we're all familiar with the ocean tides, but there are also land tides.

And the moon is doing the same thing to the Earth as it's doing to its oceans. It's doing the same thing to the crust, to the mantle, to the actual body of the earth, as happens to the oceans. So we have a whole episode about land tides. They're not as dramatic as ocean tides because the earth itself is not as flexible as the oceans are squishable and sloshable. That's a technical term. Floshability. But they are there.

As the moon goes around the earth, it changes the shape of the earth. It's making the earth more of a football and that football is pointing towards the moon. So is that like it is actually like moving things like slightly. moving tectonic plates or something or is it more that it is just the entire crust is sort of warping yeah the entire crust is sort of warping but the crust is also resisting that right if the earth was made of diamond then the moon would have a much smaller impact so the impact of the moon on the earth's shape depends on the structure of the earth and this tension in there and there's friction in there because what essentially is happening is that it's squeezing the earth this is one way

that you can like keep an object hot just through tidal forces. Some of the moons surrounding Jupiter, for example, have such strong tidal forces that they're kept hot like they have lava on the inside. That's because of the internal friction generated by Jupiter like effectively massaging its moons.

In this case, the moon is massaging the earth and in doing so is transferring heat to the earth and so the rotational system is losing that energy. So what's happening is the moon's rotation around the earth is because coming slower and the Earth and the moon's rotations are also slowing down. So the heat that is generated by the Earth sort of going a little football shaped,

that slows down the rotation of the Earth and the moon? Yeah, it slows down the rotation of both of them around their axis and of the moon around the Earth and makes the moon drift further away because it's going more slowly. So the moon very gradually is getting further away because there's less energy in that rotation as that energy is getting transferred into the earth and the moon. The heat energy comes from somewhere and it is coming from what would have been the rotational energy. And this is how tidal locking happens. In many scenarios, two bodies will be tidily locked so they're always facing each other with the same side. The moon is already tidily locked to the

earth. And given enough time, the moon will slow down the rotation of the earth. Eventually, the rotation of the earth will take 28 of our current days. So the moon is having a pretty strong effect on the rotation of the earth. I hate that. I don't like that at all, Daniel, because I don't want to wait a whole month to go to bedtime because I love bedtime and I love sleeping. I also don't want to wait 28 days to wake up in the morning because I'm going to be so hangary and so like don't even, you dare speak to me until I've had that month.

monthly coffee. I know. Wouldn't it be weird if a year was like 12 days long? That'd be really strange. Yeah. It'd be like your birthday every couple of weeks. I feel like we would have to undergo some kind of radical evolution. I mean, everything would at this point. How long is that going to take, Daniel? Because I need a plan. It's a pretty slow process, actually. Every century, it affects the rotation of the earth by 2.3 milliseconds. So this is a pretty small effect. Although, Over, you know, cosmological time scales, it's dramatic. Just after the moon was formed and a huge collision of some protoplanet with the pre-Earth, we think that the rate that the Earth was spinning was about six hours for one rotation.

So a day was just six hours long. And now it's around 24 hours long. And eventually it'll be 28 days long. All that is getting slowed down gradually by the moon. Do you think there will still be life on the planet at that point? or are we going to be undergoing some problems that would make it difficult for life to survive that situation? This is deep in the future,

and so between now and then we could get hit by comets, the sun will expand and it will get brighter, so a lot of things are going to change. It's pretty difficult to extrapolate that far in the future. I mean, if we even survive the next 10 years without blowing ourselves to smithereens, right? But this is definitely one effect. So you're an optimist is what you're saying.

You're an optimist. I'm saying we don't know, we can't know. And I think sometimes not knowing is better than knowing, yeah. I don't know if that makes me an optimist or a pessimist. Okay, so the moon is interfering with our spin here. It's a harshing our mellow or maybe enhancing our mellow. I don't know. I'm pro moon.

Don't worry about that. But is there anything else that is going on that is affecting our jam around the sun? So many other things are going on, and some of them are fighting back against the powers of the moon. So, for example, our oceans and climate change and the glaciers, all of these things are working in the other direction to actually speed up the rotation of the Earth. Whoa. So there are anti-moon forces on Earth. Yes. All right.

So I get why the oceans are anti-moon because the moon's always messing with them. But all right. So we've got glaciers. that are melting, how does that increase our spin? So even though angular momentum has to be conserved, that doesn't mean necessarily that the spin velocity of the surface has to be conserved. In the same way that if you're a figure skater

and you have fixed angular momentum, you can pull your arms in to be going faster. What you've done is you've changed where your mass is distributed. And since angular momentum depends not just on your spin velocity, but on how that mass is distributed from the spin axis, like the more mass you have far away from a spin axis, the more angular momentum you have. So if you bring that mass in closer to the axis, you have to be spinning faster to have

the same angular momentum. And so if you can somehow make the earth more compact, then you can make it spin faster. One way to do that is to bring massive stuff that's high up, i.e. frozen water in glaciers down lower. And so, for example, if you take all of the glaciers on earth and all the snow and you melt it and you bring it down so it's closer to the rotation axis of the earth, Earth, then that has the effect of speeding up the Earth's rotation. I see.

So you're more evenly distributing that mass because, like, the ocean levels rise, but these very high peaks in terms of glaciers lower down. So, like, now that mass is more evenly distributed, you know, which is bad for us, but good if you want to spin really fast. Yeah, exactly. Like, if you wanted to slow down the spin of the Earth, you could build really, really tall towers and lift a bunch of really big glaciers up to the tops of them that would slow down the spin of the earth.

The melting of the glaciers is basically the opposite. It says, oh, we already have a bunch of these glaciers kind of elevated at the tops of mountains. And so let's bring them down as low as we can. And that will speed up the spin of the earth. I see you've been peeking at my plans for Katie's sky igloo. There's another effect there, which is the weight of the glaciers also changes a little bit

the shape of the earth. because there's so much ice in the polar regions what happens if that all melts is you get this redistribution of ice and you get this post-glacial rebound where you no longer have this dramatic weight pushing down the ground in the polar regions and so that comes back out a little bit

but because it's close to the axis it doesn't affect the spin of the earth and so overall the effect is to bring more stuff closer to the spin axis okay so by losing the weight of the poles would that make it go slow? or faster? That makes it go faster, yeah.

Because you have more weight now closer to the poles. This effect is not as big as the effect of the moon. It's like negative 0.6 milliseconds per century, whereas remember the moon was plus 2.3 milliseconds per century. So overall, the long-term effect is like 1.7 milliseconds per century gets added to our day. So the moon really is dominating. The effect of the glaciers is like a quarter of the effect of the moon. the moon. Right. And we should not melt all the glaciers. I think it is important to state.

The penguins need them. Polar bears need them. This is not advice, yes. No, no. Let's keep the moon where it is. Let's keep the glaciers where they is, if we can. Like, don't do this. But if you do this and you melt all the glaciers and now you have this like evenly distributed water, it doesn't seem like it'd be just as simple as like, well, now the Earth's sort of more compact. It's not just like pulling your arms in, right, if you're an ice skater because it is, water has its own properties. Yes, there's a big water cycle on the Earth and the water interacts heavily with the atmosphere. And so the moon and the melting of the glaciers and climate change sort of dominate the longer term effects like over centuries. Definitely the length of a day is increasing.

But they're also much shorter term effects where the Earth is speeding up and slowing down due to changes in the atmosphere. Think about the Earth as a bunch of shells. You have like the inner core, you have the surface, you have the atmosphere. If you need to conserve angular momentum, you could speed up one of them and slow down another one, right? The same way that like an astronaut in space can change how they're spinning by moving their arms around. So some parts of them can be spinning faster or some parts of them can be spinning slower. And the atmosphere doesn't have to spin at the same rate as the Earth. Right. So that's kind of like having. like gyroscopes work, right?

You have like different layers and then different spinning and then you get pork and then I don't remember the rest. That's exactly right. And this is a big source of like weather on Earth and wind, right? Wind is basically when the atmosphere and the surface are not spinning at the same speed and so you feel it. Right.

Like when you're watching clouds move up ahead, it does feel like there is a, you know, a layer moving above us. Mm-hmm. And a lot of this is due to the clouds and the water cycle. Like think about what happens when water is moving through its natural progression of evaporation and precipitation. When water evaporates, it's going up, right? And so when it goes up, it can't be rotating at the same speed.

To conserve angular momentum, it needs to be going slower, right? Or think about it another way. If everything was rotating together, then things at higher altitudes are actually moving faster because they have a longer path. And sort of like runners on the outside laps of a race have to be moving faster to keep up. So as water is evaporating is that because the water starts out slower and it's like merging into the high speed lane, but at a slower speed than the water in the atmosphere, is that slowing down the atmosphere? Exactly. And so as water rises, it like falls behind because it's not moving as fast, right? So it's effectively slowing down the atmosphere. And this is why

we get hurricanes. Oh, wow. Okay. I mean, I was going to say this is just how like traffic works, right? Nobody knows how to zipper. Apparently water also doesn't know how to zipper and slows down all the traffic. But how does that cause hurricanes? So as water is rising, the direction in which it falls behind depends on the direction of the earth's spin. And also the latitude, the distance from the equator. Stuff at the equator is traveling the fastest and stuff of the poles is not moving around the earth. all just spins in place. So as water rises, some parts fall behind more than others because they're traveling at different speeds. This is basically how the Coriol's effect works. And that's why, for example, you get hurricanes going in one direction in the northern hemisphere and the other direction on the southern hemisphere. We have a whole episode about tropical storms and hurricanes and even space hurricanes

that relates to this. But toilets do flush in the same direction no matter where you are. Yes, they do. I mean, listeners, you tell me. I've never been to the sun in the hemisphere. But the idea is that essentially you have transfer of velocity and angle momentum between these two layers. And so you can make the atmosphere move slower by loading it up with water or you can make it move faster by dumping water. And if the atmosphere is moving faster or slower, the surface also moves faster or slower because again, angle and momentum is roughly conserved.

And so by speeding up one layer, you can slow down another layer. And we all know, of course, how they can transfer angular momentum between each other. That's basically wind, right? When wind is blowing across the surface of the earth, it can actually speed up the earth. Or if the earth is moving faster, it's leaving the atmosphere behind that also creates wind. So our experience of wind and storms, this is like the surface and the atmosphere exchanging angular momentum. I guess I never thought of the weather as exchanging angular momentum. So next time I'm out, I'm going to be like, wow.

Look at this exchange of angular momentum today. Lovely, isn't it? Yeah, well, this is really what dominates the change in the length of a day on the day-to-day or month-to-month cycle. Like, we talk about it more detail in a little bit, but the length of a day changes by quite a bit through the year and over the years. And these short-term effects really are dominated by what's going on in the atmosphere. So the weather changes the length of a day.

Isn't that kind of crazy? That is crazy. I've always suspected it, though, because sometimes when the weather's really bad, The day just goes on and on and on. I'm sure that's what you mean. Well, let's take a quick break. And when we get back, we're going to talk about more ways that the Earth's own issues is messing with its spin. A foot washed up a shoe with some bones in it.

They had no idea who it was. Most everything was burned up pretty good from the fire that not a whole lot was salvageable. These are the coldest of cold cases, but everything is about to change. Every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime. A small lab in Texas is cracking the code on DNA. Using new scientific tools, they're finding clues in evidence so tiny you might just miss it. He never thought he was going to get caught, and I just looked at my computer screen. I was just like, ah, gotcha.

on America's Crime Lab, we'll learn about victims and survivors, and you'll meet the team behind the scenes at Othrum, the Houston Lab that takes on the most hopeless cases to finally solve the unsolvable. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hola, it's HoneyGerman, and my podcast, Grasasas Come Again, is back. This season, we're going even deeper

into the world of music and entertainment, With raw and honest conversations with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't audition in like over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah.

We've got some of the biggest actors, musicians, content creators, and culture shifters, sharing their real stories of failure and success. You were destined to be a start. We talked all about what's viral and trending with a little bit of chisement, a lot of laughs, and those amazing vivras you've come to expect. And of course, we'll explore deeper topics dealing with identity, struggles, and all the issues affecting our Latin community.

You feel like you get a little whitewash because you have to do the code switching? I won't say whitewash because at the end of the day, you know, I'm me. But the whole pretending and code, you know, it takes a toll on you. Listen to the new season of Grasasas Come Again as part of my Cultura podcast network on the IHartRadio app, Apple Podcast, or wherever you get your podcast.

I had this overwhelming sensation that I had to call it right then. And I just hit call. I said, you know, hey, I'm Jacob Schick. I'm the CEO of One Tribe Foundation. And I just wanted to call on and let her know there's a lot of people battling some of the very same things you're battling. And there is help out there. The Good Stuff Podcast Season 2 takes a deep look into One Tribe Foundation, a nonprofit fighting suicide in the veteran community. September is National Suicide Prevention Month.

So join host Jacob and Ashley Schick. as they bring you to the front lines of one tribe's mission. I was married to a combat army veteran, and he actually took his own life to suicide. One tribe saved my life twice. There's a lot of love that flows through this place, and it's sincere. Now it's a personal mission. Don't want to have to go to any more funerals, you know.

I got blown up on a React mission. I ended up having amputation below the knee of my right leg and a traumatic brain injury because I landed on my head. Welcome to Season 2 of the Good Stuff. Listen to the Good Stuff podcast on the Iheart Radio app, Apple Podcasts or wherever you get your podcast. Hey, sis, what if I could promise you you never had to listen to a condescending finance, bro, tell you how to manage your money again.

Welcome to Brown Ambition. This is the hard part when you pay down those credit cards. If you haven't gotten to the bottom of why you were racking up credit or turning to credit cards, you may just recreate the same problem a year from now. When you do feel like you are bleeding from these high interest rates, I would start shopping for a debt consolidation loan, starting with your local credit union, shopping around online, looking for some online lenders because they tend to have fewer fees and be more affordable. Listen, I am not here to judge. It is so expensive in these streets. I 100% can see

how in just a few months you can have this much credit card debt when it weighs on you. It's really easy to just like stick your head in the sand. It's nice and dark in the sand. Even if it's scary, it's not going to go away just because you're avoiding it. And in fact, it may get even worse. For more judgment-free money advice, listen to Brown Ambition on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. All right. So the Earth is a complicated sphere. Not exactly a sphere, you know, more of an, what is it?

It's more of an oblong, right? It's a little bit of a squashed basketball, actually. Oh, there we go. That's what was said, right, by the first astronauts is like, look at that squash basketball, the little blue squashed basketball. So we've talked about the effect that the moon has. We've talked about the melting of the glaciers and also the atmosphere and weather. Are there other factors internal to Earth that affects spin?

Yeah, we talked about what's out beyond the Earth. We talked about what's above the surface. But what's going on below the surface also has a big impact on how fast the surface is spinning. The basic idea there is the same that if the core spins at different speeds, then the surface will spin at different speeds. Like if something happened to speed up the core, then the surface would slow down. Or if the core went slower, the surface would go faster

for the same gyroscopic reasons, right? Conservation of angular momentum. And we have a big, heavy core at the center of the earth that spins in weird ways. And how it spins and how that spin changes definitely affects the length of the day. When I visualize the Earth's core, I do see a lava lamp. And I know that's probably not exactly accurate, but that's how I imagine it.

Like a bunch of hot, gloopy substances kind of wiggling around each other inside there. Yeah, that's not a bad mental model. Sweet. I knew I could learn something from my bad taste and home decor. We have a few layers inside the Earth, but the core is a big blob of iron. iron and nickel. It's about the size of Pluto. And because it's so massive, small changes in its spin will affect the spin of the rest of the planet. You might wonder like, well, how do we even know what's inside the planet and how fast it's spinning? Well, nobody's been able to drill

down there and see it directly. I thought Bruce Willis did. Wait a minute. Hang on. We can kind of ultrasound the earth, right? How does an ultrasound work? How do you see a baby in a pregnant woman's belly without opening her up, of course, is you send little sound waves down in there. Ultrasound emits high frequency sound waves, higher than you can hear. Infrasound would be very low frequency. Ultrasound emits those sound waves, and then based on how those sound waves move to the body and reflect and bounce back and interfere, we get a picture of what's going on. Sort of like knocking on a wall to see whether it's hollow or not.

And as you move around, you get different sounds. You can sort of like make a mental image for what's going to. going on out there based on those sounds. And we can do the same thing with the earth. So we take the earth to the universe's largest OBGYN, do an ultrasound on it. What are we seeing in there? So imagine we have like an earthquake, which is a big sonic event. It creates pressure waves inside the earth. Those waves propagate through the earth. Earth is basically like a fluid. Those pressure waves pass through the same way like if you slap the surface of the water, you're going to get waves moving through the water. So you have a big earthquake and you get waves moving through

the earth. Now, if they meet a layer where like the density of the earth is changing a lot, then those waves are going to reflect and refract the same way that like light moving through glass or light moving through water will change direction and some of it will bounce back. Density waves moving through the earth will do the same thing. So that's how we know that there are different layers inside the earth because we see these reflections. Earthquakes send these waves down and we see how they bounce back and bounce all around. We actually have to build complicated models for how we expect these things to bounce around and then compare them to the measurements we make around the globe with seismometers

of how things are wiggling. So yeah, it's basically like a big OBGYN for the Earth. Right. So earthquakes is the OBGYN for Earth. Got it. And then we measure those and then we can figure out what is that feedback, the pattern of sort of interference and what that is saying about what's going on. How do we know like what it is made out of, right?

Like do we just expect different sort of feedback patterns from different substances or are we getting direct samples of the stuff that is the gooey center of the earth? We're effectively measuring the density because the density controls the speed of sound. as things are denser sound travels more quickly through them that's why sound moves more rapidly through water or steel than it does through the air because sound are pressure waves and if those atoms are more tightly packed and they have stronger bonds between them then rippling one is going to ripple the other one more quickly than if they're like farther apart or more loosely bound so the speed at which sound travels indicates the density of the material so by seeing how long it takes those waves to propagate through the Earth and when they return, we can get an idea for the density of each of the layers. And not just the density, we can also measure the speed of their rotation because how fast that inner layer is moving changes what the wave looks like when it bounces back. We all know about the Doppler effect that like a police siren going by you will sound

different as it's approaching you and as it's going away. We woo, we, woo, we, woo, we, yeah, exactly. The same thing is true for waves that bounce off of an eye. object. If you used radar to measure that police car's velocity as it was going by, the waves that come back to you tell you something about the velocity of the police car. And in the same way, waves that bounce off inner layers of the earth tell us about the velocity of those layers. So we can use these waves not just to image the earth and tell where stuff is, but also how fast it's going, though that takes more precise and crisper measurements. Hmm, I mean, it seems kind of hard to do that, though,

for we always have to wait for an earthquake to happen. And we can't really predict where the earthquake's going to be. How do we do that? So the best way to do that actually is to create our own sonic waves rather than just wait for earthquakes. Okay, big hammer then. Big hammer. Basically big physics hammer because there was a period after the development of nuclear weapons

and before we stopped testing them that we did tests underground. So first we had nuclear weapons and we tested them a, above ground, which was exceptionally stupid because of the atmospheric radiation, then we realized that's not such a good idea. So then we started testing them underground. My dad actually worked on some of these test sites. You would explode a nuclear bomb underground and then you would measure the impact. And that would create huge sonic oscillations in the crust of the earth and very crisp,

very clean because it was high intensity and also very brief. So it rung the earth like a perfect bell. Whoa. Okay, so I've got several questions. One is, when you explode a noop underground, where does all that radiation go? Does it just sort of sink into the earth somewhere? So that's question number one. It's absorbed by the material immediately surrounding the explosion. So it doesn't sink. It just gets deposited in the surrounding dirt and rock. So are there like pockets of radiation in these areas where we tested these nukes? Yes, there are. Gross. It's like a zit on the earth. Question number two is how big...

I've seen a basement. That doesn't seem big enough to do a nuke inside of. So like how big were these areas where they tested these? Yeah, well, the holes themselves are not that large because you want them surrounded by the rock. Yeah. Okay. So then you put it down into the hole and then it explodes into the rock

leaving what kind of... Like, how big is that explosion? These nuclear explosions have significant impact on the rock for, you know, meters and meters and tens of meters. And then you're surrounded by various sensors so you can measure the energy and the length of the shockwave and all sorts of stuff. And not only do you create sensors for your own explosions, because of the Cold War, the U.S. government invested deeply in seismic sensors so we could study the Soviet explosions. Because, you know, we wanted to see when they were testing nuclear weapons. And if you test one underground, everybody across the earth can figure it out. So it was sort of like a golden age for seismology because not only were there these crisp events that created these ripples around the earth, but also the U.S. government invested in the best possible set of seismographs so we could get data about Soviet tests.

So there's this window of like 15 years in the end of the last century when there's this excellent seismographic data about what's going on inside the earth. We were staring down nuclear annihilation, but at least we got some good data from it. You know, there's so many times when important science is riding on the back of like either whimsical consumer electronics where people spending like billions of dollars on their gadgets or the military industrial complex where, you know, they spend billions of dollars on satellites or something else and we can gather science data from it. And because science funding is a tiny fraction of consumer spending or military, spending, we're always going to take advantage of that whenever we can.

And so there were some folks who pretty recently dug up these old tapes. And this is like science heroism because I had to find these data and pull them off of magnetic tapes and remember how it was stored. And sometimes you have to like bake these tapes so the magnetic particles adhere better to the actual tape. Whatcha bacon? Oh, you know, tapes on nuclear explosions done in the 60s and 70s. And so pretty recently they found this data.

pulled it off, they analyzed it, and they discovered something fascinating about the core of the earth. We always expected that the core was rotating slightly faster than the surface of the earth, but what they found is that it was much more variable than they expected. There's sometimes when the core is rotating faster and sometimes when the core is rotating slower than the surface of the earth. The surface like catches up to it and passes it, and then the core rotates faster. Do you think that this is random or do you think there's some kind of cyclical nature to the core? What they discovered is that it oscillates in like six-year periods, so where like one is going faster and the other is going faster.

And this is not something we understand very well. You know, the inner parts of the earth are sort of a mystery and, you know, the flow of energy there and the convection cells as things are moving up and bubbling and frothing inside the earth are something we're still trying to understand. So this is a really interesting and fascinating clue for a geologist. For those people who saw news coverage about it, it was a little bit misleading.

It suggested that the Earth's core is changed. changing direction that it's like rotating one way and then stops and rotates the other way. It's not exactly what's happening. What's happening is that's going faster than the surface and then sometimes slower than the surface. So it's changing direction relative to the surface, but not like relative to the sun or something like that. It's not like it's actually changing direction. That would be much more dramatic and more awesome, but that's not the scenario. But what it does mean is that it's affecting the length of the day because it affects how quickly the surface is rotating.

Okay, so this is a call-out, so I'll keep it anonymous, but I did have a strange science teacher in elementary school who told us that the Earth's core would change directions sometime in our lifetimes and that the poles would switch and we would all get deadly skin cancer. Is that true? The Earth's core is not going to change direction except for relative to the surface of the Earth. So in that sense, yes. The magnetic north and south pole is something of a fun mystery, and it does flip every once and a while. But these flips tend to be like tens of thousands of years, so probably not within our lifetime, although it's a little bit chaotic.

It's much more chaotic than the flip in the sun, which is very regular. But again, not something that we understand. Okay. Well, you know who you are, science teacher that I had. You're wrong. We're all just learning about the nature. right everybody's just updating their information that's a much kinder way to put it all right so we are having this this oscillation of the earth's core it is sometimes slower and sometimes faster than

how the crest is moving and so that is having an impact on the spin of the earth yeah and so there are these long-term effects right the moon is the most dominant long-term effect that's slowing down the rotation of the earth and making days longer the melting of glaciers and the glaciers and is the most important effect long term that's speeding up the rotation of the earth, though it's not as dramatic as the effect of the moon. On shorter timescales, we have like the rotation of the core, which affects things on a few year timescale, it's like six year cycles. Then there's the atmosphere that changes things on a much shorter time scale.

And so, for example, there's like an annual period of the length of the day, changing of like a third of a millisecond per day, maximizing like in February and then again like in May and so there's these funny wiggles in the length of a day if you look at the data it goes up and down through the years on these longer cycles and then there's these really fast variations throughout the year so like even during a year not every day is the same length in fact recently we had a day June 29th my mom's birthday I think not a coincidence 2002 which was the shortest day ever on record of Oh, my gosh, that is so unfair to your mom.

That is so unfair. Her birthday was like a millisecond and a half shorter than 24 hours. She was totally robbed. I know. Injustice. Just make it up to her for her next birthday. Give her like 1.6 extra milliseconds of birthday time. And so overall, the length of a day is not changing on time scales

so we can really measure as much as we joke about it, a millisecond and a half. of your birthday is not something you're going to notice is it literally a blink of an eye but it is something that's changing you know these things that we think are constant like the moon and the sun and the rotation of the earth these things are functions of time their descriptions of where we are in the moment and on much longer cosmological time scales these things are changing dramatically the rotation of the earth was a six hour day and it's on its way to becoming a 28 day long day and so Here we are sort of in the middle of that vast cosmic journey at one particular moment. We think it's the moment that defines what it's like to be on Earth, but it's not really.

It's just one slice of an incredibly deep history. So if I sleep for like 10 hours, right, I could say, hey, I'm not over sleeping. I'm just planning for the future. You just incredibly far-sighted. That's right. This is actually not laziness. This is, I'm trying to evolve for our eventual lengthened day-night cycles. Well, to me, it's fascinating that if these things change but change very slowly,

life on Earth has a chance to adapt, right? It's curious to me, like, what will life be like on Earth when the day-night cycle is 28 of our current days or even a week of our current days? I feel like everything on Earth must be different. I mean, the weather patterns are going to be very different. different, the entire experience of life on Earth, and what it takes to survive will be vastly different. It is so hard to imagine because it really, that day-night cycle does determine the behavior

of every creature on Earth and how massively you would have to adapt and change to, you know, you may have just entire, you know, nocturnal species. And you'd have to also adapt to the, how cold it would get, right? if you have one side of the planet that's not facing the sun, it's going to be a lot colder than the other side and the other side's going to be a lot hotter. It is unfathomable the amount of change if there is still life on Earth,

like what the adaptations would have to be in that situation. And what would our podcast releasing schedule be like in that kind of scenario? Are we releasing them more often, less often? I'm losing track. Yeah. It'll have to be based on the commute, the once a month commute. All right. well, thanks Katie, for joining us and spinning your mind around this topic.

And thanks everybody for joining us on this trip around the surface of the earth and understanding the fundamentals of its rotation. Yeah, have a stellar day, everyone. A little bit shorter than your solar day. All right, everyone. Thanks again. Tune in next time. For more science and curiosity, come find us on social media,

where we answer questions and post-vis. We're on Twitter, Discord, Insta, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. Hi, it's Honey German, and I'm back with season two of my podcast. Grazacios, come again. We got you when it comes to the latest in music and entertainment with, interviews with some of your favorite Latin artists

and celebrities. You didn't have to audition? No, I didn't audition. I haven't auditioned in like over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending with a little bit of cheesement and a whole lot of laughs. And of course, the great bevras you've come to expect. Listen to the new season of Dresses Come Again on the IHeart Radio app, Apple Podcast, or wherever you get your podcast.

case that is a cold case that has DNA. Right now, in a backlog, will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth. He never thought he was going to get caught. And I just looked at my computer screen. I was just like, ah, gotcha. This technology's already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation,

we're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials easier. Complex problem solving. It takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.